January 17, 2019

RISAFloor & RISA-3D: Two Buildings on the Same Podium

RISAFloor is the RISA Building System’s floor design software which allows users to design with composite decks, elevated concrete slabs and more. When paired with RISA-3D, the two create a complete solution for the analysis and design of multi-story structures, including two buildings on the same podium.

Equivalent Lateral Force/Static Force Procedure

After the definition of slab edges and the application of diaphragms in RISAFloor, RISA-3D is used to determine the different lateral forces that need to be attributed to each individual diaphragm that exists at each elevation. These story forces can then be displayed graphically (as shown below) per diaphragm at each elevation.

Dynamic Analysis

If your building requires a dynamic analysis, mode shapes can be calculated and displayed in the same fashion as they are for a single structure. Similarly, building frequencies and mass participation’s are just as simple to retrieve by simply choosing “frequencies” or “mode shapes” from the Results Toolbar or the Results menu drop-down.

Intermixing Diaphragm Types

RISA also allows users to analyze with different diaphragm types (flexible, semi-rigid, rigid) at the same elevation of your separate buildings. Using RISAFloor paired with RISA-3D, engineers can analyze and design complex structures with this configuration. In addition, RISA-3D is fully capable of determining the behavior of different diaphragm types at the same elevation when separate perimeters and diaphragm types for each diaphragm are defined within RISAFloor. These disparate diaphragm types can then be shown graphically in order to review results and deflections.

Tags: RISAFloor, Diaphragms, New

June 19, 2014 | RISA-3D, Loads, New

How to Use Moving Loads

RISA-3D and RISA-2D will allow you to add a moving load pattern to your model and include it in your envelope solution. 1. Adding a New Moving Load Pattern To learn about adding new moving load patterns to your Moving Load Patterns library, please see the How Can I Add a New Pattern to the Moving Load Database blog. 2. Defining the Moving Load Path Once you have added your moving load pattern, you can apply it to your model in the Moving Loads spreadsheet (Spreadsheet > Loads > Moving Loads). In this spreadsheet, you will define the following: Tag: Label of the moving load (this cannot be changed). Pattern: Select the moving load pattern from the dropdown menu. This menu reads in all the patterns that are listed in your moving load library (Advanced > Moving Loads). Increment: Specify the distance at which the load will be stepped through the path. Both Ways: If you want the load pattern to reverse once it has reached the final node along the path, check this box. Node Entries: These define the path of the moving load. Note: You may skip intermediate points along a straight line when specifying the path. 3…

October 19, 2016 | RISA-3D, RISAFloor, New, Instability

Instabilities in RISA-3D with Flexible Diaphragms

In a model that contains both RISAFloor and RISA-3D data it is possible to define your diaphragms as either flexible or rigid for lateral design. You can do this from the Diaphragms spreadsheet in either program: Rigid diaphragms will create a rigid link mesh in RISA-3D that makes the diaphragm act as a rigid body. There is a physical effect on your model that affects the analysis by locking all nodes at the diaphragm level together. Flexible diaphragms act solely as a load attribution mechanism. The program calculates the tributary area to the lateral force resisting elements and applies the load to the collectors. However, there is no physical effect on the analysis. The flexible diaphragm behavior can cause lateral stability problems with your model. Here is an example where this could be a problem: In this scenario our braced frames in our flexible diaphragm model have no out-of-plane stability provided, as the diaphragm has no physical effect on the model. When we solve this model we will receive instabilities in the solution. To handle this scenario we will use very small spring boundary conditions in the out-of-plane directions on the frames. These are dummy boundary conditions of course. Because…

April 20, 2010 | RISA-3D, RISA-2D, New, Unbraced Lengths

How to Correctly Define Unbraced Lengths

There are four different values for Unbraced lengths in RISA-3D, RISA-2D and RISAFloor. Two are for axial calculations and two are for bending calculations. Lb is used to determine the unbraced length for axial forces. This is what is used to calculate the KL/r value. The two different directions represent the weak or strong axis of the member. For symmetrical shapes, the yy direction is the weak axis and the zz direction is the strong axis. Lcomp is used to determine the unbraced length for bending forces. The top and bottom categories represent the top and bottom of the member. To determine the “top” of the member, turn on the Member local axes in your Plot Options. The positive local y axis points to the “top” of the member. The connection type determines what values should be used for each of the four un-braced length entries. However, the same connection type doesn’t necessarily mean that the unbraced length values are the same. This varies drastically depending upon the depth of the framing members. The appropriate un-braced values is really an engineering judgment for the design engineer…