User Guide

RISA-3D User’s Guide
Version 5.0
86
We will use the Block Math feature to change the magnitude of the load. First
we will select all of the cells in the Magnitude column.
Click on the column heading for the Magnitude (this is the gray area at the top of
the column that contains “Magnitude…”).
The entire column is now selected and is colored magenta.
Now click on the Block Math
button to open the Block Math dialog.
We want the dead load to be 90psf, or 90% of the copied live load.
Enter “0.9”, select the Multiply option and the dialog looks like this:
Click OK and the surface loads now have a magnitude of 0.09ksf (90psf). Press
Ctrl-F4 to close the Plate Surface Loads spreadsheet.
Self-weight
We will include the self-weight of the structure and be finished defining loads.
We will add it to the same load case that we just placed the surface dead loads.
Simply entering a factor in the Y Gravity column on the Dead Load case will do
this.
Click in the Y Gravity column on the fourth row and type:
-1
This is how you tell RISA-3D to calculate and include the self-weight of the
model. The factor entered is a multiplier for the self-weight. In this case, we used
“-1” because we want the full self-weight applied downward (the negative Y-
direction). You can apply self-weight in the X, Y and/or Z directions.
Load Categories
The last thing to do on the Basic Load Case spreadsheet is to assign each load
case to a category. Categories are especially helpful in bringing all of your loads
together. In this model the loads are quite manageable and we could just refer to
them by their BLC number. Many structures, however, will be modeled with
many separate load cases that are part of the same family. Being able to
categorize the loads makes it easier to later combine them for solutions.
Click in the first cell of the Category column and then click on the down
arrow in that cell to see the list of categories. Choose “RLL (Roof Live Load)”.