Structural design scheme of Marriott Convention and Exhibition Building?

What is the specific content of the structural design scheme of Marriott Convention and Exhibition Building? Here, Zhong Da Consulting will answer your questions.

I. Overview of the Project

Chongqing Marriott International Convention and Exhibition Building is located in the center of Chongqing, with a height of 5 meters in the north and 22 meters in the south. The building has 69 floors above ground (including GF floor) and 5 floors underground, with a building height of 303.3m and a podium of 7 floors. The fifth floor underground is for parking garage, equipment room and commercial room, the second floor below is connected with the entrance and exit of urban light rail, the seventh floor podium above ground is for commercial use, and the seventh floor is connected with the existing Marriott Hotel through the air corridor. The standard floor plan of the 8th to 68th floors of the tower is 4 1× 4 1m, the 8th to 4th1floors are apartments, the 42nd to 68th floors are office buildings, and helicopters are arranged on the top floor. Set refuge floors on the 7th floor, 23rd floor, 4th1floor, 54th floor and top floor. The basement and podium are 4.5m-5m high, the apartment is 3.7m high and the office building is 3.9m high. The construction land area is 9 100㎡, and the total construction area is 182893㎡, including 145348㎡ above ground and 37545㎡ underground. There are more than 10 buildings around the building.

Second, the foundation and foundation

1. Geological conditions: The site category is Class I site. The building is supported by extremely thick moderately (weakly) weathered mudstone. According to geological exploration, the characteristic value of mudstone foundation bearing capacity is 4.0Mpa, and the standard value of natural compressive strength is 12.4Mpa. After the plate load test of rock foundation, the average ultimate load is 16.4Mpa, and the characteristic value of foundation bearing capacity is 5.2Mpa. This foundation is an ideal site for building high-rise buildings.

2. The foundation pit and foundation design project has five floors underground, because the terrain is high in the north and low in the south. The difference is 5m, and there are 4 floors and 22m full burial conditions. The buried depth of the building is113.8 of the building height, which meets the requirements of overturning resistance. The tower column foundation adopts belled pile (pier), and the inner tube of the tower adopts flat raft foundation. We use SOLID72 element of ANSYS 1 mechanical finite element analysis software compiled by American ANSYS company to carry out three-dimensional calculation and analysis on the pile (pier) with enlarged bottom of the tower, the raft of the tower and the foundation. The pile (pier) with enlarged bottom of tower is 4 m, the enlarged bottom is 5.5m, and the raft is 25.8×25.8×4.5m, which provides reference data for raft foundation reinforcement.

Third, wind load.

The calculation of horizontal wind load of high-rise and super-high-rise buildings is a key factor in the wind-resistant design of structures. However, for tall, especially irregular super-high-rise buildings, the wind load of buildings is greatly affected by the surrounding buildings, so it is necessary to verify the wind load in the current code. Therefore, the model wind tunnel pressure measurement, aeroelastic test and three-dimensional numerical wind tunnel simulation are carried out in this building, and the numerical comparison is made with the code to design reasonable wind load.

The basic wind pressure in Chongqing 100 is 0.45 kN/m2 1. Model Wind Tunnel Test The wind tunnel test of this project was conducted in the Wind Engineering Experimental Research Center of Southwest Jiaotong University. Using the plexiglass model of 1:250, the main buildings and environment about 500m are cut with foam plastic to simulate the atmospheric boundary conditions of class C landform.

Taking the airflow wind pressure at the height of the model roof as the reference wind pressure, the incoming wind speed in the pressure test is 7.5m/s, and this test is arranged on all surfaces of the main structure, with 457 pressure measuring points in 23 sections along the height direction. The wind direction angle of the test simulation is from 0o to 360o, and the interval is 22.5o The normal direction of the main entrance of the model is 0o, and the turntable is positive counterclockwise.

