| With flourishing development of bridge construction in our country, the structural forms of bridge are becoming more abundant. In which the precast small box girder with characteristics of larger section anti-torsion strength, bending strength, low price and rapid construction speed develops quickly and is widely used at home and abroad. However, for the reason of not comprehensive design, unreasonable construction, overload vehicle, its aging and insufficient maintenance and so on, the most of existing small box girders have diseases. Therefore the diseases analysis and reinforcement technology for the precast small box girder will have important engineering value and widespread application prospect. However, the research for the problem is not enough at home and abroad. In this paper based on one overpass in Dalian and above conditions, the main aspects of research work have been done as follows:(1) The internal force of main beam of small box girder is less than structural ultimate bearing capacity, which is calculated by traverse distributed coefficient method and spatial finite element method. Therefore longitudinal force design of main girder can meet the design requirements. Design bearing capacity of deck wet-joint can't meet requirement by analyzing force of deck of small box girder with continuous one-way slab method and spatial finite element method. This is one of causes of diseases of deck. By analyzing small box girder added diaphragm with spatial finite element model, it is proved that the whole traverse deformation and force of bridge is decreased by adding diaphragm. Furthermore by analyzing traverse force of local deck, necessity of adding diaphragm is affirmed.(2) By doing dead load test for precast small box girder of the old overpass, the measured values of longitudinal stress and deflection at middle of main girder bottom are all greater than calculated values under test load, it is showed that the main beams of this bridge have cracked and real rigidity is less than design value. The results of force test of cast-in-place deck shows that real cracking of deck is serious and the differences of force between test values and design values are great. It is showed that impact coefficient of non-barrier driving is related to driving speed. Impact coefficient tends to increase with speed increasing and the value is less than design value. Therefore the test impact coefficient of bridge can meet the requirement of codes. (3) By comparing and analyzing of each reinforcement scheme, it is ensured that the scheme of adding diagonal braces to old structure is reasonable. This scheme can not only increase lateral ties and lateral rigidity of old structure, but also has two advantages. Firstly compared to adding diaphragms, adding diagonal braces can further reduce deadweight of bridge. It is better for bridge force. Secondly adding diagonal brace can reduce the force of main girder web and is good for the force of main girder web. Thus it can increase service life of the whole structure. |
