Effect of early age drying shrinkage on the seismic response of RC structures

Reinforced concrete (RC) damage over time can cause severe structural problems (e.g. Morandi Bridge in Italy). Many factors contribute to concrete deterioration (thermal conditions, chemical attacks, shrinkage, creep, carbonation, corrosion, etc). Reinforced concrete deterioration starts at early-age and continues with structure aging. Early-age shrinkage, creep and thermal conditions or initial cracks can have a significant impact on the dynamic behavior of concrete structures. The CEOS.fr National program for instance showed that the natural frequency of a RC beam subjected to early-age restrained shrinkage is highly affected. In order to quantify the impact of early-age drying shrinkage on the dynamic behavior of structures, the GEOMAS Lab at INSA Lyon has conducted a research project combining both numerical modeling and pseudo-dynamic tests on two types of RC portal frames. The first one was kept in endogenous conditions (by covering it using a plastic sheet to stop water exchange with the surrounding environment) during its early age period in a way to limit drying effects leading to cracks, while the second one was kept in non-endogenous conditions (water exchange was possible) similar to construction site conditions, which induced cracks apparition. Both RC portal frames were subjected after their early age period to the same seismic loading. The present paper focuses on the experimental part of the project based on the use of pseudodynamic tests in order to evaluate the behavior of such structures under a seismic loading. The portal frames were instrumented using optical fiber sensors, displacement and load sensors and velocimeters. Image correlation was also used in order to monitor the structures.