(Fig. 20(c)).Closer longitudinal and horizontal spacing of adjacent stiffener welds also promotes higher ultimate resistance, for the improved confinement for concrete core, thus providing more economical efficiency of materials.
However, when longitudinal and horizontal spacing of stiffener welds both decrease to 100 mm, the improvement
of confinement can be ignored (Fig. 20(d) and (e)).
In regard to construction procedure, fabrication difficulties may arise when spacing of adjacent stiffener welds is too small.