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A methodology for the assessment of the effect of climate change on the thermal-strain–stress behaviour of structures
Abstract
Thermal loads can cause significant stresses in some structures such as bridges or arch dams. Studies in arch dams show that thermal loads have the most significant effect for causing cracking than other service loads. Moreover, since researches on climate change announce that mean temperature on Earth is expected to increase, the assessment of the impact of the future temperature increase on the structural behaviour of sensitive infrastructures should be considered. This paper proposes a methodology for the assessment of the impacts of global warming on the structural behaviour of infrastructures. The paper links future climate scenarios to the thermal, stress and displacement fields of the structure. The methodology is illustrated with a case study: La Baells arch-dam. The expected stress and displacement fields of the dam under several future climatic scenarios were computed by finite element models. Concrete temperature are expected to increase up to 5.6 K, which will make annual average radial displacements increase in some cases even more than 100%. Tensile stresses are also projected to change and should be adequately monitored in the future. Finally, several adaptation strategies are outlined.
... The experimental test results presented by this company confirm that the compressive strength and Young modulus of the dam have decreased compared to their initial values. As it was explained in detail in previous studies of the author on this dam [1,2], it can be realised that the environmental conditions of the Dez dam are special conditions that can be categorised as aggressive conditions and are not similar to the normal climate conditions considered for the other arch dams which their behaviours have investigated until today [5][6][7][8]. Hence, the long-term behaviour of concrete of the Dez dam cannot be classified as a normal behaviour according to the reference [3].Therefore, due to this important fact, the previous numerical model results of the author and the experimental results show that the stiffness and strength of mass concrete of the Dez dam do not increase with time and have been degraded heterogeneously and orthotropically over time under the effects of high temperature and moisture fluctuations [1,2,4]. ...
... Different monotonic behaviours resulted from different stress paths are simulated by the plastic part of CDP model based on these two fundamental independent behaviours. However, in load reversal case, the scalar damage d is required to known according to relation (8) for calculation of ̄i j . In multiaxial stress state, CDP model computes the scalar damage d based on the two independent scalar damages d c and d t . ...
... The trends of the change in compressive strength and elastic moduli of the Dez dam which were obtained in this new attempt of the authors are in complete agreement with the previous numerical model results of the authors [1,2] and the experimental evidence [4]. This new results confirmed that the long-term behaviour of the concrete of arch dams is not a regularised behaviour which obeys from general models such as 'Fib model code' [3] or other arch dams' behaviours [5][6][7][8], and is a case to case phenomenon which is dependent of the particular environmental as well as loading histories of the dam. According to studies of Naik, the environment of Dez dam is classified as an aggressive condition and under this condition, the strength of the concrete is reduced over time [29]. ...
In this research, the trends of degradation of stiffness and compressive strength of mass concrete of the Dez concrete arch dam, over time have been evaluated using a new and robust method. In previous studies of the corresponding author, he was successful to estimate the degradation of the stiffness of dam’s concrete at the end of a selected time interval, i.e. the Year 2007 from the interval 1965–2007 using a novel thermal inverse analysis. But, he was interested in knowing the trend of this degradation over that time interval. In previous studies, the author used isotropic and transversely isotropic elastic material models for evaluating the stiffness degradation. By these material models, the reduction of the compressive strength of the mass concrete could not be determined. In this new attempt, to overcome the above-mentioned shortcomings, it was decided that the time interval is limited to a maximum of one year from 1965 to 2007. In addition, a more sophisticated material model for concrete of the dam, named as, concrete damaged plasticity model, from the ABAQUS standard material library, was employed to simulate the long-term concrete behaviour. By this material model, the reduction of the compressive strength of the dam’s concrete could be measured. Obtained results demonstrated that the reduction of stiffness and strength of dam’s concrete have not a constant rate of change and they have been accelerated considerably after passing approximately 20 years from the commissioning of the dam.
... Due to the short sequence of monitoring data required, they can be used for safety evaluation during the design, construction, and operation. [9][10][11] However, this approach also has several shortcomings, such as the complexity of geometric modeling and the inefficiency of iterative computation. Hybrid models combine the characteristics of the statistical and deterministic models. ...
... The maximum iteration number and population size of MFOA were set to 100 and 20, respectively. 24 In the initial generation, the hyper-parameters, (M, ν, J), were randomly scattered in the analytic space [10,1000] ...
Monitoring and predicting the displacement response of concrete dams is one of the critical activities that ensure their long-term safe operation. The nonlinear interrelationships between dam displacements and their influencing factors make predictive modeling challenging. The majority of available studies focus strongly on improving the accuracy of point predictions of dam displacements, while ignoring the inherent uncertainties involved in dam systems. To quantify the uncertainties related to predictions, this study adopts the prediction intervals (PIs), rather than using point predictions, to estimate future displacements. An ensemble learning-based interval prediction model, referred to as gradient boosted quantile regression (GBQR), is proposed to construct the PIs of dam displacements. This model integrates the classification and regression tree (CART) and quantile regression (QR) methodologies into a gradient boosting framework and outputs the optimal PIs by minimizing a differentiable loss function when adding trees. Specifically, multiple CART base-learners are additively combined to model complex mappings between the inputs and the output. A redefined QR-based pinball loss, replacing the squared error loss, is also derived to determine the upper and lower limits of the PIs. Throughout the whole process, we use a gradient descent procedure to guide the training of the model parameters. The final GBQR model is formulated in this way, and then the dam displacement PIs are directly generated. The developed GBQR model is verified using long-term monitoring data of a real-world concrete dam, and its performance is compared with various state-of-the-art modeling methods. The results confirm that the proposed method performs better and can provide high-quality PIs of dam displacements, thus assisting risk analysis and decision-making. This novel model could be generalized for modeling and prediction of other types of structural behavior.
... The raising number of published works related to the thermal loading effect shows its importance in the dam engineering community. However, these works are limited either to the construction [18,97] or to the operation period [34,40,87]. While the first focus on the detailed consideration of the evolution of concrete properties at early stages [11,18,27], those dealing with the performance during normal operation emphasise the assessment of specific thermal processes such as heat exchange by night cooling [89], the effect of solar radiation or shadows [52,77,78]. ...
... Santillán et al. chose a constant value equal to 2.43 W/(m · K) for La Baells arch dam, based on experimental tests during construction [87]. The formulators of the Tenth Benchmark Workshop on Numerical Analysis of Dams [47] suggested using 2.5 W/(m · K). ...
Double-curvature dams are unique structures for several reasons. Their behaviour changes significantly after joint grouting, when they turn from a set of independent cantilevers into a monolithic structure with arch effect. The construction process has a relevant influence on the stress state, due to the way in which self-weight loads are transmitted, and to the effect on the dissipation of the hydration heat. Temperature variations in the dam body with respect to those existing at joint grouting generate thermal stresses that may be important in the stress state of the structure. It is thus essential to have a realistic estimate of this thermal field, also called reference or closing temperature. In this work, the factors involved in the calculation of the reference temperature of double-curvature arch dams are analysed: material properties, boundary conditions and numerical aspects. First, a critical review of the state of the art is made with respect to the criteria used by various authors for decision-making in the construction of the model. Next, specific analyses are made on the effect of some important elements: the time step, the size of the domain of analysis and the methodology used for the calculation of the reference temperature. The results show the relevance of a correct calculation of the closing temperature to adequately determine the stress state of the structure.
... From the pioneering work of Jin et al. [4] to the most recent works [5,6], authors have used the ray-tracing algorithm to define the shaded area caused by the surrounding terrain and the dam itself. An exception is the work of Santillán and coworkers, who computed the shading of the dam by recourse to the projection of the different surfaces in the direction of the sun rays [7,8]; however, later on, they also adopted the ray-tracing algorithm [9,10]. ...
In order to conduct thermal analysis of concrete dams, it is necessary to assess and validate the spatiotemporal representations used for modeling the solar radiation and the water temperature boundary conditions. To illustrate this procedure, the thermal analysis of a concrete multiple-arch dam is presented. The article starts by providing an overview of the problem before focusing explicitly on the estimation of solar radiation distribution. Within this section, a comparison between the solar irradiance computed on the downstream face of the dam with or without considering the beam radiation shading at different times of the year is presented. This is followed by an analysis of the seasonal behavior of the water temperature of the dam’s reservoir based on measured data. After calibrating an empirical/statistical law based on temperatures measured at different depths, it is compared with the values estimated by a hydrodynamic model and some temperature profiles measured upstream of the dam. Finally, the article compares the results obtained with the thermal analysis versus the temperature measured by thermometers installed in the concrete.
