Design of steel reinforced concrete structure for

The design of transfinite high-rise steel reinforced concrete structure with large chassis and double towers (I)

preface

the so-called transfinite high-rise building engineering refers to the high-rise building engineering that exceeds the applicable height and applicable structure type and body shape specified in the current national codes and regulations, and the relevant codes and regulations require special seismic review. Zhongguang building is a large high-rise comprehensive building integrating office, residence, shopping mall, catering and entertainment. Including three high-rise towers (buildings a, B and C). The podium has five floors and two underground floors. The first and second floors underground are equipment rooms and garage, and the second floor underground is level 6 civil air defense in wartime. The first to fifth floors above the ground are shopping malls. A. Tower B is a high-rise residential building with 6-26 floors and butterfly plane. The height of the building is 89.1 meters, including local protrusions. The total height of the building is 106.1 meters. Tower C is a large space office with 6-28 floors, and the house height is 99.6 meters. Including local protrusions, the total height of the building is 118.800 meters. The total area of the five storey shopping mall is 26745 square meters, with a total construction area of 100010 square meters

because the total length of the house is far beyond the limit of 55 meters of the maximum spacing of expansion joints in reinforced concrete structures, two anti-seismic joints are set to divide the house into three sections to form three structural units. That is, buildings a and B are high-rise buildings with large chassis and double towers; Building C depicts a blueprint for the future development of power batteries. It is a frame shear wall high-rise building with independent podium; The rest are frame structures. The seismic fortification category of buildings is class B, and the site category is class II. The foundation adopts reinforced concrete flat raft foundation, with a bottom plate thickness of 1600mm (residential part) and 1800mm (office part), the bearing layer is strongly weathered sandstone, the standard value of foundation bearing capacity is 400kPa, and the compression modulus is es=12~17mpa. The structural safety level of this building is level I, and the design reference period is 50 years. This paper focuses on buildings a and B

I. structural layout characteristics

in order to meet the comfort and regularity requirements of the upper residential building (i.e. there is no column angle in the residential room) and the use requirements of the large space of the shopping mall on the lower five floors, the high-rise buildings of buildings a and B adopt the five floor large chassis double tower frame supported shear wall structure, and the equipment floor is used as the transfer floor between the fifth and sixth floors. The beam transfer is adopted, and the elevation of the transfer floor is 23 meters. The height width ratio is 3.22, the length width ratio is 4.13, and the upper and lower shear stiffness ratio of the transfer floor γ= 1.395。

1. The height of the building exceeds the limit. The height of the high-rise buildings a and B is 89.1 meters, which exceeds the limit of 80 meters in the 8-degree zone of frame supported shear wall structure specified in the code for design and construction of reinforced concrete high rise buildings (JGJ)

2. Double tower connected structure is adopted, with uneven mass and stiffness distribution and irregular vertical

3. High level conversion: use the equipment floor as the conversion floor between the fifth and sixth floors, with an elevation of 23 meters. The conversion floor in the area exceeding 8 degrees should be controlled below the limit of 3 floors

4. Due to the requirements of residential building plane, there is secondary conversion in some parts

5. Due to the limitation of the use function of the mall, the number of floor shear walls of towers a and B is relatively small, and most of them are arranged at the rear of the mall. The ratio of the eccentric moment of the main structure and the center of the large chassis to the chassis size is greater than 0.2.6. Corner windows are set locally in the peripheral shear walls of residential buildings with 6-26 floors

II. Structural measures

after many analyses and demonstrations by our institute, it is considered that the main adverse factors are: the frame supported shear wall structure is below the transfer floor, the supporting frame and the floor shear wall coexist, forming a "supporting frame shear wall" system. Among them, the supporting frame is a weak link. When this structural system is converted at a high position, due to the sudden change of the stiffness near the transfer floor, the internal force accurate to 0.1MPa and the force transmission path, it is easy to form a weak floor, which is unfavorable to earthquake resistance. At the same time, the supporting frame column should directly bear the gravity load transmitted from the upper part, directly bear the axial force generated by the overturning moment of the upper shear wall, and directly bear a part of the direct seismic horizontal shear force that cannot be transmitted to the ground shear wall indirectly by the floor slab. In this way, the internal force of the supporting frame column below the transfer floor is far greater than the calculation and analysis results. The following measures are taken:

1. Steel reinforced concrete columns and reinforced concrete beams are used in the frame support below the fifth floor of the tower (a total of 48 steel reinforced concrete columns). As an important measure to solve high-level conversion and height overrun

2 under the influence of the high vibration mode of the tower, the roof slab of the podium building of towers a and B bears the longitudinal tensile pressure and transverse shear force under the condition of large repeated action and good prospect, and the stress is very complex. At the same time, due to the functional requirements of the building, a large hole is opened in the middle of the podium building to set up elevators, which greatly weakens the floor. In view of this unfavorable factor, the measures of strengthening the section and reinforcement of the beam around the floor slab at the large opening, increasing the thickness of the floor slab and adding inclined reinforcement are adopted in the design

3. Because the upper residence is a butterfly plane, secondary transfer beams appear in some parts of the transfer floor. According to article 10.2.10 of the technical specification for concrete structures of high rise buildings (JGJ), the vertical lateral force resisting members (walls and columns) on the upper part of the transfer floor should directly fall on the main structure of the transfer floor. When the vertical layout of the structure is complex, and the frame supported main beam supports the shear wall and the transfer secondary beam and its upper shear wall, the stress analysis should be carried out, the reinforcement should be checked according to the stress, and the reinforcement structural measures should be strengthened. For the structural transfer floor of high-rise buildings with B-level frame supported shear walls, the scheme of frame supported main and secondary beams should not be adopted. In view of this unfavorable factor, we have taken measures to strengthen the reinforcement structure of the frame supported main beam, and set up steel beams in the lower reinforcement area of the frame supported main beam

4. The opening of corner windows in the residential part weakens the integrity of the shear wall structure system, brings adverse effects on its seismic performance, and changes the good force transmission mode of the stability performance between the shear wall and the frame beam. In view of this unfavorable factor, we decided to strengthen the treatment from two aspects: stress calculation and structural measures