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CONTENTS
Volume 23, Number 2, August 2022
 


Abstract
One common method to select input ground motions to predict dynamic behavior of structures subjected to seismic excitation requires spectral acceleration (Sa) match target mean response spectrum. However, dispersion of ground motions, which explicitly affects the structural response, is rarely discussed in this method. Generally, selecting ground motions matching target mean and variance has been utilized as an appropriate method to predict reliable seismic response. The goal of this paper is to investigate the impact of target spectra variance of ground motions on structural seismic response. Two sets of ground motions with different target variances (zero variance and minimum variance larger than inherent variance of the target spectrum) are selected as input to two different structures. Structural responses at different heights are compared, in terms of peak, mean and dispersion. Results show that increase of target spectra variance tends to increase peak floor acceleration, peak deformation and dispersions of response of interest remarkably. To short-period structures, dispersion increase ratios of seismic response are close to that of Sa of input ground motions at the first period. To long-period structures, dispersions of floor acceleration and floor response spectra increase more significantly at the bottom, while dispersion increase ratios of IDR and deformation are close to that of Sa of input ground motions at the first period. This study could further provide useful information on selecting appropriate ground motion to predict seismic behavior of different types of structures.

Key Words
dispersion increase ratio; floor acceleration; floor response spectra structural deformation; inter-storey drift ratio (IDR); target spectra variance

Address
Liuyun Xu and Zhiguang Zhou: Department of Disaster Mitigation for Structures, College of Civil Engineering, Tongji University,
1239 Siping Road, Shanghai, 200092, China

Abstract
Caisson-type structures are widely used as quay walls in coastal areas. In Korea, for a long time, many caisson-type quay walls have been constructed with a low front water depth. These facilities can no longer meet the requirements of current development. This study developed a new technology for deepening existing caisson-type quay walls using grouting and rubble mound excavation to economically reuse them. With this technology, quay walls could be renovated by injecting grout into the rubble mound beneath the front toe of the caisson to secure its structure. Subsequently, a portion of the rubble mound was excavated to increase the front water depth. This paper reports the results of an investigation of the seismic behavior of a renovated quay wall in comparison to that of an existing quay wall using centrifuge tests and numerical simulations. Two centrifuge model tests at a scale of 1/120 were conducted on the quay walls before and after renovation. During the experiments, the displacements, accelerations, and earth pressures were measured under five consecutive earthquake input motions with increasing magnitudes. In addition, systematic numerical analyses of the centrifuge model tests were also conducted with the PLAXIS 2D finite element (FE) program using a nonlinear elastoplastic constitutive model. The displacements of the caisson, response accelerations, deformed shape of the quay wall, and earth pressures were investigated in detail based on a comparison of the numerical and experimental results. The results demonstrated that the motion of the caisson changed after renovation, and its displacement decreased significantly. The comparison between the FE models and centrifuge test results showed good agreement. This indicated that renovation was technically feasible, and it could be considered to study further by testbed before applying in practice.

Key Words
bumper; damping; earthquake; impact; pounding

Address
S.M. Khatami:University of Applied Science and Technology, Center of Semnan Municipality, Semnan, Iran

H. Naderpour:University of Applied Science and Technology, Center of Semnan Municipality, Semnan, Iran

A.R. Mortezaei: Seismic Geotechnical and High Performance Concrete Research Centre, Civil Engineering Department,
Semnan Branch, Islamic Azad University, Semnan, Iran

R.C. Barros:Faculty of Civil Engineering, University of Porto (FEUP), Porto, Portugal

