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In this study, quantitative evaluation on the enhancement in the ductility of 60-m long span prestressed concrete (PSC) girder to which the high-strength prestressed (PS) strands were applied will be made through the finite-element analysis. The extent of enhancement in the ductility was quantitatively evaluated by computing the deflection ductility index in accordance with the types of the PS strands. As the results of comparison with the deflection ductility index of PSC girder in which PS strands with a tensile strength of 1,860 MPa were used, the ductility was improved by about 1.38 folds when the PS strands with a tensile strength of 2,160 MPa are applied while there was approximately 1.71 folds enhancement in ductility when the PS strands with a tensile strength of 2,400 MPa were applied. In addition, the presence of large quantity of tendons can induce brittle failure of the girder due to the concrete fracturing in the compression region without the yielding of the PS strands. Therefore, it...

The primary objective of this study is to verify if the rheological properties of the lubricating layer obtained from the newly developed tribometer can give a good prediction of the real flow rates of pumped concrete. An equation for the calculation of the flow rates was derived considering the thickness and the rheological properties of the layer. Full-scale pumping tests were performed with pipelines of 350 and 548 m (383 and 599 yd) with seven different mixtures. From the test results and the comparison between the measured flow rates and the flow rates calculated from the equation, it was verified that the flow rates of pumped concrete can be accurately predicted before pumping according to the rheological properties of the lubricating layer measured with the tribometer. It was also found that the rheological properties of the lubricating layer remained constant during pumping, whereas the rheological properties of the concrete were found to vary.

The character of the lubricating layer formed near the wall of a pipe during the flow of pumped concrete is a dominant factor facilitating concrete pumping. To predict flow rates of concrete transported by pumping, it is necessary to measure the rheological properties of the lubricating layer before pumping. In this paper, a new version of a test instrument called a tribometer is developed by considering the level of shear rate that induces the lubricating layer during real pumping. A test method is also suggested based on numerical simulation of the shear flow inside the tribometer and, finally, equations capable of transforming the values measured in the new tribometer into the rheological properties of the lubricating layer are derived. Work in this paper will be extended in a subsequent paper in which full-scale pumping tests will be performed, and predictions for concrete pumping based on the measurements of the new tribometer will be verified from comparisons with the test results.