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FEATURED
PROJECT
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LEWIS STORE, FREDERICKSBURG, VA
The second floor was investigated for the future use as an office space with light storage, bookcases, meeting space, etc., with a required minimum live load of 100 psf (pounds per square foot), and dead load of 25 psf (total of 125 psf). The attic was evaluated for use as a potential storage space only, as the area does not lend itself for use as offices. The attic was investigated for a future live load of 50 psf. Upon completion of the assessment, S. Harris & Co. provided professional structural engineering and architectural design for the occupancy of the second floor. The project includes the reinforcement of the beams and girders on the second floor, the structural enhancement to the attic collector beam, and the conversion of the first floor corridor walls to bearing walls. HISTORICAL BACKGROUND The Lewis Store is one of the oldest surviving urban retail buildings in the United States. It was constructed in 1749 by John Lewis, a leading Virginia merchant and planter. Lewis was the brother in law of George Washington, as he married Washington’s sister, Elizabeth. The building is distinguished by the use of stone quoins at the corners, a feature rarely seen in small brick buildings, and carved stone lintels. These and other design elements make the Lewis Store an architecturally important urban store surviving from the colonial era. The Historical Fredericksburg Foundation, Inc. plans to operate a replica of an eighteenth-century store in the restored store as an innovative historical and educational attraction. STRUCTURAL REINFORCEMENTS
The typical truss consists of a turned up compression member, diagonal turnbuckle tension members, and turnbuckles on the lower horizontal chord acting as tension members. Due to irregular joist spacing, each element of the truss was designed to accommodate the variability. In some instances, the truss assembly did not fit into the tighter joist spaces. In these locations a steel box made from 1/4" plates was installed to transfer the loads sufficiently.
The truss spans the entire length of the building in the east-west direction, consisting of two lines: one line north and the other line south of the summer beam.
The upper portion of the truss consists of a bent 1/4" thick steel plate, which rests on top of each joist. The steel plate has three components: a turned up section, an overhang, and a flat plate. The turned up section is bent up to prevent movement of the truss system and to allow each individual truss system to come in direct contact with the next truss in the sequence. The top steel plate is also bent in order to mimic the deflected shape of the summer beam. Each top plate varies in length due to the irregular joist spacing and each angle between the top plane of the steel plate varies due to the deflection of the summer beam. The overhang serves to connect the top flat plate, acting in compression, to the upper clevis.
The upper clevis is a steel plate bent into a channel shape the connects the overhang of the top steel plate to the diagonal threaded rod (plan view, below left). the threaded rod, 1 1/8" in diameter, withstands the tensile loads of the truss and connects the diagonal turnbuckle to the lower diagonal clevis.
The lower clevis connection consists of three steel plates that are bent into a channel shape, 1/4" thick. The lower clevis is broken down by an outer clevis, an inner clevis, and a diagonal clevis (above right). A 5/8" diameter pin connects all three clevises at one point. A hole must be drilled through the bottom portion of each joist in order to insert a threaded rod. These threaded rods tie each joist together and are terminated at each turnbuckle on the horizontal lower axis. The lower turnbuckle and threaded rods are the primary source of tension in the truss system.
In addition, leveling the second floor required the removal and disposal of all existing floorboards. The leveling 2x8 pieces were screwed to the side of each joist and rest on the masonry ledges, raising the floor a total of 10 inches.
This design requires minimal alteration to the original collector beams, girder, joists, and masonry ledges. Although the irregular joist spacing lends itself to highly detailed steel fabrication, the design is elegantly simple in the fact that each individual truss can be fine-tuned by the precise tightening of a turnbuckle. METHODOLOGY & PROCEDURES
The truss was installed loosely with all of the members in direct contact but not tightened. Oversized washers were used to pack in between the turned up section of the top steel plates, providing contact with the adjacent turned up plate. A visual inspection took place prior to the "tuning" of the system. Each bolted clevis connection was tightened prior to tuning the turnbuckles and compression members. The tuning took place on the morning of 16 May 2006 and involved tightening each bolt and turnbuckle until the entire system was tight. The level of tightness was measured qualitatively. The tightening began at the center of each truss, working simultaneously with the truss on the north and south line, and headed outward toward the walls.
The tightening process continued outward from the center of the truss until the hollow steel box plates were reached in the area adjacent to the girder and the walls. The bolts for these members were tightened with crescent wrenches, snug tight.