... The Jinping I arch dam is the highest concrete dam built in the world, with a maximum dam height of 305 m. However, dams bear complex static and dynamic loads and long-term environmental erosion during operation, and the actual load may be larger than the designed scenario, such as the increase in thermal load caused by global climate change in recent years, which is likely to cause potential safety hazards [1]. To ensure dam safety, structural health monitoring plays an important role in dam construction and operation management [2]. ...
To conduct structural health monitoring, it is important to establish mathematical monitoring models with good prediction and interpretation performance. Generally, the thermal deformation effect interpreted in a displacement monitoring model of concrete dams is represented by the seasonal harmonic factor. The main purpose of this paper is to replace this factor with directly measured dam body temperatures. This approach is conducted by optimally selecting a very small number of the most representative members from hundreds of temperature monitoring points on the dam body, during which the importance of modelling factors is evaluated by a support vector machine (SVM), and automatic and manual criteria are formulated to eliminate the large number of unimportant or similar temperature monitoring points. Then, a hysteretic effect-considered hydraulic, exponential, thermal and time (HETT) model is established, and a causal interpretation of dam deformation behaviour is carried out using a partial dependence diagram to separate displacement components from the SVM model. The world’s highest concrete dam, the Jinping I arch dam, is assessed in a case study. Research results demonstrate the efficiency and rationality of the proposed approach. On average, among the 140 total temperature monitoring points in the central cantilever dam section, only 6.3% of them are selected as temperature deformation factors, and these factors can fully characterise the temporal and spatial evolution characteristics of the measured dam temperature field. The prediction accuracy of the HETT model is significantly improved, in which the mean square error, maximum error and correlation coefficient of multiple displacement monitoring points are 60.1%, 86.5% and 101.5% of those of the hydraulic, exponential, seasonal and time (HEST) model, respectively. The thermal deformation effect interpreted by the HETT model is more in accordance with the actual operation condition of the Jinping I arch dam.
... The results showed that the allowable number of cycles decreased by approximately six million and a shorter pavement life of around four years considering the final effective temperature, which was increased temperature due to climate change. Santillán et al. (2016) proposed a methodology to assess the impact of climate change on the structural performance of the structures under increased thermal loads. Modelling the thermal response of the structure included solving the heat diffusion equation by the finite element method considering air temperature, wind speed, and solar radiation computed using the Reindl model. ...
... Many of these impacts have been assessed in a quantitative manner; e.g. accelerated deterioration of infrastructure (Bastidas-Arteaga & Stewart, 2015b;Mortagi & Ghosh, 2022;Nasr, Honfi, & Larsson Ivanov, 2022;Nasr, Niklewski, Bj€ ornsson, & Johansson, 2022;Ryan & Stewart, 2021;Stewart, Wang, & Nguyen, 2011), increased scouring under submerged foundations of infrastructure (Kallias & Imam, 2016;Yang & Frangopol, 2019), and increased thermal stresses and displacements of infrastructure (Santill an, Salete, & Toledo, 2015). Nonetheless, many other identified potential impacts of climate change on infrastructure have not yet been investigated quantitatively. ...
Recent studies suggest that concrete creep may be further exacerbated by climate change. However, up to now this effect has not been quantified in literature. The current study addresses this gap and presents a probabilistic approach for quantitatively assessing this effect. For this purpose, five different stochastic creep models (i.e. Model Code 1999, Model Code 2010, B3, B4, and B4s models) are used under considerations of the historical and future climatic conditions in Sweden to assess the long-term creep coefficient and the subsequent stress redistribution of an axially loaded column. While some creep models show similar percentage increases in the long-term creep coefficient in all Swedish counties, other creep models show higher percentage increase values for northern than for southern counties. The highest increase in the end-of-century creep coefficient is found using models B4 and B4s (e.g. over 40% increase is possible for northernmost Sweden, i.e. Norrbotten county, under RCP8.5). Furthermore, the current article also shows that the end-of-century creep coefficient is more sensitive to uncertainties not related to the climate (i.e. parameter and creep modelling uncertainties) than to climate uncertainty.
... During their service life in structure, timber or other materials as concrete and steel, are subjected to the coupled effects of mechanical and climatic loadings [1,2,32,34]. For moisture, the literature review shows that, in the time, it remains the enemy of steel which corrode [35], concrete which spall [33] and timber which decay [21,32]. In equatorial regions, especially in Gabon country, where the annual precipitation (AP) and relative humidity (RH) can reach, respectively, more than 1200 mm and 90% [3], the buildings don't escape to this rule. ...
The present work deals with the beginning of the Eurocode 5 (EC5) generalization to tropical hardwoods loaded in tropical environment. For three (3) years, creep tests were performed on two types of tropical hardwoods beams, Dacryodes Buettneri (Ozigo) and Baillonella Toxisperma (Moabi) from Gabon. Three (3) environments were selected: (i) the sheltered exterior environment, (ii) the unsheltered exterior environment, (iii) and the sheltered interior environment. The environment parameters considered herein, were temperature and relative humidity, recorded versus time, during the tests in the three environments. The main mechanical response considered for analysis was the deflection of all tropical beam loaded. This parameter has been defined according to the EC5 requirement. The impact of environmental parameters on the deflection is compared for the three tested conditions. At the end, the obtained results show that the proposed values given by EC5, for the three types of environments, are much lower than those obtained for all the beams loaded in the tropical environment. Indeed, in the three (3) environments it has been observed on average, that after four (4) months of loading, the limit value proposed by EC5 is exceeded of 75%.
... Additionally, the cost-effectiveness of the different adaptation options for the increased impact of infrastructure corrosion [68] (e.g., Using cathodic protection, increasing the concrete cover thickness, or improving the quality of concrete) should be assessed under the Swedish climate conditions. Moreover, future research should address the combined effect of concrete corrosion and other potential climate change impacts on concrete structures (e.g., thermalstress-strain behaviour [69]). Lastly, assessing the impact of climate change on the reliability of structural elements made of other materials (e.g., timber, steel, and masonry) under Swedish climate conditions is worth exploring. ...
The impact of climate change on the deterioration of reinforced concrete elements have been frequently highlighted as worthy of investigation. This article addresses this important issue by presenting a time-variant reliability analysis to assess the effect of climate change on four limit states; the probabilities of corrosion initiation, crack initiation, severe cracking, and failure of a simply supported beam built in 2020 and exposed to chloride-induced corrosion. The historical and future climate conditions (as projected by three different emission scenarios) for different climate zones in Sweden are considered, including subarctic conditions where the impact of climate change may lead to large increases in temperature. The probabilities of all limit states are found to be: 1) higher for scenarios with higher GHG emissions and 2) higher for southern than for northern climate zones. However, the end-of-century impact of climate change on the probabilities of reaching the different limit states is found to be higher for northern than for southern climate zones. At 2100, the impact of climate change on the probability of failure can reach up to an increase of 123% for the northernmost zone. It is also noted that the end-of-century impact on the probability of failure is significantly higher (ranging from 3.5–4.9 times higher) than on the other limit states in all climate scenarios.
... During their service life in structure, timber or other materials as concrete and steel, are subjected to the coupled effects of mechanical and climatic loadings [1,2,32,34]. For moisture, the literature review shows that, in the time, it remains the enemy of steel which corrode [35], concrete which spall [33] and timber which decay [21,32]. In equatorial regions, especially in Gabon country, where the annual precipitation (AP) and relative humidity (RH) can reach, respectively, more than 1200 mm and 90% [3], the buildings don't escape to this rule. ...
... Temperature cracks problem was an important research topic in the field of high arch dam structure. To date, lots of achievements [3] related to thermal stress and temperature cracks of concrete dams mainly are focused on the influence of the diurnal temperature variation during the construction [8,9], and the annual temperature [10], seasonal temperature variations [4,11,12], solar radiation [13,14], and water temperature variations [1] during the operation. e results show that the cold wave or the diurnal temperature variation will affect the thermal field within a certain range below the concrete surface and lead to the surface cracks [15]. ...
