The Crack Control For RC Change-over Level Of Superposition-method Construction

The domestic and foreign high-rise buildings emerged vigorously in recent years, many projects used the change-over level to fulfill the requirements which was difficult and complex to construct, and affected construction cost greatly. Superposition -method construction was one kind of way to result these problems.Superposition-method construction was constructing the whole beam or board laminatedly, with the pre-part undertook the post-part, that is, forming laminated beam or board. Because the hydration heat of post-pouring concrete caused the thermal stress, which intensify the pre-partial bases "the stress in advance", and result in cracks in the component bottom; As the mass concrete, it is very important to control the temperature crack, to guaranteed the shearing property and the concrete integrity in the lamination place. Therefore, it was a significance topic to research the construction stage crack control of RC change-over level superposition-method construction. The paper modeled the performance theory of ordinary laminated component, the temperature field and the temperature stress theory of mass concrete, linked to actual project, researched thoroughly on construction stage crack control theory of superposition-method, provided the reference to other similar projects.Regarding the thermal stress, which intensify the pre-partial bases "the stress in advance", and result in cracks in the component bottom, the results were: delaying the form demolition time of the pre-partial bases can reduce the stress effectively, alleviate the adverse effect of "the stress in advance", make its maximum tensile stress to be smaller than the concrete limit tensile stress, avoid the cracks production.Regarding the crack controlling in the laminated surface, the results were: adopting two methods to strengthen its effective restraint in the laminated surface: one, increasing the surface roughness, designing the component which can resist the surface sliding effectively, such as concealed beam and pre-pouring board are constructed at the same time. Two, designing connection bar to improve the stress condition, guaranteeing the overall supporting capacity do not reduce on lamination construction. The supporting capacity calculations on the construction stage are also checked to make up insufficient load considering resulting in crack in the design stage.Regarding the temperature crack controlling as the mass concrete in construction and curing period, this article elaborated its production mechanism according to concrete crack basic concept, analyzed the factors of temperature crack forming and developing; inferred the interior and exterior temperature difference formula of change-over level, as well as the formula of maximum tensile stress because of temperature decrease and concrete shrinkage functioning together to cause cracks; Proposed the technical measures of temperature control and crack prevention; furthermore, linked to actual project, calculated and analyzed temperature and temperature stress of Superposition-method construction, grasped initially the temperature and the temperature stress change rule through site monitoring and ANSYS software analysis,.Finally, summarizing the construction schedule on the crack control of RC change-over level superposition-method, and brief discussing on further studies.