March 30, 2011

What Are the Seismic Design Rules in RISA-3D

The Seismic Design rules can be found in RISA-3D on the Data Entry toolbar or in the Spreadsheets menu. Below is a quick-reference description of the entries required. For further information refer to the Online Help File > Seismic Detailing.

Label

The label can be any description - it does not affect the analysis/design.

Frame Ductility

High - Meets the requirements for Special Braced and Moment Frames.
Moderate - Meets the requirements for Intermediate Moment Frames.
Minimal - Meets the requirements for Ordinary Braced and Moment Frames.

Overstrength

Check this box if this member type requires Overstrength Load Combinations. Note that only load combinations with Omega will then be used for Seismic detailing.

Moment Connection

BFP - Bolted Flange Plate - Chapter 7 of the 2009 supplement to AISC 358.
RBS - Reduced Beam Section- Chapter 5 of AISC 358.
BUEEP - Bolted Unstiffened Extended End Plate - Chapter 6 of AISC 358
BSEEP - Bolted Stiffened Extended End Plate -Chapter 6 of AISC 358.
WUF-W - Welded Unreinforced Flange - Welded Web - Chapter 8 of the 2009 Supplement to AISC 358
Other/None - All Other Frame types

Overstrength

Check this box if this member type requires Overstrength Load Combinations. Note that only load combinations with Omega will then be used for Seismic detailing.

Z Factor

The ratio between the plastic section modulus for the reduced beam section and the unreduced beam.

Hinge Location

The location of the assumed plastic hinge in inches from the face of the column.

Overstrength

Check this box if this member type requires Overstrength Load Combinations. Note that only load combinations with Omega will then be used for Seismic detailing.

KL/r

Check this box to apply Maximum slenderness to Specially Concentrically Braced Frames, K, V or inverted V braces for OCBF systems.

Tags: Seismic, RISA-3D, New

February 15, 2022 | RISA-3D, New, Analysis, P-Delta

P-Delta Analysis using Geometric Nonlinear Stiffness in RISA-3D

RISA-3D continues to be at the cutting-edge of finite elements analysis software with the release of the Geometric Nonlinear Stiffness method for use during P-Delta analysis. Traditionally, RISA-3D considered P-Delta effects using a Standard Nodal Shear methodology which applies pseudo shear loads at the individual member nodes based on the axial load, lateral deflection and member geometry. To select this method, navigate to Model Settings > Advanced. When comparing the two methods, the standard Nodal Shear Method has been used for many years when considering P-Delta effects in RISA-3D. It is a widely utilized methodology in evaluating the secondary effect of the structure and proved to have great performance in most cases. However, due to the limitations of the method itself, it diverges quickly when axial loads approach the buckling loads. As a result, the P-Delta divergence could potentially occur prematurely for some structures. Another limitation of this method is that the loading is node based, and due to this, users would have to manually add internal nodes along the member to properly consider the P-small delta effect. For additional information on the Nodal Shear Method in RISA-3D and how it handles small P-Delta effects, visit our Online Help. Search…

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…

August 23, 2018 | RISA-3D, New, P-Delta

P-Delta Instability with Gravity Only Loads

“Why am I receiving a P-Delta instability error when I run my DL + LL load combination? I don’t see this error when I run my lateral load only combination.” This is a very popular question that we receive in technical support and it is quite understandable. Why would the model solve with a lateral load but give an P-Delta error with just gravity loads? To understand this, we need to first get a better grasp at how RISA-3D is applying the P-Delta analysis. RISA-3D is calculating secondary shears based on gravity loading and member deflections. This lateral load (secondary shear) is then applied to every member in both directions. For a more comprehensive explanation of how this calculation is performed, see the link below explaining P-Delta analysis. Link: RISA-3D Help: P-Delta The critical take-away point is to recognize that this additional lateral loading is applied in both orthogonal directions of the member. For example, if your model has shear walls or moment frames in the X-direction, there may not be a P-Delta error when running a WLX or ELX load combination. However, the model may see a P-Delta error when you run a gravity load case with P-delta analysis…