By Deborah R. Huso
Photos courtesy of ATKINS (www.atkinsglobal.com)
Project: San Marcos Armed Forces Reserve Center, San Marcos, Texas
U.S. Army Corps of Engineers, Louisville District, Louisville, Ky.
Atkins, Orlando, Fla.
Satterfield & Pontikes Construction Inc.,
Schwab Structural Engineering Inc.,
New Braunfels, Texas
Heldenfels Enterprises Inc., San Marcos, Texas
When the design-build team began the design of a new $25-million Army Reserve center in south-central Texas, they had to meet goals of sustainability and blast resistance. Designers turned to a natural solution for the project – an all-precast concrete structure from the ground up.
Designed as three freestanding buildings totaling some 112,000 sq ft, the project provides space for the joint operations of the U.S. Army Reserve, the Texas National Guard and the San Marcos Armed Forces Reserve Center (AFRC) in San Marcos, Texas. The complex had to meet the U.S. Army Corps of Engineers’ sustainable building standards, based on the U.S. Green Building Council’s LEED Gold certification standards, as well as Anti-Terrorism Force Protection (ATFP) requirements. And while the requirements might seem stringent, the use of an all-precast system to build the operations center resulted in an inherent melding of both ATFP and LEED goals.
Situated on 15 acres, the AFRC includes a central training and administrative building, plus a storage building and organizational maintenance shop. “One of the reasons we selected precast was because of how quickly we could put the structure up,” says Alejandro Gonzalez with Satterfield & Pontikes Construction Inc., the general contractor for the project. “Precast allows you to work on other phases of construction while the precast components are being fabricated.”
Precast for fast-track schedule and blast-resistant design
Given the Corps of Engineers’ goals for structures that reflect the strength, security and traditions of the U.S. Armed Forces, precast concrete was a natural and efficient design fit. Precast panels are a perfect option for projects like this one, which requires rectilinear massing and symmetry. Designers enhanced the exterior facade by adding a brick veneer to the first floor by using locally manufactured brick.
Steve Moller, senior architect and project manager with Atkins, says there was really nothing architecturally complex about the structures. “The buildings are rectilinear with cubed massing and punched openings,” he notes, but the very simplicity and straightforwardness of the design made the project ideal for an all-precast system. “The design supported precast,” Moller adds.
The use of an all-precast system was a goal from the project’s start in large part to meet the Corps of Engineers’ fast-track construction goals while still achieving ATFP and LEED benefits. “Their schedule was pretty aggressive,” says Gil Heldenfels, vice president and general manager of the building systems division of Heldenfels Enterprises Inc., the precast manufacturer. Work on the project began in June 2009 and was completed in the spring of 2011.
Precast concrete offered both renewability and recyclability, and the precast plant was only four miles away from the job site. Furthermore, precast offered natural thermal mass, fire protection and insulation, thus contributing to the structures’ 34.3% energy consumption savings.
Precast concrete panels easily meet the requirements of Force I and II blast resistance from just about any distance without any unique design or manufacturing processes. “We had to ensure our design met the stand-off distance,” Heldenfels explains. “It was a minimal blast resistance requirement, and our product inherently met it.”
Moller adds that precast was a natural choice for meeting the combined needs of fast-track construction and blast resistance, since it combined easy assembly of components with reinforced concrete’s known explosion resistance. And while he notes that it was not necessarily cheaper material-wise to go with precast concrete over other possible building systems, the erection process was cheaper.
BIM allows construction simultaneously with design
All three buildings included wall panels serving as both structural support and exterior facade. Heldenfels said the three buildings make use of a mix of hollow-core and double-tee flooring, double-tee roof panels, columns and beams, and somewhat repetitive wall panels. The three-building project consisted of a total of 1,424 precast pieces. The wall panels that serve as both structure and facade are exposed, painted, elastomeric precast.
Heldenfels says the design-build team used Building Information Modeling (BIM) to design and track the project, thus providing not only a 3-D representation of the AFRC but allowing all parties involved in construction to be on the same page and contribute to the BIM as the project progressed. BIM allowed the AFRC design-build team to basically follow the life cycle of the construction project, including tracking time and costs.
The modeling meant that the precast manufacturing and construction began before the buildings’ design was even complete. “As architects,” Moller explained, “we had a kit of parts and we knew what they were, so construction was actually able to start before we finished our work as designers.” The simultaneous design and construction, however, revealed that the structures’ crawl spaces had to be re-excavated as the structural design developed.
Heldenfels says what made the AFRC especially unique despite its rather conventional facade design was that it made use of precast structural suspended slabs. The columns and beams bore directly on the piers. “We do suspended slabs, but the thing that was novel was that it was precast from the piers up,” he says. “It was the first time in my experience we were out of the hole coming up precast.”
Gonzalez agrees. “Sometimes you have elements of precast, but it was the entire structure here, which is rather unique,” he says.
Coping with challenges
Total erection of the all-precast structures took only about four months, and given the extremely wet year south-central Texas experienced in 2010, precast ended up being a distinct advantage. “Access to the job site was sometimes a challenge because of the wet weather,” Heldenfels notes, “but, in the end, precast allowed us to get going really fast.” Weather was not the only challenge. Heldenfels says if he could do the project over again, he thinks the design-build team would re-evaluate the connections systems. “We had planned to use grout-filled mechanical splices for panels and beams, but it didn’t work,” Heldenfels says. “We didn’t hit (align) the tubes in the beams with the rebar in the panels, so we had to adjust a lot.” Heldenfels says, in retrospect, they should have used JVI Mini-V connectors for their double-tee shear connections.
Prior to his work on the AFRC, Moller says he’d never designed for a total precast project, but he says he felt precast offered the ideal option for the U.S. Army Corps of Engineers. “For a project that has this kind of client where the schedule is tight and the particular qualities of concrete are needed, it’s a perfect marriage,” he notes. “Precast concrete is a renewable, recyclable material with great thermal mass, too.”
Deborah R. Huso is a freelance writer who covers home design and restoration, sustainable building and design, and home construction.