December 21, 2010

How Can I Account For Continuous Tie Rods in RISA-3D Wood Walls?

Continuous tiedown systems are used to help resist overturning forces generated by lateral loads, and can be estimated in RISA-3D using the hold-down database and the strap forces.

The Holddown Excel database is located in the RISA>Wood Schedules>HoldDowns folder and contains the parameters for the deflection calculations from the NDS 2015 Special Design Provisions for Wind and Seismic, Equation 4.3-1:

In order to account for the uplift effects of the tiedown (rod elongation, bearing deformation, fastener slip, etc.) you need to change the change Δa. A good estimate of this value is listed below:

P= Allowable Tension

L= Length of the rod

A= Area of the rod

E= Stiffness of the rod

It is important to note that this assumes a tied-off system which distributes loads at each level rather than a skipped story system.

The manufacturers of the tiedowns require the tension forces at each floor level, and you can find the Strap Forces from Wall Detail Report. This can also be used to select the appropriate tiedown for the wall from the manufacturer’s charts listed under Allowable Tension Capacity based on the wood material.

Tags: RISA-3D, Loads, New, Wood, Wind

October 19, 2016 | RISA-3D, RISAFloor, New, Instability

Instabilities in RISA-3D with Flexible Diaphragms

In a model that contains both RISAFloor and RISA-3D data it is possible to define your diaphragms as either flexible or rigid for lateral design. You can do this from the Diaphragms spreadsheet in either program: Rigid diaphragms will create a rigid link mesh in RISA-3D that makes the diaphragm act as a rigid body. There is a physical effect on your model that affects the analysis by locking all nodes at the diaphragm level together. Flexible diaphragms act solely as a load attribution mechanism. The program calculates the tributary area to the lateral force resisting elements and applies the load to the collectors. However, there is no physical effect on the analysis. The flexible diaphragm behavior can cause lateral stability problems with your model. Here is an example where this could be a problem: In this scenario our braced frames in our flexible diaphragm model have no out-of-plane stability provided, as the diaphragm has no physical effect on the model. When we solve this model we will receive instabilities in the solution. To handle this scenario we will use very small spring boundary conditions in the out-of-plane directions on the frames. These are dummy boundary conditions of course. Because…

October 30, 2020 | RISA-3D, RISAFoundation, New, Basic Load Case, v19, Loading, v13

Expanded Load Categories in RISA-3D and RISAFoundation

New to RISA-3D v19 and RISAFoundation v13 is the ability to apply up to 100 "Other Load" Categories. Previously users only had the ability to add up to 10 "Other Load" Categories. The expansion of "Other Load" Categories gives the user more flexibility to be able to apply and organize the loading in the model to fit their needs. To apply "Other Load" Categories in RISA-3D, simply select the "Other Load" Category from the drop down menu when drawing loads. To include the "Other Load" Categories in the Load Combinations in RISA-3D, you may either enter OL1-OL100 in the BLC field or you can select the ellipses to prompt the Set BLC Entry and select the "Other Load" Category from the drop down menu. To apply "Other Load" Categories in RISAFoundation, choose the "Other Loads" from the dropdown on the Distributed Loads Spreadsheet (or in the left Properties Toolbar) and choose a value between 1 and 100. To include these "Other Loads" in Load Combinations, you may either enter OL1-OL100 in the BLC field or you can select the red arrow to prompt the Set Category Entry and choose the "Other Loads" radio button and input a value between 1…

August 7, 2015 | RISA-3D, RISAFloor, New, Shape, RISASection

How to Create a Custom Shape in RISA-3D

There are multiple options in RISA-3D and RISAFloor to create a custom shape not available in the program databases. The first, is to utilize RISASection in order to create cross-sections, calculate section properties and import the shape directly into RISA-3D. For more information on integrating RISASection and RISA-3D, read the article below: In addition to using RISASection, a custom shape can be added directly to RISA-3D. The type of shape you create depends on if you want a code check for your section or you’re more interested in the analysis only and don’t require a code check. The type of material and shape type is also a factor in how you create a custom shape. We will explore the available options below. Option 1: Code Check Desired Perhaps you have a built-up section including a wide flange with a channel. You would like a code check on the section based on the wide-flange. Open up your shape selection dialog box from the Properties Panel and then choose Assign Shape Directly by clicking on the ellipsis button. Once here, select WF and click Add. In the Add Shape dialog box that pops up, you will enter in the section properties and…