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On the collapse evaluation of existing RC bridges exposed to corrosion under horizontal loads

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Abstract

The structural safety and durability of existing reinforced concrete bridges can be considered as one of the current most important research topics in structural engineering, especially after the numerous collapses that have occurred in recent years. Considering the Italian context, it is important to highlight that most of these structures were built in the 1960s and 1970s and, consequently, the effects of materials degradation phenomena have reduced their vertical and horizontal load-bearing capacity. This paper presents an efficient procedure for the collapse mechanism evaluation of existing reinforced concrete motorway bridges under horizontal loads, considering the corrosion effects due to carbonation through a simplified model that takes into account the steel rebars reduction and applying a multi-modal pushover analysis approach. In this study, three different (slight, moderate and high) corrosion scenarios are considered for two existing reinforced concrete bridges characterized by frame piers. The results of the numerical analyses, which consider both brittle and ductile failure mechanisms, highlight a significant decrease of the seismic capacity of the structures as the corrosion level increases, especially for brittle collapse mechanisms that are strongly affected by the bridge maintenance condition. Such a procedure allows identifying the first structural elements reaching the collapse, providing useful information for the maintenance of existing bridges in terms of repair and strengthening interventions.

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... The procedure proposed for the evaluation of the seismic vulnerability of the existing RC bridges, described in detail in [2,3], is based on the Multimodal pushover approach and on the implementation of a simplified Finite Element Model (FEM) through the software MIDAS Civil [4] where all the elements of the bridge (piers, pier caps and the deck) are schematized using only beam elements in order to reduce the computational effort. The elastomeric bearings, instead, are represented through elastic links having translational and rotational stiffnesses evaluated according to [5]. ...
... Another consequence of the corrosion process is a progressive reduction of piers stiffness, resulting in an increase of vibration natural periods, especially for the principal modes ( Figure 8). Finally, capacity curve for all the significant vibration modes shapes of the viaducts can be determined according to the procedure described in [2,3] for the three scenarios (Figures 9 and 10). ...
Conference Paper
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Recently, the engineering interest about the durability of existing reinforced concrete structures has significantly increased as confirmed by the conspicuous scientific literature. The results of these studies are influencing the development of new structural codes. Among the wide range of existing reinforced concrete structures, motorway viaducts stand out for their strategic relevance. Most of these structures were built between '60 and '70 years and, nowadays, the materials degradation phenomena are leading to strength capacity reduction, either in serviceability condition or in presence of exceptional loads such as the seismic action. In order to evaluate the degradation phenomena effects on the seismic vulnerability of motorway viaducts, this paper shows an efficient procedure to evaluate the seismic performance of reinforced concrete bridges starting from the modelling of the materials degradation, according to several scenarios, and by carrying out multimodal pushover analyses.
... However, both specimens followed a similar pattern after achieving the peak load and failed due to longitudinal rebar buckling. The difference in the behavior of BMRC1 and NEWRC1 could be due to the combined influence of both concrete as well as steel, as reported by [33,34]; therefore, future studies can focus on combining the HSC with NSR and NSC with HSR. served: (a) the elastic stage, i.e., the straight line before reaching the yield point, (b) the elastic-plastic stage, i.e., nonlinear response, and (c) the failure stage, i.e., shear strength degradation after longitudinal rebar buckling. ...
... However, both specimens followed a similar pattern after achieving the peak load and failed due to longitudinal rebar buckling. The difference in the behavior of BMRC1 and NEWRC1 could be due to the combined influence of both concrete as well as steel, as reported by [33,34]; therefore, future studies can focus on combining the HSC with NSR and NSC with HSR. A comparison between the backbone curves of the columns NEWRC1, NEWRC2, and NEWRC3 can be seen in Figure 9. Here, the backbone curves of all three specimens overlap before the column's yield load point, which indicates that the difference in transverse rebar spacing did not influence the initial stiffness. ...
Article
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Despite the numerous advantages high-strength reinforcement (HSR) and high-strength concrete (HSC) offer over conventional materials, the practical use of these materials for bridge column design in seismic zones has somewhat been limited. This is due to the insufficient research data and guidelines for the seismic design of bridges using HSC and HSR and the lack of a reliable analytical model. Therefore, to address this issue and promote the application of HSR and HSC, this paper investigates high-strength bridge columns’ seismic performance experimentally and numerically. Six large-scale reinforced concrete (RC) bridge columns and one multi-column bent frame were tested under a quasi-static cyclic loading with constant axial compression. The primary design parameters were axial load ratio, longitudinal and transverse reinforcement yield strength, and transverse reinforcement spacing. The failure pattern of high-strength columns was similar to conventional RC columns and satisfied the requirements for seismic design in terms of failure mode, hysteresis behavior, ductility, and energy dissipation capacity. The experimental ductility values of the high-strength columns were satisfactory and capable of meeting the ductility demand of most codes. Furthermore, a numerical model was built using the OpenSees program to predict the seismic performance of the specimens and then verified by comparing them with the test results of 12 columns. The numerical model’s results were in good agreement with the experimental results. The results suggested that numerical modeling techniques commonly used for normal strength concrete (NSC) columns can be used for HSC bridge columns by incorporating a proper material model.
... The pier shaft is responsible for sustaining the superstructure and affecting the overall stability of both structures. Pietro et al. [18,19] proposed an efficient procedure for the collapse mechanism evaluation of existing reinforced concrete motorway bridges under horizontal loads, providing useful information for the maintenance of existing bridges in terms of repair and strengthening interventions. In recent years, various researchers have applied IDA to the construction of frames, tunnels, bridges, and other fields [20][21][22][23]. ...
... According to the MLE principle and formula (18), the parameters  and  are estimated thus: Figure 6 illustrates the process for generating fragility curves. The engineering demand measure and the seismic intensity measure for aqueduct structure are estimated from the IDA, and the double parameter values of performance level at each limit state are calculated from the MSA. ...
Article
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The Concrete Damaged Plasticity (CDP) constitutive is introduced to study the dynamic failure mechanism and the law of damage development to the aqueduct structure during the seismic duration using a large-scale aqueduct structure from the South-to-North Water Division Project (SNWDP) as a research object. Incremental dynamic analysis (IDA) and multiple stripe analysis (MSA) seismic fragility methods are introduced. The spectral acceleration is used as the scale of ground motion record intensity measure (IM), and the aqueduct pier top offset ratio quantifies the limit of structural damage measure (DM). The aqueduct structure’s seismic fragility evaluation curves are constructed with indicators of different seismic intensity measures to depict the damage characteristics of aqueduct structures under different seismic intensities through probability. The results show that penetrating damage is most likely to occur on both sides of the pier cap and around the pier shaft in the event of a rare earthquake, followed by the top of the aqueduct body, which requires the greatest care during an earthquake. The results of two fragility analysis methodologies reveal that the fragility curves are very similar. The aqueduct structure’s first limit state level (LS1) is quite steep and near the vertical line, indicating that maintaining the excellent condition without damage in the seismic analysis will be challenging. Except for individual results, the overall fragility results are in good agreement, and the curve change rule is the same. The exceedance probability in the case of any ground motion record IM may be estimated using only two factors when using the MSA approach, and the computation efficiency is higher. The study of seismic fragility analysis methods in this paper can provide a reference for the seismic safety evaluation of aqueducts and similar structures.
... However, simply supported T-beam bridges are inevitably influenced by disadvantageous environmental and vehicle load factors during their service life. Reinforcement corrosion caused by chloride erosion is one of the main degeneration types [4,5] that can reduce the vertical and horizontal load-bearing and seismic capacity of bridges under service conditions [6,7]. The bearing capacity and stiffness of T-beams severely decrease with the increase in reinforcement corrosion degree, which poses a serious threat to the safety of people's property and normal traffic [8]. ...
... where R is the nonuniformity coefficient of pit corrosion, whose value range is [4,6], and it is adopted as 6 in this paper. The residual cross-sectional area of pit corrosion of reinforcement is expressed as [40]: ...
