Strand Development and Splice Device

摘要

A new device for gripping prestressing strands was developed and tested. The device could provide a means of anchoring the terminal end of a strand in order to provide a mechanism for developing bonded strand at the service limit state, to provide this mechanism at the strength limit state, and to develop unbounded strand at the strength limit state. It could also be used to mechanically splice strands together. Grouting this device into a member may reduce the development length of the strand, thereby increasing the effectiveness of the strand for reducing tensile stresses and cracking. The prestressing strands used in all tests were unstressed and were 0.5-inch diameter, 270 ksi, low-relaxation. Preliminary tests were performed on four device lengths: 6.38 in, 7.94 in, 9.56 in, and 11.38 in. The inside diameters of the devices were either 0.79 in. or 0.94 in. Sika 300PT grout was used to bond device to the prestressing strand. Load and displacement were measured throughout testing, and load was applied until there was no increase in force and excessive displacement had occurred. A Maximum load of 22 kips was attained for the 11.38-inch device. The two shorter devices carried around 14 kips. Further tests were performed on devices made from one-inch schedule 40 pipe with the interior roughened with a 0.75-inch pipe tap. Four device lengths were tested: 6, 9, 12, and 18 in. SS Mortar was used for the grout. Each device was cast in an 8 in. x 8 in. concrete block. For all specimens, the average bond stress was an average bond stress was an average of 1.36 ksi. The maximum load attained was for the 18-inch device, and was about 40 kips, or 97% of the ultimate strength of the strand. The 12-inch device would be the longest for practical use; this device strength was about 25.6 kips, or 62% of the ultimate strength of the strand.