Seismic Performance Assessment Research Articles

Seismic Performance Assessment of Clutching Inerter Damper for Isolated Bridges

Seismic Performance Assessment of Clutching Inerter Damper for Isolated Bridges

Seismic Performance Evaluation and Retrofit of Liquid Storage Tanks- Case Study

Seismic performance of existing liquid pentane storage tanks located in a tank farm in Turkey Kocaeli region, which is a high seismic region, is studied. The tanks are free-to-slide on their existing reinforced concrete foundation. The tanks seismic performance is evaluated based on the 2018-Turkish Building Seismic Code and API 650 provisions using three-dimensional (3D) finite element methods with nonlinear time-history analysis. The developed FE model for seismic performance assessment of the existing tanks includes tank-foundation dynamic interaction, tank supports uplifting, and sliding over the foundation. The study revealed poor and inadequate seismic performance for the existing tanks due to lack of tank foundation-anchorage. A practical seismic retrofit strategy is developed to anchor the tanks to the existing reinforced concrete foundation. Prefabricated and field-welding free steel split sleeves are developed for the tank anchorage. The retrofitted tank seismic performance is evaluated to verify the proposed retrofit strategy and its effects on tank seismic behavior. The base shear and uplift reactions for the retrofitted tank are monitored for the anchorage design. Tank top drift, which is an important seismic performance parameter for tank piping, and tank steel material yielding are also checked to verify adequacy of the proposed retrofit strategy.

Interactions between Seismic Safety and Energy Efficiency for Masonry Infill Walls: A Shift of the Paradigm

Currently, the upgrade of existing reinforced concrete (RC) buildings focuses only on energy retrofitting measures due to the current policies promoted in the scope of the European Green Deal. However, the structural deficiencies are not eliminated, leaving the building seriously unsafe despite the investment, particularly in seismic-prone regions. Moreover, the envelopes of existing RC buildings are responsible for their energy efficiency and seismic performance, but these two performance indicators are not usually correlated. They are frequently analyzed independently from each other. Based on this motivation, this research aimed to perform a holistic performance assessment of five different types of masonry infill walls (i.e., two non-strengthened walls, two walls with seismic strengthening, and one wall with energy strengthening). This performance assessment was performed in a three-step procedure: (i) energy performance assessment by analyzing the heat transfer coefficient of each wall type; (ii) seismic performance assessment by analyzing the out-of-plane seismic vulnerability; (iii) cost–benefit performance assessment. Therefore, a global analysis was performed, in which the different performance indicators (structural and energy) were evaluated. In addition, a state-of-the-art review regarding strengthening techniques (independent structural strengthening, independent energy strengthening, and combined structural plus energy strengthening) is provided. From this study, it was observed that the use of the external thermal insulation composite system reduced the heat transfer coefficient by about 77%. However, it reduced the wall strength capacity by about 9%. On the other hand, the use of textile-reinforced mortar improved the strength and deformation capacity by about 50% and 236%, but it did not sufficiently reduce the heat transfer coefficient. There is a need to combine both techniques to simultaneously improve the energy and structural energy performance parameters.

Seismic performance assessment of concentrically braced steel frames designed to the Turkish Building Earthquake Code 2018

The Turkish Building Earthquake Code 2018 (TBEC 2018) came into force in 2019 and superseded the previous code, the Turkish Earthquake Code 2007 (TEC 2007). Compared to TEC 2007, TBEC 2018 includes new design approaches as well as significant changes in the design of steel structures which are likely to notably affect the seismic design and performance of concentrically braced frames (CBFs). This study aims to quantify the seismic performance of CBFs designed to TBEC 2018. To this end, a set of archetypes was designed, covering a wide range of building heights, bay widths, and seismic hazard levels. Nonlinear numerical models of the archetype buildings were built to perform nonlinear static and dynamic analyses. The seismic performance assessment framework outlined in FEMA P-695 was adopted. The effects of build height, bay width, and seismic hazard levels were investigated and reported. The results of the study revealed that CBFs located in moderate-seismic regions showed acceptable performance while CBFs designed to TBEC 2018 performed poorly in high-seismic regions.

Multi-platform simulation of infilled shear-critical reinforced concrete frames subjected to earthquake excitations

This paper proposes a multi-platform simulation method for the seismic performance assessment of masonry infilled reinforced concrete (RC) frames, especially for those that, due to inadequate reinforcing details, tend to undergo shear failure during an earthquake. The multi-platform method is based on a micro–macro modeling approach in which a detailed finite element model of the RC frame is incorporated with a strut model of the infill wall. It exploits the strut model to increase its computational efficiency and the finite element model based on the modified compression field theory to capture the nonlinear behaviour of the RC frame. The proposed method is validated against previously tested frames subjected to lateral loads, and its advantages over the conventional strut models are demonstrated through both quasi-static and dynamic analyses.

