Pneumatic struts as a raker shore system

The pneumatic shore, although more expensive thaN the typical wood shore, can be a definite plus in an emergency rescue situation.

BY JOHN O’CONNELL

A raker shore system consisting mainly of pneumatic raker shores has several advantages over wood shoring systems. In the arena of collapse rescue where many times speed is an issue, these struts can be erected quickly and, in many cases, are stronger than their wood counterparts. Also, only minimal measuring is needed to place the struts. You need measure only the overall length to determine the proper size strut. In most cases when using wood, you would have to measure, cut, and insert a set of wedges for fine adjustments. Pneumatic raker shores include several varieties of bases, making them appropriate for different applications encountered in shoring operations.

THE OBJECTIVES OF RESCUE SHORING OPERATIONS

The main objective of emergency building shores is to properly maintain the strength and integrity of structurally damaged or unstable elements such as, but not limited to, beams, joists, girders, columns, arches, headers, and bearing walls.

The main objectives of the rescue shoring operation are to properly and effectively receive, transmit, and redirect the presently unstable collapse loads. These new loads many times form in specific areas and cause heavy, concentrated load effect; the overstress of the existing structural elements must be transferred ultimately to stable ground. Many times, depending on the type of structure, these loads can be transferred or directed to structural elements in the remaining parts of the building that are sound and capable of handling the additional collapse loads.

BASIC RESCUE SHORING POINTS

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Emergency shoring must be erected as a system. Unlike what you generally see in the construction industry, emergency building shores must be constructed as a complete system. By tying all the shores together, you increase the stability and the efficiency of all the shores. Your biggest concern at any structural collapse rescue operation is a secondary collapse. To prevent such a collapse and to put the safety factors on our side, all the shores must be assembled as a complete system. Keep in mind that the shoring must be able to withstand a secondary collapse.
The lateral bracing must be installed so that the system is prevented from buckling. All shores must be laterally braced, and in both directions. The shores must be able to withstand lateral pressures that may be applied to the shoring system from any direction. Sudden shifts can easily occur in unstable collapsed structures, thus applying eccentric or torsional loading.

Rescue shoring is unique compared with “normal” contractor-installed shoring. Contractor shoring is generally the friction type of shoring, which relies on the pressure of the shore against the damaged material to stay in position. A major problem with the friction type of shore is that it has very little lateral stability and can be easily vibrated or knocked loose-something that cannot be tolerated in an emergency situation. The potential for secondary collapse is always present in structural collapse rescue operations; fixed shoring systems stand up to the threat of secondary collapse better than the friction type of shore. Note: Raker shores must be erected in pairs to be effective. They are too unstable by themselves.

ADVANTAGES OF THE PNEUMATIC STRUT SYSTEM

There are several major advantages to the prepackaged pneumatic strut system.

The shores can be easily assembled with only a little bit of training; very little carpentry skills are needed to properly install the shoring systems.
There are no angles to figure out, there is no lumber to cut to size, and there are no specific nail patterns to install.
There are slightly fewer elements (pieces) in the pneumatic raker system than are normally required.
The raker strut system requires less time and effort to set up and install.
The rakers can be adjusted to sloped or leaning walls much faster than conventional raker systems.
The raker strut system is generally stronger than comparable wood shoring systems.
Wood can be damaged by storage or weather conditions; this is not the case with the raker strut system.
The components can easily be stored in areas that are less than seven feet long; this cannot be done with wood.

EXTERIOR RESCUE SHORING

Exterior rescue shores are among the most difficult and complicated shores to erect. Exterior rescue shoring consists primarily of raker shores and exterior horizontal shores used to stabilize and resupport existing bearing or nonbearing exterior walls. These walls may be cracked, leaning, bulged, or damaged in some other way and are not properly supporting their loads.

In assembling exterior raker shores, you will work with lumber ranging from 4 inches 2 4 inches up to as large as 12 inches 2 12 inches in dimension. But generally speaking, most occasions will call for 4- 2 4 inch or 6- 2 6-inch-size material. Assembling and installing exterior raker shores can get involved and exacting. These operations can be extensive and require large quantities of material. Make sure enough material is on hand to complete a given assignment.

Erecting a series of fixed raker shores properly anchored and braced together will stop an unstable wall from moving outward any farther. At least two shores should be installed in any given situation; they are usually erected in a series for stability reasons. By connecting the individual shores, you create a stable support system that can safely handle extensive loads.

The use of these pneumatic struts makes things much easier in many cases. In areas where access to lumber might be a concern, having the struts on-scene will keep the rescue operation going with no delays.

EXTERIOR SHORING SIZE-UP

The team’s exterior shoring size-up must cover several factors, including the type of construction, the extent of damage, the type and stability of the ground on which the shores will bear, secondary collapse potential, the reason the building failed, and the height of the wall being stabilized. Following is a more detailed discussion of these factors.

