July 29, 2010

How to Model a Semi-Rigid Diaphragm

RISA-3D does not inherently have the capability to define a semi-rigid diaphragm. If you’re dealing with a complex roof system then you probably need to be able to model something that behaves accurately though.

This is the perfect application for Semi-Rigid Diaphragms. A semi-rigid diaphragm is modeled with plates, and requires you to model and submesh the plates appropriately. In order to adequately mesh your plates it is good to be familiar with Plate-Member Interaction. Plates are modeled using General materials, so the first step is to set up a material with the material properties of your diaphragm.

Link: Plate-Member Interaction

Next, model your plates using the specified material, and with an accurate thickness. Be sure to check the Plane Stress option. This makes it so that the plates only have stiffness within their own plane, and as a result won’t add any composite bending strength to the rafters. With an adequate mesh you can get realistic behavior of a roof diaphragm.

Tags: RISA-3D, Plates, Diaphragms, New

March 20, 2013 | RISA-3D, Plates, RISA-2D, New

Plate Contours Compared to Spreadsheet Values

After solution in RISA-3D, you can use Results View Settings to view the Plate Contours graphically on your model. Many times, these contour values will not exactly match the values reported in the Plate Forces/Stresses spreadsheets. This is because the contour maps are created using a smoothing algorithm that connects the spreadsheet value (this is the true analysis value, taken at the center of each plate with the values of the plates around it to create the contour). You can increase the accuracy of your contours by meshing your plates into smaller plates, but for design purposes, we still generally recommend that you use the spreadsheet values…

December 13, 2010 | RISA-3D, Plates, Loads, RISA-2D

Rebar Design using the Internal Force Summation Tool in RISA-3D

When you have a plate model for a slab or wall in RISA-3D, the Internal Force Summation Tool (IFST) is a very useful analysis tool to get exactly the forces that you want to design for. To use the tool, you must: Be looking at the model in a plan or elevation view (i.e. 2D View only). Have selected ONLY the portion of the model that you want to sum the forces for (all other elements are Un-selected). Let’s look at a slab example. Here we have an elevated slab that is supported on all edges, with a column that lands in the center of the slab. The slab is modeled with plate elements. After we solve the model for that load, we can view our plate contours and use the selection tools to select a representative strip. The representative strip would be a strip through our slab/wall that we want to get the forces for so we can then design reinforcement for this strip. To use the IFST, select the button on the left side of the screen. Clicking twice on our strip will create a plane that the program cuts through the model and will then display the…

December 5, 2019 | RISA-3D, v18, New, Redesign

Using Redesign Lists in RISA-3D

RISA-3D includes Redesign Lists that are used to optimize hot-rolled steel, cold-formed steel, dimensional lumber, and concrete beams and columns. Although, the criteria used for this optimization is the Design Rules, the sizes must be chosen from the available sizes in the Redesign List. It is now possible to add, modify and update the Redesign lists for various material directly in RISA-3D. To access the redesign lists from within RISA-3D click the Redesign Lists button on the Advanced tab. Once the dialog opens, it is possible to create new redesign lists and modify or delete existing ones. Modify an Existing Design List To make modifications to a specific design list first choose a Database, Member Type, Shape Type and Design List. Then choose which shapes to add or remove from the selected list and click OK to finish modifying the list. Create a New Design List To create a new Design List, first click New and then enter a List Name. Then select shapes from the Available Shapes list to add to the Current Design List. Shapes can be selected and added one at a time or can be multi-selected by holding the Shift key. Once all the shapes have…