Out-of-Plane Shear Behavior Of Steel Plate Composite(SC) Walls For Nuclear Facilities

Steel plate composite walls consist of exterior steel plates, concrete and shear connectors. Steel plates are on the external faces, and concrete is cast in between the external plates, while connectors are used to connect the external plates and the concrete, forming steel plate-concrete-steel plate sandwich structures. This new type of structures is termed as Steel plate Concrete structures, abbreviated as SC.To take advantages of the fast modular construction and the premium impact resistant behavior of SC, AP 1000 Nuclear Power Plants(NPPs), which are under construction in the United States and China, have adopted SC as shield buildings and internal structures. Meanwhile, SC has been proposed for shield buildings and internal structures of High Temperature Gas Cooled(HTGR) NPPs of China and Korean APR1400 NPPs, and the related researches are in progress.Out-of-plane(OOP) shear could be the governing load for SC walls in NPPs under many circumstances, e.g. under strong seismic action and at connections with other types of structures. Due to material properties of concrete, concrete shear failure(diagonal tension failure) is brittle and sudden. Warnings, such as profiled cracks and yielding of reinforcement, will not exist before concrete brittle shear failure, which could lead to catastrophic results. However, SC walls used in AP 1000 NPPs are designed according to Code Requirements for Nuclear Safety-Related Concrete Structures(ACI 349-06) of American Concrete Institute(ACI), which is only applicable to Reinforced Concrete(RC) and Prestressed Concrete(PC).Therefore, the study on the OOP shear behavior of SC walls is of practical significance. The OOP shear strength of SC walls has been investigated extensively in the existing studies, where cutting strips were taken from SC walls subjected to OOP shear and were tested as beams under shear and bending. In other words, shear-bending tests on SC beams were carried out instead of OOP shear tests on SC walls. However, the shear ductile characters and the way to avoid brittle shear failure are still not clear, for SC walls subjected to OOP shear. In this study, the shear ductile characters of SC walls with shear reinforcement were investigated through testing on SC beams, in order to avoid brittle shear failure of SC walls subjected to OOP shear. The following four items were covered in this study:1. Experimental investigation on shear behavior of SC beams under different shear span-to-depth ratio and with different amount of shear reinforcementUsing shear span-to-depth ratio and shear reinforcement ratio as test parameters, several SC beam specimens were tested to find out the shear reinforcement ratio which is required to avoid brittle shear failure. Firstly, one beam specimen, which was designed per ACI 349-06 code, was tested to check the applicability of ACI 349-06 code for OOP shear design of SC structures. Subsequently, more SC beam specimens, with higher shear reinforcement ratios and under different shear span-to-depth ratios, were tested.2. Monitoring of bond-slip and deboning at the steel plate-concrete interfaceFor SC walls, the external steel plates could debond from the concrete due to difficulties of concrete casting and shrinkage of concrete, during construction stage; and the bond-slip would occur at the steel plate-concrete interface due to shear force, during service stage. Therefore, piezoceramic-based Smart Aggregates(SAs) were applied in this study to detect the interfacial debonding and bond-slip, and the Digital Image Correlation(DIC) technology was adopted to monitor the entir e development process of interfacial bond-slip and debonding during the tests. SAs based active sensing approach successfully detected interfacial bond-slip and debonding, and provided warnings for the damage of interface before failure of the specimens. By virtue of DIC technology, shear force-bond slip curves and shear force-debonding curves for the whole loading process were obtained, which provided guidance for the safe design of SC structures.3. Finite Element Modeling considering concrete shear behavior and interfacial bond slipThe Cyclic Softened Membrane Model(CSMM), which represents the most advanced shear constitutive model of concrete, was adopted to simulate shear behavior of SC beams. In the Finite Element Models(FEMs) built in Open Sees, the CSMM based membrane elements simulated the shear behavior of concrete and embedded reinforcement, and the truss elements simulated external steel plates. The effect of bond-slip was considered by reducing tangent modulus of the bottom steel plate, and a new material module Steel With Bond Q01 was developed in Open Sees.4. The minimum shear reinforcement ratio and the equations for shear strength estimationBased on analysis on the test results and with the effect of shear span-to-depth ratio taken into consideration, the minimum shear reinforcement ratio(t,min) were recommended. After the evaluation of existing equations for shear strength estimation of RC structures, modified equations were recommended for shear strength estimation of SC beams. Using the test data in this study and from the literature, the recommended minimum shear reinforcement ratio and the equations for shear strength estimation were validated.