March 16, 2011

Using Transient Loads to Verify Applied Area Loads in RISA-3D

When a model is solved that contains Member Area Loads, the program automatically attributes them to the applicable members within the defined area of the applied load. The load is attributed to the members as distributed loads that RISA-3D defines as Transient Loads.

In order to help verify the load distribution, RISA-3D automatically generates a new Basic Load Case for each Load Case that contains an area load. These new Load Cases include the Transient Loads for each original Load Case, and allow for quick verification of the distribution in the Basic Load Cases spreadsheet.

The loads can be verified graphically as well. Simply turn on the graphic view of the Basic Load Case in question and then select the Transient Area Load case from the Load Display drop down menu.

Zoom in on this new view to confirm the load distribution and verify the load magnitudes.

Tags: RISA-3D, Loads, New

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…

April 20, 2011 | RISA-3D, Loads, New, Area Load

Refining Area Load Distribution in RISA-3D

After solving a model with Member Area Loads, RISA-3D will automatically create Transient Basic Load Cases that allow the user to verify load distribution. For information on how to view this distribution, please see the article "Using Transient Loads to Verify Applied Area Loads in RISA-3D". If this load attribution is not what you’d expect, you can adjust the Area Load Mesh entry, which controls the fineness of this distribution. This feature is located on the Solution tab of Model Settings: If you have a model with closely spaced members, you can lower this value to achieve a finer area load mesh and therefore a more accurate load distribution…

August 11, 2015 | Seismic, RISA-3D, RISAFloor, New, Wind

What Loads Transfer from RISAFloor to RISA-3D?

RIAFloor designs the gravity system and then integrates with RISA-3D to design the lateral system. Only the lateral members are taken from RISAFloor over to RISA-3D. The loading is automated in this integration so one of the most common questions is: what loads are transferred when switching from RISAFloor to RISA-3D? Below is the brief explanation to answer this question. Gravity Loads: The lateral members that become part of the RISA-3D model bring over their gravity loads. This also includes the beam reactions from the gravity only members that were not transferred in to RISAFloor. The load categories in RISAFloor are automatically converted into Basic Load Cases in RISA-3D. The exception to this are the Load Categories that deal specifically with construction loads (DL Const and LL Const), which are not converted. Wind Loads: The wind loads are automatically calculated as the RISAFloor model gets integrated into RISA-3D. The wind load parameters are located in the Wind tab of the Global Parameters in RISAFloor. However, these settings may also be changed when the wind load dialog pops up when transferring to RISA-3D: The option to generate roof wind loads are only present in RISA-3D models that are integrated with RISAFloor…