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CONTENTS
Volume 15, Number 6, December 2018
 

Abstract
Seismic performance is particularly important for life-line structures, especially for long-span transmission tower line system subjected to multi-component ground motions. However, the influence of multi-component seismic loads and the coupling effect between supporting towers and transmission lines are not taken into consideration in the current seismic design specifications. In this research, shake table tests are conducted to investigate the performance of long-span transmission towerline system under multi-component seismic excitations. For reproducing the genuine structural responses, the reduced-scale experimental model of the prototype is designed and constructed based on the Buckingham\'s theorem. And three commonly used seismic records are selected as the input ground motions according to the site soil condition of supporting towers. In order to compare the experimental results, the dynamic responses of transmission tower-line system subjected to single-component and two-component ground motions are also studied using shake table tests. Furthermore, an empirical model is proposed to evaluate the acceleration and member stress responses of transmission tower-line system subjected to multi-component ground motions. The results demonstrate that the ground motions with multi-components can amplify the dynamic response of transmission tower-line system, and transmission lines have a significant influence on the structural response and should not be neglected in seismic analysis. The experimental results can provide a reference for the seismic design and analysis of long-span transmission tower-line system subjected to multi-component ground motions.

Key Words
long-span transmission tower-line system; shake table tests; multi-component ground motions; empirical model

Address
Li Tian, Ruisheng Ma, Canxing Qiu, Aiqiang Xin, Haiyang Pan: School of Civil Engineering, Shandong University, Jinan, Shandong, 250061, China
Wei Guo: School of Civil Engineering, Central South University, Changsha, Hunan, 410075, China

Abstract
Shake table testing has been regarded as one of the most effective experimental approaches to evaluate seismic response of structural systems subjected to earthquakes. However, reproducing a prescribed acceleration time history precisely over the frequency of interest is challenging because shake table test systems are eventually nonlinear by nature. In addition, interaction between the table and specimen could affect the control accuracy of shake table testing significantly. Various novel control algorithms have been proposed to improve the control accuracy of shake table testing; however, reference values for control performance assessment remain rare. In this study, reference values for control performance assessment of shake table testing are specified based on the statistical analyses of 1,209 experimental data provided by the Seismic Simulator Laboratory of National Center for Research on Earthquake Engineering in Taiwan. Three individual reference values are considered for the assessment including the root-mean-square error of the achieved acceleration time history; the percentage of the spectral acceleration that exceeds the determined tolerance range over the frequency of interest; and the error-ratio of the achieved peak ground acceleration. Quartiles of the real experimental data in terms of the three objective variables are obtained, providing users with solid and simple references to evaluate the control performance of shake table testing. Finally, a set of experimental data of a newly developed control framework implementation for uni-axial shake tables are used as an application example to demonstrate the significant improvement of control accuracy according to the reference values provided in this study.

Key Words
seismic shake table; performance assessment; root-mean-square error; spectral acceleration; peak ground acceleration

Address
Pei-Ching Chen: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, No.43, Sec.4, Keelung Rd., Taipei 10607, Taiwan
Meng-Kwee Kek, Yu-Wei Hu: Department of Civil Engineering, National Taiwan University, No.1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
Chin-Ta Lai: National Center for Research on Earthquake Engineering, National Applied Research Laboratories, No.200, Sec. 3, HsinHai Rd., Taipei 10668, Taiwan

Abstract
In this paper, an extended Cloud analysis method is developed for seismic fragility assessment of existing highway bridges in the southeast Queensland region. This method extends the original Cloud analysis dataset by performing scaled Cloud analyses. The original and scaled Cloud datasets are then paired to generate seismic fragility curves. The seismic hazard in this region is critically reviewed, and the ground motion records are selected for the time-history analysis based on various record selection criteria. A parametric highway bridge model is developed in the OpenSees analysis software, and a sampling technique is employed to quantify the uncertainties of highway bridges ubiquitous in this region. Technical recommendations are also given for the seismic performance evaluation of highway bridges in such low-to-moderate seismic zones. Finally, a probabilistic fragility study is conducted by performing a total of 8000 time-history analyses and representative bridge fragility curves are generated. It is illustrated that the seismic fragility curves generated by the proposed extended Cloud analysis method are in close agreement with those which are obtained by the rigorous incremental dynamic analysis method. Also, it reveals that more than 50% of highway bridges existing in southeast Queensland will be damaged subject to a peak ground acceleration of 0.14 g.

