Seismic testing and numerical analysis of Y‐shaped eccentrically braced frame made of high‐strength steel

In eccentrically braced frame made of high‐strength steel (HSS‐EBF), link and brace are made from conventional steel whereas other structural members use high‐strength steel. Using HSS for beams and columns in EBF can reduce steel consumption and increase economic efficiency. In this paper, one shake table test of a 1:2 scaled three‐story Y‐shaped HSS‐EBF (Y‐HSS‐EBF) specimen was carried out to study its seismic behavior underground motions with different peak ground accelerations. The dynamic properties, base shear force, displacement, and strain responses of the specimen were obtained from this test. In addition, the finite element models of two 10‐story Y‐HSS‐EBF buildings and one 10‐story conventional Y‐EBF building were evaluated for seismic effects. Nonlinear pushover and dynamic analyses were conducted to compare their seismic performance and economy. The results indicated that the specimen exhibited sufficient lateral stiffness and safety but suffered some localized damages. During the high seismic intensity earthquakes, the links of the test specimen were in inelastic to dissipate the earthquake energy, whereas other structural members remained in the elastic state. Under the same design conditions, Y‐HSS‐EBF used less steel than that of conventional Y‐EBF, which could reduce the amount of steel used in Y‐HSS‐EBF. The Y‐HSS‐EBF is a safe, dual system with reliable seismic performance.     

Seismic performance and cost‐effectiveness of high‐rise buildings with increasing concrete strength

The relationship between the seismic performance and economics of high‐rise buildings when designed to different material strengths is investigated in this paper. To represent the modern high‐rise construction, five 60‐story reinforced concrete buildings with varying concrete strengths, ranging from 45 MPa to 110 MPa, are designed and detailed to fine accuracy keeping almost equal periods of vibration. Detailed fiber‐based simulation models are developed to assess the relative seismic performance of the reference structures using incremental dynamic analyses and fragility functions. It is concluded that a considerable saving in construction cost and gain in useable area are attained with increasing concrete strength. The safety margins of high‐strength concrete in tall structures may exceed those of normal‐strength concrete buildings, particularly at high ground motion intensity levels. The recommendations of this systematic study may help designers to arrive at cost‐effective designs for high‐rise buildings in earthquake‐prone regions without jeopardizing safety at different performance levels. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic design and performance analysis of buckling‐restrained braced RC frame structures

Due to the stable hysteretic behavior, buckling‐restrained braces (BRBs) have been increasingly adopted in reinforced concrete (RC) frame structures to develop a dual structural system (BRB‐RCF). This study proposed an alternative strength‐based design approach that decomposes the dual BRB‐RCF system into two independent RC frame and BRB system using the BRB‐carrying story shear ratio. The design of RC frame is performed in an integrated manner by considering the BRB postyielding force demands. Three RC frames with five, 10, and 15 stories were employed as prototype structures, and seven story shear ratios ranging from 0.1 to 0.7 were used to generate a total of 21 structural modes. The material usage, maximum axial compression ratio of columns, and elastic interstory drift ratio were compared for different story shear ratios. Nonlinear dynamic analysis of the BRB‐RCFs subjected to 12 ground motions were carried out. The seismic response including the maximum interstory drift ratio, hysteretic energy dissipation ratio, and actual BRB‐carrying story shear ratio were systematically assessed for different design story shear ratios. Based on the considerations of material usage and seismic performance, it is suggested that the design BRB‐carrying story shear ratio should be in the range of 0.3 to 0.5.     

Seismic design of outrigger systems using equivalent energy design procedure

An outrigger system is an effective structural scheme that is commonly used in high‐rise construction to increase the stiffness of concrete core walls and to reduce the moment demand within the walls. Despite the on‐going use of outrigger systems around the world, a formal seismic design procedure is yet available. This paper presents an equivalent energy design procedure (EEDP) to design outrigger systems for seismic applications. Three prototype outrigger‐wall buildings of various heights are designed for Vancouver, Canada. Detailed finite element models are developed to assess the seismic performance of the prototype buildings and to assess the safety using the FEMA P695 methodology. The result shows that EEDP is an efficient method to design outrigger systems which results in structures that can achieve sufficient margin of safety against collapse and satisfy multiple performance objectives at different seismic hazard levels.     

