March 10, 2015

The Internal Force Summation Tool for Walls

You may be familiar with the Internal Force Summation Tool (IFST) that is currently present in RISA-3D. However, a new tool has been added which allows you to click point to point within a wall and will only sum forces between these two points. Previously when using the IFST, forces were summed across all elements within the plane of a cut.

The previous IFST is still available, but the new IFST Wall tool is located on the left side of the screen as well.

A few rules to keep in mind when using this tool:

A batch solution or single load combination must be run.
The wall or walls in question need to be selected in the model view.
The IFST Wall can be used along multiple walls. However the walls must be in the same plane.

Let’s take a look at an example using the IFST Wall. Below is a model where we are interested in the forces within a section of the wall:

1. Run a single load combination solution of the model.

2. For ease of viewing the wall panel, we will only select that element in the model. This is not necessary though unlike with the IFST. We will display the model in elevation view.

3. Select the IFST Wall and the wall panel mesh will automatically be shown.

4. Click two points to designate the cutting line. Snap points include nodes and mesh points within the wall. For this example we will click within the wall mesh.

5. This will bring up the force summation dialog box. Remember the summation is only between Points A and B. The axes labeled 1, 2, and 3 correspond to the clicked points A and B.

Tags: RISA-3D, Walls, New

May 4, 2015 | Dynamics, RISA-3D, RISA-2D, New

Ritz Vector Solver (Dynamics) now Available

RISA-3D v13 includes a new Ritz Vector Solver for the Dynamic analysis. When running a Response Spectrum analysis for seismic design, some structures experience large numbers of local modes that don’t contribute to the lateral response of the structure. The use of load-dependent Ritz vectors (rather than true mode shapes) can greatly improve the speed and accuracy of a Response Spectra analysis for these types of models. There is a new option added to the Dynamic solution options as shown to the right. This dialog can be found by clicking on the Advanced button from the Solution tab of the Model Settings. RISA-3D Output In general, the Ritz vectors will be very similar in shape and frequency to the true dynamic results, though they are not expected to be identical. For that reason, the RISA-3D results will identify them as Ritz Vectors (rather than Mode Shapes) and Ritz Frequencies in the title bar of the dynamic results spreadsheets. Simplified Overview The general concept is that a static solution in the direction of the seismic loading will form a good basis for the approximate mode shapes of the structure which then leads to natural frequency calculations. This concept is nothing new…

June 5, 2012 | New, RISAConnection

How to Account for Axial Loads in your RISAConnection Designs

With the new RISAConnection version 2.0, users now have the ability to design all connections for axial forces as well as the shear and moment forces. Entering Your Load: For beam to column or beam to beam connections, simply enter your axial force under the Loading section of the Connection Properties dialog. For vertical brace connections, enter the beam axial force as the Beam Axial Load entry under Loading, and the brace axial force as Brace Axial load. Sign Convention: RISAConnection uses the same sign convention as RISA-3D and RISAFloor. This is so the loads transfer properly if you are utilizing the program integration. Compression forces are positive (+) and tension forces are negative (-). Axial Load Minimum Threshold: To account for axial loads and shear loads, RISAConnection will often take the resultant of these two as the available load to compare to the capacity. This can expand the limit states checks. In cases where the axial load is less than 5% of the shear load, the axial load will be assumed to be zero and the limit states will look identical to that in version 1.1. Moment Flange Force: Axial loads in moment connections are considered through the flange…

September 3, 2020 | ADAPT-Builder, ADAPT, Slab, New

Precompression in Two-Way Post-Tensioned Slabs

Introduction In the design of two-way post-tensioned slabs, whether it be by use of unbonded or bonded tendons, precompression or “average minimum precompression,” is a critical serviceability requirement in ACI318. It is used to serve as a means for selecting a prestressing force and/or quantity of tendons and also directly addresses the serviceability of column-supported floor systems and the need for minimum reinforcement for shrinkage and temperature. The intent of minimum precompression is satisfied through use of crack control or total reinforcement for other major design codes, hence, a minimum limit for precompression is not required. These other design codes meet a similar need by stipulation for minimum reinforcement versus use of minimum precompression. In theory, a combination of non-prestressed reinforcement and prestressed reinforcement can satisfy code minimum requirements. It is the entirety of prestressed and non-prestressed reinforcement and proper distribution that guarantees satisfactory service-level performance of a two-way post-tensioned slab. For designs conforming to ACI318, where precompression delivered to the slab through prestressed reinforcement meets the minimum requirement of 100psi (0.69MPa), this is deemed acceptable in lieu of non-prestressed reinforcement. Other requirements related to spacing are also necessary to be met. If they are not, a combination of prestressing…