Structural Steel Post for Free standing deck:

The following tables and assumptions are for a structural steel post to support a free standing deck and are categorized for different cases of box beams and seismic locations.

Following assumptions and definitions are used:

  1. Post connection to the ground is fixed in all 3- axis (no rotation).
  2. Post connection to the deck is pinned.
  3. Low seismic area is defined as areas with smaller ground motions based on the available maps in ASCE7-10. The limit chosen here is Ss=0.4 and S1=0.2.
  4. High seismic areas are designed for Ss=1.5 and S1=0.6. If the installation location has a greater Ss or S1, the columns should be designed by a professional engineer licensed in that location.
  5. Load combination of 1.2DL+0.5LL+0.2SL+1.0E is used. Live load is less than 100psf and there is no garage or public assembly case, therefore coefficient for live load is 0.5 based on ASCE7-10 2.3.
  6. Yield stress of the steel is 46 ksi, A500 G(B) HSS square.
  7. Maximum height of post is 10’-0".
  8. Other assumptions are mentioned within the calculations.
  9. Calculations were done for different load cases, for the maximum Trex joist span, the maximum Trex cantilever length, and maximum Trex box beam span.

    (See "Column Load Assumptions Table" below for Max. Trex Span lengths used to obtain the loads on the columns.)

Column Selection Table — HSS posts for free standing deck
Load Case (psf) 50 75 100 125 150 200
Dbl BB & High Seismic 5.5 x 5.5 x 1/8 5.5 x 5.5 x 1/8 5.5 x 5.5 x 3/16 5.5 x 5.5 x 3/16 5.5 x 5.5 x 3/16 5.5 x 5.5 x 3/16
Dbl BB & Low Seismic 5.5 x 5.5 x 1/8 5.5 x 5.5 x 1/8 5.5 x 5.5 x 1/8 5.5 x 5.5 x 1/8 5.5 x 5.5 x 1/8 5.5 x 5.5 x 1/8
Sgl BB & High Seismic 3.5 x 3.5 x 1/4 3.5 x 3.5 x 1/4 3.5 x 3.5 x 5/16 3.5 x 3.5 x 5/16 3.5 x 3.5 x 5/16 3.5 x 3.5 x 5/16
Sgl BB & Low Seismic 3.5 x 3.5 x 1/8 3.5 x 3.5 x 1/8 3.5 x 3.5 x 1/8 3.5 x 3.5 x 1/8 3.5 x 3.5 x 1/8 3.5 x 3.5 x 1/8
* Column Load Assumptions Table — HSS posts for free standing deck
Load Case (psf) 50 75 100 125 150 200
Max. Trex Joist Span to obtain loads on Columns 15 14 12 10 9 8
Max. Trex. Joist Cantilever Length (ft) to obtain loads on Columns 4 4 4 3 2.5 1
Max. Trex. DBL Box Beam Span to obtain loads on Columns 13.67 12.83 12.1 12.1 11.83 11.75
Max. Trex. SGL Box Beam Span to obtain loads on Columns 10.33 9.83 9.17 8.75 8.33 8.25

*Columns shown in the "column selection table" are based on assumed span loading shown in the "column load assumptions table." the "column load assumptions table" should not be used for selecting actual trex joists or box beam members as this information is provided separately.

DISCLAIMERS:

  1. If any of the installation conditions vary from the listed assumptions, an engineer should be contacted to specify the HSS post to be used.
  2. The base plate design and connection is not considered a part of the post design. These base plates and connections should be selected by others.
  3. Trex and Trex affiliates are not responsible for the foundation or geotechnical design.
  4. See Trex post warranty information for maintenance and required site conditions. Trex post cannot be placed below grade.