Article
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The safety and reliability of bridges gradually decrease over time under the influence of disadvantageous environmental factors, primarily due to reinforcement corrosion caused by chloride ingress. The traditional lateral load distribution (LLD) theory does not consider the influence of corrosion, which degrades the accuracy of bridge performance and reliability calculation. A time-dependent reliability assessment method for simply supported T-beam bridges is proposed in this paper, which considers the influence of reinforcement corrosion on LLD. Firstly, the steel corrosion process and degree are predicted based on the chloride ingress model, into which the water/cement ratio and concrete strength are innovatively introduced in order to improve the prediction accuracy. Secondly, the effective stiffness calculation method for corroded reinforcement bridges is established with the moment of inertia and section crack condition employed. Thirdly, the modified eccentric compression method is improved by the effective stiffness and iterative algorithm, which is suitable for the LLD calculation of corroded reinforcement bridges. The time-dependent vehicle load effect can be computed combined with the probability distribution of live load. Finally, the time-dependent reliability of the flexural bearing capacity is obtained by the Monte Carlo method and Bayesian theory without prior information. A simply supported bridge with five T-beams is taken as an example for analysis. It is indicated that the results calculated by the traditional reliability method are conservative, which cannot make a true and accurate evaluation. The method proposed in this paper can effectively reduce the assessment error caused by model uncertainty while considering the interaction between reinforcement corrosion and vehicle live load effect.
... Highly corroded bridge piers can be subjected to nonuniform corrosion with corrosion pit which was not considered in the simplified FEM model. Rebar corrosion significantly affects the structural behavior of RC structures (Berto et al., 2009;Crespi et al., 2020;Crespi et al., 2022;G. M. et al., 2018) and it is important to consider mechanical damages caused by corrosion products and related cracking in the surrounding concrete (Coronelli and Gambarova, 2004). ...
Article
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Safety of the existing corrosion damaged reinforced concrete (RC) bridges during a seismic event is a matter of increasing concern. To reduce the enormous economic loss and casualties, it is important to examine the potential seismic risk of corroded RC bridge structures. This paper presents a simplified method to determine the seismic fragility of corroded RC bridge piers by developing a simplified FEM model and seismic fragility analysis. To make the proposed approach realistic, the numerical model is validated with two different experimental studies available in the literature. Obtain results from the simplified numerical model demonstrated excellent agreement with the experimental tests, making it suitable for seismic vulnerability analysis. After validation, the numerical model is further adopted to perform non-linear static pushover analysis of corroded RC bridge piers. Finally, a recently developed software tool SPO2FRAG is utilized to carry out seismic fragility analysis by defining three different damage levels.
... Furthermore, as studied by Crespi et al.[79], brittle and ductile failure mechanisms 433 controlled by shear strength of structural element and plastic hinge rotation can be critical issues 434 which should be considered. In particular, corrosion can lead to significant decreases of the shear 435 capacity of RC piers subject to extreme lateral loadings, e.g., seismic loads. ...
Article
A cost-efficient maintenance plan is crucial to ensure the reliability of decayed reinforced concrete (RC) structures. A reliability-based optimization strategy is proposed that considers a time-variant deterioration model for planning the optimal time and degree of carbon-based fiber reinforcement polymer (CFRP) strengthening of RC columns. A genetic algorithm (GA) has been used as an optimization tool, and the particle swarm optimization algorithm was used to validate the outcomes. A deteriorating RC column exposed to chloride attack was modeled to compare the time-dependent failure probabilities calculated by a recently-developed closed-form equation and the correspondent reliability indexes as lifetime performance indicators. The influence of CFRP wraps on the decayed diffusion rate, and corrosion current density has been modeled using existing formulations. The results of the decaying diffusion model also have been compared to the extreme cases of “no influence” and “complete corrosion stop”. It was found that a GA can successfully determine the optimum solution in terms of the number of required CFRP layers and strengthening time to yield the minimum life-cycle costs. The findings can assist engineers and asset owners in providing optimized maintenance and repair strategies for decayed structures. It also highlights the significance of proper modeling of the corrosion process in CFRP-strengthened RC columns.
... Failure probability of RC columns due to uniform and pitting corrosion was almost equal over the 50 years of service life. However, after 50 years, the difference between the failure probabilities of RC columns differed significantly for uniform and pitting corrosion and the results provided by the uniform corrosion were underestimated [2,46,86,87,89,95,96,98]. Fig. 8 compares the influence of corrosion degrees on three seismic failure modes of RC columns regarding the numerical analysis. ...
Article
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This paper systematically reviewed 84 journal articles published from 2010 to 2020 and structured the reviewed literature using the following categories: year-wise number of research articles, journals, country, and citations. Through a bibliometric and content review analysis, the present review found that the existing studies have mostly focused on corrosion effects, and less attention was paid to quantifying seismic damage of corroded RC bridges. It is required to develop a damage assessment methodology for corroded RC bridges based on a reliable damage index, which can consider the cumulative effects of repeated loading cycles during earthquakes combining the impact of corrosion.
... Zhang et al. [7] proposed a seismic risk assessment method for the corrosion RC bridges with shearcritical columns. Crespi [8] presented a procedure for the collapse mechanism evaluation of the existing reinforced concrete motorway bridges under horizontal loads. ...
Article
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Bridges in a marine environment have been suffering from the chloride attack for a long period of time. Due to the fact that different sections of piers may be exposed to different conditionals, the chloride-induced corrosion not only affects the scale of the deterioration process but also significantly modifies over time the damage propagation mechanisms and the seismic damage distribution. In order to investigate the seismic damage of existing RC bridges subject to spatial chloride-induced corrosion in a marine environment, Duracrete model is applied to determine the corrosion initiation time of reinforcing steels under different exposure conditionals and the degradation models of reinforcing steels, confined concrete, and unconfined concrete are obtained based on the previous investigation. According to the seismic fragility assessment method, the damage assessment approach for the existing RC bridges subject to spatial chloride-induced corrosion in a marine environment is present. Moreover, a case study of a bridge under two kinds of water regions investigated the influence of spatial chloride-induced corrosion on the seismic damage of piers and other components. The results show that the spatial chloride-induced corrosion may result in the section at the low water level becoming more vulnerable than the adjacent sections and the alteration of seismic damage distribution of piers. The corrosion of pier will increase the seismic damage probability of itself, whereas it will result in a reduction of seismic damage probability of other components. Moreover, the alteration of seismic damage distribution of piers will amplify the effect. Due to the fact that the spatial chloride-induced corrosion of piers may alter the yield sequence of cross section, it then affects the seismic performance assessment of piers. A method to determine the evolution probability of yield sequence of corroded piers is proposed at last. From the result, the evolution probability of yield sequence of piers in longitudinal direction depends on the relationship between the height of piers and submerged zone. Moreover, the height of piers, submerged zone, and tidal zone have a common influence on the evolution of yield sequence of piers in transversal direction. 