As a kind of steel structure, steel frame flat roof pipe truss structure has the advantages of excellent seismic grade, light weight, flexible use of building space, short construction period and so on, which is widely used in modern architecture.The traditional installation process of steel frame flat roof pipe truss is from the top to the top, first installing the lower shear wall, steel column and steel beam, and then installing the upper flat roof pipe truss.However, fully considering the uniqueness of some new projects, if the traditional process is adopted to carry out engineering construction, and the flat roof truss structure is installed after the installation of the lowest rigid structure, it will lead to the lifting machinery moving around the site and the battle position is difficult; if the vertical lifting machinery such as crane is selected, the necessary model selection is large and the rental cost is high,Furthermore, it endangers the installation difficulty coefficient and installation progress of all engineering projects, and expands the safety risk, which is not good for the safety work.

Therefore, the new project of Hebei Hongji Shunda Steel Structure Engineering Co., Ltd. of steel structure enterprise adopts the top-down method to install the steel structure of landing hall, which gets rid of the traditional construction process, facilitates the engineering construction, saves the construction period and costs.In this paper, according to the specific capital construction experience of landing hall project, the reverse method is introduced in detail.

The steps of this method are as follows: steel structure embedded parts → steel tube concrete column installation → flat roof main bent structure on-site assembly → flat roof main bent structure installation → flat roof secondary bent structure on-site assembly → flat roof secondary bent structure installation → first floor rigid column installation → second floor rigid beam installation → steel structure overall engineering acceptance.

1.Embedded parts of steel structure

The steel structure embedded parts shall be accurately measured according to the engineering drawings, and the construction setting out and positioning shall be carried out. After the accurate positioning, the length, size and design elevation of the anchor bolts shall be carefully checked, and the embedded bolts shall be fixed.Before the basic pouring of concrete, a part of the screw mouth of the embedded chemical bolt is wrapped with plastic film to prevent the environmental pollution caused by the wire mouth of the anchor bolt during the cast-in-place concrete.After the basic cast-in-place concrete is carried out, the residual concrete on the embedded bolts and screw ends shall be removed immediately.

2.Installation of concrete filled steel tubular column

Step 1: after the concrete pouring of embedded parts, embedded parts and basic cast-in-place concrete reaches the standard, the installation and welding of the first section of concrete-filled steel tube column shall be carried out.Firstly, the steel beam is transported into the site, then the hoisting machinery is in place to carry out the lifting of the steel beam. After the steel beam is positioned, the gas shielded welding and cable wind rope are used to carry out temporary fixation. After the calibration, the steel beam is fully welded and the concrete is poured with self compacting concrete.

Installation plan of concrete filled steel tubular column

Step 2: after the installation of the first column, carry out the installation of the second section of steel beam, erect the actual operation service platform on the top of the first column, lift the second section of column after the crane is in place, fix the steel beam temporarily with gas shielded welding and cable wind rope, and carry out penetration welding after calibration.After welding, self compacting concrete shall be poured.

Installation plan of concrete filled steel tubular column

Step 3: after the installation of the second column, the installation engineering construction of the three section column shall be carried out. The actual operation service platform shall be erected on the top of the second column. After the crane is in place, the three section column shall be lifted. After the steel beam is in place, the gas shielded welding and cable wind rope shall be used to temporarily fix the steel beam, and the welding penetration shall be carried out after calibration.After welding, self compacting concrete shall be poured.Part of the shear wall is installed.

3.Assembly and installation of sequence bent structure on site

Assembly of sequence truss structure: 

The first step: carry out accurate positioning and drawing lines of the jig frame on the hard bottom leveled road surface, and use a 25 ton crane to assemble the jig frame.

The second step: assemble the bottom chord of truss structure and fix it temporarily.

Step 3: install the upper link and the intermediate level bar and carry out temporary fixation.

Step 4: install the diagonal web members, assemble and carry out electric welding on all the intersecting joints.The truss structure is assembled, and then the next truss segment is assembled again until the whole truss structure is assembled.After the assembly of the whole truss structure is accurate, it is lifted to the top of the column according to the section.

Installation of sequence truss structure:

The first step: the 100 ton crane is used to install the temporary support point jig frame of the main truss structure.

The second step: 350 tons crawler crane is used to install the first segment module of the main truss structure.

Step 3: install the second segment module of the main truss structure.

Step 4: install the third segment module of the main truss structure.

Step 5: unload and dismantle the temporary support point platform for the formwork support system, and weld the two sides of seamless steel pipe column to avoid collapse, so as to avoid deformation and collapse. 

Step 6: apply 100 ton crane to install temporary support point jig frame of secondary truss structure.

Step 7: apply 350 t crawler crane to install the first segment module of the secondary truss structure on both sides of the main truss structure.

Step 8: install the second segment module of the secondary truss structure on both sides of the main truss structure.

Step 9: unload the temporary formwork support system of two sub truss structures which have been installed.

Repeat the above installation process to the installation of flat roof bent structure.

4.Installation of first floor rigid column and second floor rigid beam

The last step is to install the comfortable column and stiff beam in order from the inside out, which can ensure the smooth line of the crane.So far, the steel structure installation project of landing hall is completed.

The top-down method of steel structure installation of landing hall properly uses the engineering construction site with narrow indoor space. Firstly, the idle space is used to enter a part of flat roof truss structure with large hoisting machinery installation difficulty coefficient, and then the first layer of stiffening column and the second layer of stiffening beam are installed in the order of inward type and outer type, which prevents the application of hoisting machinery of large size and specification due to the restriction of the site, and ensures the safety of crane Adjust measures to the time.The practical operation of the project construction is convenient, the production and manufacturing efficiency is high, the cost is reduced, the project progress is accelerated, and the construction period is reduced.