第2期 · 20181121期 TALKER-黄用军
迪拜时间10月22日，2018 CTBUH 国际高层建筑与都市人居会议在阿联酋举行。作为中国超高层建筑设计的领先实践者-AUBE欧博设计董事副总经理、EN结构中心总经理黄用军先生及AUBE欧博设计结构中心EN2室副总监何远明先生受邀出席，与千余位来自全球高层建筑设计领域的专家学者进行了学术交流，并发表演讲，引发行业内关注。
The China Resources Headquarter Tower with building height of 400m is located in the Shenzhen Bay of Shenzhen City, as an important component of the super headquarters base of Shenzhen Hou Hai. Its architectural style is unique and original, which resemble a narrow-topped Spring Bamboo. Next to it is the China Resources Shenzhen Bay Sports Center, “spring cocoon”, these two symbolizes “spring shoots after the rain”.
Close column frame and core tube system is adopted without strengthened stories.
There are 56 columns in the outer frame, size shown subsequently. The largest thickness of the tube shear wall is 1450mm at the bottom.
The basement is consist of 4 levels. B1 mezzanine which opens up to the Sunken Plaza lined by retail and provides a continued entrance lobby for some of the people arriving from the Metro. The B1 level provide direct connection the underground retail esplanade of the master plan as well as the Museum. It is the primary access point to the tower from the metro station. Level B2 is mechanical level with loading and level B3 and B4 are car park levels.
With its circular plan the ground lobby is symmetrical and organized in quadrants and engages equally with north, south, east and west.
Zone 1 is located between levels 5~13 and has column free space spans ranging from approximately 17 meters to 18 meters.
Zone 2 is located between levels 15~23 with column free space spans ranging from 16 meters to 18 meters.
Zone 3 is located between levels 28~36 and has column free space spans ranging from approximately 18 meters to 17 meters.
Zone 4 is located between levels 38~46 with column free space spans ranging from 17 meters to 15 meters.
Zone 5 office floor is located between level 50~61. It consists of 8 levels of typical grade A office space, 2 levels of VIP executive office floors, a business center level and a dining level.
The CR office is between level 50~61. The continuous ten-storey floor is partially open, and the floor girder partition is arranged, so the cross-storey column has a larger slenderness ratio, which has a greater impact on the stability of the column.
The Sky Hall is located on level 66 at 331.5 meters above ground. A 70m high conical steel latticed shell is adopted. It is an event space with a 360 degree view and is capped by the diagonal grid structure of the spire. The Sky Hall Level is connected to two levels of amenities below. It is accessed elevators at the Sky Hall Reception Level 64 or by decorative grand stair at the north side of the floor spanning an atrium connecting all three levels.
亮 点 与 难 度
Highlights or nodus
风 荷 载
荷载规范规定，深圳10年的基本风压为0.45 kN/m2，50年的基本风压为 0.75 kN/m2 ， 构件强度设计采用规范50年基本风压的1.1倍风荷载
The basic wind pressure in Shenzhen is 0.45 kN/m2 in 10 years, 0.75 kN/m2 in 50 years, and the strength design uses 1.1 times of the 50 year benchmark wind pressure in the Chinese load code.
As the CR tower up to 400m, it has special body shape and lots of high-rise buildings around, so the wind load distribution of code may not cover the worst wind load. Contrast tests were made by RWDI and SCUT. Wind tunnel test results show that the analysis results of two independent wind tunnel test units are more consistent, and the wind tunnel test results are reliable.
抗 侧 力 体 系
Lateral Resistance System
To increase structural redundancy, the structure must have multiple system to resistant the lateral loads such as seismic force and wind loads. In this project, the shear sharing ratio of outer frame is less than 5%, however 10% is the minimum value required by code. As the close column frame without strengthened stories has weak frame axial stiffness, it’s hard to meet the requirements. So, the core tube shear wall are set to bear all lateral shear, which is magnified to 110%, to ensure the tube has sufficient bearing capacity. At the same time, the shear of the frame is adjusted to 10% to ensure limited capacity to lighten the burden of the tube.
According to geological and hydrological conditions, comparisons between man-dug caisson and bored pile are made in the SD. 56 man-dug caissons is adopted in the DD. According to the engineering experience of Pingan IFC, pile layout is changed to 44 man-dug caissons with an expanding bottom in the CD. The cap thichness is 3.5m under the core tube,and is 2.5m for the other.
搭 接 墙 转 换
Lapping Wall and Oblique Wall
Same for the core tube, two transform are emerged as shown. In the 1F, the outline of tube is square. Four corner are cut 3041mm going to the 4F, leaving 2~3F to realize the lapping.
Up to the top zone, the outline of the tube is changing from tangential square to square. Using oblique wall conversion to make this transformation.
斜 墙 转 换
Oblique Wall Transform
Oblique wall transform is set on the 48~49F, at 240.95~256.45m. Horizontal force is produced by the oblique wall under vertical load, so slab and beam is the main medium to transmit the force to neighbouring vertical members. Shear stiffness of close columns is much smaller than that of the core tube, so most force can get self-balance in the tube. A small amount of horizontal force may appear in the outer frame slab theoretically. Strengthening measures should be made in the whole floor slab.
