Cracking Control Technique for Concrete Slab of Steel-Concrete Composite Girder of Qingshuipu Bridge

The Qingshuipu Bridge is a composite girder cable-stayed bridge with a main span of 468m.The steel girder adopts the lattice girder system formed of longitudinal beams,floor beams and stringers.Deck slabs incorporate the 27cm thick precast slabs and the 28cm thick cast-in-situ slabs.To control the generation of cracks in the deck slabs,the cracking control techniques for composite girder were studied.The results of the study indicate that there are several kinds of major cracking control techniques,such as adopting structural design measures to handle local tensile stress so as to eradicate the structural cracks in the deck slab,of which the specific operations include installing longitudinal and transverse prestressing tendons in the midspan deck slabs and the deck slabs at the ends of the side spans;anchoring the stay cables to the girder using steel anchor boxes which are located at the outer sides of the outer webs of the box-shaped longitudinal girder and increasing the area of the precast deck slab as much as possible.The precast deck slabs adopt the polypropylene fiber concrete,the cast-in-situ deck slabs are made of cellulose fiber concrete,at the low temperature season,the deck slabs at the closure section of the intermediate span and the vertical bearings connecting the pylons and the girder are installed.The installation technology of the deck slab and the equipment used should be optimized so as to effectively control the generation of cracks in the construction process.Moreover,it is better to use the silicified agent protection system.