On the Compressive Strength of Plastics-Pipe against External Pressure

The effects of dimensions and supporting conditions on the compressive strength and deformation of polyvinylchloride pipes under external pressure were discussed. The following four kinds of pipe supporting conditions were used; (A) compression between two steel plates, (B) compression between a steel plate and a concave wooden block, (C) compression between two concave wooden blocks, and (D) compression between two concave hard rubber supporters. The main results obtained are as follows.(1) The relation between the compressive strength P and the dimensions of PVC pipe is given by the following formula, similar to the mid load bending for a both end fixed straight beam with a rectangular section;P=4σb·l·t2/3·Dm·c1 (a)where, l, t and Dm are the length, thickness and diameter of pipe, respectively, c1 the correction coefficient according to pipe supporting conditions, and σb the bending stress in kg/mm2. The value of correction coefficient c1 was 0.81∼1.35 for A-method, 1.35 for B-method, 8.0 for C-method and 2.3 for D-method, respectively.(2) The deflection δ under elastic deformation is given by the following formula;δ=P·Dm3/8E·l·t3c2 (b)where, E is Young's modulus in kg/mm2 of pipe material, and c2 the correction coefficient similar to c1. The value of c2 was 2.22 for A-method.(3) It seems reasonable, therefore, that the theory of straight beam may be applied to the compressive strength and deflection of plastics-pipe under external pressure by using the correction coefficient c1 or c2.