COLLAPSE SEARCH AND RESCUE OPERATIONS TACTICS AND PROCEDURES
Part 6: Window and Interior Rake Shoring
The window shore, though not as commonly used as other interior shores, is necessary in some collapse situations. An extensive collapse of exterior walls and interior floors and walls can generate tremendous amounts of debris. At times, this debris can block the main egress into the building. I have been involved in collapse situations in which the only access to the interior of the structure was from second-floor windows, due to the large amount of collapse rubble blocking the ground-floor entrances.
Generally, the window shore is installed to hold up or stabilize loose headers or lintels that have lost their integrity, to make the access point safer for rescue personnel. It prevents accidental dislodging of building materials while collapse operations are undertaken through that opening.
WINDOW SHORE, STEP BY STEP
The window shore consists of five structural components: the sill or bottom plate, header or top plate, posts, wedges, and diagonal braces. All these elements, combined properly, will make an unstable opening safe enough through which to conduct operations.
1. Install the sill plate. Clear loose debris or framing material away from the bottom of the window opening. Remember to work from a safe area—don’t place your body under the unstable window lintel. Measure the size of the area to be
shored and deduct for the width of the wedges. Generally in wood-frame and smaller brick-andjoist construction, 4 x 4s make good bracing material. If the building is larger or the window opening is greater than four feet, larger-dimensional lumber may be called for; this determination must be made on the scene. Try to keep the sill plate as level as possible during installation. Shim underneath if required. This is especially important underneath the ends, on which the posts are to be installed: The ends must have full bearing for the shore to be effective. When the plate has been laid in and shimmed level, snug up the wedges.
2. Install the header. Measure the opening at a point just under the lintel, remembering to deduct for the wedges, install the header as tightly to the lintel and as level as possible, snug up the wedges, and shim any openings, if necessary. Keeping the sill and header level ensures that the posts are the same size and the entire shore is square. The elements will fit better and, as a result, the shore will be stronger.
3. Install the posts. Take the measurements of both sides and deduct for the wedges. The measurements should be almost identical for both posts; slight differences in length can be compensated for by tightening up on the wedges. In addition to the added strength factor of a tight, square shore, posts of equal size create a logistical advantage in that you won’t become confused about which post goes on which side. Install the first post you receive under the wedge side of the header first. This will hold up the header and wedges in case some accidental or unanticipated movement occurs. Install the other post and snug up on the wedges. Keep the posts plumb for a more efficient shore.
4. Install the diagonal brace. If the window is not being use for access to the structure, diagonal braces can be erected on the face of the shore. They are anchored to the outside of the shore on both sides. The braces should be installed in opposite directions to each other, thereby taking the stress from either direction and helping to stabilize the shore if any movement occurs.
After all the elements have been installed, tighten up the wedges. Tighten them only enough to accept the weight they are to support. Do not attempt to move any structural elements back into their original positions; this may cause a secondary collapse.
WINDOW/INTERIOR RAKE SHORE
The window shore size-up, while brief, still is necessary. If the shore is not erected properly, it may be ineffective and may give the rescuer a false sense of security. The size-up consists of two main points: structural stability and load stress.
Structural stability. Determine if the area is safe enough for rescue personnel to operate in. Then examine the window and the area around it for structural stability. Determine if shoring the window will create a safe access and egress point for rescue operations.
Load stress. Mow much of an additional load stress will be exerted, and in what direction will it be exerted? Almost always, the additional stress will be applied from above—gravity constantly is trying to pull the building and any debris within to the ground. When the stress is from above, the header or top plate of the window shore should be fully supported by the posts so that the shore takes the largest amount of weight possible from above.
INTERIOR RAKE SHORE
The purpose of the interior rake shore is to support leaning or unstable walls, columns, or other structural members of a building from the interior. It is most often used to support unstable or damaged interior bearing or nonbearing partitions. These walls may be out of plumb, bulged, cracked, or under extreme pressure from collapse debris. The interior rake shore is strictly designed to halt any further movement of these unstable elements—but. as with all rescue shoring, its purpose is to stabilize, not restore structural elements to their original position. The interior rake shore is designed to transfer the additional stresses applied to these walls through the point of the rake itself to the floor, where the load can be safely and evenly distributed to other structural bearing members. It can be used alone or in conjunction with other rake shoring.
INTERIOR RAKE SHORE, STEP BY STEP
The interior rake shore consists of six structural components: wall plate, sole plate, rake, cleats, wedges, and diagonal brace.
