Inter-story Drift Ratio Research Articles

Seismic performance of flanged RC walls under biaxial cyclic loading

Flanged RC walls are frequently utilized to provide strength and stiffness in two horizontal directions, yet the coupling of the bidirectional horizontal components of ground motion are bound to have large impact on the seismic response of flanged walls. However, few data exist characterizing the performance of flanged walls subjected to biaxial cyclic loading. Aiming to provide an insight into the influence of the biaxial coupling effect on the seismic behavior of flanged RC walls, three T-shaped and two L-shaped walls were tested under uniaxial and biaxial loading. Subsequently, a finite element model was employed for parametric studies and generating numerical data for a detailed comparison of the seismic performance of the flanged walls under uniaxial and biaxial loading. The results showed that the coupling of alternating loadings in orthogonal directions intensified the cracking and damage of flanged walls, resulting in the reduction of the bearing and deformation capacities, an increase in the proportion of flexural deformation in the plastic hinge area, acceleration of the energy dissipation process, and a more significant shear lag effect as opposed to uniaxial loading. Furthermore, the damage aggravation as well as reduction in seismic performance of L-shaped wall due to the biaxial coupling effect were more obvious than that of T-shaped wall. Based on the test and numerical results, the reduction of the ultimate inter-story drift ratio caused by biaxial loading was quantified through statistical analysis and the derived reduction factors can provide reference for the performance-based seismic design and anti-collapse design of flanged RC walls under multi-dimensional seismic action.

Innovative inner sleeve composite bolted connections for modular steel constructions: Experimental and numerical studies

The application scenarios of modular steel constructions (MSCs) are becoming more and more extensive due to their exceptional advantages: minimum on-site work, and higher construction speed and quality. Inter-module connections are the critical components, which can significantly affect the integrity and seismic behavior of MSCs. This study proposed an innovative inner sleeve composite bolted connection which combines blind bolts, high-strength bolts and inner sleeve to improve the constructability and seismic behavior. Experimental tests on four full-scale cruciform connections composed of hollow structural steel (HSS) columns and H-section steel beams with different configurations were carried out under cyclic load. The failure modes, moment-rotation relations, initial rotational stiffness, ductility and energy dissipation were analyzed. GB 50011–2010 was used to evaluate the seismic performance and verify the applicability for the seismic design of the proposed connection, in which the lower limit of elastic inter-story drift ratio [θe] is 0.004 rad (or 1/250) and that of elasto-plastic inter-story drift ratio [θp] is 0.02 rad (or 1/50). The yield inter-story drift ratio, [θy] = 4.00–6.75[θe], and the ultimate inter-story drift ratio, [θu] = 1.00–2.00[θp] for the test specimens under cycle load, demonstrating the satisfactory deformation capacity and ductility. Furthermore, EC3 Part 1–8 was adopted to evaluate the stiffness characteristic of the proposed connection, indicating that the proposed connection can be classified as a “semi-rigid” and partial strength connection. Finally, refined numerical models calibrated against the experimental results were established and parametric evaluation was conducted based on the numerical models. The results demonstrate that the effect of the thickness of the inner sleeve and column in the panel zone and the diameter of the blind bolt and vertical high-strength bolt is insignificant. The presented research will provide useful references for further application and popularization of MSCs.

The Seismic Performance and Global Collapse Resistance Capacity of Infilled Reinforced Concrete Frames Considering the Axial–Shear–Bending Interaction of Columns

This paper presents a mechanism and method for simulating the axial–shear–bending interaction of a reinforced concrete (RC) column. The three-dimensional model of a multi-story infilled RC frame was modeled using the OpenSees software. Static pushover and nonlinear dynamic analyses under fortification and rare earthquakes were conducted using the model. Finally, based on the incremental dynamic analyses of 22 suites of ground-motion records, the global collapse resistance capacity of the infilled RC frame was evaluated using the evaluation method of a normal distribution. The analytical results show that the axial–shear–bending interaction is a key factor that affects the seismic response of infilled RC frames. Under the fortification earthquake condition, no obvious damage to physical structures was evident; the influence was relatively minor. However, under the condition of a rare earthquake, severe damage to physical structures was evident, resulting in the underestimation of the lateral inter-story drift ratio, while the degradation rates of the load capacity and global collapse resistance capacities for the infilled concrete frames were highly overestimated when the axial–shear–bending interaction was not considered.

