Abstract
Available test data on block shear behaviour of coped beams with double bolt-line connections are quite limited, and earlier investigations found that the test block shear capacities could not be accurately predicted by existing design rules which deal with this failure mode in an inconsistent manner. To address this, a comprehensive investigation focusing on the block shear behaviour of coped beams with double bolt-line connections was reported in this paper. The research commenced with 17 full-scale tests considering the test parameters of web block aspect ratio, out-of-plane eccentricity, connection rotational stiffness, and bolt stagger. Two specimens were found to fail by local web buckling, and the remaining 15 specimens failed by block shear. Three typical block shear failure modes were observed at ultimate load, namely, whole block tear-out (WBT), tensile fracture (TF), and tensile fracture followed by whole block tear-out (TF–WBT). The influences of the considered test parameters on the failure mode and block shear capacity of the test specimens were thoroughly discussed. The test results were then compared with existing design rules to evaluate the consistency and accuracy of the major standards, and it was found that these standards led to inconsistent test-to-predicted ratios and tended to be conservative. Summarising all available test data, including the current tests and those previously conducted by other researchers, a reliability analysis was conducted to further examine the level of safety of the major standards. Design recommendations were finally proposed aiming to achieve reliable yet economical design approaches with consistent safety levels.
1. Introduction
It is very common in structural steel design to remove part of the flange of secondary beams in order to ensure the same elevation at member junctions. The beams with removed top flange (or both flanges if necessary) near the connection zone are called coped/notched beams. While the removal of part of the flange is one of the easiest solutions to provide the required clearance, the presence of the cope will inevitably reduce the strength of the beam in the coped region, and block shear is one of the most common failure modes for coped beams. This failure mode is typically featured by a block of material torn out from the coped beam web, and it can happen in either bolted or welded connections. For a bolted connection, where different numbers of bolt lines/rows (the definitions of which are shown in Fig. 1(a)) can be arranged to cater for various design requirements, block shear failure is often featured by a tensile fracture developed on the plane along the bottom bolt row (i.e. tension area) and a shear failure (either excessive yielding or complete fracture) developed over a critical bolt line (i.e. shear area). The typical block shear failure modes for the coped beams with single bolt-line and double bolt-line connections are shown in Fig. 1(a).
7. Summary and conclusions
This paper has reported a comprehensive investigation on the behaviour and design of block shear failure of coped beams with double bolt-line connections. A total of 17 full-scale tests have been conducted, and the test parameters included web block aspect ratio, out-of-plane eccentricity, connection rotational stiffness, and bolt stagger. Two specimens were found to fail by local web buckling, and the remaining 15 specimens failed by block shear. Three typical block shear failure modes were observed at ultimate load, namely, whole block tear-out (WBT), tensile fracture (TF), and tensile fracture followed by whole block tear-out (TF–WBT). The failure mode was found to be affected by the aspect ratio and connection type. In addition, web twisting was observed in some specimens, and the significance of web twisting was influenced by the lateral stiffness of the connections.
