Tianjin Jinta is located on the north side of Xing 'an Road, Tianjin, by the Haihe River. The office building has 75 floors with a height of 336-9m. Upon completion, it will become the tallest building in Tianjin (Figure 1) and the tallest steel plate shear wall structure in the world. The Golden Pagoda Project is invested and developed by Financial Street Holdings Limited, and designed by SOM Company of the United States and East China Architectural Design and Research Institute Co., Ltd. [1].
Tianjin Jinta Project Base covers an area of 22257-9m2 and consists of 75-storey towers and 30-storey apartment buildings. There are four basements in the lower part of all single units, enjoying the same foundation layer.
1 structural system
Tianjin Jinta main building is a super high-rise building with a height of 336-9m (from the outdoor ground to the main roof). The standard story of structural system is concrete-filled steel tubular column frame+core steel plate shear wall system+outrigger lateral force resisting system. The equipment structure plan and local elevation of steel plate shear wall are shown in Figure 2~ Figure 5, in which steel plate shear wall, as an important part of lateral force resisting system, is seldom used in high-rise buildings in China, and it is used in Chinese codes. The maximum aspect ratio is 7-88, which exceeds the specification requirement of 6; The floor is partially discontinuous; The outrigger truss and waist truss strengthening layers were set on 15, 30, 45 and 60 floors, and the lateral stiffness and floor bearing capacity between the upper and lower floors changed suddenly.
The outer frame of the tower consists of concrete filled steel tubular columns and wide flange steel beams. The typical column spacing around the tower is about 6-5m, and the outer frame columns are just connected. The core tube of steel plate shear wall is composed of concrete filled steel tubular columns and wide flange steel beams filled with structural steel plates. Steel plate shear wall is located in the core tube area of the structure, around passengers and service elevators, stairs and equipment rooms. 15, 30th, 45th and 60th floors are provided with outrigger truss strengthening layers, large steel trusses are arranged between the core tube and the outer frame of the steel plate shear wall, and waist trusses are arranged in the outer frame. According to the analysis results, the steel plate shear wall elements in different positions become steel frame+steel support systems with different heights.
The foundation system of the tower is composed of the conventional reinforced concrete cushion foundation supported by 4m-thick bored piles. Bored pile diameter 1000mm, pile length 60m, pile end bearing layer 1 1, and foundation concrete C40. The foundation system will cover 400 mm thick gravel layer and 150 mm thick reinforced concrete roof.
The gravity system of the tower is composed of traditional wide flange steel frame and composite floor. The typical composite floor is 65mm closed profiled steel plate with 55mm concrete surface, with a total thickness of120 mm. Most of the composite steel beams with wide flanges are 450mm high, ranging from steel plate shear walls with core tubes to the surrounding ductile bending frames. The typical beam span is 3-25m. The concrete-filled steel tubular column at the steel plate shear wall and the surrounding ductile bending frame are also used for defying gravity load.
The lateral force and gravity system of the superstructure usually extend down to the foundation structure. The maximum diameter of concrete-filled steel tubular column is 1700 mm, and the frame structure will be composed of traditional wide flange steel frame and composite floor. Steel composite beams with wide flanges are generally 450mm high, ranging from the core tube of steel plate shear wall to the four-GAI bending frame, and the beams are generally placed in the center of 3-25m.
2 structural calculation and analysis
2- 1 structural design basis and basic design parameters
In structural design, it is necessary not only to meet domestic codes, regulations and standards, but also to
Reference is made to Canada's "Design of Steel Structures in Limit State" (CASAS16-01) and America's "Recommended Practices for New Buildings and Other Structures" in 2003.
NEHRP(FEMA450), the seismic practice of American steel structure buildings.
(AISC-34 12005) is used in the design of steel plate shear wall.
The safety level of the tower structure is Grade II, the seismic fortification intensity is 7 degrees, the design basic earthquake acceleration is 0- 15g, the design earthquakes are grouped into the first group, the damping ratio under frequent earthquakes is 0-035, and the construction site is classified into three categories, the damping ratio under rare earthquakes is 0-050, and the site characteristic period Tg=0-5s. Determine the wind load of the tower main structure, and control the wind tunnel test load according to the standard wind speed 100 according to the strength; Displacement control should be carried out according to the wind tunnel test load principle of standard wind speed once every 50 years.
2-2 The calculation and analysis of the main results of structural analysis adopts various softwares and self-compiled programs, and the overall structure is as follows
Elasticity analysis is mainly based on ETABS, supplemented by MIDAS, including dead load and live load construction simulation analysis, response spectrum analysis and wind load analysis. ABAQUS and SAP2000 are used for elastic-plastic time history analysis to verify the performance of the structure under moderate and large earthquakes.
The main elastic analysis results are shown in table 1~ table 3. The analysis results of the two softwares show that the analysis results of ETABS and MIDAS are basically the same, both of which can meet the requirements of the code, and the structure is safe and reliable.