Damage-control design and hybrid tests of a full-scale two-story buckling-restrained braced steel moment frame with sliding gusset connections

Buckling-restrained braces (BRBs) are widely adopted as supplementary energy dissipation devices in steel moment frames (MFs) in Asia to improve the energy dissipation capacity of the whole system. Such systems are referred to as buckling-restrained braced moment frames (BRB-MFs). Nevertheless, adopting BRBs does not guarantee desirable seismic performance of the whole system, as frame action may cause premature fracture or buckling of BRB corner gusset connections, and such frame-to-gusset interaction may limit the ductility of such system. In our previous studies, a sliding corner gusset connection was proposed and proved to be able to substantially reduce the detrimental frame action at the connection level. In this paper, study was extended to (1) damage-control design of BRB-MFs with such connections in pursuit of enhanced system ductility, and (2) experimental evaluation on seismic behavior of BRB-MFs with such connections at the system level. The damage-control design method was first presented and a full-scale two-story BRB-MF designed by such procedure was experimentally studied under four levels of earthquake loading through hybrid tests, followed by a pseudo-static test to examine its failure mode. Test results showed that the sliding gusset connections effectively released the frame action at the system level. By adopting the damage-control design procedure, the test BRB-MF exhibited excellent seismic performance up to an inter-story drift ratio of ± 3 %, and plastic hinges of the MFs developed in the controlled positions without fracture or buckling under four levels of earthquake loading. With the improved ductility of MFs, BRBs achieved their full potential as energy dissipation devices.

Study on numerical seismic performance evaluation of 3D building frame with smart self-centering BRBs system

Structures are generally designed to withstand the applied loads safely. However, in order to secure the stability of structures from earthquakes, which are unpredictable natural disasters, seismic damage reduction technology is required, and various technologies are being developed so far. Recently, to resist seismic loads, new materials are used to reinforce structural members, or technologies to control vibration by applying seismic devices are being developed. In particular, Shape Memory Alloy (SMA), also known as a smart alloy, has a unique re-centering capacity that exhibits a flag-shaped hysteresis curve, so when applied in a structural system, it can provide safer structural performance with higher serviceability. In this study, to prove the structural stability of the SMA buckling restrained brace (BRB) system to which the seismic isolation is applied, a study was conducted to evaluate the seismic performance according to the structural material, type, and device. Response of SMA BRB and base isolation system has been calibrated by following quasi-static and dynamic loading test and substantially matches empirical results. A prototype steel frame has been designed by following standard code which has a single-story basement assumed to be surround by well graded sandy soil. In addition, two different column system has been considered namely as, Hollow Steel Section (HSS) and Concrete Filled Steel Tubes (CFST). For the nonlinear dynamic analysis, two sets of 11 bidirectional artificial earthquakes were considered, and the interstory drift ratio (IDR) and residual interstory drift ratio (RIDR) were considered as main performance evaluation parameters. In moderate ground motion, the performance of the SMA BRB was found to be higher compared to the steel BRB and base isolation system due to its superior self-centering capacity. However, in strong ground motions, periodic damage degrades the performance of the SMA BRB, which was found to be nearly identical to the steel BRB, but still superior to the base isolation system. This performance evaluation study will help to understand design aspects of seismic protection systems for similar types of building frames.

