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TR.32.4 Area, One-way, and Floor Load Specifications

These commands may be used to specify loading over an area enclosed by beam members and the program will distribute the loading onto the perimeter beams as either a one way or two-way system. They are used mostly when the entity transmitting the load, such as a slab, is not part of the structural model. The AREA LOAD or ONEWAY LOAD may be used for modeling one-way distribution and the FLOOR LOAD may be used for modeling two-way distribution. There are three commands which should be used in the following way:

Area Load
The program will establish the direction of the shorter span and load the beams in that direction. This command is used for distributing a pressure load onto the beams that define a closed loop.
Floor Load
This command is used for distributing a pressure load onto all beams that define a closed loop assuming a two way distribution of load.
This may appear similar to the AREA LOAD command, but this command defines an area from which the program will search out closed loops of beams, similar to the FLOOR LOAD command and also has the option to define the direction of span. This command is an development of the principals defined in the FLOOR LOAD command, but the load is defined to span in a single direction.

Live Load Reduction

Floor loads and one-way loads can be made reducible according to Section 1607 of IBC 2000 if included in a Live Load case which is specified as Reducible. The following rules are implemented:

  • Reduction only applies to live loads on members with a tributary area of greater than 150 ft2.
  • Live loads over 100 psf are not reduced.
  • The reduction in live load (in percent) is = 0.08×(Atrib - 150), with a maximum reduction amount of 40% for members carrying load from one level only.
Note: Live load reduction is not not available for area loads.