The Scaffold & Access Industry Association鈥檚 (SAIA) Shoring Council created new Structural Shoring Design Guidelines for a process that Mitch Meadows, chair of the SAIA council, says 鈥渄oesn鈥檛 really fall perfectly into any current category of standards.鈥�

(Photo: SAIA)

Meadows is a professional engineer and branch manager with D.H. Charles Engineering in Cardiff, Calif., and he suggests the best-practices document leads with a list of Important Questions to answer before completing shoring design because of the demand for detailed loading and process information that must accompany any shoring design.

Shoring used for beam-splicing support during an expansion. (Photo: SAIA)

鈥淔rom our perspective, the main risks with shoring are property damage and/or bodily harm or death,鈥� Meadows says. 鈥淥bviously that鈥檚 a risk for, any construction project but the difference between a structural shoring project and an access scaffold project is that people have been building scaffolds for thousands of years.鈥�

Project people may not be as well-versed on the information details shoring engineers need to hold up a roof, the corner of a building or a bridge.

Particularly in renovation work, just determining the load that needs to be supported can be elusive. How that load will change during demolition and/or reconstruction is also a crucial influence on shoring design.

鈥淲e definitely get in situations where people are very, very hesitant to provide the appropriate information for whatever reason -- it鈥檚 a time crunch, or they鈥檙e just pushing someone to hurry up and giving them a number,鈥� Meadows says. 鈥淚t happens more often than we鈥檇 like to see, and that鈥檚 why we created this document: to help educate the industry on the best practices.鈥�

Shoring design and questions to consider

Here are a few of the 15 Important Questions that steer a shoring design in the proper direction:

• How are the members requiring support constructed?
  • What size steel members?
  • What thickness concrete?
  • What variety of timber or laminated lumber?
• Which members are being removed, replaced, or modified?
• Are there as-built drawings for the structure to be supported?

The construction project鈥檚 engineer of record is typically the best source for this information because of their knowledge of both the structure鈥檚 makeup and of the processes related to the shoring.

There鈥檚 more to it than 鈥渉ow much does it weigh?鈥�

What鈥檚 the plan for the floors or roof above the shoring? Should the design anticipate a snow load? Will the contractors add equipment or materials to the load?

• Are there retrofit or renovation drawings for the new work being performed?

鈥淓ven something like a simple roof shoring, that sounds easy enough. But why does it need to be picked up?鈥� says Meadows. 鈥淎ctually, there鈥檚 a wall at the end of the building that鈥檚 only being partially removed. Partially removed versus fully removed means two different things.

Are there new foundations or excavations nearby that will need to be accounted for during the shoring operations?

Modular cuplock shoring towers support a concrete beam. The double I-beam stack with a support I-beam installed perpendicular to the concrete beam and centered over the tower distributes the load evenly to the tower鈥檚 four posts. (Photo: SAIA)

鈥淚f you set the shoring towers on the edge of an excavation, you鈥檙e not going to have much load-bearing capacity,鈥� Meadows says. An adjacent excavation鈥檚 wall can collapse under the surcharge load from shoring tower.

There are rules of thumb for locating shoring towers, but if the construction process impacts their capacity, of course the design must change to accommodate the load.

Best shoring practices

Here鈥檚 a sample of best practices the Shoring Council鈥檚 Structural Shoring Design Guidelines lay out:

Shoring of existing steel beams during demolition should be designed properly to transfer loads through each tower to the final grade. (Photo: SAIA)

• Support structure as close to original support point as possible

鈥淥bviously there are other practices that matter, like making space for the work that鈥檚 going on,鈥� says Meadows, but confirms that the closer a tower can be placed to the original load point, the better.

• Ensure sufficient back span on members being supported to reduce loading on shoring tower

Again, Meadows points out a rule of thumb. Best if the back span, or portion of the total length of a beam being supported that鈥檚 behind the shoring tower, opposite the free end of that beam, is two-thirds of the beam鈥檚 total length. Of course, there are ways to accommodate the many situations where that鈥檚 not possible, but the more back span the better.

• Provide work platforms independent of shoring systems to avoid vibration or additional loading shoring towers outside of primary structural support

鈥淭he best practice is to avoid having people working from the shoring. We don鈥檛 want additional loads or vibration happening.鈥�

• Ensure that elements supporting the shores can adequately transfer loads to the ground without overstress or excessive deflection

Those are some Dos. Here鈥檚 a sample of Don鈥檛s:

• Avoid 鈥渉anging鈥� columns, beams, or walls from the end of members being supported by shoring. For example, directly support members that are having original supports modified or removed. Only hang members if connections have specifically been designed for such conditions and shoring towers are designed for additional loading

鈥淚f they鈥檙e demolishing just the lower part of a wall, is the remainder supposed to hang from the beams we鈥檙e supporting?鈥� says Meadows. 鈥淭hat鈥檚 additional weight. Maybe the beams aren鈥檛 even strong enough to hold that load. What seems to be simple can turn into a very major issue.鈥�

Modular cuplock shoring towers add capacity to the post shores supporting a concrete waffle slab. (Photo: SAIA)

• Avoid providing cantilevered shoring tower support beyond shoring support locations. For example, don鈥檛 provide critical structure support with brackets or cantilevered scaffold unless the shoring system is specifically designed for cantilevers.

鈥淐ould it be done? Sure,鈥� Meadows says but then describes the complexity of managing the shear loads on towers. It鈥檚 a solution he says would require professional design. 鈥淵ou would one-hundred percent need an engineer,鈥� and it would still be an exception to shoring best practices.

Support towers are properly placed, engineered with outriggers to leave workers enough room to repair the damaged steel column. (Photo: SAIA)

• Avoid supporting structural members without having fireproofing, sheathing, and all other interferences removed prior to work. Crushing and movement of structure can occur otherwise.

Getting answers to these important questions and relaying them to the design team not only supports a successful project, but almost always cuts the cost of shoring and related work.