Seismic Resistant System Research Articles

Seismic improvement of structures using hybrid self-centring dampers and rocking core

Extensive research on seismic-resistant systems aims to lower earthquake repair costs and downtime. This article presents a novel low-damage self-centring system that aims to improve the seismic resilience of buildings by enabling controlled rocking motion while reducing the risk of overturning. Significantly, the rotational movement can be entirely restored. This system combines a rocking core with damping devices, including disc springs and peripheral slit dampers. In this hybrid system, two damping devices are mounted to both first-floor columns of the rocking bays and the rigid movement of the rocking core triggers the dampers. Firstly, a comparative investigation was conducted to assess the efficacy of the endorsed hybrid system. The cyclic pushover results showed that the hybrid system is superior to other typical bracing systems in energy dissipation, with a five times higher margin. In addition, by employing the suggested system, the frame's drift ratio profile under nonlinear time history analysis (NTH) remained consistent throughout the structure, indicating its ability to withstand the soft storey mechanism. Secondly, a comprehensive assessment was conducted on the proposed system's collapse using incremental dynamic analysis (IDA) took into account various seismic intensities and engineering demand parameters for buildings with different bay lengths and included low, medium, and high-rise structures. The system's flag-shaped behavior and self-centring capability were confirmed by the average residual drift ratio of approximately 0.03% (almost zero) for all examined structures. Also, the collapse performance of the system exhibited a safety margin against collapse, with an average of 1.9 across all buildings and seismic intensities.

Self-Centering Precast Unit as Energy Dissipation Members in Precast Segmental Bridge Columns

This research aims to present a new generation of seismic-resisting systems designed for precast reinforced concrete (RC) bridge piers in modern sustainable cities to withstand moderate to high seismic activity. The proposed system consists of two self-centering (SC) systems operating in parallel to bring together all features of the required resiliency during a seismic action. The first/main system is a hollow core precast segmental bridge column, and the second is composed of an SC precast unit and energy dissipation (ED) steel reinforcements positioned in the main pier segment’s hollow core. To study the performance of the proposed system, a finite element model was first developed to capture the behavior of experimentally tested precast bridge columns. After validation, the created model was systematically studied to investigate the performance of the entire proposed system under cyclic loading. The effects of three parameters related to the ED system were investigated, including the reinforcement ratio, the unbonded length of ED bars, and the SC post-tensioned force ratio. Furthermore, the impact of FRP wrapping on the lower part of the core column of the ED system was also investigated. An analytical model predicting the characteristic points of the lateral response of the proposed system based on the superposition concept is also proposed. The FE results showed that the entire proposed system is a new design-based resilient system with the ability to dissipate energy without compromising the SC capacity of the main resisting system. Compared to the typical precast hollow core segmental column, a 6% reinforcement ratio of the ED unit can cause a 60% increase in lateral resistance and a 220% increase in the ED capacity. The analytical model can successfully be applied in the design of the proposed system to provide customized ED capabilities and controlled lateral resistance.

Multi‐level enhancement of structural behavior of bracing systems with coupling beams at floor level

SummaryDespite good rigidity, braced frames have weak nonlinear behavior and inadequate distribution of ductility in stories, which cause significant structural damage. In this research, a seismic resistant system called coupled concentrically braced frame (CCBF) is developed to enhance the performance of braced frames by coupling them with a beam. In this case, the coupling beams are the primary source for ductility of the system, and after their yielding in more severe earthquakes, the structure continues to benefit from the ductility of the braces as the secondary source; therefore, the system has two‐level behavior caused by different probable seismic excitations. In this case, in addition to maintaining the stiffness of the two concentrically braced frames, the coupling beams resist against the movement of the braced frames, and as a result, the stiffness of the system is increased. Therefore, lighter elements can be used to resist lateral loads. Linear and nonlinear analyses of CCBF, and its comparison with other braced frames, indicate that participation of the coupling beams provides an adequate stiffness and ductility. These frames have more stable nonlinear behavior than conventional ones and continue their nonlinear behavior even after fracture of coupling beams in severe earthquakes.

