OUT-OF-PLANE SHEAR BEHAVIOR OF SC COMPOSITE STRUCTURES

Steel-plate composite (SC) walls of safety-related nuclear facilities are subjected primarily to in-plane shear forces and gravity loads. They are also subjected to out-of plane shear and bending demands closer to the foundation regions and at connections or interfaces with other structures. The out-of-plane behavior of SC walls is not well understood, but it is expected to be similar to the behavior of RC walls. The out-of-plane behavior of RC walls is influenced by several parameters including the section depth, rebar ratio, spacing, and size of out-of-plane shear reinforcement. These parameters are expected to have a similar influence on the out-of-plane behavior of SC walls. The out-of-plane behavior of steel-concrete composite walls was evaluated by conducting one-way bending tests on beams that were representative of a large scale wall design in the longitudinal and transverse directions. The SC beam specimens were tested in both three and four-point bending tests with concentrated forces applied at distance (a) from the simple supports. Several SC beam specimens were tested with different shear span-to-depth (a/d) ratios, steel plate thickness (reinforcement ratio), shear stud spacing, and in the presence or absence of shear reinforcement. This paper summarizes the results of the experimental investigations including the load displacement responses and comparisons with equations that are in the current design codes. The paper also includes the results of detailed 3D finite element analyses of the specimens, and observations of behavior based on experimental and analytical results. INTRODUCTION SC walls are being considered for use in nuclear power plant construction due to their economic advantages over conventional reinforced concrete construction. These economic benefits of SC construction are due to their potential short construction duration and added efficiency of having steel plates surrounding the concrete portion. So far, this added efficiency has been demonstrated for blast and missile resistance, and in-plane shear strength with the recent SC wall related research [4, 5]. Out-of-plane shear strength of SC designs have been addressed in JEAG 4618 [3] technical guidelines based on some previous research that involved testing of beams having a/d ratios as large as 2.6 and depths less than 26 in. [6]. At these smaller a/d ratios, D region effects [8] are seen in the load carrying mechanism such as compression struts or arching action which tend to overestimate the lower bound shear strength of the SC design. Therefore in this study the shear span-depth ratio has been mostly kept above 3 to capture the lower bound strength values. Another objective of this paper is to evaluate whether the out-of-plane shear strength of SC design that is only subjected to shear and flexure can be conservatively estimated using ACI code provisions for shear strength of reinforced concrete beams. ACI 349 [1] references the ACI 318 [2] code provisions for shear strength, which are summarized using Equations 1 through 3. In these equations the total shear strength ( ) is given as summation of two parts where is the shear strength contribution of the concrete and is the shear strength contribution from the shear reinforcement that is used such as using deformed bar or wire reinforcement.