Fatigue Behaviour of Shear-Critical Deep Beams with Light Web Reinforcement

This paper investigates the fatigue behaviour of shear-critical reinforced concrete deep beams with light web reinforcement under fixed-point fatigue load. The aim is to study the behaviour of a common element of bridges, namely pier caps, which are subjected to repetitive traffic loads. This investigation is conducted via an experimental program that consists of three nominally identical beams that were subjected to three different maximum fatigue load levels, in addition to a reference beam that was subjected to monotonic loading. Other fatigue parameters were kept constant throughout the test series, i.e., load frequency (2 Hz), fatigue cycles waveform (sinusoidal), and minimum fatigue load level (10% of monotonic strength). The test results show that the shear resisting mechanisms provided by the concrete, namely the critical loading zone (CLZ), and aggregate interlock deteriorate significantly with the number of cycles. The CLZ initially developed microcracks, followed by macrocracks which eventually triggered the crushing of the concrete and the failure of the beam. On the other hand, the crack interface was gradually smoothened, where the crack edges were eroded from repetitive loading, leading to the reduction of the shear resistance provided by aggregate interlock. The paper reports the data from the tests and the results are interpreted for better understanding of the fatigue behaviour of shear-critical deep beams.