In another example, specifications called for #5 reinforcing bars at 12 inch on center, both ways, in a floor that was 5 inches thick. They also called for reinforcing bars to be continuous through joints at 12-foot spacing. The contractor believed that these requirements could result in out-of-joint cracking and also negated the need for sawed contraction joints. To support that belief, the contractor’s RFI cited Sections 6.2 and 8.3 of ACI 360R-10, “Guide for Design of Concrete Slabs on Ground.” Section 6.2 indicates that:
The continuation of a small percentage of deformed reinforcement (0.1% of the slab cross cross-sectional area) through sawcut contraction joints in combination with joint spacings [ranging from about 12 to 16 ft. for a 6-in.-thick slab] has been used successfully by some designers to provide load-transfer capability without using dowels.
Section 6.2 also states that:
As a general rule, the continuation of larger percentages of deformed reinforcing bars should not be used across sawcut contraction joints or construction joints because they restrain joints from opening as the slab shrinks during drying, and this increases the probability of out-of-joint random cracking.
Section 8.3, Reinforcement for crack width control only, further states:
To eliminate sawcut contraction joints, a continuous amount of reinforcement with a minimum steel ratio of 0.5% … is recommended.
For #5 reinforcing bars at 12 inch on center in a 5-inch-thick slab, the deformed reinforcing area was slightly greater than 0.5% of the slab cross-sectional area. Using the references cited, the RFI asked the CM if it was appropriate to saw joints given that the reinforcing steel area specified was sufficient to keep cracks tightly closed. The owner, with concurrence from the design professional, then chose to accept many narrow cracks, eliminate sawed joints and opt for a decrease in the cost offered by the contractor as a result of not having to saw joints.
Getting a response
RFIs don’t always produce the desired results for concrete contractors. Sometimes the GC or CM refuses to pass the request on to the design professional, even though that’s the person who should reply. In this case, however, contractors have documented concerns that may prevent disputes over cracking, deflection or other alleged construction defects that could be identified during the final walkthrough.
Even if the RFI is passed on to the design professional, some design firms reserve the right to respond, or not, based on their judgment as to the validity of the contractors’ concerns. Again, a written record of the concerns is useful in resolving issues brought to light when approval of final payment is sought.
Finally, specifications may dictate an unreasonable time allowance for responses to RFIs, such as 30 to 45 days. This can cause schedule delays or result in a response that, when received, can no longer be of help to the concrete contractor. As an example of a response policy that reduces project delays, Jim Larson of Larson Associates Architects, Inc. in Phoenix, Ariz., says his firm strives to answer most RFIs within 24 hours of receipt.1 Not all contractors are fortunate enough to build structures designed by architects or engineers with this fast RFI turnaround time. But it sets an example for what can be done by design professionals to move projects smoothly toward completion.
References 1. Larson, James L., Larson Associates Architects, Inc., Phoenix, AZ, personal communication. Note: ACI documents cited can be purchased at www.concrete.org and ASTM documents cited can be purchased at www.astm.org.
Ward R. Malisch, PE, PhD, FACI, technical director for the American Society of Concrete Contractors, can be reached at firstname.lastname@example.org. Bruce A. Suprenant, PE, PhD, FACI, concrete consultant, can be reached at email@example.com. This column is sponsored by the American Society of Concrete Contractors, but the views expressed are solely those of the authors.