Method for Ultimate Stress Calculation on Continuous Rigid Frame with Variable Section Reinforced by External Prestressing Force
In order to calculate the ultimate stress in the limit state of bearing capacity for external tendons in continuous rigid frame with variable section reinforced by external prestressing force,firstly,taking 2 background projects for examples,the applicability of the standard formula to ultimate stress calculation of external tendons of continuous rigid frame variable section is verified and evaluated.Secondly,based on the standard formula of plastic hinge number,the correction coefficient of the plastic hinge number represented as α1 is introduced in order to consider the section angle characteristics of continuous rigid frame as well as the actual failure mode,and a modified formula for calculating the plastic hinge number of reinforcement system in limit state is proposed.Subsequently,the section correction coefficient of the middle fulcrum represented as α2 is introduced in order to consider the effect of the section change in middle fulcrum on the effective length of the external tendons,and the analytical expression of α2 is deduced according to the analysis on the middle fulcrum failure model and the section strain distribution in equivalent plastic zone,and the modified formula for ultimate stress calculating of the reinforced system is derived.Finally,3 numerical examples in existing literature are calculated to verify the correctness and applicability of the modified formula.The result shows that(1)The application of the standard formula to calculate the external tendon ultimate stress of the continuous rigid frame with variable section will produce a large deviation,which makes the structural design unsafe,and the reason is that the plastic hinge numbers of the reinforcement system are to many calculated by the code formula in the limit state and the characteristics for the middle fulcrum section and the middle span section of the continuous rigid frame is considered insufficiently.(2)The proposed modified formula has high accuracy and good applicability for the calculation of external tendon ultimate stress in continuous rigid frame with variable section,and the maximum error is less than 10%,which can meet the requirements of engineering calculation accuracy and make the structural design safer.The study result can also provide a reference for the limit state design of bearing capacity for continuous rigid frame with variable section strengthened by external prestressing force.
bridge engineeringultimate stresstheoretical analysisexternal prestressing force reinforcementcontinuous rigid frame
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