Enhancing the Seismic Resilience of Steel Moment Resisting Frame with a New Precast Self-Centering Rocking Shear Wall System

In this paper, a new precast self-centering rocking shear wall system (PSCRSW) mainly composed of precast reinforced concrete (RC) wall, V-shaped steel brace and pre-pressed disc spring friction damper (PDSFD) are proposed to enhance the seismic resilience of steel moment resisting frame (SMRF). The mechanical behavior of PDSFD was investigated and simulated. The skeleton model of PSCRSW was theoretically derived and numerically validated, and the hysteretic performance under different design parameters was discussed and compared with that of the conventional RC shear wall. Based on the analyses, design principles and suggestions for PSCRSW were given. Then, an efficient seismic resilient design method for enhancement of SMRF was proposed, which considers performance objectives of multiple seismic hazard levels and has less design iteration. A typical SMRF was adopted as the prototype to be enhanced by the presented PSCRSW and design method. Reliable numerical models for the prototype and the enhanced SMRF were established, and nonlinear dynamic analyses were performed to assess the effectiveness of enhancing strategy. The results show that PSCRSW can realize approximate yielding behavior, displacement capacity and lateral strength to the conventional shear wall and can significantly lower the residual drift and wall damage. During the design, the ratio of preload to friction force for PSCRSW was suggested to be 1.5~2.0, and the bearing capacity for the wall was suggested to be amplified 1.2 times. Thereby, desirable bearing and self-centering performances can be guaranteed. The presented design method is capable of achieving the inter-story drift ratio targets and the expected roof drift ratios simultaneously, and the seismic resilience of the chosen SMRF was significantly improved by a large margin of reduction in residual inter-story drift and frame member damages.

Seismic responses of infill walls with sliding joints and openings in semi-rigid steel frame

Forming door and window openings in partition infill walls is a frequent activity in engineering practices, while the complexity of the mechanical behavior of such infill systems with openings due to the destructive damage to the infill walls has not been thoroughly considered. To protect the vulnerable door and window openings and mitigate the detrimental multiple diagonal struts effect of infill around the opening, the paper presents two novel precast infill walls with sliding joints and door and window openings for semi-rigid steel frames. The quasi-static cyclic tests are performed on three specimens: a reference bare steel frame and two infilled steel frames with door or window opening. Test results confirm that the developed infill systems effectively prevent potential cracking or deformation of the openings and release the adverse multiple diagonal struts effect of infill with a door or window opening. Because of the working mechanism of the developed infills, the two infilled steel frames behave with similar seismic responses to the bare steel frame, while the novel infills are significantly undamaged and no detectable opening deformation is observed even at the inter-story drift ratio of 3.33%. Furthermore, both experimental and numerical responses of the developed innovative infill systems confirm the effectiveness of the infill systems without any additional fixtures to protect the fragile door and window openings.

Predicting seismic response of SMRFs founded on different soil types using machine learning techniques

Predicting the Maximum Interstory Drift Ratio (M-IDR) of Steel Moment-Resisting Frames (SMRFs) is a useful tool for designers to approximately evaluate the vulnerability of SMRFs. This study aims to explore supervised Machine Learning (ML) algorithms to build a surrogate prediction model for SMRFs to reduce the need for complex modeling. For this purpose, twenty well-known ML algorithms implemented in Python software are trained based on the dataset achieved from Incremental Dynamic Analyses (IDAs) performed on the 2-Story, 3-Story, 4-Story, 5-Story, 6-Story, 7-Story, 8-Story, and 9-Story SMRFs modeled in Opensees. Then, important features of weight, fundamental period of structure (T1), the RSN number of record subsets, the direction of the record subsets, soil types, and Sa(T1) of analysis, which affect the results of predictions, were selected by trial and error. Having these important features, data-driven techniques developed in Python software were compared for predicting the M-IDR of SMRFs as target. Results showed that ML algorithms of GPReg, PLSReg, SReg, LReg, GReg, MLPReg, SVM, and LSVR had lower values of coefficient of determination (R2 lower than 0.5) in both train and test datasets. In addition, XGBoost, BReg, HistGBR, and ERTReg algorithms achieved higher values of R2 (i.e. upper than 0.95 in the 5-Story SMRF) with low Mean Squared Error (MSE) for prediction of M-IDR. Therefore, using these algorithms mitigates the need for computationally expensive, time-consuming, and complex analysis, while preliminary prediction of M-IDR can be considered a low computational and efficient tool for seismic vulnerability assessment.

