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Volume 16, Number 2, February 2014

Natural vibration of truss cable structures is analyzed based upon the general structural analysis software ANSYS, energy variational method and Rayleigh method, the calculated results of three methods are compared, from which the characteristics of free-vibration are obtained. Moreover, vertical seismic response analysis of truss cable structures is carried out via time-history method. Introducing three natural earthquake waves calculated the results including time-history curve of vertical maximal displacement, time-history curve of maximal internal force. Variation curve of maximal displacement of node along span, and variation curve of maximal internal force of member along span are presented. The results show the formulas of frequencies for truss cable structures obtained by energy variational method are of high accuracy. Furthermore, the maximal displacement and the maximal internal force occur near the 1/5 span point. These provide convenient and simple design method for practical engineering.

Key Words
truss cable structures; energy variational method; natural vibration; time-history analysis; finite element analysis

Wen-Fu Zhang, Ying-Chun Liu, Jing Ji and Zhen-Chao Teng:
Heilongjiang Key Laboratory of Disaster Prevention, Mitigation and Protection Engineering, College of Civil and Architecture Engineering, Northeast Petroleum University, Daqing 163318, P.R. China.

In this research the effect of seismic design level as a practical approach for progressive collapse mitigation and reaching desired structural safety against it in seismically designed concentric braced frame buildings was investigated. It was achieved by performing preliminary and advanced progressive collapse analysis of several split-X braced frame buildings, designed for each seismic zone according to UBC 97 and by applying various Seismic Load Factors (SLFs). The outer frames of such structures were studied for collapse progression while losing one column and connected brace in the first story. Preliminary analysis results showed the necessity of performing advanced element loss analysis, consisting of Vertical Incremental Dynamic Analysis (VIDA) and Performance-Based Analysis (PBA), in order to compute the progressive collapse safety of the structures while increasing SLF for each seismic zone. In addition, by sensitivity analysis it became possible to introduce the equation of structural safety against progressive collapse for concentrically braced frames as a function of SLF for each seismic zone. Finally, the equation of progressive collapse safety as a function of bracing member capacity was presented.

Key Words
progressive collapse; structural safety; failure; performance; seismic load factor; vertical incremental dynamic analysis

(1) Farshad Hashemi Rezvani:
School of Civil Engineering, The University of Queensland, Brisbane, Australia;
(2) Behrouz Asgarian:
Civil Engineering Faculty, K.N. Toosi University of Technology, Tehran, Iran.

This paper examines the behaviour of two types of practical open beam-to-tubular column connection details subjected to combined moment, axial and/or shear loads. Detailed continuum finite element models are developed and validated against available experimental results, and extended to deal with flexural, axial and shear load interactions. A numerical investigation is then carried out on the behaviour of selected connections with different stiffness and strength characteristics under various load combination scenarios. The influence of applied levels of axial tensile or compressive loads on the bending stiffness and capacity is examined and discussed. Additionally, the interaction effects between shear forces and co-existing bending and axial loads are examined and shown to be comparatively insignificant in terms of stiffness and capacity in most cases. It is also shown that the range of connections considered in this paper can provide rotational ductility levels in excess of those required under typical design scenarios. Based on these findings, a simplified component-based representation is proposed and described, and its ability to represent the connection response under combined loading is verified using results from detailed numerical simulations.

Key Words
semi-rigid joints; blind-bolted angle connections; combined channel / angle connections; combined loading conditions; interaction curves

(1) Yanzhi Liu:
College of Civil Engineering, Hunan University, China;
(2) Christian Malaga-Chuquitaype and Ahmed Y. Elghazouli:
Department of Civil and Environmental Engineering, Imperial College London, UK.

A new through-beam connection system for a concrete filled steel tube column to RC beam is proposed. In this connection, there are openings on the steel tube while the reinforced concrete beams are continuous in the joint zone. The moment and shear force at the beam ends can be transferred to column by continuous rebar and concrete. The weakening of the axial load and shear bearing capacity due to the opening of the steel tube can be compensated by strengthening steel tube at joint zone. Using this connection, construction of the joint can be made more convenient since welding and hole drilling in situ can be avoided. Axial compression and reversed cyclic loading tests on specimens were carried out to evaluate performance of the new beam-column connection. Load-deflection performance, typical failure modes, stress and strain distributions, and the energy dissipation capacity were obtained. The experimental results showed that the new connection have good bearing capacity, superior ductility and energy dissipation capacity by effectively strengthen the steel tube at joint zone. According to the test and analysis results, some suggestions were proposed to design method of this new connection.

Key Words
concrete filled steel tube; RC beam; connections; experiment; capacity

(1) Chunyu Tian, Congzhen Xiao and Tao Chen:
China Academy of Building Research, Beijing, China;
(2) Xueyi Fu:
China Construction Design International, Shenzhen, China.

Stress intensity factors are numerically investigated for interfacial edge crack between two dissimilar composite plates jointed with single side composite patch. Variation of stress intensity factor under Mode I loading condition is examined for different material models and fiber orientation angles of composite plates and patch. ANSYS 12.1 finite element analysis software is used to obtain displacements of crack surfaces in the numerical solution and repaired plates are modeled in three dimensions. Obtained results are presented in the form of graphs. It is found that fiber orientation angle of composites is an effective parameter on interfacial stress intensity factor.

Key Words
interface crack; composite patch; stress intensity factor; finite element method

(1) Fatih Cetisli:
Department of Civil Engineering, Pamukkale University, Denizli 20070, Republic of Turkey;
(2) Mete O. Kaman:
Department of Mechanical Engineering, Firat University, Elazig 23119, Republic of Turkey.

The purpose of this study was to evaluate the cyclic behavior of steel column-tree moment connections used in steel moment resisting frames. These connections are composed of shop-welded stub beam-to-column connection and field bolted beam-to-beam splice. In this study, the effects of beam splice length on the seismic performance of column-tree connections were experimentally investigated. The change of the beam splice location alters the bending moment and shear force at the splice, and this may affect the seismic performance of column-tree connections. Three full-scale test specimens of column-tree connections with the splice lengths of 900 mm, 1,100 mm, and 1,300 mm were fabricated and tested. The splice lengths were roughly 1/6, 1/7, 1/8 of the beam span length of 7,500 mm, respectively. The test results showed that all the specimens successfully developed ductile behavior without brittle fracture until 5% radians story drift angle. The maximum moment resisting capacity of the specimens showed little differences. The specimen with the splice length of 1,300 mm showed better bolt slip resistance than the other specimens due to the smallest bending moment at the beam splice.

Key Words
column-tree connection; moment resisting frame; cyclic testing; seismic performance; bolt slip

(1) Kangmin Lee, Rui Li, Liuyi Chen and Keunyeong Oh:
Department of Architectural Engineering, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon, 305-764, Korea;
(2) Kang-Seok Kim:
Facilities Operations Team, Daejeon-Chungnam District Division, Korea Electric Power CO, 9-7 Yongjeon-dong, Dong-gu, Daejeon, 300-713, Korea.

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