Coy Fuller, Co-Founder of Fuller Miller Construction
Large rooms free of interrupted space were typically an attribute only associated with warehouses and manufacturing facilities. They needed the room for storage, for operations, and for forklift maneuverability.
Now, however, the freedom of design and usage that come from these spaces has become mainstream. That wide, clear space free of those space-invading columns is great for auditoriums, schools, even retail and office space. And, with more uses comes greater flexibility in overall square footage.
That means metal buildings are reaching new heights and new widths, growing from the typical 10,000 to 20,000 square foot range to the immense 100,000 to 300,000 square-foot range. Or even larger.
In fact, in the last few years, Fuller Miller Construction has completed six 100,000-300,000 sq. ft. warehouse/manufacturing facilities using Star Building Systems. These super large metal buildings are perfect for growing businesses, but they also present special considerations that do not factor into smaller size buildings, such as special needs of the floor and roof.
Here are some things to consider:
The sheer volume of floor area makes the placing and finishing of the concrete slab a challenge, and that’s ignoring the need to maintain quality and stay on schedule.
To produce a slab of any size, the area of each pour must be maximized to reduce the number of pours required. While many normal floor pours may be as large as 10,000 to 20,000 square-feet, each floor pour for one of these super large buildings must be 45,000 to 50,000 square-feet. That is more than double the size of a typical large pour.
To make this pour happen, the following items should be addressed:
- Mix Design. The concrete mix design must be customized for this specific application in order to allow pumping during the placement of the ready mix. You can adjust the amount of water content to reduce the amount of shrinkage during the set and cure of the concrete, all without affecting the time for finishing operations.
- Pre-Pour Meetings. There are many people and processes involved in a concrete slab pour of this magnitude, and it is very important that the lead person of every crew involved knows their groups role, as well as the role of all the other groups. Each group leader must know the sequence and the timing of the entire operation, which will take about 12 to 16 hours. This is necessary to keep the entire operation from unraveling should one group falter in the dance routine. The consequences would be very expensive in terms of both time and money.
- Expansion and Contraction. Concrete slabs all shrink and contract as they set, resulting in the possibility of cracks. These cannot be eliminated, but they can be minimized by the selection of the type and placement of sub grade support material, the placement of vapor barriers, and, most importantly, the type and placement of reinforcing steel. Additionally, cracks can be controlled by providing a place for the slab to crack by utilizing saw cuts placed in a grid pattern across the surface of the floor slab. These saw cuts create a weakened plane and encourage the slab to crack at the saw cut, creating a nice straight groove that can then be filled with sealant. It is important to perform these saw cuts early enough in the process to be ahead of shrinkage and cracking and late enough to minimize curling of the slab.
- Flat and Level. The size of the individual pour creates the possibility of variation in the flatness of the area within the pour. Compounding the issue is the variation between pours. Variation in flatness of the floor and levelness of the floor can result in a finished product that ends up outside the acceptable tolerances for the use of the building. For example, forklifts with small diameter tires require a flat and level floor to keep their loads in place as they travel across a large area.
- Place and Finish Methods. The method of place and finish needs to provide a tight hard surface finish that is flat and level, while minimizing and controlling cracking. This requirement creates the need to place the concrete with these items:
• Boom pump truck. A concrete pump truck that is large enough to pump the volume of concrete necessary and at the rate required to complete the pour in a continuous and timely operation.
• Laser Screed. A self-propelled, laser controlled, screed machine that begins the finishing process with a flat and level screeded slab of wet concrete.
• Riding Trowel Machines. Riding Trowel Machines with double blades to provide the floating and the troweling of the slab as it takes its initial set and then as it starts to further set. Then the final hard trowel surface can be applied. A couple of extra machines are also necessary in case of breakdowns.
• Adequate Manpower. Today’s methods use a lot of machinery and equipment, but it is still important to have adequate manpower to perform the other tasks necessary to provide the results desired.
- Quality Control. An operation with this many moving parts means there are lots of places for something to go wrong or just go unnoticed until it is too late. Additional manpower must be on hand to perform quality control functions, such as checking the slump of the ready mix concrete in each truck as it arrives, making test cylinders of each load of concrete for compression testing, observing the concrete mix as it is dumped into the pump hopper, observing the location and adjustment of the reinforcing steel just ahead of the placement of the concrete, and performing flat and level testing of the finished slab.
Check back next Wednesday for the continuation of this article and find out what special needs factor into your larger buildings’ roof design.