Inter-story Drift Research Articles

Structural Design of a 10-Story Office Building using the Special Moment Frame System (SMFS) in Padang, West Sumatra

Indonesia is located at the convergence of the Eurasian, Pacific, and Indo-Australian tectonic plates, making it prone to significant earthquakes, such as the Aceh earthquake and tsunami in 2004 with a magnitude of 9.1, and the Padang earthquake in 2009 with a magnitude of 7.6, both known for their severe impacts. According to the Central Statistics Agency (BPS), there were 10,843 earthquakes in 2022. Given this high level of risk, all buildings, especially offices, must be designed to be earthquake-resistant due to high activity and user numbers. The city of Padang is categorized in Seismic Design Category D, indicating a high level of earthquake risk. The construction of a ten-story reinforced concrete building for office use is planned, referring to SNI 1726-2019 on earthquake resistance and SNI 1727-2020 on minimum loads, along with the Special Moment Resisting Frame System (SMRF). Structural analysis and modeling are conducted using ETABS software, with element dimensions based on the initial design. This analysis aims to ensure the building meets earthquake resistance requirements through response spectrum evaluation, including natural periods, inter-story drift, P-Delta effects, and checks for irregularities. Based on internal forces from ETABS V.18, reinforcement designs are prepared for structural elements such as columns, beams, slabs, and shear walls. A design capacity evaluation ensures the safety and optimal performance of the structure during an earthquake.

Simultaneous optimization of capacity and topology of seismic isolation systems in multi-story buildings using a fuzzy reinforced differential evolution method

Inter-story isolation systems, as an alternative earthquake protection system, reduce in-building movement compared to base isolation systems. In this context, the current study focuses on simultaneously optimizing the topology and capacity of base and inter-story isolation systems for a multi-story building exposed to multiple earthquake scenarios. In addressing this challenge, an optimization model is developed that simultaneously considers both the topology (vertical arrangement) and capacity (required stiffness) of the seismic isolators as the decision variables of the model. To attain more practical and feasible solutions, the side constraints of the problem involve the inter-story drift and the total cost of seismic isolation systems. A gradient-free and self-adaptive search method, Fuzzy Differential Evolution incorporated Virtual Mutant (FDEVM), is employed to solve the optimization problem. The FDEVM approach applies a fuzzy mechanism to adopt its search behavior with governing condition(s) of the current problem. The selected method's performance is implicitly compared with its standard version. The obtained results indicate that optimally placing inter-story isolators with an optimal configuration and capacity not only improves the seismic performance of the systems but also its more cost-efficient approach compared with conventional based isolation systems. Also, the comparative outcomes indicate that the FDEVM method exhibits a high search capability for this class of problems.

Experimental study and seismic assessment on base isolated precast concrete frame structure with box connectors

The precast construction method offers fast and environmentally friendly solutions for sustainable development in construction. Various connection methods, including wet and dry, have been proposed to enhance assembly convenience. However, challenges remain in achieving complete assembly and considering disassembly processes, hindering post-earthquake restoration. This study introduces a precast RC structure system with easily assembled joints that facilitate disassembly. To enhance the structural system's adaptability to regions with high seismic intensity, rubber-bearing base isolation technology is employed to optimize its seismic performance. Shaking table tests were conducted to evaluate the structure system's dynamic response and seismic performance. Test results indicate that the isolation layer significantly decreases the acceleration response, inter-story drift ratios, floor shear forces, and strain of reinforcements. The isolation structure has a high probability of entering operational and immediate occupancy states during rare earthquakes. The deformation of the isolation bearings has a decisive impact on the overall seismic fragility of the isolation structure system.

