Design of Diagonal Roof Bracing Rods and Tubes

The behavior of rods and tubes as horizontal tension members is investigated. In the design of double diagonal tension bracing, each member must carry the tension forces as well as its own weight either by cable action in the case of rods, or by beam action in the case of tubes. Rod tensioning experiments reveal that pretensioning forces are much higher than expected. However, excessive pretensioning of rods does not effect their ultimate capacity but would influence the design of the compression members in the bracing system. It is found that the tensile capacity of tubes is only marginally reduced by the effect of self weight and the self weight bending stresses need not be considered in combination with axial tensile stresses. Bending under self weight alone need not be checked as deflection always governs the design.