Seismic fragility relationships of reinforced concrete high‐rise buildings

A complete methodology is presented for the seismic fragility assessment of reinforced concrete high‐rise buildings. The key steps of the methodology are illustrated through an example of the fragility assessment of an existing 54‐story building with a dual core wall system. The set of rigorously derived probabilistic fragilities are the first published for high‐rise reinforced concrete buildings. The inelastic nonlinear dynamic analyses for the fragility assessments are made using a simplified lumped‐parameter model that was derived from highly detailed FE models using genetic algorithms. New definitions for performance limit states were based on the results of detailed pushover analyses of a distributed inelastic nonlinear finite element model that includes shear–flexure–axial interaction effects. To develop the fragility relationships, 1800 dynamic response history analyses were conducted. This study considered uncertainty in structural material values as well as in seismic demand. Thirty strong motion records were selected for use in the analyses that would produce an appropriate range in structural response characteristics due to variation in magnitude, distance and site condition. The overall approach is generic and can be applied to developing computationally efficient and probabilistically‐based seismic fragility relationships for reinforced concrete high‐rise buildings of different configurations. Copyright © 2007 John Wiley & Sons, Ltd.     

Verification of performance criteria using shake table testing for the vulnerability assessment of reinforced concrete buildings

Shake table experiments are conducted to support the selection of performance criteria and to verify the inelastic modeling approach for developing the fragility functions of reinforced concrete buildings. Two frames representing the lateral force‐resisting system of a preseismic code building are tested under the effect of an earthquake record with increasing severity. Shear failure is detected in columns at a PGA of 1.28g before other failure modes, which was effectively predicted by the fiber‐based numerical model, performance criteria, and shear supply approaches adopted for vulnerability assessment. Five buildings, ranging from 2 to 40 stories, are then assessed under the effect of far‐field and near‐source earthquake records, considering the experimentally verified modeling approach and shear failure prediction models that account for flexural ductility and shear‐axial force interaction. The impact of considering shear response on the vulnerability assessment results is considerable, particularly for the lower‐height wall structures when subjected to the near‐source earthquake scenario. Higher modes dominate the behavior of wall structures, principally under the latter seismic scenario, and shift their response to shear‐controlled. Therefore, seismic scenario‐structure‐based performance criteria are adopted for developing a range of analytically derived, experimentally verified fragility functions for the earthquake loss estimation of buildings with different characteristics.     

Performance‐based seismic design of an irregular tall building in Istanbul

Structural design of a 50‐story tall reinforced concrete residential building, which was planned to be constructed in Istanbul and given up afterwards by the investor, has been completed in accordance with the draft version of Seismic Design Code for Tall Buildings in Istanbul that adopts performance‐based seismic design as the basic approach as Tall Buildings Initiative Guidelines do. Seismic design of the building has formed the main part of the structural design process due to high seismicity of the proposed location and extremely irregular floor plan not conforming to usual tall building structures. The building consists of two individual buildings linked through sky floors at the top 12 stories whose design was one of the most challenging works. The building has been designed for design basis earthquake by elastic response spectrum analysis, and its seismic performance has been checked for maximum considered earthquake by nonlinear time‐history analyses carried out using PERFORM‐3D. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimum seismic design of steel framed‐tube and tube‐in‐tube tall buildings

The relatively large number of structural elements and the variety of design code requirements complicate the design process of tall buildings. This process is exacerbated when the target is to obtain the seismic code‐compliant optimal design with minimum weight. The present paper aims at providing a practical methodology for the optimal design of steel tall building structures considering the constraints imposed by typical building codes. The applicability of the proposed approach is demonstrated through the determination of the optimal seismic design for 20‐, 40‐, and 60‐story buildings with a framed tube as well as a tube‐in‐tube system. Such a design gives rise to a basis for the fair comparison of the behavior of the framed tube with that of the tube‐in‐tube system under applied loads. The optimal weight of the buildings with the tube‐in‐tube system turns out to be slightly less than that of the buildings with the conventional framed‐tube system.     

Seismic behavior of tall buildings using steel–concrete composite columns and shear walls

For the seismic design of tall building structures, the behavior under severe earthquakes should be carefully considered and the upper limit of inter‐story deformations are often defined by the design codes. To improve the performance of structures under severe earthquakes, composite structural members, including steel reinforced column and steel plate reinforced shear wall, are often adopted. In the present work, the seismic behavior of tall buildings using steel–concrete composite columns and shear walls is investigated numerically. Fiber beam–column element models and multilayer shell models are adopted to establish the finite element model of structure, and the material nonlinearities are described by the plasticity and damage models. The accuracy of the developed models is verified by the experimental results of a single shear wall. Systematic numerical simulations are performed for the tall building structures subjected to different earthquakes. The comparative study indicates that the nonlinear redistribution of internal forces plays a very important role for the performance of tall buildings under severe earthquakes.     

