In the realm of construction, steel structures are gaining popularity due to their inherent advantages over traditional RCC structures. These include higher strength, durability, lightweight nature, speedy construction, easy fabrication, and resistance to fire, moisture, and pests.
Let’s delve into the intricate process of erecting steel structures, focusing on the step-by-step procedure for steel members and joint members, along with permissible tolerances.
Before initiating the erection process, it’s imperative to devise a comprehensive working scheme that incorporates safety precautions. The importance of this planning is emphasized in the safety guidelines detailed in the article, “Ensuring Safety in Structural Steelwork.”
Proper placement and grouting of anchor bolts in designed positions are crucial for fastening steel structures securely. Flexibility is achieved by providing anchor bolts in concrete foundations with anchor channels and bolt boxes.
Gaps between the foundation and structure should be filled with cement grout after proper positioning. Damaged structural members are inspected and rectified as necessary. The mating surfaces, including strips and fillers, must be meticulously cleaned before proceeding.
To ensure stability, structural members are firmly fastened using drifts, bolts, crossing bars, and temporary tacking before removing the erection crane hook. Special attention is given to lifting trusses with spans exceeding 12m, avoiding compression stresses in the bottom tie member.
Wind bracings, purlins, and suitable supports like rocker and roller bearings are incorporated for large-span steel members.
Accurate matching of holes in joint steel members is facilitated by using temporary bolts and drifts during the erection process. The location of bolts on both members is crucial for ensuring a secure joint.
Welding, riveting, and final fastening of permanent bolts are carried out only after thorough inspection of structural elements. The head bolts, nuts, and washers should be in perfect contact with the surfaces of structures.
When erecting steel members without a crane, the maximum tolerance for line and level is +/-3.00mm. For structures involving cranes, specific tolerances are outlined in Table 1.
Table 1: Tolerance in Erection of Steel Structure using Cranes
| Component | Description | Tolerance Allowed |
|---|---|---|
| Main columns and Roof posts | A. Shifting of columns axis at foundation level: | |
| 1. In longitudinal direction | ± 5.00 mm | |
| 2. In lateral direction | ± 5.00 mm | |
| B. Deviation of major column axis from vertical: | ||
| 1. Up to 10 m height | ± 5.00 mm from vertical | |
| 2. 10 m to 40 m height, per 30m length | ± 8.00 mm | |
| C. For adjacent pairs of columns prior to truss placement | ± 5.00 mm on true span | |
| D. Deviation of any bearing level from drawings | ± 5.00 mm | |
| E. Level difference between adjacent columns | 5.00 mm | |
| Trusses | A. Deviation at center of span or upper chord from vertical plane | 1/500 of span or 10 mm |
| B. Lateral displacement of top chord at center of span | 1/250 of truss depth or 20 mm |