1. Introduction In the past decades, many coastal bridges have been built in different countries with long coastlines to meet the growing requirement of fast transport and economic development. Overall, most of these bridges are reinforced concrete structures and are located in the severe marine environments. Under such environments, chloride-induced corrosion is a major environmental stressor for RC bridges, because it may result in the decrease of the effective cross-sectional area of the reinforcing steels and the deterioration of the mechanical properties of reinforcing steels and concrete. Obviously, the performance of coastal bridges is expected to be significantly affected by chloride-induced corrosion. Therefore, it is of interest to investigate the effects of chloride-induced corrosion on the performance of aging RC bridges in marine environments and to improve the performance level of these bridges with the corrosion effects. On the other hand, chloride-induced corrosion may also result in the decrease of the seismic performance of aging RC bridges; thereby bridges exhibit different seismic damage probability as time increases. In this respect, many studies have focused on the seismic damage assessment of RC bridges with chloride-induced corrosion. Choe et al. [1] developed the probabilistic drift and shear force capacity models for corroding reinforced concrete columns to predict the service-life and life-cycle cost of the columns. Kumar et al. [2] assessed the seismic damage probability of the aging bridges with the cumulative seismic damage and chloride-induced corrosion. Alipour et al. [3] investigated the effects of reinforcement corrosion on the seismic damage probability of the aging bridge in California with different structural parameters. Thanapol et al. [4] developed the seismic fragility curves of the deteriorating piers through the field instrumentation of the corrosion measurements. Cui et al. [5] applied an improved deterioration model of the reinforced concrete steel to carry out the seismic fragility analysis of the reinforced concrete bridges with the marine chloride-induced corrosion. Panchireddi and Ghosh [6] proposed an analytical strategy to consider the deterioration of the damaged bridge through updating the pier section properties. Zhang et al. [7] proposed a seismic risk assessment method for the corrosion RC bridges with shear-critical columns. Crespi [8] presented a procedure for the collapse mechanism evaluation of the existing reinforced concrete motorway bridges under horizontal loads. Overall, the previous studies have enriched the knowledge of the seismic damage assessment of aging RC bridges. However, only uniform exposure condition was considered in these studies when performing the seismic damage assessment of aging RC bridges with the corrosion effects. In fact, exposure conditions exhibit significant spatial variation characteristic along the pier direction for many coastal bridges, and the nonuniform degradation phenomenon occurs in the corroded piers, resulting in the nonuniform distribution of seismic damage of piers. Obviously, these studies may be inappropriate and/or inadequate to completely investigate probabilistic seismic damage of aging RC bridges and to reveal the effects of spatial chloride-induced corrosion. On the other hand, the knowledge of plastic hinges of piers will contribute to the ductile seismic design of RC bridges. Recently, Yuan et al. [9] investigated the damage characteristics of the coastal bridge piers suffering nonuniform corrosion by the shaking table tests. However, the yield characteristic of piers subject to the spatial chloride-induced corrosion has not been comprehensively investigated in the previous studies, and the evolution mechanism of yield sequence of corroded piers has not been clarified. In this study, the probabilistic seismic damage assessment of aging RC bridges subject to spatial chloride-induced corrosion in marine environments is presented. Overall, the major objectives of this study are threefold: (1) to develop a probabilistic seismic damage assessment procedure for aging RC bridges suffering spatial chloride-induced corrosion, (2) to reveal the effects of spatial chloride-induced corrosion on the seismic damage characteristics of piers and other components, and (3) to discuss the evolution probability of yield sequence of piers subject to spatial chloride-induced corrosion. The paper is organized as follows: In Section 2, we describe the corrosion process of reinforcing steels and degradation properties of various materials under different marine exposure conditions. Section 3 presents the probabilistic seismic damage assessment procedure for aging RC bridges subject to spatial chloride-induced corrosion. Subsequently, details of the case study bridge are described in Section 4, and the finite element models are developed. In Section 5, the corrosion level and seismic capacity of RC piers in different exposure conditions are investigated. Moreover, the seismic damage of piers and other components is discussed in Section 6. Furthermore, a method to determine the evolution probability of yield sequence of piers subject to spatial chloride-induced corrosion is proposed in Section 7. A brief summary of the results is presented in Section 8. 2. Chloride-Induced Corrosion Effects The coastal bridges are often exposed to high concentrations of chloride ions. The concentration gradient between the exposed surface and the pore solution of the cement makes the chloride ions penetrate from the external environment through the concrete cover and reach the surface of reinforcing steels. Moreover, the chloride ions decrease the pH in the concrete and break down the passive film of reinforcing steels, resulting in the corrosion of reinforcing steels and the damage of concrete. In this section, the corrosion processes of reinforcing steels and the deterioration mechanism of RC members are presented. 2.1. Corrosion Initiation Time The corrosion initiation time is an important parameter during the chloride-induced corrosion process of RC members, which can be defined as the time when the chloride ions concentration near reinforcing steels reaches a threshold concentration . To calculate the corrosion initiation time, it is necessary to describe the diffusion process of chloride ions and determine the chloride ions concentration at different depths of RC members. In this respect, Duracrete provided a probabilistic model to predict the chloride concentration in the concrete by taking into account the time-dependent characteristics of chloride diffusion, as well as the different types of uncertainties associated with the modelling of these complex processes [10]. The chloride concentration at depth after time can be expressed as follows:where is the error function; is the empirical diffusion coefficient; is an environmental coefficient; represents the influence of test methods on determining ; is a coefficient that accounts for the influence of curing; is the reference period for ; is the age factor; is the chloride concentration at concrete surface and can be represented aswhere is the water binder ratio and and are the model parameters. If the cover depth of reinforcing steels is known, the corrosion initiation time can be determined as follows: For many coastal bridges, the bottom of piers may be submerged in the water, whereas the middle and top of piers are exposed to chloride dry-wet cycle and atmosphere environment, respectively. The discrepancies of humidity, temperature, oxygen, and chloride concentration will cause the different corrosion initiation time of reinforcing steels in various marine exposure conditions. Therefore, the corrosion level of reinforcing steels is highly dependent on the type of exposure conditions. Overall, four categories of exposure conditions are included in the Duracrete model: (a) submerged zone, (b) tidal zone, (c) splash zone, and (d) atmospheric zone. Table 1 summarizes the statistical parameters for corrosion coefficients in the Duracrete model. Parameter Distribution type Atmospheric Splash Tidal Submerged Mean Std. Mean Std. Mean Std. Mean Std. Normal 220 25.4 220 25.4 220 25.4 220 25.4 Normal 315.6 32.5 315.6 32.5 315.6 32.5 315.6 32.5 Normal 473 43.2 473 43.2 473 43.2 473 43.2 Beta (A = 0.0, B = 0.98) 0.362 0.245 0.362 0.245 0.362 0.245 0.362 0.245 Normal 2.565 0.356 7.758 1.36 7.758 1.36 10.348 0.714 Normal 0 0.58 0 1.105 0 1.105 0 0.405 Normal 0.9 0.15 0.9 0.15 0.9 0.15 1.6 0.2 Normal 0.832 0.024 0.832 0.024 0.832 0.024 0.832 0.024 Gamma 0.676 0.114 0.265 0.045 0.924 0.155 0.325 0.223 Beta (A = 1.0, B = 4.0) 2.4 0.7 2.4 0.7 2.4 0.7 2.4 0.7 Beta (A = 1.0, B = 4.0) 1.5 0.3 1.5 0.3 1.5 0.3 1.5 0.3 Determined value 1 - 1 - 1 - 1 - Beta (A = 0.4, B = 1.0) 0.8 0.1 0.8 0.1 0.8 0.1 0.8 0.1
... Therefore, the main cable of a long-span multi-tower suspension bridge across the river and sea is always subjected to electrolyte corrosion. It was reported that electrolyte corrosion is one of main failure modes of existing bridges [17,18]. ...
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The long-span multi-tower suspension bridge is widely used in the construction of river and sea crossing bridges. The load-bearing safety and anti-sliding safety of its main cable are directly related to the structural safety of a suspension bridge. Failure mechanisms of the main cable of a long-span multi-tower suspension bridge are discussed. Meanwhile, the tribo-corrosion-fatigue of main cable, contact, and slip behaviors of the saddle and service safety assessment of the main cable are reviewed. Finally, research trends in service safety assessment of main cable are proposed. It is of great significance to improve the service safety of the main cable and thereby to ensure the structural safety of long-span multi-tower suspension bridges.
... In this regard, 48 a method that can accurately predict the wave forces on the bridge decks promptly is 49 essential for the stakeholders to make critical decisions prior to the landfall of hurri-50 canes [7]. Moreover, an effective prediction method can also facilitate the safety assess-51 ment of the bridge under a probability-based framework, e.g., structural reliability anal-52 ysis [8], and enable the efficient structural analysis under the action of other extreme loads 53 such as seismic load [9][10][11][12]. 54 Over the last two decades, numerous research efforts have been devoted to the use 55 of computational fluid dynamics (CFD) method for investigating the wave forces acting 56 on bridge decks [13][14][15][16][17]. ...
