| In order to meet the demand of transportation,the widening and expansion of the existing highway network has become a new hot spot in the road and railroad construction business.Pretensioned PC hollow slab beams were widely used in highway bridges in China before 2005.The debonding of the strand at the end of the pretensioned PC hollow slab beam would lead to the weakening of the shear strength.At present,the ACI318-19 specification had simple provisions to explain the effect of the end strand debonding.The AASHTO LRFD specification only emphasized the importance of the end anchorage,but lacked clear provisions.China’s specifications also lacked provisions on the influence of this problem.Therefore,it is important to fully study the shear failure mechanism of pretensioned PC hollow slab beams.It is of great significance to clarify the effect of strand debonding on shear strength,and correctly evaluate its shear strength to ensure the safety of bridge operation.This paper addresses the shear failure mechanism and shear strength prediction of existing pretensioned PC hollow slab beams.19 existing beams with different spans were removed from the reconstruction and expansion projects of Beijing-Taiwan Expressway and Beijing-Shanghai Expressway.31 tests were conducted.The highprecision displacement gauges were used to test the displacement and slip of end strands during the whole test.The resistance strain gauges were used to test the strain of strands,reinforcement and concrete in the compression zone.3D-DIC testing technology was used to test the development and width of diagonal cracks.Combined with numerical simulation and theoretical analysis,the following innovative results were obtained.(1)The shear failure of PC hollow slab beams caused by the strands debonding.After the hollow slab beams reached the limit state,the strands slipped obviously,and the shear strength no longer increased.The slip of strands in 18 test samples was calculated,and it occurred in 16 samples.A total of 206 strands were measured during the tests,82 of which slipped,and the slip rate was 39.8%.The concrete on both sides of the failure diagonal crack rotated around the concrete at the top of the crack,showing a trend of narrow upper and wide lower.Under the same shear span ratio,the shear strength of the hollow slab beam was not improved,and the concrete strength could not be fully utilized.(2)The application range of Aachen failure diagonal crack angle prediction model was expanded.It was extended from reinforced concrete beams to prestressed concrete beams with the increase of strand stress influence.Comparing the test results,the mean value of this model was 1.08,and the coefficient of variation was 0.12.The mean value of RESPONSE-2000 was 0.97,and the coefficient of variation was 0.37.The mean value of the He model was 1.72,and the coefficient of variation was 0.16.Comparing with other calculation models,the extended Aachen model has higher precision and accuracy for predicting diagonal cracks in prestressed concrete beams.(3)A refined model to predict the shear strength subjected to pretensioned PC hollow slab beams was established.Four factors were considered:(i)the angle of the failure diagonal crack,(ii)the uncracked concrete depth,(iii)the dowel action of longitudinal reinforcements,and(iv)the strand development length.The strand stress of the existing model was calculated by the transfer length.The refined model in this paper adopted the bilinear model and calculated by the development length.It was more consistent with the strand stress in the limit state of pretensioned PC beams.The mean value and Cov were 1.08 and 0.13,respectively.Compared with the previous studies,the shear strength calculation model proposed in this paper has higher precision and accuracy. |
PDF Full Text Request