Towering Tools of the Trade
In the fall of 2000, Dodge Phelps Corporation, a global leader in the mining and manufacturing industries, contracted Ryan Companies US Inc., a leading national real estate firm offering integrated design-build, development and property management solutions, to construct its headquarters. The 27-story tower would be the second tallest structure to be built in the last eight years in downtown Phoenix. The project led Ryan Companies to call on DEI Professional Services, LLC, a 20-year local land surveying and civil engineering firm, to provide horizontal and vertical control for layout, plus as-built QA of the structural steel and concrete elevator core for each of the 27 floors. The project proved challenging at times, but the results proved that 3D laser scanning is making a name for itself.
From the Ground UpSeveral existing high rises and busy urban streets surround the rectangular project site in downtown Phoenix. These factors complicated the survey control and layout required for construction. DEI utilized everything from Topcon electronic total stations (Topcon Positioning Systems, Pleasanton, Calif.) to the Cyrax 2500 3D laser scanner (Cyra Technologies, Oakland, Calif.) to provide accurate and timely layout and as-built services required by the rigorous project specifications and schedule.
DEI began initial survey control work in 1998 with ALTA/ACSM surveys, topographic and final plat survey services, completed in support of DEI’s civil engineering division that provided site and utility design services. When construction started on the tower, DEI used Topcon’s APL1A, 213 and the GTS800A total stations to establish master building grid control points utilizing the original control from the design phase survey. As building layout proceeded from floor to floor, DEI transferred the building grid horizontal control up vertically using visible beam laser plummets and plate glass. Vertical control was completed from floor to floor using electronic distance meters (EDMs) and traditional measurement chains. DEI completed verifications by total station angle and distance checks from each floor to distant targets to provide additional independent accuracy verification.
Movin’ On UpPart of the Dodge Phelps Tower contract called for DEI to monitor verticality of the interior of the 27-story concrete elevator core, floor-by-floor ahead of the steel during construction. This proved to be one of the more challenging elements of the project. DEI’s service contract was subsequently expanded to also monitor the core thickness/position in order to avoid fit-up problems with horizontal structural steel members designed to tie into the exterior of the elevator core at higher floors.
“The sooner you catch dimensional construction errors, the better. The last thing you want to see toward the end of a project is some guy up on the 22nd floor with a welding torch,” says Rob Hudson, senior superintendent of construction for Ryan Companies US Inc.
DEI started monitoring external core geometry with total stations, measuring each exterior corner of the rectangular two-foot thick core after it was poured and set; however this method couldn’t catch variations in the concrete geometry over its full surface/thickness. Plus, it was time-consuming and hazardous.
After doing some homework on 3D laser scanners and learning of the Cyra Technologies’ upcoming acquisition by Leica Geosystems of Norcross, Ga., DEI purchased a Cyrax 2500 3D laser scanner and associated Cyclone v3.0 software in November of 2000. After training six of 30 survey staff members, DEI set out to utilize this technology on the remainder of the Dodge Phelps Tower and several other projects. On this project, DEI switched in the spring of 2001 from the conventional total station method for elevator core as-builts to the Cyrax laser scanning method on the 7th floor.
“DEI’s use of the Cyrax system dramatically reduced the fall hazard exposure to our survey staff due to the fact we were able to as-built the elevator core without a rodperson,” says Jason Kack, RLS, vice president of DEI.
“DEI’s use of Cyrax for construction QA gave us a lot of valuable geometry information, which in turn helped us to reduce risk on the project and meet schedule without any fit-up problems,” Hudson says.
Rising High Above the RestDEI used scan targets to register scans together accurately and relate scans to the building grid. The scanner was set up on a lower tower floor during construction, and also on the roof of the Crown Plaza Hotel across the street to collect geometry for the highest floors. Attaining accurate measurements from the hotel to the tower lends credibility to the Cyrax 2500’s accuracy-at-range. To determine core thickness, outside core geometry was compared with internal geometry from an independent check utilizing building grid control and conventional total stations. Thickness variations along the core surface were examined in the Cyclone software for significant warping of the surface. In addition, tie plate locations (on the exterior of the core) and steel members were directly modeled in Cyclone from scans of these objects. After registration and modeling of the elevator core, a file of 3D surfaces was exported into AutoCAD and a plan view exhibit was produced detailing the “plumbness” and thickness of the elevator core walls.
QA checks with Cyrax found that core thickness was starting to run thin of the spec at the 11th floor. This input was provided to the contractor, who triggered a minor modification to the pre-form. No other noticeable deviations were observed. All tie plate locations were within spec, although again, some were reaching tolerance limits. All checks of steel member alignments/locations were within plan.
“It’s a heck of a lot easier to modify steel in a fabrication yard vs. 180 feet up,” Hudson says. “There was not one problem with any of the steel not fitting.”
The net incremental cost to DEI on site for applying Cyrax for additional QA was only about 15 percent of the original survey contract. Once the first 3D laser scans of the core were shown to Ryan Companies, the company quickly understood how much additional and valuable QA information DEI could gather with Cyrax. Following a cost proposal, the client requested the use of Cyrax for additional QA on other key construction elements.
“People don’t realize how valuable as-built QA is on a core [construction],” Hudson says. “It’s very expensive to fix a problem.”
Ultimately, there were three applications on the Dodge Phelps Tower, all for construction as-built QA; (1) core thickness/position (to 1/2") at the 11th floor, (2) core thickness/position at the 17th floor and (3) actual alignment/locations of steel members on the 6th floor (used as input for fabrication of windows and girders to 1/8").
Overall, DEI used a two-person scanning crew for a total of four days in the field, while one person supplemented this work in the office for about a week to process/analyze data and to generate final deliverables. DEI and Ryan Companies were both very pleased with the results from the Cyrax laser scanning system. DEI has since utilized Cyrax technology on numerous construction verification projects, including other high rises, stadiums and bridges. Ryan Companies has also since exposed other internal project managers to the potential benefits of using Cyrax laser scanning on construction projects.
“The client doesn’t look at us as just surveyors anymore. Now they look at us as project consultants,” Kack says.