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CONTENTS
Volume 17, Number 6, December 2019
 

Abstract
This paper presents a study on the behavior of an RC bridge under near-field and far-field ground motions. For this purpose, a dynamic nonlinear finite element time history analysis has been conducted. The near-field and far-field records are chosen pairwise from the same events which are fits to the seismic design of the bridge. In order to perform an accurate seismic evaluation, the model has been analyzed under two vertical and horizontal components of ground motions. Parameters of relative displacement, residual displacement, and maximum plastic strain have been considered and compared in terms of nearfield and far-field ground motions. In the following, in order to decrease the undesirable effects of near-field ground motions, a viscous damper is suggested and its effects have been studied. In this case, the results show that the near-field ground motions increase maximum relative and residual displacement respectively up to three and twice times. Significant seismic improvements were achieved by using viscous dampers on the bridge model. Somehow under the considered near-field ground motion, parameters of residual and relative displacement decrease dramatically even less than the model without damper under the far-field record of the same ground motion.

Key Words
near-field and far-field; seismic behavior of RC bridge; nonlinear time history analysis; viscous damper

Address
Omid Karimzade Soureshjani and Ali Massumi: Department of Civil Engineering, Faculty of Engineering, Kharazmi University, Tehran, Iran

Abstract
Bridge piers with bending failure mode are seriously damaged only in the area of plastic hinge length in earthquakes. For this situation, a modified method for the layout of longitudinal reinforcement is presented, i.e., the number of longitudinal reinforcement is increased in the area of plastic hinge length at the bottom of piers. The quasi-static test of three scaled model piers is carried out to investigate the local longitudinal reinforcement at the bottom of the pier on the seismic performance of the pier. One of the piers is modified by increased longitudinal reinforcement at the bottom of the pier and the other two are comparative piers. The results show that the pier failure with increased longitudinal bars at the bottom is mainly concentrated at the bottom of the pier, and the vulnerable position does not transfer. The hysteretic loop curve of the pier is fuller. The bearing capacity and energy dissipation capacity is obviously improved. The bond-slip displacement between steel bar and concrete decreases slightly. The finite element simulations have been carried out by using ANSYS, and the results indicate that the seismic performance of piers with only increasing the number of steel bars (less than65%) in the plastic hinge zone can be basically equivalent to that of piers that the number of steel bars in all sections is the same as that in plastic hinge zone.

Key Words
increased longitudinal reinforcement; railway bridge piers; quasi-static test; seismic performance

Address
Jinhua Lu, Xingchong Chen, Xiyin Zhang, Zhengnan Liu and Hao Yuan: School of Civil Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, China
Mingbo Ding: School of Civil Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, China; Key Laboratory of Road and Bridge and Underground Engineering of Gansu Province, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, China

Abstract
The evaluation of the seismic hazard for a given site is to estimate the seismic ground motion at the surface. This is the result of the combination of the action of the seismic source, which generates seismic waves, the propagation of these waves between the source and the site, and site local conditions. The aim of this work is to evaluate the sensitivity of dynamic response of extended structures to spatial variable ground motions (SVGM). All factors of spatial variability of ground motion are considered, especially local site effect. In this paper, a method is presented to simulate spatially varying earthquake ground motions. The scheme for generating spatially varying ground motions is established for spatial locations on the ground surface with varying site conditions. In this proposed method, two steps are necessary. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function. An empirical coherency loss model is used to define spatial variable seismic ground motions at the base rock. In the second step, power spectral density function of ground motion on surface is derived by considering site amplification effect based on the one dimensional seismic wave propagation theory. Several dynamics analysis of a curved viaduct to various cases of spatially varying seismic ground motions are performed. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effect, to spatial ground motions with considering coherency loss, phase delay and local site effects are also calculated. The results showed that the generated seismic signals are strongly conditioned by the local site effect. In the same sense, the dynamic response of the viaduct is very sensitive of the variation of local geological conditions of the site. The effect of neglecting local site effect in dynamic analysis gives rise to a significant underestimation of the seismic demand of the structure.