Bulged walls. Bulged, bellied, or leaning walls are a sign that some type of instability is occurring in the structure. Walls are designed to accept loads through their center axis when they are plumb. If the walls become eccentrically loaded for any reason, the results can be drastic, especially if those walls are bearing. The weight on top of the wall can quickly turn into an eccentric load and possibly cause the wall to fail. Any deformation in the wall indicates that the overall strength of that wall is compromised. The wall could fail at any time, depending, of course, on how drastic the deformation is. When your team encounters these types of walls, one of the safest ways to counteract the potential problem is to erect interior shores to accept the floor load from above and exterior rakers from the outside to stabilize the damaged walls.
Cracked walls. Whenever forces are applied to concrete or masonry walls, there is the possibility that some type of cracking may occur, especially when those forces are applied laterally or horizontally to the plane of the wall. Although masonry is excellent under compression load, its lateral strength is not extremely efficient. As a result, lateral attacks against masonry walls can cause them to crack.

In reinforced concrete, cracking is an inherent part of the curing process; hairline or thin cracks in concrete do not mean anything. However, issues will develop when the cracks are large and have depth and space; this means the sections of material have sustained heavy damage and may have separated from each other.

Another major factor to consider is the concrete’s adhesion to the reinforcement bar. Concrete will keep its structural integrity until the material itself has separated from the rebar. When there is no adhesion to the steel, the concrete’s lateral strength is severely compromised. Possible collapse situations are a real concern at this point.

Cracking is much more of a concern in masonry brick than in concrete. The bond between the mortar and the masonry units keeps the wall’s integrity intact. When a lateral force is applied to the wall and it fractures that bond, the structural integrity of the wall may be compromised. Thin cracks may not be much of an issue; however, large, long cracks with noticeable depth should be of concern-in this situation, the integrity of the wall has positively been compromised.

Another situation to look for is an “X”-pattern crack on the wall. It indicates that the wall has had stresses applied to it from two separate planes. Shifting or settling of the building is occurring in two separate directions; this is a serious concern to personnel. A thorough size-up of the situation is needed when this occurs.

Another key to look for is how the cracks have been applied to the wall. For instance, if you come across a masonry wall with a crack from the base of the foundation that runs laterally while rising the length of the wall for an appreciable distance, 10 or 20 feet or the like, and there is a large gap at the base that terminates to a fine line at the top, this indicates a settlement crack that has occurred over time. It is indicative of a foundation problem that affects the stability of the wall and the building. Foundation issues, a major problem, can severely limit the rescue team in its attempts to restabilize a structure.

Foundation issues. When a building’s instability is caused by the possible yield of the footings because of unstable soil conditions or water’s undermining the building, you have a problem. All of the rescue shoring you install must bear on a surface that can support the additional loads being applied to them. In some cases, this may be another part of the structure; however, in many cases, this must be the ground or the basement level. If the foundation of the building is compromised, the rescue shoring may not be effective. You will not be able to support the structure by installing emergency building shoring. You will have to consider major efforts to resupport the structure, which will entail efforts not generally associated with the application of rescue shoring. It takes too much time and a large commitment of resources.

When your team responds to an incident involving a major foundation problem, after the structure has been evacuated, you may have to make some decisions such as turning the building over to a reputable contractor and letting him handle the operation and building stabilization.

Racked structure. On some occasions, mainly during natural disasters such as tornadoes, earthquakes, and hurricanes, the entire structure may shift and become racked. To stop the building from shifting or racking, you can raker shore the corners of the building. A set of rakers installed at each corner, especially on a smaller structure, should be enough to arrest any further racking of that structure. Of course, the percentage of racking that has occurred to the building will be a major consideration when determining whether there should be an attempt to restabilize the structure. The first consideration in making such a decision will be whether anyone is trapped in the building. If so, every effort must be made to rescue the victim(s), and the structure must be shored up before rescue forces enter. By raker bracing the corners, you will lock the four corners of the building in place, stopping the structure from twisting further.
Ground stability. Generally speaking, if you respond to a building collapse in an urban environment, you will probably be erecting your rakers on concrete or asphalt. On these types of materials, you should use solid sole raker shores. You can easily anchor this type of raker shore to the hard surfaces using any number of methods. In suburban areas, where you are more likely to encounter bare ground adjacent to the damaged structures, the split sole type of raker shore may be the easiest to use. However, if the ground is stable and firm, the solid sole raker type will work fine. In each collapse situation, you will have different anchoring options; choose the one that is the easiest and most efficient for your team.
Adjacent structures. In many instances, structures adjoining the partially collapsed building can be used to help support the damaged structure. The adjacent structures must be carefully surveyed to assess their physical condition (physical shape or structural integrity) and to ensure they were not affected by the emergency incident and can be a stabilizing force for the collapsed building. If it has been determined that the adjacent structure can handle the additional loads that may be placed against it, shoring operations can begin. If the buildings are close together, exterior horizontal shoring can be erected to support the remains of the damaged building. If the structures are farther apart, a flying shore system may have to be erected. In either case, the structure specialist on-scene, in conjunction with the incident commander, will make the determination.
Extent of damage. The extent of the damage to the structure will dictate whether or not you do any shoring at all. As you size up the structure, first determine whether the area is safe enough for rescue personnel to operate in. Check the structure’s integrity. Are the walls cracked or bulging? Is the wall out of plumb? How much of the remaining structure is relying on the wall for support? This will determine the amount of shoring you will need. A simple rule is, the more damage, the more the potential for shoring. Very extensive damage throughout a large building may dictate the use of multistory shoring systems to redirect the unstable loads to a good bearing surface, generally the ground.

