What are the calculation methods for the vertical bearing capacity of the rectangular tube:1. Calculate the compressive stress, which is the compressive stress generated by the vertical pressure acting on the cross section of the rectangular tube. The pressure (in N) divided by the cross-sectional area of the rectangular tube (in m square). The compressive stress should be less than the allowable stress of the material. 2. Calculate the stability. The tube stability calculation is complicated. It depends on whether the connection method is fixed at both ends or fixed at one end and hinged at the other end. It is estimated that you do not only use 1 column, so it can be simply calculated as a fixed connection at both ends. Simple calculation of critical pressure: P=(4*n*Pi^2*E*I)/[(L/2)^2]. N:The number of columns; pi^2: the second power of the shot; E: modulus of elasticity; I: moment of inertia; and L: column length. Those are simple calculations. Safety factors and seismic loads must be considered too. The specific situation is different, you need to analyze by experienced engineer.