Performance of short links with flush and extended end plate connections using FEM analysis

AbstractEccentrically braced frames are commonly used as a seismic resistant system, due to the good balance of stiffness and ductility. Bolted links have been proposed in the past to allow replacing the damaged dissipative components following a strong earthquake. The goal of this research work is to investigate the influence of the connection type on the performance of bolted links using the Finite Element Analysis. Numerical models of links are first calibrated using past experimental tests. Modelling criteria adopted to replicate the experimental behaviour of the links highlighted in the tests are reported. The achieved results obtained regarding a flush end plate bolted link and an extended end plate bolted link with different lengths are then used as benchmark to assess the influence of the link length and type of connections adopted on the response of the links. The Finite Element Method is used to investigate alternative solutions to the tested ones. Finally, the investigated options are compared to determine the advantages and disadvantages of each solution.

Effect of brace failure as capacity-based design component on the EBF collapse safety

Eccentrically braced frame (EBF) is considered a suitable seismic resisting system in terms of its high ductility, and stiffness simultaneously. In this frame, nonlinear behavior and energy dissipation are limited to link beam, and other members (capacity-designed members) are designed in proportion to maximum link shear force. Despite the significance of capacity-designed members, their reliability evaluation and the effect of their failure on the overall behavior of EBF have not been studied in prior research. The aim of this paper is to evaluate the effect of brace failure on the probability of collapse by considering system overstrength, varied ratios of the capacity to demand factors (ϕ/γ) in brace design, and seismic hazard curve. To achieve this aim, Incremental Dynamic Analysis (IDA) was used to study nonlinear structural models of EBF, evaluate the force demands on the braces, and the effects of brace failure on the system collapse. The reliability analysis was performed by integrating the viewpoint of LRDF component design with the FEMA P695 system reliability methodology. The results indicate that the probability of total collapse increases significantly at low spectral acceleration due to brace failure. Additionally, the appropriate value of ϕ/γ in brace design can be calculated for different seismic areas and system overstrength to ensure an acceptable margin of collapse safety.

Analysis of the behavior of reinforced concrete buildings with and without non-buckling braces under the effect of earthquake loads

The moment frame is one of the most widely used seismic resistant systems in the world, due to its high formability and flexibility, this system causes a lot of displacement in the structure and force exceeding the capacity of the structural components. The bracing system is a suitable method to control the lateral displacement of the structure and the seismic improvement of the bending frame. The new type of bracing system that is used in the design of new systems and the improvement of old structures is non-buckling bracing, and in this research, their effect on the performance of 4, 7, and 10-story concrete moment frames under the Northridge, San Salvador, and Tabas earthquake has been investigated. The research method in this research is analytical-applied, which the results of this study showed; In the 4-story structure, the amount of wasted energy under the 3 considered earthquakes is equal to 0%, 0%, and 1% without buckling braces and 39%, 48% and 50% in the case with non-buckling braces and in the 7- story structure, the amount of energy consumed under the mentioned 3 earthquakes is equal to 0%, 0% and 0% without buckling braces and 40%, 45% and 51% in the case with non-buckling braces and also in the 10- story structure, the amount of energy consumed under the above 3 earthquakes is equal to 1%, 0% and 11% without buckling braces and 35%, 42% and 45% in the case with non-buckling braces. So, it was concluded that the performance of the structure in the case with non-buckling braces is better than in the case without non-buckling braces.

The Comparison of Code-Based and Empirical Seismic Fragility Curves of Steel and RC Buildings

Seismic codes were developed to reduce the structural vulnerability and risk associated with earthquakes in earthquake-prone regions of the world. The effectiveness of the code in preventing damage is dependent on the performance level defined and the construction technology employed. The seismic fragility curves for two recent versions of the seismic code of Iran are determined by using the hybrid method. The probability of damage levels is visualized by these curves. To develop these curves, only the assumptions of the code are taken into account. These curves are compared with the empirical fragility of the recent devastating earthquake in Iran. The results indicate that, despite a similar probability of damage to the different seismic-resistant systems, steel-braced frames pose a greater risk of collapse. Concerning earthquake damage, the steel and RC moment-resisting frames have shown higher damage probability than expected from the code.

