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CONTENTS
Volume 2, Number 6, December 2002
 

Abstract
Non-linear large-displacement elasto-plastic finite element analyses are used to propose design recommendations for the eaves bracket of a cold-formed steel portal frame. Owing to the thinness of the sheet steel used for the brackets, such a structural design problem is not trivial as the brackets need to be designed against failure through buckling; without availability of the finite element method, expensive laboratory testing would therefore be required. In this paper, the finite element method is firstly used to predict the plastic moment capacity of the eaves bracket. Parametric studies are then used to propose design recommendations for the eaves bracket against two potential buckling modes of failure:rn (1) buckling of the stiffened free-edge into one-half sine wave,rn (2) local plate buckling of the exposed triangular bracket area.rnThe results of full-scale laboratory tests on selected geometries of eaves bracket demonstrate that the proposed design recommendations are conservative. The use of the finite element method in this way exploits modern computational techniques for an otherwise difficult structural design problem.

Key Words
cold-formed steel; portal frames; eaves joint; finite element analysis.

Address
The Steel Construction InstituternI.C.S.T.M.

Abstract
A finite strip method is developed for fatigue reliability analysis of steel highway bridges. Flat shell strips are employed to model concrete slab and steel girders, while a connection strip is formed using penalty function method to take into account eccentricity of girder top flange. At each sampling point with given slab thickness and modulus ratio, a finite strip analysis of the bridge under fatigue truck is performed to calculate stress ranges at fatigue-prone detail, and fatigue failure probability is evaluated following the AASHTO approach or the LEFM approach. After the failure probability is integrated over all sampling points, fatigue reliability of the bridge is determined.

Key Words
finite strip method; reliability; fatigue; fracture; AASHTO approach; LEFM approach.

Address
Department of Civil & Environmental Engineering, Carleton University, Ottawa, Ontario, Canada K1S 5B6

Abstract
In the design of bridges, it is important to consider the thermal stresses induced by the non-linear temperature distribution as well as the variation of effective temperature in the bridge deck. To cope with this, design temperature profiles are provided by design codes, which are normally based on extensive research work. This paper presents the results of a comprehensive investigation on the thermal behaviour of bridges in Hong Kong with special emphasis on composite bridges. The temperature distribution in bridges depends primarily on the solar radiation, ambient air temperature and wind speed in the vicinity. Apart from data of the meteorological factors, good estimates of the thermal properties of material and the film coefficients are necessary for the prediction of temperature distribution. The design temperature profiles for various types of composite bridge deck with bituminous surfacing and concrete slab of different thicknesses are proposed. The factors affecting the design effective temperature are also reviewed and suitable values for Hong Kong are proposed. Results are compared with recommendations of the current local code. The method facilitates the development of site-specific temperature profiles for code documents, and it can also be applied to create zoning maps for temperature loading for large countries where there are great climatic differences.

Key Words
composite bridge; extreme analysis; temperature; temperature gradient; thermal response.

Address
Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China

Abstract
This paper presents the experimental and theoretical results of SUS 304 stainless tubes with different diameter-to-thickness ratio (D/t ratio) subjected to pure bending creep. Pure bending creep occurs when a circular tube is bent to a desired moment and held at that moment for a period of time. It was found that the magnitudes of the creep curvature and ovalization of tube cross-section increase faster with a higher hold moment than that with a lower one. Due to continuously increasing curvature, the circular tubes eventually buckle. Finally, a theoretical form was proposed in this study so that it can be used to describe the relationship between the creep curvature and time. Theoretical simulations are compared with the experimental test data, showing that good agreement between the experimental and theoretical results has been achieved.

Key Words
pure bending creep; SUS 304 stainless steel tube; diameter-to-thickness ratio; creep curvature; ovalization.

Address
Department of Mechanical Engineering, Far East College, Tainan, Taiwan, R.O.C.rnDepartment of Engineering Science, National Cheng Kung University, Tainan, Taiwan, R.O.C.

Abstract
In steel bridges fatigue cracks are sometimes repaired by placing drilled holes at the crack tips. From the meaning that the drilled holes stop the propagation of cracks, they are called stop-holes. Since stop-holes are regarded as an emergency measure to delay crack propagation, usually some substantial repair follows. However, if the stress at the stop-holes is below their fatigue limit, fatigue cracks would not be expected to occur. The purpose of this study is to present the conditions under which stop-holes prevent the re-initiation of fatigue cracks. The fatigue limit of stop-holes and the equations necessary to estimate the maximum stress on the circumference of the stop-holes are provided.

Key Words
fatigue; stop-hole; crack; stress concentration.

Address
Osaka University, Department of Civil Engineering, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan


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