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CONTENTS
Volume 8, Number 6, June 2015
 

Abstract


Key Words


Address


Abstract
Post-tensioned precast segmental bridge columns have shown high level of strength and ductility, and low residual displacement, which makes them suffer minor damage after earthquake loading; however, there is still lack of confidence on their lateral response against severe seismic loading due in part to their low energy dissipation capacity. This study investigates the influence of major design factors such as post-tensioning force level, strands position, columns aspect ratio, steel jacket and mild steel ratio on seismic performance of self-centring segmental bridge columns in terms of lateral strength, residual displacement and lateral peak displacement. Seismic analyses show that increasing the continuous mild steel ratio improves the lateral peak displacement of the self-centring columns at different levels of post-tensioning (PT) forces. Such an increase in steel ratio reduces the residual drift in segmental columns with higher aspect ratio more considerably. Suggestions are proposed for the design of self-centring segmental columns with various aspect ratios at different target drifts.

Key Words
post-tensioning; precast segmental columns; earthquake loading; finite element method (FEM); lateral seismic demand; residual displacement

Address
Ehsan Nikbakht, Khalim Rashid, Iman Mohseni and Farzad Hejazi: Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Malaysia

Abstract
A model for reflection and refraction of magneto-thermoelastic SV-waves at the interface of two transversely isotropic and homogeneous solid half spaces under initial stress by applying classical dynamical theory of thermoelasticity is purposed. The reflection and refraction coefficients of SV-waves are obtained with ideal boundary conditions for SV-wave incident on the solid-solid interface. The effects of magnetic field, temperature and initial stress on the amplitude ratios after numerical computations are shown graphically with MATLAB software for the particular model.

Key Words
initial stress; reflection; refraction; relaxation time; temperature; magnetic field

Address
Rajneesh Kakar: Faculty of Engineering & Technology, GNA University, Hargobindgarh, Phagwara, Chotti Baradari, 163/1, Jalandhar-144022, India

Shikha Kakar: Department of Electronics, SBBS University, Padhiana, Chotti Baradari, 163/1, Jalandhar-144022, India

Abstract
Real-time hybrid testing (RTHT) involves virtual splitting of the structure into two parts: physical substructure that contains the key region of interest which is tested in a laboratory and numerical substructure that contains the remaining part of the structure in the form of a numerical model. This paper numerically assesses four step-by-step integration methods (Central difference method (CDM), Operator splitting method (OSM), Rosenbrock based method (RBM) and CR-integration method (CR)) which are widely used in RTHT. The methods have been assessed in terms of stability and accuracy for various realistic damping ratios of the physical substructure. The stability is assessed in terms of the spectral radii of the amplification matrix while the accuracy in terms of numerical damping and period distortion. In order to evaluate the performance of the methods, five carefully chosen examples have been studied - undamped SDOF, damped SDOF, instantaneous softening, instantaneous hardening and hysteretic system. The performance of the methods is measured in terms of a non-dimensional error index for displacement and velocity. Based on the error indices, it is observed that OSM and RBM are robust and performs fairly well in all the cases. CDM performed well for undamped SDOF system. CR method can be used for the system showing softening behaviour. The error indices indicate that accuracy of OSM is more than other method in case of hysteretic system. The accuracy of the results obtained through time integration methods for different damping ratios of the physical substructure is addressed in the present study. In the presence of a number of integration methods, it is preferable to have criteria for the selection of the time integration scheme. As such criteria are not available presently, this paper attempts to fill this gap by numerically assessing the four commonly used step-by-step methods.

