May 17, 2012

Detailed Look at Lintel Analysis for Concrete Walls in RISA

RISA-3D now has the ability to design concrete walls with openings for both in-plane and out of plane loading. For lintels we provide analysis results based on the finite element results of the region above the opening.

At solution, the program creates a finite element mesh for the wall to compute the stiffness. From this mesh the program can also calculate the stresses and forces in the individual plates. In the area that defines the region above the opening, the program uses a summation tool to calculate the forces for the region. This summation is done many times over the horizontal distance of the region and the results are then used to create axial, shear and moment diagrams for the lintel.

These diagrams (both In-Plane and Out of Plane) are presented in the opening detail report and can be used to perform concrete design for the lintel.

Tags: RISA-3D, Walls, Concrete, New

February 13, 2012 | RISA-3D, Diaphragms, New

How to Apply a Rigid Diaphragm in RISA-3D

In RISA-3D, rigid diaphragms can be added using the Diaphragm spreadsheet. Just enter the node label and then choose the horizontal plane. Internally, all rigid diaphragms are membrane diaphragms that tie all of the nodes within the diaphragm plane together for both translation and rotation, but only within the plane of the diaphragm. This is done internally using rigid links…

June 20, 2019 | RISA-3D, Diaphragms, New, Shear Walls

Understanding Wall Panel Forces with Rigid Diaphragms

When modeling building structures using steel or composite steel floors, engineers typically utilize rigid diaphragms to distribute lateral loads (wind and seismic) to lateral load resisting elements such as shear walls, moment frames and braced frames. Rigid diaphragms represent a plane of very high rigidity and distribute load to elements which connect to them solely based on the stiffness of the elements. As a result, elements located within the extents of the diaphragm (such as wall panels) will have their forces “re-distributed” based on the relative stiffness of all the elements of that given level. Internally, this is accomplished by the fact that the rigid diaphragm is represented by rigid links that connect every node within the diaphragm (including those in a wall panel) at the level of the diaphragm. The best way to investigate how a rigid diaphragm is impacting the results on a given wall panel stack is to utilize both the Wall Panel Forces spreadsheet and the Internal Force Summation Tool for Walls. To easily review the results for a given wall stack, first select only the wall that you wish to evaluate the results for. Next, select the Filter Results button from the toolbar to the…

April 7, 2020 | RISA-3D, Concrete, New, Shear Walls

Understanding Out-of-Plane Shear Capacity of Concrete Wall Panels

When designing concrete shear walls for lateral loading, RISA-3D includes design checks for both in-plane and out-of-plane shear. In the condition where a concrete wall is under both axial tension and out-of-plane shear, the out-of-plane shear limit state for a specific region within the concrete wall detailed report includes the details shown below: This limit state may cause users to ask the question: “why is the a phi*Vns term listed when no out-of-plane shear reinforcement is present?” The answer is that when calculating the out-of-plane shear capacity of the concrete wall, RISA-3D considers Shear Friction developed at the crack interface. ACI 318 code defines shear friction as the shear transfer across any given plane, such as an existing or potential crack, an interface between dissimilar materials, or an interface between two concretes cast at different times. In this case, the existing/potential cracks condition applies. When axial tension and out-of-plane shear are applied to the concrete wall, cracks will form across the wall thickness as explained by the simplified force diagram shown below: The shear sliding at the crack generates tensile forces Fs in rebar. In return, these tensile forces, Fs cause compression forces, Fc at the concrete crack interface. The…