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CONTENTS
Volume 20, Number 4, April 2021
 


Abstract
Rammed earth (RE) buildings have existed all over the world for thousands of years, and have gained increasing attention because of its sustainable advantages, however, the shrinkage cracks reduce its bearing capacity and seriously affect its durability and applicability. In this study, the shrinkage cracks test was carried out to investigate the effects of initial water content, proportion of sand and gravel, compaction degree, thickness and the additives (polypropylene fiber, cement and sodium silicate) of shrinkage cracks in RE buildings, ten groups of RE samples were prepared and dried outdoors to crack. Four quantitative parameters of geometrical structure of crack patterns were used to evaluate the development of cracks. The results show that the specimens cracking behavior and the geometrical structure of crack patterns are significantly influenced by these considered factors. The formation of crack can be accelerated with the increase of initial water content and thickness of specimen, while restricted with the increase of the compaction degree and the proportion of sand and gravel. Moreover, the addition of 1% polypropylene fiber, 10% cement and 0.5 volume ratio sodium silicate can significantly restrain the form and development of cracks. In RE construction, these factors should be considered comprehensively to prevent the harm caused by shrinkage cracks. Further works should be carried out to obtain the optimum dosage of the additives, which can benefit the construction of RE buildings in future.

Key Words
rammed earth; shrinkage cracks; influencing factors; thickness; fiber; cement

Address
Xiang Zhao:School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China

Hengli Cai:School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China

Tiegang Zhou:School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China

Ling Liu:School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China

Yijie Ding:School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China


Abstract
Thin perforated Steel Plate Shear Walls (SPSWs) are among the most common types of seismic energy dissipation systems to protect the main boundary components of SPSWs from fatal fractures in the high-risk zones. In this paper, the cyclic behavior of the different circular hole patterns under cyclic loading is reported. Based on the experimental results, it can be concluded that a change in the perforation pattern of the circular holes leads to a change in the locations of the fracture tendency over the web plate, especially at the plate-frame interactions. Accordingly, the cyclic responses of the tested specimens were simulated by finite element method using the ABAQUS package. Likewise, perforated shear panels with a new perforation pattern obtained by implementing Topology Optimization (TO) were proposed. It was found that the ultimate shear strength of the specimen with the proposed TO perforation pattern was higher than that of the other specimens. In addition, theoretical equations using the Plate-Frame Interaction (PFI) method were used to predict the shear strength and initial stiffness of the considered specimens. The theoretical results showed that the proposed reduced coefficients relationships cannot accurately predict the shear strength and initial stiffness of the considered perforated shear panels. Therefore, the reduced coefficients should be adopted in the theoretical equations based on the obtained experimental and numerical results. Finally, with the results of this study, the shear strength and initial stiffness of these types of perforated shear panels can be predicted by PFI method.

Key Words
steel plate shear panels; perforated pattern; finite element analysis; fracture tendency; topology optimization

Address
H. Monsef Ahmadi:Civil Engineering Department, Urmia University, Urmia, Iran

M.R. Sheidaii:Civil Engineering Department, Urmia University, Urmia, Iran

S. Tariverdilo:Civil Engineering Department, Urmia University, Urmia, Iran

A. Formisano :Department of Structures for Engineering and Architecture, University of Naples

Abstract
Skewed bridges, being irregular structures with complicated dynamic behavior, are more susceptible to earthquake damage. Reliable seismic-resistant design of skewed bridges can be achieved by accurate determination of nonlinear seismic demands. However, the effect of geometric characteristics on the response modification factor (R-factor) is not accounted for in bridge design practices. This study attempts to investigate the effects of changes in the number of spans, skew angle and bearing stiffness on R-factor values and to assess the seismic fragility of skewed bridges. Results indicated that changes in the skew angle had no significant effect on R-factor values which were in consonance with code-prescribed R values. Also, unlike the increase in the number of spans that resulted in a decrease in the R-factor, the increase in bearing stiffness led to higher R-factor values. Findings of the fragility analysis implied that although the increase in the number of spans, as well as the increase in the skew angle, led to a higher failure probability, greater values of bearing stiffness reduced the collapse probability. For practicing design engineers, it is recommended that maximum demands on substructure elements to be calculated when the excitation angle is applied along the principal axes of skewed bridges.

