Abstract
This paper presents an experimental research work that evaluates the pre-stress loss caused by friction in crushed limestone sand (CLS) concrete members with post-tensioning. A total of 26 full-scale pre-stressed concrete beams were constructed and tested for the friction loss experiment. The considered variables mainly included the duct-forming materials, wires of tendons and arrangement of ducts. The tensile forces at both active and passive ends of specimen were recorded by steps, and then the pre-stress friction loss for each case was calculated. The result shows that the proportion of pre-stress friction loss in specimen with multi-wire tendons is in the range of 10–40%, with the trend first increasing before decreasing. The pre-stress friction loss in specimen with curve duct accounts for 10–30%. The pressure on the curved part definitely increases the friction when compared with the straight duct. The pre-stress friction loss in specimen with rubber hose reaches nearly 40%, which is larger than the metal bellow and plastic bellow. The suggested values for each case are proposed for a deviation coefficient κ of 0.0017–0.007 and a friction coefficient μ of 0.108–0.858. This can provide reliable theoretical support for the design and construction.
Highlights
Manufactured sand has been deemed to be a suitable alternative to river sand for the application and substitution of concrete aggregate [1,2]
Because of the advantages above, crushed limestone sand (CLS) concrete is widely used in pre-stressed structures [3,4]
CLS concrete with large elastic modulus is sensitive to the increase in concrete age, and the creep and shrinkage is more obvious than normal concrete [2]
Summary
Manufactured sand has been deemed to be a suitable alternative to river sand for the application and substitution of concrete aggregate [1,2]. The effective force inevitably decreases due to the friction loss between the pre-stressing tendon and duct [10]. The deviation coefficient κ and friction coefficient μ are provided in current specifications for these effects [27] These coefficients are determined by concrete properties, duct straightness and surface of tendon and its surrounding material. The suggested values are not suitable for evaluating the pre-stress friction loss of CLS concrete. To accurately calculate the pre-stress friction loss in CLS concrete members with post-tensioning, 26 full-scale pre-stressed concrete beams were constructed based on two bridge projects. The deviation coefficient κ and friction coefficient μ are modified and proposed for the CLS concrete member with post-tensioning, which can provide theoretical support and suggestions for actual projects
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