Incorporation of machine learning into multiple stripe seismic fragility analysis of reinforced concrete wall structures

This study proposes a novel procedure that incorporates machine learning (ML) into the multiple stripe analysis (MSA) approach to efficiently produce seismic fragility curves for reinforced concrete (R/C) shear walls in building frame systems. The proposed procedure aims to mitigate computational challenges associated with the original MSA approach. In this context, ML models were developed for predicting the failure probability of R/C walls subjected to ground motions based on a specified threshold of maximum interstory drift ratio (MIDR). Specifically, the result of each numerical analysis, taken as the output variable of the ML models, was classified as either “B” (Below) or “E” (Exceeding) to indicate whether the MIDR of R/C walls was below or exceeding the specified threshold. This binary categorization was then used to calculate the failure probability points, which are necessary to derive fragility curves per the MSA approach. Data for training and testing the ML models were generated from nonlinear time history analyses of 46 distinct R/C walls subjected to 1000 ground motions. The R/C walls varied in height from four to 40 stories, and the ground motions included far-field, near-field pulse, and near-field no-pulse types. Four well-established ML methods, including random forest (RF), extreme gradient boosting, light gradient boosting machine, and categorical boosting, were considered. The performances of the ML models were compared using a confusion matrix. Based on this comparison, the RF model was selected and incorporated into the proposed procedure. Subsequently, the proposed approach was demonstrated to create the seismic fragility function of a new R/C wall structure. This study highlights the potential of ML applications in optimization problems within the earthquake engineering domain.

Parametric Analysis of Moment-Resisting Timber Frames Combined with Cross Laminated Timber Walls and Prediction Models Using Nonlinear Regression and Artificial Neural Networks

The light weight and moderate stiffness of multistorey timber buildings make them susceptible to increased lateral displacements and accelerations under service-level wind loading. Therefore, the fulfilment of serviceability requirements is a major challenge. In this study, linear elastic finite element analysis was used to perform a parametric study of moment-resisting timber frames combined with cross laminated timber walls. In the parametric study, various mechanical and geometrical parameters were varied within practical ranges. The results of the parametric study were used to derive simplified analytical expressions and to train artificial neural networks which can be used to estimate fundamental frequency, mode shape, top floor displacement, maximum inter-storey drift, and wind-induced acceleration. The analytical expressions and the artificial neural networks can be used for the preliminary assessment of serviceability performance of moment-resisting timber frames with and without cross laminated timber walls, under service-level wind loading.

Cyclic seismic pushover testing of a multi-story underground station

The experimental approach is crucial for investigating the seismic performance and damage process of underground structures. Considering the shortcomings of the 1-g, centrifuge shaking table and monotonic displacement pushover tests, a large-scale cyclic displacement pushover test method is proposed based on the soil-underground structure dynamic interaction and seismic performance quantification system. Taking a two-story three-span subway station structure as the prototype, the cyclic displacement pushover test device was designed for a 1/7-scale multi-story subway station based on the seismic response characteristics of underground structures. The corresponding numerical simulations and experiments were conducted. Typical numerical results (including the seismic damage process, capacity curves of the structural columns, and strain response) and test results (the macroscopic phenomenon of structural damage development, strain response, and deformation response) are interpreted. The results show that the proposed cyclic displacement pushover test is better than the monotonic displacement pushover test, the damage process of the tested station structure conforms to the description of the inter-story drift ratio (IDR) quantification system of seismic performance. Meanwhile, the column has greater strain amplitudes than other components, and the column strain curves reach their peaks before other components. Furthermore, the tested station structure has a similar damage pattern to the Daikai subway station. The reliability and feasibility of the proposed cyclic displacement pushover test method are verified.

Pounding impact on seismic demands for adjacent irregular buildings with collinear alignment eccentricity

