Prior to erection, the steel erection contractor is to survey all the anchor bolts, beam pockets and embedded plates on the site to ensure no remedial work is needed. This is important to do beforehand so steel erection does not come to a screeching halt if a problem is found.
If an anchor bolt is found to be damaged, it can be cut flush with the top of the concrete and a new one drilled in adjacent to it and epoxied into the concrete. The baseplate of the column will have to be modified accordingly.
If the top of concrete is too high, the concrete can be chopped down, or the column can be reworked if the difference is significant. To rework the baseplate, burn off the baseplate from the column at the welds and grind it smooth. Use a demo saw to cut the column short to the necessary length and reweld the baseplate to the end of the column.
If the top of concrete is too low, additional shim packs can be used if the difference is minor. If the difference is a few inches, then additional baseplates can be added to the bottom of the column and welded together.
Typically, crawler cranes or tower cranes are used in steel erection. The former is used for horizontal construction, such as stadiums, while the latter is used for vertical construction, such as skyscrapers. Crawlers are also used in the beginning of vertical construction, when there is no structure for tower cranes to attached to.
Receive steel and shake out Steel is delivered to the site on flatbed tractor trailers. The amount of steel on a truck is limited by the overweight and oversized dimensions dictated by the local department of transportation. If needed, permits for loads exceeding the maximum weight or size can be obtained from the DOT. Restrictions may be placed on the trucks route and an escort vehicle may be necessary.
When delivered to the site, the crane picks the steel off the trucks and lands it in the “laydown area.” This is a location that is used to “shake out” all the steel and organize it. In the construction of skyscrapers, this is usually on last completed floor. In horizontal construction, this can be anywhere. Shake out hooks are used instead of typical rigging; these do not have safety latches.
Before the first columns are erected on the footings, an ironworker goes around to the anchor bolts to “chase” the threads. This is typically done with a lubricant and running bolts down the threads to make sure they are clean; this ensures that when the columns are set, the bolts can easily be torque without any issues.
Baseplate holes are typically oversized by 1/16” greater than the anchor rod diameter to facilitate installation. A washer is used to bridge the gap between the bolt and the baseplate. The nuts are to be installed snug-tight. Grout holes can be placed near the center of the baseplate to allow for the leveling grout to be distributed evenly.
Beams are erected by the “raising gang.” This is a group of six ironworkers, consisting of a foreman, two connectors, two riggers and a signalman. The riggers hook up the chokers and cables to the steel and to the hook on the crane. The signalman directs the operating engineer on the crane on the exact movements he is to make. Sometimes this is done with hand signals and sometimes it is done with a hard wired phone line to the cab of the crane. The connectors climb up to the position where the beam is to be erected and wait for the beam to fly in. They catch the beam by the tagline and turn it into position. When the connection is close, the ironworker will use their spud wrenches to align the holes so they can install the erection bolts. Typical procedure is to use two bolts, but if it’s for a large cantilevered section of steel, the engineer should state on the erection drawing to use additional bolts to hold the beams in place.
There are three types of conditions for which bolts can be installed: snug tight, pretensioned, and slip-critical.