Critical moment of the frame rafter (example) （框架的关键时刻椽(示例)）.pdfVIP

Critical moment of the frame rafter (example) For determination of the critical moment the software LTBeam is used, which is freely available for everybody at: Setting geometry, boundary conditions, loading and running solution is intuitive. Boundary conditions to solve the critical moment of a beam are as follows: v lateral restraint (at chosen distance from shear centre), θ torsional restraint (usually secured by a couple of forces, e.g. by support of both flanges), v’ flexural restraint of the section (in lateral direction of the beam), θ ’ warping restraint of the section (e.g. zero warping is secured by hollow section vertical web stiffeners). Worked example: Determine the critical moment of the rafter according to Figure bellow. The rafter is continuously supported in horizontal direction by roof decking at upper flange level. The rafter ends are supported in lateral direction by a transverse member (lateral flexural restraint) and by the frame column in torsion (torsion restraint). Warping is not prevented. 12 kN/m IPE 550 40 kN 40 kN HE 340 B 10000 imp 1= 1,07 kN 24000 Geometry Loading case -374,6 387,1 -483,2 MEd [kNm] Moment distribution 3 variants of boundary conditions concerning lateral and torsional restrai