October 30, 2020

Seismic Factors in RISAFoundation Load Combination Generator

Seismic factors, including Omega, Rho and Ev, can now be included in automatically generated Load Combinations. Values for Omega and Rho shall be entered into the Seismic tab of the Model Settings to be considered in the analysis.

To include these factors in the non-overstrength Load Combinations, check the “Include Ev (vertical)” and “Include Rho” boxes on the Load Combination Generator dialog for the Seismic Load Options.

To generate overstrength (Omega) Load Combinations, choose a radio button under the Overstrength LC Options and select the “Include Ev (vertical)” check box.

Tags: Seismic, RISAFoundation, New

August 27, 2010 | Seismic, RISAFloor, New

What is the Dyn Load Category in RISAFloor?

The Dyn Load represents the additional load that must be included in the calculation of the total seismic weight. Total Seismic Weight = Self Weight + Dyn Load RISAFloor does not include all applied loads as part of the seismic weight. For example, the super-imposed dead loads (DLPre or DLPost) are not included. Only the self weight and dyn loads are part of the total seismic weight. The total seismic weight used to calculate the force is calculated for each diaphragm only. Therefore, any seismic weight that is not connected to diaphragms at all (e.g. walls located outside of a slab edge) not be included in the seismic force distribution…

September 27, 2018 | RISA-3D, New, Analysis

Challenges when using Analysis Offsets

In a previous article we discussed how the Analysis Offsets feature in RISA-3D works and how it can be used to model members at top of steel. In this article, we will discuss some specific situations and how the results change with the analysis offset set as top of member (local -y axis). In most cases setting the analysis offset to top of member should be used with caution since it can lead to odd and unexpected behavior within the model. While using analysis offsets may make the rendered view of your model look more realistic, your analysis model will get unnecessarily complicated. To start, let’s look at a simply supported beam example and compare the bending moment with and without the analysis offset. Moment diagram with the Analysis Offset set to None: Moment diagram with the Analysis Offset set to Local -y axis (top of member): When comparing the results, it appears that we have a fixed-fixed beam rather than a pin-pin beam. What is happening can be shown by modeling this situation as RISA does internally, adding rigid links and dropping the member down by half its depth (11.95”). The rigid link members are modeled with fixed-fixed end…

February 15, 2022 | RISA-3D, New, Analysis, P-Delta

P-Delta Analysis using Geometric Nonlinear Stiffness in RISA-3D

RISA-3D continues to be at the cutting-edge of finite elements analysis software with the release of the Geometric Nonlinear Stiffness method for use during P-Delta analysis. Traditionally, RISA-3D considered P-Delta effects using a Standard Nodal Shear methodology which applies pseudo shear loads at the individual member nodes based on the axial load, lateral deflection and member geometry. To select this method, navigate to Model Settings > Advanced. When comparing the two methods, the standard Nodal Shear Method has been used for many years when considering P-Delta effects in RISA-3D. It is a widely utilized methodology in evaluating the secondary effect of the structure and proved to have great performance in most cases. However, due to the limitations of the method itself, it diverges quickly when axial loads approach the buckling loads. As a result, the P-Delta divergence could potentially occur prematurely for some structures. Another limitation of this method is that the loading is node based, and due to this, users would have to manually add internal nodes along the member to properly consider the P-small delta effect. For additional information on the Nodal Shear Method in RISA-3D and how it handles small P-Delta effects, visit our Online Help. Search…