In order to make clear the cracking reasons in arch dam of Xiaowan Hydropower Station during operation period, the approach to combine ANSYS with finite element program COCE-3D is adopted. Firstly, the influence by element type and mesh size for the temperature field simulation result is analyzed. Subsequently, the three typical dam segments cut from Xiaowan arch dam are selected and the relevant finite element model is established; the effect of the measured diurnal air temperature on temperature field and temperature stress of arch dam is analyzed thoroughly. The results indicate that the temperature gradient in mass concrete becomes lower, whereas the affecting depth becomes deeper when the mesh size is too large. Therefore, it is advisable to use smaller size mesh to study the influence of the measured diurnal air temperature on the surface temperature distribution in mass concrete. The temperature of downstream zone in arch dam is significantly affected by air temperature; the changing laws of temperature field and temperature stress with the air temperature are basically consistent, which is sensitive to lower temperature. When the temperature sharply decreased, the temperature stress in the downstream zone is mainly in tensile stress state. The calculated results are basically consistent with the measured results, and the temperature stress induced by the day-night temperature difference is the important reason for the horizontal cracks on the downstream surface. The submodel analysis method is an important alternative approach to study the changing laws of temperature field of arch dam. The research results not only provide an evidence for temperature control and crack prevention of Xiaowan arch dam but also provide a reference for temperature field simulation of similar projects.
... Thus the HST may lead to misinterpretation of the results. Moreover, thermal loads are often the dominant contributor to the deformation fluctuation for high arch dams [16,17]. The assumption of annual periodic change of the thermal effect also leads to subpar performances especially for initial operation periods, during which the temperature field is still nonlinear and unsteady. ...
The purpose of this study is to compare the prediction performances of different commonly used data mining models for high arch dam deformation prediction during the initial operation period. Four machine learning modeling techniques, namely random forest (RF), least squares support vector machines (LS-SVM), simple boosted regression tree (SBRT), kernel extreme learning machine (K-ELM), and modified statistical models are used. With the help of hierarchical clustering on principal component analysis, the typically measured temperatures representing the unsteady dam temperature field are selected to reduce dimensionality, avoid over-fit, and facilitate explanation. The practical term for the time-dependent effect, reflecting both the exponential growth and the recovery term, is also introduced. These models are constructed, and their prediction and explanatory capabilities to model dam deformation are compared by dividing time series into training and test sets. Four different training and test combinations are investigated. The traditional hydrostatic–seasonal–time (HST) model is not enough to predict this nonlinear deformation. The SBRT, the modified HST, and its improved HTTTS (hydrostatic–thermal by measured temperature–time–season model) models show good performance. Relative influence and partial dependence plot are employed to understand the relationship between the deformation and the predictor variables. The results show that several factors, including reservoir thermal stratification, concrete temperature rise, valley contraction, and non-monotonic time-dependent effect, affect the deformation of high arch dams during the initial operation period.
... For this reason, it is very important to know the seasonal temperature distributions in concrete dams, as they affect the thermal loads, which can cause high stresses in concrete dam structures and significantly affect the occurrence and behavior of cracks, as well as displacements. The effects of climate change and global warming, which may result in a general temperature increase in these structures, need to be considered [2]. Early fundamental research in the field of thermal analysis related to nonlinear and nonstationary heat conduction through a solid, considering suitable boundary conditions, was carried out by Dilger et al. [3] and Carslaw and Jaeger [4], whereas some years later Leger et al. [5,6] presented a methodology based on the finite element method (FEM), which could be used to determine seasonal temperature and stress distributions in concrete gravity dams. ...
This study presents a procedure for modeling the heat transfer process in a concrete dam, taking into account the time-varying boundary conditions on the upstream and downstream sides of the dam (i.e., the water level of the reservoir, spillover, insolation, and shading) which affect the temperature conditions of the dam. The large concrete arch-gravity Moste Dam (in North West Slovenia) was analyzed, where an automated system for the measurement of concrete and water temperatures, and for the monitoring of meteorological effects, was installed. Thermal analyses (1D and 2D) for non-linear and non-stationary heat conduction through solids were performed using a finite element method (FEM) based program, TeEx, which was complemented by two specially developed programs for determining the effects of convection and insolation, considering also the effect of shading. A 15-day period was analyzed, as well as a period of one year. It was found that the results of the performed analyses fitted in well with the experimentally determined concrete temperature measurements. The results showed that at the insolated side of the dam, the temperature gradient was largest in a very narrow area along the concrete surface, but the temperature did not stabilize shallower than at a depth of about 6 m. As part of the thermal analyses, uncertainty analyses of the results of the calculations were also performed.
... However, the main drawback of statistical models is that statistical coefficients do not have physical meaning. On the contrary, deterministic models can effectively consider the structural operational performance by calculating hydraulic component and the temperature component with finite element method, but the finite element calculation of the temperature component is quite complex [15,16]. By contrast, hybrid models effectively integrate the merits of statistical and deterministic models. ...
Single-measuring point deformation monitoring model is the most popular method in dam health monitoring. Considering that single-point monitoring model cannot comprehensively reflect the overall deformation properties of dams, a spatiotemporal hybrid model of multi-point deformation monitoring for concrete arch dams is proposed. Meanwhile, considering the chaotic effect of residual series, the support vector machine optimized by particle swarm optimization algorithm (PSO-SVM) is adopted to analyze and forecast the residual series. Hence, a spatiotemporal hybrid model for concrete arch dam deformation monitoring considering the chaotic effect of residual series is proposed in the study. Based on the theory of single-measuring point deformation monitoring, a spatiotemporal hybrid model is established by introducing space coordinate and calculating hydraulic component with finite element method. Then, with the good nonlinear processing ability of PSO-SVM, the chaotic effect of residual series is analyzed and predicted by PSO-SVM. Subsequently, a spatiotemporal hybrid model for concrete arch dam deformation monitoring considering chaotic effect of residual series is established by superimposing the residual prediction term with the predicted value of the spatiotemporal hybrid model. Engineering example show that the proposed model has better fitting and predicting precisions compared with the conventional single-point monitoring models, and it can analyze and predict the deformations of multi-point simultaneously. In addition, the proposed model reduces the workload of modelling point by point in single-point monitoring model, which considerably improves the practicality and computational efficiency of deformation-based health monitoring of concrete arch dams.
... Therefore, mathematical thermal models constitute an important tool for preventing excessive temperature gradients which may lead to cracking. Moreover, the expected rise in temperature due to global warming will have consequences on dams in service [3,4], and may increase the cracking risk of RCC dams under construction. Thermal models are composed of three main ingredients. ...
Mathematical models for the simulation of the thermal evolution of roller-compacted concrete (RCC) dams during construction constitute an important tool for preventing excessive temperature rise, which may lead to cracking and losses of functionality. Here, we present a framework for the simulation of the thermal process. We define the boundary conditions of the problem using a careful description that incorporates the main heat exchange mechanisms. We adopt both a non-adiabatic and an adiabatic heat generation model for the simulation of the cement hydration. Our numerical framework lets us study the effect of the adopted heat generation model on the thermal field. Moreover, we study the influence of the weather conditions on the evolution of the hydration, and on the starting date of construction. Our simulations have shown that the hydration model has an important influence over the temperature field during the construction and the heat generation rate. Moreover, the hydration process and the temperature evolution are driven by the weather conditions. Once the next lift is cast, its thermal insulation effect makes the hydration take place under quasi-adiabatic conditions. As expected, dams built in cold months are prone to dissipate more heat than those built in warm seasons.
... We compute heat fluxes with the methodology proposed by Santillán et al. (2015aSantillán et al. ( , 2015bSantillán et al. ( , 2015c. The total heat flux q at a given point in the dam face at temperature θ is the sum of four heat fluxes: convection between the face and the air q c , long wave radiation exchange q r , evaporative cooling q ev , and solar radiation q s , as follows: ...
Dams are singular infrastructures whose safety assessment requires mathematical models for predicting its behavior and detecting anomalies. Here, we develop an approach based on random forest regression for dam displacement prediction. Random forest regression is a non-parametric statistical technique that can deal with non-linearities and does not need assumptions regarding relationship between predictors. Inputs to the model are the water level in the reservoir, time, and concrete temperature, and the outputs –predicted variables– are movements at the desired points. Since concrete temperature is only available at those points where thermometers are placed, we compute the thermal field at any point of the dam through a one-dimensional deterministic model. Our thermal model accounts for solar radiation, shading, night and evaporative cooling, convection with the air, and long wave radiation exchange. We assess the performance of our model by comparing its estimates with recorded data at a case study, an arch dam located in Algeria, and with outputs computed by two widely used statistical models and an artificial neural network model. Our model provides satisfactory predictions and improves the results of the other models. Our approach is a powerful tool for analyzing dam displacements and incorporates a rigorous evaluation of thermal loads. It emerges as a good alternative for practitioners and stakeholders.
