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13 March 2026
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Featured FRI Magazine article: Structural shoring Part 2: Horizontal and lateral shoring by Colin Deiner
This week’s featured Fire and Rescue International magazine article is: Structural shoring Part 2: Horizontal and lateral shoring written by Colin Deiner, chief director, disaster management and fire brigade services, Western Cape Government (FRI Vol 3 no 11). We will be sharing more technical/research/tactical articles from Fire and Rescue International magazine on a weekly basis with our readers to assist in technology transfer. This will hopefully create an increased awareness, providing you with hands-on advice and guidance. All our magazines are available free of charge in PDF format on our website and online at ISSUU. We also provide all technical articles as a free download in our article archive on our website.
Structural shoring Part 2: Horizontal and lateral shoring
By Colin Deiner, chief director, disaster management and fire brigade services, Western Cape Government
All types of structures can become compromised as a result of structural collapse. Un-reinforced masonry is a good example of a material that typically needs support. Acting against the forces of gravity is generally the simplest way to stabilise an unstable load. What if we have a structure unable to resist the forces of a lateral load? We then have to find a way to ensure that we stabilise this load and in so doing allow our rescuers to work in close proximity to it in a safe manner.
This is the second in a series of articles on structural collapse shoring. The first one, which was published in the Volume
3 no 4 edition of Fire Rescue International, focussed on vertical shoring. I will concentrate here specifically on raker shores and horizontal shores.
The purpose of raker shores is to support unstable walls, columns or other structural members of a building from the interior or exterior. These members may be out of plump, bulged, cracked or under pressure from collapsed debris.
Raker shores are specifically designed to prevent any further movement from these unstable elements by transferring the additional stresses generated by these elements, through the point of the rake to the floor. From the floor the load can be more safely distributed to other structural bearing members. Horizontal shores are used primarily to support damaged or unstable walls in hallways, alleys, air shafts or other access ways. It can also be used between two unstable structures. Its main purpose would be to provide sustained access for ongoing search and rescue operations.
How it all fits together
Let’s remember the ‘double funnel’ principle. Quite simply, this requires us to look at shoring as a double funnel (See Fig 1). The top ‘funnel’ (header) needs to be broad enough to collect the load. A normal wood post would have the risk of punching through a concrete slab if it doesn’t have a sufficiently broad header. This load is then transferred to the load bearing posts (or struts) and then transferred to the bottom ‘funnel’ (or sole) where it will be distributed over the surface of the ground.
This is of course the perfect scenario. In a structural collapse situation you are dealing with an unstable load on an uneven surface and the possibility of lateral forces are very real. For these possibilities lateral bracing is required to prevent racking (parallelogram effect) or to prevent the system from buckling (sideways movement).
Because you are working with unknown forces and load weights, it is critical that your construction has a built-in warning system, which could give you a clear indication that failure is imminent. With a vertical shore construction, a post with a length to width ratio of 25 or less, the header or sole crushing against the post will be clearly audible prior to it failing. In a vertical shoring situation it is relatively simple to work out which areas need stabilisation. In a situation where you have damaged and unstable walls, you will need to provide lateral support able to counteract approximately 10 percent of the weight of the building.
We now have to take the double funnel principle and move it ‘sideways’.
Raker shores
There are three types of rakers; flying, split-sole and solidsole. Each type features a wall plate, a diagonal raker post and some type of sole plate. A solid-sole raker is generally used when the surface at the base of the wall (where it will be installed) is firm and clear of any obstructions. Split-sole raker shores will typically be used where you have a ground surface and need to ensure additional resistance to the lateral load and requires more timber. Both can be used on solid surface although only the split sole shore can be used on uncovered ground.
The flying raker (Fig 2) is a temporary shore used only until a more substantial set of rakers can be put in place. It can be constructed and installed quickly and buy you the necessary time to construct a more permanent set of rakers to be used for a prolonged operation.
You generally will encounter two styles of solid-sole raker shores out there; the friction style and fixed style.
Simply put, the friction style maintains its position by being constantly under pressure. This works for the construction industry but would not work in a structural collapse rescue environment due to the irregular nature of the rescue operation and the possibility of unanticipated movement of loads subjected to cutting and breaking.
The fixed raker shore is more suited to rescue situations because it is a more solid unit and will be able to stand up to any forces applied to it. By tying all the structural elements together, it becomes more stable and is therefore able to deal with any possible secondary collapse risks or vibration from machinery.
Any construction of any shores must ideally be done outside of the collapse zone and only once the shore is completed, can it be moved into position. It therefore goes without saying that communication between the measuring team and construction team must be accurate.
