Shoring Systems for Structural Collapse - Part 2

In Part 2, we’ll focus on a few more shoring systems and attain a greater understanding of this type of operation. The first system we’ll look at is the Window/Door Shore. This shore can be built two different ways. One will allow for access to the...


In Part 2, we’ll focus on a few more shoring systems and attain a greater understanding of this type of operation. The first system we’ll look at is the Window/Door Shore. This shore can be built two different ways. One will allow for access to the structure, while the other will not.

As you will see in Figure 1, the opening in this window/door shore has been blocked by cross bracing. The cross bracing’s main function is not to keep us out, but to provide stability against torsional loads. This system is built in place. If you look at the diagram, you’ll see connections were made by means of triangle gusset plates and 2x4 cleats. Although they look different than the 6”x12” gussets we spoke of in Part 1 of this article, they are performing the same job.

The second method of building this shoring system is referred to as the “ALT Window & Door Shore” (see Figure 2). One huge difference between the two is that the “ALT” shoring system is built remotely then placed in the opening to be shored. When this method is used, the shoring system needs to be built smaller than the size of the opening (approximately 1 ½ inches less in each direction). Wedges are then placed on one side and the bottom (shim where necessary), allowing you to fit the system in place. If shims are needed at the top, try to avoid wedging the bottom of the system. Why? If we are shimming the top of the system, as we drive the shims in place we’re creating an up-and-down force. We would like the force traveling downward (as well as the overall load) to see a flat surface in which to transfer the load. One of the biggest benefits of this system is that it can be built in a safe area away from the collapse zone.

Now let’s venture forward into the family of raker shores. We’ll look at several different raker systems you can build, all utilizing the two most common raker angles of 45 or 60 degrees. Before we begin to tackle this shoring system family, however, you must understand a few things. The raker is the diagonal piece of lumber that runs from the upright to the sole plate. In laymen’s terms, it’s the piece of wood that connects the wall to the ground. The actual purpose of this raker is to transfer the load captured by the upright down to the soul plate and into the ground. It’s the same double-funnel principal that was featured in Part 1 of this article, just turned a bit sideways.

Alright, let’s dig in! The first raker shore we’ll look at is a solid sole raker (see Figure 3), named so because the sole plate of the raker runs on the ground from front to back. Let’s look at the diagram and pick a few things apart. The sole plate of the raker runs into what is called a thrust block. This component terminates the captured load into the ground and is generally made of the same lumber of which the shoring system is made. A minimum of 4x4 lumber is, however, specified. The job of the bottom cleat and top cleat is simple. Between the bottom cleat and the raker is where we’ll drive a set of wedges. The upward force of the wedges will provide a pushing force through the raker to the load we’re capturing. The top cleat terminates the load at the capture point, while the bottom cleat helps to terminate the load into the soul plate and subsequently into the ground.

Both ends of the raker are cut, not only with the raker degree angle, but with what are called return cuts. These cuts provide a flat surface for the wedges to sit against. With that being said, let’s reveal the secret of how we create the angle cuts needed on the raker to sit flush on the upright and soul plate. First we determine a capture point. This is the spot we want the top of the raker to hit. Basically, it’s the starting point for the load transition from the wall to the ground. Let’s say that measurement is eight feet. If we’re building a 45-degree raker, that number gets multiplied by 17, thus giving you the raker length in inches. If you’re building a 60-degree raker, the magic number is 14. If you ever forget which is which, remember that if you multiply 14 by 8 your number will be lower than if you multiplied 17 by 8, thus creating a shorter piece of wood and a tighter angle. Both sides of the 45 degree raker will have 45-degree cuts on them, equaling 90 degrees, while a 60-degree raker will have a top cut of 60 degrees and a bottom cut of...you guessed it 30 degrees. Who said you’d never use geometry once you left high school? The 60-degree raker does save space because of the shorter rake, but its load capacity is less than that of the 45-degree raker.

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