... We compute heat fluxes with the methodology proposed by Santillán et al. (2015aSantillán et al. ( , 2015bSantillán et al. ( , 2015c. The total heat flux q at a given point in the dam face at temperature θ is the sum of four heat fluxes: convection between the face and the air q c , long wave radiation exchange q r , evaporative cooling q ev , and solar radiation q s , as follows: ...
Dams are singular infrastructures whose safety assessment requires mathematical models for predicting its behavior and detecting anomalies. Here, we develop an approach based on random forest regression for dam displacement prediction. Random forest regression is a non-parametric statistical technique that can deal with non-linearities and does not need assumptions regarding relationship between predictors. Inputs to the model are the water level in the reservoir, time, and concrete temperature, and the outputs –predicted variables– are movements at the desired points. Since concrete temperature is only available at those points where thermometers are placed, we compute the thermal field at any point of the dam through a one-dimensional deterministic model. Our thermal model accounts for solar radiation, shading, night and evaporative cooling, convection with the air, and long wave radiation exchange. We assess the performance of our model by comparing its estimates with recorded data at a case study, an arch dam located in Algeria, and with outputs computed by two widely used statistical models and an artificial neural network model. Our model provides satisfactory predictions and improves the results of the other models. Our approach is a powerful tool for analyzing dam displacements and incorporates a rigorous evaluation of thermal loads. It emerges as a good alternative for practitioners and stakeholders.
... Moreover, the estimates of dam failure probabilities for specific failure modes, e.g. sliding along the rock-concrete interface [2], or the structural safety evaluation against future larger thermal loads due to the 10 climate change [3,4], are current research topics. Therefore, dam risk analysis requires numerical modeling tools capable of simulating failure modes, among which the prediction of both fracture initiation and propagation are of great importance. ...
Phase-field formulations have recently emerged as promising tools to model brittle fracture. Based on the variational approach to fracture, these models aim at overcoming some of the computational challenges found in simulating complex fracture patterns and their evolution due to external or internal loads. Since most applications and validation exercises thus far have been restricted to academic benchmarks, the evaluation of phase-field fracture models against experimental results an practical engineering scenarios remains fragmented.
Here we introduce a straightforward phase-field approach to simulate fluid and mechanically-driven fractures based on energy minimization and thermodynamical principles. We apply our methodology to several laboratory experiments of brittle fracture, and to fracturing processes in two full-scale concrete dams, taking into account the hydraulic forces inside the fractures. We conclude that phase-field models represent a promising computational tool that may be applied to realistic engineering scenarios.
... Consequently, it is relevant for the structural engineer to examine the influence of climate change on structural integrity and to possibly consider the concept of ''adaption" in the design process. The significance of climate change and adaptation in structural engineering is for example demonstrated by several recent studies on the deterioration of civil structures [14][15][16]. In the field of wind engineering attention has been paid to the advancement of structural design standards for wind loads, predominantly considering a traditional prescriptive approach [17]. ...
Climate change can impose considerable risks to the safety and performance of built infrastructure. Understanding these risks is of paramount importance, especially for long-lived infrastructure elements. This thesis contributes to this overarching aim and investigates the risks of climate change with particular focus on one of the main elements of modern built infrastructure, bridges. The thesis focuses on Swedish climate conditions and spans the different stages that typically constitute the risk assessment process, i.e., risk identification, risk analysis, and risk evaluation and treatment. The thesis starts by presenting a comprehensive identification of the potential climate change risks to bridges. Subsequently, a Multi-Criteria Decision Analysis (MCDA) method for prioritizing the identified risks for a certain bridge of interest is proposed. This method can also be adopted to prioritize an ensemble of bridges based on climate change risks. Four climate change risks are then investigated in more detail: 1) the impact of climate change on chloride induced corrosion of RC structures, 2) the impact of climate change on fungal decay of timber elements in-ground contact, 3) the impact of climate change on creep of concrete structures, and 4) the impact of climate change on local bridge-pier scour. The first three risks are analyzed through a full probabilistic analysis for illustrative case studies. On the other hand, for analyzing the impact of climate change on bridge-pier scour a novel national-level method, based on possibility theory, is proposed for identifying the catchments areas with the highest (or lowest) increase in equilibrium scour depth. Lastly, this thesis reviews the possible adaptation techniques for existing bridges and proposes a conceptual framework for the design of new bridges considering climate change risks. Although the focus of the current thesis is on bridges, many of the methods proposed in this thesis and its findings are relevant to other infrastructure elements. This thesis provides valuable insights towards the assessment of climate change risks on infrastructure and paves the way to resilient infrastructure systems in the face of a changing climate.
The paper studies the relationship between the ambient temperature change and the horizontal displacements on control points of the Dnieper Hydroelectric Station dam from 2016 to 2020. A specially developed software product analyzed the GNSS time series of measurements pre-processed by the GeoMoS system to determine the parameters of seasonal displacements and their relationship with seasonal changes in air temperature. The research established that the influence of ambient temperature in the absence of significant changes in the water level in the upper reservoir determines the cyclicity of dam deformations. It is established that the projections of velocity vectors of reference points in the ETRF-2014 system for the studied period do not exceed the absolute value of 3 mm/month. The directions of the horizontal displacement vectors in the first half of each year are opposite to the directions recorded in the second half. In the first half of the year, the dam’s body shifts towards the reservoir, while in the second half year period, it shifts-backwards. According to the three-year GNSS monitoring of the Dnieper Hydroelectric Station dam, the amplitude of semi-annual horizontal oscillations of the control points relative to the dam axis is from -9.5 to +8 mm. In winter and summer, the horizontal displacements increase from the edges of the dam to its central part, and the amplitudes of the horizontal displacements move vice versa. The obtained data establish a linear analytical relationship between the average temperature and the horizontal displacements of the GNSS control points.
Railway importance in the transportation industry is increasing continuously, due to the growing demand of both passenger travel and transportation of goods. However, more than 35% of the 300,000 railway bridges across Europe are over 100-years old, and their reliability directly impacts the reliability of the railway network. This increased demand may lead to higher risk associated with their unexpected failures, resulting safety hazards to passengers and increased whole life cycle cost of the asset. Consequently, one of the most important aspects of evaluation of the reliability of the overall railway transport system is bridge structural health monitoring, which can monitor the health state of the bridge by allowing an early detection of failures. Therefore, a fast, safe and cost-effective recovery of the optimal health state of the bridge, where the levels of element degradation or failure are maintained efficiently, can be achieved. In this article, after an introduction to the desired features of structural health monitoring, a review of the most commonly adopted bridge fault detection methods is presented. Mainly, the analysis focuses on model-based finite element updating strategies, non-model-based (data-driven) fault detection methods, such as artificial neural network, and Bayesian belief network–based structural health monitoring methods. A comparative study, which aims to discuss and compare the performance of the reviewed types of structural health monitoring methods, is then presented by analysing a short-span steel structure of a railway bridge. Opportunities and future challenges of the fault detection methods of railway bridges are highlighted.
A new analytical solution of the heat diffusion equation under specific boundary conditions is proposed. The solved problem is the flow of heat in a one-dimensional (1D) solid whose ends are in mediums at prescribed temperatures which follow a sinusoidal law in-phase. Heat is transferred by convection between the ends of the domain and the mediums. The solution is extended to other temperatures of the mediums through the discrete Fourier transformation. Moreover, several heat transfer mechanisms were accounted for by computing an equivalent temperature of the mediums.
The performance of the new model was assessed by computing the recorded temperatures at an arch dam case study. Temperatures were computed by: (a) the new 1D analytical model, (b) an improved version of the 1D analytical solution proposed by Stucky and Derron, and (c) a three-dimensional finite element model. The root mean squared error of computed temperatures was 1.23 K for model (a), 3.92 K for (b), and 0.83 K for (c). The new model provided a much better performance than (b) and similar but poorer than (c).
