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CONTENTS
Volume 13, Number 4, October 2012
 

Abstract
The risk of progressive collapse in steel framed buildings under fire conditions is gradually rising due to the increasing use of combustible materials. The fire resistance of such steel framed buildings is evaluated by fire tests. Recently, the application of performance based fire engineering makes it easier to evaluate the fire resistance owing to various engineering techniques and fire science. The fire resistance of steel structural members can be evaluated by the comparison of the limiting temperatures and maximum temperatures of structural steel members. The limiting temperature is derived at the moment that the failure of structural member results from the rise in temperature and the maximum temperature is calculated by using a heat transfer analysis. To obtain the limiting temperatures for structural steel of grades SS400 and SM490 in Korea, tensile strength tests of coupons at high temperature were conducted. The limiting temperatures obtained by the tensile coupon tests were compared with the limiting temperatures reported in the literature and the results of column fire tests under four types of loading with different load ratios. Simple limiting temperature formulas for SS400 and SM490 steel based on the fire tests of the tensile coupons are proposed. The limiting temperature predictions using the proposed formulas were proven to be conservative in comparison with those obtained from H-section and hollow section column fire tests.

Key Words
limiting temperature; fire resistance; structural steels; load ratio; tensile strength tests; column fire tests.

Address
In-Kyu Kwon : Department of Fire Protection Engineering, Kangwon National University, Korea
Young-Bong Kwon : Department of Civil Engineering, Yeungnam University, Korea

Abstract
With the advantages of large span, light deadweight and convenient construction, the steelconcrete composite beam (SCCB) has been rapidly developed as a medium span bridge. Compared with common beams, the global stiffness of SCCB is discontinuous and in a staged distribution. In this paper, the analysis model for the simply-supported SCCB is established and the vibration equations are derived. The natural vibration characteristics of a simply-supported SCCB are analyzed, and are compared with the theoretical and experimental results. A curvature mode measurement method is proposed to identify the shear connector damage of SCCB, with the stiffness reduction factor to describe the variation of shear connection stiffness. By analysis on the 1st to 3rd vertical modes, the distribution of shear connectors between the steel girder and the concrete slab are well identified, and the damage locations and failure degrees are detected. The results show that the curvature modes can be used for identification of the damage location.

Key Words
steel-concrete composite beam; shear connector; dynamic behavior; curvature mode; damage identification; stiffness reduction factor.

Address
Zhongming Hou,He Xia* : School of Civil Engineering, Beijing Jiaotong University, Beijing, 100044, China
YanLing Zhang : School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, 050043, China

Abstract
Steel suspension members subjected to tension and bending offer an economical and efficient alternative for many structural problems. This paper is concerned with the elastic and elastic-plastic behaviour of suspension members with bending stiffness subjected to vertical point and uniformly distributed loads. An experimental study is described which focuses on the response of three suspension members with various Tshaped steel hot rolled sections and geometric configurations. The tests enable direct assessment of the influence of a key parameter such as the sag-to-span ratio on the response of suspension members. Detailed nonlinear finite-element models are generated to provide a tool for theoretical analyses and to facilitate further understanding of the behaviour. Results demonstrate that experimentally obtained responses can generally be closely predicted numerically because there are relatively good agreements between finite element and tests results. The results and observations of subsequent numerical parametric studies offer an insight into the key factors that govern the behaviour of suspension members with bending stiffness in the elastic-plastic range.

Key Words
steel suspension member with bending stiffness; tests; numerical modelling; finite element nonlinear analysis; elastic-plastic behaviour; mechanism of deformation; analytical solution

Address
Faculty of Civil Engineering, Technical University of Kosice, Vysokoskolska 4, 042 00 Kosice, Slovakia

Abstract
This paper is dedicated to the buckling behaviors of strengthened perforated plates under edge shear loading, which is a typical load pattern of steel plates in civil engineering, especially in plate and box girders. The square plates considered each has a centric circular hole and is simply supported on four edges in the out-of-plane direction. Three types of strengthening stiffeners named ringed stiffener (RS), flat stiffener (FSA and FSB) and strip stiffener (SSA, SSB and SSC) are mainly discussed. The finite element method (FEM) has been employed to analyse the elastic and elasto-plastic buckling behavior of unstrengthened and strengthened perforated plates. Results show that most of the strengthened perforated plates behave higher buckling strengths than the unstrengthened ones, while the enhancements in elastic buckling stress and elastoplastic ultimate strength are closely related to sti ffener types as well as plate geometric parameters including plate slenderness ratio and hole diameter to plate width ratio. The critical slenderness ratios of shear loaded strengthened perforated plates, which determine the practical buckling pattern (i.e., elastic or elasto-plastic buckling) of the plates, are also studied. Based on the contrastive analyses of strengthening efficiency considering the influence of stiffener consumption, the most efficient cutout-strengthening methods for shear loaded perforated square plates with different slenderness ratios and circular hole diameter to plate width ratios are preliminarily identified.

Key Words
strengthened perforated plate; circular hole; shear loading; elastic buckling stress; elasto-plastic ultimate strength; cutout-strengthening.

Address
Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai, China

Abstract
In order to develop a verification method for extremely low cycle fatigue (ELCF) of steel structures, the initiation mechanism of ductile cracks is investigated in the present study, which is the first step of brittle fracture, occurred in steel bridge piers with thick-walled sections. For this purpose, a total of six steel columns with small width-thickness ratios were tested under cyclic loading. It is found that ductile cracks occurred at the column base in all the specimens regardless of cyclic loading histories subjected. Moreover, strain history near the crack initiation location is illustrated and an index of energy dissipation amount is proposed to evaluate deformation capacity of structures.

Key Words
ductile crack initiation; brittle fracture; steel bridge; cyclic loading

Address
Xiaoqun Luo : Dept. of Building Engineering, Tongji University, Shanghai 200092, P.R.China
Dept. of Civil Engineering, Meijo University, Nagoya 468-8502, Japan
Hanbin Ge : Dept. of Civil Engineering, Meijo University, Nagoya 468-8502, Japan
Masatoshi Ohashi : Central Japan Railway Company, Nagoya 450-6101, Japan

Abstract
This paper describes the refined 3-D finite element (FE) modeling of composite frames composed of concrete-filled steel tubular (CFST) columns and steel-concrete composite beams based on the test to get a better understanding of the seismic behavior of the steel-concrete composite frames. A number of material nonlinearities and contact nonlinearities, as well as geometry nonlinearities, were taken into account. The elastoplastic behavior, as well as fracture and post-fracture behavior, of the FE models were in good agreement with those of the specimens. Besides, the beam and panel zone deformation of the analysis models fitted well with the corresponding deformation of the specimens. Parametric studies were conducted based on the refined finite elememt (FE) model. The analyzed parameters include slab width, slab thickness, shear connection degree and axial force ratio. The influences of these parameters, together with the presence of transverse beam, on the seismic behavior of the composite frame were studied. And some advices for the corresponding seismic design provisions of composite structures were proposed.

Key Words
CFST; frame; seismic; floor slab; finite element.

Address
Huang Yuan*, Yi Weijian : College of Civil Engineering, Hunan Univ., Lushan South Rd, Changsha, Hunan, 410082, China
Nie Jianguo : Key Laboratory of Structural Engineering and Vibration of China Education Ministry, Department of Civil Engineering, Tsinghua University, Beijing, 100084, China


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