Key Words
fragility curve; highway bridge; Southeast Queensland; seismic hazard; ground motion record; bridge performance level; time-history analysis; failure probability

Address
Mohammad Ghalami Sfahani and Hong Guan: Griffith School of Engineering and Built Environment, Griffith University Gold Coast Campus, Queensland 4222, Australia

Abstract
After earthquakes FRP sheets are often used for the rehabilitation of damaged Reinforced Concrete (RC) beamcolumn connections. Connections with minor to moderate damage are often dealt with by applying FRP sheets after a superficial repair of the cracks using resin paste or high strength mortar but without infusion of thin resin solution under pressure into the cracking system. This technique is usually adopted in these cases due to the fast and easy-to-apply procedure. The experimental investigation reported herein aims at evaluating the effectiveness of repairing the damaged beam-column connections using FRP sheets after a meticulous but superficial repair of their cracking system using resin paste. The investigation comprises experimental results of 10 full scale beam-column joint specimens; five original joints and the corresponding retrofitted ones. The repair technique has been applied to RC joints with different joint reinforcement arrangements with minor to severe damage brought about by cyclic loading for the purposes of this work. Aiming at quantitative concluding remarks about the effectiveness of the repair technique, data concerning response loads, loading stiffness and energy absorption values have been acquired and commented upon. Furthermore, comparisons of damage index values and values of equivalent viscous damping, as obtained during the test of the original specimens, with the corresponding ones observed in the loading of the repaired ones have also been evaluated and commented. Based on these comparisons, it is deduced that the technique under investigation can be considered to be a rather satisfactory repair technique for joints with minor to moderate damage taking into account the rapid, convenient and easy-to-apply character of its application.

Key Words
retrofit/repair; earthquake damage; reinforced concrete; beam-column joints; FRP sheets

Address
Chris G. Karayannis and Emmanuil Golias: Department of Civil Engineering, Democritus University of Thrace, Xanthi 67100, Greece

Abstract
In recent years, selection of strong ground motion records by means of intensity measures representing the spectral shape of the earthquake excitation has been studied by many researchers. These studies indicate the adequacy of this record selection approach in reduction of the scattering of seismic responses. In present study, this method has been studied more in depth to reveal the sufficiency of the spectral shape in predicting structural seismic responses such as the plastic deformation and the dissipated hysteresis energy which are associated with cumulative properties of the selected records. For this purpose, after selecting the records based on the spectral shape, the correlation of some seismic responses and strong ground motion duration of earthquake records are explored. Findings indicate strong correlation of some structural responses with the significant duration of the records. This fact implies that the spectral shape could not reflect all characteristics of the strong ground motion and emphasizes the importance of additional criteria along with the spectral shape in the record selection.

Key Words
intensity measure; spectral shape; sufficiency; significant duration

Address
Gholamreza Abdollahzadeh and Mohammad Sazjini: Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

Abstract
Rocking motion have been used for achieving the \'resilient buildings\' against earthquakes in recent studies. Lowrise buildings, unlike the tall ones, because of their small aspect ratio tend to slide rather than move in rocking mode. However, since rocking is more effective in seismic response reduction than sliding, it is desired to create rocking motion in low-rise buildings too. One way for this purpose is making the building\'s structure rock on its internal bay(s) by reducing the number of bays at the lower part of the building\'s skeleton, giving it a mushroom form. In this study \'mushroom skeleton\' has been used for creating multi-story rocking regular steel buildings with square plan to rock on its one-by-one bay central lowest story. To show if this idea is effective, a set of mushroom buildings have been considered, and their seismic responses have been compared with those of their conventional counterparts, designed based on a conventional code. Also, a set of similar buildings with skeleton stronger than code requirement, to have immediate occupancy (IO) performance level, have been considered for comparison. Seismic responses, obtained by nonlinear time history analyses, using scaled three-dimensional accelerograms of selected earthquakes, show that by using appropriate \'mushroom skeleton\' the seismic performance of buildings is upgraded to mostly IO level, while all of the conventional buildings experience collapse prevention (CP) level or beyond. The strong-skeleton buildings mostly present IO performance level as well, however, their base shear and absolute acceleration responses are much higher than the mushroom buildings.

