The steel subs are responsible for putting in the steel reinforcement bars (or rebar as its commonly referred to) in the pool to increase the tensile strength of the pool shell. Without the steel, the pool shell would be much more apt to crack under the force of the water and soil against it. Concrete has great strength in compression, but it has little tensile strength. Steel has great tensile strength, so the two are combined whenever large amounts of concrete is present. The combination of the two is called reinforced concrete.
The steel subs use the plans drawn up by the structural engineer and lay the steel according to the schedule. The structural engineering plans are important because they let the steel sub know what kind of steel reinforcements are necessary at each location throughout pool due to extra surcharging forces. Most builders use the same diameter of steel, however the amount of steel varies depending your local soil and climate conditions.
If you are building a concrete pool, reinforcing steel must be installed after the plumbing is complete. The steel is installed in a grid pattern following the requirements of the engineering calculations. Steel bar size can range from 3/8" diameter to 3/4" diameter depending on the requirements.
3/8-diameter steel reinforced rebar to be placed throughout the pool structure. There will be rebar on the bottom of the pool, up the sides around the skimmer, and into the bond beam.
Concrete spacers insure the steel is not against the wall or the floor of the pool. This system allows shotcrete to be evenly distributed under and above the steel.
Be sure your builder has professionally engineered your pool to insure the structural integrity for the life of the pool.
A smaller diameter rebar may be used by some companies, nor may they be professionally engineered. Ask.
Once the formwork is in place, then the steel for reinforcing the concrete must be bent & put in place.
Depending upon the pool design & the length, width & depth & the engineer, the pool will normally use either 10 or 12mm deformed bar at 200 to 300mm centers in both directions. Be sure to tie the steel at each cross over & flatten every tie wire so it does not stick up through the concrete.
The steel will be bent at the top out to the formwork & will usually carry an extra three bars around the top in the bond/ring beam on the horizontal
Extra steel will be needed around the skimmer box & the main drain.
The steel must be set in accordance with an engineers recommendations but would usually be set to have at least 60mm cover on the dirt face & 75mm cover on the water face. This can be achieved with the use of plastic bar chairs available in both sizes.
The steel is normally bent with a 300mm radius bend at the floor wall joint in the shallow end & up to 600mm radius in the deep end.
If you are doing a flat bottom pool. then reduce the steel floor wall joint radius to 150mm.
All of the steel in the pool must be connected to an earth strap along with any other metal objects (hand rails, ladders) in the pool. This earth strap must be connected back to the main house earth at the switch board.
Concrete has extremely high resistance to compression, but no resistance to tension. A steel rod has very high tensile strength but can be bent relatively easily. However, mix them together and you have a highly adaptable product that has extremely high compression and tensile strength. For maximum strength, the rebar is placed on the opposite side of the pressure. In this way the concrete takes the compression and the tensile strength of the rebar on the opposite side prevents the concrete from cracking, splitting, and crumbling. What is a good mix of steel and concrete? A little steel goes a long way in improving concrete strength, but given how inexpensive the materials are, the rule of thumb for structural concrete is to be conservative and over reinforce concrete with tension strength. In other words the more rebar, the more strength the structure will have. (That's why in bridges you see so many layers of rebar "curtains.") Conservative industry standards recommend the use of 0.5 inch (#4 rebar) and wire the rebar together on 6 inch centers for every six to eight inches of typical concrete. Embedding #4 rebar in six inches of typical 3,000 PSI stone aggregate concrete will create an approximate strength to weight ratio of 350!
Interestingly, this is not the case in the pool industry. Standard practice here is to use 0.375 inch (#3 rebar) on one foot centers. As noted in the NSPI construction manuals, given the minimal or non-existent force placed upon a full pool of water pressing against a wall of earth, any steel reinforcement should be more than adequate.
All steel (metal) components in a pool must be electrically connected so that no voltage differences may appear between two metal objects. Once the rebar is in place and before the shotcrete starts to fly, the pool must be inspected by the City or County to ensure that the electrical bonding has been done and done properly.