LOAD TRANSFER

Many unreinforced masonry buildings are constructed in such a way that the interior weight is carried by the floor beams and transferred to the bearing walls, which in the majority of these buildings are the exterior walls. An additional impact load transferred to these exterior bearing walls during a collapse can cause deflection and instability. The purpose of the exterior raker shore is to help stabilize the bearing wall and help transfer those additional loads to the ground. As the load is applied to the raker shore, the raker itself comes under compression, causing it to slide upward on the wall and away from the wall at the base. For this reason, the raker shore must be anchored to the wall as well as the ground.

RAKER INSERTION POINT

It is critical that the raker be placed in the proper position, or it will be far less effective and may not help at all. The raker must contact the wall at the level of the floor beams or just below that level-within two feet from the top of the floor beam will be satisfactory. This the most important point in erecting your shore.

RAKER SPACING

When installing rakers, place them no more than eight feet apart, or the lateral bracing between rakers will become far less effective and the rakers may not stand up under a secondary collapse.

RAKER ANGLES

Rescue raker shoring should be erected at a 45° to a 60° angle maximum. The former results in a well-balanced system. If the angle is steeper than 60°, the shore may not hold up under load.

PNEUMATIC RAKER SHORE SYSTEM

Approximately 30 separate components are used to assemble two raker rails, regardless of which brand of shores is used. This may seem like a lot, but these shores go together quickly-more quickly than wooden ones. Two firefighters can assemble a pneumatic raker consistently in only a few minutes. Of course, the time is based on the conditions, which may change with each situation.

Both systems consist of rescue struts, strut extensions, raker rails and splice plates, raker rail joiners, junction bases, hinged base plates, raker brace nailers, and raker base angles for anchoring to the ground.

These rescue rakers are completely preassembled. They are placed in position, anchored, and then adjusted-a major plus when dealing with heavily damaged areas where the potential for major secondary collapse is present.

STEP-BY-STEP ASSEMBLY

Following is a step-by-step assembly guide for the Paratech pneumatic raker shore system. This system and the Airshore pneumatic shore system have been tested and cleared for inclusion in the FEMA US&R tool cache. Both systems are put together in almost the same way. As you can see, almost no measuring is needed.

Pick a suitable spot close to the area to be shored; it should be outside the areas in which there is potential for collapse. Preconstruct the shores in a safe area, away from the damaged and leaning wall. Remember, the safety of the rescue personnel is the top priority. Make sure the area is big enough (an area approximately 20 feet by 20 feet would not be too large) and is relatively level; this will make it easier to put the components together. Photo 1 shows the components needed to assemble two raker shores-struts, extensions, rails, plates, and the various fittings. The 31/2-inch aluminum extensions and struts are in the foreground.

Photo 2 presents a closeup of the raker rails-aluminum channels of various lengths that are assembled together to hold the struts up against the wall.

Photo 3 shows the additional accessories needed to assemble the shores-anchor plates, couplings, splice plates, junction bases, and even a load cell, if you are concerned about the load being applied to the rakers.

