The installation of a main steel truss is one of the most important stages in a steel structure project. Because main trusses usually have large dimensions, considerable weight, and high installation accuracy requirements, the lifting, positioning, temporary stabilization, alignment, and connection procedures must be carefully planned.

A proper installation sequence helps ensure structural stability, construction safety, and dimensional accuracy throughout the steel erection process.

1. Main Truss Lifting

The main truss is generally lifted using two lifting points and rotated into its final installation position by crane.

When the truss is lifted to approximately 1 meter above the ground, the component should be checked and leveled to ensure smooth positioning.

Because large trusses may have relatively large cross-sections, they can be vulnerable to deformation or instability during lifting and turning.

To reduce this risk, temporary reinforcement should be installed before lifting.

For example, temporary steel pipes or reinforcing members can be installed along the truss to improve its overall stiffness during lifting.

2. Trial Lifting Before Formal Installation

A trial lift should be carried out before the main truss is officially lifted into position.

During trial lifting, the truss may first be raised approximately 200 mm above the ground and temporarily held in position.

The installation team should then inspect:

• Crane stability

• Ground bearing conditions

• Lifting points

• Wire ropes and slings

• Connection points

• Temporary reinforcement

• Overall balance of the truss

Only after confirming that all lifting components and supporting conditions are safe should the formal lifting operation begin.

Additional safety wire ropes may also be used where required to provide extra protection during lifting.

After the truss is positioned, preliminary alignment should be carried out immediately.

Temporary guy ropes, angle steel supports, or other bracing systems should then be installed to keep the truss stable.

3. Main Truss Alignment

After the truss is positioned, its alignment must be checked carefully.

The main items include:

• Horizontal position

• Elevation

• Verticality

• Support position

Horizontal Position

The horizontal position is generally controlled during support and bearing installation.

The centerline of the truss should match the designed structural axis.

Elevation Adjustment

The elevation at one end of the truss can be adjusted during bearing installation.

The opposite end can be adjusted using temporary support frames, steel plates, or shims until the required design elevation is achieved.

Verticality Adjustment

The verticality of the main truss can be adjusted using guy ropes or temporary bracing systems.

The alignment should be checked carefully to prevent multiple trusses from leaning in the same direction.

4. Temporary Stabilization of the Main Truss

Temporary stability is extremely important during main truss installation.

After the first main truss is installed, temporary guy ropes, braces, or other stabilization measures should be installed immediately.

The first truss should not remain unsupported while subsequent components are being erected.

Once the second main truss is positioned, secondary trusses or connecting members should be installed as soon as possible.

These members connect the two main trusses and gradually form a stable structural system.

Where required by the design and approved construction procedure, the connections can then be welded or bolted.

5. Installation of Adjacent Main Trusses

Adjacent main trusses should be installed using the same procedure as the first truss.

The general sequence includes:

1. Lifting

2. Positioning

3. Temporary fixing

4. Alignment

5. Stabilization

6. Connection to adjacent structural members

Each truss should be checked before temporary supports are removed.

6. Installation of Secondary Trusses

Secondary trusses are generally installed after two adjacent main trusses have been positioned and their primary connections have been completed.

The secondary trusses help connect and stabilize the main structural system.

During installation, attention should be paid to:

• Connection accuracy

• Member orientation

• Elevation

• Spacing

• Welding or bolting quality

• Structural alignment

Secondary members should be installed according to the approved erection sequence to avoid unnecessary deformation or instability.

7. Complete Installation of Main and Secondary Trusses

The erection process continues in sequence until all main and secondary trusses within the designated construction area have been installed.

After the structural members are installed, all required welding and bolted connections should be completed.

A comprehensive inspection should then be carried out.

Inspection items normally include:

• Truss position

• Elevation

• Verticality

• Structural dimensions

• Weld quality

• Bolt connections

• Temporary support removal conditions

• Overall structural stability

The completed steel truss system should comply with the project drawings, erection requirements, and applicable engineering standards.

Key Points for Main Steel Truss Installation

Successful steel truss installation depends on several important factors:

• Accurate lifting point selection

• Proper temporary reinforcement

• Trial lifting before formal erection

• Reliable temporary bracing

• Accurate alignment

• Correct erection sequence

• Timely installation of secondary members

• Proper welding or bolted connections

• Continuous safety inspection

• Final dimensional and quality inspection

Conclusion

Main steel truss installation requires careful coordination between lifting, positioning, temporary stabilization, alignment, connection, and inspection.

For large-span steel structures, special attention should be given to truss stability during lifting and before the complete structural system is formed.

A well-planned erection sequence can improve installation efficiency, reduce deformation risks, and ensure that the completed steel structure meets the required safety and quality standards.