STEEL FABRICATION PROCESSES BASICS AND TUTORIALS

STEEL FABRICATION BASIC PROCESSES
What Is Steel Fabrication?

When considering fabrication, as well as erection of the fabricated product, the designer must taken into account contractual matters, work by others on the construction team, schedule implications of the design, and quality assurance matters.

Fortunately, there are well established aids for these considerations. Contractual questions such as what constitutes structural steel, procedures for preparing and approving the shop detail drawings, and standard fabrication procedures and tolerances are all addressed in the AISC’s Code of Standard Practice.

Insights on economical connection details and the impact of material selection on mill material deliveries are generally available from the fabricator’s engineering staff. These engineers are also able to comment on unique erection questions.

Quality assurance questions fall into two categories, fabrication operations and field operations. Today, sound quality control procedures are in place in most fabrication shops through an AISC program which prequalifies fabricators.

There are three levels of qualification: I, II and III, with Level III being the most demanding. Fabricators with either a Level I or Level II certification are suitable for almost all building work. Most engineers incorporate the AISC’s Code of Standard Practice in their project specification.

Shop Detail Drawings

Detail drawings are prepared by the fabricator to delineate to his work force the fabrication requirements. Because each shop has certain differences in equipment and/or procedures, the fabricator develops details which, when matched with his processes, are the most economical.

To accomplish this end, the design drawings need to be complete, showing all structural steel requirements, and should include design information on the forces acting at connections.

Designers should avoid specifying deck openings and beam penetrations through notes on the drawings. This is a frequent cause of extra costs on fabrication contracts.

Fabrication Processes

Mill material is cut to length by sawing, shearing, or flame cutting. Columns may also be milled to their final length. Holes for fasteners are drilled or punched.

Punched and reamed holes are seldom used in building construction. Cuts for weld preparation, web openings, and dimensional clearances are flame cut. AISC guidelines for each of these processes are associated with the AISC’s fabricator prequalification program.

Welding for building construction is performed in accordance with the provisions of the AWS Structural Welding Code, D1.1. Most requirements can be satisfied using pre-qualified welding procedures.

DAMAGE TO ADJACENT PILES DURING DRIVING BASICS AND TUTORIALS

DAMAGE TO ADJACENT PILES DURING DRIVING BASIC INFORMATION
What Are The Damage To Adjacent Piles During Driving?

Driven cast-in-place piles can be damaged by driving adjacent piles too close or before the concrete has reached a suitable strength. The piles may be damaged by lateral forces or by tensile forces, as the ground heaves.

When it is suspected that pile damage of this type has occurred it may be decided to carry out a pile load test or integrity test as a check.

On a pile which is cracked by this means, a load test may yield an apparently satisfactory result but the long-term performance of the pile may be impaired if the steel reinforcement is exposed via the cracks.

To lessen the risk of cracking caused by soil movements, a minimum spacing of 5D, centre to centre is often employed when driving adjacent piles when the concrete is less than 7 days old. The use of integrity tests may be considered to provide sufficient information to modify this rule if necessary.

During installation of cast-in-place piles with relatively thin bottom-driven permanent steel casing, collapse of the tube can occur from lateral soil displacement if the piles are driven at centres that are too close.

This has sometimes resulted in the loss of the hammer at the base of the pile, when the collapse occurs above the hammer as the pile is driven. The occurrence is more likely, however, when driving piles inside a coffer-dam.

Where this problem is encountered, and there is no way to reduce the piling density, pre-boring may be considered as a method of reducing the effect over the upper part of the pile.

At the design stage, if high-density piling is unavoidable in soils prone to heave such as stiff clays, a low displacement ‘H’ section pile may be selected as more suitable. Alternatively, the multi-tube technique described by Cole (1972) can be employed.

All piles within 12 diameters of each other are considered to form a part of a group, and are driven (and if necessary, re-driven) to final level before basing out and concreting.