Bond of bundled strands under static and cyclic load and freezing-thawing effect

Abstract

The bond behavior of prestressing strands is of great importance for the capacity of precast prestressed concrete structures. There are cases in design and manufacturing practice where strands need to be bundled. However, the current design codes have no design guidelines for application of bundles of strands in precast prestressed concrete structures and there is a lack of information about their bond behavior. Therefore, the investigation of bond behavior of two bundled three-wire strands is presented in this article. Twenty three hinged beam specimens were tested to study unidirectional constant amplitude cyclic load (different amplitude and number of load cycles) influence as well as freezing and thawing effect on bond properties of two bundled three-wire strands. The three mechanisms: adhesion, friction, and several mechanical interlocking actions were found to be present at the strand concrete interface at different slip values. The results from the experiments showed that cyclic load did not negatively influence the bond strength of two bundled strands. Additionally, combined action of cyclic loading, freezing and thawing resulted in a decrease of bond strength. Based on experimental results the new static and cyclic bond parameters for two bundled three-wire strands are proposed on the basis of τ-s and S-N models provided in Model Code 2010.