# Nonlinear analysis of hollow reinforced high strength concrete beams with web openings and different types of stirrups under torsion

## TL;DR

This study uses computer modeling to explore how web openings and different types of reinforcement affect the twisting strength of high-strength concrete beams.

## Contribution

The study introduces a novel numerical analysis of hollow concrete beams with web openings and various stirrup types under torsion.

## Key findings

- Web openings reduce torsional capacity by 37.58% to 48.35% in high-strength concrete beams.
- GFRP stirrups nearly double torsional capacity compared to other reinforcement types.
- Equations for torsional capacity showed reasonable agreement with experimental results.

## Abstract

In this research, a nonlinear finite element analysis was conducted to investigate the effect of large web openings on the torsional behavior of high-strength hollow reinforced concrete (RC) beams under different transverse reinforcement scenarios. The study presents an extensive numerical program comprising eighty-four specimens modeled with various parameters to develop a wide range of web opening dimensions and transverse reinforcement scenarios. The considered parameters included the web opening size (length and height), transverse reinforcement type (steel, glass fiber reinforced polymer—GFRP—, or no stirrups), transverse reinforcement ratio, longitudinal reinforcement ratio, and concrete strength. All specimens had a constant cross section of 300 × 400 mm, and a total length of 2400 mm. The numerical results revealed that introducing web openings in hollow concrete significantly reduces their torsional capacity by about 48.35%, 46.20%, and 37.58% for beams with concrete strengths of 60 MPa, 80 MPa, and 100 MPa, respectively. Additionally, reducing stirrup spacing and increasing both stirrup diameter and longitudinal reinforcement ratio had a considerable effect in improving torsional capacity. Furthermore, a significant improvement—nearly double—of torsional capacity of hollow beams was observed when using GFRP stirrups as a transverse reinforcement system. Moreover, two numerical equations were adopted to determine the torsional capacity of both the hollow beams considered in the present study and solid beams from other experimental work. The compatibility between the outputs of the proposed equations and the experimental results of others showed reasonable agreement.