The excess pore water pressure generated under the combined vertical and horizontal earthquake excitations is generally greater than that under the unidirectional excitation, which may further affect the dynamic response of soil-pile-superstructure-quay wall (SPSQ) system. This study conducted a coupled effective-stress analysis for the response of SPSQ system to liquefaction-induced lateral displacement under horizontal and vertical earthquake excitations. To accurately describe the lateral displacement behind the quay wall, the liquefaction behavior of soils was described by a modified generalized plasticity model with parameters properly determined from laboratory tests. The numerical model of the SPSQ system was validated against the previously reported centrifuge model tests. The results show that the earthquake excitation with abundant low-frequency component causes greater residual lateral displacements of pile cap (ux,RC) and quay wall (ux,RQ) than that with abundant high-frequency component. The ux,RC and ux,RQ tend to increase as the peak vertical acceleration increases for both vertical and inclined piles. Increasing the fixity of the quay wall significantly reduces the influence of vertical ground motion on the ux,RC and ux,RQ. The polarity reversal of the vertical ground motion also has a significant effect on the ux,RC and ux,RQ and should be considered in the analyses. In addition, the lateral displacement of liquefied ground causes an amount of rotation of the cap of the inclined pile, probably leading to the potential shear failure at the head of piles. Special consideration should be given to the earthquake-induced shear force at deeper location because the shear force could be significantly greater than that at the head of both inclined and vertical piles in certain cases.
Many countries exposed to high levels of seismic risk, including Italy, are facing a huge challenge in promptly quantifying post-earthquake damages to their built historical heritage. In this context, structural health monitoring plays a fundamental role allowing to continuously track changes in selected damage-sensitive features. However, monitoring data interpretation is often not univocal and may be affected by large uncertainty, provoking false positives and false negatives. Hence, this research proposes a novel approach for post-earthquake structural condition assessment by exploiting the aggregation of different sources of information, notably steering from both monitoring and visual inspection campaigns, in order to take risk-informed decisions. More in depth, an automatic tool is proposed to detect and locate structural damages in monumental structures with the aid of a data fusion approach including vibration-based system identification, static and dynamic measurements, finite element (FE) and surrogate modeling, Bayesian-based model updating and visual inspections. In a preliminary phase, potential damage-sensitive regions in the structure are identified through FE-based numerical analysis and engineering judgment. Then, the solution of the inverse problem aimed at deriving the Bayesian posterior statistics of the uncertain parameters is entrusted to a computational-effective surrogate model (SM). Finally, the Bayesian-based updated parameters are adjusted considering the different allowable sources of information to achieve a final assessment. The effectiveness of the proposed approach is demonstrated by using the recorded data acquired in the Consoli Palace, an historical building located in Umbria, central Italy, which has been continuously monitored since 2017 using dynamic, static and environmental sensors and which has been hit by low-intensity earthquakes in 2021.
Italian reinforced concrete precast industrial buildings featuring frictional beam-to-column connections suffered from severe losses following recent earthquakes. Despite the relevance of this topic, the current literature includes only few works investigating the seismic behaviour of these buildings, the influence of vertical records on their modelled dynamic response, as well as the sensitivity of their seismic fragility to the friction type implemented in-situ. The above considerations imparted momentum to this research. First, a sensitivity analysis was conducted considering both concrete-to-concrete and neoprene-to-concrete friction types, as well as the presence or absence of vertical records in the vulnerability analyses. Within a multiple-stripe analysis framework, a number of nonlinear dynamic analyses were carried out on two precast building models created in OpenSees and assumed to be located in three Italian cities subjected to different hazard levels. Fragility curves related to the limit states of Serviceability Preventing Damage and Life Safety were derived. Then, epistemic uncertainty in the friction type and the influence of vertical records on the fragility curve was treated by employing a logic tree framework, allowing for the derivation of weighted average fragility curves, one per city. While the latter are structure-specific and site-dependent, they may be considered as generic or typological fragility curves, for use by researchers or practitioners who are interested in carrying out a fragility analysis on a reinforced concrete precast industrial building but are not confident on the friction type implemented in-situ and the influence of vertical records for the site and structure at hand.
This paper describes a comprehensive characterisation of liquefaction resistance of a sandy soil collected from the ‘Terreiro do Paço’ in the historical centre of Lisbon (Portugal), denominated as TP-Lisbon sand. This natural sand has experienced earthquake-induced liquefaction caused by the 1755 earthquake. The characterisation was carried out by combining in situ with laboratory tests. The results of in situ tests allowed obtaining the factor of safety profiles against liquefaction, liquefaction potential index and liquefaction severity number. On the other hand, an experimental programme conducted in the laboratory allowed defining the cyclic resistance ratio for different relative densities and mean effective stresses of TP-Lisbon sand. Besides, the effects of inversion and rotation of principal stresses on liquefaction resistance were examined by advanced testing procedures (i.e. cyclic triaxial and cyclic direct simple shear tests). The results of this study were analysed within the critical state soil mechanics framework by comparing the state parameter reported by in situ and laboratory testing, particularly when using remoulded soil specimens. The data presented in this study provide a database for numerical analyses and cyclic or seismic geotechnical design, following a framework appropriate to natural sands susceptible to liquefaction phenomena.
Automated Rack Supported Warehouses, consisting of huge steel buildings offering optimized storage solutions, have been facing a huge diffusion in the last decade, mainly due to the necessity of having bigger and more efficient places to stock and handle goods through automated systems. However, there is not a specific regulatory framework for them, and they are currently being designed to adopt the approach used for traditional steel racks. Even if traditional steel racks and ARSWs have several common aspects, there are relevant differences that do not allow to adopt the same design approach, especially for seismic actions. To highlight the factors and parameters currently influencing the seismic design and the behavior of these constructions, and the consequent need for a different design approach, the present paper presents a critical analysis of the seismic design approach currently adopted by technicians and designers. Then, a set of 5 structures designed by 5 of the major European companies specialized in this field is used to perform both the critical analysis of the different design approaches adopted and the assessment of the seismic performance. The seismic assessment results highlight the typical criticalities and the necessity of a novel proper design approach.
