Construction Concerns: Double Flitch-Plate Girders

Article and photos by Greg Havel

A flitch beam is made up of two layers of wood with a steel plate (the flitch plate) sandwiched between them. The resulting beam has the same strength with less depth (vertical dimension) than a solid wood beam; less weight than a steel beam of the same strength and dimensions; and can be connected using the fasteners common to wood frame construction.

Flitch beams are used less today than in the past, since equivalent strength can be achieved using manufactured wood components like laminated veneer lumber (LVL) and parallel strand lumber (PSL).

Flitch beams are still used in some buildings whose needs cannot be served by solid beams of manufactured lumber or structural steel. In addition, North America has thousands of buildings in which flitch beams are present from construction in the past.

A chapel building is presently under construction on a college campus in Wisconsin. The configuration of the building site–which sits on a corner lot between two existing buildings and two roads–coupled with the college’s desire for a flat ceiling with a clerestory prompted the architect to run the main girders to support the clerestory parallel with the long walls of the chapel. In this case, there are no columns to break up the interior space. Double flitch plate beams were selected to carry the load.

The ends of the double flitch plate beams

Photo 1 shows the ends of the double flitch plate beams, each 7.5 inches (19.1 cm) wide, 24 inches (61 cm) deep, and 60 feet (18.3 m) long; and each weighing more than 8,000 pounds (3,636.4 kg). They are each made of three layers of LVL and two flitch plates, each 0.75 inch thick. The steel flanges that are bolted to the ends of the beams will be unbolted and welded to the structural steel supports. The beams will be set in place with a crane and the bolts will be re-installed.

Two double flitch plate beams in place

Photo 2 shows the two double flitch plate beams in place, supported at both ends by a welded assembly of a tubular steel girder and tubular steel columns. The dimensional lumber bracing is only temporary and will be removed when the rest of the building frame is in place to prevent the beams from flexing sideways.

One of the flitch plate beams with the clerestory framing in place

Photo 3 shows one of the flitch plate beams with the clerestory framing in place. The square openings above the beam will be windows. Also visible in this photo are some of the bolts that hold the beam’s five layers together.

A view of the incomplete building from the street on the narrow side of the chapel

Photo 4 shows a view of the incomplete building from the street on the narrow side of the chapel, with one of the flitch plate beams visible where the clerestory framing is not complete. Some of the structural steel that supports the flitch plate beams is also visible.

When the chapel is complete, the flitch plate beams and structural steel will be concealed behind gypsum drywall board and other interior finishes. Although the building is a hybrid that depends on structural steel and manufactured lumber components for integrity, it will appear to be a simple wood-frame, Type V building, like many of the others on this campus.

This building will not have an automatic fire sprinkler system since it is smaller than the minimum size that is allowed by state building and fire codes.

This building is another argument in favor of preincident planning that begins during the construction or remodeling of buildings, so that emergency responders may have a clear idea of their workplace if they are ever dispatched to this location.

Download this article as a PDF HERE (2.4 MB).

Greg HavelGregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 35-year veteran of the fire service. He is a Wisconsin-certified fire instructor II, fire officer II, and fire inspector; an adjunct instructor in fire service programs at Gateway Technical College; and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College; has more than 35 years of experience in facilities management and building construction; and has presented classes at FDIC.

 

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