The end conditions consisted of a hollow box shape with "legs" at the wall to distribute the load over the masonry ledge. OBSERVATIONS & ANALYSIS When tightening the turnbuckles, the tension was physically observed and felt within the steel members, The joists did not move or experience residual side effects from the tightening of the truss. Once the steel truss was tightened between joists 1 and 5 on the south line, the compression members at joist 3 were observed to lift up from the joist, This effect was observed slightly at the north end of the truss but was not as severe as on the south line of the system at joist 3. In order to ensure that this location does not become a future "soft-spot" within the floor, S. Harris & Co. installed a structural assembly just to the east of joist 3, on the south line of the summer beam, to prevent uplift of the steel trusses on each side. The structural assembly involves passing two threaded rods through the top steel plate of the truss to attach to a base plate beneath the lower clevis. This assembly fastens the upper plates in compression to the lower members in tension, providing uplift.
CONCLUSIONS
ADDITIONAL PHOTOS Before Construction:
During Construction:
After Construction:
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The
Historic Fredericksburg Foundation, Inc. retained S. Harris & Co. to investigate
and determine the structural condition of the Lewis Store, which is
located in Fredericksburg, Virginia. The focus of the investigation was to
assess and calculate the load capacity for expanded use of the second floor,
second floor corridor, stairwells, and the attic space. 
After
a thorough investigation and design phase, the renovation improvements to the
Lewis Store took place between March and August 2006 by Norman Company, Inc.
The construction improvements began by installing temporary shoring on the first
floor, directly under the second floor summer beam. The North-South timber
girder requires additional support to increase its loading capacity by
reinforcing the second floor (East-West) corridor wall by converting it to a
load bearing wall. The conversion required the removal of plaster on one
side and installing additional wall studs and structural posts on each side of
the door
opening. Also, additional support was provided on the basement in order to
distribute the loads generated from the new bearing walls located directly above
on the first floor. New 4x4 posts and 2'x2' square footing foundations
were placed in the basement in order to accommodate these loads from the first
floor.
The
layout of the pieces of the truss was important prior to the installation
because each truss was custom made for the irregular joist spacing and deflected
shape of the summer beam. The contractor, Norman Company, Inc., laid out
each piece as it was fabricated by Hermitage Steel, Inc. prior to the
installation. Each joist was drilled to allow 1 1/8" diameter all-threaded
rods to pass through. The distance between the top of the joist to the
first floor ceiling was increased for accessibility by installing a 1 1/2" thick
blocking material. This increase in dimension provided additional
clearance for the drilled holes in the joist. A sufficient amount of the
material remained under the drilled hole to prevent damage to the joists.
The increase in space between the top if the truss and the ceiling also aided in
the placement of the truss and the tightening of the bolts and turnbuckles.
First,
the bolts at the turned up compression members were tightened using crescent
wrenches, snug tight. Second, the turnbuckle on the lower chord was
tightened, finger tight, and then mechanically tightened with a crowbar one more
half revolution. The turnbuckle on the opposite side of the truss was
tightened immediately after. Third, the diagonal turnbuckles were tightened,
finger tight, and then mechanically tightened one more half revolution. At
the completion of the tightening of the truss on the south line, the respective
truss on the north line was tightened in the same fashion.
Finally,
the steel rods that were fastened to the second floor summer beam and ran
vertically to the attic summer beam were cut. The contractor installed
timber blocking reinforcements at the adjacent joists prior to the removal.
The removal of the steel rods caused minor cracks in the plaster ceilings of the
first floor because the rods were carrying the dead load of the member.
The cracks were repaired and the temporary shoring was removed.
A
time capsule was buried within the existing joist system on 1 June 2006.
Included in the time capsule were construction documents and Lewis Store
memorabilia. The renovations at the Lewis Store
were completed in August 2006. There was on open house reception on the
evening of Thursday, November 9. Members of the Historic Fredericksburg Foundation,
Inc (HFFI) attended the gala event. The administration of HFFI has
completely moved in and are now occupying the building for office space.
The second floor is being used for administrative offices as well as archival
storage. Sam
Harris and Melanie Kasper both plan to write technical papers based on their
findings at the Lewis Store, primarily on the subject of "Structural
Conservation Utilizing Substitute Reinforcements."