Seismic performance assessment of high asphalt concrete core rockfill dam considering shorter duration and longer duration

The particular interest produced by the seismological characteristics impacting structural response has given a new challenge in the performance-based design of high dams. Recent research has shown that the seismological characteristics of frequency and amplitude inherent in ground motion (GM) records govern the dynamic response of high dams. Therefore, these seismological characteristics have been accepted and incorporated into the seismic design codes of high dams in most countries. However, the duration of strong GMs, as one of the critical seismological characteristics of earthquakes, also needs to be fully understood to carry out a more effective performance-based design of high dams. Based on this observation, the effect of the duration of strong GMs has been explored, investing in the seismic performance of high asphalt concrete core rockfill dams (ACCRDs) by employing an integrated duration (ID) concept that can reflect the duration of all components of GMs. A high ACCRD was firstly built in the commercial software ABAQUS considering the dam-reservoir-foundation interaction systems. Subsequently, the coupled multiple stripe analysis and maximum likelihood estimate method generate seismic fragility curves for a dam according to two damage indicators. Comparison of the results for the seismic performance of the high ACCRD revealed that the longer-duration GMs could give rise to the higher relative settlement ratio, stress demand-capacity ratios, and probability of exceedance (POE) of the dam than shorter-duration GMs. It is recommended that in the current seismic design and seismic performance evaluation, the effects of GM duration, frequency, and amplitude should be considered.

Fragility-based seismic performance assessment of modular underground arch bridges

Seismic performance assessment of modular underground arch bridges (MUABs) can help mitigate structural damage to MUABs during earthquakes. This study proposed an efficient procedure to evaluate the seismic performance of a three-hinge MUAB by using fragility-based analysis. Firstly, a novel proposal for damage states was presented using the relationship between the crack depth and thickness of the arch component. The relationship between ground motion intensity and structural failure probability was then described using stratum-uncertainty characteristics. The multiple stripe analysis approach with the maximum likelihood function was introduced to detail the uncertainty characteristics of strata by allowing various ground motions at distinct seismic intensity levels. Finally, the collapse probability considering stratum-uncertainty characteristics was specified for seismic intensity and probability levels. The results revealed that the proposed procedure to randomly select ground motions from the strong-motion database of the Pacific Earthquake Engineering Research Center is feasible for evaluating the seismic vulnerability of MUABs. Therefore, the seismic performance of MUABs can be reasonably predicted under earthquakes.

IMPA versus Cloud Analysis and IDA: Different Methods to Evaluate Structural Seismic Fragility

Well-known methods for seismic performance assessment, such as incremental dynamic analysis (IDA), multi-stripes analysis (MSA) and the cloud method, involve nonlinear response time-history analyses to characterize the relationship between the chosen damage measure versus intensity measure. Over the past two decades, many authors have proposed simplified procedures or nonlinear static approaches to develop fragility. In these procedures, the capacity of the system is evaluated by nonlinear static procedures (i.e., the capacity spectrum method (CSM), the N2 method, modal pushover analysis (MPA)) and the demand is derived by response spectra. In addition to the familiar ones, incremental modal pushover analysis (IMPA) is a novel nonlinear static procedure proposed in recent years, and it is used in this research to present an IM-based fragility estimation. The accuracy and effectiveness of different methods to assess vulnerability are investigated by comparing fragility curves derived by MPA-based cloud analysis, IMPA and cloud analysis against IDA. The comparison gives valuable insights on the influence of scaling on different sets of records; however, a more extended validation is needed to confirm the obtained results and draw more general conclusions. Results arise from two relatively small bins of record motions differing by ranges of Joyner-Boore distance and scattered in a range of magnitude are presented.

Seismic Performance Assessment of a Single-Layer Spherical Lattice Shell Structure with Multifunctional Friction Pendulum Bearings

The dynamic responses of spatial lattice shell structures with friction pendulum bearings (FPBs) under multidimensional seismic excitations are complex. In addition, FPBs may experience uplift and separation of the bearing components owing to excessive displacements. In this study, a novel multifunctional FPB (MFPB) with a multi-defense system was developed, and its effectiveness in reducing and controlling the seismic responses of spherical lattice shell structures was evaluated. The proposed MFPB comprises an FPB, superelastic shape-memory alloy cables, and sleeve restrainers. A mechanical model of the MFPB was established, and its isolation and control behaviors were investigated through numerical simulations. Furthermore, the main characteristics and advantages of the isolation system were analyzed. Subsequently, the MFPB system was applied to a single-layer spherical lattice shell structure with surrounding columns. A computational model of the controlled structure was developed using the OpenSees software. Finally, nonlinear time history analyzes were conducted to analyze the seismic performance of controlled and uncontrolled lattice shells. The results demonstrate that the MFPB isolation system can effectively control the structural responses of isolated spatial lattice shell structures under horizontal and vertical seismic excitations and improve their seismic resilience.

