Install 11,000 tons of structural steel where the official building survey dictates and creating a 162-foot wall that resembles the body of a guitar on the new Music City Center in Nashville.
Schuff Steel Atlantic
Earl Dudley, Inc.
Schuff Steel Atlantic is erecting structural steel that will form the interior backbone of what is arguably the Music City Center's most distinctive architectural feature: a 162-foot wall at the north end of the main structure that rises out of the main roof and resembles the body of a guitar from a bird's-eye view. The metal panel wall will enclose the grand ballroom on the ninth floor.
The contractor is using high-speed precision scanning technology to lay out the structural steel for the radial shape of the guitar wall.
Schuff Project Superintendent John Fugera notes that the design tolerance is 1/4 of an inch and 3/8 of an inch around glass. A failure to adhere to the tolerances would cause an undesirable snowball effect, Fugera points out. Work from contractors installing glass, cut stone and metal panels would also be off. ""We drive the bus - if we're wrong, then everybody else is going to have issues down the road."
In March 2011, Schuff began laying out and erecting the steel framework for the guitar wall on the north side of the building. The contractor worked in a clockwise direction from the north side, ensuring that every quarter-inch of the steel beams was positioned precisely in the as-built surveys it had contracted to provide. Schuff used a total station for this task on the straight wall section it started on. "It wasn't until we got into the curvature section that we figured that the scanner would give us a lot more accuracy," Fugera says of Topcon Positioning Systems GLS-1000 and GLS-1500 laser scanners. Given the design of the radius walls, determining the X, Y and Z dimensional locations of every quarter-inch of the steel beams using conventional surveying equipment would have been too costly, according to Fugera. Schuff rented the scanners from Earl Dudley, Inc., a surveying and geospatial equipment dealer with five locations in the Southern United States.
This process would have been especially cumbersome on the east side of the Music City Center where the guitar wall on features eight radius variations and five pitch variations at the roof.
Fugera estimated that it would take at least two weeks to shoot the estimated two million points required to as-built survey Schuff's steelwork on the long east side of the guitar wall, which has an estimated 4,000 to 5,000 connections to the main steel structure. He estimated it would likely take three or four more weeks to determine where Schuff's steelwork was located relative to the main steel structure. The laser scanner allowed surveying from ground level, whereas the total station would have been operated on an aerial lift at various levels.
Chris Clay, RLS, Schuff's licensed surveyor on the project, operated the total station on the project. "Shooting two million points - I don't know that you could get it in two weeks," he said. "Even if you stayed out here 24/7, you'd run out of battery on your total station." Clay agreed with Fugera that laser scanning was the only realistic way to develop an as-built survey of the steelwork.
In late fall 2011, Schuff was erecting steel near the southeast corner of the facility and continuing to work its way around in a clockwise direction. Clay set up the GLS-1500 outside of the guitar wall at ground level. He identified several magnetic targets that had been placed on several steel beams forming a large horizontal rectangle on the eighth level. The target locations were surveyed with a total station and tied to the grid formed by control points based on the official building survey and a three-dimensional BIM model of the entire building. He measured the center of the targets from building control points using a total station and scanned the targets. The GLS-1500 resectioned in order to establish the position of the instrument relative to each target. By doing this, Clay tied the target locations to both the building model and the official survey grid.