Macro-Seismic Assessment for Residential Buildings Constructed in the Soviet Union Era in Almaty, Kazakhstan

Southern and southeastern Kazakhstan is a region of intraplate seismicity characterized by several destructive earthquakes. Almaty, the largest metropolis in this region, has many structures with different construction materials and seismic-resistant systems. Among them, residential buildings constructed in the Soviet Union era (before the 1990s) may possess low seismic resisting capacities due to limited seismic design and detailing provisions. Therefore, it is essential to assess seismic risks for these buildings. This paper collected information from a government agency (i.e., KazNIISA), including construction materials, lateral force-resisting systems, and structural ductility capacities for residential buildings constructed in this era. These buildings were then categorized in terms of their seismic vulnerabilities following the European Macro-seismic Scale (EMS-98). Vulnerability curves and probability of damages were developed under different earthquake intensities and peak ground accelerations. The likelihood of varying levels of damage was established for the design basis and maximum considered earthquakes in the Almaty region. It was found that unreinforced masonry and wood buildings tend to be very heavily damaged and even collapse under the maximum considered earthquake. The reinforced and precast concrete buildings have a high probability of heavy to very heavy damage, which may require further analytical assessment since the structure at this damage level will undergo a significant nonlinear response and has a high uncertainty in the seismic performance.

Design and analysis of dissipative seismic resistant heavy timber frame structures equipped with steel links

The recent development of timber structures, thanks to new materials more and more efficient from the mechanical point of view, allows the application, as seismic resistant systems, of both framed and braced multistory multispan timber structures, which are already well consolidated in the field of steel constructions, they offering excellent seismic performances. Although materials are different, the structural systems have the similarity to be assemblage of structural members connected each other. Therefore it is possible to apply the same seismic design approach, by transferring the knowhow from steel to timber structures and adapting the design rules to the peculiarities of timber. In particular the seismic design parameters are to be calibrated and the dissipative zones to be characterized, they being the connections themselves or specific dissipative devices.In this context, the paper deals with the application of steel links for the development of seismic resistant dissipative heavy timber frames: steel links have the aim of dissipating seismic energy, while timber elements and steel connections remain in the elastic field, according to capacity design. Specifically, 2D single-storey timber structures equipped with dissipative links, in different structural configurations, are studied. They have been designed through linear dynamic analyses. Therefore, non-linear static analyses are performed, using the structural calculation program SAP2000, with the aim of evaluating the global behaviour and determining the behaviour factors for each structural type. The study proves the suitability and the efficiency of the proposed system and design procedure.

Seismic behavior and nonlinear analysis of Hybrid Coupled Shear Walls

Hybrid Coupled Shear Walls are an innovative seismic-resistant system that aims at merging the advantages of the classical Coupled Shear Walls with the dissipative capacity and easy-to-repair characteristics of steel elements. They are constituted by a reinforced concrete wall connected to two side steel columns by dissipative steel links. Depending on the stiffness/strength of the links, it is possible to obtain different distributions of the seismic forces between the wall and the columns. As resulting from previous research activity on this topic, the seismic behavior of this structural system can be strongly influenced by the higher modes, especially for mid/high-rise buildings, making classical pushover analyses unable to catch the correct behavior. In this regard, the paper presents the comparison between the results of Incremental Dynamic Analyses and of different Pushover Analyses, giving indications about a more reliable procedure for the assessment of the seismic performance through suitable pushover analysis.

Introducing a new seismic resisting system with dual linked column frame and rocking motion

This paper proposes a novel Dual-Linked Column Frame (DLCF) system with the rocking motion of moment frame column bases. The novel Dual-Linked Column Frame with Rocking motion (DLCFR) increases the seismic capacity of the moment frame and the linked beam as a structural fuse to dissipate energy. Rocking column bases can dissipate energy through fuses that can be repaired easily by being bolted to the column. A dual-linked column pattern in the frame center increases the seismic performance of the linked column frame (LCF) system. The effect of rocking motion on the seismic performance of LCF and DLCF systems has been evaluated by analyzing 13 models with different rocking motion placements and comparing these models with the fixed base condition. The seismic performance of the models has been compared and one model with the desirable seismic performance has been proposed. Incremental Dynamic Analysis (IDA) has been performed to examine the behavior of the 3, 6, and 9-story proposed models using OpenSees. The results showed that rocking motion reduces the failure of the moment frame in the DLCF system. The absorption of the base shear in the Moment Frame (MF) and the Linked Column (LC) in the DLCFR model is 1 and 99% of the total base shear, respectively. The probability of failure in the proposed models of 3, 6, and 9-story are 20%, 15%, and 10% less than the model with a fixed base, respectively. The new seismic system proposed has been able to significantly reduce the probability of failure, floor acceleration, and base shear.

