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CONTENTS
Volume 7, Number 2, April 2007
 

Abstract
This paper presents some of the results from an experimental research project on the behavior of extended end-plate connections subjected to moment conducted at the Structural Laboratory of Jordan University of Science and Technology. Since the connection behavior affects the structural frame response, it must be included in the global analysis and design. In this study, the behavior of six full-scale stiffened and unstiffened cantilever connections of HEA- and IPE-sections has been investigated. Eight high strength bolts were used to connect the extended end-plate to the column flange in each case. Strain gauges were installed inside each of the top six bolts in order to obtain experimentally the actual tension force induced within each bolt. Then the connection behavior is characterized by the tension force in the bolt, extended end-plate behavior, moment-rotation relation, and beam and column strains. Some or all of these characteristics are used by many Standards; therefore, it is essential to predict the global behavior of column-beam connections by their geometrical and mechanical properties. The experimental test results are compared with two theoretical (equal distribution and linear distribution) approaches in order to assess the capabilities and accuracy of the theoretical models. A simple model of the joint is established and the essential parameters to predict its strength and deformational behavior are determined. The equal distribution method reasonably determined the tension forces in the upper two bolts while the linear distribution method underestimated them. The deformation behavior of the tested connections was characterized by separation of the column-flange from the extended end-plate almost down to the level of the upper two bolts of the lower group and below this level the two parts remained in full contact. The neutral axis of the deformed joint is reasonably assumed to pass very close to the line joining the upper two bolts of the lower group. Smooth monotonic moment-rotation relations for the all tested frames were observed.

Key Words
steel connections; high strength bolts; moment rotation curves; experimental.

Address
Civil Engineering Department, Jordan University of Science and Technology, P.O. Box 3030, Irbid-22110, Jordan

Abstract
On September 11th 2001, the twin towers of the World Trade Center in New York City were struck by two hijacked airplanes. Despite severe local damage induced by the impact, the towers were able to sustain 102 and 56 minutes of the subsequent multi-storey fires before collapsing. The purpose of this study is to contribute to the understanding of the in-fire performance of composite trusses by examining the behaviour of the longer-span type used in the towers. It makes no attempt to be a forensic study of the actual events. Using the finite element package Vulcan, the structural mechanics of typical long-span composite floor trusses are explained, under a variety of scenarios, as the fire temperatures rise. Different boundary conditions, degrees of protection and loading are all covered, the results being presented mainly in the form of graphs of deflection and internal force of members against time.

Key Words
composite truss; catenary action; numerical modelling; progressive collapse; structural fire engineering; World Trade Center.

Address
Seng-Kwan Choi; Department of Fire and Engineering Service Research, Korea Institute of Construction Technology, Ilsan, Goyang 411-712, Korea
Ian Burgess; Department of Civil and Structural Engineering, University of Sheffield, Mappin Street,
Sheffield S1 3JD, UK
Roger Plank; School of Architecture, University of Sheffield, Western Bank, Sheffield S10 2TN, UK

Abstract
(Received June 27, 2006, Accepted March 9, 2007) Abstract. Based on stability theory of current rigid steel frames and using the three-column subassemblage model, the governing equations for determining the effective length factor (m-factor) of the columns in semi-rigid composite frames are derived. The effects of the nonlinear moment-rotation characteristics of beam-to-column connections and composite action of slab are considered. Furthermore, using a two-bay three-storey composite frame with semi-rigid connections as an example, the effects of the non-linear moment-rotation characteristics of connections and load value on the m-factor are numerically studied and the m-factors obtained by the proposed method and Baraket-Chen\'s method are compared with those obtained by the exact finite element method. It was found that the proposed method has good accuracy and can be used in stability analysis of semi-rigid composite frames.

Key Words
effective length factor; semi-rigid connection; composite frame; moment-rotation characteristics.

Address
Jing-Feng Wang; School of Civil Engineering, Tsinghua University, Beijing, 10084, People\'s Republic of China
Guo-Qiang Li; School of Civil Engineering, Tongji University, Shanghai, 200092, People\'s Republic of China
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, People\'s Republic of China

Abstract
Recently, CFT column has been well-studied and reported on, because a CFT column has certain superior structural properties as well as good productivity, execution efficiency, and improved rigidity over existing columns. However, CFT column still has problems clearing the capacity evaluation between its steel tube member and high-strength concrete materials. Also, research on concrete has examined numerical values for high-strength concrete filled steel square tube columns (HCFT) to explain transformation performance (M-f) when a short-column receives equal flexure-moment from axial stress. Moment-curvature formulas are proposed for HCFT columns based on analytic assumption described in this paper. This study investigated structural properties (capacity, curvature), through a series of experiments for HCFT with key parameters, such as strength of concrete mixed design (58.8 MPa), width-thickness ratio (D/t), buckling length to sectional width ratio (Lk/D) and concrete types (Zeolite, Fly-ash, Silica-fume) under eccentric loads. A comparative analysis executed for the AISC-LRFD, AIJ and Takanori Sato, etc. Design formulas to estimate the axial load (N)-moment (M)-curvature (f) are proposed for HCFT columns based on tests results described in this paper.

Key Words
high-strength concrete filled steel square tube column; D/t ratio; buckling length to sectional ratio; eccentric ratio; axial load capacity ratio; curvature; ductility.

Address
Beom Structural Engineering Co., 675-9 2F Hwanggeum 2-dong, Suseong-gu, Daegu 706-852, Korea

Abstract
The use of composite semi-rigid connections is not fully exploited, in spite of its great number of advantages. Composite semi-rigid connections may lead to an optimal moment distribution that will render lighter structures. Furthermore, using the appropriate semi-rigid connection design, the stability of the frames against lateral loads may entirely rely on the joint stiffness, thus avoiding bracing systems and permitting more diaphanous designs. Although modern codes, such as the Eurocode 4 (EC4), propose thorough methods of analysis they do not provide enough insight and simplicity from the design point of view. The purpose of this paper is to introduce practical and efficient methods of analysis that will facilitate the work of a structural analyst starting from the global analysis of the composite frame and ending on the final connection design. A key aspect is the definition of the stiffness and strength of the connections that will lead to an optimal moment distribution in the composite beams. Two examples are presented in order to clarify the application of the proposed methods and to demonstrate the advantages of the semi-rigid composite design with respect to the alternative pinned and rigid ones. The final aim of the paper is to stimulate and encourage the designer on the use of composite semi-rigid structures.

Key Words
composite semi-rigid connections; semi-rigid frame; component method.

Address
Department of Structural Analysis and Design, School of Architecture, University of Navarra, 31080 Pamplona, Spain


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