Long-span cable-stayed bridges often have a design service life of more than a hundred years, during which they may experience multiple earthquake events and accumulate seismic damage if they are located in seismic-prone regions. Earthquake occurrence is discretely and randomly distributed over the life cycle of a long-span cable-stayed bridge and often causes sudden drops in the structural performance instead of yearly fixed seismic performance degradation. This study thus proposes a digital twin-based life-cycle seismic performance assessment method for long-span cable-stayed bridges. The major components of this method include: (1) a seismic hazard analysis-based generation method of earthquake occurrence sequence; (2) a digital twin-based structural response prediction method considering lifetime earthquake occurrence and sequence; and (3) a service life quantification method. The proposed method is applied to a scaled long-span cable-stayed bridge with a series of shake table tests. The results show that the digital twin can closely reproduce the life-cycle seismic response of the bridge under sequential earthquakes. The proposed assessment method provides a more intuitive presentation of the life-cycle seismic damage accumulation process and a more accurate estimation of the service life of a long-span cable-stayed bridge. Keyword Long-span cable-stayed bridge.-Life-cycle-Seismic performance assessment-Digital twin-Earthquake sequence Footnote Information Abstract ong-span cable-stayed bridges often have a design service life of more than a hundred years, during which they may experience multiple earthquake events and accumulate seismic damage if they are located in seismic-prone regions. Earthquake occurrence is discretely and randomly distributed over the life cycle of a long-span cable-stayed bridge and often causes sudden drops in the structural performance instead of yearly fixed seismic performance degradation. This study thus proposes a digital twin-based life-cycle seismic performance assessment method for long-span cable-stayed bridges. The major components of this method include: (1) a seismic hazard analysis-based generation method of earthquake occurrence sequence; (2) a digital twin-based structural response prediction method considering lifetime earthquake occurrence and sequence; and (3) a service life quantification method. The proposed method is applied to a scaled long-span cable-stayed bridge with a series of shake table tests. The results show that the digital twin can closely reproduce the life-cycle seismic response of the bridge under sequential earthquakes. The proposed assessment method provides a more intuitive presentation of the life-cycle seismic damage accumulation process and a more accurate estimation of the service life of a long-span cable-stayed bridge.
Previous researches on the constant ductility inelastic displacement ratio spectra (Cμ) of self-centering structures have been conducted based on the typical flag-shaped self-centering (FS) model. However, the arising shape-memory-alloy-friction self-centering structures (SMAFSs) own their specialized force–displacement relationship different from the typical FS model. In this research, a hybrid force–displacement model composed of the typical FS model and Coulomb friction model is employed and an efficient calculating procedure is proposed to statistically investigate the Cμ of SMAFSs. Comparison with the Cμ of the typical FS system with similar self-centering capacity shows that the Cμ of the SMAFS is significantly different from that of the typical FS system, which explains the necessity of employing the hybrid model for SMAFSs and the effects of the friction. The effects of seismic parameters and structural parameters on the Cμ of SMAFSs are investigated. Furthermore, the formula for estimating the Cμ of SMAFSs is proposed through statistical regression. This proposed formula could estimate the Cμ of SMAFSs and describe the effects of structural parameters more accurately. The research could provide a basis of estimating the Cμ of SMAFSs to obtain reliable seismic design results of the structures.
This study investigates the effect of damage control methods on the seismic performance of masonry infilled walls in reinforced concrete (RC) frames, by experimentally investigating three full-scale infilled RC frames with different treatment details and finite element method (FEM) analysis. The control methods included full-length connecting steel rebars, styrene butadiene styrene (SBS) sliding layers, and two gaps between the wall and frame columns. The results indicated that the ductility, wall damage, and residual deformation of the frame with gaps or SBS layers were significantly improved. However, the initial stiffness, energy dissipation capacity, and lateral load-carrying capacity of the frames with SBS sliding layers all were reduced. The fully infilled frames exhibited a better lateral load-carrying capacity, stiffness, and energy dissipation capacity, but presented larger lateral residual deformation and lower ductility. The damage of the infilled walls in RC frames can be controlled by using longer connecting rebars. The gaps and sliding layers can both significantly reduce the in-plane damage of the walls. A simplified FEM model was proposed and applied to conduct a parametric analysis for an in-depth study of fully infilled RC frames with and without sliding layers. The results show that SBS is the optimal sliding layer material, and its optimal spacing in RC frames is recommended as 1000 mm.
On August 7th, 2020, a magnitude Mw = 5.0 earthquake shook 5 km north of Mila city center, northeast of Algeria, causing substantial damage directly to structures, and indirectly from induced impacts of landslides and rock falls, ultimately disrupt to everyday civilian life. Given the recent significant seismic occurrences in the region, a detailed and comprehensive examination and assessment of post-earthquake damage is critical to Algeria. This is primarily because masonry, concrete, and colonial-era structures are sensitive to horizontal motions caused by seismic waves, and because masonry and concrete structures constitute a substantial portion of today’s Algeria's build environment. We present a post-earthquake investigation of the Mila earthquake, starting from the earthquake source, and a catalogue of buildings type, damage categorization, and failure patterns of residential structures in Mila's historic old town, where colonial-era brick buildings prevail. We find that structures that represent notable architectural achievements were severely damaged as a result of the earthquake. Data acquired during the immediate post-earthquake analysis was also evaluated and discussed. The graphical representations of the damages are detailed and complemented by photos. This seismic event has shown the fragility of Algeria's building stock, which must be addressed properly in future years. This study reports on an overall estimate of residential buildings in Mila's lower city, as well as an evaluation of the seismic vulnerability of three neighborhood towns (El-Kherba, Grareme-Gouga, and Azzeba). A generic database for graphical surveys and geometric research was developed and implemented making it possible to evaluate the shear strength on-site. The broad observations, collated data, and consequences were then loaded into the 3Muri structural verification program. Nonlinear static analysis was conducted to analyze probable failure paths and compare the real damage to the software results.
This study presents the analysis of the methodology of a seismic exposure model in Guatemala City. In the last years, progress in the investigation of regional seismic hazards has revealed the need to study the vulnerability of buildings in Central America. In addition, in recent years there have been earthquakes of moderate magnitude in Guatemala causing damage in some areas of the country. An accurate exposure model and updated threat scenarios are essential for a detailed vulnerability study. This exposure study for Guatemala City reveals the presence of structural typologies that are very vulnerable to earthquakes: adobe and simple masonry. Similarly, the study reveals the majority presence of reinforced masonry and the growing construction of reinforced concrete buildings. The characteristic of this model is the use of historical aerial photographs of Guatemala City to determine the relationship between constructive typologies. The lack of exposure studies in the country has prevented the creation of policies to reduce vulnerability to a catastrophe like the earthquake in 1976. The analysis and methodology presented in this study are the preliminary step in formulating seismic risk prevention and mitigation plans in Guatemala City; knowledge of the city’s exposure contributes to making subsequent actions more effective. Based on the results obtained, matrices are proposed according to the age and material of the buildings for the typological classification of the structures.
This paper focuses on seismic fragility and damage scenario assessment of minor Italian historical centres through the development of urban fragility curves. With reference to the case study of Balvano, a small centre located in Basilicata Region of Italy, two hybrid models have been adopted. The frst is a mechanic-based hybrid model developed by the authors to derive urban fragility curves specifcally; the second is the macroseismic method, originally conceived to derive typological fragility curves for single building classes, expanded to derive urban fragility curve herein. Balvano was strongly struck by 1980 Irpinia-Basilicata earthquake (Ms=6.90) and hence subjected to an intense reconstruction process during 1980s, where almost the 80% of the buildings were reconstructed with reinforced concrete structures in the place of unreinforced masonry ones. Seismic vulnerability and damage scenarios before and after 1980 have been assessed and compared with the purpose of validating the efectiveness of the urban scale fragility curves obtained through hybrid methodologies and quantifying the efect of the ‘new’ seismic hazard maps and frst seismic codes and recommendations released by the Italian Government in the aftermath of 1980 for the construction of new buildings or for retroftting the existing ones.