Performance of an RC building under seismic and tsunami actions in sequence via nonlinear dynamic analysis including soil-structure interaction

This research presents a methodology to study the behavior of buildings subjected to seismic and tsunami loading in sequence, considering soil structure interaction effects through a complete dynamic analysis. The case-study building is an RC frame, which is assumed to be located in a coastal city in Chile, and built on sandy soil. A 3D Soil-Structure Interaction (SSI) model, including the non-linear behavior of both the structure and the soil using finite element method (FEM) was presented. Synthetic seismic ground motion records and tsunami inundation time histories were generated, consistent with the same earthquake source. Building performance was first assessed considering the SSI model for each hazard separately and compared to a Fixed Base (FB) model. Then, the SSI model was subjected to seismic and tsunami loading in sequence. Engineering Demand Parameters (EDPs) of roof displacement, interstory drift ratio (IDR) and reinforcement strain in beams and columns were analyzed. These EDPs presented a larger response to the tsunami when the response to the previous earthquake was larger. Finally, two vertical evacuation building scenarios were studied: the location of the refugees and the effect of an aftershock occurring simultaneously with the tsunami inundation. Results showed that the location of the refugees did not generate significant differences in the building response, and the aftershock increased the response only when it coincided with the maximum tsunami force.

Friction Tuned Mass Dampers in Seismic-Excited High-Rise Buildings with SSI Effects: A Reliability Assessment

The probabilistic performance of the seismic-excited structures supplemented with passive control devices has recently received attention. Friction tuned mass damper (FTMD) devise as a novel passive control device is inspired by the idea of the combination of the friction mechanism with the traditional tuned mass damper (TMD) device. Although the application of the FTMD device has recently been considered for seismic control of structures, to the best of the authors’ knowledge, a probabilistic reliability evaluation of the high-rise building equipped with FTMD under near-field earthquakes considering soil-structure interaction (SSI) effects has not yet been addressed in the literature. In the presence of uncertainties considered for the structural model, FTMD model, foundation and soil model, and stochastic near-fault ground motion model, the reliability analyses are carried out on a benchmark 40-story building equipped with FTMD considering SSI effects to estimate the failure probabilities of both structures with and without FTMD. Three soil types, three earthquake magnitudes, three fault distances, and three seismic performance levels which include 162 reliability analyses are considered for the extension of the study. Considering different near-fault earthquake model parameters, a total average reduction of 51.13%, 49.42%, and 17.50% is given for the maximum inter-story drift ratio response of the structure equipped with FTMD than the uncontrolled ones. It is found that ignoring the uncertainties may result in an inaccurate estimation of the seismic responses of the tall buildings especially those built on soft soil near faults. The results show that the FTMD passive device is not able to satisfy the requirements of the seismic codes at the performance level of immediate occupancy, especially in high earthquake magnitudes and structures built near the fault. However, for the seismic performance levels of life safety and collapse prevention, the FTMD reduces failure probabilities of the structures for most conditions of the earthquake magnitudes and fault distances. The efficiency of the FTMD in the reduction of failure probability is often declined by increasing the softness of soils, especially for severe earthquakes closer to the fault.

Multi-Objective Optimization of Viscous Damper Placement for Building Structures Subjected to Ground Motion

Viscous dampers mitigate the interstory drift ratios (IDRs) and peak floor accelerations (PFAs) of buildings subjected to earthquakes. This leads to a multi-objective optimization problem (MOOP) for a viscous damper placement along the building height to minimize IDRs and PFAs simultaneously. This paper proposes innovative methods to address the MOOP and compares those proposed methods to non-dominated sorting algorithm II (NSGA-II) through case studies. Subsequently, the meaning of solutions on the Pareto optimal front in future earthquake events is investigated. The case studies apply each method to a two-dimensional ten-story shear building and adopt four measures to evaluate the performance of searched solutions in multiple aspects. The results show that the proposed methods, by executing fewer number of time history analyses and with convergence comparable to that of NSGA-II, successfully offer improvement against NSGA-II in the aspect of productivity and diversity. As for understanding solutions on the Pareto front in future earthquake events, the knee point solution’s design, which proposed methods can arrive at or approach, successfully reduces both peaks IDR and PFA under 20 ground motions.