A multi-performance seismic design procedure to incorporate Crescent Shaped Braces in mid-rise frame structures

This paper introduces a novel procedure for the seismic design of a new class of seismic-resisting systems for mid-rise buildings obtained by incorporating special yielding steel braces known as Crescent Shaped Braces (CSBs) into Not Moment-Resisting Frames (NMRFs). The proposed design procedure is grounded on the Performance-Based Seismic Design (PBSD) framework through the imposition of multiple seismic performance objectives with the aim of obtaining an almost uniform along-the-height seismic behavior. The desired uniform seismic behavior is ensured by imposing: (i) uniform inter-storey drifts under frequent earthquakes; (ii) widespread yielding of the braces along the building height under occasional earthquakes; (iii) minimum ductility capacity at all storeys to be exploited under rare earthquakes; (iv) minimum hardening stiffness for the mitigation of the second order (P-Δ) effects under very rare earthquakes. The desired performances are made possible by the specific features of the CSBs in terms of initial lateral stiffness, yielding strength, ductility capacity and final hardening response. The procedure is articulated in four conceptual phases and several steps to guide the professional engineer through all the main design phases, from the selection of the seismic performance objectives to the preliminary sizing of the CSB devices, up to the final design/verification through non-linear time-history analyses. The effectiveness of the proposed design procedure is finally demonstrated through an applicative example.

A critical review of cold-formed steel seismic resistant systems: Recent developments, challenges and future directions

Cold-formed steel (CFS) systems have seen an increased application in the past few decades, especially in the construction of low- to mid-rise buildings. CFS members offer considerable structural and environmental advantages, such as low weight, ease and speed of construction, greater manufacturing flexibility, recyclability and low embodied carbon. Despite the significant potential offered by CFS structural systems, the seismic design of lateral force-resisting systems (LFRS) for CFS multi-story buildings is challenging. There are many different types of systems capable of providing the lateral load resistance capacity of the CFS framing, and this paper provides a comprehensive review of the research developments made in CFS braced-wall systems and moment-resisting frames, as the most conventional systems, to study their structural performance and identify the research gaps, challenges, and future directions. The major research developments are summarised in terms of load capacity, stiffness, energy dissipation capacity and failure mode. As an outcome of the crucial review, it was found that CFS LFRSs can generally offer more efficient design solutions regarding seismic characteristics such as high ductility and energy dissipation capacity. Despite a rather large body of research on CFS braced walls, it is necessary to assess the response of these systems in various aspects, such as developing an optimisation framework to withstand the combination of vertical and horizontal loading plus resist the impact of severe fire. With respect to moment-resisting frames, one of the main research needs is to develop systems suitable for multi-story buildings, especially in seismic regions.

Machine learning-driven probabilistic residual displacement-based design method for improving post-earthquake repairability of steel moment-resisting frames using self-centering braces

Owing to their sufficient ductility, conventional steel moment-resisting frames (MRFs) are widely used as seismic-resistant systems in building structures. However, the ductile behavior introduces significant residual displacement after earthquakes, leading to massive economic losses caused by difficult or even unfeasible repairs. This paper intends to propose a machine learning-driven probabilistic residual displacement-based design method for retrofitting MRFs using self-centering braces (SCBs) and improving the post-earthquake repairability by reducing the residual displacement to a target level. The influence of the SCB's design parameters on the peak and residual displacements of the enhanced MRF are first investigated through parametric dynamic analysis of single-degree-of-freedom (SDOF) systems. The probabilistic residual displacement prediction models are developed using different machine learning algorithms. Analysis results indicate that the artificial neural network (ANN) models demonstrate the highest accuracy with the greatest coefficient of determination (R2) and lowest root mean squared error (RMSE). A software was developed based on the ANN models for predicting the probabilistic peak and residual displacement responses of the retrofitted MRF (RMRF). Then the proposed probabilistic residual displacement-based design steps are introduced. Finally, a three-story benchmark MRF is retrofitted using the proposed design method with two different performance objectives. Nonlinear static and dynamic analyses are conducted to investigate the seismic responses of the designed RMRFs. The analysis results show that the RMRFs can achieve the desired performance objective, confirming the effectiveness of the proposed design method. The SCB can significantly reduce the residual displacement of the RMRFs, where the RMRFs are fully recoverable (with a probability of 100%) without any need for repair after maximum considered earthquakes.

