Minimum Design Requirements for Insulated Concrete Form Wall Systems

Thesis (Master's)--University of Washington, 2021Insulated concrete form (ICF) walls are used in low- to mid- rise construction and are cost-competitive with wood and masonry walls. In addition, these wall systems meet increasingly strict insulation requirements in building codes and therefore have the potential to be more cost-effective than wood construction. There is one drawback, however, and that is that their minimum reinforcing requirements are determined by ACI 318-19, including maximum spacing limits and minimum reinforcement ratios. These reinforcement requirements exceed what is required to meet strength demands. As such, there is a need to investigate the required spacing and amount of reinforcement. In addition, there is an interest in using steel fibers to replace some of the wall reinforcement. Previous studies have not investigated these design parameters. This research project utilized non-linear finite element modeling (FEM) to investigate the impact of reducing minimum steel requirements as well as the use of steel fiber in planar walls. The FEM was based on prior work and validated using in-plane and out-of-plane tests. The wall models were subjected to monotonically increasing shear in the out-of-plane direction and a constant, distributed axial load at the top of the wall. The reference wall geometry was selected to meet a single bay of a one-story structure as well as future test specimens. Using the validated modeling approach and reference geometry, a parametric study was conducted to investigate the impact of the following design parameters on the structural response of the wall: (1) bar spacing, (2) number of curtains of steel, as well as (3) steel fiber dosage in conjunction with the first two variables. The research findings are as follows: (1) the peak strength of the wall is determined by the tensile capacity of the plain or fiber-reinforced concrete (FRC), (2) the bar spacing and the number of curtains of steel only impact the residual strength increase after cracking, and (3) it appears possible to use FRC with starter bars for some walls as this concrete provides shear, moment and axial capacity and the starter bars transfers the forces to the foundation. The findings suggest more economical bar layouts for ICF walls are possible without compromising the structural response