COLLAPSE SEARCH AND RESCUE OPERATION: TACTICS AND PROCEDURES PART 14: HORIZONTAL SHORING
BY JOHN P. O`CONNELL
The horizontal shore can be used for interior and exterior shoring. It is used primarily to support damaged or unstable walls in hallways, alleys, access ways, air shafts, and between structures. Generally, it is used in larger structures, such as office buildings, commercial establishments, or larger residential structures of brick-and-joist or concrete construction. The main purpose of the shoring is to stabilize normal access ways that have been compromised. Horizontal shoring allows for continued collapse rescue operations and provides a relatively safe area for both personnel and rescued victims.
SIZE-UP
In any collapse rescue situation, you must take the time necessary to survey the area and determine the best means of access and egress before heading into an unstable area. After making those decisions, proceed with the size-up for determining the need for horizontal shoring. The size-up inspection should include the following: a check of
the amount and extent of damage, the location(s) of possible victim(s), leaning walls, damaged structural elements, and bulging walls.
ELEMENTS OF THE HORIZONTAL SHORE
Wall plates. These are the two vertical members of the horizontal shore, positioned on each wall, directly opposite each other and as plumb as possible. For interior operations, use 4 ¥ 4 or 4 ¥ 6 lumber for the wall plates; for exterior operations, use 6 ¥ 6 lumber. In frame buildings, if stability conditions warrant, the wall plates will be toe-nailed into the top and bottom plates in the existing wall for full effectiveness. For masonry block, brick, or concrete walls, plywood is installed between the wall plate and the wall to provide greater support coverage area and ensure that most of the surface area of the wall plate contacts the wall, for greater strength. In this case, the plywood-wall plate assembly is secured to the wall by connections made through the plywood. However, when any wall–concrete, masonry block, brick, or wood frame–is so unstable such that vibrations must be limited, the wall plates will be anchored by the pressure of the struts alone.
Struts. These supports keep the wall area open for the rescue team. Depending on the situation, two or three struts are used. They should be of the same width/dimension as the wall plates for ease of installation and proper transfer of loads. Determining the number and locations of the struts will depend on several factors: the extent of the damage, the amount and location of debris, the type of wall construction, the locations at which the greatest amount of force is being applied to the walls, the known or possible locations of victims, and whether the area will be used for access or egress. Placing the struts at four feet on center, as is done in trench operations, does not apply to collapse rescue shoring in buildings, since the amount of pressure applied to the walls in a collapsed structure will vary and the areas of greatest pressure should be supported. (Note that manufactured rescue support struts available on the market will make erection of the shore much faster.)
Hanger cleats. The hanger cleats support the struts while they are being installed. They also help support the struts after they are in place should someone inadvertently step or lean on them. The cleats, for this reason, should always be installed as an additional safety factor. Generally, hanger cleats are short pieces of 2 ¥ 4 lumber; they should be approximately 12 inches long–any shorter, and they tend to split when nailed. They are nailed directly to the wall plate. Once the struts are positioned on top of them, the struts can be toe-nailed into the cleats as added insurance against vibrations that may occur, such as aftershocks in earthquake situations.
Wedges. A set of wedges is placed together or “married“ with each strut and tightened. This is done to apply pressure securely to the struts against the wall plates that will transfer the load from the damaged wall through the shore to good bearing material. The wedges are toe-nailed after the shore has been tightened so they will not become accidentally dislodged.
Gusset plates. These plywood plates, anchored onto the outside face of the connections between the struts and wall plates, help guard against these shore members` loosening and dislodging. The gusset plates provide additional protection against aftershocks following earthquakes or from vibrations caused by secondary collapses in other sections of the structure. These elements are necessary, and sufficient, only on one side of the shore. Usually, the gussets are constructed of 34-inch plywood and their width should be the same as or greater than the width of the struts.
Diagonal braces. The last elements of the horizontal shoring to be installed, diagonal braces are used if the area is not being used for access or egress. They are installed to lock the entire shore together as one unit and help provide resistance to eccentric loads that may be applied to the shore. Two-by-four or 2 ¥ 6 lumber may be used for the braces; they are nailed on both sides of the shore in opposite directions of each other (making an “X”) for greater lateral load resistance.
STEP-BY-STEP CONSTRUCTION
After the initial safety shoring has been erected and installed, step-by-step construction of the horizontal shoring can begin.
1. Shore locations. Determine where the shores are to be located. Check for cracks in the walls, damaged structural elements, possible victim location(s), leaning or bulged walls, large areas of debris, and other telltale signs that indicate an area may need shoring. Spacing between the horizontal shores normally is from eight to 10 feet apart, depending on conditions and extent of the damage.