Key Words
performance assessment; real-time hybrid testing; step-by-step integration; stability; accuracy

Address
Mohit Verma, J. Rajasankar and Nagesh R. Iyer: Academy of Scientific and Innovative Research, New Delhi, India

Mohit Verma, J. Rajasankar: CSIR-Structural Engineering Research Centre, Chennai, India

Abstract
This paper presents an analytical study aimed at evaluating the effectiveness of using buckling-restrained braces (BRBs) in mitigating the seismic response of a case study 6 storey reinforced concrete (RC) building. In the design of the BRBs with non-prismatic cross-sections, twelve combinations of α and β design parameters that influence the strength and stiffness of the BRBs, respectively, were considered. The response of the structure with and without BRBs under earthquake ground accelerations were evaluated through nonlinear dynamic analysis. Two sets of ground motions representative of the design earthquake with 10% and 50% exceedance probability in fifty years were taken into account. By comparing the structural performance of the original and buckling restrained braced structures, it was observed that the use of the BRBs were very effective in mitigating the seismic response as a retrofit scheme. However, the selection of the strength and stiffness parameters of the BRBs had considerable effect on the response characteristics of RC structures. For instance, by increasing the value of α and by decreasing the value of β of the buckling-restrained braces, the maximum deformation demand of the structures increased.

Key Words
buckling restrained brace; nonlinear dynamic analysis; reinforced concrete building; seismic response

Address
Esra Mete Güneyisi, Osman Tunca and Ibrahim Azez: Department of Civil Engineering, Gaziantep University, 27310, Gaziantep, Turkey

Abstract
The October 23 2011 Van Earthquake is studied from an earthquake engineering point of view. Strong ground motion processing was performed to investigate features of the earthquake source, forward directivity effects during the rupture process as well as local site effects. Strong motion characteristics were investigated in terms of peak ground motion and spectral acceleration values. Directiviy effects were discussed in detail via elastic response spectra and wide band spectograms to see the high frequency energy distributions. Source parameters and slip distribution results of the earthquake which had been proposed by different researchers were summarized. Influence of the source parameters on structural response were shown by comparing elastic response spectra of Muradiye synthetic records which were performed by broadband strong motion simulations of the earthquake. It has been emphasized that characteristics of the earthquake rupture dynamics and their effects on structural design might be investigated from a multidisciplinary point of view. Seismotectonic calculations (e.g., slip pattern, rupture velocity) may be extended relating different engineering parameters (e.g., interstorey drifts, spectral accelerations) across different disciplines while using code based seismic design approaches. Current state of the art building codes still far from fully reflecting earthquake source related parameters into design rules. Some of those deficiencies and recent efforts to overcome these problems were also mentioned. Next generation ground motion prediction equations (GMPEs) may be incorporated with certain site categories for site effects. Likewise in the 2011 Van Earthquake, Reverse/Oblique earthquakes indicate that GMPEs need to be feasible to a wider range of magnitudes and distances in engineering practice. Due to the reverse faulting with large slip and dip angles, vertical displacements along with directivity and fault normal effects might significantly affect the engineering structures. Main reason of excessive damage in the town of Erciş can be attributed to these factors. Such effects should be considered in advance through the establishment of vertical design spectra and effects might be incorporated in the available GMPEs.

Key Words
thrust fault; seismotectonic; engineering parameters; the 2011 Van Earthquake; seismic design code; directivity effects; hanging wall effect; footwall effect

Address
Kemal Beyen: Department of Civil Engineering, Kocaeli University, Kocaeli, Turkey

Gülüm Tanircan: Kandilli Observatory and Earthquake Research Institute, Boğaziçi University, İstanbul, Turkey

Abstract
Masonry bridges are the vital components of transportation systems. Although these bridges were constructed centuries ago, they have served a purpose from ancient times to the present day. However, the bridges have needed local renovation and therefore have been rebuilt over different periods in many places. This study focuses on Low Bridge, which is an example of renovated masonry bridges in Turkey. It essentially assesses the structural behavior of the masonry bridge and investigates the integrity of the renovated components. For this purpose, the mechanical properties of the bridge material have been primarily evaluated with experimental tests. Then the static, modal and nonlinear time history analyses have been carried out with the use of finite element methods in order to investigate the structural behavior of the current form of the bridge.

Key Words
bridges; earthquake/seismic behavior; dynamic analysis; finite element method; mode shapes; modeling; time history

Address
Ferit Cakir: Department of Architecture, Faculty of Architecture, Amasya University, Amasya, Turkey

Burcin S. Seker: Merzifon Vocational School, Amasya University, Merzifon, Amasya, Turkey

Abstract
The objections raised by researchers to the design provisions reported in Eurocode 8 make the efficient seismic performance of the eccentrically braced structures designed according to this code unlikely. Given the rationality and the number of the objections, this paper aims to summarize the criticism of researchers and report the opinion of the Authors. The objections raised to the design procedure of eccentrically braced structures regard aspects common to the design of steel structures and aspects specifically related to the design of eccentrically braced structures. The significance of these objections is also shown by means of exemplary cases.

