Through the analysis for the section deformation in externally prestressed simple supported concrete beam with random reinforcement,the variety law of section deformation along the beam is determined,so the displacement in anchoring zone and deviation points is calculated and the tendon stress increment obtained directly.

In order to comprehensively grasp stable performance of variable cross-section box column and influence of various parameters on its stable performance,considering the effect of web tapering radio and section s ratio of length to width on variable cross-section box column eigenvalue buckling,it is analysed its elastic overall buckling by finite element software ANSYS.

The computation of stress resulted by external load is relatively complex because the deformation of unbonded prestressed strand cannot comply with the plane section assumption.