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To facilitate the establishment of the probabilistic model for quantifying the vulnerability of coastal bridges to natural hazards and support the associated risk assessment and mitigation activities, it is imperative to develop an accurate and efficient method for wave forces prediction. With the fast development of computer science, surrogate modeling techniques have been commonly used as an effective alternative to computational fluid dynamics for the establishment of a predictive model in coastal engineering. In this paper, a hybrid surrogate model is proposed for the efficient and accurate prediction of the solitary wave forces acting on coastal bridge decks. The underlying idea of the proposed method is to enhance the prediction capability of the constructed model by introducing an additional surrogate to correct the errors made by the main predictor. Specifically, the regression-type polynomial chaos expansions (PCE) is employed as the main predictor to cap-ture the global feature of the computational model, whereas the interpolation-type Kriging is adopted to learn the local variations of the prediction error from the PCE. An engineering case is employed to validate the effectiveness of the hybrid model, and it is observed that the prediction performance (in terms of residual mean square error and correlation coefficient) of the hybrid model is superior to the optimal PCE and artificial neural network (ANN) for both horizontal and vertical wave forces, albeit the maximum PCE degrees used in the hybrid model are lower than the optimal degrees identified in the pure PCE model. Moreover, the proposed hybrid model also enables the extraction of explicit predictive equations for the parameters of interest. It is expected that the hybrid model could be extended to more complex wave conditions and structural shapes to facilitate the life-cycle structural design and analysis of coastal bridges.
... Thus, hanger replacement is a very common measure in the repair process of arch bridges [12][13][14][15]. Even beam bridge structures such as reinforced concrete bridges or steel bridges will fail or collapse due to material degradation, and some necessary maintenance and reinforcement measures need to be taken during their service period [16][17][18][19]. In China, more than 30 out of over 600 arch bridges have undergone the hanger replacement process [12,20]. ...
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The hanger often needs to be replaced many times during the operation period of hanger arch bridges. To ensure the safety of the hanger replacement in the construction process of pocket hanging, the structural response in the whole construction process needs to be precisely controlled. In this paper, aiming at half-through arches with a suspended deck by cable hangers, the precise displacement controlling method for hanger replacement of an arch bridge based on the pocket hanging method has been proposed. Firstly, the equivalent model of an arch bridge in the hanger replacement process is established, and the boundary conditions of the equivalent model are calculated precisely. Secondly, in the hanger replacement process, including old hanger demolition and new hanger installation, the precise displacement expressions of the suspended deck are derived on the basis of the equivalent model. Finally, the correctness and feasibility of the proposed precise displacement controlling method are verified by the hanger replacement engineering of an arch bridge. Through this research on the hanger replacement of an arch bridge, the equivalent model adopted in this paper has been proven accurate, and only partial boundary conditions need to be considered in practical engineering applications to get accurate results. Meanwhile, the calculation results are accurate enough through the practical engineering verification, and the precise displacement controlling method is feasible in the hanger replacement process of an arch bridge based on the pocket hanging method. It is also found that satisfactory results can be achieved using hanger demolition and installation by equal step length.
... For example, Zhuang and Miao (2020) established a simplified finite element model satisfying the accuracy of fatigue analysis by using the comprehensive framework of reliability analysis, and calculated the fatigue reliability of the hanger with or without corrosion by Monte Carlo method. Pietro et al. (2020) investigated the influence of steel corrosion on the time reliability curve of reinforced concrete structure through cluster analysis based on Gaussian mixture model. ...
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Bridge construction is one of the cores of traffic infrastructure construction. To better develop relevant bridge science, this paper introduces the main research progress in China and abroad in 2020 from 16 aspects. The content consists of four major categories in 16 aspects. The first part is about the bridge structure, including concrete bridge and high-performance materials, steel bridges, composite girders. The second part is about the bridge disaster prevention and mitigation, including bridge seismic resistance, wind resistance of bridge, train-bridge coupling vibration research, bridge hydrodynamics, the durability of the concrete bridges, fatigue of steel bridge, temperature field and temperature effect of bridge; The third part is about the bridge analyses, including numerical simulation of bridge structure, box girder and cable-stayed bridge analysis theories. The last part is concerning the bridge emerging technologies, including bridge informatization and intelligent bridge, the technology in bridge structure test, bridge assessment and reinforcement, prefabricated concrete bridge structure.
... Rapid screening methods for classifying existing structures damage using advanced soft computing techniques, such as the artificial neural network, fuzzy logic, and machine learning have recently started to gain focused attention [15][16][17]. Recent studies have addressed evaluation approaches of existing bridges under earthquake loads, considering material degradation [18]. Recent studies have also conducted fragility analysis for the seismic performance assessment of complex structures, such as truss and cable-stayed bridges [19,20]. ...
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The vulnerability of bridges and the effectiveness of suitable mitigation techniques in regions exposed to different seismic scenarios, while lacking reliable fragility assessment studies for existing bridge inventory, need focused attention. Further, while several retrofit techniques were proposed for improving the seismic performance of existing bridges, the limitations of such approaches need further investigation. Thus, this study assesses the seismic vulnerability of a benchmark structure representing pre-seismic code multi-span bridges in an earthquake-prone region before and after the retrofit to mitigate earthquake-related losses. The numerical modeling approaches of the selected bridge and retrofit systems were verified using the results of previous experimental studies. Detailed three-dimensional fiber-based (3DFB) simulation models were then developed to assess the seismic response of the benchmark bridge under the effects of diverse earthquake records representing far-field and near-source seismic scenarios in both longitudinal and transverse directions. The obtained results from several inelastic pushover analyses (IPAs) and incremental dynamic analyses (IDAs) confirmed the vulnerability of the benchmark bridge and the pressing need for mitigation actions to reduce the expected seismic losses under different seismic scenarios. Higher damage probabilities were observed under the effects of far-source events and at lower intensities than their near-field counterparts. Based on the probabilistic assessment study, it is concluded that retrofitting the bridge with buckling restrained braces (BRBs) is an effective mitigation measure to increase the lateral strength and overcome the high curvature ductility (CD) demands observed in bents, particularly under the most critical seismic scenario. The study provides insight into the impacts of contemporary retrofit techniques on improving the seismic performance of substandard bridges and presents a range of fragility functions for the assessment and mitigation of earthquake risks.
... Modal response spectrum analysis (MRSA); • Nonlinear pushover (NPA) [18]; • Nonlinear time-history analysis (NLTH) [19]. ...
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Since few years ago only one typology of racks was used to store Grana cheese wheels for aging, which was designed focusing on the sole static behavior. Battened steel columns made by vertical tubes welded to horizontal angles were connected by means of wood boards supporting the wheels. In 2012, a strong earthquake occurred in Emilia Romagna (Italy) and a great number of these structures collapsed owing to the absence of checks for resistance against earthquakes. This catastrophic event plus the need to maximize the structural efficiency led to the development of a new typology of rack systems based on the use of cold-formed steel members. Owing to an extremely limited state-of-the-art on these modern cheese rack, design is carried out in agreement with the standard provisions calibrated and proposed for adjustable pallet racks, despite the non-negligible differences between these structural systems. The paper is focused on the comparison between the available seismic design approaches for cheese rack in order to highlight their main advantages and limits. In particular, among the four design approaches admitted in the European standards, the modal response spectrum analysis (MRSA) and the nonlinear time-history (NLTH) have been considered and the associated results compared in terms of maximum safety index of the members, global displacements and interstorey drifts. Research outcomes stress the differences associated with the considered approaches in terms of expected performance underlining the importance of an accurate definition of the behavior (q-) factor.
