Research On Seamless Design Of Super-length Reinforced Concrete Structure

The research of crack control of super-length concrete structure attracts more and more attention in engineering field and it becomes a hotspot for study. Research of scientific and reasonable seamless structure design method, enrich and perfect super-length structure crack control theory and method, has certain academic value and practical significance. Combination with a super-long underground garage project in Yangling, Shaanxi, using the ANSYS finite element analysis software, response under the action of temperature shrinkage and temperature shrinkage crack control method were studied. The main achievements were as follows:(1) The calculation results of each model shows that, the structure will shrink from the end to the center fixed point under the influence of temperature and shrinkage, the displacement at the end of roof, such as relatively small part is bigger. Structure deformation restrained caused temperature contraction stress, part of structure has a smaller compressive stress, the almost all are tensile stress in the structure. The garage structure plane arrangement is irregular, that has a greater influence on the temperature shrinkage stress distribution, In the hole wall, the wall corner have large stress concentration. Compared with the results of each model, temperature difference and constraints are the main factors influencing the super-long concrete structure temperature shrinkage effects. If reduce the temperature difference, can reduce temperature shrinkage stress in different degree. Through the set of fine sand layer under foundation pad as a horizontal sliding layer, and ensure that the sliding layer performance well to reduce the structural constraints, can significantly reduce temperature shrinkage stress of the structure.(2) The analysis results of second phase structure show that, the temperature and shrinkage stress of Model 6 is bigger than concrete tensile strength design value in a wide range. If using the second phase roof as a construction site, cracks may occur. It suggests that, arrangement construction time or take heat insulation measures, control the structure initial average highest temperature is not higher than 15℃,and take heat preservation measures for the roof to ensure that the lowest average temperature is above 5℃of the structure, reduce the structure integrated temperature to 13.9℃, and ensure that the sliding layer has good performance. Through analysis, the temperature shrinkage stress will be under tensile strength of concrete after take measures, only about 1.1 MPa. In the second phase of construction, according to the experience of engineering practice, choosing materials, reducing length of post-cast strip (35-40m), put off post-cast strip indwelling time (about 42d-60d) to reduce temperature shrinkage stress. After taking the above measures, structure stress is also very large in a part of area, suggested to increase fine and dense temperature steel bar or prestressed reinforcement in the form of "resistance" to avoid structural cracking. In addition, monitoring structure in each construction stage at any time of temperature shrinkage effect, can cope with conditions that may occur in a timely manner.(3) Super-length concrete structure crack control is mainly based on the principle of "resistance" and "put", from material, design and construction of comprehensive measures. Using the medium strength grade concrete, selection cement, aggregate, admixtures, and the dosage of various raw materials, reduce shrinkage and improve the crack resistance of concrete. In the design phase, decorate the structure reasonably, strengthen the constructed measures of heat preservation and heat insulation, determine the temperature and shrinkage reasonably, configurate temperature steel and prestressed steel or directly choose prestressed concrete structures, to control the structure cracks based on "resistance", and reduce structural constraints by the "put" approaches such as setting sliding layers. During the period of construction, good quality management and ready work, choosing rational construction scheme, pay special attention to the construction process of concrete casting quality to control the concrete shrinkage, and reduce the environment temperature influence, strengthen concrete insulation moisture curing, structure monitoring through information technology means, timely response to the appeared cracks in the process of construction and using.