A three-dimensional finite element analysis is carried Out to determine the thermal stresses of a concrete arch darn. Appropriate heat transfer boundary conditions in the dam body are used for air and reservoir temperature as well as solar radiation variations. A finite element model is used to determine annual variation of temperature and thermal stress in the body of Karaj arch darn in Iran as a case study. The rate of convergence of the numerical solution is examined. The temperatures predicted by the model are satisfactorily compared with the instrumentation records at Karaj Dam. Results of the finite element analysis show that probable cracks Occur in a very narrow region of the downstream face. Thermal loads have the most significant effects for causing downstream cracks in comparison with self-weight and hydrostatic loads. The cracked areas of the downstream face conform to the regions that have the highest temperature in the downstream face. This can be associated with the solar radiation, which shows that two-dimensional analysis of an arch dam cannot yield accurate results and three-dimensional analysis is necessary.
This paper presents a design-office procedure for calculating the shrinkage and creep of concrete using the information available at design, namely, the 28-day specified concrete strength, the concrete strength at loading, element size, and the relative humidity. The method includes strength development with age, relationship between modulus of elasticity and strength, and equations for predicting shrinkage and creep. The method can be used regardless of what chemical admixtures or mineral by-products are in the concrete, the casting temperature, or the curing regime. The only arbitrary information are factors appropriate to the cementitious materials, which can be improved from measured strength-age data. At the most basic level, the proposed method requires only the information available to the design engineer. The predicted values can be improved by simply measuring concrete strength development with time and modulus of elasticity. Aggregate stiffness is taken into account by using the average of the measured cylinder strength and that back-calculated from the measured modulus of elasticity of the concrete. The predictions are compared with experimental results for 185 data sets for compliance and 115 data sets for shrinkage. The comparisons indicate that shrinkage and creep can be calculated within ±30%. Comparisons with the same experimental data are presented for ACI 209, CEB MC1990, and B3.
Carbonation affects the performance, serviceability and safety of reinforced concrete (RC) structures when they are placed in environments with important CO 2 concentrations. Since the kinetics of carbonation depends on parameters that could be affected by climate change (temperature, atmospheric CO 2 pressure and relative humidity (RH)), this study aims at quantifying the effect of climate change on the durability of RC structures subjected to carbonation risks. This work couples a carbonation finite element model with a comprehensive reliability approach to consider the uncertainties inherent to the deterioration process. The proposed methodology is applied to the probabilistic assessment of carbonation effects for several cities in France under various climate change scenarios. It was found that climate change and local RH have a significant impact on corrosion initiation risks.
Chloride ingress and carbonation cause corrosion of reinforced concrete (RC) structures affecting its operational life. Experimental evidence indicates that these deterioration processes are highly influenced by CO2 emissions and climatic conditions in the surrounding environment – i.e., temperature, humidity, etc. Since studies on global warming announce changes in climate, the impact of changing climate on RC durability should also be considered. This paper links RC deterioration mechanisms to CO2 emissions and global warming. Based on various studies on climate change, models for estimating the effect of CO2 emissions and temperature/humidity changes due to global warming are described. Furthermore, various scenarios of global warming that can be used to assess the effect of climate change in structural reliability are proposed. The proposed approach is then illustrated with a numerical example that calculates the probability of failure of a RC bridge beam for future climate scenarios. The paper then outlines some adaptation strategies, particularly focusing on the needs for risk-based selection of optimal adaptation measures.
At early age, temperature in massive concrete structures may reach over 70°C because hydration is an exothermic chemical reaction. Temperature evolution (increasing followed by decreasing temperature) can lead to damage risks in the short and long term. Firstly, cracking due to self-restrained strains (essentially thermal strains) can occur (which increase the transport properties and so the kinetics of degradation); and secondly, delayed ettringite formation can appear. In addition, if autogenous and thermal strains are restrained, compressive stresses and then tensile stresses increase, which can cause crossing cracks. However, this paper will not deal with these phenomena. In the first part, sensitivity to delayed ettringite formation and early age cracks by self-restrained strains are studied with regards to the environmental conditions by a numerical approach. This part shows that the external temperature has a significant impact on the maximal temperature reached, but that the temperature difference between the core and the surface is mainly impacted by the wind velocity. Then, a parametric study on the effect of the variation of thermal properties at early age has been achieved and shows that it needs to be taken into account. Finally, visco-elastic mechanical calculations show the impact of thermal property variation on the stresses generated by self restraint.
The performance of daily and hourly diffuse horizontal solar irradiation models and correlations is examined using an assembled data set of multivariate meteorological time series from countries in the North Mediterranean Belt area. The correlations reviewed use only daily global, hourly global or daily diffuse irradiation as input, for the daily or hourly time scale. The best overall performance was presented by the Frutos correlation for the estimation of the daily diffuse radiation by an adapted version of the Liu and Jordan correlation for the mean daily diffuse radiation profile, and by the Hollands and Crha model for estimation of hourly diffuse values from the corresponding global values. The results show that the best correlation for each site varies. Two empirical piecewise correlations were also developed by the authors with the help of the data bank available, yielding models that showed even better fits to the data. The results show some seasonal and location dependence.
Members of the Passive Solar Research Group have undertaken a project to measure the radiant cooling component of a cool storage roof at the Solar Energy Research Test Facility located at Allwine Prairie near Bennington, Nebraska. There are over fourteen hundred data points taken in a year's period of time that measure sky and surface water temperatures, night sky radiation, ambient temperature and dew point temperature. The purpose of this study is to develop a relationship between night sky emissivity values and dew point temperatures in order to develop an algorithm to predict radiant cooling.
An analytical method is described for calculating the daily averages or effective values of the sun's elevation, azimuth, hour angle, angle of incidence and air mass. A particular case is considered first and corresponds to the extraterrestrial radiation. The general derivation takes into account atmospheric effects in a simple way, provided that long-term averages of solar radiation are available. Examples of application are given for the climate of Montreal, Canada. In particular, it is shown that monthly averages of beam radiation on the horizontal may be directly converted to normal incidence values (and vice versa) by use of the mean solar elevation.
The durability of concrete is determined largely by its deterioration over time which is affected by the environment. Climate change may alter this environment, causing an acceleration of deterioration processes that will affect the safety and serviceability of concrete infrastructure in Australia, U.S., Europe, China and elsewhere. This investigation of concrete deterioration under changing climate in Australia uses Monte-Carlo simulation of results from General Circulation Models (GCMs) and considers high greenhouse gas emission scenarios representing the A1FI schemes of the IPCC. We present the implications of climate change for the durability of concrete structures, in terms of changes in probability of reinforcement corrosion initiation and corrosion induced damage at a given calendar year between 2000 and 2100 across Australia. Since the main driver to increased concrete deterioration is CO2 concentration and temperature, then increases in damage risks observed in Australia are likely to be observed in other concrete infrastructure internationally. The impact of climate change on the deterioration cannot be ignored, but can be addressed by new approaches in design. Existing concrete structures, for which design has not considered the effects of changing climate may deteriorate more rapidly than originally planned.
A method for adjusting dynamically downscaled precipitation and temperature scenarios representing specific sites is presented.
The method reproduces mean monthly values and standard deviations based on daily observations. The trend obtained in the regional
climate model both for temperature and precipitation is maintained, and the frequency of modelled and observed rainy days
shows better agreement. Thus, the method is appropriate for tailoring dynamically downscaled temperature and precipitation
values for climate change impact studies. One precipitation and temperature scenario dynamically downscaled with HIRHAM from
the Atmospheric-Ocean General Circulation Model at the Max-Planck Institute in Hamburg, ECHAM4/OPYC4 GSDIO with emission scenario
IS92a, is chosen to illustrate the adjustment method.
Reinforced concrete (RC) structures are subjected to environmental actions affecting their performance, serviceability and safety. Among these actions, chloride ingress leads to corrosion and has been recognized as a critical factor reducing service life of RC structures. This paper presents a stochastic approach to study the influence of weather conditions and global warming on chloride ingress into concrete. The assessment of chloride ingress is carried out on the basis of a comprehensive model that couples the effects of convection, chloride binding, concrete aging, temperature and humidity. A simplified model of temperature and humidity including seasonal variations and global warming is also proposed in this work. Three scenarios of global warming are defined based on: gas emissions, global population growth, introduction of new and clean technologies and use of fossil sources of energy. The proposed approach is illustrated by a numerical example where the preliminary results indicate that climate changes may yield to significant lifetime reductions.
