
October 21, 2014
How are Cantilevered Slabs designed?
Concrete buildings often have large cantilevers. In RISAFloor ES, the Support lines can be drawn to support points but also they can be drawn as cantilevers (shown below).
We often get asked: “Should I model my foundation as a slab or a spread footing in RISAFoundation?” While both are valid options, they use very different analysis methods, and the results can vary accordingly. In this article, we’ll walk through a side-by-side comparison, using the same modeled conditions to highlight how the results differ — and why. Model Setup To keep things consistent, we modeled a single condition in two ways: once with a spread footing and once with a mat slab. Mat Dimensions: 10' x 10' x 1' Pedestal: 1' x 1' x 2' Loads Applied: 40 k vertical dead load 10 k lateral dead load 15 k lateral wind load 14.79 k concrete self-weight Soil Overburden: Set to 0 for both elements Slab Mesh Size: Refined below default for more detailed results Load Combinations: A basic set used for clarity (see screenshots in RISAFoundation) Analysis Methodology Feature Spread Footing Slab Element Analysis Type Rigid body Finite Element Analysis (FEA) Support Model Single support point Compression-only springs (based on subgrade modulus) Mesh Behavior No submesh Submeshed into smaller plate elements Lever Arm for Lateral Loads Spread Footings: Full pedestal height + full footing thickness Slabs: Full pedestal height…
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Concrete buildings often have large cantilevers. In RISAFloor ES, the Support lines can be drawn to support points but also they can be drawn as cantilevers (shown below).
In RISAFloor ES, you draw a support line from support point to support point to define the Design Strips. The program will automatically create Design Strips based on the tributary width. When you have walls in the model, it is often a question of how you draw in the support lines.
By default RISA-3D draws all members as line elements located at the centroid of the cross-section. However, connections between members are not always aligned with a member’s centroid. There may be horizontal or vertical offsets in the connection. To account for these you can add rigid links to...
A rigid link is a member element in RISA-3D that can be used for many advanced modeling procedures. It is so useful that it is included as one of the default member Section Sets, as you’ll see below.
The deflected shape is really helpful to understanding your model’s behavior.
RISA-3D and RISA-2D will allow you to add a moving load pattern to your model and include it in your envelope solution.
RISAFloor now has the capability to model column outriggers. This feature can be found on the Cantilevers tab within the Draw Beams dialog.
Print reports can contain spreadsheet information, graphic views, detail reports for specific members and load combinations, and external images such as hand calculations, title pages, etc. When in a model view, you will notice a button with an image of a camera on it in the toolbar:
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