Abstract
Validity of the approximate equation for predicting compressive stress in the posttensioned anchorage zone presented in the AASHTO LRFD Bridge Design Specifications was investigated in this study. Numerical analysis based on the finite element method (FEM) and theoretical analysis showed that the AASHTO formula gives relatively accurate stress values when the effect of duct holes is neglected. However, it was found that the formula can significantly overestimate the stresses in the actual prestressed concrete member with spaces occupied by ducts. Therefore, an improved equation was proposed for the existing AASHTO equation to consider the effect of the duct holes on the stress distribution. This resulted in relatively accurate prediction of the distribution and magnitude of the compressive stresses even with the presence of the duct holes. The proposed equation was also validated by comparing with the stresses measured in the test of a posttensioned full-scale specimen. This study is expected to contribute to the design of the anchorage zone in prestressed concrete structures by suggesting a more reasonable way to assess the appropriateness of anchorage devices.
Highlights
For the design of the anchorage zone, the following design methods can be used [2]: (1) equilibrium-based inelastic model; (2) refined elastic stress analyses; or (3) other approximate methods using predictive equations. e design concept of the anchorage zone given by AASHTO has been adopted in many countries including Korea [3]
It was found that the original AASHTO equation can significantly overestimate the stresses in an actual prestressed concrete (PSC) structure with spaces occupied by ducts. erefore, an improved equation was proposed in this study that can yield more accurate stresses in the anchorage zone. e proposed equation was validated by comparing with the stresses obtained from finite element (FE) analyses and with those measured in the test of a posttensioned full-scale specimen
Among several design methods used for a posttensioned anchorage zone, a simplified approximate approach using the predictive equations specified in the AASHTO load-and-resistance factor design (LRFD) Bridge Design Specifications has been often used in practice
Summary
In order to cope with any harmful situation anticipated in the anchorage zone shown in Figure 1(a), the simplified approximate calculation method presented in the AASHTO LRFD Bridge Design Specifications [2] provides equations for predicting the magnitude and location of bursting forces and spalling forces associated with tensile stresses and cracks that can occur in the anchorage zone. In the case of a special anchorage device [11] that does not satisfy the specifications for bearing stress, the compressive stress induced inside the anchorage zone should be calculated and should be kept below the allowable value according to equation (1) in terms of load-and-resistance factor design (LRFD). Equation (1) was adopted in the AASHTO LRFD Bridge Design Specifications based on previous studies [17, 18] If the effect of the duct hole is taken into account, the compressive stresses calculated using equation (1) significantly differ from those obtained using a more accurate methodology such as FE analysis. e reasons for this difference and possible improvement are investigated
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