A good matching between predicted and occurred damage scenario from the research outcomes emerged, confrming the efectiveness of the urban scale hybrid fragility curves to assess seismic vulnerability at urban scale. Moreover, the comparison of the damage scenarios pre and post-reconstruction highlighted the crucial role played by the code prescriptions adopted in that years for reducing the seismic vulnerability of the municipality and the importance of the ‘new’ seismic hazard maps introduced in 1980s. Finally, the diferences between mechanical-based hybrid and macroseismic model have been discussed in the paper.
In the last years, many research efforts have been focusing on the development of fragility and risk models of different building classes and structural typologies for large-scale seismic risk applications. Although the role of masonry infills is well recognised, less attention has been paid to the quantification of the variability surrounding their mechanical properties and how this might affect the collapse fragility curves and loss estimates. This study investigates and quantifies, in a thorough manner, the impact of the variability in the characteristics of masonry infill on the expected annual losses (EALs) of existing infilled reinforced concrete frames of different configurations. To do so, a fully integrated portfolio, representative of buildings designed according to the Italian codes in force between 1970 and 1980, is used as case-study. Infill-related variability is accounted for by means of a macro-level distinction of five common infill types, defined in terms of stiffness and shear strength. Moreover, building-to-building variability is also included through different geometrical configurations. Multiple-stripe analyses are carried out and fragility curves are developed for buildings with different heights, in-plan layouts and structural typologies. Finally, EALs are computed and analysed in a statistical fashion in order to quantify, in a simplified manner, the uncertainty induced by the variability of the masonry infill properties, as a function of the number of storeys and masonry infill typology.
The loss of containment due to seismically induced liquid overtopping tanks with floating roofs was addressed by introducing a risk-targeted freeboard seismic design. The proposed practice-oriented procedure can be applied to new or existing tanks for which the freeboard was designed based on the tank wall height or liquid height, respectively. It combines the conventional seismic risk equation, and the code-based equation for the maximum vertical liquid displacement at the tank wall corresponding to the seismic action. The inconsistency in the intensity measures used in the two equations was solved by a carefully estimated mean acceleration spectrum that was used to convert spectral accelerations at different periods. The proposed design approach was verified in two numerical examples based on the previously assessed seismic risk for a given freeboard of a broad liquid storage tank located in Italy. Parametric studies were conducted to obtain insights into the sensitivity of risk-targeted freeboards to the design input parameters. It was realised that the assumed standard deviation of the logarithmic values of the spectral accelerations causing the loss of containment did not significantly affect the design, whereas the seismicity level at the site and the target probability of loss of containment had a significant impact. A design procedure was also used to develop risk-targeted freeboard maps for Slovenia. It was demonstrated that variation in the risk-targeted freeboard in Slovenia could be as much as 12-fold, which is certainly not negligible when selecting tank sites or defining the maximum liquid height for existing tanks.
This paper presents an experimental study on the seismic response of a 2/5 scale, 3-storey, 2-bays non-ductile reinforced concrete frame building retrofitted with glass fibre reinforced polymer sheets and weakening of the floor slab around the strengthened beam hinge region, following a partial retrofit strategy involving an upgrade of the exterior beam column (b-c) joints only. The research comprised two uni-directional shake-table experiments, including a different earthquake record each, with similar PGA, but different duration and frequency content. During the short-duration test, the specimen experienced limited inter-storey drift ratios (less than 0.6%) and presented no visible damage. During the long-duration test, instead, the specimen undertook large inter-storey drifts ratios, particularly in the first storey (3.7%), and showed large cracking in the exterior beams and crushing of the concrete at both ends of the central columns. An analysis of the spectrograms of the input and top-storey displacement motions shows that the large-amplitude response of the specimen during the long-duration test was apparently due to resonance. It was concluded that the proposed retrofit strategy was able to attain, under an adverse scenario with large inter-storey drift demands, the fundamental objectives of: (a) inverting the hierarchy of strengths and sequence of events in the critically vulnerable exterior b-c joints, relocating the damage from the panel zone into the beams at the weakened part of the slab; and (b) improving the global inelastic mechanism of the structure by shifting it from brittle/unstable to ductile/stable.
Performance-based earthquake engineering offers a versatile framework for quantifying the seismic performance of structures. Its implementation requires a comprehensive description of the nonlinear structural behavior, facilitated typically via multiple nonlinear response history analyses (NLRHAs). This burden can be very high when high-fidelity finite element models (FEMs) are used to describe structural response. To alleviate it, approximations are commonly employed, using a moderate number of analyses, or even replacing altogether the NLRHA with a nonlinear static analysis. This contribution explores two alternative paths for accommodating the desired computational efficiency: (a) use of reduced order models that are calibrated to closely match the original FEM; (b) adoption of multi-fidelity Monte Carlo (MFMC) that combines the original FEM to guarantee unbiased predictions and the aforementioned reduced order models to accelerate the Monte Carlo implementation. Advancements are established for the MFMC implementation, in order to accommodate the efficient propagation of the different sources of uncertainty across the estimation of the different seismic performance statistics of interest. The accuracy and computational benefits are illustrated for two benchmark structures over two different output variables: repair cost (resiliency quantification) and embodied energy associated with repairs (sustainability quantification).
The earthquake hazard and seismic risk in Iceland are highest in the Southwest due to the transform faulting in the South Iceland Seismic Zone (SISZ) and Reykjanes Peninsula Oblique Rift (RPOR) being in close proximity to a large part of the population. Reliable probabilistic seismic hazard assessment (PSHA) is therefore critical in this region which in turn requires two of its key elements: the most appropriate ground motion models (GMMs) and the specification of seismic sources. In this study, we address this by employing a suite of new hybrid Bayesian empirical GMMs and a new physics-based finite-fault system model for the SISZ–RPOR. By ranking the GMMs using the deviance information criterion against the Icelandic strong-motion dataset we propose backbone GMMs (i.e., the most appropriate models), which along with their backbone Δ-factors not only comprehensively capture the characteristics of Icelandic data but also the epistemic uncertainties of their ground motion prediction. We then simulate suites of synthetic finite-fault earthquake catalogues that are consistent with the physics-based fault system and long-term seismic activity of the region. We carry out a Monte-Carlo PSHA for two representative near-fault (the town of Selfoss) and far-field (the capital city of Reykjavik) sites in Southwest Iceland, and compare the results with those of a classical PSHA. We show that the backbone PSHA is consistent with classical PSHA point estimates but more importantly, the backbone approach reveals the “body” of the hazard i.e., the majority of realistically expected hazard values, which dwarfs any differences in the results from the two approaches. The PGA results show that the body of hazard values varies from 0.07-0.13 g and 0.4-0.6 g for Reykjavik and Selfoss, respectively. The scale factor is distance- and period-dependent that results in a constant body of the backbone hazard values for a far-field site at all periods while at long periods and decreasing annual exceedance rates, the body progressively increases. Moreover, the disaggregation showed that the modal event for a 475 year return period is a Mw ~ 6–6.5 at distance ~ 14–26 km for the far-field site, but at ~ 6 km for the near-fault site. We conclude that the backbone approach and the models used in this study make ideal candidates for improved PSHA for Iceland.