In this wind tunnel test, the wind pressure coefficient of each pressure hole on each side is given under the direction of 16 wind. The test results show that the positive pressure on the windward side of each working face is smaller in the transverse direction than in the middle, and changes smoothly in the height direction, reaching the maximum at 4/5 height (from the top 15-30m) and gradually decreasing along the upper height. The negative pressure on the leeward side and both sides is relatively uniform, with little change along the height. Due to the influence of high-rise buildings around buildings on airflow, there will be local high wind pressure areas around buildings, especially in areas below the height of surrounding high-rise buildings, which have both amplification and reduction effects, and sometimes even wind pressure coefficient inversion. When the wind direction angles are 1350 and 900, the total shear force of the foundation in X direction and Y direction reaches the maximum.

Numerical wind tunnel simulation This project entrusts the School of Aeronautics and Astronautics and Mechanics of Tongji University to conduct numerical wind tunnel simulation. Numerical wind tunnel simulation is similar to the general laboratory wind tunnel, which needs to be equipped with a wind tunnel with entrance, exit, ground and wall. The numerical model of the building and its surrounding buildings is established in the wind tunnel. The numerical model is modeled according to the prototype size (1: 1) and is a rigid model. Modeling, calculation and post-processing are completed by CFX5.5, a leading computational fluid dynamics software in the world.

The report provides the average wind force along the X and Y directions and the total moment around the Z axis of each layer under the wind of 16. The results show that the maximum total shear force of basement in X direction is135 wind direction; The maximum total shear force of Y-direction base is 90o, and the maximum total torque around Z-axis is 0o. At the same time, the contour map of the maximum wind pressure on each surface of the building under different wind forces is given, which provides a basis for the design of glass curtain wall. According to the wind pressure isoline distribution map, most areas in the middle of the windward side of each surface are positive, while a small part of the area near the edge is negative pressure because of the separated flow, and the leeward side is generally a relatively uniform negative pressure.

Comparison and value of wind load We compare the static wind load and dynamic wind load on the windward side obtained by three methods, as shown in Figures 3 and 4. The wind tunnel test shows that under the influence of the surrounding buildings, the wind load value of the wind tunnel test is greater than the standard value, but above 37 stories, the wind load value of the wind tunnel test is less than the standard value. The total wind load calculated according to the load code is about 9% higher than the wind tunnel test results.

The numerical simulation results are basically consistent with the wind tunnel test results, and the maximum wind pressure along the height direction is about 4/5 of the building height. The wind load calculation value of each layer is the largest, followed by the numerical simulation value and the wind tunnel test value is the smallest. The maximum wind pressure calculated by the code is at the top of the building, which is unreasonable and unreasonable, and the resultant point of wind pressure is high. The total wind load is greater than that calculated by numerical simulation and wind tunnel test, so the calculation according to the code is conservative. The results of numerical simulation and wind tunnel test show that when the wind direction angles are135 and 90, the total shear force in X direction and Y direction is the largest, which is difficult to be realized by the existing high-rise calculation software. According to the results of wind tunnel test and numerical simulation, a large negative pressure appears at the lower part of the tower or at the edge of the building. Although the overall calculation of the structure has little influence, it has a great influence on the design safety of glass curtain wall, which should be paid attention to.

In the overall calculation, the incoming winds of 0o, 90o and 135o are calculated respectively. The wind load is taken according to the current code, but the top of the building is taken according to the model wind tunnel test results, and the torque measured by numerical simulation and wind tunnel test is properly considered.

Fourth, the superstructure

1. Structural scheme The superstructure of this project has 69 floors, including 7 podium floors, and the total building height of the tower is 303.3m, which is the highest among the high-rise steel structures built and under construction in China. The height-width ratio is 7.34, which is an out-of-code high-rise building. The basic period of the building structure is 8s, which is a rare long-period high-rise building.

According to the building function, building layout and building height, two structural schemes are considered, namely, all-steel structure and steel-concrete structure. According to the comprehensive comparison of structural seismic performance, construction speed, structural weight and cost, the tower of this project adopts all-steel structure scheme, and the podium and basement are still cast-in-place reinforced concrete structures outside the tower.

