Internal and external steel-tube strengthened RC columns: Impact tests and numerical simulations

Reinforced concrete (RC) piers are frequently used in bridges although vehicle-pier collisions have increasingly highlighted their poor impact resistance. Specifically, RC columns exhibit a small shear-to-span ratio when subjected to vehicle impacts, resulting in shear-dominated failure and, in extreme cases, complete loss of axial capacity. Therefore, the development of strengthening methods for RC columns with small shear-to-span ratios under impact loading is pivotal to guarantee their safety. In this context, the present investigation employs pendulum impact testing to assess the structural performance of RC columns. Specifically, the study focuses on two distinct types of square-section steel-tube strengthened RC columns, each with a small shear-to-span ratio. The same area of steel is adopted in the two cases. The first type is an internal steel-tube strengthened RC (ISRC) column, while the second is an external steel-tube strengthened RC (ESRC) column. To provide a comparative baseline, a single square-section RC column is also tested using the same pendulum impact apparatus. Moreover, the dynamic and static finite element (FE) models are developed using LS-DYNA and validated against the aforementioned pendulum impact tests and one static loading test taken from the literature, respectively. The so-validated FE model is then adopted to evaluate the damage modes, mechanical behavior, and energy absorption characteristics of the ISRC and ESRC columns under impact and static loads. The test and simulation results show that both the internal and external steel tubes can significantly enhance the impact resistance of RC columns. The use of an internal steel tube offers superior enhancements to both the dynamic and static shear resistance of the column core concrete in comparison to an external steel tube.