On October 30, 2020 14:51 (UTC), a moment magnitude (Mw) of 7.0 (USGS, EMSC) earthquake occurred in the Aegean Sea north of the island of Samos. Turkish and Hellenic geotechnical reconnaissance teams performed reconnaissance immediately after the event and their findings are documented herein. The predominantly observed failure mechanism was that of earthquake-induced liquefaction and its associated impacts. Such failures are presented and discussed together with the preliminary assessment of the performance of building foundations, slopes and deep excavations, retaining structures and quay walls. On the Anatolian side (Turkey), and with the exception of the Izmir-Bayrakli region where significant site effects were observed, no major geotechnical effects were observed in the form of foundation failures, surface manifestation of liquefaction and lateral soil spreading, rock falls/landslides, failures of deep excavations, retaining structures, quay walls, and subway tunnels. In Samos (Greece), evidence of liquefaction, lateral spreading and damage to quay walls in ports were observed on the northern side of the island. Despite the proximity to the fault (about 10 km), the amplitude and the duration of shaking, the associated liquefaction phenomena were not pervasive. It is further unclear whether the damage to quay walls was due to liquefaction of the underlying soil, or merely due to the inertia of those structures, in conjunction with the presence of soft (yet not necessarily liquefied) foundation soil. A number of rockfalls / landslides were observed but the relevant phenomena were not particularly severe. Similar to the Anatolian side, no failures of engineered retaining structures and major infrastructure such as dams, bridges, viaducts, tunnels were observed which can be mostly attributed to the lack of such infrastructure on the island.
Turkey is in an active earthquake zone. Recently, Izmir city was shaken by a major earthquake in October 2020. The earthquake caused extensive structural damage and more than 100 casualties. Therefore, the analysis of the dynamic response of local soils in this region is of great importance. In this study, the shear modulus and damping ratio of natural silts obtained from Izmir province are determined. A total of 29 cyclic triaxial tests and 12 tests with pre-loading were performed to establish a general framework for understanding the behavior of local silt soils before and after an earthquake. Besides the effect of an earthquake, the characteristic behavior of Izmir silts of different levels of plasticity was also investigated and significant changes were observed. In addition, the effect of void ratio, effective confining pressure, plasticity, and shear stress amplitude of the pre-loading stage on the dynamic characteristics of the low plasticity silts were investigated. It is understood that after seismic action, changes in the small strain behavior of silts are remarkable.
Masonry often requires strengthening to withstand against extreme actions such as earthquakes, cyclones and flooding. Recently, new methods have been developed to strengthen masonry, such as fabric reinforced cementitious matrixes and fibre reinforced polymers. However, other strengthening systems such as welded wire meshing (WWM), reticulatus and plastering with cementitious matrixes/mortar (CP) have been also practiced to reinforce masonry, conversely no systematic design guidelines are available for these methods. In this study, an attempt has been made to establish rational design approaches to predict the shear resistance of WWM, reticulatus and CP methods. Three sets of experimental database have been developed for design verification. The effectiveness of these strengthening methods was appraised by comparing their structural performances. The available formulations to predict the shear resistance of unreinforced masonry (URM) and CP strengthened masonry were assessed against the established database, and suitable modifications were proposed to effectively account the contribution of cementitious matrix. A unified approach to estimate the shear strength was proposed based on the contribution of URM, CP and reinforcements. The design approach is shown to conservatively predict the shear strength of strengthened masonry.
The functionality of community buildings not only depends on the damage to individual buildings but also on the interactions with other infrastructure systems. This paper incorporates these interactions by applying the systems thinking approach to analyze community resilience. The proposed framework starts with identifying the physical infrastructure systems and key components in a community. Then, the seismic hazard scenarios are defined, and the component damage and recovery are assessed by utilizing fragility and consequence functions. After that, a network model, considering the interdependencies between the utility networks and the dependency of utility networks on the community buildings, is introduced to evaluate the component-level building functionality. Finally, community resilience is assessed by proposing community-level indicators including inherent resilience, community functionality, and access to essential facilities. The proposed model is illustrated on a community consisting of building portfolios, water, and electric power systems under four hazard scenarios. It is concluded that the systems thinking approach considered at a community level provides important insights into community resilience such as building functionality, utility demand, and supply, and access to essential facilities, among others.
To alleviate the detrimental diagonal bracing effect of the traditional rigid-connected reinforced concrete (RC) flight to the boundary frame under lateral inputs, the study proposes an innovative low-damage stair system: prefabricated RC stair isolated by high damping rubber (HDR) bearings. The remarkable properties of the HDR bearings are firstly verified by material tests. To understand the behavior of the novel system, a quasi-static test is conducted on two full-scale stair systems, and a parametric study of the design parameters of the HDR bearings is carried out. Test results confirm that the proposed system could mitigate the detrimental diagonal bracing effect of traditional RC flight by the HDR bearings. Consequently, no crack can be observed in the RC flight at the inter-story drift ratio (ISDR) of 2.0%, and only three horizontal cracks are detected at the bottom of the RC flight under the ISDR of 4.0%. Moreover, benefitting from the sliding mechanism of the developed stair system, the novel stair system is characterized by stable hysteretic responses and energy dissipation capacity at each loading stage and has about twice the equivalent viscous damping ratio to the traditional stair system. The parametric study shows that the rubber thickness of the HDR bearings has a remarkable effect on improving the seismic performance of the developed stair system, while the shear modulus and rubber hardness of the HDR bearings have a slight contribution to enhancing the lateral bearing capacity of the system.
The seismic response of monopile foundations is a growing area of research as the offshore wind industry expands worldwide, including in earthquake prone regions of the world. This paper presents dynamic centrifuge tests aimed at investigating the dynamic response of monopiles in both dry and saturated sandy soils. The latter case includes soil liquefaction under strong input motions, with measured excess pore pressures indicating liquefaction. The natural frequency of the monopile-soil system is experimentally determined by measuring the response to a sine sweep motion. Strong earthquakes are then applied at this frequency and its harmonics. This paper discusses the response of the monopile in terms of the peak accelerations observed in the dry and saturated tests, as well as using response spectra and amplification ratios. The dynamic bending moments along the pile are also measured to infer the bending moment profile with depth. Finally, two identical monopiles are pushed-over in each of the centrifuge tests to establish the pre and post-earthquake monotonic response, including the lateral stiffness and capacity, which are compared for the dry model tests and the saturated case.
