April 22, 2014

How can I check a Slab on Grade for Post Loads?

Need to first know how to model a slab on grade? See our Slabs on Grade article to learn how to model slabs on grade:

Slab on Grade Design with RISAFoundation

One of the most critical aspects of slab on grade design is the consideration of punching shear due to posts/columns/racks which bear directly on the slab. With RISAFoundation it is easy to model these conditions and get complete punching shear checks. In the example below an L-shaped slab has four concentrated loads from an equipment rack which is sitting atop the slab.

Post Design 01

The slab will automatically be designed for flexure and one-way shear, but in this case it is the punching shear which will most likely control the design. In order to check for punching shear you must model the profile of the baseplate at the bottom of each post. Click the button highlighted in the image above in order to draw a post. Choose to draw a Post/Column, as opposed to a concrete pedestal, and define the dimensions of the baseplate:

Post Design 02

Posts are always centered on a node, and any load which the post is carrying should also be applied directly to that node:

Post Design 03

After solving you can review the punching shear results, which include a unity check (UC) showing the ratio of punching shear stress to capacity. As long as this value is less than 1.0 your slab on grade is thick enough to handle the post load.

Post Design 04

Tags: RISAFoundation

You may also be interested in

Nov 8, 2018 | Tips & Tricks
Mat Slab Overturning and Sliding Safety Factors

RISAFoundation v11.0 includes two new tabs in the Safety Factors resul...
Read More

Aug 21, 2019 | Tips & Tricks
RISA-3D v18 Sneak Peek Videos

The new release of RISA-3D is right around the corner! Check out our t...
Read More

Jul 12, 2019 | Tips & Tricks
Implementing Realistic Behavior for T/C Members in RISA-3D

Tension or Compression (T/C) Only members are commonly used in steel b...
Read More

Jun 20, 2019 | Tips & Tricks
Understanding Wall Panel Forces with Rigid Diaphragms

Rigid diaphragms represent a plane of very high rigidity and distribut...
Read More