Prestressed Concrete Lecture 11 - Anchorage zones
Prestressing anchorage zone In pre-tensioned concrete the force from the prestressing strand is transferred to the concrete by bond between the concrete and the strand. release ("cut") the strand - it will want to retract prestress force in the beam the strand is prevented from fully retracting because it is bonded with the concrete distance along the beam Lpt € The length at transfer over which the force in the strand builds up to the effective prestress value is called the transmission length, Lpt. AS 3600 says that for strand, Lpt = 60 db (762 mm for 12.7 mm, and 912 mm for 15.2 mm strand), and the first 10% of that length has no stress in the strand. As well as the transmission length which applies at transfer, we also have to consider the development length Ly of the strand, which is the bonded length needed to develop the strength of the strand at failure of the cross section. AS 3600 says that, Lp=0.145(@pu - 0.67op.ef )db ? 60db where Opu is the stress in the prestressing steel at failure of the cross section (see Lecture 9), and Op.ef is the stress due to Per For example, if Opu= 0.85 fpb = 1520 MPa and Op.ef= 0.6fpb = 1070 MPa then Lp = 1470 mm for 12.7 mm, and 1770 mm for 15.2 mm strand. CVE80004 Advanced Concrete Design - Geoff Taplin
Prestressing anchorage zone In post-tensioned concrete the force from the prestressing tendon is transferred to the concrete as a concentrated force that cause large local stresses in the concrete. These local effects have to be designed for. CVE80004 Advanced Concrete Design - Geoff Taplin