Experimental and finite element dynamic analysis of incrementally loaded reinforced concrete structures

• Values of the static and dynamic modulus of concrete determined experimentally.
• Reduction of vibration frequencies captured from the modal testing of RC beams.
• Load-induced frequency shifts can be utilised as damage indicators for RC structures.
• Changed frequencies of RC structures accurately predicted by non-linear FE analysis.
• Dynamically validated FE models of RC structures can identify damage in concrete.

This work investigates influence of damage in reinforced concrete (RC) structures on their dynamic properties through modal testing and non-linear finite element (FE) analysis. Five RC beams were designed with the fundamental flexural mode frequencies in the range of 6.5–18.0 Hz for the uncracked state. Mechanical properties of concrete, such as static and dynamic elastic moduli were determined from standard tests and ultra-sonic pulse velocity readings. The beams were incrementally loaded until the span/250 deflection limit was reached and their natural frequencies were measured from the free decay vibrations. The progressive damage reduced fundamental frequencies of tested beams by up to 25%. The non-linear FE analysis was carried out for RC beams and one two-span slab and the calculated reduced frequencies of the 1st and 2nd vibration modes were in excellent agreement with measurements. This led to the conclusion that, given that the non-linear analysis can capture degradation of dynamic stiffness due to cracking, the future dynamic performance and damage identification on the RC structure can be reliably determined from the same FE model. The results reveal potential of the combined modal testing and FE analysis to improve inspection and assessment of the in-service RC structures.