| The safety assessment of assembly voided slab bridges often adopts the code-based method,which includes load effects calculation,structural resistance calculation,and partial modification coefficients calculation.For multi-beam structures,load effects calculation requires the concept of lateral load distribution,but the methods commonly used are not completely consistent with actual situation.The existing shear capacity calculation formula of Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts JTG 3362—2018(Highway Bridges Code for short)is a kind of semi-theoretical and semi-empirical formula which is based on test data.Since the test data it refers to have been more than 35 years,both the number of members and the range of parameters have certain limitations.For assembly voided slab bridges with load cracks,the partial modification coefficients are used to take cracks into account,but the theoretical basis is not clear.Besides,for the problem of insufficient shear capacity at the ends of voided slab bridges,the existing shear strengthening methods are not suitable.Therefore,to solve the above problems,this paper studies the code-based safety assessment method and shear strengthening method of assembly voided slab bridges,as listed below:⑴ From the perspective of load effects calculation,taking the 13 m voided slab bridge of Yancheng-Jingjiang Expressway as the background,the commonly used lateral distribution calculation methods of assembly voided slab bridges,such as hinge-jointed slab and beam method,lever principle method,etc.,are compared and analyzed with finite element method in depth.Meanwhile,the impact of bearing elasticity,hinge joints stiffness,and integration concrete layer on lateral load distribution are mainly investigated.Moreover,according to the lateral mechanical behavior of deep hinged assembly voided slab bridges,two more accurate calculation methods are proposed.⑵ From the perspective of structural resistance calculation,the source and characteristics of the existing shear capacity calculation method in Highway Bridges Code are reviewed,its deficiencies are pointed out,and the revised principle is determined.Based on the statistical method,the shear test data of 1749 reinforced concrete rectangular beams is collected so that the coefficients of shear capacity of concrete and stirrups in the existing formula are modified.On this basis,the influence of compression flange,prestress,and calculation position are further investigated.The shear test data of 175 reinforced concrete T-beams and 179 prestressed concrete beams is supplemented to improve the existing coefficients of compression flange and prestress,the suggestion for adjusting the calculation position is given as well.In addition,the data collected is used to analyze the error of the revised formula and the existing formula,combined with a 13 m voided slab shear test,the pros and cons of the two formulas are compared.The result shows that the revised formula has higher prediction accuracy and better applicability to parameters.⑶ From the perspective of modification coefficients calculation,the common cracks of assembly voided slab bridges in recent years are classified,and their status and causes are analyzed.On this basis,several safety assessment methods for old bridges based on crack characteristics are proposed,and the direct relationship between the cracks condition and the load effects or structural resistance calculation is established.Besides,targeted maintenance countermeasures are also given.⑷ From the perspective of post-assessment countermeasures,the shear strengthening methods are inappropriate for assembly voided slab bridges.Based on the characteristics of slab bridges,a grouting shear strengthening method is proposed,and the construction process with its key points is also given.The test shows that the grouting method has the advantages of no interruption of traffic,less damage to the beam,higher efficiency,and lower cost. |
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