Shunsuke SAITO

Mechanical Properties of Pretensioned PC Members with Stainless Steel

Takumi SHIMOMURA

In recent years, stainless steel (SUS), a highly durable steel material, is expected to be used for civil engineering structures. This study presents mechanical recommendations for the design of pretension PC structures with SUSPC steel stranded wire as the tensioning material. 
Currently, design methods and stress-strain models have not been studied when using SUSPC steel stranded wire. Differences in adhesion properties with concrete due to differences in surface conditions have also been reported, but no recommendations for design have been made.
In this study, tensile tests were conducted to determine the tensile properties of SUSPC steel stranded wire. As a result, it was found that the steel breaks at less than 20,000 microns.
Next, to examine the bending load-bearing characteristics, basic bending load tests were conducted on SUSPC and ordinary PC beam specimens.  As a result, the crack initiation load and subsequent stiffness reduction were similar to those of ordinary PC, indicating that the conventional design method can be sufficiently applied. However, because the breaking strain of the SUSPC strand was smaller than that of the ordinary PC strand, the SUSPC specimens reached the end of life due to steel rupture at the end of life. This indicates that the steel strain at the end of life, which is conventionally omitted, should be taken into account, and that in actual design, it is necessary to verify whether the steel strain reaches the allowable value when the top edge concrete is crushed.
Prestress transfer and anchorage performance, which depend on the adhesion characteristics between the SUSPC steel strand and concrete, were investigated. As a result, it was found that SUSPC steel strands have better adhesion performance than ordinary PC steel strands.
Based on these experimental results, a new stress-strain model of SUSPC strand wire for use in design and analysis was proposed, and its validity was demonstrated by reproducing beam loading tests using the proposed model. In addition, a limit of 17,000 μ was set for the SUSPC steel strand strain to prevent steel rupture at the end of bending. It was also clarified that there is no need to impose significant restrictions on current design methods for the transmission length and anchorage performance of pretension PC members with concrete, since they have superior adhesion properties than ordinary PC steel stranded wire.