The raker shores can be constructed at 45 degree to 60 degree angles. They are always installed in a series of at least two with a maximum separation of 2,5m and are braced together for additional stability. A single raker shore will not be able to absorb the stresses of an entire wall and therefore they must always be installed in series. At least two shores must be installed at the start of shoring operations in any given situation. By connecting all the shores together (lace-posting), you are creating a much more stable platform, which can more safely absorb the load intended to be supported by them. (Fig 3)
Raker shore placement
No two collapse situations are ever the same.
Obviously, having thorough knowledge of the types of structures in your district will give you some idea of what you might encounter in a structural collapse emergency and help you to plan the types of shoring you will need and the sizes of timber to achieve this.
Your shoring size-up will include several considerations.
The type of construction will help you in determining the size of material to use. Light frame construction will not pose many problems and you should get away with using 100mm x 100mm timbers to construct your shores.
As buildings get larger and their walls are constructed from brick and concrete, I would recommend not going lower than 150mm x 150mm. It would not always be possible to decide beforehand what the size of the timber is that you might need for a particular collapse.
Timber larger than 150mm x 150mm are not readily available and are more labour intensive to work with.
You might need to source specialised timber yards that are able to provide it. You might also need some mechanical construction equipment to move large timbers around.
The severity of the damage to the structure will dictate the level of shoring required. You firstly have to determine if the structure is safe enough to conduct any rescue work and if anyone actually would have survived the collapse.
If it is indeed viable to conduct rescue operations in the structure, you need to then focus on the affected wall areas. Check their structural integrity. Is the wall out of plump? Are there any cracks or bulges? And most importantly, how much of the remaining structure is being supported by the wall you are considering. Depending on the severity of the collapse, the forces applied to the wall may cause numerous and extensive cracks causing the wall to lose its entire structural integrity. Trying to support such walls may serve no purpose.
As with any rescue operation an important question to address is what caused the collapse? If it occurred due to forces of nature ie winds and earthquakes, care should be taken to ensure that these conditions are still not prevailing. In an earthquake situation, major aftershocks could still occur for several days after the initial quake.
Buildings that have fallen into disrepair and collapsed for that reason may have the risk of further collapse due to the entire structure suffering from the same neglect.
Always consider the possibility of secondary collapse and plan for these eventualities.
The ground stability will also play a major role in determining what shore will be needed. A built-up industrial area will most likely be the most viable for solid-sole rakers while a suburban environment will possibly require a split-sole raker. The height of the wall will dictate the height at which the rake will intersect the wall and which angle will be the best. It will further indicate whether your available timber will be sufficient for the job.
Raker shore components
Because we have to stabilise a lateral load and transfer the forces onto the ground surface, we need to view the materials needed to achieve this differently. The main components of the solid-sole and flying raker shore are roughly the same and consist of the following:
Wall plate: This component collects the weight being transferred and spreads it throughout the shoring system.
I strongly believe that the minimum timber size that should be used should be 150mm by 150mm (6’ x 6’). The wall plate can be backed up by 50mm timber or plywood to widen the surface contact area, if needed.
Top cleat: This is a short length of (approximately) 50mm timber that is nailed to the top of the wall plate to keep the raker from riding up the wall plate. The tip of the raker will be in full contact with the bottom of the top cleat when complete.
Sole plate: On a solid sole raker, the sole plate collects the weight being transferred laterally and distributes it to the ground or other structural supporting member. The minimum timber size that should be used is 150mm x 150mm. The sole plate can be secured against a solid component such as another structure or a curb. However, if this is not available a minimum 100mm x 100mm timber can be placed against stakes driven into the ground to prevent the shore from sliding backwards.
U-channel sole plate: Is used on a split-sole raker and collects the weight being transferred laterally and distributes it to the ground or other structural supporting member. It is mostly used in on open ground in suburban and rural environments.
Bottom cleat: Is used on a solid sole raker and is a short piece of 5cm or 2 inch timber that is nailed to the rear of the sole plate to keep the raker from riding back on the sole plate. A gap the width of the wedges is left between the bottom cleat and the raker to later pressurise the shore. Similar to the top cleat, a 60cm or 2 foot cleat is used for 45 degrees rakers and for 60 degrees rakers.
Raker: This is the main part of the system as it supports the weight being collected by the wall plate and transfers it to the sole plate. The width of the raker should be the same as the wall plate and sole plate to ensure the secure attachment of gusset plates, cleats and braces. We are again looking at 150mm x 150mm here.
Wedges: A sufficient number of wedges must be available to fill the gaps between the shore and the structure. Wedges should be used in pairs with the cut side of each wedge flush against each other for better holding capability and for a better striking surface for the hammers when pressurising.
Gusset plates: These are 300mm x 300mm plywood squares or triangles that secure the connections between the different parts of the shore like the wall plate and sole plate. On the raker shore, they should be placed on both sides of the joints.
