8、 The embedded bolts of bearing shall not be inspected and accepted before the installation of steel roof truss

Before the installation of steel roof truss, the installation unit does not check and accept the anchor bolts embedded in the column head support by the civil engineering unit.In this way, it is not known whether the pre buried limb bolts are consistent with the design drawings and the dimensions of the reserved installation holes at both ends of the steel roof truss. When installing, it is found that the position, size and elevation are wrong or out of tolerance, so that the steel frame can not be installed. It needs to be lifted down and the bolts or the reserved holes at the end of the roof truss can be installed, which not only delays the construction period but also increases the construction costUse.

Preventive measures:

Before the installation of steel roof truss, the civil engineering, manufacturing and installation parties shall carry out the following inspection and acceptance on the civil engineering column head: check whether the size, elevation, pitch, exposed length of thread, etc. of anchor bolt are within the tolerance range, whether the span is consistent with the steel structure size, and whether it is consistent with the drawing requirements.The steel roof truss can be installed only after the handover acceptance is qualified, so as to ensure the correctness of the installation position, elevation, span, etc. 

9、 The span size of the steel roof truss is out of tolerance and does not fit closely with the joint plate at the end of the column

The span size of the steel roof truss is out of tolerance, that is, the span size of individual roof truss is too large or too small; there is a gap between the steel roof truss and the end joint plate which is connected with the column laterally.

Causes:

The former is that the manufacturing process of the steel roof truss is unreasonable, the arch is too large or too small (too large will produce negative deviation, too small will easily produce positive deviation), and it will be installed without correction.

The latter is caused by the steel column installation verticality out of tolerance and roof truss manufacturing span size out of tolerance.

Because the span size is out of tolerance, and it is not close to the joint plate of column end, the perpendicularity or parallelism of column will be affected, or the mechanical performance of column and roof truss will be affected.

Preventive measures:

(1) The same bottom sample or mould shall be used for the fabrication of steel roof truss, and the retaining iron shall be used for assembly to ensure the correct camber and span size.

(2) After the roof truss is welded and corrected, the embedded supports should be assembled with each other according to the span size position, so as to ensure the correct span and height and facilitate installation.In order to facilitate the adjustment of the span size during installation, the embedded connection support can not be assembled with the roof truss at first, but be attached to the roof truss with temporary bolts, so as to be connected according to the span size of roof truss and its specified position during site installation.

(3) Before hoisting, the roof truss should be carefully checked, and the out of tolerance parts should be corrected, and then the hoisting should be carried out after the span size is ensured.

(4) For non embedded connection support, if the hole position of column roof is inconsistent with that of roof truss support, external force shall not be used for forced positioning. Instead, elliptical hole or reaming method shall be used to adjust the location, and thick washer shall be used to cover and weld, and bolts shall be tightened.

If the roof truss is not adjusted by reaming or forced by large external force, the span of roof truss will produce infinite positive or negative deviation.The perpendicularity and lateral bending difference of the steel roof truss and skylight frame after installation exceed the allowable value of the specification.

The causes are as follows:

Improper operation methods and unreasonable process in the production of steel roof truss and window frame, such as inaccurate positioning of assembly retaining iron, horizontal assembly platform, inclined support plate at both ends or improper hoisting method.

Or steel column, steel roof truss and purlin are out of tolerance.For example, the verticality of steel column is out of tolerance, the elevation (height dimension) of column head plate is not uniform, the plane does not reach the required levelness, and the distance between adjacent steel roof trusses (upper chord) is inconsistent with the corresponding purlin position.

Due to the large deviation of perpendicularity and lateral bending, the force will not be in a plane, which will affect the mechanical performance and stability of roof truss and skylight frame.

10、 The installation quality of horizontal support does not meet the requirements

After the horizontal support of roof truss is installed, it will produce arch or down deflection, which exceeds the allowable value of the code.

The causes are as follows:

The size (length, hole center) of horizontal support is not accurate, and the position is not consistent with the roof truss combination connection.

Or the deflection of the cross support due to its own weight.Or horizontal support hoisting technology is unreasonable.

Because the quality does not meet the requirements, the support force is not in a plane, which reduces the mechanical performance of the bearing, and affects the lateral stability of the roof truss.

Preventive measures:

(1) Strictly control the dimensional deviation of component fabrication and installation.During hoisting, reasonable hoisting technology shall be adopted. For example, the length of cross horizontal support is long and the rigidity is poor. Round timber rod shall be used for reinforcement. The position of lifting point shall be reasonable to keep it in a plane as far as possible, so as to make the center of gravity of force uniformly bear force in the plane, so as to prevent bending and down warping deformation.

(2) When installing, the horizontal support should be slightly arched, slightly larger than the horizontal state, and connected with the roof truss, so as to eliminate the downward deflection.If the connection position has a large deviation and cannot be installed in place, the pulling tool shall not be used to force the connection into place with external force, so as to avoid lateral bending of the bottom chord of the roof truss or excessive camber or downward deflection of the horizontal support, and the greater internal stress of the connector.The horizontal support shall be fixed with temporary bolts and welded immediately after alignment.

11、 Installation bolt hole dislocation

The dislocation (displacement) of component mounting holes is not coincident, and the bolt cannot be penetrated,

The causes are as follows:

The bolt hole number line is not accurate, there is no template, and the projection production deviation is large.

Or the steel parts are small, and the accumulative assembly deviation is large.

Or bolt tightening degree is different, resulting in bolt hole displacement.