This work presents the simulations of the non-linear dynamic response of a three-dimensional finite-discrete element model. The model simulates a half-scale masonry building aggregate tested on a shake table by other Authors. The aggregate is made of two un-connected building units having different heights and slightly different wall thicknesses. The floors are made of timber beams and boards. The modelling approach accounts jointly for in-plane and out-of-plane responses, which can be expected given the high flexibility of the floors, and for the separation between the two building units. The simulations are related both to the blind predictions, according to a scheduled testing sequence, and to the post-dictions according to the actual testing sequence and some model calibrations. The prediction model overestimates displacements, underestimates base shear and fairly predicts the damage pattern of comparable experimental runs. The use of the recorded shake table motion improves the accuracy of the post-diction simulations, while still delivering beam unseating. A higher Young’s modulus of the blocks improves markedly the predictions. The strengthening intervention with steel angles connecting floors to walls is only approximately modelled and does not improve the outcomes of the simulations. In summary, the adopted modelling approach is capable of accounting for the pounding between the two building units, predicting the most significant damage as well as estimating approximate average of peak values of base shear and displacements, while individual time histories are less accurately estimated.
This article presents a study about new type mechanical systems effectiveness to reduce the coupling beam damages using non-destructive experimental measurement results. Five half-scaled reinforced concrete (RC) coupling beams were constructed to be examined in laboratory conditions. In the first three test specimens, different rebar configurations were considered to eliminate the difficulties in the construction of existing rebar layouts and to improve the seismic performances of RC coupling beams. In the last two test specimens, replaceable and innovative metallic systems were proposed to increase the energy dissipation capacity of RC coupled shear wall systems. The modal parameters for undamaged and damaged situations of the test specimens were identified by ambient vibration tests. The enhanced frequency domain decomposition method in the frequency domain and the stochastic subspace identification method in the time domain were utilized for system identification. To simulate lateral loads such as earthquakes, quasi-static cyclic tests were executed. As a result of the studies, it is observed that the damages significantly decreased the natural frequencies. Also, there is no agreement between the mode shapes before and after the loading tests. The maximum differences on natural frequencies caused by damages are calculated as 68.41% for diagonally-reinforced coupling beam (DRCB), 68.50% for mesh reinforced coupling beam with 19° mesh angle (MRCB-19), 65.33% for diagonal bundled mesh reinforced coupling beam with 45° mesh angle (DBMRCB-45), 29.48% for teeter-totter coupling beam (TETOD), and 21.45% for prefabricated teeter-totter coupling beam (PF-TETOD) coupling beams. Also, it is observed that the crack widths and propagations on the shear wall piers of TETOD and PF-TETOD are quite limited compared to the DRCB, MRCB-19, and DBMRCB-45 specimens. The damage propagations and changes in modal parameters have shown that the proposed mechanical systems provide the desired level of performance even under large displacements.
Infill Masonry Walls (IMWs) are used in the perimeter of a building to separate the inner and outer space. IMWs may affect the lateral behavior of buildings, while they are different from those partition walls that separate two inner spaces. This study focused on the seismic vulnerability assessment of Steel Moment-Resisting Frames (SMRFs) assuming different placement of IMWs incorporating nonlinear Soil-Structure Interaction (SSI). The aim is to explore the damage states of IMWs and use their ability for improving the vulnerability of SMRFs. For this purpose, the three, five, seven, and nine story levels (3-Story, 5-Story, 7-Story, and 9-Story) SMRFs were modeled considering four soil types. Incremental Dynamic Analyses (IDAs) were performed to determine the seismic performance limit-state capacities of SMRFs considering the Far-Fault (FF) record subset suggested by FEMA P695. To accurately model the influence of IMWs on the seismic response of SMRFs, a Tcl programming algorithm was developed to intelligently monitor the damage states of IMWs in each floor level. Results of the analysis show that assuming different placement of IMWs can significantly increase the seismic limit-state capacities of SMRFs with and without considering SSI effects. In addition, IMWs can play a crucial role to improve the seismic performances as well as the seismic collapse probability, which may be suggested for retrofitting purposes.
A twin girder 7-pier bridge, belonging to the "Egnatia" highway that has been facing numerous challenging geohazards, is built within an active landslide. Its seismic performance is investigated here through a comprehensive analysis of the interaction between bridge, foundation, and the precarious slope, which might affect 4 of the piers. The numerical 3D modeling considers in a realistic way the coupled effects of topography, soil nonlinearity, slope instability, and reinforced-concrete plasticity during seismic loading (kinematic and inertial). Alternative foundation schemes and slope stabilizing techniques are generically compared and evaluated. The aim is to develop a multi-hazard risk assessment platform that could facilitate the long-term management of motorways while shedding some light on the multi-hazard soil-structure interaction (MH-SSI).
Seismic damage due to pounding between adjacent buildings is often observed after significant earthquake events in old urban centers and globally recognized as a potential trigger for complete collapse. This is relevant for unreinforced masonry (URM) structures, which are particularly vulnerable to horizontal actions and seldom feature appropriate seismic detailing. Quantifying pounding damage between dynamically interacting URM buildings, however, is a challenging task, the details of which are difficult to simulate through analytical modeling alone. Numerical simulation of pounding failures, on the other hand, involves impact, separation and re-contact phenomena that often require advanced 3D micro-modeling strategies, often entailing a high computational expense that is not feasible when modeling the coupled seismic response of multiple buildings. To enable simulation of pounding damage in URM structures with relatively low computational cost, this paper investigates the use of a recently developed Macro-Distinct Element Model (M-DEM) approach. To this end, a M-DEM is herein used to simulate the shake-table biaxial pounding response of two dynamically interacting stone building prototypes, tested within the framework of the Seismic Testing of Adjacent Interacting Masonry Structures (AIMS) project sponsored by the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA). Numerical results were obtained before the experimental test and then subsequently evaluated against the experimental results. The M-DEM predictions satisfactorily reproduced the measured base shear and interface opening, although they underestimated the floor displacement demand, especially in the transversal direction. Building on these encouraging outcomes, a post-test refined M-DEM model was also developed, and results are discussed alongside the lessons learned and proposed enhanced strategies to improve the quality of predictions.
The dynamic response of post-tensioned rocking walls in a mass timber building can be
reduced to a single-degree-of-freedom (SDOF) model. In this model, the rocking wall
panel is simplified as a rigid block, while the base rotation represents the degree of freedom of the entire structure. The paper presents an analytical approach to develop and calibrate this nonlinear model using shake table tests of a full-scale two-story building with
CLT rocking walls. The experimental data are used to estimate the parameters of the governing equation using least-squares optimization. The correlation between the obtained
parameters and the cumulative dissipated energy led to a nonlinear model with degradation
behavior captured. After that, the calibrated model was used to assess the fragility functions of the structure under repetitive seismic events.