Your first priority is to determine the raker shore’s insertion point (photo 4). This will determine the length of the wall plate, which should extend at least 12 inches past the raker insertion point-for example, if your insertion point is 10 feet high, you would use two six-foot channel plates. This is a universal procedure for setting the raker against the wall in question. The idea is to take the overload from the floor and transfer it out through the raker to the ground. The raker must be in this zone to be effective.
The first step in assembling the raker would be to lay out the channel plates for the wall plate. Lay them in line with each other; the plates should be parallel with the wall to be shored. This will make it easier when you pick up the preassembled shore to install it. Splice the plates together using the raker splice plate. Insert both channel plates into the splice plate. Make sure they lock up properly. Next, place the raker rail latch bases onto the wall plate. Place the bases in the holes you have determined you will use. Place the bottom base into the bottom hole or one hole higher off the ground. Photo 5 shows the rail assembled with the latch bases in their proper position.
At this time, determine the size of the struts and the extensions you will be using. Do this for the bottom strut and the raker strut. Place the extensions in the rail latch bases first. Align them on the approximate angle of the raker. Any extensions you install should be located directly into the wall plate; the strut pistons must be facing the bottom of the shore (photo 6). The two extensions are in position; the longer extension must be placed at the top in the raker position.
Insert the struts into the extension pieces. Place the larger strut into the top extension. Lock them in place. Make sure the pistons of both struts face down to the base of the raker shore. Align the struts so that they intersect at the base; it should be the shape of a triangle. Pull the pistons out until the struts are almost touching each other. Keep the bottom strut at right angles to the wall plate as much as possible. Photo 7 shows the two struts anchored to the extensions and ready for the next step in the assembly process.
Place the raker junction base into the two struts. The swivel end of the fitting will go into the raker strut, and the fixed end will be assembled to the base strut. You must assemble it this way for it to work properly. Photo 8 shows the raker junction base in position ready to be assembled. The swivel end of the base must be attached to the raker strut for the shore to assemble properly. Photo 9 shows the base and the two struts attached properly, ready for the next step.

Place the hinged base plate into the swivel end of the raker junction base to complete the shore assembly. Photo 10 shows the base of the shore properly assembled, ready to be placed into position.
Place the assembled raker against the wall in question. Make sure the wall plate contacts the wall at the base and at the raker insertion point. If necessary, pad out the wall to accomplish this. Set the hinged base plate flat on the ground; tighten the pistons up on the base strut and the raker strut.
Anchor the shore to the ground; use at least two one-inch-thick steel pins. You can also use the raker base angle if you wish; anyone of them can be utilized. Photo 11 shows the anchor plate locked down and pressurized against a substantial piece of lumber. Notice the use of the angle plate behind the anchor plate. This spreads the load out more evenly.
Anchor the raker to the wall using the holes provided in the raker rails. Depending on the type of wall, you can use nails, bolts, or pins. There are openings in the raker rails to accept these anchors.
Retighten the nuts on the struts, if necessary, to establish firm contact with the wall in question. The rakers must be in full contact with the wall to be shored.
Always place two raker shores into position; one is not laterally stable enough to do the job. After the second raker has been assembled and installed, cross-brace them. To do this, you will have to use the two raker brace clamps. Place the brace clamps on the shores. Place one clamp close to the raker rail latch, approximately 12 inches down from the raker rail. Lock into position. Place the other clamps down near the base plate onto the piston end of the rakers-again, approximately 12 inches up from the bottom of the raker connections. Lock into position. Photo 12 shows the two rakers with brace clamps in position to accept the 2 2 6 bracing.
Using 2 2 6 lumber, place two pieces horizontally, one at the top and one at the bottom. Using the proper nail patterns will tie the two shores together. Photo 13 shows the two horizontals in position. They are to be nailed to the blocks with five 16-penny common nails.
Cross-brace the shore as shown in photo 14. Use 2 2 6s here also. Each intersecting point is to be nailed with five 16-penny nails. The shore is now finished. Shown in photo 14 are the two rakers cross-braced with an eight-foot-high or less insertion point. One large cross-brace will be sufficient. Photo 15 shows the completed system from another angle.

THE AIRSHORE SUPPORT SYSTEM

The Airshore pneumatic shoring system is similar in principle to the Paratech system described above. Both use a piston and a shaft assembly, and both are braced in the same way. The Airshore system has a different configuration for the piston and the piston locking mechanism; it has a collar that swivels and two locking pins that must be inserted into the piston after it is set. Two Airshore rakers set in position and ready to be braced are shown in photo 16.

The pneumatic shore, although more expensive than the typical wood shore, can be a definite plus in an emergency rescue situation. The struts can be assembled faster, and they will not deteriorate with age or long-term storage. It represents another method of stabilizing a leaning wall and does not require extensive training to learn.

JOHN O’CONNELL has been a member of the Fire Department of New York for 23 years, assigned to Collapse Rescue Company No. 3, where he has served for the past 14 years. He is a principal member of the NFPA 1670 committee and has taught and developed classes for the state and city of New York, the U.S. Military, and the FEMA US&R program. He is a member of the FEMA Incident Support Team at major disasters. He has written numerous articles on structural collapse and is an editorial advisory board member of Fire Engineering and a H.O.T. instructor in structure collapse at FDIC and FDIC West.

Photos 1-7 by the author unless otherwise noted. Photos 8-16 courtesy of Airshore Inc.