November 2, 2018

Masonry Lintel Analysis using FEA

In RISA-3D, the current method of design for masonry lintels is Simply Supported where the masonry lintels are idealized into a simply supported pin-pin beam configuration. Now, masonry lintels can instead be analyzed using finite element analysis. With this method, the lintel will be fully integrated as part of the wall.

In the Wall Design Rules spreadsheet, choose the FEA analysis method for the masonry lintel.

With the FEA analysis method, the forces that are experienced by the lintel are based on finite element analysis rather than a simply supported beam condition. The shear and moment diagrams can be seen in the Opening section of the Wall Detail Report.

Note: Reinforcement for the masonry lintel is only provided for the Simply Supported analysis method.

Tags: RISA-3D, New, Analysis, Masonry

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…

September 28, 2018 | RISA-3D, New, Analysis

Analysis Offsets now Available

RISA-3D v15 includes "analysis offsets" which moves the centroid of the member for analysis allowing for flexibility in how members are designed. Let's use a WT brace to demonstrate how this feature can be utilized. When you model a WT brace it exists at the member centroid, which means that no bending ends up in the brace due to the fact that the brace is actually eccentric to the braced frame. Recently, we've added a feature called “Analysis Offset” which moves the centroid of the member for analysis. In the example below the flange of the WT is bolted to a gusset that is ¾” thick, so we would want the centroid to be moved to the face of the flange, plus half the gusset thickness (3/8”): With this offset applied, when the model is solved you’ll note that the brace bows out of plane, indicating that it does have bending. The detail report confirms this. Note how much the Code Check value increases when the real-life bending due to eccentricity is considered in the RISA model…

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

Using Analysis Offsets in RISA-3D

Have you ever wondered what the Analysis Offset feature does? Let’s take a look at how this feature can be used to model members at top of steel. The analysis offset feature allows a member to be offset from its centerline for analysis. When it is enabled the member is actually shifted to the offset location for analysis. In order to provide connectivity the program places hidden rigid links to connect the member to the nodes that define the member’s I/J Joints. Joints which fall along a physical member are also automatically connected to the member’s actual analysis location via hidden rigid links. You can access the analysis offset by clicking on the member or through the Advanced tab of the Members spreadsheet. When the analysis offset dialogue is opened, the software will present the user with options for offsetting the member from its original centerline. The most common option for analysis offset is Local -y axis, which equates to setting the analysis line at top of member. Using this setting for the beam in a simple frame system allows for a more realistic representation of the structure (which can be seen graphically when the rendered view is enabled). It…