The structural frames for steel buildings are erected at a fast pace. Thus, the alignment of the structure must be "true" if the building is not to lean like the tower of Pisa. To avoid these problems, the surveyor checks the alignment of the columns with
a transit, and then the iron worker checks each column with a plumb bob. If the surveyor or the iron worker find out that the columns are out of alignment, then cables are placed at the top and bottom of the columns and turn buckles are installed (see Exhibit 7-10) to straighten the structure. The permissible alignment of interior columns for the first 20 floors is 1 in., with an increase of 1/32 in. for each additional floor with a maximum for the full building of 2 in. For exterior columns, the displacement for the first 20 floors is no more then 1 in. inside the building line and no more then 2 in. outside the building line. Above the 20th floor, the limits may increase by 1/16 in. for each additional story but no more then 2 in. toward the building line or 3 in. away from the building line. However, all alignment criteria should be obtained from the owner's design team.
Was this article helpful?