Key Words
seismic areas; eccentrically braced frames; Eurocode 8; design provisions; capacity design

Address
Melina Bosco, Edoardo M. Marino and Pier Paolo Rossi: Department of Civil Engineering and Architecture, University of Catania, Viale A. Doria 6, 95125 Catania, Italy

Abstract
The performance of masonry infilled frames during the past earthquakes shows that the infill panels play a major role as earthquake-resistant elements. Experimental observations regarding the influence of infill panels on increasing stiffness and strength of reinforced concrete structures reveal that such panels can be used in order to strengthen reinforced concrete frames. The present study examines the influence of infill panels on seismic behavior of RC frame structures. For this purpose, several low- and mid-rise RC frames (two-, four-, seven-, and ten story) were numerically investigated. Reinforced masonry infill panels were then placed within the frames and the models were subjected to several nonlinear incremental static and dynamic analyses. In order to determine the acceptance criteria and modeling parameters for frames as well as reinforced masonry panels, the Iranian Guideline for Seismic Rehabilitation of Existing Masonry Buildings (Issue No. 376), the Iranian Guideline for Seismic Rehabilitation of Existing Structures (Issue No. 360) and FEMA Guidelines (FEMA 273 and 356) were used. The results of analyses showed that the use of reinforced masonry infill panels in RC frame structures can have beneficial effects on structural performance. It was confirmed that the use of masonry infill panels results in an increment in strength and stiffness of the framed buildings, followed by a reduction in displacement demand for the structural systems.

Key Words
seismic strengthening; reinforced masonry infill panels; nonlinear static analysis; nonlinear incremental dynamic analysis; low- and mid-rise reinforced concrete frames

Address
Ali Massumi, Behnam Mahboubi and Mohammad Reza Ameri: Department of Civil Engineering, Faculty of Engineering, Kharazmi University, Tehran, 15719-14911, Iran

Abstract
In this article the non-linear behavior of the shear wall with low yield stress retrofitted with Glass Fiber Reinforced Polymer (GFRP) is investigated under pushover loading. The models used in this study are in 1/2 scale of one story frame and simple steel plates with low yield stress filled the frame span. The models used were simulated and analyzed using finite elements method based on experimental data. After verification of the experimental model, various parameters of the model including the number of GFRP layers, fibers positioning in one or two sides of the wall, GFRP angles in respect to the wall and thickness of the steel plate were studied. The results have shown that adding the GFRP layers, the ultimate shear capacity is increased and the amount of energy absorbed is decreased. Besides, the results showed that using these fibers in low-thickness plates is effective and if the positioning angle of the fibers on the wall is diagonal, its behavior will improve.

Key Words
steel plate shear wall; low yield stress plate; GFRP; shear capacity; energy waste

Address
S.A. Edalati: Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran

Y. Yadollahi: Department of Civil Engineering, Shomal University, Amol, Iran

I. Pakar: Young Researchers and Elite club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

M. Bayat: Department of Civil Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran

Abstract
This research aims to develop an empirical model for simulation of time-varying frequency in earthquake ground motion so as to be used easily in engineering applications. Briefly, 10545 recordings of the Next Generation Attenuation (NGA) global database of accelerograms from shallow crustal earthquakes are selected and binned by magnitude, distance and site condition. Then the wavelet spectrum of each acceleration record is calculated by using one-dimensional continuous wavelet transform, and the frequencies corresponding to the maximum values of the wavelet spectrum at a series of sampling time, named predominant frequencies, are extracted to analyze the variation of frequency content of seismic ground motions in time. And the time-variation of the predominant frequencies of 178 magnitude-distance-site bins for different directions are obtained by calculating the mean square root of predominant frequencies within a bin. The exponential trigonometric function is then use to fit the data, which describes the predominant frequency of ground-motion as a function of time with model parameters given in tables for different magnitude, distance, site conditions and direction. Finally, a practical frequency-dependent amplitude envelope function is developed based on the time-varying frequency derived in this paper, which has clear statistical parameters and can emphasize the effect of low-frequency components on later seismic action. The results illustrate that the time-varying predominant frequency can preferably reflect the non-stationarity of the frequency content in earthquake ground motions and that empirical models given in this paper facilitates the simulation of ground motions.

