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CONTENTS
Volume 13, Number 6, December 2017
 

Abstract
The surrounding rocks of underground openings are natural materials and their mechanical behavior under seismic load is different from traditional man-made materials. This paper proposes a framework to comprehensively model the mechanical behavior of surrounding rocks. Firstly, the effects of seismic load on the surrounding rocks are summarized. Three mechanical effects and the mechanism, including the strengthening effect, the degradation effect, and the relaxation effect, are detailed, respectively. Then, the framework for modelling the mechanical behavior of surrounding rocks are outlined. The straindependent characteristics of rocks under seismic load is considered to model the strengthening effect. The damage concept under cyclic load is introduced to model the degradation effect. The quantitative relationship between the damage coefficient and the relaxation zone is established to model the relaxation effect. The major effects caused by seismic load, in this way, are all considered in the proposed framework. Afterwards, an independently developed 3D dynamic FEM analysis code is adopted to include the algorithms and models of the framework. Finally, the proposed framework is illustrated with its application to an underground opening subjected to earthquake impact. The calculation results and post-earthquake survey conclusions are seen to agree well, indicating the effectiveness of the proposed framework. Based on the numerical calculation results, post-earthquake reinforcement measures are suggested.

Key Words
rock material; material strengthening; material degradation; relaxation zone; earthquake effect; numerical analysis

Address
Yuting Zhang, Xiuli Ding, Shuling Huang, Qitao Pei and Yongjin Wu : Key Laboratory of Geotechnical Mechanics and Engineering of the Ministry ofWater Resources,
Yangtze River Scientific Research Institute,Wuhan, Hubei 430010, China

Abstract
In this paper, the seismic behavior of BRBF structures is studied and compared with special concentric braced frames (SCBF). To this purpose, three BRBF and three SCBF structures with 3, 5 and 10 stories are designed based on AISC360-5 and modelled using OpenSees. These structures are loaded in accordance with ASCE/SEI 7-10. Incremental nonlinear dynamic analysis (IDA) are performed on these structures for 28 different accelerograms and the median IDA curves are used to compare seismic capacity of these two systems. Results obtained, indicates that BRBF systems provide higher capacity for the target performance level in comparison with SCBF systems. And structures with high altitude (in this study, 5 and 10 stories) with the possibility of exceeding the collapse prevention performance level, further than lower altitude (here 3 floors) structures.

Key Words
incremental nonlinear dynamic analysis (IDA); buckling restrained braced frame (BRBF); special concentric braced frame (SCBF); seismic performance; level exceedance probability; analytical fragility curve

Address
M. Khorami : Facultad de Arquitectura y Urbanismo, Universidad Tecnológica Equinoccial, Calle Rumipamba s/n y Bourgeois, Quito, Ecuador
/Facultad de Ingeniería Civil y Ambiental, Escuela Politécnica Nacional, Ladrón de Guevara E11-253L, Quito, Ecuador
M. Khorami : Civil Engineering Department, Islamic Azad University, Tehran, Iran
M. Alvansazyazdi : Facultad Ingeniería Ciencias Físicas y Matemática, Carrera Ingeniería Civil, Universidad Central del Ecuador, Quito, Ecuador
5Facultad de Arquitectura, Universidad Laica Eloy Alfaro de Manabí, Ecuador
M. Shariati and A. Jalali : Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran
Y. Zandi : Department of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran
M.M. Tahir : UTM Construction Research Centre, Faculty of Civil Engineering, Institute for Smart Infrastructure and
Innovative Construction, UTM, 81310, Johor Bahru, Johor, Malaysia

Abstract
Existing reinforced concrete frame buildings designed for vertical loads could only suffer severe damage during earthquakes. In recent years, many research activities were undertaken to develop a reliable and practical analysis procedure to identify the safety level of existing structures. The Incremental Dynamic Analysis (IDA) is considered to be one of the most accurate methods to estimate the seismic demand and capacity of structures. However, the executions of many nonlinear response history analyses (NL_RHA) are required to describe the entire range of structural response. The research discussed in this paper deals with the proposal of an efficient Incremental Modal Pushover Analysis (IMPA) to obtain capacity curves by replacing the nonlinear response history analysis of the IDA procedure with Modal Pushover Analysis (MPA). Firstly, In this work, the MPA is examined and extended to three-dimensional asymmetric structures and then it is incorporated into the proposed procedure (IMPA) to estimate the structure‟s seismic response and capacity for given seismic actions. This new procedure, which accounts for higher mode effects, does not require the execution of complex NL-RHA, but only a series of nonlinear static analysis. Finally, the extended MPA and IMPA were applied to an existing irregular framed building.

Key Words
modal pushover analysis; existing building; capacity curve, incremental dynamic analysis

Address
A.V. Bergami, A. Forte and D. Lavorato : Department of Architecture, University of Roma Tre, Rome, Italy
C. Nuti : Department of Architecture, University of Roma Tre, Rome, Italy
/College of Civil Engineering, University of Fuzhou, Fuzhou, China

Abstract
A large number of isolation systems are designed without considering the non-uniform friction distribution in space. In order to analyze the effects of non-uniform friction distribution on the structural response of isolation system, this paper presented a simplified rolling-damper-spring isolation system and analyzed the structural responses under earthquakes. The numerical results indicate that the calculation errors related to the peak values of structural acceleration, relative displacement and residual displacement are sequentially growing because of the ignorance of non-uniform friction distribution. However, the influence rule may be weakened by the spring and damper actions, and the unreasonable spring constant may lead to the sympathetic vibration of isolation system. In the case when the friction variability is large and the damper action is little, the nonuniform friction distribution should be taken into consideration during the calculation process of the peak values of structural acceleration and relative displacement. The non-uniform friction distribution should be taken into full consideration regardless of friction variability degree in calculating the residual displacement of isolation system.

