With the continuous progress of social economy and the rapid development of science and technology, China’s construction engineering industry has been greatly developed. The construction of the conversion layer occupies an important position in the construction of high-rise building projects. In the construction of the project, the construction enterprises must strictly follow the construction specifications for construction and operation, improve the level of construction technology, fully understand and master the characteristics and forms of the conversion layer, which can not only ensure the overall quality of the project construction and extend the service life of the project, but also promote the healthy development of the enterprise.
Structural arrangement of high-rise conversion layer
In the building structure with conversion layer at the bottom, some vertical members of the upper part of the conversion layer cannot be directly connected to the ground, therefore, safe and reliable conversion members must be set. According to the existing engineering experience and research results, the conversion members can be used in the form of conversion beams, analysis frame, hollow analysis frame, diagonal bracing, box structure and thick plate.
Due to the conversion of thick plate in the seismic zone less experience, can be used in the non-seismic zone and 6 degrees seismic design, for large space basement, because of the surrounding restraint, seismic response is less than the above-ground frame support structure, so 7 degrees, 8 degrees seismic design of the basement can be used thick plate conversion layer.
The arrangement of floor shear walls and frame struts plays a very important role in preventing the collapse of the substructure in the earthquake. The design of the conversion layer occupies an important position in the construction of building projects. In the construction of building projects, only by improving the design level of the conversion layer and accurately mastering the design points can ensure the quality of construction.
Construction companies must pay great attention to technology and practical experience, etc., in the construction process to increase the scientific nature of the design of the building conversion layer, in order to improve the quality and safety of the building.
1, reduce the conversion.
When laying out the vertical structure of the main body above and below the conversion layer, pay attention to make as much as possible the upper vertical structure can be down to the ground continuous through, especially the core of the core of the frame core structure should be up and down through.
2.Direct force transmission.
When laying out the upper and lower main vertical structure of the conversion layer, pay attention to make the horizontal conversion structure transfer force directly as far as possible, avoid multi-level complex conversion as far as possible, carefully use the complex force transfer, seismic adverse flat thick plate conversion, such as the upper and lower column network really can not be aligned, try to use box conversion.
3, strengthen the lower, weaken the upper.
For the conversion layer of the shear wall structure or cylinder structure, the following measures can be taken: strengthen the lower structure to increase the thickness of the cylinder and floor wall, improve the concrete strength level, if necessary, can be placed around the house part of the additional shear wall, wall frame or stairwell cylinder, improve seismic capacity; can take the following measures to weaken the upper: no floor shear wall openings, openings, reduce wall thickness, etc..
4、Optimize the conversion structure.
Seismic design, when the building function must not be converted to a high level when the conversion structure should be preferred not to cause the seismic action of the frame pillar (side column) column top bending moment too large, column shear too large structural forms, such as diagonal web truss, hollow web truss and flat beam, etc., while paying attention to the need to meet the strength and stiffness requirements under the action of gravity loads.
5.Comprehensive and detailed calculation.
The transformation structure must be taken as an important part of the overall structure, and a calculation model conforming to the actual state of stress and deformation must be used to calculate and analyze the overall structure in three dimensions. If necessary, the finite element method can be used for local supplementary calculation of the conversion structure, at least two layers of the structure above the conversion structure into the local calculation model, and pay attention to the model boundary conditions in line with the actual working state.
6.Technical points of building conversion layer
In recent years, with the continuous and rapid development of China’s economy, people’s functional requirements for high-rise buildings tend to be diversified, integrated and comprehensive. In order to meet the requirements of the building it is necessary to set the conversion layer at the floor where the upper and lower different structural systems are converted.
The cross-sectional size of frame column is mainly controlled by the axial compression ratio and should meet the requirements of shear compression ratio. In order to ensure that the frame column has sufficient ductility, the axial compression ratio should be strictly controlled. Project frame pillar seismic grade for the special level, axial pressure ratio shall not be greater than 0.6, part of the formation of large cross-sectional size and “short column”, shall not be greater than 0.55. Column section ductility also has a close relationship with the hoop rate, so the frame pillar hoop rate is also much larger than the general frame column.