Predictions of natural climate variability and the human impact on
climate are inherently probabilistic, due to uncertainties in the
initial conditions of forecasts, the representation of key processes
within models, and climatic forcing factors. Hence, reliable estimates
of climatic risk can be made only through ensemble integrations of Earth
system models in which these uncertainties are explicitly
incorporated.The ENSEMBLES project, funded through a 5-year contract
with the European Commission, aims to provide probabilistic estimates of
climatic risk through ensemble integrations of Earth system models in
which the uncertainties noted here are explicitly incorporated.
In this article, an analytical model is presented for the simulation of the thermal behavior of dams that are subjected to the environmental thermal action during service. The method of solution adopted as well as the evaluation of the different parameters is described in detail. Also, the theoretical results that are predicted by the model are compared with experimental results obtained through the monitoring of temperature in several dams in Spain. The dams considered are currently in use, of different types and in distinct locations. Peer Reviewed
In the design of a high dam it is necessary to predict the water temperature at various depths in the reservoir. For example, in order to determine the temperature of the dam body at which the contraction joints of a gravity dam are grouted, the yearly mean temperature of water must be known. To determine the temperature loads on an arch dam, the amplitude of variation of water temperature must be given. There is no appropriate method for determining water temperature at present. On the basis of a large amount of observational data, a series of formulae are proposed for determining water temperature in a deep reservoir (with depth not less than 30m). These formulae have been adopted in the 'Design Specifications for Concrete Arch Dams' of China.
A model for the characterization of concrete creep and shrinkage in the design of concrete structures is recommended. It is simplier, agrees better with the experimental data and is justified better theoretically than the previous models. The model complies with the general guidelines recently formulated by RILEM TC 107. Justification of the model and various refinements are to be published shortly in two parts.
Thermal effects are significant loads for assessing concrete dam behaviour during operation. A new methodology to estimate thermal loads on concrete dams taking into account processes which were previously unconsidered, such as: the evaporative cooling, the night radiating cooling or the shades, has been recently reported. The application of this novel approach in combination with a three-dimensional finite element method to solve the heat diffusion equation led to a precise characterization of the thermal field inside the dam. However, that approach may be computationally expensive. This paper proposes the use of a new one-dimensional model based on an explicit finite difference scheme which is improved by means of the reported methodology for computing the heat fluxes through the dam faces. The improved model has been applied to a case study where observations from 21 concrete thermometers and data of climatic variables were available. The results are compared with those from: (a) the original one-dimensional finite difference model, (b) the Stucky-Derron classical one-dimensional analytical solution, and (c) a three-dimensional finite element method. The results of the improved model match well with the observed temperatures, in addition they are similar to those obtained with (c) except in the vicinity of the abutments, although this later is a considerably more complex methodology. The improved model have a better performance than the models (a) and (b), whose results present larger error and bias when compared with the recorded data.
A methodology for computing thermal loads in arch dams is proposed. The methodology considers the nonuniform distribution of solar insolation over dam faces because of shading, curvature of dam faces, orientation, and slopes. Because, in most cases, the mean daily global solar radiation is the only type available, a methodology for estimating hourly solar energy reaching dam faces is described. The methodology is applied to a case study where observations from 21 thermometers embedded in the concrete and data of climatic variables are available. The concrete temperature field is successfully computed, with good agreement between observations and predictions. The proposed methodology is compared with other approaches, and the consequences on the stress calculations are analyzed.
A changing climate which leads to increases in atmospheric CO2 concentration, and changes in temperature and relative humidity (RH), especially in the longer term, will accelerate the deterioration processes and consequently decline the safety, serviceability and durability of reinforced concrete (RC) infrastructure. This paper presents an investigation of carbonation-induced deterioration in three typical Chinese cities (Kunming, Xiamen and Jinan) under a changing climate. The changing trends of atmospheric CO2, local temperature and RH of typical Chinese cities are projected based on the latest CO2 emission scenarios. The time-dependent analysis is based on Monte Carlo simulation, and includes the uncertainty of climate projections, deterioration processes, material properties, dimensions and accuracy of predictive models. Deterioration of RC structures is represented by the probabilities of reinforcement corrosion initiation and damage. It was found that the mean carbonation depths by 2100 may increase by up to 45% for RC structures in China due to a changing climate. It was also found that climate change can cause an additional 7-20% of carbonation-induced damage by 2100 for RC buildings in temperate or cold climate areas in China. The findings provide a basis for the development of climate adaptation strategies through the improved design of concrete structures.
In its lifetime, a dam can be exposed to significant water level variations and seasonal environmental temperature changes. The structural safety control of a concrete dam is supported by monitoring activities and is based on models.
In practice, the interpretation of recorded concrete dam displacements is usually based on HST (hydrostatic, seasonal, time) statistical models. These models are widely used and consider that the thermal effect can be represented by a seasonal function. The main purpose of this paper is to present an HTT (hydrostatic, thermal, time) statistical model to interpret recorded concrete dam displacements. The idea is to replace the seasonal function with the use of recorded temperatures that better represent the thermal effect on dam behavior. Two new methodologies are presented for constructing HTT statistical models, both based on principal component analysis applied to recorded temperatures in the concrete dam body. In the first method, principal component analysis is used to choose the thermometers for the construction of the HTT model. In the second method, the thermal effect is represented by the principal components of temperature of selected thermometers.
The advantage of these methods is that the thermal effect is represented by real temperature measured in the concrete dam body. The HTT statistical models proposed are applied to the 110 m high Alto Lindoso arch dam, and the results are compared with the HST displacement model. Copyright
The exposures and risks of coastal built as well as natural assets to storm-tide inundation are expected to be more pronounced as a result of the reduced recurrence interval or the increased occurrence frequency of storm tides in Australia due to sea-level rise. This study investigates the distributions of direct damage losses and adaptation benefits for residential buildings considering uncertainties of storm tides under projected sea-level rises in South East Queensland, one of the fastest-growing regions in Australia in the last two decades. The study subsequently indicates that ‘deterministic decision-making’ based on an individual hazard or scenario could be fundamentally flawed for coastal planning and adaptation as a result of uncertain natures in coastal hazards under changing climate. The developed knowledge can eventually facilitate better decision-making processes for adapting coastal residential buildings to future climate change under considerable uncertainties. It is also found that constructing new buildings with higher floor heights is a relatively inexpensive but also a highly effective approach insensitive to uncertainties for reducing future damage losses of storm-tide inundation.
This paper presents the application of the advanced probabilistic slope stability model with precipitation effects developed to assess the performance of small homogeneous earthfill embankment dam slopes, when exposed to future seasonal precipitation scenarios. Here, the UK's latest probabilistic climate model known as UKCP09 is applied. To reflect the critical conditions conducive to slope failure, a benchmark has been developed to identify the change, if any, in the risk classification of the slope's performance level due to precipitation. Thus, enabling the reassessment of the dam's risk classification, as categorised by the Flood and Water Management Act 2010. Such an approach could therefore be well placed to support and enhance the decision-making process, its impact on the public, especially in relation to future climate effects.
The present paper investigates the impact of the global climate change on typhoon-induced wind risk for residential buildings in Japan. It is based on (1) the output from a climate model for an assumed climate change scenario, (2) probabilistic typhoon hazard modelling, (3) reliability-based fragility modelling and (4) failure cost modelling. The objective of the present paper is to demonstrate the availability and effectiveness of a general methodology for carrying out the impact assessment. It also aims at clarifying missing information required for a more precise and reliable impact assessment. Under the employed climate model, assumed climate scenario and vulnerability model and other assumptions made in the present paper, it is found that the typhoon-induced wind risks for residential buildings in Japan are not likely to change significantly in the future.
In the future, the more frequent occurrence of severe heat waves and long dry periods due to climate change can cause lowering of the ground water level and therefore consolidation of the soil. Consequently, increased differential settlements are expected that may damage underground water infrastructure. Models were developed to assess the impact of differential settlements on pipe failure. The main concept of these models is that the pipe-soil system is schematized as a beam on an elastic foundation using Winkler type springs. For climate change induced settling, a parametric function of the soil settlement is proposed. A Monte-Carlo analysis has been applied to predict pipe failure probabilities.