Key Words
seismic isolation; friction variability; rolling friction; spring; viscous damper

Address
Biao Wei, Peng Wang, Xuhui He and Zhen Zhang : School of Civil Engineering, Central South University, 22 Shaoshan South Road, Changsha, China
/National Engineering Laboratory for High Speed Railway Construction, 22 Shaoshan South Road, Changsha, China
Liang Chen : School of Civil Engineering, Hefei University of Technology, 193 Dunxi Road, Hefei, China

Abstract
Seismic base isolation has been accepted as one of the most popular design procedures to protect important structures against earthquakes. However, due to lack of information and experimental data the application of base isolation is quite limited to nuclear power plant (NPP) industry. Moreover, the effects of inelastic behavior of soil beneath base-isolated NPP have raised questions to the effectiveness of isolation device. This study applies the wavelet analysis to investigate the effects of soil-structure interaction (SSI) on the seismic response of a base-isolated NPP structure. To evaluate the SSI effects, the NPP structure is modelled as a lumped mass stick model and combined with a soil model using the concept of cone models. The lead rubber bearing (LRB) base isolator is used to adopt the base isolation system. The shear wave velocity of soil is varied to reflect the real rock site conditions of structure. The comparison between seismic performance of isolated structure and non-isolated structure has drawn. The results show that the wavelet analysis proves to be an efficient tool to evaluate the SSI effects on the seismic response of base-isolated structure and the seismic performance of base-isolated NPP is not sensitive to the effects in this case.

Key Words
nuclear power plant; base isolation; seismic behavior; soil-structure interaction; wavelet analysis

Address
Shafayat Bin Ali : Institute of Earthquake Engineering Research (IEER), Chittagong University of Engineering & Technology, Chittagong-4349, Bangladesh
Dookie Kim : Department of Civil and Environmental Engineering, Kunsan National University, South Korea

Abstract
The earthquake input is required when the soil-structure interaction (SSI) analysis is performed by the direct finite element method. In this paper, the earthquake is considered as the obliquely incident plane body wave arising from the truncated linearly elastic layered half space. An earthquake input method is developed for the time-domain three-dimensional SSI analysis. It consists of a new site response analysis method for free field and the viscous-spring artificial boundary condition for scattered field. The proposed earthquake input method can be implemented in the process of building finite element model of commercial software. It can result in the highly accurate solution by using a relatively small SSI model. The initial condition is considered for the nonlinear SSI analysis. The Daikai subway station is analyzed as an example. The effectiveness of the proposed earthquake input method is verified. The effect of the obliquely incident earthquake is studied.

Key Words
seismic soil-structure interaction; layered half space; oblique incidence; artificial boundary condition; site response analysis

Address
Mi Zhao, Zhidong Gao, Litao Wang, Xiuli Du, Jingqi Huang and Yang Li : Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, China
/Beijing Collaborative Innovation Center for Metropolitan Transportation, Beijing University of Technology, Beijing 100124, China

Abstract
In this paper, dynamic response of the horizontal concrete beam subjected to seismic ground excitation is investigated. The structure is reinforced by Fe2O3 nanoparticles which have the magnetic properties. The hyperbolic shear deformation beam theory (HSDBT) is used for mathematical modeling of the structure. Based on the Mori-Tanaka model, the effective material properties of concrete beam is calculated considering the agglomeration of Fe2O3 nanoparticles. Applying energy method and Hamilton\'s principle, the motion equations are derived. Harmonic differential quadrature method (HDQM) along with Newmark method is utilized for numerical solution of the motion equations. The effects of different parameters such as volume fraction and agglomeration of Fe2O3 nanoparticles, magnetic field, boundary conditions and geometrical parameters of concrete beam are studied on the dynamic response of the structure. In order to validation of this work, an exact solution is used for comparing the numerical and analytical results. The results indicated that applying magnetic field decreases the of the structure up to 54 percent. In addition, increase too much the magnetic field (Hx>5e8 A/m) does not considerable effect on the reduction of the maximum dynamic displacement.

Key Words
dynamic response; Fe2O3 nanoparticles; seismic ground excitation; HDQM; magnetic field

Address
Hossein Mohammadian, Reza Kolahchi and Mahmood Rabani Bidgoli : Department of Civil Engineering, Jasb Branch, Islamic Azad University, Jasb, Iran

Abstract
This paper improves seismic fragility of a typical steel-concrete composite bridge with the deck-to-pier connection joint configuration at the concrete crossbeam (CCB). Based on the quasi-static test on a typical steel-concrete composite bridge model under the SEQBRI project, the damage states for both of the critical components, the CCB and the pier, are identified. The finite element model is developed, and calibrated using the experimental data to model the damage states of the CCB and the bridge pier as observed from the experiment of the test specimen. Then the component fragility curves for both of the CCB and the pier are derived and combined to develop the system fragility curves of the bridge. The uncertainty associated with the mean system fragility has been discussed and quantified. The study reveals that the CCB is more vulnerable than the pier for certain damage states and the typical steel-concrete composite bridge with CCB exhibits desirable seismic performance.

Key Words
seismic fragility; steel-concrete composite bridge; quasi-static test; concrete crossbeam; damage state

Address
Yang Liu and Da-Gang Lu : School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, P.R. China
Fabrizio Paolacci : Department of Engineering, Roma Tre University, Rome, Italy

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