Seismic Behavior of Screen Grid Core Insulated Concrete Form Walls

The use of the insulated concrete form (ICF) walls in residential buildings has increased over the past few decades. Much research has been conducted to evaluate the lateral strength of these walls by applying monotonic and cyclic loadings. In the current study, full-scale shake table experiments were employed to evaluate the in-plane behavior of four screen grid insulated concrete form (SGICF) walls. The first two wall specimens utilized dry fit insulated form blocks made from recycled expanded polystyrene granules that were bonded together with cement. When stacked, the cavities in the blocks formed a grid of cores that are evenly spaced vertically and horizontally. The walls consisted of four circular vertical cores and five circular horizontal cores reinforced with a single rebar placed nominally in the center of each core. The rest of the wall specimens were newly suggested pattern of SGICF walls, which consisted of three circular vertical cores and five circular horizontal cores. Two rebars were placed in each vertical core, and a single rebar was placed nominally in the center of each horizontal core. Each wall was built on top of a foundation block that was designed such that failure would occur within the walls themselves. For each type of SGICF walls, steel fiber-reinforced concrete was used in one of the walls to evaluate the effect on failure modes, drift capacity, and shear strength. The results showed that the use of fiber-reinforced concrete in the cores of the SGICF walls that were built out of ICF blocks had not significantly improved the drift capacity, and had exhibited lower strengths than the wall with conventional concrete. These outcomes were mainly attributed to voids in the cores that had resulted despite similarities in workability of the concrete mixes and in techniques used to place the concrete in the walls. On the other hand, the use of the steel fiber-reinforced concrete in the cores of the newly suggested pattern of SGICF wall and the two rebars in the vertical cores had improved the drift ductility of the wall by about 63%. The evaluation of the steel fiber-concrete was conducted at the component levels of the SGICF walls. Six simply supported reinforced concrete beams (3 ft. long) were tested in a three-point bending configuration by applying a cyclic loading protocol. Results showed that the steel fiber-concrete did not improve the lateral strength and the drift capacity. Steel fiber dose played an essential role in this investigation. Analytical approaches were used to estimate the initial stiffness and the lateral strength of the SGICF walls. None of the approaches managed to provide an acceptable estimation of the initial stiffness. Meanwhile, the summation of individual vertical core plastic moment capacity and the ACI equation for the minimum shear strength of the concrete methods were successful in estimating the in-plane lateral strengths. Finally, a computer model was created to predict the lateral in-plane behavior of the SGICF walls. Results showed that the computer model provided good estimations for the peak lateral strength and the initial stiffness