Bottom braces: These braces connect the wall plate to the raker, maintain distance and provide strength for the shore by preventing separation of the shore components. The minimum size timber to be used is one 50mm x 150mm or two 50mm x 100mm.
Midpoint braces: Are used to increase the raker load bearing capability by resisting the ‘buckling’ effect. These are required when the 100mm x 100mm raker is greater than 3,5m in length or a 150mm x 150mm raker is greater than 5m in length.
Horizontal braces: Are used to connect the raker shores together near the top and bottom of the raker to provide additional stability.
Cross braces: Provide additional stability and resists lateral deflection of the shores. They are used at the end of each raker shore system and no further than 12m apart. Following the size-up and determination of the size of timber to be used, the construction of the raker shore can begin.
The solid-sole raker shore (fig 4)
Wall plate: Erecting the wall plate will be the first step. Ensure that the wall plate is sufficiently higher than the intended point of the rake to ensure that there is enough room for installing the cleat. The wall plate should be erected as vertically level as possible in both directions. Raise the wall plate at the base of the wall and gently lay it against the building. The two points of the wall plate that must be in contact with the damaged wall, are where the rake meets the building and at the base where the sole plate interjects with the base. It might be necessary to use wedges to achieve this.
Sole plate: Before moving the sole plate in place make sure that the entire area is clear of debris. You will need some additional space to allow for rescuers to move around while they are constructing the shore. Move the sole plate into position and ensure that it is butted snugly into the base of the wall plate. Ensure that it is in direct alignment to the wall plate and flush with the floor surface; you might need to shim it to achieve this. The length of the sole plate will be depended on the type of anchoring systems to be used.
Raker: Once the height of the wall and angle of the rake have been determined, the raker must be cut to precisely the same length with the proper angles. Place the bottom of the raker into its position on the sole plate and gently position it onto the wall plate. It might be necessary here to move it slightly up and down to achieve the best fit. Ensure that the raker is held in place temporarily by toenailing it into the wall and sole plates.
Top cleats: The main function of the cleats is to stop the raker from moving upward or outward when pressure is applied to it. If it was not possible to install the top cleat earlier it will be necessary to do so now. It will, however, be preferable to fit the top cleat before placing the wall plate against the structure. A minimum 50mm timber of the same width as the wall and sole plate must be used. Its minimum length should be 600mm, which should be sufficient for its purpose. It should be nailed in using the five-nail method.
Bottom cleats: The bottom cleat should be of the same dimensions but its length might differ depending on how the shore will be anchored. When installing the cleat, make sure that enough space is allowed for inserting wedges between the cleat and the raker. The wedges will be used to ensure a snug fit.
Gusset plates: The gusset plates’ function is to lock the shore connections together (the weakest part of the shore is its connecting points). The gusset plates will prevent the raker shore’s elements from moving if an unexpected force (like an aftershock) is exerted onto it. The top gusset should be installed above the top of the rake, which will tie all the elements together. The gusset plate must be nailed into all these elements ie wall plate, top cleat and raker. The bottom gusset plate should be fitted flush with the front edge of the wall plate and level with the bottom edge of the sole plate. After the plates have been fitted on the shore, it is time to install the diagonal brace. It must be installed on the outside of the gusset plate and nailed through the gusset plate into the wall plate and sole plate. The back gusset plate should be installed after the set of wedges at the base have been securely tightened and should only be nailed into position when you are sure that the shore is in position and able to absorb the forces it is intended to withstand. Nail the plate flush with the bottom of the sole plate and slightly ahead of the wedges for maximum coverage.
Centre braces: The centre braces, installed on each side of the raker, provides stability to the shore by helping to stop deflection in the raker when a force is applied to the shore. The braces are nailed over the bottom cleat and at the centre of the raker.
The split-sole raker shore (Fig 5)
As already mentioned, the split-sole raker shore is erected in mainly suburban or rural areas where a solid surface is not an option. It can either be pre-erected or erected in place. For safety reasons it would be better to go for the first option, although it will require precise calculations.
Erecting a split-sole raker shore is fundamentally different to that of a solid-sole shore in two areas.
Firstly, the length of the raker here will be larger than the solid-sole raker and the sole plate is made up of two (normally 20mm x 100mm or 150mm) beams. The preparation of the ground area for the placement of the base of the rake is different where it is necessary to excavate an opening in the ground to accommodate its base. It is important here to ensure that you have sufficient wedges to ensure compromise for any errors in the excavation.
The first and most important consideration when erecting this shore is to determine the height at which the rake will intersect with the damaged wall.