Key Words
ground motion; spatial variability; simulation; wave propagation; coherency loss; local geological site effect

Address
Rachid Derbal: RISk Assesment & Management Laboratory (RISAM), University of Tlemcen, Po Box 230, Tlemcen, Algeria; Department of Civil Engineering, Ctr. Univ. Ain Temouchent, Po. Box 284, Ain Temouchent, Algeria
Nassima Benmansour, Mustapha Djafour, Mohammed Matallah: RISk Assesment & Management Laboratory (RISAM), University of Tlemcen, Po Box 230, Tlemcen, Algeria
Salvador Ivorra: Department of Civil Engineering, University of Alicante, San Vicente del Raspeig, Apartado 99, 03080, Spain


Abstract
In order to investigate the dynamic impact resistance of steel fiber reinforced full light-weight concretes, we implemented drop weight impact test on a total of 6 reinforced beams with 0, 1 and 2%, steel fiber volume fraction. The purpose of this test was to determine the failure modes of beams under different impact energies. Then, we compared and analyzed the time-history curves of impact force, midspan displacement and reinforcement strain. The obtained results indicated that the deformations of samples and their steel fibers were proportional to impact energy, impact force, and impact time. Within reasonable ranges of parameter values, the effects of impact size and impact time were similar for all volumetric contents of steel fibers, but they significantly affected the crack propagation mechanism and damage characteristics of samples. Increase of the volumetric contents of steel fibers not only effectively reduced the midspan displacement and reinforcement strain of concrete samples, but also inhibited crack initiation and propagation such that cracks were concentrated in the midspan areas of beams and the frequency of cracks at supports was reduced. As a result, the tensile strength and impact resistance of full light-weight concrete beams were significantly improved.

Key Words
steel fiber; full light-weight concrete; impact resistance; failure mode; midspan displacement; reinforcement strain

Address
Yanmin Yang, Yunke Wang, Yu Chen and Binlin Zhang: School of Civil Engineering, Jilin Jianzhu University, Changchun 130118, China

Abstract
The seismic response of structures to strong ground motions is a complex problem that has been studied for decades. However, most of current seismic regulations do not assess the potential level of damage that a structure may undergo during a strong earthquake. This will happen in spite that the design objectives for any structural system are formulated in terms of acceptable levels of damage. In this article, we analyze the expected damage in single-degree-of-freedom systems subjected to long-duration ground motions generated in soft soil sites, such as those located in the lakebed of Mexico City. An energybased methodology is formulated, under the consideration of input energy as the basis for the evaluation process, to estimate expected damage. The results of the proposed methodology are validated with damage curves established directly with nonlinear dynamic analyses.

Key Words
seismic energy; expected damage; energy-based approach

Address
Pablo Quinde, Eduardo Reinoso, Salvador Ramos: Intitute of Engineering, UNAM, Circuito Escolar, Ciudad Universitaria, 04510, CDMX, Coyoacán, México
Amador Teran-Gilmore: Departamento de Materiales, Universidad Autonoma Metropolitana, Av. San Pablo 180, Col. Reynosa Tamaulipas, 02200, México

Abstract
The most recent shaking experiences have demonstrated that the predictions of the seismic models are not always in agreement with the registered responses, especially in the face of extreme earthquakes. Records collected from 1960 to 2011 at a rock-like site are used to develop a neural network that permits to estimate peak ground accelerations via the magnitude, the focal depth, the site-source distance and a seismogenic zone. The neural model is applied to the 8th and 19th September 2017 events that hit Mexican territory and the obtained results show that the network is flexible enough to work appropriately to various conditions of intensity and sites-sources with remarkably predictive capacity. The neural-attenuation curves are compared with those obtained from Ground Motion Prediction Equations and their performance is assessed for events, in addition to the devastating Mexican events, from Japan, Taiwan, Chile and USA.

Key Words
neural networks; attenuation laws; peak ground acceleration; September 19th 2017 earthquake

Address
Silvia R. García: Geotechnical Department, Instituto de Ingeniería, Universidad Nacional Autónoma de México, México
Leonardo Alcántara: Seismology Department, Instituto de Ingeniería, Universidad Nacional Autónoma de México, México

Abstract
After an earthquake, a quick seismic assessment of a structure can facilitate the recovery of operations, and consequently, improve structural resilience. Especially for facilities that play a key role in rescue or refuge efforts (e.g., hospitals and power facilities), or even economically important facilities (e.g., high-tech factories and financial centers), immediately resuming operations after disruptions resulting from an earthquake is critical. Therefore, this study proposes a prompt postearthquake seismic evaluation method that uses displacement and acceleration measurements taken from real structural responses that resulted during an earthquake. With a prepared pre-earthquake capacity curve of a structure, the residual seismic capacity can be estimated using the residual roof drift ratio and stiffness. The proposed method was verified using a 6-story steel frame structure on a shaking table. The structure was damaged during a moderate earthquake, after which it collapsed completely during a severe earthquake. According to the experimental results, a reasonable estimation of the residual seismic capacity of structures can be performed using the proposed post-earthquake seismic evaluation method.