Interstory drift based scaling of bi‐directional ground motions

AbstractThe interstory drift‐based scaling procedure (IDS) developed recently by the authors for plane frames under single component horizontal ground motions, has been extended to three‐dimensional structures possessing torsional coupling under bi‐axial ground motions which are represented by their geometric mean spectrum. The ground motion‐scaling factor is defined as the ratio of average interstory drift along building height under target spectrum versus that under the associated ground motion spectrum. Hence, scaling is conditioned on structural response, which is in turn a function of seismic intensity. IDS for 3D systems is applied to 20‐story and 3‐story concrete space frames with mass and stiffness eccentricity, respectively. Accuracy and efficiency of the IDS procedure is assessed under a set of near‐fault strong motion pairs from large magnitude events. The results revealed that the proposed procedure is accurate and noticeably more efficient as compared to conventional procedures suggested in seismic codes and in literature. Further, the intensity measure employed in the IDS procedure is proved as a good predictor of fundamental demand measures (maximum interstory drift ratio and maximum plastic rotations) obtained from nonlinear dynamic analyses under individual ground motion pairs. Hence, employing the intensity measure of IDS for ground motion scaling in intensity‐based evaluation of structures is proposed for reliable estimation of structural performance under code‐prescribed seismic hazard.

Seismic and damping performance of frame-distributed rocking tubes-core tube structure

In order to improve the economical deficiency of the traditional frame-core tube (FCT) structure due to the large tube area proportion, a new high-rise structure of the frame-distributed tubes-core tube (FDCT) is proposed based on the design concept of the distributed tube. Combining the distributed tubes with the rocking system, the frame-distributed rocking tubes-core tube (FDRCT) is further proposed, which aims to solve the problem of insufficient seismic capacity of the FDCT structure due to the decrease of structural stiffness. Simplified dynamic models and equations of FDCT structure and FDRCT structure are established. Frequency domain dynamic analysis and ground motion random analysis are performed based on dynamics principles, which prove that the FDRCT structure can reduce the structural dynamic response. The elastic and elastoplastic time history analysis of the FCT structure, FDCT structure and FDRCT structure are carried out by finite element simulation. FDRCT structure can make the structure deformation uniform and reduce the acceleration response, but the top displacement increases. Compared with the beam ends hinged in the FDRCT structure, the inter-story drift ratio of the structure with the beam ends fixed decreases but the acceleration increases. Increasing the mass of the distributed rocking tubes can effectively improve the seismic and damping capacity of the FDRCT structure. According to the shaking table test and the economic analysis, it is evident that the FDRCT structure can not only improve the economy of the structure, but also have better seismic and damping performance.

Experimental and design strategy of precast exterior wall panels with damage-control function for steel buildings

This paper proposes an innovative precast exterior wall panel with the damage-control function (denoted as DCPW) for steel building frames. The DCPW consists of a wall panel and four connectors between the steel beam and the wall panel. Vertically and horizontally slotted bolt holes are introduced in the connections between the wall panel and beams for controlling the deformability and the damage of the wall. The desired nonlinear behavior of the DCPW was introduced. A group of five specimens was designed and tested under cyclic loading to investigate the performance of the proposed DCPW. The preloads of the bolt and the geometries of the bolt hole were set as the test parameters. The lateral force-resistant capacity (i.e., stiffness and strength), energy dissipation, deformability, and damage states of the tested specimens were systematically analyzed. The test results indicate that the proposed DCPW can achieve the desired nonlinear behavior where the DCPW can be damage-free before the bearing action in bolt connections and damaged to show larger strength and energy-dissipation capacity after that. The tested DCPW specimen showed sufficient initial stiffness that is up to 16 kN/mm and excellent deformability that is up to 4% inters-tory drift ratio where the strength reduces to 85% of the ultimate strength. It was also observed that larger deformability can be achieved by reducing the preload of the bolt and increasing the geometries of the bolt hole. Based on the test results and theory analysis, simplified models were provided to calculate the stiffness and strength of the proposed DCPW. The analysis results confirm the acceptable accuracy of the provided simplified model for capturing the test results.

