RESCUE SYSTEMS 1
CHAPTER 30
SLOPED SURFACE SHORE WITH CRIBBING
CHAPTER 30 - SLOPED SURFACE SHORE WITH CRIBBING
The use of cribbing as shoring is very advantageous and one of the most effective and simplest
stabilization methods. It can be easily adjusted to proper height and can be applied to sloped surfaces.
Cribbing can be diagonally braced to increase lateral support and it can be used to brace crossbeams
that support a large area of a structure. Crib shoring, when applied, is relatively wide and stable. It
effectively transfers the collected loads over multiple shoring elements that are working together to
hold the load.
Figure 30.1
Sloped Floor Shoring
Since the crib shoring system uses basic lumber materials that can be precut and ready for immediate
use even in small confined areas, the process of making measurements, cutting, and nailing to install
the shore up can be eliminated unlike with the process of installation with the other shoring systems.
The greatest advantage of cribbing shoring systems over all other systems is that when they start to
fail, they fail from crushing. This failure will be slow and noisy which act as a warning system for
rescuers that the shoring system is overloaded. Although there are advantages of using cribbing, there
are some disadvantages that rescuers need to consider. Cribbing uses a large amount of materials and
requires a fairly level base to build on.
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CHAPTER 30
SLOPED SURFACE SHORE WITH CRIBBING
RESCUE SYSTEMS 1
Cribbing shores can be built in a box using two members per layer or crosstie configuration using three
members per layer for increased capacity. The capacity of a two-member box crib using 4"x4" lumber
is 24,000 pounds and three-member crosstie crib using 4"x4" lumber is 55,000 pounds
To maximize crushing failure of
cribbing, the tails of each layer should
extend approximately its dimension
past the layer of cribbing below. When
the crib bed is loaded to capacity it will
crush uniformly, creating saddles
similar to Lincoln logs preventing
pieces from squirting out. This method
only works if the load remains
relatively square to the ground. If the
object is not square to the ground the
cribbing tails or ends will be loaded
and cause a cantilever effect. The crib
bed can become unstable and reduce its
load-carrying capability.
When cribbing to sloped surfaces,
place the ends of the cribbing closest to
the load flush with the layer below to
increase crib bed stability and reduce
the cantilever effect.
Cribbing shoring systems used to
support floor and roof assemblies or
buildings, lateral stability of the crib
bed must be considered. Lateral
stability will be dependent on the
width-to- height ratio of the assembly.
Figure 30.2
A rule of thumb is that you can build a crib bed three times as high as the width of the crib area for
level surfaces. Example: If the width of the crib area is 3', then the crib can be built 9' high and still
maintain stability.
When shoring sloped surfaces with 2' cribbing pieces, the maximum allowable height is 3'. The
maximum angle that cribbing can be used for sloped surfaces is 15° or 30% (3' elevation within a 10'
distance). The potential for large slabs to slip off the crib beds increases when steeper surfaces are
shored.
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RESCUE SYSTEMS 1
CHAPTER 30
SLOPED SURFACE SHORE WITH CRIBBING
COMPONENTS OF THE SLOPED SURFACE SHORE
Cribbing: Lumber size and minimum length:





2"x4"x18"
2"x4"x2'
4"x4"x18"
4"x4"x2'
6"x6"x2'
Many departments use 18" long cribbing. This size makes it convenient for storage and allows more
pieces per 8' lumber stock but is limiting to shoring operations due to a shorter overall shoring height
that can be reached.
A maximum of 8' between cribbing systems under a sloped surface is allowed under most conditions.
If the sloped surface is severely damaged or is heavily weighted, the maximum space allowed between
crib beds should be reduced to 4' or less.
Wedges: Usual size:


2"x4"x12"
4"x4"x18"
Wedges are used primarily as single pieces to fill voids spaces and to change the angle of cribbing
surface contact. The crib bed is built flat and level with the angle change occurring at the top of the bed
next to the sloped surface.
OVERLAP ENDS
SAME DIMENSION
OF CRIBBING FOR
BETTER STABILITY
CANTILEVER
EFFECT WITH
SLOPED SURFACE
LOADS MAY OCCUR
December 2000
Figure 30.3
Sloped Floor Shore with Cribbing
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CHAPTER 30
SLOPED SURFACE SHORE WITH CRIBBING
RESCUE SYSTEMS 1
Header: Used to collect the weight from the structural element shored and to spread it throughout
multiple crib beds in the shoring system. The minimum lumber size used is a 4"x4".
SLOPED SURFACE SHORE WITH CRIBBING ASSEMBLY
No body parts are placed under unsupported
loads during the assembly of the sloped surface
shore.
Prior to assembly or installation, rescuers must
consider the access and egress pathways. A crib
bed can take up significant access space that
may get in the way of rescue operations and
personnel movement. Well-placed shores will
ensure maximum level of safety and access
possible in the collapsed structure.
When placing cribs or wedges, no more than
two parallel layers of the same material should
be stacked on top of each other. Stacking more
than two parallel layers in the same direction
greatly reduces the stability of the shore.
Figure 30.4
1. Place first layer of cribs.

Ends of crib perpendicular to the object.

On soft surfaces, use a solid layer of cribbing parallel to the object.

Lay cribs level to the ground.
2. Place second layer of cribs.

Perpendicular to the first layer.

Maintain 3½" overlap from ends of the first layer.

Use another crib to push the crib members into position under the unsupported sloped
surface.
3. Place additional layers.

Continue alternating direction on each layer until the crib bed components are in near
contact with the object to be shored.
4. Change the angle.

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Use the last two crib layers to change the angle of the shore to make contact with the shored
surface.
December 2000
RESCUE SYSTEMS 1
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CHAPTER 30
SLOPED SURFACE SHORE WITH CRIBBING
Thinner cribbing material can be used under the sloped surface area farthest away from the
rescuer.
5. Fill void spaces.

Fill all void spaces to ensure full surface contact.

Gently tap the wedges to "snug" up the shore.
6. Evaluate shore and structure.
December 2000
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