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Recent collapse events of existing reinforced concrete bridges have increased the attention on the mandatory and suitable maintenance of these strategic constructions. In fact, most of these failures were due to an inadequate scheduling of maintenance interventions. One of the main issues concerning the load-bearing capacity of existing reinforced concrete structures is related to the corrosion of steel reinforcement caused by the carbonation phenomenon. Such aspect should not be even more overlooked considering the strategic role of infrastructures like the bridges of the Italian motorway network, mainly built around the 1960’s and widely used even right now. Consequently, reinforced concrete bridges require the execution of maintenance interventions in order to guarantee an adequate safety level under both serviceability conditions and exceptional loads, also considering that they were often designed without taking into account seismic actions. This paper analyses the seismic performance of five existing reinforced concrete bridges under several corrosion scenarios of piers steel reinforcement caused by the carbonation phenomenon. In particular, three different corrosion levels (slight, moderate and high) are considered by analysing the evolution of the phenomenon effects for a lifetime of the structure equal to 75 years. The seismic vulnerability is then evaluated by defining appropriate risk indices expressed in terms of peak ground acceleration and corresponding return period. The risk indices are determined by performing modal pushover analyses on finite element models, considering the corrosion effects in terms of steel rebars cross section reduction. Some correlations between corrosion levels and risk indices are drawn.
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Optical frequency domain reflectometry (OFDR) optical fiber is characterized to monitor corrosion-induced mortar cracking, including localization and determination of crack initiation time, crack size, and crack length. Mortar cylinders containing a steel bar were prepared and subjected to accelerated corrosion test. The change of mortar surface condition due to steel bar corrosion was recorded with an OFDR optical fiber which was attached by using epoxy resin before corrosion test. Three fiber wrap spacing were considered including 20 mm, 50 mm, and 100 mm. Visual inspection was performed after corrosion test. Calibration test was also conducted to determine the transfer coefficient of cracking. Results show non-uniform corrosion occurred on steel bar and resulted in mortar surface cracking, which was reflected by the strain peaks appeared in the OFDR fiber strain curve. OFDR optical fiber can be used to identify the time of crack initiation, localize the position of cracks, and determine the width and length of cracks. Both the sensitivity and spatial resolution of OFDR optical fiber sensor increase with a decrease of the fiber wrap spacing.
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Bridge deterioration models are used for prioritization and maintenance of bridges. These models can be broadly classified as deterministic and stochastic models. There are mechanistic models (or physical models) as well as artificial intelligence (AI)-based models, each of which can be stochastic or deterministic in nature. Even though there are several existing deterioration models, state-based stochastic Markov chain-based model is widely employed in bridge management programs. This paper presents a critical review of different bridge deterioration models highlighting the advantages and limitations of each model. The models are applied to some case studies of timber superstructure and concrete bridge decks. Examples are illustrated for arriving at bridge deterioration models using deterministic, stochastic and artificial neural network (ANN)-based models based on national bridge inventory (NBI) data. The first example is based on deterministic model and the second on stochastic model. The deterministic model uses the NBI records for the years 1992–2012, while the stochastic model uses the NBI records for one year (2011–2012). The stochastic model is state-based Markov chain model developed using transition probability matrix (TPM) obtained by percentage prediction method (PPM). The two deterioration models (i.e., deterministic and stochastic models) are applied to timber highway bridge superstructure using NBI condition data for bridges in Florida, Georgia, South Carolina and North Carolina. The illustrated examples show that the deterministic model provides higher accuracy in the predicted condition value than the stochastic Markov chain-based model. If the model is developed based on average of transition probabilities considering the data for the period 1992 to 2012, the prediction accuracy of stochastic model will improve. Proper data filtering of condition records aids in improving the accuracy of the deterministic models. The third example illustrates the ANN-based deterioration model for reinforced concrete bridge decks in Florida based on the NBI condition data for the years 1992–2012. The training set accuracy and testing set accuracy in the ANN model are found to be 91% and 88% respectively. The trained model is utilized to generate missing condition data to fill the gaps due to irregular inspections of concrete bridges. This paper also discusses scope for future research on bridge deterioration modeling.
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The scope of this paper is to evaluate different approaches for the prediction of the probability of failure of uncertain railway bridges subjected to high-speed trains. The peak acceleration of a bridge, which is commonly the governing response quantity for dynamic bridge design and failure, depends strongly on the type of train and the train speed. Since in many cases the critical speeds related to response maximums are below the design speed and failure, and during operation the speed varies up to the design speed, the assessment of the probability of failure is not straightforward. In this contribution, several more sophisticated measures of the probability of failure of the bridge-train interaction problem are proposed, considering the peak acceleration as a function of the speed in a certain interval and the distribution of the actual train speed. These measures are tested on two random test bridges, taking into account the main sources of uncertainty, i.e. damping, track irregularities, and the environmental impact. The mechanical model used for the prediction of the dynamic bridge response is composed of a beam bridge crossed by a planar mass-spring-damper model of the train. In this simplest approach that considers explicitly dynamic bridge-train interaction, random irregularity profiles capture the effect of track irregularities. It is shown that in certain speed intervals the predicted probability of failure strongly depends on the underlying measure of the probability of failure. In the first example bridge, whose response is governed by a pronounced resonance peak, exceedance of the serviceability limit state is predicted by all measures at virtually the same speed. The second example problem, where track irregularities lead to considerable response amplifications, only some of the measures predict failure. The results of this study may serve as an impulse for a more in-depth discussion on the appropriate prediction of the probability of failure of bridge-train interaction.
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This paper presents a novel, bridge-dependent approach for quantifying the increase of design quantities due to spatially variable earthquake ground motion (SVEGM). Contrary to the existing methods for multiple support bridge excitation analysis that are either too complicated to be applied by most practitioners or oversimplied (e. g. Eurocode 8, Annex D provisions), this method aims to strike a balance between simplicity, accuracy and computational efficiency. The method deliberately avoids generating support-dependent, acceleration or displacement, asynchronous inputs for the prediction of bridge response. The reasons behind this decision are twofold: (a) first, the uncertainty associated with the generation of asynchronous motion scenarios, as well as the exact soil properties, stratification and topography is high while, (b) the response of a bridge is particularly sensitive to the above due to the large number of natural modes involved. It is therefore prohibitive to address SVEGM effects deterministically in the framework of a design code. Instead, this new method is based on two important and well-documented observations: (a) that SVEGM is typically globally beneficial but locally detri-mental [1], and (b) that the local seismic demand increase is very closely correlated with the excitation of higher modes, which are not normally activated in the case of uniform ground motion [2,3]. Along these lines, a set of static analyses are specified herein to complement the standard, code-based response spectrum analysis. These static analyses apply spatially distributed lateral forces, whose patterns match the shape of potentially excited anti-symmetric modes. The amplitude of those forces is derived as a function of the expected amplification of these modes according to the process initially proposed by Price et al. [4]. Two real bridges with different structural configurations are used as a test-bed to demonstrate the effectiveness of the new method. Comparison of the results with those obtained through rigorous response history analysis using partially correlated, spatially variable, spectrum-compatible input motions [5] shows that, the simplified method presented herein provides a reasonably accurate estimation of the SVEGM impact on the response of the bridges examined at a highly reduced computational cost. This is essentially an elastic method that is found to be simple, yet precise enough to consist an attractive alternative for the design and assessment of long and/or important bridge structures in earthquake-prone regions. Download fulltext: https://authors.elsevier.com/c/1aTYdytxOFGx~
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Infrastructure aging is an important problem nowadays, in particular for countries like Italy in which the main motorways were built 50 years ago. Huge budgets are necessary to keep infrastructure and bridges in service. In addition, the lack of a proper and timely maintenance, entails an increase of the deterioration and therefore higher costs of repair. Thus, the need of methods capable of assessing the reliability of the infrastructure in the frame of Bridge Management System (BMS), is patent. The aim of this work is to provide a robust decision-support tool for the analysis of the data collected within the BMS with field inspection. The innovative aspect of the proposal is the introduction of two factors which take into account the location of the damage, and the mechanical characterization of the material in the definition of a Condition Rating Number (CRN). The analysis of an existing Reinforced Concrete (RC) bridge network is presented in order to show the accuracy of this new method.
