Experimental Procedures for Displacement-Controlled Pure Torsion Tests on Reinforced Concrete Shells
Edvard P. G. Bruun1, Evan Charles Bentz2
1 M.A.Sc. Candidate, University of Toronto
Civil Engineering Department, 35 St. George Street
edvard.bruun@mail.utoronto.ca
2 Associate Professor, University of Toronto
Civil Engineering Department, 35 St. George Street
bentz@ecf.utoronto.ca
Abstract. Torsion in reinforced concrete structures is a common but complex phenomenon that requires further study, a fact that is reflected in the relative lack of well-documented experimental programs, and empirical and overly conservative provisions in structural design codes. This gap in our knowledge can be partially explained by the difficulty in constructing, executing, and properly documenting torsion experiments – non-standard experimental setups with complex boundary conditions and specimen geometry are often necessary, while the effect of torsion is itself difficult to decouple from flexural and shear effects. To remedy this, a pilot project was launched at the University of Toronto to assess the feasibility of gathering high-quality data on the mechanics of torsion in reinforced concrete. This led to the world’s first pure torsion tests (no coupled effects) on two large-scale reinforced concrete shells (1626 x 1626 x 285 mm), one with and one without shear reinforcement, conducted using the Shell Element Tester (SET). Adding to the ground-breaking nature of this work, these tests were also performed in a newly developed and implemented displacement-controlled framework, which allowed for the gathering of stable post-peak data for each specimen. Previously, the SET was run in a force-controlled manner, whereby the 60 servo-controlled actuators were instructed to exert forces that were simply incremented until failure. This experimental program also constituted the most well-documented set of shell tests to date from a data perspective, with both in-plane and out-of-plane instrumentation used to measure the behaviour of the shell throughout the duration of the experiment. In addition to the standard surface-mounted Linear Variable Differential Transformers (LVDTs), a state-of-the-art 3D imaging camera system was used to measure the detailed in-plane surface strains and deformations of the specimen. For the out-of-plane strain measurements, a series of embedded concrete gauges and Linear Potentiometers (POTs) were placed through the thickness of the shell in the planes of the main longitudinal reinforcement.
This paper presents a clear procedure for the construction and instrumentation of the shell specimens, followed by the implementation of the displacement-controlled testing framework used with the SET necessary to achieve post-peak behaviour. The data processing methods for the various types of instrumentation are also explained, with a final discussion on the improvement in strength and ductility for shells in pure torsion resulting from the addition of out-of-plane shear reinforcement.
Keywords: Torsion, Reinforced Concrete, Shell, Displacement Control, Post-Peak.
