RISAFloor Concrete Floor Slabs can design be transferred into RISA-3D for lateral design using either a Rigid Diaphragm or Semi-Rigid diaphragm. In RISA-3D, the wind and seismic loads are calculated and then applied into the diaphragm level to distribute the forces to the Lateral Resisting System.
Let’s consider the example of the frame shown below. Suppose there is a diaphragm present at the framing level, and that the wall shown is intended only to handle the lateral loads. In reality the columns will be in-line with the wall, and the cantilever beams will pass over the wall without...
In RISA-3D, rigid diaphragms can be added using the Diaphragm spreadsheet. Just enter the node label and then choose the horizontal plane. Internally, all rigid diaphragms are membrane diaphragms that tie all of the nodes within the diaphragm plane together for both translation and rotation, but...
When using rigid diaphragm analysis in RISA-3D it can be useful to evaluate the story shear in each frame. This is a perfect application for the Internal Force Summation Tool. The first step is to solve the desired load combination.
When you model your building in RISAFloor, make sure that you define your slab edge as flexible. That will ensure that the entire contents of the diaphragm will use flexible behavior.
RISA-3D does not inherently have the capability to define a semi-rigid diaphragm. If you’re dealing with a complex roof system then you probably need to be able to model something that behaves accurately though. This is the perfect application for Semi-Rigid Diaphragms. A semi-rigid diaphragm is...