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Experimental works in literature have paid proper attention to the seismic response of hollow circular piers only quite recently, despite their widespread use in existing bridges. More attention should be certainly paid to these elements to reliably assess their seismic capacity. Herein, experimental cyclic tests on two scaled reinforced concrete piers with hollow circular cross section, representative of typical existing Italian bridges, are carried out. Depending on the aspect ratio, flexure and flexure-shear failure modes have been observed. Design criteria, adopted setup, experimental response and damage evolution are presented and discussed. A focus on shear-critical piers has been performed, collecting a proper experimental database of tests from literature. The very few specific shear strength models existing in literature and main models by codes are compared with the collected data. Model by Ranzo and Priestley (2001), also in conjunction with proposal by Turmo et al. (2009), has finally shown promising results.
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Reinforced concrete with lower environmental footprint (lower CO2 emission) can be obtained by reducing the clinker content in the cements. As the carbonation of concrete is faster, corrosion of steel in carbonated concrete during the propagation phase is becoming important both for science and practice. The present literature review summarizes the state of the art, reporting corrosion rate data for a broad range of cement types, w/b ratios and environmental conditions. Correlations between corrosion rate and the main influencing parameters are elaborated and discussed. It confirms that the corrosion rate of steel in carbonated concrete is not under ohmic control. More important are the degree of pore saturation and the effective steel area in contact with water filled pores. It also emerges that the new blended cements have to be systematically studied with respect to the corrosion behavior of steel in carbonated concrete in order to make reliable service life prediction.
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The paper presents the seismic vulnerability analysis of the military dry dock built in 1861 inside the Messina’s harbor. The study appears very important not only for the relevance of the dry dock itself, but also for its social, military and symbolic role. As a first step, the historical documentation about the dry dock delivered by the Military Technical Office, in charge of its maintenance, was thoroughly examined. This activity was fundamental to understand the construction methods, the rehabilitation works executed after the severe earthquake of 1908 and, finally, the works carried out to increase the size of the dry dock in 1950. After this first step, numerical seismic analyses were done with some implemented finite element models (FEM) of the structure. In each FEM, the vertical loads were applied according to the “construction stages” analysis technique, in order to achieve an appropriate representation of the soil stresses around the structure. The analysis results were evaluated according to the Italian design code (NTC 2008) in order to determine the seismic vulnerability of the dry dock.
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In recent years, Italian technical-scientific community has increased its interest on the evaluation of the seismic vulnerability of existing structures. Among this wide range of structures, motorway viaducts stand out for their strategic relevance and technical complexity. Most of these structures were built between '60 and '70 years, according to design procedures which ignored nowadays knowledge in seismic engineering. Thus, the necessity to evaluate the real strength capacity of these structures with modern analysis techniques has become essential, leading to the determination of their safety level in case of an earthquake. For the assessment of several bridges of a motorway network, a multi-modal pushover analysis approach has been considered. This analysis technique allows considering the nonlinear behaviour and the complex dynamic response of such a structures without exceeding in high computational costs. Some basic rules were defined (constitutive laws of materials, finite element type, plastic hinge models, etc.) for the modelling of viaducts in a commercial FEM software, in order to guarantee homogeneous comparable results among the large number of bridges of a network. Furthermore, a specific software routine was implemented. This routine starts from the pushover results of a FEM commercial software and executes the modal combinations and the safety verifications, reducing the time cost and the possibility of errors, following in the evaluation of the seismic vulnerability indexes. These risk indexes are then reported in seismic vulnerability forms collected by the Italian Hazard Management Agency (Italian Civil Protection) for risk management purposes.
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Corrosion is one of the most critical problems that impair the durability of RC structures. Both carbonation-induced and chloride-induced corrosion widely prevail in civil infrastructure around the globe. Expansive products are formed due to corrosion at the interface between concrete and reinforcing bar (rebar). The cracking and spalling in concrete due to expanding corrosion products and the reduction in the cross-sectional area of rebar jeopardize the safety and serviceability of RC structures. From an outsider perspective, this literature review summarizes the state of the art on the mechanisms of the two types of corrosion, mechanical degradation in RC structures as a result of these mechanisms, the analytical methods to predict the basic parameters most related to corrosion, and the available laboratory and field corrosion measurement techniques.
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Due to the corrosion of steel in reinforced concrete structures, the concrete with low water–cement ratio (w/c), high cement content, and large cover thickness is conventionally used for prolonging the passivation period of steel. Obviously, this conventional approach to durable concrete structures is at the sacrifice of more CO2 emission and natural resources through consuming higher amount of cement and more constituent materials, which is against sustainability. By placing an economically affordable conductive mesh made of carbon fiber or conductive polymer fiber in the near surface zone of concrete acting as anode we can build up a cathodic prevention system with intermittent low current density supplied by, e.g., the solar cells. In such a way, the aggressive negative ions such as Cl−, , and can be stopped near the cathodic (steel) zone. Thus the reinforcement steel is prevented from corrosion even in the concrete with relatively high w/c and small cover thickness. This conductive mesh functions not only as electrode, but also as surface reinforcement to prevent concrete surface from cracking. Therefore, this new type of covercrete has hybrid functions. This paper presents the theoretical analysis of feasibility of this approach and discusses the potential durability problems and possible solutions to the potential problems.
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Carbonation is often the dominant influence on service life of reinforced concrete structures. In some concepts for service life design the carbonation resistance is measured in the laboratory on samples without applied load. If an applied load has an influence on the rate of carbonation, however, this method cannot be considered to be reliable. The real service life may be significantly shorter than the calculated design service life. In this contribution the influence of compression and of tension on the rate of carbonation has been determined experimentally on beams under sustained four point bending. These beams were exposed to an atmosphere with an elevated CO2 content for 30 days. Carbonate profiles have been determined by grinding successively thin layers starting from the surface of the carbonated samples. Even a moderate applied tensile stress increases the rate of carbonation significantly. Compressive stress has little influence until a critical value. Above this value an applied compressive stress also increases the rate of carbonation. The obtained results will serve as a basis for the calculation of an applied stress on service life of reinforced concrete constructions.
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Several procedures for non-linear static and dynamic analysis of structures have been developed in recent years. This paper discusses those procedures that have been implemented into the latest European and US seismic provisions: non-linear dynamic time-history analysis; N2 non-linear static method (Eurocode 8); non-linear static procedure NSP (FEMA 356) and improved capacity spectrum method CSM (FEMA 440). The presented methods differ in respect to accuracy, simplicity, transparency and clarity of theoretical background. Non-linear static procedures were developed with the aim of overcoming the insufficiency and limitations of linear methods, whilst at the same time maintaining a relatively simple application. All procedures incorporate performance-based concepts paying more attention to damage control. Application of the presented procedures is illustrated by means of an example of an eight-storey reinforced concrete frame building. The results obtained by non-linear dynamic time-history analysis and non-linear static procedures are compared. It is concluded that these non-linear static procedures are sustainable for application. Additionally, this paper discusses a recommendation in the Eurocode 8/1 that the capacity curve should be determined by pushover analysis for values of the control displacement ranging between zero and 150% of the target displacement. Maximum top displacement of the analyzed structure obtained by using dynamic method with real time-history records corresponds to 145% of the target displacement obtained using the non-linear static N2 procedure. KeywordsNon-linear dynamic analysis–Non-linear static methods–Pushover analysis–N2, NSP and CSM methods
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In this paper we report on some laboratory testing on the carbonation and weathering of concrete. Each study involves accelerated test methods. In the carbonation study the effects of humidity level, grade of concrete and pore size on carbonation depths are investigated. Experiments using mechanical and thermal cyclic loading have been carried out to study deterioration of concrete by weathering; the rates of deterioration are determined by the measurement of dynamic modulus using an elastrosonic apparatus. The paper contains results and analysis of these two studies.
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The present study concerns the failure analysis for a 15-tons bridge crane. In particular, the investigation is performed through a numerical simulation of the whole system, in order to extract the displacement reached when the system undergoes to the maximum in service payload. The failed element is one of the two spline coupling used for transmitting the torque from the gearbox to the drums, responsible for winding the cables. In addition, it is also presented an estimation of the wear phenomenon, by comparing the actual material performance with the once generally considered in literature. At the end, some advices to overcome the problem are introduced.
