EFFICIENCY OF SAG RODS AS LATERAL SUPPORTS FOR STABILITY OF PURLINS

Taking the bottom flange of purlins as compressed bars and the sag rods as lateral elastic supports along the length of purlins，threshold rigidities of elastic supports which make purlins buckle between adjacent sag rods were found analytically，and the relation of the buckling load and the lateral support rigidity was presented in case the rigidity was less than the threshold values. Calculation was carried out for 24 purlins with thickness of 1. 5 ～ 3 mm and height of 140 ～ 250 mm to check whether sag rods could be regarded as full lateral supports for stability of purlins，and it was found that if the sag rods were close to the centroid of purlins，the purlins were thin，and the distance between sag rods small, then the sag rods could not be regarded as full lateral supports, and measures should be taken in design of purlins.