Seismic Response and Economic Study of New Light Steel-Wood-Plastic Structure in Rural Yunnan, China

A new type of light steel-wood-plastic residential structure in rural has popular in recent years in rural Yunnan, China. The application of light steel, wood, and new plastic materials in practical engineering is gradually increasing due to its advantages of green ecology and waste utilization, and its response characteristics under earthquakes have attracted great attention. In this paper, seismic-resistant models, seismic-isolated models, and seismic-damped models for multistorey light steel-wood-plastic structures were established using the SAP2000 finite element software based on different seismic response methods. The seismic-isolated model is divided into five schemes, namely, LRB400, LRB500, LRB600, high damped, and friction pendulum-isolated bearings, and the seismic-damped model is divided into three schemes, namely, ordinary bracing, soft-steel bracing, and BRB bracing at the same locations around the 2nd floor of the building. Nonlinear time analysis was carried out for the nine schemes, comparing the period, structural interstorey displacement, base shear, top displacement, top acceleration, and economy of the structure under the action of an 8-degree earthquake. Results show that the period of the seismic-isolated system increased by approximately 130% compared to the seismic-resistant system, and the period of the damped system decreased slightly compared to the seismic system, the interstorey displacement, base shear, and top acceleration of both the seismic-isolated system and the damped system were smaller than those of the seismic-resistant system, and the seismic-isolated system decreased by approximately 40% compared to the damped system, and the seismic-isolated system was more effective than the damped system. From the comparison of postearthquake damage cost and full-cycle cost, the economic performance of the seismic-isolated structure is better than that of the damped and seismic-resistant structures. The conclusions of this paper can provide a scientific reference for promoting the use of new light steel-wood-plastic residential buildings.

Topology and shape optimization of steel plate shear walls for enhancing the seismic energy dissipation capacity

In recent years, steel plate shear walls (SPSW) have been considered as one of the reliable passive seismic-resisting systems, which are classified into two general categories of stiffened and unstiffened types. Unstiffened SPSWs experience early buckling at low shear loads and hence, the pinching occurs in obtained hysteretic curves and this event significantly reduces the amount of dissipated seismic energy. To address this issue, this paper aims to optimize the performance of unstiffened SPSWs considering different loading conditions and achieve an optimized SPSW with a simple configuration and no need for additional buckling-restrained plates. For this purpose, after validation of the finite element modeling and optimization procedures by ABAQUS, optimized SPSWs were obtained considering the strain energy as the objective function along with the plate volume and planar symmetry as the constraints. Then, all the obtained configurations were superimposed using AutoCAD and a final optimized configuration was proposed. The cyclic performance of unstiffened, ring-shaped and optimized SPSWs with the same weight was evaluated under a quasi-static cyclic loading protocol. Finally, the models of two 5-story building frame systems equipped with unstiffened and optimized SPSWs were subjected to Tabas, Manjil and Bam records to investigate their seismic performance. Based on the obtained results, it was concluded that the performance of the introduced optimized SPSW improved in all cases compared to the ring-shaped SPSW and it can be a reliable alternative to this type of SPSW.