This research aims to evaluate the impact of pounding on seismic demands for neighboring irregular buildings with collinear alignment eccentricity and provide valuable recommendations for seismic design. To achieve this, a numerical simulation is conducted to calculate the effects of pounding on the seismic response requirements in different scenarios where two irregular adjacent buildings with eccentric center of mass are considered, plan irregularity is reflected with eccentricities between the rigidity center and mass center of the building’s superstructure. Adjacent buildings with three different heights involve four-, eight-, and twelve-story buildings with moment-resisting frame (MRF) structural system. To ensure reliable estimation of engineering seismic demands, three different ground motions, which are fully compatible with the design spectrum, are applied to different adjacent building configurations. A nonlinear time history analysis is performed to determine the response demands for different adjacent buildings with collinear alignment eccentricity, such as displacement, inter-story drift, story shear force, impact force, and acceleration responses. The Engineering Design Parameters (EDP) are thoroughly examined to gain a comprehensive understanding of the structural behavior and performance of the adjacent irregular buildings. The findings hold for all these scenarios, suggest that the colinear eccentricity of the irregular building in the closing/convergence direction, promotes the pounding and increases the number of impacts, while the eccentricity in the opening/divergence direction, reduces the pounding probability and the number of impacts between adjacent buildings. Moreover, the findings highlight the impact of eccentricity on peak acceleration responses and emphasize the importance of considering eccentricity in assessing the dynamic response of adjacent buildings with insufficient separation.

Shaking table test of a full-scale lightweight bolt-connected concrete sandwich wall panel structure: Overview and seismic analyses

This study proposed a novel lightweight bolt-connected concrete sandwich wall panel structure with the advantages of thermal insulation, construction efficiency, demountability and remountability. The seismic design of the structure was employed a non-equivalent cast-in-place method, resulting in appropriate configurations of horizontal and vertical bolted joints. Subsequently, a shaking table test was carried out to investigate the damage pattern, dynamic characteristics and dynamic responses of a full-scale structure. The test results demonstrated that the overall damage was moderate, which exerted a few impacts on the structural capacity or integrity. The global responses, including small displacement response, minor torsion response, and high energy dissipation capacity were found, as well as local responses, such as small strains in the steel plates and a slight loss of bolt prestress. The maximum inter-story drift ratio was below the elastoplastic inter-story drift ratio limit θu = 1/120 defined in Chinese code GB 50011. In general, the structure presented high lateral stiffness and sufficient capacity against high-intensity ground motions. A numerical model was developed, wherein precast components were established by multi-layer shell elements and bolted joints were simulated by 3-DoF nonlinear springs. Linear modal and nonlinear time history analyses were performed and compared with the experimental results. The simulation results showed good agreement with the experimental ones, confirming the ability of the model to capture global responses.

Seismic assessment of glulam frames with dual-tube self-centering buckling-restrained braces

The development of resilient lateral load-resisting systems is essential for multi-story and high-rise timber buildings in earthquake-prone areas. In this paper, an attempt is made to integrate dual-tube self-centering buckling-restrained braces (DT-SCBRBs) to glulam frames, aiming to improve their structural resilience to earthquakes. To assess the seismic effectiveness of such a DT-SCBRB glulam frame, nonlinear time-history analyses (NLTHAs) were conducted on a series of prototype DT-SCBRB glulam frames with different building heights and design parameters of DT-SCBRBs. The seismic performance of these prototype structures was evaluated in terms of maximum inter-story drift ratios (MaxISDRs), residual inter-story drift ratios (ResISDRs), and inter-story drift uniformity. The results show that the frame with lower post-tensioning-to-yielding ratios of DT-SCBRBs tended to exhibit lower MaxISDRs but could sometimes lead to higher ResISDRs under major earthquakes. Low deformability of tendons could result in tendon fracture under major earthquakes. The ResISDRs of all the prototype frames were lower than 0.5 %, the drift limit for the “Repairable” performance level. Compared to minor and moderate earthquakes, the DT-SCBRB glulam frames deformed more uniformly during major earthquakes. Incremental dynamic analyses (IDAs) were also conducted on these prototype structures, developing a database to quantify performance levels of DT-SCBRB glulam frames. The MaxISDRs of 0.5 %, 0.7 %, and 2.6 % were recommended for immediate occupancy (IO), life safety (LS), and collapse prevention (CP) limit states of DT-SCBRB glulam frames.

