Behaviour of composite haunched beam connection

Abstract

This paper is concerned with the behaviour of steel–concrete composite haunch connections. Experiments were carried out to investigate the moment-rotation characteristics and ultimate moment capacity of these connections. Details of the experiments giving information on test specimens, instrumentation, test set-up and test procedures are described. Results obtained for connection moment capacity, rotation capacity and failure modes are presented. It is found that through proper design and detailing, these connections display the characteristics of a rigid connection.

Introduction

Strong demand for large column-free space in buildings in recent times has necessitated further research into the behaviour of haunched beams since they are considered to be an efficient and economical form for long span construction [1], [2]. Haunched beams are designed by assuming a rigid moment connection between the beams and columns [3]. Depth and length of a haunch are chosen so that they result in an economical method of transferring moment into the column and in a reduction of beam depth to a practical minimum. Haunched composite beams in which steel beams are designed to act in conjunction with a concrete slab of definite width could result in shallow beams, provide a long unobstructed space for services and increase speed of construction. The haunch can be designed to provide sufficient rotation capacity of the connection that will permit a redistribution of the moment and thus mobilise a full sagging capacity of the beam resulting in an economical design. Researchers [4], [5], [6], [7], [8], [9] have proposed design methods for composite beams, simple or continuous. Required and available rotation capacities for a section have been considered and the accuracy of the prediction method assessed by comparing the theoretical and experimental results. A comprehensive guideline has been proposed [10] for the design of semi-continuous composite beams in braced frames where special attention is given to the effects of joint rotational stiffness. Tests were carried out [11], [12] in order to calibrate analytical models [13] and to investigate rotation and moment capacities in composite beams. Local buckling and moment redistribution in composite beams have also been studied [14], [15]; it has been concluded that the redistribution of elastic bending moment allowed by Eurocode 4 [16] is safe, economical and reflects the real behaviour of two-span composite beams. For beams continuous over more than two spans, the method is believed to be slightly conservative. Extensive investigations [17], [18] into the behaviour of composite connections and continuous composite frames have shown that properly designed and detailed composite connections are capable of providing moment capacity up to the full hogging resistance of the beam. It has also been concluded that elastic analysis assuming full continuity is not acceptable for composite frames because it fails to meet the moment capacity requirement at the support section and it is over conservative for sections within the span. Despite the detailed studies on composite beams, information available on composite haunched beams that can be designed similar to continuous beams is limited. Recent works [19], [20] have shown that haunch is sufficiently stiff to assume such connections at the toe are restrained when a full depth stiffener is provided on both sides of the web. In order to study further the application of haunch connections in long-span composite construction a study has been undertaken by the authors on the behaviour of haunch connections. Sub-assemblies of composite haunch beams have been tested to examine the moment rotation characteristics and the failure modes of these connections. The object of this paper is to report on the experimental results obtained from the present study of haunch connections. The experimental program is described in detail and the results for ultimate moment capacity of the tested connections are given.