Steel web effects on shear mechanism of steel shell-concrete composite structure

The steel shell-concrete (SSC) composite structure is firstly used in the ceilings, floors, side and middle walls of the two-way eight-lane rectangle immersed tunnel in Shenzhen-Zhongshan Link Project. The SSC composite structure consists of steel shell and concrete filled inside the shell. The steel shell is made up of double outer steel plates, longitudinal diaphragms and transverse webs. The transverse shear force of tunnel is resisted by steel webs together with concrete, so that the effect of steel webs on shear mechanism is essential for design and practice of SSC composite immersed tunnel structures. Hence, shear experiments and numerical simulations on 3 SSC composite specimens, scaled basing on the tunnel ceiling of Shenzhen-Zhongshan Link Project, were carried out to investigate effects of steel web on the structural shear mechanism. The experimental results indicate that the main diagonal compression zone in concrete is formed and the steel web is under tension. The damage of SSC composite structure with steel web is due to concrete compression failure after steel web yielding. Compared to specimen without steel web, the ultimate capacities of specimens with 4 mm and 8 mm thick steel webs are increased by 42.8% and 76.4%, respectively. Steel web can significantly improve the ultimate bearing capacity of SSC composite structures, not only carrying the shear force but also improving the performance of concrete. The effects of steel web on concrete exhibit a positive correlation with the thickness of steel web, leading to higher capacities than simple combination of shear resistance of two materials. Numerical results from validated finite element model shows that the principal compressive stresses of concrete closing to the web are increased and uneven distribution of compressive stress in the transverse direction is obvious due to the effect of steel web. The experimental results are compared with current codes and coefficient considering the effects of steel webs on concrete contribution is proposed.