Typically, the columns of the prefabricated reinforced concrete (RC) industrial buildings and warehouses with large clear storey heights are very slender, with aspect ratios (shear span to width) larger than 10. In addition to supporting the gravity loads, the columns also provide strength, stiffness, dissipation and displacement capacity of the primary lateral-load resisting system. However, current empirical relationships that predict the non-linear response and failure mechanisms of RC columns have been developed mainly for lower aspect ratios (< 7), typical of ordinary multi-storey buildings or short-to-medium bridge piers. What makes slender columns different is their predominant flexural response, larger drifts at nominal strength and corresponding lower ductility demands, smaller ratios between the strain penetration and plastic hinge lengths to the element shear span and risk of P-Delta instability. Therefore, the direct application of analytical models available in the literature to slender columns poses a risk of overestimation of their deformation and dissipative capacity. In turns this could lead to the underestimation of their displacement demand, overall damage and collapse probability of the primary seismic-resisting and load-bearing system. In the present research extensive analysis on the non-linear response of slender columns was performed based on observed post-earthquake damage to buildings in Italy and Turkey, experimental data and numerical predictions of the failure patterns through non-linear fiber element models. The influence of the foundation flexibility and the presence of industrial floor was also investigated. The outcome is a simplified analytical methodology for the prediction of the non-linear force–deformation response and possible failure mechanisms of slender precast columns due to rebar buckling or P-Delta effects, as a fundamental step towards the seismic assessment of the global structural performance and cost-efficient retrofit solutions for precast concrete industrial buildings.
We apply the Probabilistic Seismic Hazard Analysis (PSHA) and compute Physics-Based Simulations (PBS) of ground motion for three dams in the Campotosto area (Central Italy). The dams, which confine an artificial water reservoir feeding hydroelectric power plants, are located in an active seismic zone between the areas that experienced the 2009 L'Aquila and 2016-2017 Central Italy seismic sequences. The probabilistic disaggregation estimated for a return period of 2475 years, corresponding to the collapse limit state for critical facilities , indicates that the most dangerous fault is associated with a maximum magnitude of 6.75 ± 0.25 within a distance of 10 km. This fault is used in PBS to emulate the Maximum Credible Earthquake scenario. To capture the ground motion variability, we input a pseudo-dynamic source model to encompass spatial and temporal variations in the slip, rise time and rupture propagation, heavily affecting the near-source ground motion. Indeed, the ground motion above the rupture volume is mainly influenced by the epistemic uncertainties of rupture nucleation and slip distribution. The computed broadband seismograms are consistent with the near-source shaking recorded during the 2016 M W 6.6 Norcia earthquake and constrain the upper bound of the simulated ground motion at specific sites. Our modelling reinforces the importance of considering vertical ground motion near the source in seismic design. It could reach shaking values comparable to or larger than those of the horizontal components. This approach can be applied in other areas with high seismic hazard to evaluate the seismic safety of existing critical facilities.
The extensive injury caused to buildings by liquefaction during past earthquakes, with the uneven spatial distribution of damage, raises the need for rapid predictive tools, applicable at a large scale, that comprehensively account for the properties of earthquake, subsoil and structure. A method is herein proposed to quantify the angular distortion of framed low-rise buildings based on a simple characterization of the above factors. The analysis moves from past literature criteria introduced to quantify the vulnerability of buildings under static conditions and extends their applicability to liquefaction assessment integrating parametric two-dimensional numerical analyses with recent literature predictive formulas and machine learning inference. The numerical calculation, performed for variable stratigraphic and mechanical characteristics of the subsoil, ground motion and equivalent flexural stiffness of the foundation, quantifies the role of each factor on the absolute settlement and angular distortion. Then the dependency on the different factors of the angular distortion is inferred with an artificial neural network, grouping parameters to limit the number of input variables and express results with charts that make prediction more accessible.
Heritage structures are an important part of the history of each community as well as an economic resource. This study aims to investigate the earthquake damage and failure mechanism of a historic Bazaar located in Kashan (center of Iran), which dates back to the eighteenth century. Numerical models were built by a macro method, considering two cases of fixed support and soil-structure interaction (SSI). To assess the structural behavior, modal, nonlinear static, and dynamic time history analyses were performed using a three dimensional finite element method. The results of SSI analysis show an intense weakness of the structure against the required demand based on the design spectrum. Also, foundation flexibility has a great impact on the vibration characteristics, displacement demand, and damage distribution. By comparing the results of time history analysis to the pushover procedure, a lower shear value and higher displacement are obtained. Furthermore, the damage process is as dome collapse alongside short arch, consequently long arch collapse followed by pier wall overturning.
Recent seismic events worldwide have demonstrated the high vulnerability of existing school buildings and the urgent need to have reliable tools for the rapid seismic performance assessment and damage and loss quantification. Indeed, the significant damage observed on structural and non-structural components may have a significant impact in terms of direct and indirect losses making critical the recovery of stricken communities. Although a significant amount of work has been done in developing fragility curves for the residential building stock, only few contributions clearly refer to school buildings that significantly differ in terms of the main characteristics from the residential ones. This research work proposes fragility curves for reinforced concrete and unreinforced masonry public school buildings typical of the Italian building stock, based on the damage observed in the aftermath of the 2009 L’Aquila earthquake. A comprehensive and unique database including data on damaged and undamaged school buildings (2037 records) in the Abruzzo region was built using data from four different sources. Due to limited amount of data, the fragility curves can be very sensitive to the method adopted for their derivation, thus three different approaches (i.e. empirical, empirical-binomial, heuristic) are considered in the paper and the results are compared. Finally, a direct comparison with fragility curves available in the literature for the Italian residential building stock is presented.
Seismic performance of a 253 m tall reinforced concrete core wall building constructed in Istanbul, designed according to performance-based seismic design principles, is assessed for determining the response parameters that control the serviceability, safety and collapse performance limit states. Serviceability performance is evaluated under the 50-year wind and 43-year earthquake whereas safety performance is assessed under the 2475-year earthquake. Collapse performance is elaborated through incremental dynamic analysis. Our study revealed that the service performance is controlled by the maximum interstory drift limits specified for wind loads, and safety performance is controlled by the flexural steel strain limits of coupling beams. Collapse occurs in two consecutive stages: flexural collapse of coupling beams, followed by crushing of concrete at critical shear wall segments. Collapse spectra are defined for these two collapse limit states. Collapse spectra can be extrapolated from the 2475-year maximum considered earthquake spectrum provided that the prevailing inelastic mechanisms are similar under the MCE and collapse ground motions. The building displays a significantly higher seismic performance at all performance levels, which is primarily attributed to the overstrength due to the limitation of axial stresses on vertical members under design earthquake load combination. The annual frequency of the mean earthquake ground motion that leads to incipient collapse is determined as 8·10⁻⁵, which is significantly lower than the annual frequency of 2475-year ground motions.