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The evaluation of the seismic behaviour of shallow multi-propped underground structures (e.g. metro stations, parking, etc.) can be considered as one of the most important and actual research topics in structural earthquake engineering. Over the last decades, different types of analysis approaches have been proposed, but several issues are still open, especially for multi-propped structures embedded in granular soils. In this paper, the main limitations of the decoupled approach are investigated and discussed through a large set of numerical simulations involving: i) a multi-propped underground structure; ii) five natural and one synthetic accelerograms; iii) four different soil profiles characterized by the same mechanical properties but different values of the shear modulus that are related to the shear wave velocity ranging between 360 m/s and 750 m/s. The results, in terms of bending moment acting on RC retaining walls, obtained through the decupled approach are discussed in comparison with those obtained through the coupled approach (non-linear dynamic analysis), highlighting the main differences and limitations. This study shows that the decoupled approach provides consistent results only for soil profiles characterized by low values of stiffness due to the main assumptions underlying the approach.
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This paper investigates the failure of the underdeck maintenance gantry of the metro crossing bridge in Istanbul, Turkey on January 4, 2014, which resulted in the injury of four workers. First, a brief description of the gantry and the bridge has been provided, which is followed by the findings of the on-site investigation which involved the review of the video record of the incident, interviews with the field staff, overview of the project drawings and the investigation of the parts of the collapsed gantry. Additionally, the finite element model of the part where the collapse initiated was created and loaded in accordance with the operation procedures of the gantry during the incident. Finally, on-site investigation and finite element analysis results revealed that collapse of the gantry occurred by exceeding the shear capacity of the bolts in the connections. Moreover, the exceedance of the shear capacity was the consequence of unexpected operating practices used by the workers during the incident, which caused unforeseen shear stress concentration in the bolts.
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The aim of this paper is to present the different effects of reinforcement corrosion on reinforced concrete buildings. A hypothetical five-storey reinforced concrete building frame was designed for this purpose. Three different modes of action were selected – corrosion on the ground floor alone, corrosion on one facade and corrosion on two neighbouring facades of the building. For each mode of action, different corrosion scenarios were selected, which were arranged in terms of mass loss from zero to 15% in ascending order an in 3% steps. Pushover analyses of the building were performed for each corrosion scenario and the results of these analyses were used to perform a structural performance evaluation conforming to Eurocode 8. A general decrease in structural performance was determined with significant changes in the dynamic characteristics of the building. The level of decrease depended on the corrosion scenarios and the modes of action. Important structural behaviour alterations and premature damage occurrences were found, in addition to a reduction in the displacement ductility of the building. For severe-corrosion scenarios, reductions in moment and curvature capacities could shift the structural behaviour of the load-bearing members from ductile to non-ductile.
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Existing models for predicting the time to the commencement of serious reinforcement corrosion in chloride conditions provide results that do not compare well with long-term observations and practical experience for actual concrete structures. Many high-quality concrete structures show little or no evidence of serious corrosion, even after decades of exposure to chloride conditions. Earlier it was proposed that the mechanisms for corrosion initiation differ from those for long-term corrosion. This is reviewed. New research shows corrosion initiation is dominated by the presence of air voids adjacent to the reinforcement. For good concretes this is mainly a short-term transient effect. Long-term active corrosion is the direct result of the usually slow loss of concrete alkalinity, a process accelerated by chlorides. This, rather than direct chloride attack, is the cause of damaging reinforcement corrosion. It is argued also that the role of concrete cracking intersecting the reinforcement must be reconsidered. These new interpretations open up the way for improved modelling and prediction of ‘chloride-induced’ corrosion.
Conference Paper
The cement industry is responsible for around 7% of all man-made global carbon emissions, mainly related to Portland clinker production. Recent research is facing this problem by considering different strategies, i.e. the production of innovative and Portland-alternative clinkers. The production of these types of clinker is more sustainable thanks to lower temperatures needed in the kiln and to different raw materials used, resulting in 20% less CO2 emissions. The use of CSA cement in structural concrete is not considered in standards and codes, and there are some concerns about its usage due to higher carbonation rates, lower pH of the pore solution, and less effectiveness in steel rebar protection, especially with chloride penetration. This study aims to propose and validate a new technology based on the combination of a high-performance concrete produced with a sulfoaluminate binder and a non-corrosive reinforcement. Glass Fiber-Reinforced Polymers (GFRP) bars are a promising alternative to traditional steel reinforcement thanks to the fact that they do not corrode. In addition, they show good durability and high mechanical performance. Furthermore, the deployment of non-corrosive reinforcement allows the use of recycled materials (such as concrete or asphalt as aggregates) or materials available in large quantities (for example seawater), even if contaminated by chlorides. This improves the sustainability of the proposed solution. This paper presents the results of a laboratory investigation performed to prove the good mechanical and durability performance of the aforementioned solution, even when seawater is used for concrete mixing.
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In the railway network of Iran, a large number of masonry arch bridges exist which most of them was constructed 80 years ago. Despite these types of bridges have shown an appropriate behavior under the influence of gravity (vertical) loads, they have not been designed seismically. Concerning to the seismic hazard zoning map of Iran, most of these railway infrastructures are placed in the very high seismicity zones and constructed near the major faults. So the seismic assessment of these types of bridges has become a significant subject for the engineers to explain the failure and seismic performance levels of these structures. Thus, they can be rehabilitated or removed if it is found required. Among various methods for seismic estimation of the capacity of the structures under seismic loading, the non-linear dynamic method or the incremental dynamic analysis (IDA) may be mentioned as the most precise and complete method for near-field excitations. For this purpose, by selecting 28 near-field earthquake records, this study has seismically surveyed two railway masonry arch bridges, which are respectively placed in the kilometers 23 (2L20 bridge) and 24 (5L06 bridge) of the old railway of Tehran-Qom. The macro-modeling approach was used in the finite element method. In total, 316 non-linear dynamic analyses have been carried out for the seismic assessment of the masonry arch bridges under near-field ground motion. The results found from the IDA analysis specified that the near-field seismic performance of the masonry arch bridge with lower span length (i.e., 5L06 bridge) is safer than the bridge with longer span length (i.e., 2L20 bridge). Mostly, it has to decide to retrofit the masonry bridge with longer span length to improve their performance since the seismic behavior of those has been found inappropriate under near-field earthquakes.
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The Gorkha Earthquake Sequence of 2015 affected hundreds of bridges in central, eastern, and part of western Nepal. This paper presents empirical fragility functions of highway bridges affected by the earthquake sequence. The fragility functions are based on the damage data collected during the assessment campaign conducted after the earthquakes. Fragility functions are presented for reinforced concrete and steel bridges based on data collected from 154 bridges. The results show that these highway bridges are very vulnerable to earthquake shaking and sustain damage even at low peak ground acceleration.
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Recently, corrosion prevention and monitoring of reinforced concrete (RC) structures became an important issue for seismic assessment of such kind of structures. Therefore, it is important to develop adequate models to represent material degradation into seismic behavior simulation of RC structures. Because of its effects, corrosion represents the most important form of degradation for materials and structures, both for wide diffusion and the amount of danger it presents. To understand the corrosion process is critical in order to design RC structures that are able to guarantee the required service life and in order to understand the residual service life and strength of an existing structure. The seismic behavior of a corroded framed RC structure is analyzed by means of push-over analyses, which allow understanding the development of the global behavior of the structure. Three different degrees of corrosion penetration were simulated, by means of the reduction of bars and stirrups’ diameters and concrete cover cracking and spalling, and three different configurations of corrosion, depending on the number of corroded frames and sides of the structural elements.
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Multi-scale finite element (FE) modeling is an effective method to balance the computational efficiency and accuracy using different elements to simulate different parts of structures considering the demands of engineering practice. In order to analyze the earthquake-induced damage and collapse of Gaoyuan bridge in Wenchuan earthquake, the simplified rigid surface coupling method is developed to achieve the coupling between solid element and beam element based on LS-DYNA program at this study. The numerical results have shown that the failure of A2 abutment and strong pounding force cause the bridge superstructure lost longitudinal constraints, and the girders of the third span and forth span fell down due to oversize longitudinal displacement. Obviously, the multi-scale FE modeling is a high-efficiently analytical method for simulating local damage and even collapse of bridges structures under strong earthquake excitations. The inclined degree of bridge bents and the damage of concrete in different bridge piers using the multi-scale FE modeling method improved in this paper agrees well with actual earthquake damage of Gaoyuan highway bridge.
