Concrete Floor Deflection

In our concrete specifications we indicated required f f and f l numbers for floor flatness and levelness.

Concrete floor deflection.

See the table below. Got bounce appeared in the august 2012 issue of prosales and dealt with mitigating floor deflection in new home construction. The australian standard as 3600 2001 recommends a limit of l 250 table 1. The main reason these are spec d is for requirements of the flooring.

The concrete society publication. It covers the consideration of crack formation and its impact on a concrete floor s deflection a critical consideration for conventionally reinforced slabs. For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360. Design issues a few years ago floors we r e de signed using astm a36 steel 36 000 psi yield strength and al.

To minimize floor leve l n e s s p r oblems in composite constru c tion both the designer and con t r actor should be aware of design and construction decisions that af fect deflection. For new home builders a squeaky or bouncy floor is a sign of substandard or code minimum construction practices the effect of which can erode their reputation for delivering comfortable quality. Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection. Deflection calculations it is backed by site based research.

Per aci 117 these measurements are to be taken at a maximum of 72 hours after the concrete has been poured ie prior to shoring being removed. Detailed numerical examples illustrate the application of each of the methods presented. A comparative evaluation of. The concrete structures code limits the maximum mid span deflection of a beam spanning either between columns or in a two way beam system between its supporting beams.

If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6. This rigorous method is described in greater detail elsewhere e g. Deflections in concrete slabs and beams 2005 or how to design concrete structures using eurocode 2. Crack width calculation where applicable is also discussed.

This difference in the values of modulus of elasticity shows that concrete can only withstand a small amount of deflection and will experience cracking sooner than steel. Concrete structures codes also recommend limits for the calculated total deflection of floors.