Solar radiation induces non-uniform temperature distribution in the bridge structure depending on the shape of the structure and shadows cast on it. Especially in the case of curved steel box girder bridges, non-uniform temperature distribution caused by solar radiation may lead to unusual load effects enough to damage the support or even topple the whole curved bridge structure if not designed properly. At present, it is very difficult to design bridges in relation to solar radiation because it is not known exactly how varying temperature distribution affects bridges; at least not specific enough for adoption in design. Standard regulations related to this matter are likewise not complete. In this study, the thermal behavior of curved steel box girder bridges is analyzed while taking the solar radiation effect into consideration. For the analysis, a method of predicting the 3-dimensional temperature distribution of curved bridges is used. It uses a theoretical solar radiation energy equation together with a commercial FEM program. The behavior of the curved steel box girder bridges is examined using the developed method, while taking into consideration the diverse range of bridge azimuth angles and radii. This study also provides reference data for the thermal design of curved steel box girder bridges under solar radiation, which can be used to develop design guidelines.
The purpose of this research work is to identify the effect of the daily variation of the air temperature on the structural response of a concrete dam. It is intended to obtain a better knowledge about structural behaviour of concrete dams. In current day to day activities, quantitative interpretation models are used for the assessment of structural dam behaviour of concrete dams. Most models ignore the temperature effect of a wave with a daily variation. However, in dams with automated data acquisition systems this daily effect can be used to anticipate the detection of abnormal behaviour.In this paper, the Short Time Fourier Transform analysis of the residuals is used, obtained by the quantitative interpretation models and measurement data, to identify the signature that the daily variation of the air temperature has on the structural behaviour of a concrete dam. A case study is presented based on the analysis of a horizontal displacement measured on a pendulum, in the Alto Lindoso concrete dam. As a result, the relation between magnitudes of daily variations of the horizontal displacement analysed and the air temperature was defined. The relation obtained can be used to assess if there is alterations or not in the dam response to short period loads corresponding to the daily variations analysed.
This article considers the issues surrounding climate change and the rail industry in two ways. First, it discusses the role that railways could play in reducing overall greenhouse gas (GHG) emissions and thus help to reduce and mitigate the global temperature increase that will occur over the coming decades. It is argued that, while railways in general have lower emissions than other modes, if a significant decrease in emissions is to be attained, then the capacity of the current rail network needs to be greatly increased to encourage a significant modal shift from road and domestic air travel. Electrification and the provision of high-speed lines can also play a role in this regard, but only if the power that is drawn from the grid is supplied by low carbon sources. Second, the article considers the effect of climate change on the operation of the railway in the next few decades and the adaptations that will be required. The main effects of such changes are likely to be an increase in the track buckling problem, severe strain on railway drainage systems, and the increased likelihood of disruption because of extreme weather events. Ongoing work in this field, aimed at making the railways more resilient, is discussed. It is concluded that, for each of the two areas considered, there is a need for overall system modelling, both to fully evaluate possible mechanisms to reduce GHG emissions, taking account of transfer between modes, capacity limitations, and the national energy mix; and to properly evaluate the major climate change risks to railway operation and to prioritize the use of resources in tackling these issues.
This paper discusses the importance of climate change for the UK building stock and reviews the predictions of the United Kingdom Climate Impacts Programme 2002 (UKCIP02) scenarios for the future climate that are of relevance to buildings and construction. The possible impacts of these changes on flooding, wind damage, driving rain impact, subsidence and the internal environment of buildings are reviewed and the steps that might be taken to mitigate these impacts discussed. The current response of regulators, standardisation bodies, building owners and the insurance industry to these impacts is examined, and it is shown that each body acts in different ways to different impacts. Some bodies, such as government departments responsible for building regulations and the insurance industry, are taking the possibility of climate change very seriously. However, the uncertainty of future climate predictions, especially as regards wind speed, means that it is not easy to incorporate these issues in formal legislation. The whole culture of standardisation, which is based on well-established data, such as mean climate data over the last 30 years, makes it difficult for British and European Standards, which underpin regulations, to react to the changing climate.
This paper presents frequency domain solution algorithms of the one-dimensional transient heat transfer equation that describes temperature variations in arch dam cross sections. Algorithms are developed to compute the temperature T(x,t), spatial distribution, and time evolution for the "direct" problem, where the temperature variations are specified at the upstream and downstream faces, and for the "inverse" problem, where temperatures have been measured at thermometers located inside instrumented dam sections. The resulting nonlinear temperature field is decomposed in an effective average temperature, T-m(t), and a linear temperature difference, T-g(x,t), from which the dam thermal displacement response can be deducted. The proposed frequency domain solution procedures are able to reproduce an arbitrary transient heat response by appending trailing temperatures at the end of thermal signals, thus transforming a periodic heat transfer problem in a transient one. The frequency domain solution procedures are used to develop the HTT (hydrostatic, temperature, time) statistical model to interpret concrete dam-recorded pendulum displacements. In the HTT model, the thermal loads are arbitrary and can contain temperature drift or unusual temperature conditions. The explicit use of T-m(t) and T-g(x,t) in the HTT dam displacement model allows extrapolation for temperature conditions that have never been experienced by the dam before (within the assumption of elastic behavior). The HTT model is applied to the 131-m-high Schlegeis arch dam, and the results are compared with the HST (hydrostatic, seasonal, time) displacement model that is widely used in practice.
Temperature distribution on the exposed face (especially the downstream face) of arch dams is non-uniform, to a certain extent, due to the variation in solar radiation striking the surface. However, the temperature at the same elevation across the dam axis is generally assumed to be uniform in the design specifications for arch dams because there is no accepted procedure for defining the non-uniform temperature field. In this paper, a practical model for predicting the non-uniform temperature of the exposed face is presented by considering both solar radiation and shading effects. The ASHRAE clear sky model was adopted to calculate the solar radiation, and a ray-tracing algorithm was used to analyze the shade of surrounding terrain and the structure per se. The real-life case study presented in this study shows that the proposed model was effective in simulating and accessing reasonable thermal distribution. Subsequently, the case study also reveals that the non-uniform temperature had a significant effect on surface thermal stress and crack propagation.
This paper presents the performance of 10 arithmetic models used to estimate diffuse solar irradiance on inclined surfaces in a comparative study with actual data readings made available on an hourly and a daily basis. The data readings have been taken from a south facing surface inclined at 42° in an area at some distance from the provincial capital in the Spanish province of Valladolid. In order to confirm the results, three statistical parameters have been used in the study; root mean square error (RMSE), mean bias error (MBE) and Stone’s t-statistic. The results obtained favour the Muneer model, followed by the Reindl model, for hourly as well as for daily values. The Temps–Coulson model gives rise to great discrepancies with respect to the values measured. The results for the Perez model are not good due to the use of parameters that are not specifically calculated for the area in this study, which underlines the need to take an area’s features into account so that predictions for diffuse irradiance measured on inclined surfaces may be as accurate as possible.
The safety control of large dams is based on the measurement of some important quantities that characterize their behaviour (like absolute and relative displacements, strains and stresses in the concrete, discharges through the foundation, etc.) and on visual inspections of the structures. In the more important dams, the analysis of the measured data and their comparison with results of mathematical or physical models is determinant in the structural safety assessment.In its lifetime, a dam can be exposed to significant water level variations and seasonal environmental temperature changes. The use of statistical models, such as multiple linear regression (MLR) models, in the analysis of a structural dam’s behaviour has been well known in dam engineering since the 1950s. Nowadays, artificial neural network (NN) models can also contribute in characterizing the normal structural behaviour for the actions to which the structure is subject using the past history of the structural behaviour. In this work, one important aspect of NN models is discussed: the parallel processing of the information.This study shows a comparison between MLR and NN models for the characterization of dam behaviour under environment loads. As an example, the horizontal displacement recorded by a pendulum is studied in a large Portuguese arch dam. The results of this study show that NN models can be a powerful tool to be included in assessments of existing concrete dam behaviour.
Temperature distributions in concrete bridges are nonlinear and induce self-equilibrated stress distributions. Such distributions depend on several variables (environmental conditions, physical and material properties, and location of bridge). On the other hand, temperature and stress distributions in concrete box girder bridges depend on the cross-section geometry. In this paper an analytical model to predict temperature and stress distributions is briefly presented. The results derived from the analytical model are compared with the experimental results obtained by other authors. In addition, several parametric studies needed to analyze the influence of the cross-section geometry on the thermal response and stress distributions in concrete box girder bridges are carried out. Some remarks related to the vertical and transverse temperature differences are presented. Finally, some considerations about the thermal response in concrete box girder bridges are identified.
