Strain compliance crack model for RC beams: primary versus secondary cracks

Abstract

This study proposes the Strain Compliance Crack (SCC) model to capture, as reported by tests, the specifics of various cases of crack spacing and width analysis involving primary and secondary cracks in RC beams. The model dwells on calculating crack spacing based on the reinforcement strain profile. As part of the model, a new concept of the limit effective depth, dlim, is proposed to classify crack patterns. When d ≤ dlim (small beam), the pattern consists of primary bending cracks only; when d > dlim (large beam), both primary and secondary cracks are taken into account. Being dependent on the reinforcement ratio, modular ratio, cover, and bar diameter, for most practical cases, dlim ranges from 0.12 to 0.64 m. While the model can predict mean spacing between primary and secondary cracks, only primary cracks are considered for the crack width analysis. A linear crack width profile is assumed for small beams. A bilinear shape (including a fish shape) of the width profile is taken for primary cracks of large beams: between the tips of primary and secondary cracks, width is governed by the primary crack spacing, whereas the remaining part is also affected by the secondary cracks. Crack spacing and width predictions by the proposed model agreed well with the tests.