July 2, 2013

How to use Live Load Special

In RISAFloor, there are several different Load Categories that define Live Load. The IBC and the ASCE7 both have provisions that allow you to reduce the tributary area of the Live Loads. These codes have equations that adjust the Live load based on the tributary area and usage (KLL*AT). In RISAFloor, the Live Load Reducible (LL-Reduce) calculates the reduced live load based on the tributary area.

Live Load Special (LLS) should be used when the loads exceed 100 lb/ft2, there is no live load reduction except when there are multiple stories. This designation should be used for the following cases:

Heavy Live Loads: Live Load is considered a Heavy Live Loads when it exceeds 100 lb/ft2.
Passenger Vehicle Garages

There is live loading associated with Assembly loading (or previously named Special Occupancy Live Loads). Assembly loads should be considered as Live Loads not Live Loads Special. In the ASCE7-10, you cannot reduce assembly live loads so they would be LLS- Non. In IBC 2012, the assembly load is not specified, and the Load Combination (f1=1), so you would need to use LLS-Non.

In the previous years, you could not reduce any loads under 100psf and they could not get the multi-story reduction, so you would want to use LLS-Reduce for 100psf or higher, LLS-Non for loading under 100psf.

Tags: Loads, RISAFloor, New

June 7, 2017 | Loads, RISAFloor, New

Parapet Wind Loading

RISAFloor v11 allows users to add parapets while allowing the program to calculate the wind loads per the ASCE 7 parapet wind loading requirements. How to add a parapet to your model? The Floors spreadsheet has a parapet height per floor which is the default for the entire floor level. You can then go into the Columns and Wall Panels spreadsheets to customize the height of your parapets around the edges of your roof. For columns, the program will go around the edge of your roof and find the column parapet height at each location. The smaller of the two values between the two columns is the parapet height. Once this is complete you can solve your model and use the Director to go to RISA-3D, where you view the Wind Load Generation dialog. From here you can see the defined geometry and the wind load at each parapet. This load is then lumped in with the regular roof wind load to give a total wind force in each direction…

May 5, 2021 | RISAFloor, New, Equivalent Uniform Load, Steel Joists

Equivalent Uniform Load Method in Steel Joist Design under…

When a steel joist has special loading that requires extra consideration, the most economical solution may be to use a standard joist that is capable of resisting the non-standard or special loading. When this type of design arises, RISAFloor will add an (SP) extension to the joist designation in order to indicate that it is resisting a non-standard load. Because this loading falls outside the normal design criteria for the joist tables, these (SP) joists may warrant further detailing by the engineer or joist manufacturer to insure adequate performance. The RISAFloor detail report provides a Special Joist Load Diagram which shows the Point Loads, Distributed Dead, and Distributed Live loads with their magnitudes and dimensions. RISAFloor will choose a joist such that the capacity shear envelope of the joist under a standard uniform load is still greater than the actual shear at all locations along the length of the joist. Because the joist will have a shear strength greater than zero at the midspan of the beam, the shear envelope for a joist with a maximum uniform load capacity of W, would be given by the figure shown below: In addition to checking the shear envelope, the program will make…

November 17, 2011 | Loads, RISAFloor, New

How Do I Assign Drift Snow Loads to the Roof in RISAFloor?

RISAFloor has the ability to apply tapered snow loads on your building’s roof to simulate drift snow loads. Go to the roof framing level in your model and select Draw Area Loads from the Drawing toolbar. This will open the Create Area Loads dialogue box. Select the Tapered Area Loads option and enter in your Base and Peak Magnitude values for your load. Select SL (Snow Load) as the load category and select PY as the Direction. There are three options for Direction; PY, y and Y. Y represents the global Y direction, y represents the local y direction of the members and PY is the projected load in the global Y direction. See "Using Projected Loads in RISA-3D" for more information on how projected loads are applied. Click Apply and select the four points that will make up the perimeter of your snow load. Note that the first two points you select will be the base of the tapered load and the last two points will be the peak. These tapered area loads can be drawn as any four sided polygon and are not required to be rectangular or square. To view your area load in an isometric view…