Wall plate
Determining the intersecting height of the wall plate and the rake will determine the angle you can use with the size timber available. If, for example, the height of the rake is to be 3,5m up the face of the wall and the length of the material you are using is 5m long, a 54- or 60-degree angle would be most effective. If a 45-degree angle was used, the rake would have to be longer than 5m. Sourcing and transporting timbers larger than this is not only very expensive but also impractical (you will be looking at laminated beams). For strength and stability, a 60-degree-angle rake should be the maximum angle used in collapse shoring operations.
Base
Determine the length, the location for the base of the rake and prepare the ground. The best method for this would be to calculate the position of the base of the rake at the determined angle (take into account the depth of the hole and the point where it intersects with the sole plates.
This will be the distance away from the wall at which you will start digging the hole that will hold the raker shore. The hole should be approximately 300mm deep (roughly the depth of your shovel blade) and on an angle to match the square end of your rake.
On softer ground, place two blocks in the hole. Nail a piece of plywood to the blocks to make one pad, then wedge it under the rake to help transfer the load over a wider surface. If you are working on more stable ground you will only need to dig only the width of one block. Place the wedge under the rake and tighten it to a snug fit. While you are busy with this, have another team getting to work cutting the angle on the rake and then cut the rake to the predetermined length.
Cleats and gussets
Nail the top cleat to the wall plate at the point where you intend the raker to intersect the wall plate. Nail the rake into the wall plate directly under the top cleat. Make sure the fit is correct. Nail the gusset plate to the wall plate and rake and then temporarily nail down one of the bottom braces to the wall plate and rake to keep the shore together as it is installed.
Rake placement
Now place the raker shore up against the wall and lower it into the hole before anchoring the shore into the wall. Finally knock the wedges into position.
Bottom braces
Install both bottom braces on each side of the rake, as close to the ground as possible. Place a filler block in the space to help stop any deflection of the bottom braces, which may weaken the shore and tighten up the wedges at this point and tack in place.
Diagonal brace
The diagonal brace must be installed on both sides of the rake just above the bottom braces and up to the rake, on both sides.
Your shore is now complete.
Horizontal shoring (Fig 6)
The main purpose of horizontal shores is to stabilise normal access routes that have been compromised. By shoring these routes, a safe area is created for rescuers and victims.
The important consideration when deciding on whether to shore such an area will again be to ascertain the viability of finding live victims in the area and the extent to which it has been damaged.
Again the shoring structure will start by placing two 150mm x 150mm wall plates against the walls facing each other as plumb as possible. After this has been done it will be time to install the horizontal struts. They must be the same dimensions of the wall plates.
Determining how many struts should be used will depend on a number of factors. These include: extent of damage, location of debris, type of wall construction, locations at which the greatest force is being applied to the walls, possible locations of victims and whether the area will be used as a sustained access route.
To ensure additional stability, cleats are nailed directly to the wall plates just below each strut. This just provides that added assurance against vibrations such as earthquake aftershocks or people accidentally shoving or stepping on the struts.
At the one end of the struts, a set of equal and opposing wedges are placed (between the strut and the wall plate) and lightly hammered together to ensure a snug fit. For additional protection, a range of plywood gusset plates can also be anchored onto the outward face of the connections between the wall plates and struts.
If the shore is not going to be used for sustained access, a series of diagonal braces can be nailed onto the assembly to lock the shore together as one unit.
Mechanical shores
Over the last number of years a range of mechanical shoring systems have become available to rescue services. These systems started out in the trench rescue environment but have since been modified to be adapted to structural collapse incidents. These struts are extremely strong and can be set into position really quick, allowing for rescuers to enter an area safely. Struts can also be repositioned easily through a pin or threaded locking system and set by means of an air actuated system. It is important, however, for operators to be careful when actuating these systems under unstable loads. While the struts are not designed for lifting operations they may, if the pressure settings are incorrect, cause such a load to be upset.
Certain suppliers have also developed a small hydraulic strut that can provide you with that little bit of space you might need to gain an access point for pneumatic lifting bags or wedges.
These struts are also provided with a wide range of bases and fittings, which provide many options for their placement. I do, however, believe that mechanical (or pneumatic) shores must be used in conjunction with timber shoring. Relying purely on mechanical shores lets you run the risk of losing them all if the structure shifts for some reason. You will then have to write them off or wait for the building to be delayered before you can start digging in the debris to get them back; only then will you know how badly they have been compromised. Mechanical struts are not cheap items and must be used with great care.
They are, however, invaluable for a rapid shoring operation or for stabilising an area that is difficult to access.
In closing
Now that we have reached the end of the series on shoring, I am hoping that the one message that I have left with you is that structural shoring is a very precise and equipment intensive task, which requires plenty of pre-planning and identification of resources. Very few fire and rescue services are able to acquire and store the huge amount of timber needed to stabilise a large collapsed structure. In most cases, they have only enough to fit onto their trench collapse unit.