Experimental validation and numerical simulation of a dual-self-centering variable friction braced frame under strong ground motions

The dual self-centering variable friction brace (DSC-VFB) is a novel resilient system with a loading stiffness higher than the unloading stiffness and an enhanced energy dissipation capability. This study presents experimental and numerical analyses of a 1/3-scaled dual-self-centering variable friction braced frame (DVBF). The pinned beam–column, column–base connections in the DVBF ensured that the DSC-VFBs were a standalone lateral seismic resisting system. Three ground motions scaled to six shaking intensities were conducted to evaluate the seismic responses of the DVBF. The ground motions were subjected to far- and near-field earthquakes. Owing to the high seismic resistance of the DVBF, the stiffness degradation could be omitted after several strong earthquakes. The frame returned to its initial position with nearly zero residual drift, although the maximum drift exceeded 2.5%. The grooved friction plates and self-centering system, which could be disassembled and replaced conveniently, had no observable damage after the tests. A 3D simulation model was developed based on practical constructions. The nonlinear analysis results were compared with the experimental results. The two exhibited good agreement. The results showed that the DVBF under near-field pulse earthquakes resulted in larger displacement and acceleration responses than those under far-field and near-field no-pulse earthquakes. The present study verified the effective working mechanism and good resilience of the DSC-VFB and DVBF even under strong seismic shaking intensities.

Performance-Based Seismic Design of Corrugated Steel Plate Shear Walls

Corrugated steel plate shear walls (CoSPSWs) consist of corrugated steel wall plates and a steel boundary frame, which could be adopted as seismic-resistant systems for high-rise buildings. In this study, a performance-based seismic design (PBSD) method was proposed for CoSPSWs, in which an ideal yield mechanism and target drifts were selected as performance objectives to evaluate and control the inelastic behavior of the system. Two 10-story CoSPSW structures were then designed with the PBSD method and the traditional method respectively, and static pushover analyses as well as nonlinear dynamic time-history analyses were conducted on both structures. It turned out that the CoSPSW structure designed with the PBSD method presented the ideal yield mechanism, all inter-story drifts were well below the target drift of 2.5%, and the drifts distributed more smoothly under rare earthquakes. Structural and nonstructural fragility curves of both CoSPSW structures were obtained through probabilistic seismic demand analysis using Incremental Dynamic Analyses. The results showed that for the structural repair states of RS1 to RS5, the 25th percentile PGA values of the fragility curves of the CoSPSW structure designed with the PBSD method were 220%, 98%, 84%, 51 % and 13% higher than the CoSPSW structure designed with the traditional method, respectively. For the nonstructural damage states of Slight to Complete, the 25th percentile PGA values of the fragility curves of the CoSPSW structure designed with the PBSD method were 145%, 98%, 36%, and 7% higher than the CoSPSW structure designed with the traditional method, respectively. Therefore, CoSPSW structure designed with the PBSD method had lower seismic vulnerability as well as probability of nonstructural damage.

Performance assessment of various seismic resistant systems for a multistory structure in different seismic zones of Bangladesh

Purpose This study aims to present the variations of optimal seismic control of reinforced cement concrete (RCC) structure using different structural systems. Different third-dimensional mathematical models are used to examine the responses of multistory flexibly connected frames subjected to earthquake excitations. Design/methodology/approach This paper examined a G + 50 multi-storied high-rise structure, which is analyzed using different combinations of moment resistant frames, shear walls, seismic outrigger systems and seismic dampers to observe the effectiveness during ground motion against soft soil conditions. The damping coefficients of added dampers, providing both upper and lower levels are taken into consideration. A finite element modeling and analysis is generated. Then the nature of the structure exposed to ground motion is captured with response spectrum analysis, using BNBC-2020 for four different seismic zones in Bangladesh. Findings The response of the structure is investigated according to the amplitude of the displacements, drifts, base shear, stiffness and torsion. The numerical results indicate that adding dampers at the base level can be the most effective against seismic control. However, placing an outrigger bracing system at the middle and top end with shear wall can be the most effective for controlling displacements and drifts. Originality/value The response of high-rise structures to seismic forces in Bangladesh’s soft soil conditions is examined at various levels in this study. This study is an original research which contributes to the knowledge to build earthquake resisting high-rises in Bangladesh.

Numerical Study for Evaluating the Effect of Length-to-Height Ratio on the Behavior of Concrete Frame Retrofitted with Steel Infill Plates

AbstractNowadays, steel shear walls are widely used as a seismic lateral resistant system all over the world. In this paper, a parametric study is presented to calculate the ratio of length to heig...