A complete high-quality steel structure building, in addition to high-quality production quality, the assembly of various components is also a key stage, this stage is called “on-site installation”, good materials without good installation, it is also difficult to make a good steel structure building. 　　

 1、 The pre assembly site of steel structure should be flat and solid. The strength and stiffness of the pre assembled support frame should be checked. The accuracy of each supporting point can be measured and adjusted point by point with measuring and testing instruments.The supporting frame of heavy and large trusses shall be checked and calculated. According to the component type of the pre assembled unit, the pre assembled support pad can be in the form of steel platform, support stool and section steel. 　　

 2、 The datum point and elevation line shall be set for pre assembly. 　　

 3、 If necessary, temporary connection plates can be set for steel members before pre assembly. 

4、 According to the structural form, the pre assembly can adopt single pre assembly, plane pre assembly and three-dimensional pre assembly.The steel members shall be assembled in free state, and shall not be fixed by force.The credit shell structure is a three-dimensional pre assembled well, which can be equipped with clamps and clamps, and other structures are generally plane pre assembled. The pre assembled components shall be in free state and shall not be fixed by force. The pre assembled quantity can be implemented according to the design or contract requirements.　　

5、 The steel members shall be pre assembled, hoisted and positioned according to the site setting out dimensions.Site samples shall meet the following requirements. 　　

 ① The setting out size shall include the control size of construction drawing, the required camber value, the welding shrinkage allowance of welded joint and other required control dimensions. 　　

 ② The site setting out shall correspond to the vertical projection of the pre assembly, and shall include the center line of the bar and the datum line of the node end face. 　　

 ③ Before pre assembly, the size of site setting out shall be checked. 　　

 ④ The mark of points and lines for setting out shall be clear. 

6、 The pre assembly sequence and assembly unit of steel structure shall be determined according to the design requirements and structural form, and the main component shall be first followed by the secondary component.The portal steel frame shall be assembled vertically with steel beam first, and then assembled with steel column on the plane after correction.

 7、 For multi-layer laminated plates connected by high-strength bolts and ordinary bolts, punching screws should be used for positioning and temporary bolts should be used for fastening during pre assembly. The number of trial installed bolts in a group of holes should not be less than 20% of the number of bolt holes, and no less than 2 bolts.

 8、 When the passing rate of the holes on the stack does not meet the above requirements, the holes should be repaired.When the staggered hole is less than 3.0 mm, reamer, milling cutter or file cutter shall be used to enlarge the hole, and the hole diameter after reaming shall not exceed 1.2 times of the bolt diameter. When the staggered hole is more than 3 mm, welding rod shall be used to repair and block the hole, and the welding rod shall be smooth without concave convex phenomenon. The low oxygen type electrode matched with the base metal shall be used.It is strictly forbidden to fill the hole with steel block. Filling with steel block is actually a false hole plugging, which will cause serious consequences and is absolutely not allowed. 

9、The member shall be in a free state during dimensional inspection.The so-called “free state” means that in the pre assembly process, temporary fixed components such as clamps, clamps, spot welding and tensioning devices can be used. After adjusting the size of each part, no more than 1 / 3 and no less than two ordinary bolts are used to fix each group of holes in the connection part, and then the fixture, central fixture, spot welding, tensioning device and other temporary fixing devices can be removed to check the size of the spare parts.

 10、 When the components in the pre assembly unit are connected by friction surface, the tightness between the plates at the friction surface connection shall be checked. The inspection method is to plug the edge depth of the inserted plate by 20 mm. The clearance between the plates shall meet the following requirements. 

11、 After the pre assembly is completed and passed the self inspection, the supervision unit shall be invited to carry out acceptance inspection and make quality records.

 12、 After the pre assembly of steel structure is qualified, the center line, control datum line and other marks shall be marked, and the positioner shall be set accordingly.