Evaluation of seismic response of coupled wall structure with self-centering and viscous damping composite coupling beams

In order to reduce the residual displacement and floor acceleration of coupled wall structures, a novel self-centering and viscous damping composite coupling beam is proposed. The proposed coupling beam consists of the elastic beam segments and the fuse part, which incorporates self-centering friction dampers and viscous dampers. The self-centering friction damper can provide strength and stiffness for the proposed coupling beam and reduce the residual displacement of the coupled wall structure. The viscous damper can add supplemental damping to the system, and this can control the peak lateral displacement demands and floor accelerations of the structure. Moreover, the proposed coupling beam can eliminate the beam elongation effect of the self-centering coupling beam with a rocking behavior. Design methodology and nonlinear numerical model of the proposed coupling beam are developed. The seismic behaviors of the coupled wall structure with the self-centering and viscous damping composite coupling beams (CW-SCVCCB) are assessed and compared with the structure with reinforced concrete coupling beams (CW-RCCB), the structure with steel coupling beams (CW-SCB) and the structure with self-centering coupling beams (CW-SCCB). Analysis results showed that the supplemental viscous damping can effectively reduce the peak interstory drift ratio and floor accelerations of the structure. The residual displacement of the novel coupled wall system is larger than that of the CW-SCCB, however, it is significantly reduced compared with the CW-SCB and the CW-RCCB.

A Framework to Assess Seismic Resilience of Self-Centering Steel Frame Buildings

Resilience can be treated as an integrated measure to assess the seismic performance of buildings. Available methods to assess the seismic performance of self-centering structures mainly consider inter-story drift ratios, peak floor accelerations, and energy dissipative capacities, however, their seismic resilience is poorly understood. This paper proposes a framework to estimate the seismic resilience of self-centering energy dissipative braced steel frame office buildings. In this context, a new damage ratio assessment model is presented to assess functionality. Unlike the traditional method that only considers the economic loss or repair time in the functionality assessment, the proposed model accounts for the contribution of four performance measures such as downtime. To estimate the repair cost, repair time, casualties, and unsafe placarding, the FEMA P58 methodology is used. Based on the proposed model, the new damage ratios and recovery times of the self-centering structure are estimated. Obtained damage ratios are combined with fragility analysis to calculate the functionality loss. After considering an appropriate recovery model, seismic resilience is assessed. For comparison, the traditional method (i.e. HAZUS) is also used to assess seismic resilience. The whole framework is applied to a three-story self-centering energy dissipative braced steel frame, and the results show that the traditional method often underestimates the seismic resilience, and the proposed method may be more suitable for predicting the seismic resilience of self-centering energy dissipative braced steel frame office building. Sensitivity analysis is performed to identify uncertain parameters to which seismic resilience is most sensitive, and the result indicates that the control time and damage ratio at the extensive damage state have a major influence on seismic resilience. The framework can be modified and extended to assess the seismic resilience of ordinary building structures and other complex structural systems such as isolated structures.

Cyclic loading tests of a resilient hinged self-centering RC wall

To reduce the residual drift of the reinforced concrete shear wall (RCSW), this paper proposes a resilient hinged self-centering shear wall (RHSCSW) in which two tension–compression-symmetrical disc spring devices (TCSDSDs) and a restraint plate form a resilient bottom that prevents plastic deformation on the wallboard. Cyclic loading tests are conducted on a TCSDSD specimen, an RCSW specimen, and two RHSCSW specimens to investigate their hysteretic responses. The experimental results indicate that the TCSDSD exhibits a symmetrical flag-shaped hysteretic behavior, and its macro-mechanical properties can be described by eight stiffness variables and four force variables. Benefiting from the self-centering characteristic of the TCSDSD, the maximum residual inter-story drift ratio of the RHSCSW is only 0.37% with a maximum inter-story drift ratio of 4%, while that of the RCSW reaches 0.94% with an inter-story drift ratio of only 2%. Moreover, the total energy dissipation of the RHSCSW is found to be 25.4% higher than that of the RCSW. The equivalent viscous damping ratio of the RHSCSW is almost constant because the axial displacements of the TCSDSDs are almost linear with the lateral drift of the RHSCSW.

