Ground assembly of sections (or pod assembly) of a building’s roof structures can be a very safe and efficient way to erect a building. However, it doesn’t work in every instance.
There are several things to consider before you choose to pod assemble. Here are a few examples:
- Does the building design allow for safe pod erection?
- Is there enough floor space in the building footprint to erect the pods?
- Can access be cut off for other trades while the structure is being assembled?
- Will there be access for equipment for erection once pods are assembled?
- Will assembly be structurally sound for erection?
- Can we prevent any overhead load hazard for connectors?
Assuming the answer to the questions above is “yes”, pod assembly can be done in several configurations.
- Two roof beams with purlins or truss purlins bolted to both frames.
- Purlins only with bridging installed.
- Truss purlins only assembled with bridging.
Let’s look at things to consider with scenario 1.
- You must consider column placement and secondaries. Will the column interfere with hoisting the pod?
- Weight of assembled pod and available hoisting equipment.
- Rigging needed to hoist pod.
- One crane or two.
- Will the assembled section be a critical pick? A critical pick would be any pick that exceeds 70% of one crane capacity or any pick where 2 cranes are used on the same pick.
Things to consider for scenarios 2 and 3.
- Is a jig needed to assemble purlins or truss purlins?
- How are the purlins or truss purlins rigged for hoisting?
- Placement of assemblies in the proximity of hoisting equipment.
These are just a few of the things that must be considered when determining whether pod erection is the right way to go. Once you have determined that pod erection is the best option, you must choose which bays benefit most by ground assembly.
Consider ground assembling the bay with rod bracing or framed roof openings to reduce the work at elevation later. Ground assembly can help with utilization of your less experienced labor and reduce equipment cost.
If ground assembly and pod erection are used correctly, you can save significant time and have a much safer work site by having more construction take place on the ground rather than in the air.