Experimental and Numerical Investigation for Torsional Behavior of UHPFRC Shallow and Deep Beams

With increasing the use of ultra-high performance fiber reinforced concrete (UHPFRC) in recent years, torsional design of UHPFRC beams has become of great importance. This paper presents an experimental and numerical study to investigate the torsional behavior of UHPFRC shallow and deep beams with f(cu) equal to 190.2 MPa. Ten UHPFRC beams with steel fibers volume fraction of 1.5% subjected to pure torsion were investigated. The provided torsional web reinforcement ratio, the area of longitudinal bars and the tested span to total height ratio (L/h = 6.0, 4.0, 2.0 and 1.0) were the studied parameters. A numerical model has been proposed to predict the torsional response of tested beams. Experimental results showed that increasing stirrups' spacing for the beams of the same L/h ratio (to be 235% of the maximum given by ACI 318-2019 code), reduced the experimental ultimate torsional strength by only 6.7%. The torsional web reinforcement ratio of UHPFRC shallow and deep beams can be safely taken to be 40% of the minimum required by ACI 318-2019. The maximum stirrups spacing can be safely taken the lesser of twice the beam width or 300 mm. The equation used by ACI 318-2019 and ECP-203-2020 for calculating the cracking strength in torsion has been modified to be suitable for UHPFRC beams by taking into consideration the L/h ratio and steel fibers percent. The proposed 3-D numerical model showed good predictions for the torsional strength of tested UHPFRC shallow and deep beams.

Automated summary

This paper investigates the torsional behavior of UHPFRC shallow and deep beams with a compressive strength of 190.2 MPa through experimental and numerical studies. The experiment results show that increasing the stirrups' spacing has a minimal effect on the ultimate torsional strength of the beams. It is found that the torsional web reinforcement ratio can be safely taken to be 40% of the minimum required value, and the maximum stirrups spacing can be determined by the lesser of twice the beam width or 300 mm. The cracking strength equation used in current codes is modified to account for the L/h ratio and steel fibers content.