Retrofit of damaged reinforced concrete frame by autoclaved aerated concrete blocks infill wall: Experimental validation and strength estimation

This study introduces a novel approach for the global retrofitting of seismic performance in destructively damaged reinforced concrete (RC) frames through the application of autoclaved aerated concrete (AAC) blocks infill walls to enhance both structural strength and stiffness. Three full-scale RC frames are designed and fabricated, comprising an intact bare frame, a damaged frame strengthened by carbon fiber-reinforced polymer (CFRP), and a damaged frame retrofitted with the same CFRP and AAC blocks infill walls. To verify the cyclic behaviors and working principle of the retrofitted system, the two frames undergo a pre-damage scenario with a maximum inter-story drift ratio (MIDR) of 2.52%, and then both specimens are retrofitted. Afterward, a pseudo-static cyclic test is conducted on three specimens, with a MIDR of 3.36%. The test data is analyzed and discussed in terms of hysteretic responses, secant stiffness, displacement ductility, and energy dissipation capacity. The findings indicate a significant improvement in the lateral strength and stiffness of the seismic-damaged frame through the implementation of AAC blocks infill walls, demonstrating performance comparable to the intact RC frame. Also, the slight local crushing of AAC blocks and their interaction with mortar joints effectively dissipates a considerable amount of input energy, thereby reducing the energy dissipation demands on retrofitted structural components. Moreover, the theoretical deduction of the lateral strength of the retrofitted RC frames is presented. The errors between the predicted and test results fall within 5%, suggesting that the analytical outcomes can reasonably predict the lateral strength of the specimens.

Seismic behavior and design of concrete-filled steel tubular frame-RC core tube structures

In the design of frame-core tube structures, the method for adjusting the frame bearing capacity and stiffness to ensure the structure as a dual system is a critical issue. This study investigates the effects of frame shear distribution ratio, frame bearing capacity, and column pattern on the seismic performance of concrete-filled steel tubular frame to reinforced concrete core tube structures (CFRCTs). Time-history and seismic fragility analyses on eight representative models are performed and the distribution pattern of inter-story drift ratios, structural damage modes, and collapse safety margins are compared. The study results show that CFRCTs possess superior seismic performance (with a collapse margin ratio > 9.3) compared to the structures with reinforced concrete columns and the collapse margin ratio continuously increases from 9.3 to 11.2 with increasing frame stiffness. Enhancing the frame bearing capacity mitigates the frame damage, while improving slightly on structure’s collapse resistance (< 0.1 %). Without adjusting the frame for the second fortification line, damage to the column is not serious and the frame can still effectively withstand the increased shear force transmitted from the core tube during an extremely severe earthquake. The frame experiences more shear force and damage as the frame shear distribution ratio increases; while the core tube damage is effectively alleviated. Due to the redistribution of internal forces, the distribution pattern of inter-story drift ratios under the collapse state is markedly distinct from that under the elastic stage and severe earthquakes. Based on the analysis, design suggestions considering both collapse resistance and economic efficiency are proposed for CFRCTs.

Experimental investigation on seismic performance of a super high-rise mega frame-double core tube composite structure

Increasing population density and urbanization have intensified the need for high-rise buildings in recent years. The seismic resistance of high-rise buildings should be carefully concerned in seismic regions, especially for super high-rise buildings which are most vulnerable to long-period earthquakes. This paper introduced the model design of a 499 m super high-rise mega frame-double core tube composite structure and presented the shaking table test results of the 1/50 scaled structural model. This super high-rise building possesses many conducive merits to resist seismic hazard, including steel reinforced concrete members, high-strength concrete and double core tube. In the test, there were three groups of long-period earthquakes and four incremental seismic intensity levels considered. The test phenomena indicated that the coupling beams of exterior tube were the first line of defense to resist seismic actions. The existence of inner tube improved the shear resistance of this building and there was no observed shear damage on the walls. Based on the instrumented data, the vibration characteristics, acceleration, displacement and strain responses of the structure were reported. The seismic performance of this super high-rise building meets the requirements of design specifications and its collapse resistance capacity is physically proved under severe earthquakes. However, the whiplash effect of acceleration is serious on the roof due to the reduction of mass and constraint for the mega column end. Furthermore, the inter-story drifts and strain responses of trusses in the top region are significantly larger. For the seismic measurement, great attentions should be paid to the exterior coupling beams and structural members in the top region of this super high-rise building. The presented work provides well experimental confirmation and reference for super high-rise buildings with mega frame-double core tube composite system.