We have a further challenge that most timber yards don’t stock the dimensions that are generally recommended for rescue. Make a point therefore of finding out what is quickly available to you and what you need to do to get it to your rescue scene.
It will be those small details that are going to let you down when you get called upon to perform a large scale shoring operation.
Structural shoring Part 2: Horizontal and lateral shoring
By Colin Deiner, chief director, disaster management and fire brigade services, Western Cape Government
All types of structures can become compromised as a result of structural collapse. Un-reinforced masonry is a good example of a material that typically needs support. Acting against the forces of gravity is generally the simplest way to stabilise an unstable load. What if we have a structure unable to resist the forces of a lateral load? We then have to find a way to ensure that we stabilise this load and in so doing allow our rescuers to work in close proximity to it in a safe manner.
This is the second in a series of articles on structural collapse shoring. The first one, which was published in the Volume
3 no 4 edition of Fire Rescue International, focussed on vertical shoring. I will concentrate here specifically on raker shores and horizontal shores.
The purpose of raker shores is to support unstable walls, columns or other structural members of a building from the interior or exterior. These members may be out of plump, bulged, cracked or under pressure from collapsed debris.
Raker shores are specifically designed to prevent any further movement from these unstable elements by transferring the additional stresses generated by these elements, through the point of the rake to the floor. From the floor the load can be more safely distributed to other structural bearing members. Horizontal shores are used primarily to support damaged or unstable walls in hallways, alleys, air shafts or other access ways. It can also be used between two unstable structures. Its main purpose would be to provide sustained access for ongoing search and rescue operations.
How it all fits together
Let’s remember the ‘double funnel’ principle. Quite simply, this requires us to look at shoring as a double funnel (See Fig 1). The top ‘funnel’ (header) needs to be broad enough to collect the load. A normal wood post would have the risk of punching through a concrete slab if it doesn’t have a sufficiently broad header. This load is then transferred to the load bearing posts (or struts) and then transferred to the bottom ‘funnel’ (or sole) where it will be distributed over the surface of the ground.
This is of course the perfect scenario. In a structural collapse situation you are dealing with an unstable load on an uneven surface and the possibility of lateral forces are very real. For these possibilities lateral bracing is required to prevent racking (parallelogram effect) or to prevent the system from buckling (sideways movement).
Because you are working with unknown forces and load weights, it is critical that your construction has a built-in warning system, which could give you a clear indication that failure is imminent. With a vertical shore construction, a post with a length to width ratio of 25 or less, the header or sole crushing against the post will be clearly audible prior to it failing. In a vertical shoring situation it is relatively simple to work out which areas need stabilisation. In a situation where you have damaged and unstable walls, you will need to provide lateral support able to counteract approximately 10 percent of the weight of the building.
We now have to take the double funnel principle and move it ‘sideways’.
Raker shores
There are three types of rakers; flying, split-sole and solidsole. Each type features a wall plate, a diagonal raker post and some type of sole plate. A solid-sole raker is generally used when the surface at the base of the wall (where it will be installed) is firm and clear of any obstructions. Split-sole raker shores will typically be used where you have a ground surface and need to ensure additional resistance to the lateral load and requires more timber. Both can be used on solid surface although only the split sole shore can be used on uncovered ground.
The flying raker (Fig 2) is a temporary shore used only until a more substantial set of rakers can be put in place. It can be constructed and installed quickly and buy you the necessary time to construct a more permanent set of rakers to be used for a prolonged operation.
You generally will encounter two styles of solid-sole raker shores out there; the friction style and fixed style.
Simply put, the friction style maintains its position by being constantly under pressure. This works for the construction industry but would not work in a structural collapse rescue environment due to the irregular nature of the rescue operation and the possibility of unanticipated movement of loads subjected to cutting and breaking.
The fixed raker shore is more suited to rescue situations because it is a more solid unit and will be able to stand up to any forces applied to it. By tying all the structural elements together, it becomes more stable and is therefore able to deal with any possible secondary collapse risks or vibration from machinery.
Any construction of any shores must ideally be done outside of the collapse zone and only once the shore is completed, can it be moved into position. It therefore goes without saying that communication between the measuring team and construction team must be accurate.
The raker shores can be constructed at 45 degree to 60 degree angles. They are always installed in a series of at least two with a maximum separation of 2,5m and are braced together for additional stability. A single raker shore will not be able to absorb the stresses of an entire wall and therefore they must always be installed in series. At least two shores must be installed at the start of shoring operations in any given situation. By connecting all the shores together (lace-posting), you are creating a much more stable platform, which can more safely absorb the load intended to be supported by them. (Fig 3)
Raker shore placement
No two collapse situations are ever the same.