M. Maddah

Abstract
In most self-center braces, decreasing residual deformation is possible only by increasing pretension force, which results in lower energy dissipation capacity. On the other hand, increasing energy dissipation capacity means higher values of residual deformation. The goal of this research was to find the best design for a self-centering buckling restrained brace (SCBRB) system by balancing self-centering capability and energy dissipation. Three, six, and nine-story structures were investigated using OpenSees software and the TCL programming language to achieve this goal. For each height, 62 different SC-BRBs were considered using different values for the pretension force of cables, the area of the buckling restrained brace (BRB) core plate, and the yield stress of the core plate. The residual deformation and dissipated energy of all the models were calculated using nonlinear analyses after cyclic loading was applied. The optimum design for each height was determined among all the models and was compared to the structure equipped with the usual BRB. The residual deformation of the framed buildings was significantly reduced, according to the findings. Also the reduction of the energy dissipation was acceptable. The optimum design of SC-BRB in 6-story building has the most reduction percent in residual deformation, it can reduce residual deformation of building 83% while causing only a 57% of reduction in dissipated energy. The greatest reduction in residual deformation versus dissipated energy reduction was for the optimum SC-BRB design of 9-story building, results indicated that it can reduce residual deformation of building 69% while causing only a 42% of reduction in dissipated energy.

Key Words
buckling restrained brace; dual steel moment resisting system; energy absorption self-centering; optimum design; residual deformation

Address
Mohammadreza Ahadpour Khaneghah:School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

Esmaeil Mohammadi Dehcheshmaeh:School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

Vahid Broujerdian:School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

Gholamreza Ghodrati Amiri:Natural Disasters Prevention Research Center, Iran University of science and Technology, Tehran, Iran

Abstract
Torsion is one of the most important causes of building collapse during earthquakes. Sometimes, despite the symmetric form of the building, infill walls disturb the symmetry of the lateral resisting system. The purpose of this research is to investigate the effect of urban layout on developing torsion caused by infill walls. For this purpose, a typological study was conducted based on the conditions of perimeter walls on 364 buildings and then 9 cases were selected. The dimensions of the selected buildings are constant and the conditions of the perimeter walls including facades with openings and cantilevered facades are variable. The selected buildings with 60 different layouts of infill walls were analyzed and the behavior of each one was evaluated based on the torsional irregularity criteria of seismic codes. The results of the analyses showed that if the perimeter walls of a building are symmetric, asymmetric interior walls will not be important in developing torsion and effective parameters in symmetry of the perimeter infill walls are the number of walls, area of openings, aspect ratio, and construction details. Finally, architectural solutions to mitigate the torsional effects of infill walls were proposed for buildings with solid infill walls on some sides, for buildings where the perimeter walls of one side are on the cantilevered part, and for buildings where the perimeter walls of two adjacent sides are on the cantilevered part. In three-sided buildings, where two adjacent façades are cantilevered, it is often impossible to use the potential of the infill walls.

Key Words
cantilevered façade; façade with opening; infill wall; seismic codes; torsion; urban layout

Address
Azadeh Noorifard: School of Architecture, College of Fine Arts, University of Tehran, Tehran, Iran

Mohammad Reza Tabeshpour:Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran

Fatemeh Mehdizadeh Saradj: School of Architecture and Environmental Design, Iran University of Science and Technology, Tehran, Iran

Abstract
To research the dynamic response of the high-rise structure under the rocking ground motion, which we believed that the effect cannot be ignored, especially accompanied by vertical ground motion. Theoretical analysis and shaking table seismic simulation tests were used to study the response of a high-rise structure to excitation of a H-V-R ground motion that included horizontal, vertical, and rocking components. The use of a wavelet analysis filtering technique to extract the rocking component from data for the primary horizontal component in the first part, based on the principle of horizontal pendulum seismogram and the use of a wavelet analysis filtering technique. The dynamic equation of motion for a high-rise structure under H-V-R ground motion was developed in the second part, with extra P-Δ effect due to ground rocking displacement was included in the external load excitation terms of the equation of motion, and the influence of the vertical component on the high-rise structure P-Δ effect was also included. Shaking table tests were performed for H-V-R ground motion using a scale model of a high-rise TV tower structure in the third part, while the results of the shaking table tests and theoretical calculation were compared in the last part, and the following conclusions were made. The results of the shaking table test were consistent with the theoretical calculation results, which verified the accuracy of the theoretical analysis. The rocking component of ground motion significantly increased the displacement of the structure and caused an asymmetric displacement of the structure. Thus, the seismic design of an engineering structure should consider the additional P-Δ effect due to the rocking component. Moreover, introducing the vertical component caused the geometric stiffness of the structure to change with time, and the influence of the rocking component on the structure was amplified due to this effect.

