Study Of Precasting Technology Of Large Tonnage Simply Supported Monolithic Box Beams Of High-speed Railroad

With the promising of high-speed railroads throughout the world, the maximum speed of railroads in China has been improved greatly. Special passenger railways have been built successively and high-speed railways are being constructed rapidly. Trains at present in China run more steadily and passengers feel more comfortable. Simply supported monolithic box beams of long span, huge volume, large cross section, and continuously once-grouting attract great attention in current works.This beam can provide transverse and vertical rigidity, twisting rigidity, and self-vibration frequency, all of which are superior to those provided with a free T-beam. Meanwhile, both of its top plate surface and bottom plate surface are of larger areas which can bear positive and negative bending movements effectively and satisfy the requirements for allocating steel bars. The cross section of a single box is monolithic. The materials used are economical and the construction is convenient. The structure of the beam is simple but its outline looks beautiful. The twisting rigidity is large. The construction speed is fast. Little curing works are needed after the beam is completed besides lower noises. Therefore, this box beam has been widely accepted in the construction of bridges of passenger railways and high-speed railways. Certainly, the precasting and erection of the simply supported monolithic box beams become the key factors during construction.In the present work, experiences during the construction of large tonnage simply supported monolithic box beams on the Zhenzhou-Xi'an express railway, test data at the Lintong bridge precasting plant under China Railway First Group Corporation, and test files at Lingxian county along TJ-2 contract section on the Beijing-Shanghai express railway are taken into account to focus on the in-situ precasting technique and the grouting crafts of high performance concrete. The introduction is not only meaningful for construction of analogue work in China, but provides mature experiences in the construction of high-speed railways by using prestressed concrete simply supported beams in large scales. Three parts, including the design of a precasting plant, prefabrication of box beams, and hoisting and installation, are discussed in this work.1) The plan and design pattern in the construction of large tonnage simply supported monolithic box beams of high-speed railways were summarized and optimized;2) The precasting construction of a simply supported monolithic beam was summarized. Some key techniques in the course of precasting was stated in details, which mainly refer to the in-situ precasting technique and the grouting crafts of high performance concrete.3) Factors that exert influence on the concrete grouting time of a beam body was analyzed and confirmed, on the basis of which the construction crafts were renewed. The improvement of the grouting aging was discussed in details.