by Author | Steel Structure Business Department of the Third Construction Co., Ltd.
of China Construction Fifth Engineering Bureau (He Jie, Zhu Qiwu, He Guiyuan, Zeng Qihai) With the improvement of steel structure construction technology, the design of steel structure joints is becoming more complex, with strange shapes, and the phenomenon of overweight, over-length and over-width of steel members is common.
The design of huge overweight components has brought higher requirements to the lifting equipment.
How to scientifically and economically lift overweight components in sections under the condition that the lifting equipment has been determined is a difficult problem.
During the implementation of Changsha Shimao Plaza super-high-rise project, the huge and overweight components were split at the position where the steel components inevitably need to be segmented during the fabrication, which effectively reduced the weight of single hanging components, and ensured the structural quality and construction safety.
[Project overview] Changsha Shimao Plaza is an urban complex composed of super high-rise office buildings and commercial podiums.
There are 4 floors underground, 5 floors above the ground podium and 75 floors of tower, with a total building height of 348.5m and a total building area of about 230000 m2.
The project site is located in the center of the urban area, and there are other projects under construction on the north and southeast sides of the adjacent area.
The construction site is extremely small.
The steel members can only be transported to the construction site by the temporary construction road on the northeast side.
The heavy steel members are stacked in the steel member yard on the northeast side.
The steel members on the southwest side are only used for stacking light members, and a jib tower crane is used for unloading and hoisting the steel members.
The structural form of the tower in the layout plan is concrete-filled steel tube frame+concrete core tube+outrigger truss system, wherein the outrigger truss is located at 21-24F, 37-39F and 51-54F respectively.
Diameter of conventional round pipe column of outer frame φ 900～ φ 2500mm, wall thickness 18-32mm.
After the installation of on-site hoisting equipment, the wall thickness of the steel pipe column at the location of the nodes connected with the outrigger truss buckling restraint support and chord is changed to 55~60mm, and the designed joint vertical plate penetrates the steel pipe column.
The steel pipe column of the outer frame of the reinforced section is divided into sections according to one layer, and the component weight still exceeds the lifting performance of the existing tower crane, which cannot meet the lifting requirements.
Node splitting · splitting principle The split component must meet the structural safety of the original design and meet its use function; The disassembled components can meet the requirements of long-distance transportation; The weight of the disassembled components can meet the lifting performance requirements of the lifting equipment at the construction site; After the component is disassembled, the number of original welds shall not be increased as much as possible to reduce the safety and quality risks of the structure· Component analysis: under the action of 1.5 times of control load on the first stiffening layer of the giant super-heavy outrigger truss node, only the steel at the supporting connection end reaches yield, most of the connecting gusset plates and stiffening plates are elastic, and the steel pipe is elastic.
Under the control load, the first stiffening layer of the section steel stress is the giant over-weight outrigger truss node, which is 4584mm long φ two thousand and five hundred × 55mm steel pipe column, – 80 through steel pipe column × three thousand three hundred and forty-four × 4949mm gusset plate and 40mm thick diaphragm.
The circumference of the round pipe column is 7850mm, and two 2300 pieces are required × The 7850 steel plate is processed by rolling and then assembled and welded.
There is inevitably a circumferential splicing weld in the middle of the steel column.
The gusset plate and diaphragm plate can be directly finished by blanking the whole plate.
The first strengthening layer of the giant super-heavy outrigger truss node · splitting scheme will split the giant outrigger truss node into three parts and make them in the factory without increasing the number of original welds.
The vertical plate is manufactured as a whole in the factory, and two 2300mm steel columns and their corresponding diaphragms are processed in two parts.
After the steel pipe column is processed and formed, two “T” shaped supports are added at one end close to the slot opening and “m” shaped supports are added at the other end to prevent the deformation of the steel pipe column during the slot opening, transportation and hoisting.
When the steel pipe column is grooved in the factory, a 100mm long pull joint shall be reserved every 800mm along the vertical direction, which shall be cut before the installation on site to avoid the increase of the deformation of the component due to premature removal.
The steel pipe column I shall be installed at the node.
After the measurement and correction, the welding with the upper column shall be completed.
After the retest is qualified, the next process shall be started.
Once the steel pipe column is installed in place, remove the “m” shaped support and pull node respectively.
During the removal of the tie point, the diameter change of the slotted end of the steel pipe column shall be tracked and measured in the whole process.
When the deformation is large, the construction shall be suspended and measures shall be taken for correction.
Install the vertical plate, measure and position it, temporarily weld and fix the vertical plate, and loosen the hook of the tower crane after confirming the safety and stability of the vertical plate.
Insert the vertical plate into the steel pipe column and install it in place.
Remove the secondary pull joint of the steel pipe column.
Install the steel pipe column II.
After measurement and positioning, temporarily weld and fix it.
The steel pipe column II shall be installed from the inside to the outside, from the bottom to the top.
The transverse weld between the diaphragm and the vertical plate shall be welded first, then the transverse weld between the butt weld of the steel pipe column, and finally the vertical weld between the vertical plate and the steel pipe column.
Thick plate welding adopts electric heating for pre-welding preheating and post-welding heat preservation.
The preheating zone is located on both sides of the weld groove, with a width greater than 1.5 times of the plate thickness at the welding point, and no less than 100mm.
The preheating temperature is measured at the back of the heating surface.
The minimum preheating temperature before welding is 80 ℃.
The interlayer temperature shall be controlled within 230 ℃.
The heat preservation temperature after welding is 250~350 ℃, not less than 1.5h.
After welding and ultrasonic flaw detection, remove all reinforcement measures.
Re-measure the whole node and record the data.
[Conclusion] During the construction of the outer frame steel structure of the strengthened floor of Shimao Plaza Project, the technology of giant overweight outrigger truss node splitting and installation was adopted, which successfully solved the problem that the weight of the giant overweight outrigger truss node in the later design exceeded the lifting performance of the lifting equipment and could not be lifted.
On the premise of not affecting the structure safety and use function, the giant node is split, which effectively reduces the weight of the single hanging member, reduces the cost of construction measures, speeds up the construction progress, and provides an application example for the construction technology of the split and installation of the giant overweight outrigger truss node in the future.
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