Calculation Method for External Cable Stress Increment Under Nornal Use
In order to solve the efficiency and accuracy issues of the calculation method for the stress external prestressing under normal use at limit state,based on experimental results and relevant assumptions,continuous rigid frame reinforced by external prestressing is considered as a single span reinforcement system.Considering the deformation characteristics of the external prestressing curve under load and the geometric relationship with the relative position changes of beam,and through theoretical derivation,a simplified formula for calculating the stress increment of external prestressing of a single span reinforced system under load is derived,and the calculation formula for total stress increment of the external prestressing of entire bridge is derived by superimposing the stress increment of the external prestressing of each single span reinforcement system.The calculation formula for the stress increment of the external prestressing under different loads and beam arrangement forms is discussed.Taking a continuous rigid frame bridge reinforced with external prestressing for an example,the stress increment of external prestressing under normal use at limit state is calculated by using the above method,and the calculation results are compared and verified with FEM and reference results.The result shows that(1)in the early stage of normal use,the stress increment of the external cables in continuous rigid frame reinforced with external tendons depends on the load,the tension control stress has little effect on it,and in the later stage of use,the influence of tension control stress on the increment of external beam stress gradually increases;(2)the proposed formula has high accuracy in calculating the stress increment of the external prestressing under normal use at limit state with a maximum average error of less than 5%,which can meet the requirements of engineering calculation accuracy,and the structural design is biased towards safety;(3)at the same time,the formula with simple form avoids complex finite element modeling and energy variation operations,that is convenient for engineering and technical personnel to master and has good practicality.
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