October 26, 2018
What’s New in the NBC 2015?
The 2015 NBC compliant codes have been implemented into RISA-3D v17.0, RISAFloor v13.0 and RISAFoundation V.11.0!
Rigid diaphragms in RISA-3D are a powerful way to model how floor systems distribute lateral loads. By forcing all connected nodes to move together in-plane, they effectively capture the stiffness of a concrete slab or diaphragm deck—often simplifying analysis without sacrificing accuracy. However, when rigid diaphragms are combined with sloping members, they can introduce unexpected behavior that changes how the structure resists loads—sometimes creating a hidden “tension tie” that doesn’t exist in the real system. When Rigid Diaphragms Alter the Model’s Behavior Consider a simple moment frame with sloped beams under gravity loads—common in pre-engineered metal buildings. Model 1: No rigid diaphragm applied Model 2: Identical frame, but with a rigid diaphragm located at the eaves When reviewing the strong-axis bending moments, column base reactions, and thrust forces: The first frame behaves as expected. The second frame (with the rigid diaphragm) shows reduced bending moments and smaller thrust reactions at the column bases. At first glance, this might seem like an improvement—but it’s actually unrealistic behavior caused by the diaphragm. Why It Happens: The “Hidden Tension Tie” In the model with the rigid diaphragm, the diaphragm prevents the eaves from moving apart under load. This effectively turns the diaphragm into…
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The 2015 NBC compliant codes have been implemented into RISA-3D v17.0, RISAFloor v13.0 and RISAFoundation V.11.0!
The 2016 edition of ASCE Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 7-16) is now available in RISA-3D v17.0, RISAFloor v13.0, and RISAFoundation v11.0!
Eurocode lateral torsional buckling capacity is calculated per equations in Annex F in the ENV 1993-1-1:1992. This calculation uses variables C1, C2 and C3. Since there is no generic formula in the Eurocode to calculate the moment gradient factor, C1, RISA will use the widely accepted López, Yong...
With the initial implementation of wood wall design in RISA-3D, the wall aspect ratio was calculated as the full height of the wall divided by the width of the region.This was intended to accommodate balloon framed multi-story walls that were drawn as one continuous wall stack. With recent...
With the recent release of RISA-3D v17 the program now offers the user the option to use Chord Straps between floors of a wood shear wall building in lieu of using hold downs. Chord Straps are a great option for transferring tension load between floors of a multi-floor building and can be installed...
RISA-3D v17.0 now has the ability to model partial fixity member end releases. Partial fixity end releases can be utilized in RISA to model the behavior of a partially restrained or semi-rigid connection that cannot be idealized as fully fixed or pinned. Partially restrained connections are common...
The new AWC NDS 2018 code has been implemented into RISA-3D v17.0 and RISAFloor v13.0. To select this code for your design, simply choose this code from the Codes tab within Model Settings.
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...
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).
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