SC Wall Piers and Basemat Connections: Numerical Investigation of Behavior and Design

This paper presents the development and benchmarking of 3D finite element models for predicting the lateral load (in-plane shear) behavior of SC wall piers and their anchorage to the concrete basemat. The benchmarking is done using the results of selected experimental investigations (tests) from the overall database. The benchmarked models are used to conduct parametric studies, and the results from these studies are used to: (i) evaluate the lateral load-deformation of SC wall piers, and (ii) to develop recommendations for the SC wall-to-basemat anchorage design. Full-strength connection design, which requires the anchorage to be stronger than the wall pier, is recommended for the SC wall-tobasemat anchorage. A potential test matrix is recommended for further verifying the results of the numerical studies presented in this paper. INTRODUCTION AND OUTLINE Steel-concrete (SC) composite walls are being used for current safety-related nuclear facilities, and being considered for small modular reactors of the future. There are no approved US codes or standards for the design of SC walls and their connections to the concrete basemat at this time. This paper focuses on the in-plane shear behavior of SC wall piers, and proposes recommendations for anchoring them into the concrete basemat. The in-plane shear behavior of SC walls has been studied extensively in Japan, Korea, and the US. Experimental investigations have been conducted on SC wall specimens with and without flanges (or boundary elements) in Japan (Funakoshi et al. 1998) and the US (Varma et al. 2011a). In-plane shear tests have been conducted on SC wall panels with or without accident thermal loading (Ozaki et al., 2000). Takeuchi et al. (1998) have also evaluated the behavior of SC walls under axial compression, and under in-plane shear. Experimental investigations of SC wall to basemat connections have been very limited. Fujita et al. (1998) conducted tests on SC walls anchored to the concrete basemat using anchor rods or dowel bars. More recently, researchers in the US (Epackachi et al., 2013) have tested four SC wall pier specimens with different reinforcement ratios, shear stud spacing, and tie bar spacing. The tests focused on the in-plane behavior of SC wall piers, not their anchorage to the concrete basemat. This paper presents the development and benchmarking of 3D finite element models for predicting the lateral load (in-plane shear) behavior of SC wall piers and their anchorage to the concrete basemat. The benchmarking was done using the results of selected experimental investigations (tests) from the overall database including lateral loading (in-plane shear) tests of SC walls with and without flanges. The benchmarked models were used to investigate the lateral load capacity of SC wall piers without flanges. The parameters included were the wall thickness, the wall aspect (height-to-length) ratio, and steel plate reinforcement ratios. The results from the analytical parametric studies are presented along with insights into the behavior of SC wall piers. The benchmarked models were used to further investigate behavior and develop recommendations for the SC wall pier-to-concrete basemat anchorage. Full-strength connection design, which requires the 22 Conference on Structural Mechanics in Reactor Technology San Francisco, California, USA August 18-23, 2013 Division X anchorage to be stronger than the SC wall pier, is recommended based on the analysis results because it results in ductility and energy dissipation through yielding and plastification of the SC wall pier. The parametric analyses are used to recommend the relative strength ratio () of the anchorage to the SC wall pier to achieve full-strength connection design. EXPERIMENTAL STUDIES SELECTED FROM THE DATABASE This section presents relevant details of the tests that were included in the benchmarking analysis of the 3D finite element models. These included tests conducted on SC walls with flanges (Takeuchi et al. 1998) and SC walls without flanges (Epackachi et al. 2013) that were selected from the overall database mentioned earlier. SC Walls with flanges The typical configuration of specimens tested by Takeuchi et al. (1998) is shown in Figure 1(a). The bottom portion of the specimen is embedded into a concrete base slab. Another concrete loading slab is located at the top of the specimen. The specimen is subjected to cyclic lateral loading, which is applied using hydraulic actuators connected to the top loading slab. A total of seven in-plane tests were conducted on specimens with varying aspect ratios, wall thickness, and steel plate thicknesses. Three different steel reinforcement ratios, namely 1.3%, 2% and 4 % are used with wall aspect (H/L) ratios of 0.87, 1.09 and 1.53. The specimen wall length (L) was equal to 1660 mm for all the experiments. The wall thicknesses were 4.5 in., 9 in. and 13.5 in. The steel faceplate thickness was equal to 0.09 in. for all the specimens. The steel faceplates were anchored to the concrete infill using headed shear studs at equal horizontal and vertical spacing. The stud spacing was equal to 33 times of web steel plate thickness for all specimens. Figure 1. Typical configuration of test specimens (Takeuchi et. al, 1998)