The Effect of Column Length and Size on the Maximum Achievable Load Carrying Capacity of Prestressed Stayed Columns

This paper presents the results of a systematic study on the effects of the cross-arm size (cross sectional diameter and thickness) and the cable stay cross sectional diameter on the maximum load carrying capacity of single cross-arm prestressed stayed column system. As a result of the addition of cross-arms and prestressed cables, the traditional slenderness ratio definition for ordinary unstayed columns is not applicable for this type of structural system. Therefore, the effects of the cross sectional size of the additional cross-arm and stay on the load bearing capacity are studied for different lengths and cross sectional size of the main column. Nine different combinations of column length (short, intermediate and long) and column cross-section size (small, medium and large) are investigated. It is shown that the column cross section size has a negligible effect on the maximum load carrying capacity while the effect is much more significant with varying column length. An enhancement ratio, i.e. the ratio of maximum load carrying capacity of the stayed column to the critical buckling load of unstayed column is also presented. It is shown that optimum cross-arm and stay size leading to the maximum achievable enhancement ratio and maximum load bearing capacity is independent of the size of the column. The enhancement ratio varies from about 14 with a corresponding 27.9% added volume (material) to about 40 with a corresponding 15% added volume (material) with increasing column length.