Studying Out-plane Effective Length Of The Portal Frame's Beam

As a popular form of the light-weight building for steel structures, portal frame is widely used at present. When designing portal frame, people are puzzled by how to get out-plane effective length of the frame's beam. In the design specifications, there is only a principle item provided. For example, it point out in the code [1] that "out-plane effective length of solid-web steel beams should take the distance of the lateral brace". However, if knee-brace can be used as a lateral brace? In the actual engineering, when using the item "knee-brace and the joint of brace between pillars can be used as lateral brace", designers do not consider the additional effects that knee-brace press on purlin, so it is not reasonable to regard as lateral brace to knee-brace.In this paper, firstly, carry on the contrast to the two methods about out-plane effective length of portal frame's beam at present. Sencondly, three single-span portal frames are studied: i .pinned connections at all column bases; ii. rigid connection at column base;iii.portal frames with a leaning column in the span-center. At last, make recommendations about out-plane effective length for the reference design.