The tower adopts a steel frame-core tube structure system with strengthened stories. The outer frame consists of steel columns and steel beams; The core tube is composed of steel columns, steel beams and steel supports. The outrigger truss arm and waist truss of the steel structure are set up by the refuge floor, which is a building equipment, to form a strengthening floor (4 lanes).

The podium and basement below the tower 7F have a total of 13 floors, and steel reinforced concrete columns are used. This is mainly to solve the problem of harmonious connection between steel tower and concrete podium, which is beneficial to the treatment of joint structure, and at the same time, make full use of the compressive strength of high-strength concrete and reduce the section of steel reinforced concrete.

Below 7F, there are steel-reinforced columns, the cross-sectional dimensions of reinforced concrete are1400x1400x and1500x1500x, and the steel-reinforced columns are cross-shaped with flanges. Above 8F, it is a box-shaped steel column, with the section size of 1200x 1200mm to 600x600mm, and the thickness of the steel column is 80mm to 20mm. Three supports are arranged in the longitudinal direction and the transverse direction of the inner cylinder, and a central support and a splayed eccentric support are adopted. The bracket is made of H-beam, and the cross sections are H400x400x25x30 and H400x400x25x40.

Steel beams are all H-shaped. The outer frame beam below 8F is 700 mm high, and the outer frame beam above 8F is 650mm high, which meets the requirements of building clear height; In order to ensure the overall lateral stiffness of the structure, the inner tube frame beams are all 900mm high, and the secondary beams are hinged with the main beam of the frame, which is calculated as composite beams. In order to make the corner frame beam stress evenly, the secondary beam is added at the corner to change the interlayer direction.

The floor adopts profiled steel plate and cast-in-place reinforced concrete non-composite floor.

Seismic and wind-resistant design

(1) design requirements According to reference [3], the basic intensity values corresponding to the 50-year exceeding probability of this project of 63%, 10%, 5%, 3% and 2% are 5.2, 6. 1, 6.3, 6.4 and 6.6 respectively, according to Chongqing. (2) Overall design

1) Conditions set by use and building requirements:

A. The plane and elevation of the tower are very regular, basically symmetrical in two directions, and the combination between the building and the structure is good, which provides very favorable conditions for the earthquake resistance of the structure. B. All-steel structure, with uniform materials and good ductility, can well meet the requirements of seismic secondary fortification.

2) Design of lateral force component:

A. Support structure of inner tube frame: steel supports are arranged between columns, some of which are eccentric supports, and small columns are added between columns of conditional frame to strengthen the lateral stiffness of frame support. B. In order to improve the horizontal stiffness of the lateral force resisting system supported by the inner tube frame and increase the height of the frame, the bearing capacity of the beam and the requirement of increasing the horizontal stiffness should be weighed in the design. C, setting four layers of reinforcement, wherein the 23rd, 4th1,54th and top layers are composed of outrigger trusses and outer frame waist trusses, and the inner tube support of the reinforcement layer is the center support. In the design, the influence of different floors with strengthened stories on horizontal stiffness is compared, and the current story number is the best. D. Steel reinforced concrete columns and steel beams are used under the podium: Considering the overall rigidity, the connection with the podium (reinforced concrete frame structure) will play a certain role in improving the overall horizontal rigidity of the structure.

2) According to Article 8.2.3 of the Code for Seismic Design of Buildings, "The calculated seismic shear force of the frame part shall be multiplied by the adjustment factor, so as to achieve the requirement of not less than 25% of the total seismic shear force at the bottom of the structure. This requirement has been considered in the design of this project and meets the specified requirements.

3) More than 7 floors above the ground are supported by restrained buckling energy dissipation, which can play a role in damping under the action of rare earthquakes. 4) Strengthening of weak parts:

A. Possible weak parts of the bottom floor: The use of steel reinforced concrete enhances the seismic capacity of the structure under rare earthquakes, and the use of steel beams and steel supports can also make the plastic hinge first occur on the support or beam instead of the column to ensure that the structure will not collapse. B. Adjacent frame columns above and below the strengthening story: Because of the sudden change of the stiffness of the strong story, the connected frame columns are complicated and easy to become weak parts. According to the internal force results of elastic calculation, the section should be strengthened appropriately, leaving a considerable reserve, and then the mechanical and deformation properties should be checked by elastic-plastic time history analysis. C. Through elastic-plastic time-history analysis, the layers and members of the superstructure with plastic hinges are checked, and the section of the members is adjusted with restrained buckling energy dissipation braces, so that the plastic hinges are transferred to less important members, and the structure can meet the goal of not falling down in a big earthquake.

