DESTRUCTIVE MECHANISM OF LARGE SPAN COLD-FORMED SECTION ROOF TRUSS

Publisher Summary In order to obtain the information of ultimate bearing capacity and destructive characteristics of the cold-formed section roof truss, the test of a full-scale roof truss is carried out. The size and fabricated conditions of the testing truss are all same as the actual one. On the basis of the test results, the destructive mechanism of the truss is analyzed and the improved suggestions of design and fabrication for this type of truss are presented. Ultimate bearing capacity is larger than design load-carrying capacity. The enhanced strength is due partly to the effect of cold-forming. The strength should be utilized to save steel. The cold-forming residual stresses and the sub-stresses influence considerably on the local buckling of plate elements, which may not only cause the instability of members earlier but also damage the joints. The width-to-thickness ratio of the plate elements in compression chords should be strictly controlled. The cold-forming and welding residual stresses exist simultaneously in the members, but the former plays an important part in local buckling of flanges of the compression chord. As far as possible, the fabricating eccentricity between the end sectional center of web members and the axis of chord should be small to avoid the considerable torsional deformation in the chord.