Forty 10-ton wireless compression load cells from Straightpoint were used to monitor forces on temporary shoring columns used to support two tower cranes during the Century City Mall project on Santa Monica Boulevard in Los Angeles, CA.
Two cranes from rental company Mr. Crane, supplied by Morrow Equipment Co., were supported by the existing columns and shoring posts, as load cells calculated total mass and center of gravity of the cranes and subsequent lifted loads.
Both cranes were located on an existing two-floor underground parking garage. A Liebherr 630 EC-H 20 Litronic was stationary, while a 542 HC-L18 Litronic operated on rails and traversed the length of the project in stages. The cranes used to erect them on the garage were a Liebherr LR1300 crawler crane and a LTM1400-7.1 hydraulic truck crane. A third 630 tower crane was used on a standard foundation on the "Macy’s side" of the project.
Each crane was supported from the deck down to the final slab of the structure using jackscrew shoring posts on both floors of the car park, positioned at each of the four corners of the stationary crane and along the pathway for the traveling crane.
According to Mark Sovocool, engineering manager, Mr. Crane, "The track system is a typical Liebherr bogie and track system with electrically driven bogies. What is under the track is anything but typical. We came up with a block system, with blocks designed by Coreslab Structures (LA) Inc., to support the track and crane that can be easily removed once the project is complete."
Traversing the Roof
The tracks sat on two rows of 20,000-lb. concrete blocks extending approximately 100 yds. across the top of the parking garage. The temporary shoring columns and wireless load indicating compression load cells were moved across the parking garage below as the crane traversed the rooftop overhead.
John Molidor, general manager, Straightpoint Inc., explained, "A sampling of the shoring column loads was provided by 40 wireless 10 ton compression load cells. The wireless load data was transmitted to a Windows PC (or tablet) running our SW-MWLC software. The software’s web server function transmitted the real-time load data via a local area network to the tower crane operators high above, allowing them to view the live loads on mobile technology such as an iPhone or Android device. Our SMS alert system was employed to monitor the loads associated with the cranes. Maximum load thresholds were established and, if reached, key engineers and project administrators would be automatically notified via email and text of the alarming conditions."
Sovocool added, "It was important to monitor loads so we could check that there was a good distribution of force onto all of the shores in the immediate vicinity of the crane. The load cells allowed our personnel to walk around the shoring posts and get wirelessly live readings of the force under a sampling of the shore posts, giving us some idea as to what the posts were actually seeing as the crane swung, and in some cases traveled. The goal was to ensure that no single post was overloaded."
The whole project was a remodel and expansion of the mall. It involved clearing existing structures on the top floor (shops), reinforcing structural components and erecting steel for the new sections of the mall. Typical loads were below 20,000 lbs., with some critical lifts up to 42,000 lbs.