2-3 Design of Steel Plate Shear Wall
Steel plate shear wall (SPSW) structure is a new type of lateral force resisting structural system developed in 1970s. The steel plate shear wall unit consists of embedded steel plates, vertical edge members (columns or vertical stiffeners) and horizontal edge members (beams or horizontal stiffeners). When steel plates are continuously arranged from top to bottom along the structural span, a steel plate shear wall system is formed. As a new type of lateral force resisting member, steel plate shear wall has the characteristics of large elastic initial stiffness, large deformation capacity, good plastic performance and stable hysteretic characteristics. Up to now, there are dozens of buildings with steel plate shear walls as lateral force resisting structures, which are mainly distributed in high-intensity earthquake areas such as North America and Japan. Appendix 4 of China's Technical Specification for Steel Structures of High-rise Civil Buildings (JGJ99—98-98-98) stipulates the calculation standards and methods of steel plate shear walls. The design angle is to avoid buckling failure of steel plate, that is, the elastic buckling strength is taken as the design limit state of steel plate shear wall, and the elastic local buckling strength of steel plate is not used, so it is usually called thick steel plate shear wall. However, the development of thick steel plate shear wall is limited because of its high steel content. The core tube of Jinta office building has a large bay and the width-thickness ratio of steel plate shear wall is also large. The design using the concept of thick steel plate shear wall will greatly increase the cost. Jinta office building is popular all over the world at present.
The design concept of steel plate shear wall, that is, allowing the steel plate to buckle locally under the action of horizontal force, and using the tension field effect generated by the strength of the buckled steel plate to continue to resist the action of horizontal force, has the following five characteristics:
(1) Steel plate shear wall does not bear vertical load in principle, but it inevitably bears the influence of vertical load in practice (such as floor live load, etc.). ), resulting in vertical compressive stress;
(2) Under the combined design value of frequent earthquakes and wind loads, the design of steel plate shear wall meets the requirements of Appendix 4 of the Code (JGJ99—98-98-98), that is, only elastic deformation occurs without buckling (Figure 6a), and the buckling calculation of steel plate should meet the three-dimensional stress stability calculation formula of thin plate;
(3) In moderate and rare earthquakes, local buckling of steel plates is allowed, and the tension field effect generated after buckling of steel plates becomes the main mechanism to resist lateral force (Figure 6b);
(4) Under the action of moderate earthquakes and rare earthquakes, plastic hinges may appear at the ends of horizontal boundary elements (beams), but they shall not be damaged or lose strength;
(5) Under moderate earthquake, there will be no plastic hinge at the end of vertical boundary element (column). Under the rare earthquake, except the vertical boundary members below 16 story, plastic hinges can appear at the ends of other columns, but they cannot be destroyed or lose strength.
Through the above design concepts and methods, the steel plate shear wall of Jinta office building can meet the requirements of bearing capacity limit state and normal use state.
2-4 Construction Simulation Analysis
As a super-high-rise complex building structure system with outrigger truss and steel plate shear wall, the structural mechanical characteristics of gold tower are highly related to construction. The internal forces of steel tube column and steel plate wall are very different under different construction conditions, and because of the different construction progress of steel plate wall, the steel plate will produce different degrees of compressive stress during construction, which is also very important for the buckling analysis of steel plate. Therefore, the construction simulation analysis must be carried out during the design of Tianjin Tower, as shown in Figure 7. In the analysis process, the following factors are mainly considered:
(1) Installation sequence of steel plate shear wall: Early installation of steel plate shear wall is conducive to ensuring the overall stiffness of the structure at different stages in the construction process, which is conducive to the construction progress, but it is easy to cause the steel plate shear wall itself to bear a large vertical load, and the vertical stress difference between the inner and outer columns of the core tube is large; Late installation is the opposite.
(2) Installation sequence of outrigger trusses: Early installation of outrigger trusses is conducive to improving the structural rigidity and integrity at different stages in the construction process, which is conducive to the construction progress. At the same time, more internal load can be unloaded to the outer pipe string through the outrigger truss, which reduces the pressure value of the inner pipe string under constant load, but it is not conducive to the tensile design of the inner pipe string under the earthquake.
The construction simulation analysis adopts ETABS software, and the whole installation process is divided into 2 1 stages, each stage has different structural state and load state, and P-δ effect is considered in the construction process. The state after the completion of construction simulation is taken as the reflection of dead load on the structure, and it is combined with live, wind and earthquake in the subsequent design (small earthquake design stage), or as the initial state of elastic-plastic analysis of medium and large earthquakes.
In the design process, the above factors were compared and analyzed, and finally the steel plate shear wall system with delay 15 story and the installation and construction scheme of outrigger truss were determined, as follows:
(1) steel plate shear wall lags behind the installation of 15 main structure (column, beam and floor concrete);
(2) The inner tube support above the steel plate shear wall is similar to the steel plate shear wall, and it also lags behind the installation of the main structure 15 floor;
(3) Cantilever truss: diagonal bars are installed behind the main structure (column, beam and floor concrete) of 15 floor, and horizontal bars are installed in turn.
The above construction process plays the following roles
(1) The installation of the steel plate shear wall lags behind a certain floor, and a balance is achieved between the construction progress, the overall stiffness of the structure and the vertical stress of the steel plate shear wall itself, that is, under the premise of bearing a certain vertical dead load, the steel plate shear wall is designed to resist small earthquakes, which is beneficial to the overall stiffness of the structure and the construction progress;
(2) The outrigger truss is installed at a certain floor behind, so that the pressure of the inner and outer cylinders can be balanced, and the tension design at the bottom of the inner cylinder is more reasonable.
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