Obviously, having thorough knowledge of the types of structures in your district will give you some idea of what you might encounter in a structural collapse emergency and help you to plan the types of shoring you will need and the sizes of timber to achieve this.
Your shoring size-up will include several considerations.
The type of construction will help you in determining the size of material to use. Light frame construction will not pose many problems and you should get away with using 100mm x 100mm timbers to construct your shores.
As buildings get larger and their walls are constructed from brick and concrete, I would recommend not going lower than 150mm x 150mm. It would not always be possible to decide beforehand what the size of the timber is that you might need for a particular collapse.
Timber larger than 150mm x 150mm are not readily available and are more labour intensive to work with.
You might need to source specialised timber yards that are able to provide it. You might also need some mechanical construction equipment to move large timbers around.
The severity of the damage to the structure will dictate the level of shoring required. You firstly have to determine if the structure is safe enough to conduct any rescue work and if anyone actually would have survived the collapse.
If it is indeed viable to conduct rescue operations in the structure, you need to then focus on the affected wall areas. Check their structural integrity. Is the wall out of plump? Are there any cracks or bulges? And most importantly, how much of the remaining structure is being supported by the wall you are considering. Depending on the severity of the collapse, the forces applied to the wall may cause numerous and extensive cracks causing the wall to lose its entire structural integrity. Trying to support such walls may serve no purpose.
As with any rescue operation an important question to address is what caused the collapse? If it occurred due to forces of nature ie winds and earthquakes, care should be taken to ensure that these conditions are still not prevailing. In an earthquake situation, major aftershocks could still occur for several days after the initial quake.
Buildings that have fallen into disrepair and collapsed for that reason may have the risk of further collapse due to the entire structure suffering from the same neglect.
Always consider the possibility of secondary collapse and plan for these eventualities.
The ground stability will also play a major role in determining what shore will be needed. A built-up industrial area will most likely be the most viable for solid-sole rakers while a suburban environment will possibly require a split-sole raker. The height of the wall will dictate the height at which the rake will intersect the wall and which angle will be the best. It will further indicate whether your available timber will be sufficient for the job.
Raker shore components
Because we have to stabilise a lateral load and transfer the forces onto the ground surface, we need to view the materials needed to achieve this differently. The main components of the solid-sole and flying raker shore are roughly the same and consist of the following:
Wall plate: This component collects the weight being transferred and spreads it throughout the shoring system.
I strongly believe that the minimum timber size that should be used should be 150mm by 150mm (6’ x 6’). The wall plate can be backed up by 50mm timber or plywood to widen the surface contact area, if needed.
Top cleat: This is a short length of (approximately) 50mm timber that is nailed to the top of the wall plate to keep the raker from riding up the wall plate. The tip of the raker will be in full contact with the bottom of the top cleat when complete.
Sole plate: On a solid sole raker, the sole plate collects the weight being transferred laterally and distributes it to the ground or other structural supporting member. The minimum timber size that should be used is 150mm x 150mm. The sole plate can be secured against a solid component such as another structure or a curb. However, if this is not available a minimum 100mm x 100mm timber can be placed against stakes driven into the ground to prevent the shore from sliding backwards.
U-channel sole plate: Is used on a split-sole raker and collects the weight being transferred laterally and distributes it to the ground or other structural supporting member. It is mostly used in on open ground in suburban and rural environments.
Bottom cleat: Is used on a solid sole raker and is a short piece of 5cm or 2 inch timber that is nailed to the rear of the sole plate to keep the raker from riding back on the sole plate. A gap the width of the wedges is left between the bottom cleat and the raker to later pressurise the shore. Similar to the top cleat, a 60cm or 2 foot cleat is used for 45 degrees rakers and for 60 degrees rakers.
Raker: This is the main part of the system as it supports the weight being collected by the wall plate and transfers it to the sole plate. The width of the raker should be the same as the wall plate and sole plate to ensure the secure attachment of gusset plates, cleats and braces. We are again looking at 150mm x 150mm here.
Wedges: A sufficient number of wedges must be available to fill the gaps between the shore and the structure. Wedges should be used in pairs with the cut side of each wedge flush against each other for better holding capability and for a better striking surface for the hammers when pressurising.
Gusset plates: These are 300mm x 300mm plywood squares or triangles that secure the connections between the different parts of the shore like the wall plate and sole plate. On the raker shore, they should be placed on both sides of the joints.
Bottom braces: These braces connect the wall plate to the raker, maintain distance and provide strength for the shore by preventing separation of the shore components. The minimum size timber to be used is one 50mm x 150mm or two 50mm x 100mm.
