# Experimental/Numerical Evaluation of Steel Trapezoidal Corrugated Infill Panels with an Opening
## 4 Numerical Analysis  
### Numerical Modeling and Verification  
The numerical modeling was performed using a general-purpose nonlinear program. Similar to [PERSON] et al. [8], the infill plate of each specimen was modeled seamlessly and connected directly to the adjacent beams and columns. A four-node reduced integration shell element, which is a double-curved shell element with hourglass control, was used to model all members, including the top and bottom beams, columns, stiffeners and infill plates. The clamped boundary conditions were applied to the bottom beam, and the out-of-plane displacement of the nodes at the left and right ends of the top beam was restrained. The finite element models of both tested specimens are shown in Figure 18.  
Figure 17: Cumulated energy of tested specimens.  
Figure 18: Finite element models of tested specimens.  
Both material and geometrical nonlinearities were considered in the analysis. The material nonlinearity was taken into account with the assumption of a multi-linear stress-strain curve for steel material using the coupon test results (see Figure 19). The [PERSON] yield criterion and a combined isotropic-kinematic hardening model based on the work of [PERSON] and [PERSON] [36] were applied in the numerical analysis. The analysis of both tested specimens was implemented without an initial imperfection and under the cyclic horizontal displacement-controlled loading. Figure 20 indicates the force-displacement curves of both specimens due to cyclic loading obtained by numerical modeling and the experimental investigation. Figure 21 shows the envelope of the experimental force-displacement curves due to cyclic loading along with the numerical force-displacement curves for both specimens.  
Figure 19: Stress-strain behavior of steel material.  
Figure 20: Hysteretic behavior of tested specimens.  
As illustrated in Figure 20 and similar to the results reported by [PERSON] et al. [9] for CSIFPs without opening, the hysteresis loops are stable, and no pinching is seen in the hysteresis loops. It should be noted that both tested specimens reached almost 6% story drift without collapse. The differences seen in Figures 20 and 21 between the experimental and numerical results could be related to the idealization of the stress-strain curve of material behavior with a multi-linear curve along with the effects of welding and bending of flat steel plates implemented to create corrugated plates.  
Figures 22 and 23 show the numerical results for the final deformation form of specimens 1 and 2, respectively. As specified in Figures 22 and 23, the maximum deformation of the infill plate in the z-direction (out-of-plane direction) is, respectively, 84 mm and 98 mm for specimens 1 and 2, which is close to the experimental measurement. Deformations of the infill plate in the z-direction appeared in the form of depression and protrusion in the sheet. Figures 22 and 23 also show that the amount of deformation in the y-direction is low.  
Figure 21: Force-displacement curves of tested specimens.  
Figure 22: Final deformation form of specimen 1 (mm).