EXPERIMENTAL DETERMINATION OF STATIC AND DYNAMIC ELASTIC MODULI OF RC SLABS
Abstract
The purpose of this paper is to experimentally determine the static (Ec) and dynamic (Ed) elastic
moduli of reinforced concrete (RC) from both static and dynamic techniques. Initially, the
aforementioned parameters were estimated from the concrete compressive strength of the used mix, using
compressive strength machine. Subsequently, the RC slab specimens themselves were dynamically tested
dynamically under free boundary conditions. Then from, the experimentally measured natural frequency,
the static and dynamic moduli were determined. To check the reliability of the dynamic test for estimating
the natural frequency, the intact and defected slabs were utilized. The dynamic test was performed on four
RC square slab samples of dimensions 600 mm × 600 mm × 40 mm. The first set, two intact slabs, is used
as control specimens were prepared with no artificial voids. While, the second set, two defected slabs, is
used as defected specimens. The defected slabs contained the artificial void by fixing a polystyrene block
at the center of the steel reinforcement of the slabs prior to pouring concrete. In the latter technique, a RC
slab specimen is hanged by using elastic ropes to approach fully free boundary conditions. The slabs were
excited by an impact hammer, to induce vibration, whilst the accelerometers were employed to record the
response under such excitation. Pico Scope 6 device and amplifier was used to acquire, magnify and
analyze the data. In addition, MATLAB software is used to convert the time domain to the frequency
domain as well as to plot Frequency Response Function (FRF). The first natural frequency is determined
as the first resonant peak on the FRF plot. It is showed that the use of the first natural frequency-based
method can be usefully employed to determine the dynamic modulus of elasticity of concrete. It was found
that the testing sequence did not significantly affect the measured results for the obtained Ec and Ed in
this study
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