الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
One of the most widely used structural systems in Egypt for slab construction is the post-tensioning system with H-anchorage dead end (onion dead end). The H-anchorage dead end is formed on site by using a specific hydraulic jack that enables the shaping of the H-anchorage dead end. It is considered as an economic fixed dead end embedded inside the concrete with a good resistance for tensioning force applied on the strand at the live end. However, the successful use of the strand with H-anchorage dead end depends on the length of strand embedment inside the concrete which is known by the development length. The development length should be sufficient in order to transfer forces safely from the strand to the concrete without concrete cracks or strand slippage. As the development length assessment is a vital factor in the post-tensioning process, it was important to study the safe development length that ensures safety of the structural member at time of tensioning and all over the service life of the member. The current code provisions for development length assessment are based actually on experimental test results of pretension members, and as there are several differences between both pretension and post-tension systems, one of these differences is the bond mechanisms that influence the bond between concrete and strand, so this study was important to be performed. In this research two phases were carried out by using of (0.6 in) diameter prestressing strand with H-anchorage dead end. The first phase was indirect pull-out tests performed on nine cylindrical specimens with concentric strand and variable bonded length, to study the bond behavior between concrete and strand with H-anchorage. In this phase a bond model was predicted to express the contribution of each bond mechanism on the bond behavior between concrete and the strand H-anchorage dead end and on the overall strand resistance. A very good correlation between the predicted equations and the experimental values was concluded. Also the maximum load and stress achieved by each specimen was determined and compared with the ultimate strand stress. A Total bonded length equal 720 mm was suggested to reach the strand to its ultimate strength, as the specimens with 720 mm total bonded length exceeds the initial prestressing stress according to ECP 203-20 and ACI 318-19 by 25% and 16% respectively.
In the second phase 48 slab specimens was tested representing the dead end zone of post tensioning slab. Two stages was performed according to two concrete compressive strengths 48 MPa and 70 MPa respectively. In each stage three different slab thickness was tested (160, 200 and 250 mm) with three different specimen lengths (750, 900 and 1050 mm). An indirect pull-out tests was performed to assess the development length of bonded post-tensioning strand with H-anchorage dead end in slabs and to evaluate the implemented length currently used on site. from the experimental test results it was concluded that 850 mm and 1000mm total bonded length implemented on site is suffient for full bond between concrete and strand with H-anchorage dead end in case of concrete compressive strength equal 48 MPa. And also 700 mm bonded length is suggested to be sufficient in case high concrete compressive strength is used.