The Portal Frame Structure Analysis Of The Uitimate Bearing Capacity

Portal frame structure member will appear the initial bending, initial stress and initial torsional force phenomenon inevitably, so the structure of the force at the space is already at the state of bending and torsion stress at the beginning.If there isn’t enough plane of the lateral support system, portal frame is likely to occur the space bend torsion buckling at first. In practical engineering, in order to reduce the longitudinal component and reduce the flange width of beam and column, lateral stiffness and stability of portal frame often need knee brace and purlin to provide security.In order to study the buckling form and the influence of the ultimate bearing capacity of the knee brace and purlin system, this article is based on the finite element program ANSYS, adopting the plate and shell unit detailed finite element method that can consider bending torsional buckling, local buckling and plastic zone development. Combined study design, conducted bearing bracing system buckling analysis and ultimate bearing analysis of the potal frame-purlins-keen brace system, the results showed that:1.The knee brace layout impact the overall stability of portal frame structure greatly. Relative to the setting of the knee brace portal frame, when the knee brace is not set, the stability bearing capacity of the portal frame is reduced greatly. Portal frame in smaller span (below 36m span) of scope, the knee brace arrangement and quantity affect the stability ultimate bearing capacity lightly. With the increasing of span, setting knee brace at the portal frame beams and columns within the flank edge compressive zone for improving bearing capacity is better than that of setting knee brace at lateral support; Every once in a purlin decorating a knee brace and every purlin decorating a knee brace, while the ultimate bearing capacity with the increasing of the number of knee brace, but increased modestly; Setting knee brace at the portal frame beam and column flank edge compressive zone is the most reasonable way.2The impact of purlin to the stability of portal frame in different with the different of span. For small span frame, increasing the purlin stiffness have little effct on its load-carrying capacity. For large span frame, increasing the purlin stiffness have significantly impact on the capacity.3.Because of the stiffness of knee brace steel has a little influence on ultimate bearing capacity of the lightweight steel portal frame, only the design of knee brace meet the strength requirements of the frame.4.To increase the potral frame stability bearing capacity, the effect of adding knee brace is more obvious than improving purlin stiffness.