Tall tilt-up: Pinal County superior courthouse, Florence, Arizona

Concrete Construction, June, 2003

The new four-story Pinal County courthouse was originally designed to have cast-in-place elevator/stair cores, but in the interest of saving both money and time, D.L. Withers, the general contractor, accepted Riggs' proposal to expedite the project by using 80- to 87-foothigh tilt-up panels.

In addition to the elevator shaft panels, the building was originally designed with over 500 panels, stacked four high, to make up the building's exterior. Grouping many of the panels and eliminating two horizontal connections reduced the number of exterior panels to 104. That decreased the time as well. Twenty exterior columns were also precast.

With the size of the panels, the bracing and the wind load engineering were critical. The longest available braces were 52 feet, leaving the top third of the panels above the brace point. After the panels were erected and braced, the upper portion of the panel would deflect in the wind by 3/8" to 5/8" in either direction until welded off. Consequently additional reinforcing was installed in the panels to deal with the wind load. The 52-foot braces were so large, an additional crane was needed to remove the braces once the panels were welded off and stable.

The five interior elevator cores and stairways consist of 37 individual panels, the heaviest weighing 220,972 pounds. Changing the elevator shaft walls from cast in place to tilt-up required substantial reengineering. The shear for the entire structure was applied through the elevator shafts, so the connections and foundation support had to be solid. Due to the weight of each panel, there was little option for "walking" the panel into place. Therefore, each panel had to be placed close to erect and had to swing directly to its final setting position. With the height of the panels, nearly the entire building footprint was used for panel casting.

PROJECT PARTICIPANTS

* Concrete tilt-up contractor: Riggs Contracting, Inc.

* General Contractor: D.L. Withers, LC

* Project Manager: Mark Tutelo

* Owner: Pinal County

* Project Architect: Durant Architects

* Engineer of Record: TLCP Structural, Inc.

* Erection Engineering: Meadow Burke Engineering

* Reinforcing Installation: C&S Reinforcing