1 Function and classification of structural transfer stories in high-rise buildings
1. 1 Building function of transfer floor. Setting the transfer floor in a high-rise building can achieve the following architectural functions:
1. 1. 1 provides a large indoor space.
In the traditional shear wall structure, the shear wall spacing is small, which is suitable for arranging the guest room floor of hotels and houses. When shops, conference rooms, restaurants, cultural entertainment and other public buildings with large space need to be arranged at the bottom, some shear walls can be transformed into frame-supported shear walls through the transfer floor, and frame columns can be used instead of shear walls to form a large-space shear wall structure, which can meet the requirements of building functions. The large space shear wall structure can form a large space on one or more floors below the building.
1. 1.2 provides large entrances and exits.
Transfer members are arranged along columns or corner columns around the building plane. The transfer floor of the outer frame tube can adopt various transfer structures such as truss, beam and arch.
2 Transfer stories are classified according to structure and function
From the structural point of view, the transfer floor mainly realizes the following structural transformation:
2. 1 upper and lower structure type conversion
In order to create more internal free space, the transfer floor converts the original upper shear wall into a lower frame. This kind of transfer story can be widely used in frame-shear wall structures and shear wall structures, and this type of transfer story is called Class I transfer story.
2.2 The change of the network and axis of the upper and lower floors does not change the structural form of the upper and lower floors, but expands the column spacing of the lower columns of the transfer floor, thus forming a large column network. This kind of transfer floor is mostly used when the bottom of the outer frame forms a large entrance. This type of transfer floor is called the second type of transfer floor.
2.3 At the same time, change the structural form and the position of the structural axis.
Through the transfer floor structure, the shear wall structure of the upper floor can be changed into a frame structure, and at the same time, the axis of the upper floor and the column network is staggered, thus realizing the staggered layout of the upper and lower structures. This type of transfer floor is called the third type of transfer floor.
3 High-rise building structure transfer floor construction technical points
3. 1 reinforcement engineering construction
3. 1. 1 Reasonably arrange the sequence of steel bars in place.
Because of the dense steel bars, long main bars and high steel content in beam-column joints, some high-rise buildings even use large-diameter steel bars and I-beams for long-span beams. Therefore, it is the most critical point of steel bar construction to arrange the placing order of steel bars reasonably and carry out blanking and sample turning correctly. Before the reinforcement project starts, it is necessary to master the relevant provisions of the current code, consult familiar design documents and find out the design intention. The binding sequence, installation sequence and production size should be determined when the steel bars are turned over, and the interpenetration and avoidance relationship between steel bars should be considered.
3. 1.2 Welding of steel joint
I-beams in the transfer floor structure of high-rise buildings are generally welded. After welding, all these welding points must be NDT. After meeting the requirements of testing standards and obtaining the license, the next step of steel bar installation and binding can be carried out. Mechanical connection should be adopted for steel bars with a diameter greater than 32mm, flash butt welding should be adopted for steel bars with a diameter less than 32mm, and cold extrusion sleeve connection and taper thread connection can be adopted for continuous connection. When the thickness of transfer plate is large or the height of transfer beam is large, necessary measures should be taken to ensure the stable operation of steel skeleton.
3.2 concrete engineering construction
In the concrete construction of long-span super-high transfer beam and transfer thick plate, measures should be taken to prevent temperature cracks from occurring in newly poured concrete. At present, the measures taken in practical engineering are:
3.2. 1 According to the concrete mix proportion, predicted construction climate and site conditions, the temperature state of the whole process of large-span ultra-high transfer beam and transfer thick plate is simulated and calculated by using the three-dimensional finite element temperature analysis program of mass concrete structure, and the temperature change law of each part of concrete within one month after pouring is mastered, which provides scientific prediction analysis and basis for the construction of large-span ultra-high transfer beam and transfer thick plate.
