Seminar - Tim Wilkinson- Plastic Behaviour of cold-formed rectangular hollow sections

Thursday, May 13, 1999, 3 - 4 pm
Civil Engineering Lecture Room 1

Abstract

This seminar will summarise the major parts of the PhD of postgraduate student, Tim Wilkinson.

The main aim of this thesis is to assess the suitability of cold-formed rectangular hollow sections for plastic design. The project involved an extensive range of tests on cold-formed Grade C350 and Grade C450 (DuraGal) RHS beams, joints and frames. A substantial set of finite element analyses were also carried out on models of RHS beams. The main conclusion is that cold-formed RHS can be used in plastic design, but stricter element slenderness limits and consideration of the connections are required. Further examination, particularly on the effect of axial compression on element slenderness limits, is required before changes to current design rules can be finalised.

Bending tests were performed to examine the web and flange slenderness required to maintain the plastic moment for a large enough rotation suitable for plastic design.

Connection tests were performed on various types of knee joints in RHS, suitable for the column - rafter connection in a portal frame. The connection types investigated were welded stiffened and unstiffened rigid knee connections, bolted plate knee joints and welded and bolted internal sleeve knee joints for use in RHS portal frames. The ability of the connections to act as plastic hinges in a portal frame was investigated.

Tests on pinned-base portal frames were also performed. There were three separate tests, with two different ratios of vertical to horizontal point loads, simulating gravity and transverse wind loads. Two grades of steel were used for comparison. The aim of the tests was to examine if a plastic collapse mechanism could form in a cold-formed RHS frame to examine if plastic design was suitable for such frames.

A large number of finite element analyses were also performed to simulate the bending tests summarised above, and examine various parameters not studied in the experimental investigation. In order to simulate experimental rotation capacity of the RHS beams, a sinusoidal longitudinal local imperfection was included in the model.