This paper explores and validates the use of ground shaking scenarios generated via 3D physics-based numerical simulations (PBS) for seismic fragility studies. The 2009 L’Aquila seismic event is selected as case-study application, given the availability of a comprehensive post-earthquake database, gathering observed seismic damages detected on several building typologies representative of the Italian built environment, and of a validated numerical model for the PBS of ground shaking scenarios. Empirical fragility curves are derived as a function of different seismic intensity measures, by taking advantage of an improved statistical technique, overcoming possible uncertainties in the resulting estimates entailed by data aggregation. PBS-based fragility functions are compared to the corresponding sets of curves relying on updated ShakeMaps. The predictive capability of the adopted simulation strategies is then verified in terms of seismic damage scenarios, by respectively coupling PBS- and ShakeMap-based fragility models with the corresponding ground shaking scenarios. Comparison of observed and predicted damage distributions highlights the suitability of PBS for region-specific seismic vulnerability and risk applications.
To protect the acceleration-sensitive non-structural components in a multi-story building, a proper seismic design of them against the peak floor acceleration (PFA) is needed. The PFA, therefore, should be estimated in advance. To efficiently estimate the PFA of multi-story buildings at the inelastic stage, a nonlinear modal combination approach is provided in this study. First, for the single-story building (single-degree-of-freedom system), a PFA spectral ratio δ, defined as the ratio between the inelastic PFA and the elastic spectral amplitude, is proposed to measure the nonlinear reductions in PFA. A series of time history analysis (THA) revealed that there is a dependable relationship between the PFA spectral ratio δ, the strength reduction factor R, the post-yield stiffness ratio α, and the period T of the structure. The scatter of δ is notably smaller than the ductility demand, showing the good feasibility of a δ-R-T-α relationship for predicting δ. Second, for the multi-story building (multi-degree-of-freedom system), the floor acceleration is decoupled in the modal space, the contribution of each mode to the elastic PFA is multiplied by δ to account for the nonlinear reduction in PFA at the inelastic stage. Here δ can be determined by an appropriate δ-R-T-α relationship, while R and α are determined via a modal pushover analysis. The modified modal contributions are combined via the complete-quadratic combination (CQC) rule, forming the inelastic CQC approach. The PFAs of some 2-, 5-, and 8-story building structures with different degrees of nonlinearity are computed via the THA and the inelastic CQC approach. Results demonstrate the satisfactory accuracy of the latter. Notably, the effects of nonlinearities associated with the higher-order modes on the nonlinear PFA are well considered in the inelastic CQC, thus the un-acceptable over-estimations of the inelastic PFA, which occurs in conventional methods, are avoided.
The local topography hugely impacts the characteristic of earthquake ground motion, further affecting the seismic response of the train-bridge coupled system. Based on the theory of viscous-spring artificial boundary, an analytical model for a train-bridge system subjected to multi-support seismic excitations considering valley topography is established, by applying the displacement time histories of the seismic ground motion to the bridge supports. The influences of the height-to-width ratio of the valley topography, the shear wave velocity of the site soil, and the incident angle of the seismic wave on the seismic responses and running safety of the train-bridge coupled system are investigated by means of parametric investigations, with a 344 m long bridge subjected to the obliquely incident P-wave taken as a case study. The results from the case study demonstrate that the shear wave velocity of the site soil and the incident angle of the seismic wave affect the seismic responses of the train-bridge coupled system in terms of peak occurrence time. The peak values of seismic responses are mainly influenced by the height-to-width ratio of the valley topography as well as the incident angle of the seismic wave.
This study proposes an improved method for rapid visual screening (RVS) to assess the seismic vulnerability of reinforced concrete (RC) buildings in the hilly region, especially in the northern part of the Indian Himalayan region. Several small towns in the Indian Himalayan region are rapidly expanding their building infrastructure to meet the demand of ever-increasing population and tourists. An extensive survey of the existing buildings in Mandi, which is one of the populous towns of the Himachal Pradesh state in northern India, is carried out to assess the seismic vulnerability of buildings. A total of 573 RC buildings were assessed using existing pre-earthquake RVS guidelines, and critical attributes that are known to be associated with the performance of the buildings under earthquake shaking were noted. It was noticed that there is an inconsistency in counting the number of stories in the hilly buildings when different RVS methods are employed. Therefore, a numerical study is also performed to establish guidelines for counting the number of stories in hilly buildings for their RVS. Further, based on the vulnerable attributes in the buildings of hilly region, an improved RVS method is proposed. It is shown that the proposed method is convenient to use for segregating the RC buildings in the hilly region according to the damage that they are expected to experience.
We present the results of the forced-vibration experiments performed at the large-scale prototype structure of EuroProteas founded on gravel-rubber mixture (GRM) layers acting as a means of Geotechnical Seismic Isolation (GSI). Three GRM with different rubber content per mixture weight (0%, 10%, and 30%) but the same mean grain size ratio were used as foundation soil. Each GRM-structure system was subjected to harmonic forces in a wide range of excitation frequencies and force amplitude. It was found that a 0.5 m thick GRM foundation soil layer with 30% rubber content can effectively isolate the structure. The strong effect of the rubber fraction was expressed in the detected period elongation and the dominating rocking component which leads to a more “rigid-body” response of the structure. Moreover, the developed base shear and base moment are significantly reduced regardless of the excitation frequency, while the increased damping of the system and the important energy dissipation demonstrate the effectiveness of the GRM foundation soil layer. Overall, the experimental results demonstrated that the use of GRM as a GSI system can be considered as a low-cost alternative seismic isolation technique.
Seismic hazard varies greatly during an earthquake sequence. Understanding this variation can be useful to end-users, such as emergency managers, as it would enable them to make more informed decisions about potential risk reduction measures. This article presents examples of how two commonly-used products of probabilistic seismic hazard assessments: uniform hazard spectra and disaggregated earthquake scenarios, vary during two severe seismic sequences in western Greece. These calculations are made using a recent time-dependent seismic hazard model based on a Bayesian ETAS approach. The examples show that time-dependent uniform hazard spectra for short return periods (1 and 10 years) are significantly higher than standard time-independent spectra but that uniform hazard spectra for the commonly-used return periods of 475 and 2475 years are similar to those from time-independent assessments. The time-dependent spectra generally converge within a couple of days to the time-independent spectra. The examples also show that the dominant earthquake scenarios evidenced by the disaggregation for the time-dependent assessment can show significant differences from the time-independent scenarios. This is particularly true when the earthquake sequence is distant from the location of interest as the aftershocks contribute greatly to the overall hazard. To show these changes more clearly this article introduces a new graphical representation of the disaggregated results: contour maps showing the magnitude or distance of the dominant earthquake scenario with axes of the structural period and response spectral acceleration.
Different nonergodic Ground-Motion Models based on spatially varying coefficient models are compared for ground-motion data in Italy. The models are based different methodologies: Multi-source geographically weighted regression (Caramenti et al. 2022), and Bayesian hierarchical models estimated with the integrated nested Laplace approximation (Rue et al. 2009). The different models are compared in terms of their predictive performance, their spatial coefficients, and their predictions. Models that include spatial terms perform slightly better than a simple base model that includes only event and station terms, in terms of out-of sample error based on cross-validation. The Bayesian spatial models have slightly lower generalization error, which can be attributed to the fact that they can include random effects for events and stations. The different methodologies give rise to different dependencies of the spatially varying terms on event and station locations, leading to between-model uncertainty in their predictions, which should be accommodated in a nonergodic seismic hazard assessment.
