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Volume 31, Number 6, June25 2019

In Special Concentrically Braced Frames (SCBFs), vertical and horizontal components of the brace force must be resisted by column and beam, respectively but normal force component existing at the gusset plate-to-column and beam interfaces, creates out-of-plane action making distortion in column and beam faces adjacent to the gusset plate. It is a main concern in Hollow Structural Section (HSS) columns and beams where their webs and gusset plate are not in the same plane. In this paper, a new gusset plate passing through the HSS columns and beams, named as through gusset plate, is proposed to study the force transfer mechanism in such gusset plates of SCBFs compared to the case with conventional gusset plates. For this purpose, twelve SCBFs with diagonal brace and HSS columns and twelve SCBFs with chevron brace and HSS columns and beams are considered. For each frame, two cases are considered, one with through gusset plates and the other with conventional ones. Based on numerical results, using through gusset plates prevents distortion and out-of-plane deformation at HSS column and beam faces adjacent to the gusset plate helping the entire column and beam cross-sections to resist respectively vertical and horizontal components of the brace force. Moreover, its application increases energy dissipation, lateral stiffness and strength around 28%, 40% and 32%, respectively, improving connection behavior and raising the resistance of the normal force components at the gusset plate-to-HSS column and beam interfaces to approximately 4 and 3.5 times, respectively. Finally, using such through gusset plates leads to better structural performance particularly for HSS columns and beams with larger width-to-thickness ratio elements.

Key Words
through gusset plate; force transfer mechanism; special concentrically braced frame; HSS column and beams

(1) S. Ebrahimi:
School of Civil Engineering, College of Engineering, University of Tehran, Iran;
(2) S.M. Zahrai:
Center of Excellence for Engineering and Management of Civil Infrastructures, School of Civil Engineering, College of Engineering, University of Tehran, Iran;
(3) S.R. Mirghaderi:
School of Civil Engineering, College of Engineering, University of Tehran, Iran.

Spiral spacing effect on axial compressive behavior of reinforced concrete filled steel tube (RCFST) stub column is experimentally investigated in this paper. A total of twenty specimens including sixteen square RCFST columns and four benchmarked conventional square concrete filled steel tube (CFST) columns are fabricated and tested. Test variables include spiral spacing (spiral ratio) and concrete strength. The failure modes, load versus displacement curves, compressive rigidity, axial compressive strength, and ductility of the specimens are obtained and analyzed. Especially, the effect of spiral spacing on axial compressive strength and ductility is investigated and discussed in detail. Test results show that heavily arranged spirals considerably increase the ultimate compressive strength but lightly arranged spirals have no obvious effect on the ultimate strength. In practical design, the effect of spirals on RCFST column strength should be considered only when spirals are heavily arranged. Spiral spacing has a considerable effect on increasing the post-peak ductility of RCFST columns. Decreasing of the spiral spacing considerably increases the post-peak ductility of the RCFSTs. When the concrete strength increases, ultimate strength increases but the ductility decreases, due to the brittleness of the higher strength concrete. Arranging spirals, even with a rather small amount of spirals, is an economical and easy solution for improving the ductility of RCFST columns with highstrength concrete. Ultimate compressive strengths of the columns are calculated according to the codes EC4 (2004), GB 50936 (2014), AIJ (2008), and ACI 318 (2014). The ultimate strength of RCFST stub columns can be most precisely evaluated using standard GB 50936 (2014) considering the effect of spiral confinement on core concrete.

Key Words
RCFST; spiral spacing; axial compression; ultimate strength; ductility

(1) Qiyun Qiao, Wenwen Zhang, Wanlin Cao:
College of Architecture and Civil Engineering, Beijing University of Technology, Beijing, 100124, P.R. China;
(2) Ben Mou:
School of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, P.R. China.

The main focus of this study is to numerically investigate the influence of strong earthquake and tsunami-induced wave impact on the response and behavior of a cable-stayed steel bridge with large caisson foundations, by assuming that the earthquake and the tsunami come from the same fault motion. For this purpose, a series of numerical simulations were carried out. First of all, the tsunami-induced flow speed, direction and tsunami height were determined by conducting a twodimensional (2D) tsunami propagation analysis in a large area, and then these parameters obtained from tsunami propagation analysis were employed in a detailed three-dimensional (3D) fluid analysis to obtain tsunami-induced wave impact force. Furthermore, a fiber model, which is commonly used in the seismic analysis of steel bridge structures, was adopted considering material and geometric nonlinearity. The residual stresses induced by the earthquake were applied into the numerical model during the following finite element analysis as the initial stress state, in which the acquired tsunami forces were input to a whole bridge system. Based on the analytical results, it can be seen that the foundation sliding was not observed although the caisson foundation came floating slightly, and the damage arising during the earthquake did not expand when the tsunami-induced wave impact is applied to the steel bridge. It is concluded that the influence of tsunami-induced wave force is relatively small for such steel bridge with large caisson foundations. Besides, a numerical procedure is proposed for quantitatively estimating the accumulative damage induced by the earthquake and the tsunami in the whole bridge system with large caisson foundations.

