S4, S9 and S10: stiffened specimens with tensile strips, shown in Figs. 1(e) and 2(d).
The tensile strips, with cross-sectional dimensions of 20 mm (height) 2.0 mm (thickness) or 20 mm (height) 3.5 mm (thickness), were installed through the prefabricated holes with dimensions slightly larger than those of the stiffeners.
The tensile strips were then welded at two ends, with the spacing of 100 mm along the length.
The steel tensile strips were made of the same steel plates of the tubes.
This hole-drilling fabricating method can avoid heat-induced initial imperfection by traditional gas-cutting method.