Key Words
capacity assessment; damage detection/assessment; earthquake/seismic response; residual displacement; stiffness degradation

Address
Ting-Yu Hsu: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan; Taiwan Building Technology Center, National Taiwan University of Science and Technology, Taipei, Taiwan
Quang-Vinh Pham: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan

Abstract
Precast concrete structure has many advantages, but the assembled seam will affect potentially the overall seismic performance of structure. Based on the sidewall joint located in the bottom of assembled monolithic subway station, the main objectives of this study are, on one hand to present an experimental campaign on the seismic behavior of precast sidewall joint (PWJ) and cast-in-place sidewall joint (CWJ) subjected to low-cycle repeated loading, and on the other hand to explore the effect of shape and position of assembled seam on load carrying capacity and crack width of precast sidewall joint. Two fullscale specimens were designed and tested. The important index of failure pattern, loading carrying capacity, deformation performance and crack width were evaluated and compared. Based on the test results, a series of different height and variablyshape of assembled seam of precast sidewall joint were considered. The test and numerical investigations indicate that, (1) the carrying capacity and deformation capacity of precast sidewall and cast-in-place sidewall were very similar, but the crack failure pattern, bending deformation and shearing deformation in the plastic hinge zone were different obviously; (2) the influence of the assembled seam should be considered when precast underground structures located in the aquifer water-bearing stratum; (3) the optimal assembled seam shape and position can be suggested for the design of precast underground concrete structures according to the analysis results.

Key Words
precast sidewall joint; low-cycle repeated loading experiment; numerical analysis; assembled seam shape; assembled seam position; seismic performance

Address
Hongtao Liu: Key Laboratory of Urban Security and Disaster Engineering of the Ministry of Education, Beijing University of Technology, Beijing 100124, China; Faculty of Construction and Environment Department of Building and Real Estate, Hong Kong Polytechnic University, Hong Kong, 999077, China
Xiuli Du: Key Laboratory of Urban Security and Disaster Engineering of the Ministry of Education, Beijing University of Technology, Beijing 100124, China

Abstract
A large number of available concrete buildings designed only considering gravity load that require seismic rehabilitation because of failure to meet plasticity criteria. Using steel bracings are a common type of seismic rehabilitation. The eccentric bracings with vertical link reduce non-elastic deformation imposed on concrete members as well as elimination of probable buckling problems of bracings. In this study, three concrete frames of 10, 15, and 20 stories designed only for gravity load have been considered for seismic improvement using performance-based plastic design. Afterwards, nonlinear time series analysis was employed to evaluate seismic behavior of the models in two modes including before and after rehabilitation. The results revealed that shear link can yield desirable performance with the least time, cost and number of bracings of concrete frames. Also, it was found that the seismic rehabilitation can reduce maximum relative displacement in the middle stories about 40 to 80 percent. Generally, findings of this study demonstrated that the eccentric bracing with vertical link can be employed as a suitable proxy to achieve better seismic performance for existing high rise concrete frames.

Key Words
concrete frame; seismic parameters; shear link; eccentric bracing; finite element; rehabilitation

Address
Rouhina Karimi and Sepideh Rahimi: School of Civil Engineering, Islamic Azad University, Nour Branch, Nour, Mazandaran, Iran

Abstract
Tests and theoretical studies for seismic responses of a transmission tower-line system under coupled horizontal and tilt (CHT) ground motion were conducted. The method of obtaining the tilt component from seismic motion was based on comparisons from the Fourier spectrum of uncorrected seismic waves. The collected data were then applied in testing and theoretical analysis. Taking an actual transmission tower-line system as the prototype, shaking table tests of the scale model of a single transmission tower and towers-line systems under horizontal, tilt, and CHT ground motions were carried out. Dynamic equations under CHT ground motion were also derived. The additional P-A effect caused by tilt motion was considered as an equivalent horizontal lateral force, and it was added into the equations as the excitation. Test results were compared with the theoretical analysis and indicated some useful conclusions. First, the shaking table test results are consistent with the theoretical analysis from improved dynamic equations and proved its correctness. Second, the tilt component of ground motion has great influence on the seismic response of the transmission tower-line system, and the additional P-Aeffect caused by the foundation tilt, not only increases the seismic response of the transmission tower-line system, but also leads to a remarkable asymmetric displacement effect. Third, for the tower-line system, transmission lines under ground motion weaken the horizontal displacement and acceleration responses of transmission towers. This weakening effect of transmission lines to the main structure, however, will be decreased with consideration of tilt component.

Key Words
transmission tower-line system; tilt ground motion; foundation tilt; shaking table test

Address
Wenhui Wei, Ying Hu, Hao Wang: Hubei Key Lab. of Road Bridge and Structure Engineering, Wuhan University of Technology, Wuhan, Hubei, China
YongLin Pi: Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering,
UNSW Australia, UNSW Sydney, NSW 2052, Australia


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