The Critical Load on Quadrilateral and Circular Hollow Pipes under Pure Bending and Pure Torsion

Instability is one of the factors causing damage and injury that results in permanent disability. To increase the stable load-carrying capacity, a simplified and efficient computational method for determining the first critical load is necessary for the structure's structural design, application and safety. This study aims to determine the characteristics of the critical bending moment Mbcr and the critical torsion moment MTcr due to geometric size variations in the square, diamond, and circle cross-sectional hollow pipes so that consideration of the selection of hollow pipe size and cross-sectional shape is obtained under pure bending and pure torsion to minimize the occurrence of instability of the structure. The geometric size variation is carried out by changing the value of a/t in the quadrilateral pipe, the value of D/t in the circular pipe, and the length of the pipe L in each cross-sectional shape. This research was conducted using Finite Element Analysis-based software with linear and nonlinear buckling analyses. The moment load is given at the centre point of the model end, and the boundary conditions are set to see the deformation on the mid-span section of the pipe. The results showed that Mbcr and MTcr were inversely proportional to the values of a/t, D/t, and . The largest value of Mbcr belongs to the circular pipe. The value of Mbcr in the diamond pipe is greater than the square pipe but getting closer to the same as the value of L increases the MTcr value of both cross-sections is the same. The MTcr curve in the cross-section of the circle has a higher degree of steepness than the square and diamond cross-section. At the same value, the more the value of a/t and D/t increases thickness change has more compared to the circular pipe. At the same L, the greater the value of a/t and D/t, the difference in the Mbcr between the cross-section of the circle and the quadrilateral is smaller, but the difference in MTcr tends to be the same. At the same value of a/t and D/t, the oval deformation value and angle of twist will get bigger, but the Mbcr and MTcr values are getting smaller and will be constant at a given pipe length.