Mitigating inter-story drift concentration in seismic-resistant self-centering braced frames by using strong backup systems

Seismic-resistant self-centering concentrically braced frames (SC-CBFs) are susceptible to the concentration of inter-story drifts during earthquakes owing to the relatively low energy dissipation ability of braces. To address this limitation, this study proposed a novel solution by designing a strong backup (SB) system to mitigate inter-story deformation concentration in “weak” stories. The proposed SB system consisting of truss members can be attached to the existing SC-CBF through pin connections, forming a system, termed strong backup SC-CBF (SC-CBF-SB), to promote a more uniform distribution of inter-story drifts along the height of the frame and mitigate the weak story behavior. A six-story chevron-braced frame is adopted to investigate the seismic performance of SC-CBF and SC-CBF-SB. Finite element models of SC-CBF and SC-CBF-SB are built. The mechanical characteristics and dynamic responses of the SC-CBF-SB are examined. To comprehensively evaluate the performance of both SC-CBF and SC-CBF-SB, static pushover analyses and nonlinear time-history analyses are conducted. Additionally, incremental dynamic analysis (IDA) is performed to evaluate the responses (particularly drift concentration) of both frame types subjected to increasing seismic intensity levels. Numerical results show that the maximum value of the drift concentration factor (DCF) is around 1.3 and 1.8 for SC-CBF-SB and SC-CBF, respectively, indicating that SC-CBF-SB can effectively mitigate inter-story drift concentration of SC-CBF. Meanwhile, the proposed SB system has a minimal negative impact on the favorable SC ability of the frame.

Evaluate the Dynamic response of Buildings to Seismic Forces, Considering the Interaction between human Occupants and Structural vibrations

Damage to buildings and other structures may occur when dynamic loads, caused by earthquake vibrations, drive the ground and everything related to it to shake in a complicated way. Civil engineers are always thinking of new methods to deal with this inevitable problem. Humans put stress on a variety of buildings, including floors, footbridges, stadiums, and more. Modern material and manufacturing technology, together with human desire for aesthetics, have made it possible to build long span structures like bridges, stadiums, floors, etc. that are sleek, lightweight, and slim. To dampen a structure's dynamic reaction, engineers use devices called (TMDs), which consist of a mass and a spring, are tuned mass dampers. When it comes to managing the structural reactions to wind and harmonic excitations, Tuned Mass Damper (TMD) is the way to go. Specifically, the shear beam and 1D lumped-mass beams are the models under consideration. The main purpose of this piece is to demonstrate how methods that use records of ambient vibration may enhance and supplement seismic risk assessments of preexisting structures. To compare the structure's reaction with and without TMD, or tuned mass damper, is mounted on the building's exterior. Using a model calculated from outside vibrations and recorded within the structure, we were able to effectively compare the building's motion to a fake ground motion. It was also determined the inter-storey drift and the stiffness of each floor.

Assessment of structural performance, materials efficiency, and environmental impact of multi-story hybrid timber structures in high seismic zone