1.Install the wall plate. Place the wall plate against the area to be shored and plumb up in both directions. It is important that any shoring be installed plumb and level so that the shore will be stabilized properly and work efficiently. Anchor the shore where possible. If the area is bulged or cracked due to the strain exerted by collapse debris, the wall plate may have to be shimmed. There are two important points at which to shim the wall plate: First, full contact must be main- tained between the base of the wall plate and the area in question. This keeps the plate plumb and stabilizes the base of the shore when the other elements are erected. The second point, and perhaps the most critical, is to shim at the point of contact between the wall plate and the rake. Full, solid contact must be maintained—this is where the majority of the pressure is supported and the load transferred to other structural supporting members.
2.Install the sole plate. Make sure the sole plate is long enough to extend at least several feet past the point at which the rake intersects at the floor. Install the sole plate as level as possible and anchor it to the wall plate. The wall plate and sole plate should be plumb, level, and at right angles to each other, thereby ensuring that the rake fits properly. Anchor the sole plate to the ! floor where possible and shim if necessary, particularly at the point where the rake intersects the floor area—another critical point of the shore. Maintaining full contact properly absorbs and transfers the load stress to the proper areas.
3.Install the rake. The interior rake shore works most effectively at an angle of between 30 and 45 degrees from the floor. A 45-degree angle generally is the easiest to use, since both the top and bottom angles of the rake will be cut the same. Determine the length of rake, cut to the proper length, cut the top and bottom angles, and install the rake. To install, position the rake as close as possible to where it will be anchored in the sole plate. Then gently lower the rake into the wall plate. Do not drop the rake into position— the additional impact load may cause additional problems. Slide the rake up or down, if necessary, until the angle cut of the rake is in full contact with the wall plate. The rake must have full bearing on the wall plate and the sole plate for the shore to work effectively. Anchor the rake into position. This holds the brace in place while the top and bottom cleats and the wedges are being installed.
4. Install the top deat. A deat is a small block or strip of wood anchored on a member or on a surface to support a brace or hold a member or object in place. Cleats must be attached to both ends of the shore. They keep the shore in its original position when pressure is applied to the rake.
Generally, for installing interior rake shoring, two-inch dimensional lumber is sufficient for cleats. For full strength and continuity, the cleat should be the same thickness as the wall plate and rake. If the wall plate and rake are both 4×4 dimensional lumber, the cleat should be a 2 x 4. Typical conditions call for cleat lengths of between 18 and 24 inches. Anchor the deat by using the “five-pattern” method.
The top cleat keeps the rake from riding up the wall plate. As pressure is applied to the shore, the rake comes under compression, but with the top cleat installed, the load stresses are transferred down the center of the rake and the shore is used to its fullest efficiency.
5. Install the bottom cleat. Anchor the bottom cleat on the sole plate just behind the base of the rake, with room left to apply wedges. The bottom cleat stops the rake from riding back on the sole plate when the shore is placed under pressure. The best way to do this is to have the cleat return back to a solid object, such as an adjoining wall; this places the cleat under compression, utilizing the material to its fullest capacity. If this is not possible, anchor the deat to the sole plate using the “five-pattem” anchoring method. However, in this situation, you are relying on the cleat’s shear strength, so the bottom deat should be at least three feet long.
6. Install the wedges. Snug up wedges at the base of the rake. Tighten up shims or spacers between the wall to be braced and the wall plate, After they have been tightened sufficiently to ensure full contact from the wall to the point of the rake, then fully tighten up the wedges at the base of the rake. This locks the entire shore together and enables the rake to accept the load from the wall and transfer that load to additional structural supporting members.
7. Install the diagonal brace. Depending on conditions, length of the rake, and amount of pressure being applied to the rake, a diagonal brace may be required for added stability. How- ever, for additional safety, it is a good idea to install a diagonal brace on every interior rake shore.
Note: In our previous illustration of interior rake shoring (Fire Engineering, August 1993, page 131), the bottom cleats were erroneously identified as wedges. The illustration above is correct.
The diagonal brace is intended to stop any deflection of the rake as pressure is applied to the shore. By taking the deflection out of the rake, the shore becomes more stable and capable of more effectively absorbing the load applied to it.
For a rake constructed of 4 x 4s, a 2 x 4 or 2 x 6 will wosic well for the diagonal brace. For rakes built of larger lumber, such as 6 x 6 or 8 x 8, use 2 x 8 or 2 x 10 for the brace.
A diagonal brace should be installed on each side of the rake for maximum efficiency, ft should be placed from the base of the shore where the wall plate and sole plate intersect to the center of the rake. It should be anchored by using the “fiveI pattern” method at both points.