Seismic Performance Assessment of RC Buildings Reinforced with Plain Rebars

Seismic Performance Assessment of RC Buildings Reinforced with Plain Rebars

Seismic Performance Assessment of Ordinary Moment Resisting Frame Equipped with Viscous Dampers under Pulse-Like Earthquakes

In conventional structures, the earthquake-resistant design is based on flexibility after yielding of structural members to provide a loss of earthquake input energy, while, using dampers, the input energy loss can be concentrated in predetermined points to prevent the nonlinear behavior of the main members that are also in the gravity bearing path. However, near-fault earthquakes might cause unexpected failure and severe structural damage, especially those with the pulse-like effect. A pulsed movement in the near field records in this system will, however, result in unusual behavior. Technology advances and the creation of vibration control systems have helped control this type of behavior since the earthquake forces are applied indirectly to the structure. For further investigation of this issue, in this study, some traditional two-dimensional frames were modeled for 3, 8, and 12 floors. Seven near-fault pulsed and seven far-fault nonpulsed accelerometers are applied. The structural behavior in four modes is examined: (1) without damper and soil-structure interaction effect, (2) without damper and considering soil-structure interaction effect, (3) with damper and considering soil-structure interaction, and (4) with damper without considering soil-structure interaction. Each model is analyzed in OpenSees software under incremental dynamic analysis. Then, the fragility curve is plotted based on the results. The results indicate that frame (4) reaches the failure level at a higher spectral acceleration, which means that the performance of the viscous damper in reducing drift between floors is one of the main criteria for predicting damages. It also shows the effect of soil-structure interaction on increasing the drift between floors and reaching failure at lower spectral acceleration in all models. Also, by comparing the fragility curves of the models under near-field and far-field records, it is found that the probability of failure under far-field documents (without pulse) is less than that under near-field documents (with a pulse).

Seismic performance assessment of an existing multispan bridge in eastern Canada retrofitted with fiber reinforced elastomeric isolator

A seismically resilient transportation network entails preprioritized retrofit plans for conventionally designed highway bridges. This is particularly important for the province of Ontario in Canada, where more than 44% of the multispan bridges have been constructed prior to 1970. To support future seismic risk mitigation efforts, this study evaluated the seismic performance of a multispan continuous reinforced concrete bridge in Ontario, Canada, in its as-built and retrofitted conditions. Seismic retrofit is conducted utilizing novel Fiber Reinforced Elastomeric Isolators (FREIs). Analytical fragility curves are developed using Incremental Dynamic Analysis (IDA) on a three-dimensional nonlinear finite element model of the bridge using 45 synthetic ground motion records for eastern Canada. Results indicate that seismic isolation can effectively mitigate the seismic demand on columns and transfer the shear forces to the end abutments resulting in excessive backfill soil deformation. However, this deformation does not necessarily result in bridge failure and traffic disruption.

Glass-box model representation of seismic failure mode prediction for conventional reinforced concrete shear walls

The recent surge in earthquake engineering is the use of machine learning methods to develop predictive models for structural behavior. Complex black-box models are typically used for decision-making to achieve high accuracy; however, as important as high accuracy, it is essential for engineers to understand how the model makes the decision and verify that the model is physically meaningful. With this motivation, this study proposes a glass-box (interpretable) classification model to predict the seismic failure mode of conventional reinforced concrete shear (structural) walls. Reported experimental damage information of 176 conventional shear walls tested under reverse cyclic loading was designated as class types, whereas key design properties (e.g., compressive strength of concrete, axial load ratio, and web reinforcement ratio) of shear walls were used as the basic classification features. The trade-off between model complexity and model interpretability was discussed using eight Machine Learning (ML) methods. The results showed that the decision tree (DT) method was a more convenient classifier with higher interpretability with a higher classification accuracy than its counterparts. Also, to enhance the practicality of the model, a feature reduction was conducted to reduce the complexity of the proposed classifier with higher classification performance, and the most relevant features were identified, namely compressive strength of concrete, wall aspect ratio, transverse boundary, and web reinforcement ratio. The ability of the final DT model to predict the failure modes was validated with a classification rate of around 90%. The proposed model aims to provide engineers interpretable, robust, and rapid predictions in seismic performance assessment.