Advancements in wooden manufacture and the inherent sustainable merits of timber have stimulated studies on high-rise wooden structures and their structural performances. Considering the height restrictions of timber structures in Taiwan, two types of hybrid structure systems, reinforced concrete (RC) structure mixed with timber components, were proposed as substitution solutions to explore their feasibility and environmental impact in high seismic zones. A fifteen-story RC structure was adopted as the benchmark building, and building weight, material substitution efficiency, and embodied carbon were thus compared with the proposed hybrid timber structures after determining wind and seismic impacts. The results showed that structure system Type 1, which replaced original RC slabs and RC walls with timber, weighs only 61.3 % of the RC structure, reducing seismic forces by 38.7 % and base shear by 30.6 %, while inter-story drift ratio was smaller than that of RC structure; meanwhile, Type 2, which maintained the original RC service core and replaced timber structure for rest of the area, was only 44.5 % of the structural weight of RC structure, with a reduction of 36.4 % in seismic forces and 21.1 % in base shear. Furthermore, Type 1 featured reduced embodied carbon of 34.8 % and 35.4 % respectively using imported and domestically produced timber, while Type 2 features reductions of 47.4 % and 49.3 % respectively. The study indicated that the RC-timber hybrid structure system not only has significant structural performance in the face of the challenges of high seismic zones but also offers new solutions in terms of environmental sustainability.

Seismic Performance Prediction of RC, BRB and SDOF Structures Using Deep Learning and the Intensity Measure INp

The motivation for using artificial neural networks in this study stems from their computational efficiency and ability to model complex, high-level abstractions. Deep learning models were utilized to predict the structural responses of reinforced concrete (RC) buildings subjected to earthquakes. For this aim, the dataset for training and evaluation was derived from complex computational dynamic analyses, which involved scaling real ground motion records at different intensity levels (spectral acceleration Sa(T1) and the recently proposed INp). The results, specifically the maximum interstory drifts, were characterized for the output neurons in terms of their corresponding statistical parameters: mean, median, and standard deviation; while two input variables (fundamental period and earthquake intensity) were used in the neural networks to represent buildings and seismic risk. To validate deep learning as a robust tool for seismic predesign and rapid estimation, a prediction model was developed to assess the seismic performance of a complex RC building with buckling restrained braces (RC-BRBs). Additionally, other deep learning models were explored to predict ductility and hysteretic energy in nonlinear single degree of freedom (SDOF) systems. The findings demonstrated that increasing the number of hidden layers generally reduces prediction error, although an excessive number can lead to overfitting.

Ground motion parameters and damage correlation in plan irregular L-shape steel structure with BRB

Irregularly designed structures frequently experience greater damage compared to regular buildings as a result of elevated torsional reactions and stress concentration, as indicated by evaluations of damage carried out subsequent to past seismic events. The irregularities in the plan configuration provide significant issues for building seismic design. One example of an irregularity is the re-entrant corners found in L-shaped structures, which can lead to early collapse by causing stress concentration from abrupt changes in stiffness and torsional response amplification. More than ever, a thorough investigation into the relationship between the issue of ground motion parameters (GMPs) and Damage is required because of the complex way that L-shaped buildings respond to earthquakes. The current study examines the relationship between a large number of commonly used GMPs and the associated damage for three-, six-, nine-, and twelve-story 3D buildings—that is, low-, mid, and high-rise structures—with asymmetric L-shaped plan layouts. The system of lateral load resistance that was used was Buckling Restrained Brace Frames (BRBFs). To assess a building's seismic performance, 15 bidirectional earthquake ground motions were applied using Nonlinear Time History Analysis (NTHA) for incident angles of 0°, 45°, 135°, 225°, and 315°. The structural response is reported in terms of the average and maximum inter-story drift as well as the total Park-Ang damage index. The relationship between GMPs and structural damage was then investigated using Pearson's correlation coefficient. The results indicate that the highest link with damage measurements is found for 3- and 6-story structures when looking at the spectral acceleration at the fundamental period, Sa(T1). However, PGD and SMV exhibit a stronger correlation than other GMPs for structures with nine and twelve stories. Additionally, Classification and Regression Trees (CART) is a decision tree algorithm used for predictive modeling. In this study suggested using CART (Classification and Regression Trees) algorithms to estimate the link between GMPs and Damage Indices. The findings demonstrate the ability of CART algorithms to extract the rules and correlations governing earthquake damage.