Key Words
earthquake ground motion; time-varying frequency; non-stationarity of frequency; empirical models; envelope function

Address
Ruifang Yu, Yanxiang Yu: Institute of Geophysics, China Earthquake Administration, Mingzu Daxue South Road No. 5, Haidian District, Beijing, 100081, China

Meiqiao Yuan: Huaian Guangan Seismic Safety Evaluation Technology Co. Ltd., Huaihai Road 254, Qinghe District, Huai\'an, Jiangsu, 223001, China

Abstract
Vertical earthquake ground motion may magnify vertical dynamic responses of structures, and thus cause serious damage to bridges. As main support structures, piers and bearings play an important role in vertical seismic response analysis of girder bridges. In this study, the pier and bearing are simplified as a vertical series spring system without mass. Then, based on the assumption of small displacement, the equation of motion governing the simply-supported straight girder bridge under vertical ground motion is established including effects of vertical deformation of support structures. Considering boundary conditions, the differential quadrature method (DQM) is applied to discretize the above equation of motion into a MDOF (multi-degree-of-freedom) system. Then seismic responses of this MDOF system are calculated by a step-by-step integration method. Effects of support structures on vertical dynamic responses of girder bridges are studied under different vertical strong earthquake motions. Results indicate that support structures may remarkably increase or decrease vertical seismic responses of girder bridges. So it is of great importance to consider effects of support structures in structural seismic design of girder bridges in nearfault region. Finally, optimization of support structures to resist vertical strong earthquake motions is discussed.

Key Words
vertical seismic response; girder bridge; support structure; pier; bearing; earthquake ground motion; differential quadrature method

Address
Tong Wang: College of Civil Engineering, Shanghai Normal University, Shanghai 201418, China

Hongjing Li: College of Civil Engineering, Nanjing Tech University, Nanjing 211800, China

Tong Wang, Yaojun Ge: Department of Bridge Engineering, Tongji University, Shanghai 200092, China

Abstract
The yielding mechanisms of reinforced concrete (RC) structures are the main cause of the collapse of RC buildings during earthquake excitation. Nowadays, the application of earthquake energy dissipation devices, such as viscous dampers (VDs), is being widely considered to protect RC structures which are designed to withstand severe seismic loads. However, the effect of VDs on the formation of plastic hinges and the yielding criteria of RC members has not been investigated extensively, due to the lack of an analytical model and a numerical means to evaluate the seismic response of structures. Therefore, this paper offers a comprehensive investigation of how damper devices influence the yielding mechanisms of RC buildings subjected to seismic excitation. For this purpose, adapting the Newmark method, a finite element algorithm was developed for the nonlinear dynamic analysis of reinforced concrete buildings equipped with VDs that are subjected to earthquake. A special finite element computer program was codified based on the developed algorithm. Finally, a parametric study was conducted for a three-story RC building equipped with supplementary VD devices, performing a nonlinear analysis in order to evaluate its effect on seismic damage and on the response of the structure. The results of this study showed that implementing VDs substantially changes the mechanism and formation of plastic hinges in RC buildings.

Key Words
earthquake; reinforce concrete; viscous damper; seismic damage; yield surface; finite element

Address
Farzad Hejazi, Mohammad Dalili Shoaei, Mohd Saleh Jaafar and Raizal Saiful Bin Muhammad Rashid: Department of Civil Engineering, University Putra Malaysia, 43400, Selangor, Malaysia

Farzad Hejazi, Mohammad Dalili Shoaei, Mohd Saleh Jaafar and Raizal Saiful Bin Muhammad Rashid: Housing Research Centre, Faculty of Engineering, UPM, 43400, Selangor, Malaysia

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