Vertical spectra consistent with horizontal seismic hazard

Construction of vertical spectra (V) for scenario- and intensity-based seismic performance assessment is proposed based on scaling of the associated horizontal spectral ordinates (H) through respective V/H spectral ratios. Geometric mean of the spectra along and normal to the principal plane components is considered as the intensity measure of the horizontal component. V/H spectral shape is constructed using a large database (PEER-NGA-WEST2) of strong motion records contingent on the magnitude of the event, epicentral distance and average shear wave velocity. The procedure is based on the ratio of median vertical-to median horizontal-spectral ordinates which are shown to be well representative of the median of V/H spectral ratio. The construction is based on median response of the scenario and also applies to the design level (of a particular facility located in a specific site, which is also governed by a scenario) under certain assumptions and involves two steps: construction of normalized V/H spectra with unity at zero period scaled by the ratio of median vertical-to median horizontal- PGA (beta). The normalized V/H spectrum is shown to be characterized by three control points. An empirical estimate is proposed for beta as a function of epicentral distance. Normalized V/H spectra are further idealized for use with the intensity-based assessment per seismic codes. Vertical spectra using the proposed framework are compared with the various recommendations reported in the prior art including seismic codes and recorded events. PESMOS and COSMOS databases of strong motion events recorded in the Indian subcontinent are also used during the assessment.

Reducing uncertainty in seismic assessment of multiple masonry buildings based on monitored demolitions

A significant part of the existing building stock in regions of low to moderate seismic hazard has been designed without modern seismic considerations and is, in the meantime, exceeding its design life span. The assessment of seismic performance poses an engineering challenge, due to unknown material properties, undocumented structural interventions and the scarcity of event-based information. Operational modal analysis has been applied in some cases to verify model assumptions beyond visual inspection. However, masonry buildings exhibit amplitude-dependent stiffness even at very low response amplitudes, raising questions about the validity of such methods. Planned demolitions provide engineers with the opportunity to leverage higher-amplitude vibrations generated during demolition activities to better understand the dynamic behaviour of existing buildings. This paper introduces a Bayesian model-updating framework, which aims at reducing uncertainty in seismic analysis, by fusing dynamic measurements with best-practice structural models. The proposed hybrid framework is applied to nine real masonry buildings, representative of existing residential buildings, as typically encountered in Switzerland, that have been monitored during controlled demolition. A vast reduction in prediction uncertainty is achieved through data-driven model updating, additionally exposing intra- and inter-typological differences in terms of seismic capacity and ductility. In addition, differences between updated model predictions and typical engineering assumptions and generic typological curves are discussed. Overall, this contribution demonstrates, applies and discusses the practical benefits of a straightforward methodology for fusing monitoring data into the seismic evaluation of existing masonry structures.

Seismic performance assessment of high-rise steel moment frame building with Reinforced Concrete (RC) core wall based on nonlinear time history analysis

This paper focuses on seismic responses of a 30-story high-rise building with a dual lateral system of Reinforced Concrete (RC) core shear wall and steel moment frame. To assess the seismic performance of the building, a nonlinear finite element model is built by using the OpenSees software. This three-dimensional model is created by using the fiber-beams for members and multi-layer shell elements for RC core walls. The numerical simulation has been examined under the thirteen sets of strong ground motion records which are scaled with the design and maximum seismic levels, Design-Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE) level hazards respectively. In consequence, the desirable performance of high-rise steel moment frame building with RC shear core consisting of coupling beams and rectangular shear walls is shown. The outcome of nonlinear time history analyses reports the acceptable seismic performance of tall buildings designed. Results showed that maximum inter-story drift is significantly lower than allowable drift. Also, the RC core wall absorbed almost two-third of the total shear forces from the base level to one-third of height. However, the shear values of the core wall were significantly reduced by increasing the height while the shear values of the steel moment frame stayed constant.

Seismic Performance and Reliability Evaluation of Ductile RC Frame Structures with Infills

Ductile RC frames are often considered to have superior seismic performance even with infills. However, the seismic performance of this type of structure needs to be reassessed considering the additional shear requirements produced by the infills-column interaction and the increased seismic hazard due to the impact of infills on the vibration period of the structure. This paper presents a performance-based earthquake engineering framework aimed at the assessment of the comprehensive seismic performance of ductile RC frames with infills. A series of common configurations are considered in the analysis: bare frame (BF), upper-infilled frame (UIF), all-infilled frame (AIF), and corresponding stirrup-reduction frames with both infills-induced shear failure behavior of column and influence of structural vibration period considered. The results show that infills changed the failure modes and dynamic characteristics of ductile structures and shear failure occurs in all-infilled frame columns. Even though the all-infilled frame meets the shear requirement, its collapse probability is higher than the bare frame due to the high seismic hazard caused by a shorter vibration period.