Key Words
resilient building; directed-damage design; mushroom skeleton; energy dissipators; seismic performance level; nonlinear time history analyses

Address
Vahid Mahdavi: Department of Civil Engineering, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
Mahmood Hosseini: Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES),Tehran, Iran
Alireza Gharighoran: Faculty of Civil and Transportation Engineering, University of Isfahan, Isfahan, Iran

Abstract
Shield tunnels are widely used throughout the world. However, their seismic performance has not been well studied. This paper focuses on the seismic response of a large scale model tunnel in compacted sand. A9.3 m long, 3.7 m wide and 2.5 m high rigid box was filled with sand so as to simulate the sandy soil surrounding the tunnel. The setup was excited on a largescale shake table. The model tunnel used was a 1:8 scaled model with a cross-sectional diameter of 900 mm. The effective shock absorbing layer (SAL) on the seismic response of the model tunnel was also investigated. The thickness of the tunnel lining is 60 mm. The earthquake motion recorded from the Kobe earthquake waves was used. The ground motions were scaled to have the same peak accelerations. A total of three peak accelerations were considered (i.e., 0.1 g, 0.2 g and 0.4 g). During the tests, the strain, acceleration and soil pressure on the surface of the tunnel were measured. In order to investigate the effect of shock absorbing layer on the dynamic response of the sand- tunnel system, two tunnel models were set up, one with and one without the shock absorbing layer of foam board were used. The results shows the longitudinal direction acceleration of the model tunnel with a shock absorbing layer were lower than those of model tunnel without the shock absorbing layer, Which indicates that the shock absorbing layer has a beneficial effect on the acceleration reduction. In addition, the shock absorbing layer has influence on the hoop strain and earth pressure of the model tunnel, this the effect of shock absorbing layer to the model tunnel will be discussed in the paper.

Key Words
large-scale model tunnel; double shake table test; dynamic soil pressure; shock absorbing layer

Address
Hao Zhou, Xinghua Wang and Yan Liang: Department of Civil Engineering, Central South University, Changsha 410075, China
Xiaoyang Qin: Department of Civil and Environmental Engineering, University of Auckland, New Zealand

Abstract
In eccentrically braced steel frames (EBFs), the links are fuse members which enter inelastic phase before other structure members and dissipate the seismic energy. Based on the force-based seismic design method, damages and plastic deformations are limited to the links, and the main structure members are required tremendous sizes to ensure elastic with limited or no damage. Force-based seismic design method is very common and is found in most design codes, it is unable to determine the inelastic response of the structure and the damages of the members. Nowadays, methods of seismic design are emphasizing more on performance-based seismic design concept to have a more realistic assessment of the inelastic response of the structure. Links use ordinary steel Q345 (the nominal yielding strength fy>=345 MPa) while other members use high strength steel (Q460 fy>=460 MPa or Q690 fy>=690 MPa) in eccentrically braced frames with high strength steel combination (HSS-EBFs). The application of high strength steels brings out many advantages, including higher safety ensured by higher strength in elastic state, better economy which results from the smaller member size and structural weight as well as the corresponding welding work, and most importantly, the application of high strength steel in seismic fortification zone, which is helpful to popularize the extensive use of high strength steel. In order to comparison seismic behavior between HSS-EBFs and ordinary EBFs, on the basis of experimental study, four structures with 5, 10, 15 and 20 stories were designed by PBSD method for HSS-EBFs and ordinary EBFs. Nonlinear static and dynamic analysis is applied to all designs. The loading capacity, lateral stiffness, ductility and story drifts and failure mode under rare earthquake of the designs are compared. Analyses results indicated that HSS-EBFs have similar loading capacity with ordinary EBFs while the lateral stiffness and ductility of HSS-EBFs is lower than that of EBFs. HSS-EBFs and ordinary EBFs designed by PBSD method have the similar failure mode and story drift distribution under rare earthquake, the steel weight of HSS-EBFs is 10%-15% lower than ordinary EBFs resulting in good economic efficiency.