Shake table tests of a corrugated steel sheathed cold-formed steel structure

The corrugated steel sheathed cold-formed steel (CFS) shear wall is an innovative lateral force-resistant system with excellent potential for development. Many research has been conducted on the seismic behavior of this innovative shear wall system. However, dynamic properties as well as the failure mechanism of the CFS structures with corrugated steel sheathing are still unclear. This study aimed to increase knowledge of the seismic performance of CFS structures through the shaking table test, of which the seismic force resisting system was provided by corrugated steel sheathed shear walls. Importantly, this test also took into account the extremely rare precautionary intensity. The main results indicated that damage of CFS structure began to occur in the walls and floors under rare earthquakes and increased further with the seismic intensity. The final damage primarily occurred through the failure of connections and inner panels under extremely rare precautionary intensity. The degree of variation in the dynamic properties of the structure increased further as the damage accumulated. In particular, the damping ratio of the structure in the non-linear phase ranged from 5% to 7.5%. It was unreasonable to assume that the trend of the acceleration amplification factor with structural height was determined as a linear relationship. The peak inter-story drift ratio of the corrugated steel sheathing CFS structure could meet the multi-level seismic precaution requirements of the code. Finally, the seismic performance parameters of the CFS structure were evaluated by numerical simulations. This research will provide a reference for the seismic design of CFS structures under extremely rare conditions.

Seismic performance and design of the damped-outrigger system incorporating buckling-restrained brace for buildings with various heights

The keen purpose of this study is to investigate the seismic performance of buildings equipped with damped-outrigger system using the buckling-restrained brace (BRB) system (BRB-outrigger) and to propose the optimal design recommendation for buildings with a different height. The numerical models with building heights of 72, 144, 216 and 288 m, each contains two layers of BRB-outrigger and a 40 m by 40 m structural plan are analyzed using response spectral analysis (RSA) and nonlinear response history analysis (NLRHA) procedures. To get more closer to the actual reality, the member-by-member benchmark models are designed based on the seismic code requirement. In the response spectral analysis procedure, the equivalent damping ratio is computed in order to include the BRB’s inelastic response. For the main purpose of parametric study, a simplified model which will be using a Timoshenko beamcolumn element in order to capture shear-type to flexural-type lateral deformation for a lower to higher raising buildings are proposed. The dimensionless parameters that actually describe the relationships between the core structure stiffness, outrigger flexural stiffness, the axial stiffness of BRB and perimeter column in the parameter study are considered based on practical design and allowable structural sections. The optimization targets include the maximum roof drift, inter-story drift ratio, core structure base shear, core structure overturning moment and the BRB energy dissipation performance. Based on the analyzed result, the ranges of optimal design parameters vary in the different optimization targets and building heights. This study concludes with a design recommendation for building equipped with BRB-outrigger system with different building heights.

Evaluating maximum inter-story drift ratios of building structures using time-varying models and Bayesian filters

This paper presents a method for evaluating the maximum inter-story drift ratios (IDR) of building structures using a time-varying model and Bayesian filters. During earthquakes, parameters of the time-varying model walked randomly according to Gaussian distributions to adapt to time-varying stiffness and time-varying damping of real building structures, and then the time-varying model and Bayesian filters were combined in the state space to estimate the maximum IDRs. Three Bayesian filters were investigated in this study: the unscented Kalman filter (UKF), second-order extended Kalman filter (sEKF), and particle filter (PF). The performance of the proposed estimation method, including accuracy, robustness, computational efficiency and uncertainty, was studied by using a numerical four-story shear model and three-story steel frame shaking table test. In addition, the benefits of using the time-varying model and the Bayesian filters were revealed by comparing estimated results from the time-varying model-based and time-invariant model-based estimation methods with calculated and measured results.