Seismic performance of torsionally stiff and flexible multi‐story concentrically steel braced buildings

It is expected that application of torsion provisions in typical seismic codes shows different levels of efficiency for torsionally stiff and flexible buildings. This paper studies difference in performances of a range of code designed torsionally stiff and flexible five‐story building models. The models are classified in eight configurations to cover common range of buildings designed with the seismic provisions of Iranian Standard 2800 as a typical seismic design code. Seismic nonlinear dynamic time history behavior of eight building models subjected to seven horizontal bi‐directional design spectra compatible ground motions is investigated. These models cover a wide band of very torsionally stiff to very flexible buildings. Response parameters are element ductility demand and building story drift ratio. These criteria are appropriate indices for structural and nonstructural damages, respectively. The results indicate that the present linear static procedure of building codes such as the Iranian Standard 2800 is not generally adequate for structures with very low torsional stiffness. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental study on a novel replaceable yielding‐based energy dissipater for rocking and seesaw buildings

The use of energy dissipaters for creation of earthquake‐resilient buildings has been paid more and more attention in recent years, and some newly developed structural fuses or dampers have been proposed to be employed in rocking and seesaw buildings. In this study, a new type of yielding‐based dampers, called curved‐yielding‐plates energy dissipater (CYPED), is introduced. CYPEDs are installed at the bottom of rocking or seesaw building's circumferential columns at the lowest story and have hysteretic behavior in their deformation occurring in vertical direction. The initial curvature of the yielding plates prevents them from buckling and gives the device a smooth force–deformation behavior. First, by performing a set of cyclic tests on three specimens of CYPED, their hysteretic force–displacement behavior was investigated. Then, to show the efficiency of this energy dissipating device in reducing the seismic response of buildings, they were employed numerically as multilinear plastic springs in the computer models of a sample seesaw steel building, and a series of nonlinear time history analysis (NLTHA) were performed on both seesaw building and its conventional counterpart. Results of NLTHA show that the proposed seesaw structural system equipped with appropriate CYPEDs not only gives the building a longer natural period, leading to lower seismic demand, but also leads to remarkable energy dissipation capacity in the building structure at base level and, therefore, keeping the seismic drifts in elastic range in all stories of the building. In this way, the building structure does not need any major repair work, even after a large earthquake, while the conventional building suffers from heavy damage and is not usable after the earthquake.     

The effect of design drift limit on the seismic performance of RC dual high‐rise buildings

Current building codes aim to ensure the acceptable performance of structures implicitly. Because these provisions are empirically developed for low‐ to medium‐rise buildings, their applicability to high‐rise building warrants further investigation. In this paper, the effect of design drift limit on the seismic performance of reinforced concrete dual high‐rise buildings is considered. Nine buildings are designed for 3 drift limits: the code limit (i.e., 2%), one that is lower than the code limit (i.e., 1.5%), and one that is higher than the code limit (i.e., 3%). For each drift limit, buildings of 3 heights (20, 25, and 30 stories) are designed. Finite element models are constructed in OpenSees, and incremental dynamic analysis is performed. The results are used to develop probabilistic seismic demand models, where model parameters are determined using maximum likelihood estimation to incorporate equality and censored data. Reliability analysis using probabilistic demand models is conducted to derive seismic fragility and demand hazard curves. In addition, the collapse performance of the drift limits is evaluated using the Federal Emergency Management Agency (FEMA) P695 procedure. The study results show that the design drift limit affects the building's seismic performance, and the effect depends on the performance level considered. Moreover, from a structural integrity perspective, a larger design drift limit does not induce a significantly higher risk and might yield a more cost‐effective design.     