An innovative variable target time method for probabilistic-based seismic performance assessment of multi-storey buildings

Incremental dynamic analysis is one of the most widely used methods to develop fragility curves due to its ability to deal with various inherent uncertainties in the prediction of earthquake recurrence and characteristics. The dependence of the results to the selected ground motion records, uncertainties associated with the selection of appropriate earthquake input records and high computational costs are among the challenges limit the practical applications of this method. In this study, an innovative variable target time (VTT) method is developed based on the concept of endurance time (ET) analysis for structural reliability assessment of 3D multi-storey structures. A novel low-computational cost process is proposed to develop the database of desired statistical population and estimate the probabilities for constant hazard levels (EDP-based method) by taking into account the uncertainties in the frequency content of the input earthquakes. To verify the accuracy of the outcomes, the results are compared with the fragility curves derived based on different damage levels (IM-based method) and Incremental Dynamic Analysis (IDA) for moment-resisting steel and tunnel-from concrete 3D structures with 5- and 10-storeys. The results indicate that the proposed method is capable of providing highly accurate probabilistic models for structural performance under different levels of earthquake intensity. For the selected steel moment-resisting structures, the maximum difference in the reliability results obtained by the two methods of analysis for the Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) performance levels under the Design Basis Earthquake (DBE) and the Maximum Considered Earthquake (MCE) are around 2, 7 and 5%, respectively. Similarly, the reliability results for the 3D tunnel-from concrete structures show around 6, 7, and 6% errors between the two analysis methods for the IO, LS and CP performance levels, respectively. The proposed method reduces the computational costs of the IDA-based methods by 80%, and hence, can be considered as a suitable alternative for the conventional methods to develop fragility curves of 3D structures.

A comparative study of seismic analysis, design, and collapse safety margins of tall buildings in the United States and Japan, Part I: Performance-based analysis and design

Performance-based seismic analysis and design of tall buildings have become increasingly common in the United States and have been the standard practice in Japan for a long time. The methodologies for seismic hazard analyses, selection of earthquake records for design, and acceptance criteria, however, are widely different in the two countries. Japan experiences large earthquakes and strong shakings of buildings significantly more frequently than the United States, and the data on actual seismic performance are richer in Japan than in the United States. Comparison of performance and calibration between the two design procedures can help to improve the quantitative assessment of seismic performance of buildings in the United States. This article presents the application of US and Japanese procedures to a tall building archetype once proportioned, analyzed, and designed according to US practices and once per Japanese practices. The structural systems selected are very different; for the United States, the archetype is designed using a core reinforced concrete shear wall building with composite floor systems and steel columns as the gravity system, whereas for Japan, the archetype is designed using a steel moment frame made of square concrete-filled steel tube (CFT) columns and composite beams and installed with oil dampers. Although the design procedures followed are vastly different, the seismic performances of the systems are rather similar during serviceability, design basis, and maximum considered events. As will be presented in the second part of this article, the collapse safety margins of the two designs are significantly different.

Modeling Approaches for the Assessment of Seismic Vulnerability of Masonry Structures: The E-PUSH Program

The assessment of seismic performance of existing masonry structures is a key aspect for the risk mitigation strategies of existing buildings and preservation of historical heritage. The increasing availability of modelling approaches for the assessment of seismic response of masonry structures calls for the need of verifying their reliability and correct use. In fact, these procedures are very sensitive to modelling hypotheses, so that the results of the assessment could vary in a wide interval depending on the adopted software and on the user’s skill. Aiming at enhancing the classical software packages for the structural analysis of masonry buildings, especially in terms of easiness of use, simplicity of modelling and limited computational demand, the authors developed a reliable and sound push-over program, called E-PUSH, which allows a quick and nearly user-independent assessment of the seismic risk index. In the paper, available commercial codes for the seismic assessment of unreinforced masonry buildings are illustrated and discussed, in comparison with the E-PUSH program, highlighting the differences in terms of modelling assumptions, choice of masonry mechanical parameters and failure criteria, focusing on the impact of the assumptions adopted for the estimation of capacity curves and seismic risk index of a simple benchmark structure. Then, a relevant case study, consisting in the assessment of the “Niccolò Machiavelli” masonry school in Florence, is investigated adopting two different software packages, the original E-PUSH and a commercial one, discussing the sensitivity of the results on the assumptions made by the user in the modelling phase.