# Investigation on Shear Behavior of Precast Monolithic ECC Composite Beams

## TL;DR

This study explores how using ECC composite beams improves structural performance compared to traditional concrete beams, especially in terms of crack control and load-bearing capacity.

## Contribution

A new precast monolithic ECC composite beam is proposed, showing enhanced mechanical performance and reduced stiffness degradation.

## Key findings

- ECC composite beams showed 8.2% higher peak load and 29.3% greater displacement at peak load compared to RC beams.
- ECC beams exhibited finer cracks and less concrete spalling, with a 8.2% lower load degradation coefficient.
- Higher stirrup ratios improved ultimate load-bearing capacity by 28.8% and reduced stiffness degradation by 40–50%.

## Abstract

This study applied precast engineered cementitious composite (ECC) shells to replace conventional concrete in precast assembled monolithic composite beams to enhance mechanical performance. A new type of precast monolithic ECC composite beam was proposed. Five ECC composite beams and one reinforced concrete (RC) composite beam were designed and fabricated for the experimental study. The failure pattern, failure mechanism, load-bearing capacity, deformability, and stiffness degradation were quantitatively analyzed through the tests. The main findings were as follows: ECC composite beams developed finer and more densely distributed cracks compared to RC composite beams, without significant concrete spalling. The peak load of ECC composite beams was 8.2% higher than that of RC composite beams, while the corresponding displacement at peak load increased by 29.3%. The ECC precast shell delayed crack propagation through the fiber bridging effect. The average load degradation coefficient of the ECC composite beams was 8.2% lower than that of the RC beam. The stiffness degradation curve of ECC composite beams was more gradual than that of RC composite beams, providing an optimization basis for the design of precast beams in structures with high seismic demands. As the shear span ratio increased from 1.5 to 3, the load-bearing capacity decreased by 32.0%. When the stirrup ratio increased from 0.25% to 0.75%, the ultimate load-bearing capacity improved by 28.8%. Furthermore, specimens with higher stirrup ratios showed a 40–50% reduction in stiffness degradation rate, demonstrating that increased stirrup ratio effectively mitigated brittle failure.