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  • STRUCTURAL INSPECTION - Aluminum Platform Design


    I. Purpose of Investigation:

    At the request of the Client, we have performed a
    structural analysis of the 4'x4' platform as described in the specification, furnished
    by the Client. The scope of this preliminary report includes checking the current
    design for 80 psf floor live load, and the handrail for Code prescribed forces of
    50 lb/ft (uniform load) / 200 lb (point load).


    II. Description of Platform:

    The platform consists of nominally 4 ft. square segments, which are to be connected
    end to end, in order to form a continuous walkway approximately 18" above the
    ground surface. Each segment has 4 legs which bear upon the ground. Handrails
    are continuous along 2 opposite edges. Materials are 6061-T6 aluminum structural
    shapes and extrusions. Decking (by others) is to be 2x6 High Density Polyethylene
    (HDPE) by US Plastic Lumber


    III. Analysis:

    The various structural members were analyzed for the loads indicated above.

    Floor:

    The 1" x 1" tubes and the 1.5x1.5 angles running perpendicular to each other do not
    themselves have adequate strength to resist the 80 psf floor load. The Client
    has indicated that they performed a load test utilizing 2x6 lumber decking over the
    aluminum framing members, and that the system held the load with no significant
    deformation. Calculations for 1.5" thick lumber deck boaDrs show that they have
    adequate strength and nearly adequate stiffness, to span the 5 feet without the
    help of the tubes and angles. In the test, it is likely that the sub-framing acted
    essentially as stiffeners. That is, they helped stiffen the lumber, but the lumber
    itself was stiff enough to prevent the aluminum framing from absorbing excessive
    load.

    The HDPE decking called for in the Architectural specification, however, has only about
    1/10th the stiffness of regular lumber. (Reference - US Plastic Lumber published structural properties.) Use of the HDPE will result in nearly all the load being transferred into the aluminum subframing, which cannot resist the 80 psf loading.

    The 4" siderail extrusion checked out as adequate for the loading.


    Handrail:

    The members comprising the handrail are adequate for code loadings. The U-bolt size
    and grade was not noted in the pdf drawings. The required diameter likely falls between 1/4" and 3/8", depending on material grade.

    The 2"x2" tube kickers at 45 deg. angle are necessary for adequate stiffness and strength.


    IV. Recommendations:

    If the HDPE decking is utilized, some sort of modification will be necessary to bolster
    the strength of the aluminum subframing.


    V. Referenced Documents:

    U.S. Plastic Lumber HDPE Technical Data, 2 pgs.
    Page 1



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Grand Rapids, MI 49546
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