The Continuous Transformation Technical Research On Multi-span Simply Supported Hollow Slab Bridge

With the increasing of traffic, simply supported beam bridges which have been serviced for many years in China appear distress in joints and induce other related distress. With the aggravation of diseases, the phenomenon of insufficient capacity in simply supported girder bridge will appear. Although the new expansion joint construction and materials continue to emerge, but the problem has not been solved. This paper put forward the continuous trasformation for existing voided slab bridges with such distress, the overall mechanical performance of transformed bridge and the interface between new and old concrete were analyzed, AHP (hierarchical analysis) mathematical model was used to optimize transformation parameters. The main contents and work are listed as following:(1) Based on the results of Zhangzhou ten-mile bridge inspection and environmental pulsating test results, continuous transformation is selected as a better option through scheme comparison.(2) After the continuous transformation of simply supported beam bridge, the positive bending moment of mid-span is decreased under dead load, with a maximum reduction of 26.4%; Carrying capacity of live load is increased obviously, which is 1.45 to 1.65 times the original; Shearing of outside bearings in side span is decreased, with a percentage of 6.8%-7.6%;Shearing of other bearings is lager with a percentage of 5.6%-8.4%;(3) The finite element program Midas-FEA is adopted for the continuous transformation of simply supported beam bridge, as the presence of positive and negative bending moments at the top of pier, phenomenon of minimum principal stress occurs inflection is caused at this position, the shear resistance of this region is also decreased,the shear resistance should be carefully checked during the design of continuous transformation;(4) After the continuous transformation, lateral distribution is more uniform and cooperativity between each beam is enhanced, which will reduce the probability of distress of single beam bearing.(5) The bending moment is positive which is caused by the shrinkage and creeping due to the difference of age between new and old concrete, it is disadvantageous to the mid-span, the largest increasement can reach 3.9%; The peak and scope of negative bending moment at the top of pier is eased, the reduction of peak can reach 4.3% which is not obviously affected.(6) During the continuous transformation of Ten-mile Bridge in ZhangZhou, the interface between new and old concrete can work cooperatively under long-term loading, such as shrinkage and creeping, thermal action. However, the safety stock of tensile strength at the interface is low, the micro-expansion concrete, low-shrinkage material or by mechanical means could be adopted for local reinforcement during the transformation design.(7) Mathematical model for optimized selection of single and double bearings was established by the Analytic Hierarchy Process (AHP) from four structural level analysis, they are load effects, temperature effects, construction conditions, geological conditions. It was applied to the analysis of simply supported continuous optimization during the reconstruction of ZhangZhou Ten-mile Bridge..