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  • Load Test - Aluminum BoaDrwalk


    I. Purpose of Investigation:

    At the request of the client, we have performed a
    structural analysis of the platform as described in the pdf files, furnished
    by the fabricator

    The scope of this report includes checking the current design for 100 psf floor live load,
    and the handrail for Code prescribed forces of 50 lb/ft (uniform) / 200 lb (point) loads.


    II. Description of Platform:

    The platform consists of nominally square segments, which are to be connected
    end to end, in order to form a continuous walkway approximately 20” 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.

    Note that some different joist members have been considered. The final design for this
    report utilizes aluminum channel sections for joists going both directions, which is not yet
    reflected in the fabricator pdf files.

    The aluminum floor joists are 2.00” channels oriented for weak axis bending, with tips
    of flanges pointed down. Three upper joists ran perpendicular to the deck boaDrs, and
    two lower joists ran perpendicular to the upper joists.

    The decking is 1-1/8” deep polypropylene.
    The stiffened version has ” square
    aluminum alloy hollow extrusions embedded into the polypropylene at an average 6” o.c.
    spacing.

    The siderail extrusions are as described by the section drawing A1.


    III. Analysis and Design:

    The various structural members of the assembly were analyzed for the loads indicated
    above. The member stresses were then compared to allowable stresses as determined
    from the appropriate steel (AISC-ASD) or aluminum (AA ASM 35) design specification.

    Analysis of the joists revealed that the center upper joist is overstressed 33.9%, with
    a corresponding deflection of 0.774”. The other joists, and the siderails are within
    allowable stress limits. The stiffened decking is within allowable stress limits for span-
    ning the 16” joist spacing.

    It was decided to perform a load test to determine actual center deflection, and thereby
    be able to back figure center joist stress using the modulus of elasticity of the material.

    A load test was performed under the direction of Mr. Price, with the client
    and helpers participating. From the test data, load vs. deflection curves were
    generated for overall structure response to gravity load.

    80 lb. sacks were laid on the platform in layers, allowing for the center deflection to be
    measured at load increments of 12 psf. The maximum load level was 128 psf. Two
    separate tests were conducted: One with stiffened decking, and one with unstiffened
    decking.

    We will use the 128 psf data for comparison to the 0.774” calculated deflection since
    the calculations included for the dead load being added to the 100 psf live load.

    Unstiffened Deck:

    Use of the unstiffened deck resulted in a deflection of 0.625”. Calculations show that
    this reduces the 33.9% overstress to 8.1% over. This result indicates that the unstiffened deck is not suitable for achieving a 100 psf rating.

    Stiffened Deck:

    Use of the stiffened deck resulted in a deflection of 0.438”. Calculations show that
    this reduces the 33.9% overstress to 24.3% under. This result indicates that the stiffened deck is suitable for achieving a 100 psf rating.

    The measured deflection of 0.438” represents the combined deflection of the siderails and the joists. Calculations show that the siderail deflection represents approximately
    0.137” of this, leaving 0.309” ascribable to the joists. This is equivalent to L/200.

    Floor live load deflection limits in most building codes call for a maximum of L/240 which equals 0.250” for the spans in question. The L/200 is not a safety problem. However, it should always be verified with the end owner and local building official as to whether they are insisting on the L/240. It is the opinion of this design office that for most outdoor boaDrwalk applications, this oveDreflection is not a concern. Other uses of
    this structural assembly should be considered on a case by case basis. The L/240
    criteria is intended for longer spans (20’ +), typical of building framing, and is intended
    to (among other things) ensure that excessive vibration underfoot of longer spans does not
    occur. The short spans and light self weight of this platform make it unlikely that
    vibration would ever be an issue.

    Handrail:

    The members comprising the handrail are adequate for code loadings. The U-bolt size
    and grade was not noted in the shop drawings. Use of 3/8” dia. Stainless steel, or an appropriately coated 3/8” dia. A307 steel, are acceptable U-bolt choices, Ensure that any material used does not have adverse reaction to contact with the aluminum alloy materials.

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


    IV. Recommendations:

    The platform can be utilized for 100 psf floor live load applications, provided that
    the stiffened version of the decking is utilized, and appropriate approval is obtained
    for relaxing the common L/240 deflection limit to L/200.

    The pdf drawings should be updated to reflect the member sizes and dimensions of
    the test platform. All weld symbols and fastener sizes must be called out. Material
    specifications should be listed, along with notes calling out the design loads, and
    soil pressure of the platform legs. These updates are required in order for the drawings
    to be considered complete enough for Professional Engineer certification.


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Structural Solutions LLC
1200 Troon Ct. SE
Grand Rapids, MI 49546
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