Key Words
earthquake-induced damage; tsunami-induced wave impact; steel bridge; large caisson foundation; accumulative damage

(1) Lan Kang:
School of Civil Engineering and Transportation, South China University of Technology, Guangzhou, 510640, China;
(2) Hanbin Ge:
Department of Civil Engineering, Meijo University, Nagoya, 468-8502, Japan;
(3) Kazuya Magoshi:
Seismic Analysis Research Inc. 3-21-19 Harunonisi Bld., Haruyoshi, Chuo-Ku, Fukuoka City, 810-0003, Japan;
(4) Tetsuya Nonaka:
Nagoya Institute of Technology, Department of Civil Engineering, Nagoya, Aichi 466-8555, Japan.

Based on the energy-variational principle, a coupling vibration analysis model of high-speed railway simply supported beam bridge-track structure system (HSRBTS) was established by considering the effect of shear deformation. The vibration differential equation and natural boundary conditions of HSRBTS were derived by considering the interlayer slip effect. Then, an analytic calculation method for the natural vibration frequency of this system was obtained. By taking two simply supported beam bridges of high-speed railway of 24 m and 32 m in span as examples, ANSYS and MIDAS finite-element numerical calculation methods were compared with the analytic method established in this paper. The calculation results show that two of them agree well with each other, validating the analytic method reported in this paper. The analytic method established in this study was used to evaluate the natural vibration characteristics of HSRBTS under different interlayer stiffness and length of rails at different subgrade sections. The results show that the vertical interlayer compressive stiffness had a great influence on the high-order natural vibration frequency of HSRBTS, and the effect of longitudinal interlayer slip stiffness on the natural vibration frequency of HSRBTS could be ignored. Under different vertical interlayer stiffness conditions, the subgrade section of HSRBTS has a critical rail length, and the critical length of rail at subgrade section decreases with the increase in vertical interlayer compressive stiffness.

Key Words
timoshenko; high-speed railway; interlayer slip; shear deformation; critical length

(1) Lizhong Jiang, Yulin Feng, Wangbao Zhou:
School of Civil Engineering, Central South University, Changsha 410075, China;
(2) Lizhong Jiang, Yulin Feng, Wangbao Zhou:
National Engineering Laboratory for High Speed Railway Construction, Changsha 410075, China;
(3) Binbin He:
University of Chinese Academy of Sciences, Beijing 100049, China.

In cold-formed steel (CFS) structures, such as trusses, wall frames and columns, the use of back-to-back built-up CFS angle sections are becoming increasingly popular. In such an arrangement, intermediate fasteners are required at discrete points along the length, preventing the angle-sections from buckling independently. Limited research is available in the literature on the axial strength of back-to-back built-up CFS angle sections. The issue is addressed herein. This paper presents the results of 16 experimental tests, conducted on back-to-back built-up CFS screw fastened angle sections under axial compression. A nonlinear finite element model is then described, which includes material non-linearity, geometric imperfections and explicit modelling of the intermediate fasteners. The finite element model was validated against the experimental test results. The validated finite element model was then used for the purpose of a parametric study comprising 66 models. The effect of fastener spacing on axial strength was investigated. Four different cross-sections and two different thicknesses were analyzed in the parametric study, varying the slenderness ratio of the built-up columns from 20 to 120. Axial strengths obtained from the experimental tests and finite element analysis were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparison showed that the DSM is over-conservative by 13% on average. This paper has therefore proposed improved design rules for the DSM and verified their accuracy against the finite element and test results of back-to-back built-up CFS angle sections under axial compression.

Key Words
back-to-back sections; built-up columns; cold-formed steel; direct strength method; finite element analysis

(1) G. Beulah Gnana Ananthi:
Division of Structural Engineering, College of Engineering Guindy Campus, Anna University, Chennai, India;
(2) Krishanu Roy, James B.P. Lim:
Department of Civil and Environmental Engineering, The University of Auckland, Auckland, New Zealand.