Energy-based seismic design is being rapidly developed and suggests that the seismic demands are met by the energy dissipation capacity of the structural members. Equivalent damping ratio is a measure of energy dissipation in structural members that accounts for the post-elastic behavior of the member and provides insight regarding the dynamic response reduction during a seismic event. The present study implements a machine learning algorithm to estimate the equivalent damping ratio in reinforced concrete shear walls at displacements corresponding to a 1.0% lateral drift ratio. Five different machine learning models, namely, Robust Linear Regression, K-Nearest Neighbor Regression, Kernel Ridge Regression, Support Vector Regression, and Gaussian process regression were evaluated in order to choose the model with the highest accuracy. Among all models, Gaussian process regression, a machine learning method with successful implementation experiences in civil/structural engineering related problems, is selected to identify the equivalent damping ratio. The developed GPR-based algorithm uses a database of 161 rectangular shear walls subjected to quasi-static reversed cyclic loading with geometry and mechanical properties commonly found in building stocks of many earthquake-prone countries. The proposed algorithm estimates the equivalent damping ratio for each specimen by predicting the cyclic dissipated energy and lateral force values as two dependent variables. The model validation results show a mean coefficient of determination (R²) of about 0.89; a relative root mean square error of about 0.14 and a mean absolute percentage error of 10.44%, which is considered a substantially accurate prediction for such a complex problem. An open-source model and the entire database are provided which can be used by researchers and also design engineers. The proposed predictive model enables comparing the damping capacity of shear walls and the outcomes of this study are believed to contribute to the energy-based design or performance evaluation procedures in terms of predicting the energy capacity of shear walls.
A new tool for seismic design is presented, called Yield Displacement Charts (YDC). As with its predecessors, the Yield Point Spectra (YPS) and the Yield Frequency Spectra (YFS), the YDC concept takes advantage of the simple features of yield displacement (uy), to use uy in a performance-based design instead of a force-based period-dependent approach. A self-contained and comprehensive approach to YPS and YFS is presented, enabling the novel aspect of YDC to be introduced: a tool for a multi-performance objective design that only depends on the location of the structure to be designed. Once the yield displacement chart has been calculated for a particular place, it can be used for the preliminary design of any structure. For a given value of yield displacement, the YFS are obtained from the Yield Displacement Chart. The suitability of the methodology proposed is illustrated by means of a simple case study of a concrete bridge pier.
This paper proposes a novel hybrid tuned mass damper (TMD) and tuned liquid damper (TLD) system (TMD + TLD) for vibration control of multi-degree of freedom structures under seismic excitations. The proposed system is introduced using equations of motions of a five-degree of freedom structure which is modeled as a shear-type with a lateral degree of freedom at each floor under harmonic and earthquake excitations. The proposed hybrid TMD + TLD system is introduced to the building structure in the model. Several case studies are investigated to evaluate the performance of the proposed system. In the first case, both TMD and TLD are tuned to the first frequency of the structure, and the TMD is fixed to the top floor, and the TLD is fitted to the fourth floor of the primary structure. In the second case, the TMD is tuned to the first frequency of the structure, whereas the TLD is tuned to the second frequency of the structure. All the cases are investigated under harmonic force and real earthquake ground motions. The earthquakes selected in this study are classified as low, intermediate, and high-frequency content earthquakes. Results indicated that with comparatively less mass ratio, the earthquake-induced structural vibration is successfully suppressed when the TMD is tuned to the 1st frequency, and the TLD is tuned to the 2nd frequency of the structure. The focus of the investigation is to develop a practical framework to demonstrate the efficiency of such a hybrid damper.
A key task when developing a ground-motion model (GMM) is to demonstrate that it captures an appropriate level of epistemic uncertainty. This is true whether multiple ground motion prediction equations (GMPEs) are used or a backbone approach is followed. The GMM developed for a seismic hazard assessment for the site of a UK new-build nuclear power plant is used as an example to discuss complementary approaches to assess epistemic uncertainty. Firstly, trellis plots showing the various percentiles of the GMM are examined for relevant magnitudes, distances and structural periods to search for evidence of “pinching”, where the percentiles narrow excessively. Secondly, Sammon’s maps, including GMPEs that were excluded from the logic tree, are examined to check the spread of the GMPEs for relevant magnitudes and distances in a single plot. Thirdly, contour plots of the standard deviation of the logarithms of predicted ground motions from each branch of the logic tree (σµ) are compared with plots drawn for other relevant hazard studies. Fourthly, uncertainties implied by a backbone GMM derived using Campbell (2003)’s hybrid stochastic empirical method are compared to those of the proposed multi-GMPE GMM. Finally, the spread of the percentile of hazard curves resulting from implementing the GMM are examined for different return periods to check whether any bands of lower uncertainty in ground-motion space result in bands of lower uncertainty in hazard space. These five approaches enabled a systematic assessment of the level of uncertainty captured by the proposed GMM.
A significant proportion of existing bridges in high seismic regions were constructed prior to the 1970s. As a result of poor reinforcement detailing, pre-1970s bridge columns are susceptible to lap-splice or shear failure in the plastic region. Given the high economic impact of retrofitting all pre-1970s reinforced concrete (RC) bridges, it is essential to identify the most vulnerable bridges for retrofit prioritisation. Analytical fragility functions are useful for quantifying the seismic vulnerability of existing bridge stock. However, the accuracy of these fragility functions relies on the adequacy of the adopted modelling approach. This paper presents a hinge-type modelling approach for capturing the seismic response of as-built splice-deficient and retrofitted RC bridge columns. Fragility analysis is carried out for typical seat and diaphragm abutment two-span bridges using the proposed hinge-type modelling approach. The results showed that the vulnerability of the bridges depends on the column failure mode and the limit state under consideration. Also, the common notion that the column is the most vulnerable component may not necessarily be true. The study underscored that retrofitting columns without retrofitting other components may not effectively mitigate the damage and associated risk.
This study addresses the modeling of different energy dissipation mechanisms for numerical prediction of the vertical acceleration demand in regular moment-resisting steel frame structures. One of the issues discussed is the consideration of viscous damping in the structural model. It is shown that well-established Rayleigh-damping may highly overestimate the damping of the vertical modes, resulting in much too low vertical acceleration response predictions. A study with different damping models provides an appropriate damping modeling strategy that leads to reasonable predictions of both horizontal and vertical frame acceleration demands. Another open question is the effect of inelastic material behavior on the vertical acceleration demand on the considered regular structures. The results of a shell model of a frame structure exposed to high intensity ground motion excitation demonstrate that inelastic material behavior has virtually no impact on the vertical acceleration demand, while structural inelasticity leaves the horizontal acceleration response significantly smaller compared to the elastic demand. This leads to the conclusion that common frame models that capture the inelastic horizontal response but behave elastic in the vertical direction are suitable for the computation of both the horizontal and vertical acceleration demand.