Key Words
asymmetric displacement response; high-rise structure; H-V-R ground motion; seismic simulation shaking table test

Address
Wenhui We, Ying Hu and Zhihan Jiang:Hubei Key Laboratory of Road Bridge and Structure Engineering, Wuhan University of Technology, Wuhan, Hubei, China

Abstract
Reduced beam section (RBS) moment connections used in special moment resisting frames are currently limited to beam sections that are not larger than nominal depths of 920 mm, weight of 447 kg/m and flange thickness of 44 mm. Due to the higher demand for structural components with jumbo sections, which can potentially be applied in the transfer girders in long-span building structures, the newly available steel heavy members are promising. To address this issue, advanced numerical models are developed to fully evaluate the distribution of stresses and concentrations of plastic strains for such jumbo RBS connections. This paper first presents a brief overview of an experimental study on four specimens with large beam and column sections. Then, a numerical model that includes initial imperfections, residual stresses, geometric nonlinearity, and explicitly modeled welds is presented. The model is used to further explore the behavior of the test specimens, including distribution of stresses, distribution of plastic strains, stress triaxiality and potential for fracture. The results reveal that the stresses are highly non-uniform across the beam flange and, similarly, the plastic strains concentrate at the extreme fiber of the bottom flange. However, neither of these phenomena, which are primarily a function of beam flange thickness, is reflected in current design procedures.

Key Words
cyclic behavior; fracture potential; jumbo section; Reduced beam section (RBS) connection; residual stress

Address
Liangjie Qi:School of Civil Engineering, Xi'an University of Architecture & Technology, Xi

Abstract
Seismic response control has always been a grave concern with the damage and collapse of many buildings during the past earthquakes. While there are several existing techniques like base isolation, viscous damper, moment-resisting beamcolumn connections, tuned mass damper, etc., many of these are succumbing to either of large displacement, near-fault, and long-period earthquakes. Keeping this viewpoint, extensive research on the application of smart materials for seismic response control of buildings was attempted during the last decade. Shape Memory Alloy (SMA) with its unique properties of superelasticity and shape memory effect is one of the smart materials used for seismic control of buildings. In this paper, an exhaustive review has been compiled on the seismic control applications of SMA in buildings. Unique properties of SMA are discussed in detail and different phases of SMA along with crystal characteristics are illustrated. Consequently, various seismic control applications of SMA are discussed in terms of performance and compared with prevalent base isolators, bracings, beamcolumn connections, and tuned mass damper systems.

Key Words
seismic response control; shape memory alloy; shape memory effect; superelasticity

Address
Moka Eswar, Ajay Chourasia and N. Gopalakrishnan: Structural Engineering Division, CSIR – Central Building Research Institute, Roorkee 247667, India/ Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India

Abstract
Recently, steel-timber hybrid buildings have become prevalent worldwide because several advantages of both steel and timber structures are maintained in the hybrid system. In Taiwan, seismic design specification related to steel-timber hybrid buildings remains void. In this study, the ductility capacity of steel-timber hybrid buildings in Taiwanese seismic design specification is first proposed and evaluated using nonlinear incremental dynamic analysis (IDA). Three non-linear structural models, 12-story, 8-story, and 6-story steel-timer hybrid buildings were constructed using OpenSees. In each model, Douglas-fir was adopted to assemble the upper 4 stories as a timber structure while a conventional steel moment-resisting frame was designated in the lower part of the model. FEMA P-695 methodology was employed to perform IDAs considering 44 earthquakes to assess if the ductility capacity of steel-timber hybrid building is appropriate. The analytical results indicate that the current ductility capacity of steel moment-resisting frames can be directly applied to steel-timber hybrid buildings if the drift ratio of each story under the seismic design force for buildings in Taiwan is less than 0.3%. As a result, engineers are able to design a steel-timber hybrid building straightforwardly by following current design specification. Otherwise, the ductility capacity of steel-timber hybrid buildings must be modified which depends on further studies in the future.

Key Words
ductility capacity; incremental dynamic analysis steel-timber hybrid building; seismic design

Address
Pei-Ching Chen and I-Ping Su:Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, No.43, Sec.4,
Keelung Rd., Taipei 106335, Taiwan


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