3.2.2 During the construction of mass concrete transfer structure, measures should be taken to control the temperature difference between the inside of concrete and the surface of concrete to be less than 25℃.
process flow
Optimization scheme → support system design → formwork design → formwork support → steel member fabrication → steel member installation → steel bar binding → concrete raw material selection → mix design → concrete mixing → concrete transportation → concrete pumping → temperature probe layout → concrete distribution → concrete vibrating → bleeding and surface treatment → concrete temperature curing.
Concrete pumping
(1) According to the requirements of the construction scheme, check whether there is concrete residue in the pipeline before laying the pipeline. If there is, clean it in time and fix the pipeline, especially the inclined pipe and vertical pipe, so as to reduce the pumping pressure loss.
(2) Before pumping, wet the pipeline with clear water, and then lubricate the pipeline and pump with cement mortar.
(3) Before pumping the hopper, someone should be on duty to check the large stones and sundries in the mixture. In the process of pumping, the amount of concrete in the hopper should be kept at least 20 cm to avoid the low suction speed of the pump or the blockage of the inhaled air.
(4) When the pumping is temporarily interrupted, measures should be taken to make the pump reverse, so that the concrete in the pipe can reciprocate back and forth and maintain good pumpability.
Concrete mixing
① Feeding sequence. Using the same mixing method, the admixture is diluted with mixing water and mixed with other materials at the same time. Fly ash and cement should be added to the mixer at the same time.
(2) stir evenly. Admixtures should be evenly distributed in concrete to avoid adverse consequences caused by local excess, so the mixing time should be extended by 1min.
(3) After feeding, ensure that the stirring time is more than 2.5 minutes.
3.3 Transfer floor bottom formwork support system
The concrete dead weight and construction load of the transfer floor of high-rise building structure are very large, so it is one of the keys to determine the bottom formwork support system of the transfer floor. Generally, there are three supporting systems for the bottom formwork of transfer floor:
3.3. 1 full house red steel pipe support frame
This support system is suitable for the construction of slab transfer floor structure, with relatively small construction load and structural self-weight, and dense transfer beams. This support system usually has 200mm×50mm wooden mats under the vertical poles, and the spacing between the vertical poles is between 600mm×600mm, using steel pipe scaffolding. This support system was adopted by Huaxi Beauty House and Manhattan International Apartment (the first one).
3.3.2 Steel pipe supports shall be arranged along the direction of transfer beam.
The support system is suitable for structures with low transfer beam position, heavy construction load and heavy transfer beam weight. Before construction, vertical bracing and horizontal bracing must be set reasonably, and the spacing and step distance of vertical poles must be determined.
Steel frame support
The support system is suitable for structures with high transfer story position, heavy construction load and heavy transfer beam. The method is: the steel frame is used as the formwork support system of the transfer beam, the steel corbel is buried in the lower column, and the vertical load is transmitted by the column.
3.4 Prestressed concrete transfer floor structure construction technology
Because the transfer beam (slab) of high-rise building bears several or even dozens of loads, the load pressure is relatively large, and the amount of prestressed tendons is correspondingly large, so attention should be paid to avoid excessive anti-arch or cracking in the pre-tensioning area during construction.
3.4. 1 Selective tensioning technology can be adopted, that is, after seven or eight floors are constructed on the upper part of the transfer structure of high-rise buildings, prestress is tensioned again. It is worth noting that support under the transfer structure must be strengthened.
3.4.2 The staged tensioning technology is adopted, that is, the load of each stage is constantly balanced by gradually applying prestress, but the cost will be slightly higher, which is due to more tensioning times and higher corresponding costs.
3.4.3 Configure a certain number of prestressed tendons in the pre-tensioned area to realize the reverse arch.
4 conclusion
In a word, the transfer floor structure has become one of the development trends of modern high-rise buildings. The application of transfer floor structure in high-rise buildings has brought the development of high-rise buildings into a new development period, which has great economic value and social benefits and is worth discussing.