Midpoint braces: Are used to increase the raker load bearing capability by resisting the ‘buckling’ effect. These are required when the 100mm x 100mm raker is greater than 3,5m in length or a 150mm x 150mm raker is greater than 5m in length.
Horizontal braces: Are used to connect the raker shores together near the top and bottom of the raker to provide additional stability.
Cross braces: Provide additional stability and resists lateral deflection of the shores. They are used at the end of each raker shore system and no further than 12m apart. Following the size-up and determination of the size of timber to be used, the construction of the raker shore can begin.
The solid-sole raker shore (fig 4)
Wall plate: Erecting the wall plate will be the first step. Ensure that the wall plate is sufficiently higher than the intended point of the rake to ensure that there is enough room for installing the cleat. The wall plate should be erected as vertically level as possible in both directions. Raise the wall plate at the base of the wall and gently lay it against the building. The two points of the wall plate that must be in contact with the damaged wall, are where the rake meets the building and at the base where the sole plate interjects with the base. It might be necessary to use wedges to achieve this.
Sole plate: Before moving the sole plate in place make sure that the entire area is clear of debris. You will need some additional space to allow for rescuers to move around while they are constructing the shore. Move the sole plate into position and ensure that it is butted snugly into the base of the wall plate. Ensure that it is in direct alignment to the wall plate and flush with the floor surface; you might need to shim it to achieve this. The length of the sole plate will be depended on the type of anchoring systems to be used.
Raker: Once the height of the wall and angle of the rake have been determined, the raker must be cut to precisely the same length with the proper angles. Place the bottom of the raker into its position on the sole plate and gently position it onto the wall plate. It might be necessary here to move it slightly up and down to achieve the best fit. Ensure that the raker is held in place temporarily by toenailing it into the wall and sole plates.
Top cleats: The main function of the cleats is to stop the raker from moving upward or outward when pressure is applied to it. If it was not possible to install the top cleat earlier it will be necessary to do so now. It will, however, be preferable to fit the top cleat before placing the wall plate against the structure. A minimum 50mm timber of the same width as the wall and sole plate must be used. Its minimum length should be 600mm, which should be sufficient for its purpose. It should be nailed in using the five-nail method.
Bottom cleats: The bottom cleat should be of the same dimensions but its length might differ depending on how the shore will be anchored. When installing the cleat, make sure that enough space is allowed for inserting wedges between the cleat and the raker. The wedges will be used to ensure a snug fit.
Gusset plates: The gusset plates’ function is to lock the shore connections together (the weakest part of the shore is its connecting points). The gusset plates will prevent the raker shore’s elements from moving if an unexpected force (like an aftershock) is exerted onto it. The top gusset should be installed above the top of the rake, which will tie all the elements together. The gusset plate must be nailed into all these elements ie wall plate, top cleat and raker. The bottom gusset plate should be fitted flush with the front edge of the wall plate and level with the bottom edge of the sole plate. After the plates have been fitted on the shore, it is time to install the diagonal brace. It must be installed on the outside of the gusset plate and nailed through the gusset plate into the wall plate and sole plate. The back gusset plate should be installed after the set of wedges at the base have been securely tightened and should only be nailed into position when you are sure that the shore is in position and able to absorb the forces it is intended to withstand. Nail the plate flush with the bottom of the sole plate and slightly ahead of the wedges for maximum coverage.
Centre braces: The centre braces, installed on each side of the raker, provides stability to the shore by helping to stop deflection in the raker when a force is applied to the shore. The braces are nailed over the bottom cleat and at the centre of the raker.
The split-sole raker shore (Fig 5)
As already mentioned, the split-sole raker shore is erected in mainly suburban or rural areas where a solid surface is not an option. It can either be pre-erected or erected in place. For safety reasons it would be better to go for the first option, although it will require precise calculations.
Erecting a split-sole raker shore is fundamentally different to that of a solid-sole shore in two areas.
Firstly, the length of the raker here will be larger than the solid-sole raker and the sole plate is made up of two (normally 20mm x 100mm or 150mm) beams. The preparation of the ground area for the placement of the base of the rake is different where it is necessary to excavate an opening in the ground to accommodate its base. It is important here to ensure that you have sufficient wedges to ensure compromise for any errors in the excavation.
The first and most important consideration when erecting this shore is to determine the height at which the rake will intersect with the damaged wall.
Wall plate
Determining the intersecting height of the wall plate and the rake will determine the angle you can use with the size timber available. If, for example, the height of the rake is to be 3,5m up the face of the wall and the length of the material you are using is 5m long, a 54- or 60-degree angle would be most effective. If a 45-degree angle was used, the rake would have to be longer than 5m. Sourcing and transporting timbers larger than this is not only very expensive but also impractical (you will be looking at laminated beams). For strength and stability, a 60-degree-angle rake should be the maximum angle used in collapse shoring operations.