This project has carried out a special review of the earthquake resistance of the out-of-code high-rise building. Experts suggest that the building is highly flexible and the comfort problem should be solved.

Aeroelastic model wind tunnel test results Because Chongqing Marriott International Convention and Exhibition Building is tall and flexible, located in the urban area of Chongqing, with dense high-rise buildings, its surrounding buildings and topography have a significant impact on the wind field, so its wind effect under strong wind is very complicated, and its dynamic effect under strong wind can not be ignored. Therefore, the aeroelastic model wind tunnel test was carried out. Through the aeroelastic model test of Chongqing Marriott International Convention and Exhibition Center 1:250 model, the wind-induced vibration response of the building under 16 wind direction is obtained. After analyzing the test results, the following conclusions are drawn:

1), vortex-induced resonance is not found in Marriott International Convention and Exhibition Building in all wind directions and design wind speed ranges. There is no dancing phenomenon of vibration divergence. When b=0o, the maximum crosswind vibration displacement (unilateral amplitude) at the top of the structure is 0.297m, and when b=270o, the maximum downwind vibration displacement (unilateral amplitude) is 0. 133m.

2) The maximum vibration acceleration at the top of the building is less than 0.2m/s2, and the angular velocity of torsional vibration under the return air pressure of 10 is less than 0.00 1rad/s, which meets the comfort requirements. 3) When the wind direction acts on a certain surface of the structure, the lateral displacement and acceleration vibration response of the structure is greater than that along the wind direction, so the lateral load effect can not be ignored for this kind of high-rise building structure. 4) Due to the influence of surrounding buildings on airflow, local high wind pressure will appear around buildings, so attention should be paid to this problem in curtain wall design. In addition, the influence of surrounding building structure on building wind pressure is more significant within its own height range, but less in the top area of the building. 5) The maximum negative pressure on each side of the building is greater than the maximum positive pressure.

5) Structural analysis

1) According to the particularity of the structure, three softwares, SATWE (editor-in-chief of China Institute of Building Research) and MTS (Tongji University, China), are used for structural design.

The main calculation results of ETABS (American CSI company) are similar.

2) Calculation model: According to the frame-support space model, the seismic force is calculated according to the wind loads in the X, Y directions and 135 degrees directions, and the coupling is considered, and a total of 45 vibration modes are obtained.

And CUZI- 1. The maximum value of seismic acceleration time-history curve used in time-history analysis is 35cm/s2.

In China, there is little research on calculating the acceleration response of buildings, especially under the action of crosswind. When formulating the specification, we referred to foreign standards and made adjustments according to the actual situation in China. Therefore, the author uses China Code and Canadian Code to calculate the acceleration respectively.

Verb (abbreviation of verb) conclusion

1. Through the analysis of the dynamic characteristics of Chongqing Marriott International Convention and Exhibition Building, it is known that the basic period of this structure is 8s, which is a highly flexible structure. P-δ effect should be considered in structural analysis, and the structural layout is basically symmetrical, which is beneficial to structural earthquake resistance, and the design is controlled by wind load. 2. Using outrigger truss and outer frame waist truss is an effective method to control the story displacement. The ideal leg position and pass can be found through multiple trial calculations, and the more legs, the better. 3. The steel reinforced concrete column is used at the bottom of the super high-rise steel structure, which can not only save steel, but also appropriately increase the lateral stiffness of the structure, and also solve the connection problem with the reinforced concrete beam of the podium. 4. The comfort of super high-rise buildings is an important factor for designers to consider, so it is advisable to check and analyze them in various ways, and the aeroelastic model test is more reliable.

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