Key Words
Skewed Bridge; Response Modification Factor (R-factor); fragility assessment; Elastomeric Rubber Bearing (ERB); Incremental Dynamic Analysis (IDA); seismic excitation angle

Address
Amir Khorraminejad:Department of Civil Engineering, Shahid Beheshti University, Tehran, Iran/Department of Infrastructure Engineering, University of Melbourne, VIC, Australia

Parshan Sedaghati:Department of Civil Engineering, Semnan University, Semnan, Iran/ Department of Infrastructure Engineering, University of Melbourne, VIC, Australia

Greg Foliente: Department of Infrastructure Engineering, University of Melbourne, VIC, Australia

Abstract
Following the dynamic property analysis and elaboration, linear response spectrum analysis (RSA) and response history analysis (RHA) were conducted on a representative hyperbolic cooling towers (HCT) in present study. The seismic responses in tower shell were illustrated in detail, including the internal force amplitude, modal contribution, influence from damping ratio, comparison of results got from RSA and RHA and especially the latitude distributions of internal forces. The results show that the eigenmodes could be classified in a new method into four types according to their mode shapes and only the lateral bending modes and vertical stretching modes are meaningful for horizontal and vertical earthquake correspondingly. The bending modes and seismic deformation display the same feature which is global lateral bending accompanied by minute circular flow displacement of section. This feature also decides the latitude distributions of internal forces as sine or cosine. Moreover, the following method is also proposed for approximate estimation of internal force amplitudes without time-consuming response history analysis: getting the response spectrums of the selected ground accelerations and then comparing values of response spectrums at the natural period of first lateral bending mode because it is always prime dominant for horizontal seismic responses.

Key Words
hyperbolic cooling towers; dynamic property feature; horizontal earthquakes; vertical earthquakes; response spectrum analysis; response history analysis; modal contribution latitude distributions of internal forces

Address
Jun-Feng Zhang:School of Civil Engineering, Zhengzhou University, Zhengzhou 450001, China

Yuan-Hao Wang:School of Civil Engineering, Zhengzhou University, Zhengzhou 450001, China

Jie Li:School of Civil Engineering, Zhengzhou University, Zhengzhou 450001, China

Lin Zhao:State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
Due to functional requirements, SRC column-RC beam abnormal joints with characteristics of strong beam weak column, variable column section, unequal beam height and staggered height exist in the Steel reinforced concrete (SRC) frame-bent main building structure of thermal power plant (TPP). This paper presents the experimental results of these abnormal joints through cyclic loading tests on five specimens with scaling factor of 1/5. The staggered height and whether adding H-shaped steel in beam or not were changing parameters of specimens. The failure patterns, bearing capacity, energy dissipation and ductile performance were analyzed. In addition, the stress mechanism of the abnormal joint was discussed based on the diagonal strut model. The research results showed that the abnormal exterior joints occurred shear failure and column end hinge flexural failure; reducing beam height through adding H-shaped steel in the beam of abnormal exterior joint could improve the crack resistance and ductility; the abnormal interior joints with different staggered heights occurred column ends flexural failure; the joint with larger staggered height had the higher bearing capacity and stiffness, but lower ductility. The concrete compression strut mechanism is still applicable to the abnormal joints in TPP, but it is affected by the abnormal characteristics.

Key Words
thermal power plant; steel-concrete hybrid structure; abnormal joint; cyclic loading test; seismic behavior; stress mechanism

Address
Bo Wan:School of Civil Engineering, Chang'an University, Xi'an 710061, China

Guorong Cao:School of Civil Engineering, Chang'an University, Xi'an 710061, China

Ke Yang:School of Civil Engineering, Chang'an University, Xi'an 710061, China

Huijuan Dai:School of Civil Engineering, Xi'an University of Science and Technology, Xi'an 710054, China

Chaogang Qin:School of Civil Engineering, Chang'an University, Xi'an 710061, China

