Damage assessment of reinforced concrete flat slabs through modal tests using impact excitation

Abstract

Purpose In reinforced concrete (RC) structures, an evidence of damage is the presence of cracking. In order to evaluate the effect of damage on cracking pattern and natural frequency in RC slabs, two of such structures with different dimensions and reinforcement ratios were tested, in which cracks were induced through application of static load, followed by modal tests using impact excitation. The paper aims to discuss this issue. Design/methodology/approach The gradient of the fundamental natural frequency along the decay, the crack opening rate and also a global damage index based on changes of the fundamental natural frequency were evaluated. Findings The behaviour of the aforementioned gradient was distinct for both slabs, increasing monotonically with the cracking level for the slab with lowest reinforcement ratio, and increasing until 33 per cent of the collapse load and then decreasing afterwards for the slab with the highest ratio. Changes of the gradient were consistent with changes of the crack opening rate. Both results of gradient changes and cracking pattern brought evidence that the balance between open (old) and breathing (new) cracks differed between the slabs, and may be responsible for such differences. Originality/value Damage assessment in RC structures using vibration tests is mostly concentrated on beams. In this work, an advance is made by investigating slabs. The lack of a unique pattern of changes of the gradient implies that its absolute value is not generally suitable for the association with the damage level. However, the impact tests can be effectively used to detect early damage on slabs using this proposed parameter.

Fatigue damage severity assessment of RC beam

“…The occurrence of the first crack was detected at SEC A as the maximum fatigue load increased to 0.8P cr (19 kN) (Figure 6). Due to the present of this crack, the AE intensity plot collected from SEC A falls in the middle of intensities Zone C and Zone D. Ferreira et al (2019) stated that it is considered as damage if there is the presence of crack in the RC structure. Zone C indicates the intermediate crack and requires follow-up evaluation.…”

Corrosion-induced degradation assessment of steel beam using vibration-based scheme

“…On another note, damage assessment leads to quantification or severity evaluation of a damaged state that helps to evaluate the future performance. For example, Ferreira et al (2019) used the modal hammer test for static load induced damage assessment of RC slabs. The authors investigated the gradient of fundamental natural frequency along the decay, the crack opening rate and also a global damage index based on changes of the fundamental natural frequency.…”