Study on seismic performance of a super‐tall steel–concrete hybrid structure

Many steel–concrete hybrid buildings have been built in China. The seismic performance of such hybrid system is much more complicated than that of steel structure or reinforced concrete (RC) structure. A steel–concrete hybrid frame‐tube super‐tall building structure with new type of shear walls to be built in a district of seismic intensity 8 in China was studied for its structural complexity and irregularity. Both model test and numerical simulation were applied to obtain the detailed knowledge of seismic performance for this structure. First, a 1/30 scaled model structure was tested on the shaking table under different levels of earthquakes. The failure process and mechanism of the model structure are presented here. Nonlinear time‐history analysis of the prototype structure was then conducted by using the software PERFORM‐3D. The dynamic characteristics, inter‐story drift ratios and energy dissipation conditions are introduced. On the basis of the comparison between the deformation demand and capacity of main structural components at individual performance level under different earthquake level, the seismic performance at the member level was also evaluated. Despite the structural complexity and code‐exceeding height, both experimental and analytical results indicate that the overall seismic performance of the structure meet the requirements of the Chinese design code. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural design of high‐rise buildings using steel‐framed modules: A case study in Hong Kong

Steel‐framed modular buildings afford certain advantages, such as rapid and high‐quality construction. However, although steel‐framed modules have been adopted in several countries, most of them are limited to low‐to‐medium‐rise structures; modular high‐rise buildings are rare. This study proposes a feasible structural design solution for high‐rise buildings using a steel‐framed modular system. A 31‐story student hostel building in Hong Kong is redesigned as a steel‐framed modular building and used as a case study. The finite element models of the building are formulated, and the structural behaviors under wind and earthquake load scenarios are compared. Moreover, the structural design process used for the 31‐story building is applied to design a hypothetical 40‐story modular building to further examine the proposed design solution. The numerical analysis results indicate that the roof lateral displacements and interstory drift ratios of the redesigned modular building are within the allowable limits of design codes; moreover, the modular connections behave elastically under the most adverse loading scenarios. Accordingly, the proposed solution can be used to design steel‐framed modular buildings of up to 40 stories, while complying with relevant wind and seismic codes.     

Effect of vertical structural irregularity on seismic design of tall buildings

Many tall buildings are practically irregular as an entirely regular high‐rise building rarely exists. This study is thus devoted to assessing the approach and coefficients used in the seismic design of real‐life tall buildings with different vertical irregularity features. Five 50‐story buildings are selected and designed using finite element models and international building codes to represent the most common vertical irregularities of reinforced concrete tall buildings in regions of medium seismicity. Detailed fiber‐based simulation models are developed to assess the seismic response of the five benchmark buildings under the effect of 40 earthquake records representing far‐field and near‐source seismic scenarios. The results obtained from a large number of inelastic pushover and incremental dynamic analyses provide insights into the local and global seismic response of the reference structures and confirm the inferior local response of tall buildings with severe vertical irregularities. Due to the significant impacts of the severe irregularity types on the seismic response of tall buildings, the conservative code approach and coefficients are recommended for design. It is also concluded that although the design coefficients of buildings with moderate irregularities are adequately conservative, they can be revised to arrive at more consistent safety margins and cost‐effective designs.     

Performance evaluation of infilled rocking wall frame structure

Conventional reinforced concrete (RC) frame structures are prone to soft‐story mechanism. This deficiency can be eliminated by introducing rocking wall system. Previously studied rocking wall systems usually have the rocking wall situated outside the frame, which results in some challenges and inconvenience. In the study, a novel infilled rocking wall frame (IRWF) system is proposed, which uses infilled RC wall to create a rocking wall within the RC frame. To evaluate seismic performance of the proposed system, both an IRWF model and an RC frame (RCF) model were designed according to Chinese seismic design code. Time history analysis and incremental dynamic analysis were conducted to compare both systems. The results show that IRWF system has more uniform drift and higher collapse margin ratio compared to the RCF system. Economic evaluation of IRWF system was investigated using the state‐of‐the‐art ATC‐58 performance‐based assessment methodology. The result shows superior performance of the IRWF system. The annualized loss of the IRWF model is about 28% less than the RCF model. This shows IRWF system is a viable and efficient alternative resilient seismic force resisting system.     

底部框剪配筋砌块砌体房屋弹塑性地震反应的数值模拟

在总结底部框剪砖房和配筋砌块砌体的抗震性能研究成果的基础上,对底部框剪上部配筋砌块砌体结构的抗震特性进行了初步研究。采用层间剪切模型和三折线骨架曲线恢复力模型,分别按6、7、8度区的多遇烈度、基本烈度和罕遇烈度,输入ElCentro地震波,模拟此类房屋的线性和非线性地震反应。通过分析加速度和位移地震反应,恢复力和层间位移角的变化,考察了该结构的抗震性能和抗震能力。结果表明:底部两层框剪上部六层配筋砌块砌体结构(高25.5m)可用于8度地震区,这种结构的底部框剪层是薄弱部位;应提高框剪层的水平地震剪力设计值,增强延性设计,提高抗倒塌能力。