Theoretical models and reliability assessment of steel-UHPC-steel composite beams in offshore structures

Steel-concrete-steel composite structures (SCS-CS) with ultra-high performance concrete (UHPC) exhibit wide potential applications in civil constructions. This paper aims to revealing the failure mechanism, proposing the theoretical models and conducting the reliability assessment of SCS composite beams with UHPC (SUS-CB). Firstly, several static tests on SUS-CB were summarized to analyze the failure features and failure modes. A nonlinear finite element (FE) model of SUS-CB was developed and validated. Parametric study was carried out to explore the structural behaviors of SUS-CB, including matching relationship between steel plate (SP) and core UHPC, and bond-slip. Subsequently, failure mechanism of SUS-CB was revealed and failure modes were defined systematically. Considering slippage and effects of steel fibers, the novel theoretical model of calculating ultimate capability of SUS-CB was proposed and compared with existing design codes. Based on these theoretical models, uncertainties of statistics variables were calculated, and reliability analysis of SUS-CB was conducted. Results indicate that reliability index of these theoretical models and design codes is lower than target reliability index. Consequently, adjustment factors of ultimate capacity were calculated to confirm reaching the target reliability index in offshore structures. Finally, sensitivity analysis of statistic variables was performed to provide advices for offshore structural design.