So it is difficult to install and fasten the components.

Preventive measures:

(1) Template shall be set for bolt hole drilling to ensure correct size and position.Before installation, the bolt hole and installation surface shall be trimmed.Pay attention to eliminate small assembly deviation of steel parts to prevent accumulation.The tightening degree of bolts shall be consistent.

(2) There should be at least two installation holes at each end of the steel structure member to reduce the hole position deviation caused by the steel member’s down deflection. Generally, the steel punch is used to pre select the upper and lower holes of the connector.The reasonable process of tightening the bolt is: the first bolt must be tightened for the first time. After the second bolt is tightened, check the first bolt and continue to tighten it to keep the same tightening degree.

12、 Missing welding between steel support and roof truss, column and other connecting plates

The installation of steel supports is fast. After the supports between columns and roof trusses are installed and corrected, they are temporarily fixed by positioning welding, and then the next section of column and roof truss support are installed.After the hoisting of all columns and roof truss is completed, the support permanent weld shall be welded and fixed.

The harm of this is that due to the low strength of the positioning welding, external forces (such as wind, hoisting collision, tether, etc.) are encountered during the construction stage, which will make the support positioning weld crack and lose its function, resulting in the instability of the column and roof truss, and in serious cases, the powerhouse bent will collapse.

Preventive measures:

After the supports between columns and roof trusses are installed and corrected and fixed by temporary positioning welding, another group of welders shall immediately conduct full welding for permanent fixation, and strengthen the inspection to prevent the missing weld length and height of individual joints. When the support is subjected to external force, the welding seam of connection node is damaged, which makes the column and roof truss unstable.

13、 The influence of sunshine and temperature difference is ignored in steel column installation

The steel column installation ignores the influence of sunshine and temperature difference, and does not make temperature difference correction. When correcting steel column under sunlight, the temperature on the sunny side of the column (referred to as the sunny side) is higher than that on the back sunny side (referred to as the negative side). The temperature difference between the two sides will make the steel column bend to the shady side, resulting in a horizontal displacement of the column. With the change of sunshine direction, the bending of steel column will also change.

Therefore, if the influence of sunshine and temperature difference is ignored in the installation of steel structure, it is difficult to determine the reference state of component correction and affect the installation accuracy.Similarly, if the steel structure installation ignores the influence of temperature difference, does not make the temperature difference correction, or does not take certain measures to eliminate the temperature difference, it will also affect the installation accuracy of the steel column or increase the installation stress.

Preventive measures:

During the installation and correction of steel structure, the deformation of components caused by sunshine temperature difference should be considered, and some measures should be taken to eliminate or reduce the influence of sunshine

(1) Sunshine is more sensitive to the influence of single steel column, so other load-bearing components of the connection system should be installed in time after the steel column is installed in place to form a relatively stable space unit system, so as to reduce the displacement impact of sunlight on the end of steel column.

(2) The review and final correction of steel column or column beam structure section should be arranged in the morning or after 16:00 p.m. or cloudy day when the sunlight has little influence.

(3) Finally, the joints of the steel structure after the final correction should be fixed in time.

(4) The influence of temperature difference is mainly on the steel column with large length. For the column above 10m, the temperature difference conversion should be conducted for the length measurement value in each stage of construction, and the conversion standard is 20 ℃; for the steel column within 10m, the influence of temperature difference can not be considered generally.

14、 After the steel structure is installed to form a space unit

After the steel structure is installed to form a space unit, the column bottom is not grouted and fixed in time. After the space stiffness unit is formed in the single-layer steel structure, the space between the column bottom plate and the top surface of the foundation is not grouted and fixed in time.

After the space stiffness unit has been formed in the steel structure section installation, the structure is no longer necessary to be corrected. However, there is still a gap between the bottom of the steel column and the top surface of the foundation by pouring fine aggregate concrete, and there is still a gap to form a hinge. Once the steel structure is subjected to external force, it will move, resulting in the deviation that cannot be corrected (corrected) and even make the structure skew.

Preventive measures:

After the steel structure is installed to form a spatial stiffness unit, the gap between the bottom plate of the column and the top surface of the foundation should be poured with fine aggregate concrete in time, and finally fixed, so that the bottom end of the column will be changed from hinged connection to fixed connection, which will enhance the overall stability of the whole.

15、 Deformation and coating shedding of steel members

During the installation of steel members, local deformation, paint coating peeling off and damage occurred.

The causes are as follows:

During the installation of components, improper binding positions of supporting points and lifting points in transportation and stacking, disordered installation sequence, collision of components or forced placement of external forces cause deformation of components, resulting in installation difficulties, forming over limit stress and affecting structural bearing capacity.

The durability of the structure will be affected by the damage and falling off of the paint coating due to friction, impact or poor painting quality.

Preventive measures:

(1) The positions of supporting points for component transportation, stacking and hoisting and binding points of components shall be correct to prevent bending and deformation of components.The installation shall be carried out according to the sequence determined by the scheme. Collision shall be prevented during hoisting. When the installation cannot be carried out, external force shall not be applied to force the installation in place, so as to avoid over limit stress and deformation of components.

(2) During the binding of components, sack pieces and waste tires should be padded between the sling and the edges and corners of the components, so as to avoid friction and collision between the components during hoisting, so as to prevent the components from wearing and the paint coating falling off.Before installation, the painting quality of the components shall be inspected. If it does not meet the requirements or local parts fall off or rust, it shall be repaired.