Abstract
T-shaped column is usually used as side column in buildings, which is one of the weak members in structural system. This paper presented a quasi-static cyclic loading experiment of six specimens of reinforced concrete (RC) T-shaped columns under compression-flexure-shear-torsion combined loadings to investigate the effect in the ratio of torsion to moment (T/M) and axial compression ratio (n) and height-thickness ratio of flange plate (Φ) on their seismic performance. Based on the test results, the failure characteristics, hysteretic curves, ductility, energy dissipation, stiffness degradation and strength degradation were analyzed. The results show that the failure characteristics of RC T-shaped columns mainly depend on the ratio of torsion to moment, which can be divided into bending failure, bending-torsion failure and shear-torsion failure. With the increase of T/M ratio, the torsion ductility coefficient increased, and in a suitable range, the torsion and horizontal displacement ductility coefficient of RC T-shaped columns could be effectively improved with the increase of axial compression ratio and the decrease of height-thickness ratio of flange plate. Besides, the energy dissipation capacity of the specimens mainly depended on the bending and shear energy dissipation capacity. On the other hand, the increase of axial compression ratio and the ratio of torsion to moment could accelerate the torsional and bending stiffness degradation of RC T-shaped columns. Moreover, the degradation coefficient of torsion strength was between 0.80 and 0.98, and that of bending strength was between 0.75 and 1.00.

Key Words
T-shaped column; reinforced concrete (RC); compression-bending-shear-torsion; seismic performance

Address
Chen Zong Ping:College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China/ Key Laboratory of Disaster Prevention and Structure Safety of Chinese Ministry of Education, Guangxi University, Nanning 530004, China

Su Weiwei:College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China

Yang Yang:College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China

Abstract
Lake Van Basin, located in Eastern Turkey, is worth examining in terms of seismicity due to large-scale losses of property and life during the historical and instrumental period. The most important and largest province in this basin is Van. Recent indicators of the high seismicity risk in the province are damage occurring after devastating earthquakes in 2011 (Mw=7.2 and Mw=5.6) and lastly in 2020 Khoy (Mw=5.9). The seismic hazard analysis for Van and its districts in Eastern Turkey was performed in probabilistic manner. Analyses were made for thirteen different districts in Van. In this study, information is given about the tectonic setting and seismicity of Van. The probabilistic seismic hazard curves were obtained for a probability of exceedance of 2%, 10% and 50% in 50-year periods. The PGA values in the Van province vary from 0.24 g – 0.43 g for earthquakes with repetition period of 475 years. Risk priorities were determined for all districts. The highest risk was calculated for Caldiran and the lowest risk was found for Gurpinar. Risk priorities for buildings in all districts were also determined via rapid seismic assessment for reinforced-concrete and masonry buildings in this study.

Key Words
seismic hazard; risk priority; rapid assessment; Lake Van; micro scale

Address
Aydin Buyuksarac:Can Vocational School, Canakkale Onsekizmart University, TR-17100, Canakkale-Turkey

Ercan Isik:Department of Civil Engineering, Faculty of Engineering and Architecture, Bitlis Eren University, TR-13100, Bitlis, Turkey

Ehsan Harirchian:Institute of Structural Mechanics (ISM), Bauhaus-Universitat Weimar, 99423 Weimar, Germany

Abstract
This study aims at providing a simple and effective methodology to define a meaningful characteristic period for special class of earthquake records named "pulse-like ground motions". In the proposed method, continuous wavelet transform is employed to extract the large pulse of ground motions. Then, Fourier amplitude spectra obtained from the original ground motion and the residual motion is simply compared. This comparison permits to define a threshold pulse-period (𝑇𝑝∗) as the threshold period above which the pulse component has negligible contributions to the Fourier amplitude spectrum. The effect of pulse on frequency content of motions was discussed on the light of this definition. The advantage and superior features of the new definition were related to the inelastic displacement ratio (IDR) for single-degree-of-freedom systems with period equal to one half of the threshold period. Analyses performed for the proposed period at three ductility levels u=2,4,6 were compared with the results obtained at half of pulse period derived from wavelet analysis, peak-point method and the peak of product of the velocity and the displacement response spectra (Sv x Sd). According to the results, pulse effects on inelastic displacement ratio seem to be more important when 𝑇𝑝∗𝑇=2 (T is the fundamental vibration period of system). The results showed that utilizing of the proposed definition could facilitate an enhanced understanding of pulse-like records features.

Key Words
pulse-like motions; characteristic period; pulse period; fourier amplitude spectrum; wavelet transform

Address
Saman Yaghmaei-Sabegh:Department of Civil Engineering, University of Tabriz, Tabriz, Iran


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