As an extremely destructive accident, progressive collapse is defined as the spread of an initial local failure from element to element, resulting eventually in the collapse of an entire structure or disproportionately large of it. To prevent the occurrence of it and evaluate the ability of structure resisting progressive collapse, the nonlinear static procedure is usually adopted in the whole structure design process, which considered dynamic effect by utilizing Dynamic Increase Factor (DIF). In current researches, the determining of DIF is performed in full-rigid frame, however, the performance of beam-column connection in the majority of existing frame structures is not full-rigid. In this study, based on the component method proposed by EC3 guideline, the expression of extended endplate connection performance is further derived, and the connection performance is taken into consideration when evaluated the performance of structure resisting progressive collapse by applying the revised plastic P-M hinge. The DIF for structures with extended endplate beam-column connection have been determined and compared with the DIF permitted in current GSA guideline, the necessity of considering connection stiffness in determining the DIF have been proved.

Key Words
Dynamic Increase Factor (DIF); extended endplate connection; the component method; the revised P-M hinge

(1) Ying Huang:
School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055, China;
(2) Yan Wu, Changhong Chen, Yao Yao:
School of Mechanical and Civil Engineering, Northwestern Polytechnical University, Xi'an, 710129, China;
(3) Zhaohui Huang:
Department of Civil and Environmental Engineering, Brunel University, Uxbridge, Middlesex UB8 3PH, UK.

The investigation of retaining wall structures behavior under dynamic loads is considered as one of important parts for designing such structures. Generally, the performance of these structures is under the influence of the environment conditions and their geometry. The aim of this research is to design retaining wall structures based on smart and optimal systems. The use of accuracy and speed to assess the structures under different conditions is one of the important parts sought by designers. Therefore, optimal and smart systems are able to have better addressing these problems. Using numerical and coding methods, this research investigates the retaining wall structure design under different dynamic conditions. More than 9500 models were constructed and considered for modelling design. These designs include height and thickness of the wall, soil density, rock density, soil friction angle, and peak ground acceleration (PGA) variables. Accordingly, a neural network system was developed to establish an appropriate relationship between data to obtain safety factor (SF) of retaining walls under different seismic conditions. Different parameters were analyzed and the effect of each parameter was assessed separately. According to these analyses, the structure optimization was performed to increase the SF values. The optimal and smart design showed that under different PGA conditions, the structure performance can be appropriately improved while utilization of the initial (or basic) parameters leads to the structure failure. Therefore, by increasing accuracy and speed, smart methods could improve the retaining structure performance in controlling the wall failure. The intelligent design process of this study can be applied to some other civil engineering applications such as slope stability.

Key Words
retaining wall structures; smart design; dynamic condition; optimization

(1) Haiqing Yang:
School of Civil Engineering, Chongqing University, Chongqing, China 400045;
(2) Mohammadreza Koopialipoor:
Faculty of Civil and Environmental Engineering, Amirkabir University of Technology, 15914, Tehran, Iran;
(3) Danial Jahed Armaghani:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam;
(4) Behrouz Gordan:
Department of Geotechnics and Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia (UTM), 81310 Skudai, Johor, Malaysia;
(5) Majid Khorami:
Universidad UTE, Facultad de Arquitectura y Urbanismo, Quito, Ecuador;
(6) M.M. Tahir:
UTM Construction Research Centre, Institute for Smart Infrastructure and Innovative Construction (ISIIC), School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia.

In this paper, wave propagation is studied and analyzed in double-layered nanotubes systems via the nonlocal strain gradient theory. To the author\'s knowledge, the present paper is the first to investigate the wave propagation characteristics of double-layered porous nanotubes systems. It is generally considered that the material properties of nanotubes are related to the porosity and hygro-thermal effects. The governing equations of the double-layered nanotubes systems are derived by using the Hamilton principle. The dispersion relations and displacement fields of wave propagation in the double nanotubes systems which experience three different types of motion are obtained and discussed. The results show that the phase velocities of the double nanotubes systems depend on porosity, humidity change, temperature change, material composition, non-local parameter, strain gradient parameter, interlayer spring, and wave number.

Key Words
wave propagation; double-layered nanotubes systems; phase velocity; hygro-thermal environment

(1) Gui-Lin She, Yi-Ru Ren:
Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha, 410082, China;
(2) Fuh-Gwo Yuan:
Department of Mechanical and Aerospace Engineering, North Carolina State University, 911 Partners Way, Raleigh, NC 27695, USA.

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