BY JOHN P. O’CONNELL
The “T” shore has been around for quite a while, and several versions have been in use for the past couple of years. The major (and only) reason the “T” shore should be used is as a quick type of safety shore before your main shoring systems are brought into play.
The major reason for placing this quick shore in position is to give your shoring team some degree of safety while the members assess, size up, and erect the more permanent systems. The concept behind this shore is to make it simple and easy to erect and portable enough so that one firefighter can maneuver it around in close quarters. Huge, complicated “T” shores that cannot be easily handled by one person defeat the purpose of that shoring scenario and are not recommended. With this in mind, keep the fabrication of the shore to a minimum. Don’t waste too much time, personnel, or materials constructing these shores; it is counterproductive. I have seen extremely large “T” shores erected with as many pieces of material as would be needed for a 10-foot-long vertical shore (not the same size material, of course-just the same number of pieces). These types of “T shores need at least two people to erect and move them around and another person to help set them. Remember, the “T” shore is marginally stable at best.
Don’t overbuild this shore. All shoring systems should be balanced systems: The shore will be only as strong as its weakest link, just like a chain. Here, the weak link will be the stability, or instability, of the single post in the shore. Remember, if the post is not loaded through its center axis, it will be less efficient. How off center or eccentrically loaded the post is will determine how inefficient it will be-something you cannot readily tell in a collapse situation. When installing the shore, of course, try to install it as plumb as possible. However, even though you install the shore plumb, that does not mean the post will evenly absorb the load applied to it.
SIZES
Recently, two sizes have been used in several areas-the standard “T” with a 36-inch header and the standard “T” with a 48-inch header. These are the simple rules of thumb: With a 36-inch header, you could use a 12- × 12-inch gusset plate; with the 48-inch header, you need a larger (18- × 18-inch), gusset plate, to help the header and post connection absorb more torque from the load above in case it was unbalanced. As our engineers got more involved in US&R operations and more testing was done on standard shores, the engineers have come up with some conclusions:
• As a safety shore, the “T” shore, if it is to be safer, should not have a header any longer than 36 inches. This will help keep it more stable and make it less likely that will be knocked over or fail under an unbalanced load. This is the recommendation of the FEMA technical subcommittee. There may be situations where a 48-inch header will work without compromising the shore’s stability. If this is the case, you can use it; but it is not recommended for general use.
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DOUBLE “T” SHORE OPTIONS
Although the “T” shore is a preliminary safety shore, there will be many instances where stability will be a major issue along with supporting an unstable load. When you have determined that there is a stability issue, especially laterally, use of the double “T” may be warranted. It is also ideal when a heavier load is anticipated.
Double “T” Shore Rules of Thumb
• Use when more stability or support is required.
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• It is prefabricated and walked into position.
• The head should be 36 inches maximum.
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• The post can be 18 inches or 24 inches apart.
• The top two gusset plates are 12 inches × 24 inches.
• The single center gusset plate is 12 inches × 24 inches.
• The crushing strength of the double “T” can exceed more than twice that of the single “T” shore.
• “T” shores and double “T” shores are constructed of 4 × 4s and ¾-inch plywood.
Two-Post “T”
Use a two-post “T” with the posts spaced, outside to outside, 18 inches apart. This will give you a more stable and stronger shore without the shore’s dimensions being much greater than the one post. The shore size will be easy to maneuver in a tight environment. This shore with the two posts will have a 36-inch header and will be fabricated with 12- × 24-inch plywood gusset plates.
Note: In this option, there will be a nine-inch overhang of the header over both posts. This is to keep the header tighter and to lessen the chance for an unbalanced load, which would affect the stability of the shore. It also makes the shore more maneuverable-there is less header length to get hung up on anything while shifting and placing the shore in position. This shore will be prefabricated and then carried into position. Assemble the header, gusset plates, and posts first. Then bring in the preassembled section with two sets of wedges and the sole plate; the sole plate should be the same length as the header. Determine the location, assemble all the components, and pressurize. This shore goes up quickly, is portable, and for the most part is stronger and more stable than the single-post “T” shore.
Step-by-Step Erection of the Double “T” Shore
Following are instructions for erecting a double “T” shore:
1First determine the width of the post spacing you will require. Nail the posts into the header with two 16d nails, toenailing from the post into the header, following the grain of the material. Drive the nails flush to the face of the 4 × 4. Make sure you square up the posts to the header after you nail the posts in place. Use a framing square (photo 6).
