Abstract:
Excessive deflections of reinforced concrete slabs can cause severe serviceability
problems. In recent years, realistic estimation of slab deflection under service loads
has become more important due to the increasing use of high strength materials and
due to the ultimate limit state design that generally leads to thinner members. Shortterm
deflection of concrete slab is affected by level of cracki ng and cannot be
calculated by elastic analysis. Long-term deflection is further increased due to the
effect of creep and shrinkage of concrete. Deflection calculations of slabs using
nonlinear Finite Element (FE) analysis are complicated and time consuming. The
main objective of this work is to develop an easy method of deflection estimation
that will be useful in selecting thickness of flat plate slabs.
The effect of cracking in flat plate slab can be simulated using a number of nonlinear
FE models of which ACI/Branson equation is the simplest. A global plate sti ffness
approach incorporating this equation has been used in this cunent work. The
performance of ACI/Branson crack model in predicting short- and long-term
experimental deflections is reasonably good. However, use of this rigorous nonlinear
FE analysis is not particularly suitable for everyday use of the designer. With an aim
to develop a simplified method of deflection calculation, a general purpose Artificial
Neural Network (ANN) prediction software has been selected. A large number of FE
analysis has been carried out on slabs with varying spans, column sizes, loads,
material properties etc. and a database have been created for training the ANN
prediction tool. The ANN program has been trained using this database until the
amount of enor in predicting deflection become very small. Once trained, the
prediction tool has been validated against experimental and numel1cal results from
previous FE analysis. Use of the trained ANN software to estimate short-and longterm
deflections have been demonstrated with example. Now, a designer will be able
to estimate deflection of flat plate slab easily for different span, column size, loading,
material properties etc. by using the developed ANN prediction tool and will be able
to select the appropriate thickness for the flat plate slab.