Effect of connection modes on seismic responses of a diaphragm wall-subway station system subjected to mainshock-aftershock sequences

Most existing seismic behavior analyses of underground structures simply consider a single earthquake. Meanwhile, the diaphragm wall, as an enclosure structure, is regarded as a security reserve and is always ignored in current studies. Herein, the characteristics of a diaphragm wall-subway station system with different connection modes under earthquake sequences were investigated using numerical simulation. The damage degree of the structural component was calculated through quantitative analysis of the tensile damage picture. The seismic damage level of the station structure was evaluated to characterize the damage transition effect induced by the aftershock according to the inter-story drift angle. Moreover, an empirical model for predicting the inter-story drift angle with respect to different peak accelerations was proposed. The research results indicate that the effect of the connection mode between the sidewall and the diaphragm wall on the damage evolution and deformation behavior of the station structure is significant. Compared with that of the compound wall structure, the seismic damage to the sidewall of the composite wall structure is much less severe, but the slabs become more vulnerable and suffer more severe damage. The accumulative damage triggered by aftershocks aggravates the extent of structural damage and even leads to damage transition. The conclusions illustrated in this paper contribute to a better understanding of the seismic resistance design of diaphragm wall-subway station systems under earthquake sequences.

Comparative seismic analysis of frames with shape memory alloy slip friction dampers

This study investigated the seismic performance of 6-, 9-, and 12-story concentrically braced steel frames utilizing shape memory alloy slip friction dampers (SMASFDFs). For comparison purposes, identical frames equipped with self-centering braces (SCBFs) and buckling-restrained braces (BRBFs) were also designed and analyzed. The seismic performance of considered frames was evaluated through nonlinear static and nonlinear time history analysis (NLTHA) under three seismic hazard levels, i.e., frequently occurred earthquakes (FOE), design basis earthquakes (DBE), and maximum considered earthquakes (MCE). Incremental dynamic analysis (IDA) was conducted to examine the seismic responses, including peak interstory drift ratios (PID), peak floor accelerations (PFA), and residual interstory drift ratios (RID), of the designed frames under varying levels of seismic intensity. Fragility curves considering single and multiple seismic responses were obtained based on the IDA results. The results show that the SMASFDFs have comparable deformation control capacity as the BRBFs while exhibiting zero RID and more uniform deformation distribution over the building height. Moreover, in most circumstances, the joint failure probability is lowest for the SMASFDFs when considering multiple seismic responses. From a seismic design perspective, current results suggest that the SMASFDFs can be designed with the same strength reduction factor (R) if the PID is especially concerned.

Comprehensive evaluation of seismic fragility in base isolated buildings enhanced with supplemental dampers considering pounding phenomenon

Base isolation is a proven technology effective in minimizing earthquake-induced damage to both the structural and non-structural elements (especially freestanding contents) of buildings. Nevertheless, it has been shown that allowing the flexible isolation layer to endure substantial demand displacements might subject the isolated structure to failure. This vulnerability arises from potential superstructure yielding due to increased deformations and reduced stiffness, such as those occurring through pounding against a moat wall during intense earthquakes. One alternative to controlling these large deformations is to use supplementary dampers at the isolation plane of the building, creating a hybrid base isolation system (HIS), which adds damping to the isolation system. In this research, the seismic performance of base isolated structures with lead-rubber bearing (LRB) are studied in conjunction with linear viscous dampers (LVD). Due to this aim, a base-isolated steel frame with 2 story X-type braces and a surrounding moat wall is modeled with two various configurations: LRB, and LRB with LVD. Fragility curves are developed for an ensemble of near-field (NF) pulse-like ground motions and for the maximum inter-story drift ratio (MIDR) as an engineering demand parameter (EDP). The incremental dynamic analysis (IDA) is conducted to calculate the damage probability of the structure by assuming different threshold values for damage states. It was found that adding viscous dampers to the isolation system balanced the behavior of the structure under near field pulse-type records; resulting in reduced isolation displacement while its adverse effects are insignificant and can be ignored. Moreover, the median spectral acceleration, namely the spectral acceleration associated to a probability of exceedance (POE) equal to 50 %, at the specific limit state, in the hybrid base isolation system is higher compared to the conventional one.