Bond behaviour of structural concrete - Pull-out-tests for the analysis of bond shear stress models and the development of a cone breakout model

Pull-Out-Tests for the Analysis of Bond Shear Stress Models and the Development of a Cone Breakout Model

(original title: Verbundverhalten von Stahlbeton - Ausziehversuche zur Analyse von Verbundmodellen und Entwicklung eines Kegelausbruchmodells)

Authors: Rafael Dubs, Severin Haefliger
Language: German

Abstract

This Master's thesis investigates the bond behaviour of reinforcing steel bars embedded in concrete over a varying length. A total of 67 pull-out tests were performed on a single specimen, while intentionally enabling a concrete cone breakout at the loaded bar end. The experiments are documented in a separate report. The influence of the following parameters was studied with regard to their effect on the relative displacement between steel and concrete (slip) and on the concrete cone’s failure depth: the bar diameter, the embedment length, the steel quality and the bar position during concrete casting.
The general principles behind the bond models proposed by Eligehausen et al., Shima et al., Sigrist and the fib Model Code 1990 and 2010 are identified in a series of analytical and numerical calculations. These bond models operate with bond stress-slip relationships to describe the bond behaviour and consider different phenomena that cause slip. The range of their validity is ascertained by comparing their predictions with the test results.
The concrete cone breakout is examined on a mechanical basis in a further study, and a concrete cone breakout model is developed. The model is capable of predicting an interval of the breakout depth based on the bond stress distribution along the bar. The findings obtained with the model and the results of measured depths in the tests are applied to adjust existing bond models. This approach leads to improved slip behaviour predictions in situations where a concrete cone breakout occurs. The bond models might be further meliorated in tests with continuous strain measurement to ascertain the influence of the bar’s lateral contraction in the post-yield range and to examine bond-relevant cracks within the specimen.