Pool Expert Witness discusses the importance of non-contact lap splices in reinforcing steel (rebar) for shotcrete (gunite) pool structures.
Since most concrete swimming pools are constructed out of shotcrete (sprayed concrete, sometimes also incorrectly called "gunite"), the placement of the reinforcing steel is critical.
Placing bars adjacent to each other (contact lap splice) is permissible for poured or cast concrete structures. It is easy and efficient.
Contact Lap Splices
In sprayed concrete applications, contact lap splices can cause shadowing, honeycombs and voids within the structure.
If the contact lap splices are stacked & orientated towards the direction of the sprayed concrete, shadowing will be minimized.
However, this will also cause the reinforcing steel to be thicker, resulting in the use of additional concrete (equal to the thickness of the stacked bars). On a large project that additional concrete cost could be substantial.
Non-Contact Lap Splices
A simpler and more economical method is the non-contact lap splice method. Bars from opposing directions are staggered and separated by two to three inches. This allows the concrete to encase and encapsulate each bar and virtually guarantees no voids behind groupings of bars.
Both Contact Lap Splices and Non-Contact Lap Splices can be seen in the above image. It is not particularly important on this project, as the floor will be cast in place concrete.
Contact the author, Paolo Benedetti of Aquatic Technology Pool and Spa at:
info@aquatictechnology.com or 408-776-8220.
Visit his website at: www.aquatictechnology.com.
All Contents © Aquatic Technology Pool & Spa, 2013.
All rights reserved.
Aquatic Consultant, International Pool Designer, Pool Construction, Watershape Engineering
Reinforcing steel - the bones that hold the body together.
Why does shotcrete require reinforcement?
Concrete is very high in compression, but week in tension. That means that concrete does not flex well. However, steel is very high in tension and weak in compression. So this is a marriage made in heaven - each compliments the other.
Placement - where does it go?
The placement of the reinforcing steel within the shotcrete wall is very critical. The structural engineer may specify that the steel be installed closer to the outside or the inside of the concrete, depending upon the anticipated loads.
Incorrect placement of the steel will result in a structure that is not as strong as the engineer intended.
Lap Splices - Contact or Non-Contact?
Pieces of reinforcement steel come in finite lengths. This means that splices will need to occur.
But how do you to create proper splices?
Remember, the steel exists to reinforce the concrete. Therefore, the bars of reinforcing steel do not have to make contact with each other when they are spliced. Because shotcrete is applied with air at tremendous velocities, the steel needs to be arranged to allow the concrete to completely encase the reinforcement. If bars begin to create congestion in an area, then it is almost guaranteed that there will be voids and honeycombs behind them.
ACI 506R-95, Guide to Shotcrete, Section 5.4.2 states that non-contact lap splices shall be utilized to prevent this very occurrence. This is the standard and code across the United States, since the American Concrete Institute (ACI) standards have been adopted and incorporated into the International Building Code (IBC). The IBC is the building code for the entire United States.
Non-contact lap splices shall also be spaced so they do not exceed the ACI guidelines. Otherwise, excessive spacing could create unreinforced areas of concrete.
Contact the author, Paolo Benedetti of Aquatic Technology Pool and Spa at:
info@aquatictechnology.com or 408-776-8220.
Visit his website at: www.aquatictechnology.com.
All Contents © Aquatic Technology Pool & Spa, 2013.
All rights reserved.
