I have a few questions regarding CMU walls in RAM SS. How are CMU shear walls handled in RAM structural system to obtain lateral load distribution? I have a steel structure with exterior CMU walls which I want to use as shear walls. The CMU shear walls were modeled as other material using the following properties for a f'm=2000 Psi.
Thickness= 4.9 Inches (Equivalent solid thickness for an 8" CMU with 32" O.C grouted vertical cores)
E= 1800 ksi
Unit Weight= 105 Pcf
Poissons ratio= 0.2
Are these properties appropriate for an 8" CMU wall? Should the crack factor be directly applied to the thickness/young's modulus? The CMU walls were modeled at 6" away from the perimeter beams and connected to the beams using a "Other beam" at the ends to satisfy RAM SS requirement's to connect wall ends. The CMU walls fall under the slab edge.
Using the above mentioned approach, looking at the model with CMU shear walls, the lateral force distribution is not making sense. I have uploaded the model for reference.
The file name uploaded is: RAM_Building 2 - Copy.rss
Just to clarify a bit more, the CMU walls were modeled as lateral and none of the steel framing was lateral.
Your approach seems fine. I like to apply the reductions due to cracking directly to E. If you are going to be considering out of plane stiffness in the analysis, then I suggest that you maintain a nominal thickness and further reduce E for partial grouting, rather than reducing thickness. Also be aware that the final self weight will be the product of the unit weight and the thickness.
Thanks Seth. Have you had chance to check the uploaded model? The shear distribution in the CMU walls varies greatly and I am not even seeing a ballpark value comparing it to manual calculations.
The model seems to be working fine. The walls stiffness is reasonable. The walls are generally separated at the corners so that they act independently, and there are semi-rigid diaphragms connecting things together. The wall out-of-plane stiffness is currently turned off. The steel frames are fairly flimsy given the height and section sizes used, despite being all fixed-ended.
Thanks Seth! The steel in the model still needs to be optimized for lateral. I wanted to get a clarification on the CMU walls shear distribution.