Actually, the slab in the tube and the outer frame are not build when the oblique wall is completed for the reason of construction procedure. The vertical load is produced by the gravity of the wall itself and the load of construction platform, including the construction live load. Generally, the frame will be 15~20 floors later than the core tube during the construction. The oblique wall appears on the 48F, and the whole building is just 66F tall. This case that the tube is completed with no frame slab and beam at the oblique wall position is calculated.As the result shown,the oblique wall cannot support the load by itself without slab,and coupling beam is the key component.
According to parameter analysis, the oblique wall can just afford 6 floors above, so the floor frame and slab of 48F must be completed when the core tube is up to 56F.
平 面 布 置
According to the architectural plan, plan A is an apparent choice. However, some owners may want to buy two floors or more. Stairs indoor would be necessary in this case. In consideration of the flexibility of sale and rental, some adjustments are made, shown as the plan B.
塔 冠 结 构
Cone top structure
Elastic eigenvalue analysis shows that the critical eigenvalue reaches 28 under gravity, and the first instability mode under gravity is shown as above.
The initial geometric imperfections of various latticed shells have great influence on the stability bearing capacity and should be considered in the calculation. The geometric initial defects of reticulated shells include the installation deviation of joints, the initial bending of bars, the eccentricity of bars to joints and so on. The results show that the initial geometric imperfection is the most unfavorable value when the initial geometric imperfection is distributed according to the lowest order buckling mode, so the geometric initial imperfection imposed is based on the first order buckling mode.
完 全 偏 心 节 点
Totally Eccentric Joints
To meet people’s desire of column free space in a luxury office, totally eccentric joints are adopted. It’s the first time to use this kind of joints to a tall building up to 400m, which is a big challenge.
As mentioned before, lots of totally eccentric joints are used in this project. Joint stiffness input in the calculation model is simulated by finite element analysis. Just one slab zone is linked between the frame column and beam. How to make it have reliable path of force transmission and easy to construct is the key link.
交 叉 节 点
A bamboo shoot, both ends are tiny and the middle is large. There are 56 columns in the middle zone, and it gets narrower on the top and the lower zone.
There are two columns in the first floor, and three columns in the second floor. The minimum cross section of joint area is much smaller than the cross section itself.How to support the upper part of the structure is the most important matter in this project.
多 柱 交 叉 节 点
Multi-column Intersection Joints
Since the façade of the building is curved, each intersecting bar is not in the same vertical plane. The connecting plates in the joint area are misaligned and the number of the junction plates is large which lead to complex force condition.
A big column grid is required at the bottom,and the transition is completed by the oblique grid. The section of the upper and lower column is not very different. There are 3 columns on the upper floor and only 2 columns on the lower floor, forming a fine waist at the intersecting joints of the bars. The fine waist leads to a significant reduction of the axial compression area. Special analysis for its load carrying capacity is required.
Since the elevation is an arc, the panel is designed as a plane in joint zone and the elevation of the joint zone is a straight line, which is the secant of the arc line. The upper and lower columns theoretically intersect at one point, which is the theoretical center of the steel column. However, the actual center of the section has some deviation from the theoretical intersection. Therefore, under the axial force of the upper and lower columns, the joint zone is not an axially loaded member and will have some bending moments and torque moments.
The joint zone shows the mechanics characteristics under the bending moment action, mainly due to the bending moment generated by the component Fx of the column axial force in the direction perpendicular to the face panel. In the same way, the bending moment that is out of the plane of face panel of the joint zone will also be generated. The internal force in column C1 and column C2 will differ in value, forming a couple of forces: under the action of the Fy2 component of column C2, there will be some torque Mz in the joint zone. Therefore, the joint configuration causes additional bending moments and torques in the joint zone. It is found through calculation that the additional stress generated by the bending moment in the joint zone accounts for 40% of the axial compressive stress of the joint and cannot be ignored. The joint design should be fully considered to ensure the structural safety.
In the load case of frequent earthquake at –x direction, the stress cloud diagram and plastic strain diagram are shown. Stress concentration occurs at the joint position of the components (which can be eliminated in actual construction by smoothing). Only part of area yielded and most of area still remain elastic working stage which meet the requirements of joint design.
Under the action of rare earthquake at +y direction, the stress and plastic deformation are shown. It can be seen from the figure that the stress concentration occurs at the position where the cross section is changed, and only local yielding happened, and most of regions still remain in elastic working condition.
A stable bearing capacity is applied at the bottom end of the column. The three-direction displacement is constrained at the top end of the column. The equal-strength joint check is performed on the joint.
It can be seen that most area of the joint is in elastic working condition except that the thin waist slightly yields, which satisfy the requirements of joint design.
The results of experiment and finite element analysis show that the joint is in elastic working condition under the action of design load, and the thickness of each plate is basically reasonable which can transfer the vertical load effectively. The joint has good bearing capacity, stiffness and ductility.
The results of the finite element analysis are consistent with the experimental results and have a high degree of confidence under the action of design loads.
The simplification of the configuration of the joints will bring additional internal forces to the joints. In this project, the additional stress caused by the treatment of the face panel of the joints accounts for 40% of the initial stress and cannot be ignored.
The reliability of force transfer path and the possible influence of the detailed configuration of joints should be comprehensively analyzed during the joint design to ensure the safety.
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