Key Words
Eccentrically Braced Frames (EBFs); high strength steel; performance-based seismic design (PBSD); story drifts; failure mode

Address
Shen Li, Chao-yu Wang, Xiao-lei Li: School of Civil Engineering and architecture, Xi\'an University of Technology, Xi\'an 710048, China
Zheng Jian, Jian-bo Tian: State Key Laboratory Base of Eco-hydraulic Engineering in Arid Area, Xi\'an University of Technology, Xi\'an 710048, China

Abstract
This paper investigates the pseudo-static analysis of reinforced slopes with geosynthetics under the influence of the uniform surcharge to evaluate the maximum tensile force of reinforcements. The analytical approach has basically been used to develop the new practical procedure to estimate both tensile force and its distribution in the height of the slope. The base of developed relationships has been adapted from the conventional horizontal slice method. The limit equilibrium framework and the assumptions of log-spiral failure surface have directly been used for proposed analytical approach. A new analytical approach considering a single layer of non-cohesion soil and the influence of uniform surcharge has been extracted from the 5n equation and 5n unknown parameters. Results of the proposed method illustrated that the location of the surcharge, amount of internal friction and the seismic coefficient have the remarkable effect on the tensile force of reinforcement and might be 2 times increasing on it. Furthermore, outcomes show that the amount of tensile force has directly until 2 times related to the amount of slope angle and its height range. Likewise, it is observed that the highest value of the tensile force in case of slope degree more than 60-degree is observed on the lower layers. While in case of less degree the highest amount of tensile force has been reported on the middle layers and extremely depended to the seismic coefficient. Hence, it has been shown that the tensile force has increased more than 6 times compared with the static condition. The obtained results of the developed procedure were compared with the outcomes of the previous research. A good agreement has been illustrated between the amount results of developed relationships and outcomes of previous research. Maximum 20 and 25 percent difference have been reported in cases of static and seismic condition respectively.

Key Words
analytical method; geosynthetics; tensile force; slope; seismic

Address
Ali Tafreshi Motlagh, Ali Ghanbari: Faculty of Civil Engineering, Department of Engineering, Kharazmi University, Tehran, Iran
Pouyan Abbasi Maedeh, Wei Wu: Institute of Geotechnical Engineering, University of Natural Resources and Life Science, Vienna, Austria

Abstract
Many bridges in Algeria were constructed without taking into account the seismic effect in the design. The implantation of a new regulation code RPOA-2008 requires a higher reinforcement ratio than with the seismic coefficient method, which is a common feature of the existing bridges. For better perception of the performance bridge piers and evaluation of the risk assessment of existing bridges, fragility analysis is an interesting tool to assess the vulnerability study of these structures. This paper presents a comparative performance of bridge piers designed with the seismic coefficient method and the new RPOA-2008. The performances of the designed bridge piers are assessed using thirty ground motion records and incremental dynamic analysis. Fragility curves for the bridge piers are plotted using probabilistic seismic demand model to perform the seismic vulnerability analysis. The impact of changing the reinforcement strength on the seismic behavior of the designed bridge piers is checked by fragility analysis. The fragility results reveal that the probability of damage with the RPOA-2008 is less and perform well comparing to the conventional design pier.

Key Words
fragility curves; seismic performance; damage states; vulnerability; pier bridge

Address
Fouad Kehila, Abderrahmane Kibboua, Hakim Bechtoula and Mustapha Remki: Department of Civil Engineering, National Earthquake Engineering Research Center CGS, 01 Rue Kaddour RAHIM, BP 252, Hussein Dey, Algiers, Algeria


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