2. Work area. Clear a work area of at least three to four feet wide.
3. Wall plate measurement. Determine the height of the wall plates and cut to proper size. Generally, they should be as long as possible to cover the greatest height, but make them a couple of inches shorter than the opening so they are not too tight and will not have to be forced into place–never a safe way to operate in a building collapse situation.
4. Number and position of struts. Determine how many struts you will use and where you will place them (how high on the wall).
5. Hanger cleats. Especially if the floor is level, it is easier to install the cleats prior to erecting the wall plates. Mark where you want to install the struts onto the wall plates. Use these marks to nail the 12-inch cleats, level, to both wall plates. A three-nail diagonal pattern is sufficient to anchor the cleats to the wall plates. Most often, struts installed on the side that will accept the wedges will need additional blocking. Several equally effective methods for doing this are available. One method is to nail a second cleat on top of and at a right angle to the original one, thereby creating a shelf for the wedges and strut. Another effective method is to nail a single wedge against the first cleat, creating another “shelf.”
6. Wall plate installation. Erect the wall plates, one on each side, in line with each other. Keep them as plumb in both directions as possible for a stable and efficient shore. If necessary, shim them to keep them straight. For masonry, brick, or concrete walls, first connect a plywood sheet to each wall plate, nailing through the face of the plywood. Then raise and position the assembly against the wall, securing it in place.
7. Strut measurement. Measure all strut locations; don`t forget to deduct for the width of the wedges. Try to keep the same measurement for all the struts; this makes the cutting and installation much simpler (you won`t have to worry about which one is which while you are installing them).
8. Strut installation. Normally, the center strut (when placing three struts in the shore) is installed and tightened first; this helps stabilize the entire shore and makes it easier to place the other struts in position. Install the struts as level as possible. Place them on the hanger cleats for easier installation. Nail the strut to one wall plate; then install a set of wedges at the other end. (If only one wall is damaged and bracing is against a good wall, place the wedges on the good-wall side.) Tighten the wedges together until the strut is snug to the wall plates. Place the other struts into position and tighten up the wedges. After all struts are in place, make sure the wall plates are shimmed properly if necessary. After checking the shim, retighten the wedges on the struts a final time, properly transferring the loads applied to the shore. Then nail the strut and wedges to the wall plate.
9. Gusset plates. If the collapse is the result of an earthquake, the use of gussets is highly recommended. The gusset plates should be plywood, generally 34-inch thick, and preferably of a larger width than the width of the struts, to provide more nailing room to anchor the plates using the five-nail pattern. The gusset plates need be erected only on one side of the horizontal shore to be effective. If no plywood is available, 2 ¥ 4 lumber can be used in the same manner to tie in the wall plates and struts but, in lieu of the five-nail pattern, place three nails into the strut and three nails into the wall plate.
10. Diagonal braces. Installing these braces is the last step in erecting the horizontal shoring. These braces are installed only if your team is not using the area as an access way. Nail each 2 ¥ 4 or the 2 ¥ 6 brace into the wall plates and struts, using three nails for each element. The diagonal braces are installed in an “X” pattern on both sides of the shore and in opposite directions, similar to the cross bracing of the vertical shore. The diagonal braces must be long enough to contact the top and bottom of the wall plates and all the struts so that the shore will be locked together as one unit, making it that much stronger. n
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(Top left) Wall plates, with hanger cleats secured, are erected. (Top center) Install the center strut first for enhanced stability during shore construction. (Top right) Struts must be as level as possible. For safety/stability,place wedges on the “good-wall” side, if applicable. (Bottom left) A 4 ¥ 4 wedge used as a cleat provides enough room for 212-inch-thick wedges and the strut, even after the wedges are fully tightened. (Bottom center) Two 212-inch wedges properly “married” against the 4 ¥ 4 strut. The strut can be readjusted during operations if the need arises. Constantly check for movement on any shoring you erect. (Bottom right) Diagonal braces are installed only when the area will not be used as an access way. To be completely effective, the braces must contact the wall plates at top and bottom. (Photos by author.)
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JOHN P. O`CONNELL has been a firefighter with the City of New York (NY) Fire Department for 16 years and, as a member of Rescue Company 3 in the Bronx, has more than eight years of collapse rescue experience. He is an instructor of shoring and building collapse at FDNY`s Training Academy and has been involved in the writing and teaching of the department`s collapse and shoring training curriculum. O`Connell is a member of New York Task Force 1 of FEMA`s urban search and rescue network and is a rescue specialist instructor for FEMA. He is a New York state-certified fire instructor and spent more than 10 years in the building construction industry.
