Separate Placing Boom Chosen for 40-Story High Rise
The 40-story, Market Square Tower in Houston is progressing at one floor per week with commercial concrete contractor TAS, self-performing the reinforcing steel, pump, place and finish. A Schwing Separate Placing Boom and stationary pump combination is helping to keep the concrete construction on schedule for a planned 13-month completion from mat pour to top out.
The continuous mat pour was a 7,810 cubic yard event that took place last November. Prior to the pour, TAS ironworkers tied more than 1.7 million pounds of rebar in thirteen days. A weekend was chosen for the mat pour because of reduced traffic in the downtown core and easier access for the 136 truck mixers loading from four batch plants and cycling two trucks at a time to each pump.
The pour started on a Saturday at 11:00 a.m. and was completed with the help of two shifts of finishers on Sunday at 1:00 p.m. Six Schwing boom pumps participated in the casting of the 25,000 square foot thick monolith that varied in thickness from six to twelve feet. Schwing S 39 SX and S 43 SX boom pumps were used – all are equipped with 2525-6 120/85 MPS pump kits and Big Rock Valves for efficient filling of the 10-inch material cylinders with 98-inch strokes. The pumps’ 216 yard per hour capabilities were not challenged because of ready-mix delivery delays. The pumps averaged 100 yards per hour. A time lapse video of the entire pour is displayed on the TAS home page http://www.tasconcrete.com.
Schwing boom pumps continued to access the site from adjoining streets to build the non-typical first three levels that measure 34,000 square feet each and included mechanical rooms, a lobby and a pool area. The Schwing S 43 SX with 138-feet of reach was influential in the speed of construction. The pump’s RZ5 5-section Roll and Fold boom with 270-degree tip section was able to maneuver around the one tower crane on the site and other equipment to reach most areas of the core, walls, columns and decks. The pump features Super X outriggers that helped it to set-up tight to the perimeter even when jobsite obstructions were present.
At level three, the company switched to a self-climbing form system with a Schwing SPB 37 separate placing boom. It was established that the separate placing boom was the best method because of the demand on crane time and limited access for mobile pumps on the downtown streets. The separate placing boom was mounted to the custom form system using a zero-elevation bolt-on X-frame that accepts the boom and headset. “Schwing was very helpful with input on the boom size, mounting, servicing advice, pipeline set-up and choosing the right pump for the job,” according to Ross Baird, TAS structural operations manager. The company owns a Schwing S 39 X with detachable boom, but elected to keep that unit intact as a mobile pump rather than dedicating the boom to the project for nearly a year.
Starting at level three, the floors are 20,000 square feet. The 120-foot horizontal reach of the boom allows the SPB 37 to reach all areas without adding extra system. “We construct the core ahead of the decks which gives the boom operator a tremendous two-story vantage point to safely pour out the walls, columns and floors,” Baird says. Not only was the horizontal reach important but also the ability of the Roll and Fold design boom to place tight up against the core. Each floor is cast in two pours of 250 cubic yards each in four hours. “The pumping equipment has been flawless. We have been reliably staying on a one floor per week schedule since we began the typical floors,” Baird reports.
Contributing to the reliability of the equipment is the Schwing SP 4800 stationary pump placed strategically on the job site. Powered by the CAT C13 Tier 3, 442 HP engine, the SP 4800’s all-hydraulic 2020-5 180/90 pump kit offers 106 cubic yards per hour on rod side and 2364 psi on the piston side. The design of the open loop system contributes to fuel efficiency according to the owner. The compact 6’ 4” wide by 23’ long footprint makes it ideal for tight urban jobsites. Standard features of the pump include a jobsite axle, hydraulic outriggers and 80-gallon fuel capacity.
The horizontal pipeline to reach the standpipe measures more than 100-feet and the ultimate height of the pipeline will be over 500-feet. Clean out is accomplished with a diversion valve, just after the pump discharge, that routes returned ready-mix into a dumpster. Compressed air and a sponge ball at the top of the climbing core provide the motivation. “Mix designs for the 9,000 psi wall mix and 6,000 psi decks have proven very pumpable,” according to Baird. The SP 4800 utilizes a high pressure Rock Valve with dual shifting cylinders to easily handle the harshest mixes.
TAS is a longtime Schwing boom pump customer with an equipment owning philosophy, “Early on we learned the value of owning our own equipment. Not only does it keep our costs down, it also gives us more control in scheduling our projects. This allows us to provide the ‘get in and get out’ service our clients have come to expect,” states Baird, “This is our first venture with a separate placing boom and pump. It is another tool in our equipment fleet that will help our customers.”
Scheduled for occupancy in 2017, Market Square Tower will offer 463 luxury rental residences with wrap-around rooftop amenities and a breathtaking panoramic vista of the downtown skyline. It will be the tallest residential high rise in Houston.
Owner: Woodbranch Investments Corp., Houston, Texas
General Contractor: Harvey Builders, Houston
Architect: Jackson & Ryan Architects, Houston
Concrete Pumping Contractor: TAS, Houston
Concrete Pumping Equipment: Schwing S 39 SX and S 43 SX truck-mounted concrete pumps with placing booms, SP 4800 stationary concrete pump and SPB 37 separate placing boom.