2The proper spacing for the 12- × 24-inch ¾-inch plywood gusset plate nailing patterns is shown in photo 7. Nail the top section into the header; anchor just like a 24-inch raker cleat. Use the five-nail pattern, five inches apart. There will be 17 8d nails in the header. Along each post, anchor five more 8d nails, using the same five-nail pattern. Keep the nails one inch up from the bottom and one inch below the end of the post. This will give your nail pattern a six-inch spacing.
3Photo 8 shows the 12- × 24-inch plywood gusset plate properly anchored to the 36-inch header and posts with a 24-inch post spacing.
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4Photo 9 depicts the 12- × 24-inch plywood gusset plate properly anchored to the 36-inch header and the posts with 18-inch post spacing. Note the three-inch indent of the posts inside the plywood gusset plate.
5Place a gusset in the center of the posts, to secure the two posts together at the 24-inch spacing. This will ensure that the posts do not spread apart when you move the shore around. You need use these only when the shore is six feet or higher. Notice the 8d nail spacing-two five-nail patterns spaced six inches apart. This gusset is also 12 inches × 24 inches (photo 10).
6The nail pattern and gusset plate layout when spacing the posts 18 inches apart is shown in photo 11. Note again the three-inch overhang over the end of each post. The 8d nail pattern is the same as for the previous center gusset plate.
Prefabricating the Shore
The procedure for prefabricating the shore is outlined below.
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1Double check that the posts are square to the header. Anchor the top gusset plate in position. Make sure it does not overhang the top of the header. It must be flush with the top face of the header at all times. Measure the length of the posts, and place the other gusset plate in the center of the posts. Anchor in place as shown in photo 12.
2Flip the shore over. Anchor another 12- × 24-inch top gusset plate to the header and posts in the same position as the first one (photo 13). Check to see that all the nails in the first gusset went into the header and posts. If any did not for some reason, flip the shore back over and fix it. Use the same nail pattern as for the first top gusset plate. The section is now ready to be installed.
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3The completed 24-inch spaced double “T” shore section: a header, two posts, two 12- × 24-inch gusset plates, and one 12- × 24-inch center gusset plate. Prefabricate the shore to this configuration outside the collapse area. You can then take it inside as one piece. Place the shore on top of a 4 × 4, 36-inch-long sole plate with a set of wedges under each post. After tightening the wedges, use two 24-inch 2 × 4 cleats to hold the items in place. Three 16d nails into the post and sole plate should be sufficient for most operations (photo 14).
4Photo 15 shows the shore is in position, wedged up under the floor. This 18-inch spaced “T” shore is positioned under two floor joists that are 16 inches on center. Place a set of 12-inch 2 × 4 wedges under each post, and tighten. The sole plate should be 4 × 4 and 36 inches long.
LOADING THE “T” SHORE
It is very important, if not imperative, that “T” shores, whether single or double, are loaded properly. Any off-center loading of the shores can cause them to shift or fail; if they do not fail, their strength will be greatly reduced. In many situations, the single “T” may be good only for approximately 4,000 pounds of support just because of its inherent instability issues. Even a double “T,” which should give 16,000 pounds of support, may not come close to that if the load is not centered over the two posts. When installing these posts, make sure they are loaded properly, or your team may be working under a sense of false security. Photos 16-19 show ‘T” shores installed in various positions. ■
■ JOHN P. O’CONNELL recently retired after 26 years of service with the Fire Department of New York, where he was assigned to Rescue Company No. 3 for the past 18 years. He is a principal member of the NFPA 1670 committee and task group chair for the structural collapse section. A former task force leader for New York City’s US&R Task Force 1, he has served on several FEMA development committees in the past 15 years, as a lead instructor for FEMA’s rescue specialist training, and as a member of the FEMA Incident Support Team at major disasters. O’Connell is president of Collapse Rescue Systems Inc., an international training company specializing in technical rescue. He has instructed extensively throughout the United States and in Canada, China, the Middle East, and Japan. Over the past 15 years, he has been involved in curriculum development for FDNY, the New York State Office of Fire Prevention and Control, and the FEMA Urban Search & Rescue system. O’Connell is the author of Emergency Rescue Shoring Techniques (Fire Engineering, 2005) and numerous articles on structural collapse and technical rescue. He is a member of the Fire Engineering and the FDIC advisory boards.
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