November 19, 2011

RISA-2D Educational Version

Students and Professors can utilize a special version of RISA-2D which is aimed at teaching and understanding the basics of structural analysis. While this version has a limited number of features, it will prove to be a useful tool in expanding the students structural engineering knowledge.

Link: RISA-2D Education Version

Link: RISA-2D Educational Tutorial

Note: This version is for educational purposes only. If you are a practicing engineer, please download the RISA-2D Demo Version which includes the full capabilities of the software.

Link: RISA-2D Demo Version

Tags: RISA-2D, New, Educational

August 18, 2011 | RISA-3D, Loads, RISAFloor, RISA-2D, New

Using Projected Loads in RISA-3D

RISA-3D, RISA-2D and RISAFloor have the capability to project distributed and area loads onto members. Consider the case of snow load on two buildings: one with a flat roof and one with a sloped roof. Ignoring the concept of shedding, if both buildings have the same footprint then they should both have the same total weight of snow applied to them. This is because the snow doesn’t care what the shape of a building is as it falls. The same total amount of snow will fall on a given acre regardless of what’s on it. Below is an image illustrating roof rafters from both the sloped and flat roof beams. In both cases a vertical snow load of 100 lbs/ft has been applied in the global Y direction. Note that the total end reaction on the sloped rafter is 1.41k versus only 1.00k for the flat rafter. This is because the sloped rafter is actually 14.1 ft long, and we have applied the load as 100 lbs per linear foot of rafter. In order to get the correct behavior for snow we need to project the load onto the horizontal plane. The image below shows the same members, but with…

May 24, 2010 | RISA-3D, RISA-2D, New, Analysis, Eccentricity

Define a Beam Eccentricity in RISA-3D

When you have a deep column, it is necessary to model the beam so that it connects to the face of the column. This results in an eccentricity at the joint. RISA-3D offers two ways to model this eccentricity. Open the Members Spreadsheet and go to the Advanced tab. There are two options labeled I Offset and J Offset. These represent the offset at the start (I) and end (J) of the member, respectively. You may also specify the I Offset and J Offset by first selecting the beam, and modifying the Additional Properties section of the Properties Grid. For the beam member you can either enter the exact value of the member offset (i.e. half the depth of the column) or you can enter the column member number. If you enter the column member number the program will automatically calculate the offset assuming half the column depth. This feature is very useful because it will automatically update the offset value when you change the column size. Please note that using the offset feature will reduce the total length of your beam by the offset amounts which will affect your design code check calculation. For example, in a portal frame…

December 16, 2010 | RISA-3D, New, Instability

How Should I Model Boundary Conditions for a Truss in RISA-3D?

When it comes to trusses in RISA-3D, boundary condition definitions (pin vs. roller) can make a huge difference. Let’s take an example of a typical roof truss. Note that a pin-pin boundary condition has been applied to the ends. First we must make sure to give the truss out of plane stability by setting this up as a 2D Model within RISA-3D. Then, after solving, you will find that this is not at all behaving like a truss. There are huge axial compression forces in the top chords, and there is no tension in the bottom chord. The reason is that the pin-pin boundary condition prevents the bottom chord from elongating. If it cannot elongate then there cannot be axial strain in the member. You will recall from your Mechanics of Materials class that if there is no strain there cannot be stress, and therefore there can be no axial tension in the bottom chord. The program works out statics the only way it knows how by using arching action with the top chords instead of looking at truss behavior. Now instead try a roller boundary condition on one end of the truss: Now the bottom chord is experiencing a…