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  • Sample of building investigation


    I. Purpose of Investigation:

    Preliminary analysis of roof purlins and main frames to determine nature and extent
    of reinforcement necessary to accommodate building modifications. Installing additional
    roof top mechanical units and new roofing are the modifications being examined in this report.

    II. Description of Building:

    The building in question is a metal building manufactured by MBMA manufacturer. Dimensions
    are 100'-0" x 200'-0" x 20'-0" eave, symmetric gable 1/2: 12 roof.

    III. History:

    NBS documents indicate original construction occurred in 1995.

    IV. Referenced Documents:

    Architect drawings S21, S22, S23, S24, S25.

    Mfg. construction drawings.

    V. Field Observations and Notes:

    Field inspection took place Tuesday, for the purpose of reviewing the intended
    building modifications.

    VI. Investigation Results:

    Roof purlins:

    The existing purlins are 5 span continuous (lapped), 10" light gauge steel zee shapes.
    Spans are 27'-0", 3 @ 28'-4", 27'-0". They are 5'-0" o.c.

    Mfg. drawings indicate purlin material thicknesses of .105", .086", .076", .086", .105"
    for the 5 spans.

    Under original loadings plus 2 psf for additional roofing, the existing purlins are at
    105%, 80%, 85%, 80%, 105% of their capacities for the 5 spans. The 5%
    apparent overstress can be justified by considering it to use up 2 psf of the original
    10 psf collateral dead load, leaving 8 psf remaining for mechanical and ceiling weight.

    3 of 5
    Additional justification lies in the Code provision K602.1, which allows for structural
    modifications that increase stresses less than 5%. Of original 48 psf total gravity roof
    load, 2 psf represents 4.2%.

    If the roof is to also meet a 42.4 psf roof snow load, (7.4 psf more than original 35 psf),
    the typical purlin will be in the range of 5 to 20% overstressed. This would necessitate
    reinforcing all purlins along their full length, or adding additional purlins throughout
    roof, to cut the spacing from 5'-0" to 2'-6" ("doubling").

    The regions at and near roof units will require purlin doubling, and special bracing:

    Main Frames:

    The existing frames are 6 span rigid frames with column to rafter fixity at all columns.

    Under original loadings plus 2 psf, the existing frame members show overstress (5%) at
    only 2 locations. A few web shear stiffeners can take care of this. Note:
    Frame connections have not been reviewed at the time of this report.

    Various frame reinforcing will be required in the regions at and near the roof units:


    Foundation investigation not in current scope of work.

    VII. Additional Comments:

    AHU-2 is located at the building ridge, which can create problems with roof panel
    thermal expansion stresses. Using short steel posts bearing upon WF beams may
    be a better approach. The only penetrations through the roof are the posts, and the

    This approach may be worth considering for the other units, especially the heavier ones.

Contact Information

(517) 403-6875 
(517) 403-6875
Postal address:
Structural Solutions LLC
1200 Troon Ct. SE
Grand Rapids, MI 49546
Electronic mail:

General Information:     ssllc.tp@mail.com

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