Flexural behaviour of bolted joints of corrugated steel plates

Abstract

Even though the design of corrugated steel plate culverts is based on compression ring theory, soil-steel structure interaction will likely lead to the development of bending moments in the steel plates. Successful application of these structures requires that these moments be accommodated without distress, while the plate carries axial thrust. This requires ductile flexural behaviour.The results of 13 flexural tests, with two-point loading, on lap joints of 3, 5, and 7 mm thick corrugated steel plates, as well as one test on plain 5 mm thick corrugated steel plate, are reported. Bolt configurations consisting of 2, 3, and 4 bolts per complete corrugation were tested to investigate the postulate that lap joints subject to bending moments can be made in a correct or incorrect manner. Correct lap joints are those that do have a bolt near the edge of the lap on the tension side where prying tends to occur, that is, where the gap between the lapped plates tends to open up when the joint is subject to moment. Incorrect laps do have a bolt at this location. Laps with 2 bolts are either correct for both positive and negative bending moments or incorrect for both. Statistically, laps with 3 bolts will be incorrect 75% of the time and laps with 4 bolts all the time.The tests confirm the postulate and show that, in the incorrect laps, tearing of the corrugated plates, starting at the edges of the bolt holes in the critical location where there is prying, occurs shortly after the maximum moment is reached. The tearing leads to a reduction in the moment resistance and reduced ductility even though the maximum moment for incorrect laps may be comparable to that for correct laps. Correct laps exhibit tremendous ductility, achieving joint rotations of 0.4 radians or more. Laps with 4 bolts per corrugation are weaker flexurally than laps with 2 bolts per corrugation because the critical net area on the tension side is less. Shaped washers placed under the bolt heads at the critical location do not improve the behaviour. Inadequate torquing in the bolts leads to increased flexibility, and reduced strength of the lap joints and increased opening of the gap between the plates. Key words: bolted, corrugated, culvert, ductility, flexure, joints, lap, moment resistance, plate, steel, tearing.