Base
Determine the length, the location for the base of the rake and prepare the ground. The best method for this would be to calculate the position of the base of the rake at the determined angle (take into account the depth of the hole and the point where it intersects with the sole plates.
This will be the distance away from the wall at which you will start digging the hole that will hold the raker shore. The hole should be approximately 300mm deep (roughly the depth of your shovel blade) and on an angle to match the square end of your rake.
On softer ground, place two blocks in the hole. Nail a piece of plywood to the blocks to make one pad, then wedge it under the rake to help transfer the load over a wider surface. If you are working on more stable ground you will only need to dig only the width of one block. Place the wedge under the rake and tighten it to a snug fit. While you are busy with this, have another team getting to work cutting the angle on the rake and then cut the rake to the predetermined length.
Cleats and gussets
Nail the top cleat to the wall plate at the point where you intend the raker to intersect the wall plate. Nail the rake into the wall plate directly under the top cleat. Make sure the fit is correct. Nail the gusset plate to the wall plate and rake and then temporarily nail down one of the bottom braces to the wall plate and rake to keep the shore together as it is installed.
Rake placement
Now place the raker shore up against the wall and lower it into the hole before anchoring the shore into the wall. Finally knock the wedges into position.
Bottom braces
Install both bottom braces on each side of the rake, as close to the ground as possible. Place a filler block in the space to help stop any deflection of the bottom braces, which may weaken the shore and tighten up the wedges at this point and tack in place.
Diagonal brace
The diagonal brace must be installed on both sides of the rake just above the bottom braces and up to the rake, on both sides.
Your shore is now complete.
Horizontal shoring (Fig 6)
The main purpose of horizontal shores is to stabilise normal access routes that have been compromised. By shoring these routes, a safe area is created for rescuers and victims.
The important consideration when deciding on whether to shore such an area will again be to ascertain the viability of finding live victims in the area and the extent to which it has been damaged.
Again the shoring structure will start by placing two 150mm x 150mm wall plates against the walls facing each other as plumb as possible. After this has been done it will be time to install the horizontal struts. They must be the same dimensions of the wall plates.
Determining how many struts should be used will depend on a number of factors. These include: extent of damage, location of debris, type of wall construction, locations at which the greatest force is being applied to the walls, possible locations of victims and whether the area will be used as a sustained access route.
To ensure additional stability, cleats are nailed directly to the wall plates just below each strut. This just provides that added assurance against vibrations such as earthquake aftershocks or people accidentally shoving or stepping on the struts.
At the one end of the struts, a set of equal and opposing wedges are placed (between the strut and the wall plate) and lightly hammered together to ensure a snug fit. For additional protection, a range of plywood gusset plates can also be anchored onto the outward face of the connections between the wall plates and struts.
If the shore is not going to be used for sustained access, a series of diagonal braces can be nailed onto the assembly to lock the shore together as one unit.
Mechanical shores
Over the last number of years a range of mechanical shoring systems have become available to rescue services. These systems started out in the trench rescue environment but have since been modified to be adapted to structural collapse incidents. These struts are extremely strong and can be set into position really quick, allowing for rescuers to enter an area safely. Struts can also be repositioned easily through a pin or threaded locking system and set by means of an air actuated system. It is important, however, for operators to be careful when actuating these systems under unstable loads. While the struts are not designed for lifting operations they may, if the pressure settings are incorrect, cause such a load to be upset.
Certain suppliers have also developed a small hydraulic strut that can provide you with that little bit of space you might need to gain an access point for pneumatic lifting bags or wedges.
These struts are also provided with a wide range of bases and fittings, which provide many options for their placement. I do, however, believe that mechanical (or pneumatic) shores must be used in conjunction with timber shoring. Relying purely on mechanical shores lets you run the risk of losing them all if the structure shifts for some reason. You will then have to write them off or wait for the building to be delayered before you can start digging in the debris to get them back; only then will you know how badly they have been compromised. Mechanical struts are not cheap items and must be used with great care.
They are, however, invaluable for a rapid shoring operation or for stabilising an area that is difficult to access.
In closing
Now that we have reached the end of the series on shoring, I am hoping that the one message that I have left with you is that structural shoring is a very precise and equipment intensive task, which requires plenty of pre-planning and identification of resources. Very few fire and rescue services are able to acquire and store the huge amount of timber needed to stabilise a large collapsed structure. In most cases, they have only enough to fit onto their trench collapse unit.
We have a further challenge that most timber yards don’t stock the dimensions that are generally recommended for rescue. Make a point therefore of finding out what is quickly available to you and what you need to do to get it to your rescue scene.
It will be those small details that are going to let you down when you get called upon to perform a large scale shoring operation.
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