Hoop reinforcement shall not be less than Ф10 @ 100, full-length encryption, and the hoop rate shall not be less than 1.5%. In the project, individual frame pillars also do shear wall end columns, so should also meet the constraints of the edge members with hoop characteristic value of not less than 0.2 requirements, converted into the hoop rate (C50 concrete) that is 2.64%. The frame pillar is a very important member, in order to increase the safety, the column end shear force and column end bending moment should be multiplied by the corresponding increase factor, each floor frame pillar to bear the sum of shear force should be taken as 30% of the base shear force. Because the program calculation, generally assume that the floor stiffness is infinite, horizontal shear force according to the stiffness of the vertical components distribution. The bottom shear wall stiffness is much larger than the frame pillar, making the frame pillar shear force very small.
However, considering the deformation of the floor slab and the decrease in stiffness of the shear wall after cracks appear in the actual project, the frame column shear force will increase. Therefore, the increased shear force of the frame column is separately specified. In addition, in order to strengthen the upper and lower connection of the conversion layer, the longitudinal reinforcement within the upper wall of the frame strut should be extended into the upper wall within the first layer; the rest of the longitudinal reinforcement outside the wall range is anchored horizontally into the conversion layer beam slab to meet the anchorage requirements LaE.
The cross-sectional size of the frame supported beam is generally controlled by the shear compression ratio, the width is not less than 2 times the thickness of the upper wall and not less than 400mm; the height is not less than 1/6 of the calculated span; the width of the frame supported beam is uniformly set at 800mm; the frame supported beam is subjected to huge and complex forces, it is not only the transmission hub of the upper and lower loads, but also the key part to ensure the seismic performance of the frame supported shear wall, which is a complex and important force-bearing member. The longitudinal reinforcement rate of the frame supported beam shall not be less than 0.6% for the special seismic grade.
The reinforcement rate of frame-supported beams shall not be less than 0.8% if the calculation requirements are met. Box-supported beams are generally eccentric tension members with axial forces in the beam, and therefore should be equipped with sufficient number of lumbar bars. Girders Ф16, along the beam height spacing of not more than 200mm, and should be reliable anchor into the support. Frame beam shear is very large, and for such an important part of the seismic, more emphasis should be placed on the “strong shear weak bending” principle, in the case of longitudinal reinforcement has a certain surplus, the hoop reinforcement should be strengthened. Hoop uniform use of Ф14 @ 100 eight limb hoop full-length encryption, with a hoop rate of 1?.53%, much greater than the literature on the special grade seismic conditions of the frame support beam with hoop rate requirements.
3、Conversion floor slab
The frame supported shear wall structure is divided by the conversion floor, and the internal force distribution law is different between the upper and lower parts. In the upper floor, the horizontal force generated by the external load is largely distributed in proportion to the equivalent stiffness of each shear wall; while in the lower floor, due to the difference in stiffness between the frame strut and the floor shear wall, the horizontal shear force is mainly concentrated on the floor shear wall, i.e., the load distribution at the conversion level produces sudden changes. The conversion floor slab assumes the task of completing the redistribution of the shear force between the upper and lower parts.
And because the conversion floor slab itself in-plane force is very large, and the deformation is also very large, so the conversion floor slab must have sufficient stiffness for guarantee. Conversion floor slab using C50 concrete, thickness 180mm. Ф14@ 150 steel double two-way whole plate pull through, reinforcement rate of 0.28%. In addition, in order to assist the conversion floor slab to complete the redistribution of shear forces, the layer above the two layers and the following layers of the floor slab is also appropriate to strengthen, are taken thickness of 150mm.
To sum up, with the rapid growth of national economy, the construction industry as an important support of national economy, the development of its industry plays a decisive role in the growth of national economy.
As an important part of the construction industry, high-rise building occupies an important position in the development of the construction industry. As an essential construction link in the construction of high-rise buildings, the construction of conversion layer
In order to ensure the overall quality of the building, construction enterprises must improve the technical level of the construction of the conversion layer and do a good job of maintenance, only in this way can provide a strong guarantee for the development of the enterprise.