Article
Cracks in reinforced concrete structures accelerate the ingress of chlorides and therefore cause a higher risk for corrosion. In this research, autonomous healing of cracks by encapsulated polyurethane was investigated as a possible method to reduce reinforcement corrosion. Reinforced concrete beams were exposed weekly to a chloride solution and electrochemical parameters were measured to determine the influence of the self-healing mechanism on the corrosion process. The rebars were visually examined afterwards. For the cracked beams an active state of corrosion was detected within an exposure period of 10 weeks and clear pitting corrosion was observed on the rebars. Autonomous crack healing with low viscosity polyurethane could significantly reduce the corrosion in the propagation stage. For these specimens no visual damage to the rebars was detected. In conclusion, the application of self-healing concrete with a low viscosity polyurethane is able to enhance the durability of reinforced concrete structures in marine environments.
Article
Many existing reinforced concrete (RC) buildings were designed in Southern European countries before the introduction of modern seismic codes and thus they may be potentially vulnerable to earthquakes. Recent seismic events have also shown that RC buildings designed without specific seismic provisions can experience several types of failures or even collapse during moderate-to-strong earthquakes. Therefore, simplified methodologies for a preliminary and suitable seismic assessment and retrofitting of existing RC buildings are required, along with reliable and effective seismic rehabilitation techniques. In this study, a simplified displacement based procedure using non-linear static analyses is applied to obtain a preliminary estimation of the overall inadequacy of an under-designed four-storey RC frame and to propose suitable retrofitting interventions based on different rehabilitation strategies. To this aim, accurate numerical models are developed to reproduce the seismic response of the RC frame in the original and retrofitted configurations. The effectiveness of three different retrofitting solutions countering the main structural deficiencies of the RC frame is evaluated through the displacement based approach. Then, non-linear dynamic analyses are performed to assess and compare the seismic response of the RC frame in the original and retrofitted configurations. A combined use of different approaches may provide a valuable insight to accurately address the retrofitting interventions and to assess their effectiveness in order to reduce the seismic vulnerability of poorly designed RC buildings.
Article
The unreinforced masonry (URM) is a complex and variegate construction material characterized by a prominent nonlinear response. For this reason, advanced numerical simulations are required to assess URM buildings, especially in case of severe loading conditions as earthquakes. However, given the theoretical and computational difficulties of detailed non-linear analyses, linear elastic methods are still adopted in current practice. This results in conservative seismic assessments and, consequently, invasive and expensive strengthening interventions to guarantee seismic safety. Starting from these statements, the aim of the paper is to provide closed-form equations useful for a preliminary strength and ductility assessment of unreinforced masonry rectangular cross-sections. Expressions for direct calculation of M-N (bending moment – axial load) strength domains and M-v (moment – curvature) ductility diagrams for different constitutive laws are provided. The expressions are firstly applied to a representative URM cross-section and secondarily used for the numerical simulation of a recent out-of-plane loading experimental test available in the literature. For a better comprehension of URM members behavior under axial-bending loading condition, 3D M-N-v diagrams are presented in the paper.
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In this paper the use of fly ash for particular High Strength Concrete (HSC) realizations is investigated. The use of fly ash as a partial replacement of Portland cement in HSC seems a valid solution in particular for a sustainable construction design, considering the interesting HSC performances (in terms of strength and durability) and the economic aspects (in terms of waste material's reuse from industrial process). Fly ashes have been employed in the past especially for underground structures. Nowadays, their use is under evaluation also for elevation structures. In this paper, the most important technical regulations about the use of fly ash for the concrete mix design are discussed. The increase of the mechanical resistance, the better protection against chemical agents attacks and freezing - thawing cycles using fly ashes are also show. Moreover, in comparison to the fresh concrete, the benefits related to the minor water/cement (w/c) ratio are presented, in the same workability conditions. Additional considerations are carried out about the hydration process: the mixture produces less heat for the lowering of the C3A and C3S percentages using fly ash. Finally, a greater concrete impermeability obtained using fly ash, due to the presence of a lower hydrolysis content, which leads to an increment of the cement paste porosity, has been evidenced. All of mentioned benefits shows the fly ash use in the High Strength Concrete (HSC) is a valid solution against many problems interested negatively the concrete mix - design and the mix - production.
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This chapter briefly presents the mechanism of reinforcement steel corrosion in concrete, focusing on chloride-induced pitting corrosion, which is generally the main deterioration mechanism in reinforced concrete infrastructures. Corrosion inhibitors have long been proposed as one of many possible corrosion mitigation strategies. This chapter presents the state-of-the-art on corrosion inhibitors used as admixtures, with particular emphasis on long-term and especially field studies. While there is a general agreement from both laboratory and field studies that mixed-in corrosion inhibitors can delay the onset of chloride-induced corrosion by a factor of two to three, there are no results clearly demonstrating that corrosion inhibitors can reduce the corrosion rate after corrosion initiation. A particular lack of knowledge concerns organic corrosion inhibitors where conclusive long-term field results are lacking.
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A comprehensive, though relatively simple, non-linear method for the seismic damage analysis of reinforced concrete buildings (the N2 method) has been elaborated. The basic features of the method are: the use of two separate mathematical models, application of the response spectrum approach and of the non-linear static analysis, and the choice of a damage model which includes cumulative damage. The method yields results of reasonable accuracy provided that the structure oscillates predominantly in the first mode. Three variants of a seven-storey building have been used as illustrative examples for the application of the method. Four different types of the analysis, with different degrees of sophistication, have been performed in order to estimate the influence of several assumptions and approximations used in the N2 method.
Article
Developed herein is an improved pushover analysis procedure based on structural dynamics theory, which retains the conceptual simplicity and computational attractiveness of current procedures with invariant force distribution. In this modal pushover analysis (MPA), the seismic demand due to individual terms in the modal expansion of the effective earthquake forces is determined by a pushover analysis using the inertia force distribution for each mode. Combining these ‘modal’ demands due to the first two or three terms of the expansion provides an estimate of the total seismic demand on inelastic systems. When applied to elastic systems, the MPA procedure is shown to be equivalent to standard response spectrum analysis (RSA). When the peak inelastic response of a 9-storey steel building determined by the approximate MPA procedure is compared with rigorous non-linear response history analysis, it is demonstrated that MPA estimates the response of buildings responding well into the inelastic range to a similar degree of accuracy as RSA in estimating peak response of elastic systems. Thus, the MPA procedure is accurate enough for practical application in building evaluation and design. Copyright © 2001 John Wiley & Sons, Ltd.
Article
This paper reports results of a study conducted to assess the effect of degree of corrosion of reinforcing steel bars on their mechanical properties. Reinforcing steel bars, 6 and 12 mm in diameter, that were corroded in reinforced concrete specimens were removed and tested in tension. Results indicated that the level of reinforcement corrosion does not influence the tensile strength of steel bars, calculated on the actual area of cross-section. However, when the nominal diameter is utilized in the calculation, the tensile strength is less than the ASTM A 615 requirement of 600 MPa when the degree of corrosion was 11 and 24% for 6- and 12-mm diameter steel bars, respectively. Furthermore, reinforcing steel bars with more than 12% corrosion indicates a brittle failure.
Article
In this work, the mathematical-numerical model of carbonation process in reinforced concrete (RC) structures, which has been developed by the authors, is applied to different cases of study to take into account the probabilistic nature of durability assessment procedure even if within the framework of a rough and ready approach. In particular, the aim of this Part I of the work is to study how the variability of the parameters defining the differential equations in the model influence the assessment of the corrosion initiation time of RC structure. Comparison with experimental results and numerical simulations are undertaken in Part II of this work.