Strut-and-tie Model For Anchorage Zone Of Prestressed Concrete Structures With Its Appliction

Based on the strut-and-tie model (STM) theory, the anchorage zones in post-tensioned concrete structures were investigated in detail. The STM models were proposed for design of anchorage zone. The distribution of interior stresses in anchorage zones was analysed by finite element method (FEM). According to the results of FEM analysis for concentric end anchorage zone and concentric interior anchorage zone, an approach to extend the present STM model was presented. In order to verify the safety and applicability of the approach, a series of experimental tests were conducted. According to the results of FEM analysis for eccentric end anchorage zone and eccentric interior anchorage zone, formulas were given for calculation of internal forces. The detailed procedures were also presented for construction STM model in eccentric anchorage zone. Following new findings are obtained:(1) Stress distritution pattern in anchorage zone are confimed. According to the results of FEM analysis, there exist bursting stress, tie-back stress, tie stress, and flexural tensile stress in anchorage zone. The stress distribution is mainly affected by the dimension ratio of anchor (a/h) and eccentricity of prestressing load (e/h). The resultant forces of the aforementioned stresses decrease with the increase of a/h. However, there are different changes for different resultant with the increase of e/h.(2) The application range of FIP-STM model is extended. FIP model is applicable under the condition that a/h is equal to or less than 1/9, such as massive concrete structure. However, if a/h is larger than 1/9, internal forces decrease with the increase of a/h. The amount of non-prestressing rebar based on FIP-STM model becomes more than that required. Therefore, the internal force ratio and dimension ratio (F/P-a/h) curve was proposed to determinate internal forces. Based on F/P-a/h curve, the detailed procedures were also presented for modifying FIP-STM model. The analytical results shows that for concentric interior anchorage zone about 30% of non-prestressing rebar can be reduced using the proposed method compared with that using FIP-STM model if a/h is equal to 3/10.(3) The approach to extend STM model is verified by a series of experiments. According to the results of experiment, the non-prestressing rebar should be superposed on the position of the center line ofσburst as much as possibly and uniformly allocated. By translating the whole M?rsch model to the position below bearing plate, the model can be modified. The distance of translation is equal to a/4. The result by the modified model is safe, and much closer to test result than M?rsch model. According to test result of concentric interior anchorage zone, the modified FIP model is also safe, and more economic than FIP model.(4) Simple formula to calculate internal force is proposed for interior anchorage zone. According to the results of FEM analysis for eccentric interior anchorage zone, the Guyon's formula of bursting force is too conservative. Based on the Guyon's method, the internal forces in anchorage zone were studied in detail. The formula for calculation of internal force was proposed. The FIP model was also modified further in order that it can be used under the condition that e/h is not equal to 0.