Options for the Anchorage of Composite SC Walls to a Concrete Basemat

Abstract

Steel-plate composite (SC) walls consist of a plain concrete wall reinforced with steel plates on the two (interior and exterior) surfaces. The steel faceplates are anchored to the concrete infill using steel headed stud anchors that are welded to the inside surfaces of the steel faceplates and embedded in the concrete. Additionally, the steel faceplates are connected to each other using tie bars that are also embedded in the concrete infill. These tie bars brace the steel faceplates during concrete casting, and act as transverse reinforcement for the finished SC walls. SC walls facilitate modular construction options where the steel modules can be fabricated in shops or factories, assembled on site, and then filled with concrete. Modular construction approaches can improve construction schedule and thus economy. SC walls are being used in the third generation of nuclear power plants being built in the U.S. and China. They are being considered for small modular reactors (SMRs) of the future, and for multi-story commercial structures as part of the core structure providing lateral stiffness and strength. The design of SC walls for nuclear facilities is governed by AISC N690s1 (2015) and for commercial buildings by AISC 341-17 (upcoming). These specifications include prescriptive provisions for the design of SC walls, but only performance-based provisions for the anchorage of the SC walls to the concrete basemat or foundation. Two performance options are permitted for the anchorage of SC walls to the concrete basemat: (i) where the anchorage is designed to be stronger than the SC walls, and (ii) where the anchorage is designed for 200% of the calculated seismic demand + 100% of other demands. This paper discusses two anchorage options for SC walls: (i) with welded rebar anchors designed to be 25% stronger than the SC walls, and (ii) with embedded dowel bars designed with 200% overstrength with respect to the calculated seismic demands. Both these anchorage options have been considered and built for SC wall designs in the U.S. and China. The first option that anchors the full strength of SC walls is preferred for commercial buildings where ductility is a significant performance requirement. Both the full strength and the overstrength anchorage option can be used for SC walls of nuclear facilities where strength with respect to calculated design demands is a significant performance requirement. The paper discusses the experimental behaviour, analysis models, and design and detailing recommendations for both these anchorage options. The focus is on the cyclic lateral load-deformation responses and failure modes of SC walls anchored to the concrete basemat using these options. The paper also discusses the advantages and limitations of both these anchorage options from construction ease, schedule and economy perspectives.