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I. Purpose of Investigation:
Preliminary analysis of roof purlins and
main frames to determine nature and
of reinforcement necessary to accommodate
building modifications. Installing
roof top mechanical units and new roofing
are the modifications being examined in
II. Description of Building:
The building in question is a metal
building manufactured by MBMA
are 100'-0" x 200'-0" x
20'-0" eave, symmetric gable 1/2: 12
NBS documents indicate original
construction occurred in 1995.
IV. Referenced Documents:
Architect drawings S21, S22, S23, S24,
Mfg. construction drawings.
V. Field Observations and Notes:
Field inspection took place Tuesday, for
the purpose of reviewing the intended
VI. Investigation Results:
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
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
10 psf collateral dead load, leaving 8
psf remaining for mechanical and ceiling
3 of 5
Additional justification lies in the Code
provision K602.1, which allows for
modifications that increase stresses less
than 5%. Of original 48 psf total gravity
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
reinforcing all purlins along their full
length, or adding additional purlins
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
The existing frames are 6 span rigid
frames with column to rafter fixity at
Under original loadings plus 2 psf, the
existing frame members show overstress
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
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
- 1200 Troon
- Grand Rapids, MI
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2012 Structural Solutions LLC, 1200 Troon Ct. SE
Grand Rapids, MI 49546 Kent County