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I. Purpose of Investigation:
At the request of the manufacturer, Thomas R. Price P.E., of Structural
Solutions LLC, inspected the damaged canopy in Southfield, MI, in order to
determine the extent of repairs necessary for returning the structure to a safe and
acceptable condition. It was indicated that the canopy had been struck by a vehicle,
causing significant damage, and may have been struck on previous occasions, as well.
II. Description of Structure:
The canopy is approximately 66 ft. by 24 ft. in plan, with a vertical clearance to the
underside of the roof framing of 12 to 13 ft. For the purposes of this report, it is
assumed that the 66 ft. dimension is running East-West, and the 24 ft. dimension is run-
There are 6 round concrete columns supporting the roof. The roof framing consists of 2 main beams running the 66 ft. direction, bearing concentrically on the columns, and 8 purlins bearing on top of the main beams, running the 24 ft. direction. Both main beams and purlins appear to be glue laminated timber members. A timber plank deck lays across the purlins, forming the roof. There appears to be some slope to the roof. This is achieved by tapered shim boards on top of the purlins, and/or the south row of columns being slightly taller than the north row.
III. Field Observations and Notes:
The inspection took place on April 31, 2007, at 1:00 pm. It was sunny, and the area
was well lit for viewing the structure.
The most apparent damage is to the southwest corner, where the main beam cantilevers out from the last column approximately 9 ft. The main beam was pushed to the north. The nearest support column restrained the beam, and in doing so, caused a diagonal rupture of the beam, starting from the bottom, at the column, to the top, approximately 4 ft. out along the cantilever. Due to the large distance that the beam end was pushed, it has remained in a severely distorted position, after the vehicle was removed from the area. The end of the beam is rotated on its longitudinal axis approximately 30 degrees, and the rupture crack is opened up approximately 2 inches.
Approximately 3 inches of main beam material has been removed from the underside
of the cantilevered portions, extending to approximately 4 ft out from the columns.
This will require that shear and bending be checked on the reduced section. It is likely
that these checks will show that the reduced section is adequate, however, it must be part of any repair design that may be carried out.
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The nearby column appears to have remained plumb. It lines up with the other columns
in the south row. The relatively great stiffness of the column prevented structural damage
from extending throughout the structure. It forced the beam to ‘break off” at its cantilever support point. The energy absorbed by the beam undergoing large deformation, acted as a spring, reducing the potential maximum impact force that the column ended up having to resist.
Though the overall column and foundation are likely in good condition, the top of the
column suffered a diagonal shear rupture, as it restrained the beam’s lateral movement.
The large crack width indicates that circular reinforcing may not be present at the column
top. It certainly is not present in the top 5 or so inches of the column – as there is a “saddle” at the top of each column.
Lateral shear cracking was observed at 5 of the 6 columns, indicating that this canopy
has been hit by vehicles on other occasions, but with lower impact forces. The cracks
in the other 4 cracked columns are not opened up nearly as much as the southwest column.
The primary and most significant repairs required for this canopy are the replacement of
the ruptured main beam, and a complete rebuild of the column tops.
The column tops must be rebuilt with structural details appropriate for a pin connection to the main beams, capable of transferring lateral and uplift forces from the beam, to the column. It is not possible to see the existing connection, nor judge its suitability. It is possible that a single steel rod, similar to the rods connecting the purlins to the main beams, was run down into the columns. This may be an appropriate detail, but it depends upon the length of embedment being deep enough past the top of the vertical column reinforcing, so as to properly transfer load into the vertical bars. It is necessary to determine the size and location of the column reinforcing bars, both the vertical main bars, and the horizontal ties:
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Section 406.5.2 of the Michigan Building Code requires that “Canopies under which
fuels are dispensed shall have a clear, unobstructed height of not less than 13 feet 6 inches, to the lowest projecting element in the vehicle drive through area.”
Signage installed on this canopy indicates clearances from grade varying from 12 ft 0 in
to 12 ft 5 in. If this is verified to be accurate, then the scope of needed repairs to this canopy must include provisions to raise the structure approximately 1-1/2 to 2 ft
- 1200 Troon
- Grand Rapids, MI
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Grand Rapids, MI 49546 Kent County