The durability of concrete is determined largely by its deterioration over time which is affected by the environment. Climate change may alter this environment, especially in the longer term, causing an acceleration of reinforcement corrosion that will affect the safety and serviceability of concrete infrastructure in Australia, US, Europe, China and elsewhere. This paper reviews advanced simulation procedures to predict increases in damage (corrosion) risks under a changing climate in Australia in terms of changes in probability of reinforcement corrosion initiation and corrosion induced damage due to (i) increase in the concentration of CO2 in the atmosphere, and changes to (ii) temperature and (iii) humidity. These time and spatial variables will affect the penetration of aggressive agents CO2 and chlorides into concrete, and the corrosion rate once corrosion initiation occurs. The effectiveness of adaptation measures for new and existing buildings, bridges, and other concrete infrastructure is then assessed. Carbonation-induced damage risks may increase by more than 16% which means that one in six structures will experience additional and costly corrosion damage by 2100. We show that the impact of climate change on infrastructure deterioration cannot be ignored, but can be addressed by changes to design procedures including increases in cover thickness, improved quality of concrete, and coatings and barriers. For example, an increase in design cover of 10 mm and 5 mm for structures where carbonation or chlorides govern durability, respectively, will ameliorate the effects of a changing climate.
Over 150 research articles relating three multi-disciplinary topics (air pollution, climate change and civil engineering structures) are reviewed to examine the footprints of air pollution and changing environment on the sustainability of building and transport structures (referred as built infrastructure). The aim of this review is to synthesize the existing knowledge on this topic, highlight recent advances in our understanding and discuss research priorities. The article begins with the background information on sources and emission trends of global warming (CO(2), CH(4), N(2)O, CFCs, SF(6)) and corrosive (SO(2), O(3), NO(X)) gases and their role in deterioration of building materials (e.g. steel, stone, concrete, brick and wood) exposed in outdoor environments. Further section covers the impacts of climate- and pollution-derived chemical pathways, generally represented by dose-response functions (DRFs), and changing environmental conditions on built infrastructure. The article concludes with the discussions on the topic areas covered and research challenges. A comprehensive inventory of DRFs is compiled. The case study carried out for analysing the inter-comparability of various DRFs on four different materials (carbon steel, limestone, zinc and copper) produced comparable results. Results of another case study revealed that future projected changes in temperature and/or relatively humidity are expected to have a modest effect on the material deterioration rate whereas changes in precipitation were found to show a more dominant impact. Evidences suggest that both changing and extreme environmental conditions are expected to affect the integrity of built infrastructure both in terms of direct structural damage and indirect losses of transport network functionality. Unlike stone and metals, substantially limited information is available on the deterioration of brick, concrete and wooden structures. Further research is warranted to develop more robust and theoretical DRFs for generalising their application, accurately mapping corrosion losses in an area, and costing risk of corrosion damage.
This study investigates the performance of the isotropic and four anisotropic hourly tilted surface radiation models by using monthly average hourly utilizable energy as a standard of measure. Utilizable energy is the radiation above a specified threshold level. Differences between the utilizable energy measured and the utilizable energy predicted are observed for various surface slope/azimuth orientations and critical radiation levels. Normalized root mean square difference and normalized mean bias difference statistics are formed to quantify the ability of each model to estimate the utilizable energy on a tilted surface. The influence of horizontal diffuse radiation on tilted surface model performance is examined by comparing the predicted utilizable energy on a tilted surface using both measured horizontal diffuse and estimated horizontal diffuse found from diffuse fraction correlations. On an overall basis, the isotropic sky model showed the poorest performance and is not recommended for estimating the hourly radiation on a tilted surface. The anisotropic models have comparable performance to each other. There was no significant degradation of tilted surface model performance when the diffuse radiation is estimated from a diffuse fraction correlation rather than obtained from measurements.
The finite difference method was used to simulate the unsteady state cooling of spheres, infinite slabs and infinite cylinders of food materials subject to both convection and evaporation at the product surface. Simulations were conducted across wide ranges of air temperature, surface heat transfer coefficient, product initial temperature, surface water activity and air relative humidity. Algebraic equations are proposed for finding three parameters—the product equilibrium temperature as time → ∞, a slope parameter of semi-log plots relating unaccomplished temperature change to time and an intercept parameter of the same plots. The first of these equations is based on psychrometric theory and the other two were derived by using non-linear regression to curve-fit the numerically simulated cooling rates. These equations allow the numerically simulated cooling times to be predicted within about ±5%. In Part 2 the accuracy of these equations as a simple chilling time prediction method is tested experimentally for model food systems. In Part 3 their application to real foods is considered.
This study evaluates the performance of 12 models to estimate hourly diffuse solar irradiation on inclined surfaces from those measured on horizontal surfaces. Total solar irradiation incident on a tilted surface consists of three components including: beam, diffuse and reflected from the ground. On a semi-hourly basis, the beam component can be calculated by the ratio of the incidence angle to the solar zenith angle. The reflected component has a small effect on calculations and may be calculated with an isotropic model. In contrast, models for estimating the diffuse component show major differences, which justify the validation study that this paper discusses. Twelve models were tested against recorded south- and west-facing slope irradiances at Karaj (35°55′N; 50°56′E), Iran. The following models were included: Badescu [Ba], Tian et al. [Ti], Perez et al. [P9], Reindl et al. [Re], Koronakis [Kr], Perez et al. [P8], Skartveit and Olseth [SO], Steven and Unsworth [SU], Hay [Ha], Klucher [Kl], Temps and Coulson [TC], and Liu and Jordan [LJ].The relative root mean square error (RMSE), for the south-facing surface ranges from 10.16% to 54.89% for the SO and TC models, respectively. For the west-facing surface, RMSE ranges from 30.71% for the P9 model to 63.53% for the TC model. Statistical indices show that all models produce large errors for the west-facing surface. Statistical indices for the south-facing surface show reasonably good agreement with measured data.
Accurately computing solar irradiance on external facades is a prerequisite for reliably predicting thermal behavior and cooling loads of buildings. Validation of radiation models and algorithms implemented in building energy simulation codes is an essential endeavor for evaluating solar gain models. Seven solar radiation models implemented in four building energy simulation codes were investigated: (1) isotropic sky, (2) Klucher, (3) Hay–Davies, (4) Reindl, (5) Muneer, (6) 1987 Perez, and (7) 1990 Perez models. The building energy simulation codes included: EnergyPlus, DOE-2.1E, TRNSYS-TUD, and ESP-r. Solar radiation data from two 25 days periods in October and March/April, which included diverse atmospheric conditions and solar altitudes, measured on the EMPA campus in a suburban area in Duebendorf, Switzerland, were used for validation purposes. Two of the three measured components of solar irradiances – global horizontal, diffuse horizontal and direct-normal – were used as inputs for calculating global irradiance on a south-west façade. Numerous statistical parameters were employed to analyze hourly measured and predicted global vertical irradiances. Mean absolute differences for both periods were found to be: (1) 13.7% and 14.9% for the isotropic sky model, (2) 9.1% for the Hay–Davies model, (3) 9.4% for the Reindl model, (4) 7.6% for the Muneer model, (5) 13.2% for the Klucher model, (6) 9.0%, 7.7%, 6.6%, and 7.1% for the 1990 Perez models, and (7) 7.9% for the 1987 Perez model. Detailed sensitivity analyses using Monte Carlo and fitted effects for N-way factorial analyses were applied to assess how uncertainties in input parameters propagated through one of the building energy simulation codes and impacted the output parameter. The implications of deviations in computed solar irradiances on predicted thermal behavior and cooling load of buildings are discussed.
The relative humidity (RH) and the dewpoint temperature (td) are two widely used indicators of the amount of moisture in air. The exact conversion from RH to td, as well as highly accurate approximations, are too complex to be done easily without the help of a calculator or computer. However, there is a very simple rule of thumb that can be very useful for approximating the conversion for moist air (RH > 50%) which does not appear to be widely known by the meteorological community: td decreases by about 1°C for every 5% decrease in RH (starting at td = t, the dry bulb temperature, when RH = 100%). This article examines the mathematical basis and accuracy of this and other relationships between the dewpoint and relative humidity. Several useful applications of the simple conversion are presented, in particular the computation of the cumulus cloud-base level (or lifting condensation level) as zLCL (20 + t/5) (100 - RH), where zLCL is in meters when t is in degrees Celcius and RH in percent. Finally, a historical perspective is given with anecdotes about some of the early work in this field.