AVENTURA RETAIL STORE

Background

Located in the new wing of the vibrant Aventura Mall, the new two-story building consists of a large open volume with a tree-filled atrium, an amphitheater and stone feature wall capped by an undulating roof made of precast concrete beams and vaults.

The roof, which takes inspiration from Miami’s art deco roots, consists of 80-foot precast concrete beams, which span 60 feet clear between columns. The beams are joined by concrete arches, which contain building systems, lighting, and are clad with acoustic fabric on the underside. The support columns are clad with pre-cast concrete sections as well, and the entire assembly has been grouted to create a seamless integrated whole.

The execution of the project required an unprecedented level of integration in the engineering, design and detailing, requiring all parties to be flexible, creative and collaborative to achieve the project goals.

Design Challenges

There were several key challenges to overcome with the design: First, the integration of engineering of the pre-cast roof, the structural steel superstructure, and the mullioned glass façade. Wind loads on the façade transferred through the steel to the roof, and the roof movements transferred back through to the façade. Solving this took a consolidated all-in-one engineering approach, covering the fabrication, assembly methods and sequencing, and the final building reactions.

The second design challenge was the exceptionally high quality control required of the pre-cast, given the various shapes, sizes and weights of different pre-cast elements. Each size and shape member cured and cooled at a different and often unpredictable rate. Multiple mockups were prepared to test how the curing would evolve, and adjusting batch mixes to align with the goals for the finish, and to avoid alligator cracking. Multiple aggregate patterns were reviewed until the right mix design was approved. Multiple grouting methods were explored until the final application was approved.

The third design challenge was the precast column covers used to clad the tall steel columns along the front façade. The pre-cast both covered the steel columns, but also integrated with the façade glazing and mullion systems, requiring extremely tight tolerances, and little room for installation attachments and adjustments. The solution came through a lightweight design, improving maneuverability and workability. In all, seventy-seven column cover sections were installed, with half rounds cast to fit perfectly together on either side of the glazing.

Innovations

Not only was this a “Project of Firsts” in precast design but also production, transportation and installation.

Production Innovations and Accomplishments

• Fabrication of structural beams with multiple shapes and connections. Creating the beams in the required length took ingenuity. The form was designed to travel on casters so once cast, the sections could be separated and rolled away from each other, and removed as three separate sections with the outer two sections weighing 55,569 lbs each and the inner weighing 59,330.

• The three sections were removed from the casting tables and brought to the yard where an assemble station was designed/developed where beam sections could be cradled on racks -again with casters/rollers – reassembled with sections placed in their original as-cast positions. Tolerances were paramount, essentially ¼ of the allowable PCI tolerances.

• The interior ends of beams which interface with the middle beam were textured, and treated with epoxies (Bruce – please confirm) and post-tensioned together in the yard to provide better control and alleviated congestion at the site.

• In addition to creating the diaphragm for the structure, the 14 edge vaults – 13’-5” wide x 18’-1” long edge vaults also had to provide a keyway for the upper windows to “disappear” into and encapsulate the frame.

Transportation Accomplishments

The following coordination efforts of the contractor and the precaster proved successful in the transporting challenges associated with loads carrying 80-ft heavy beams which required special services to meet local regulations:

• Carefully plan a route and timetable to deliver pieces due to the turning radiuses needed for such weight and length on flatbed trucks

• Trucks could not drive after sunset, or use free-ways or turnpikes, requiring them to navigate through surface streets around several lakes in the region.

• Each truck required a police escort to make the approximately 250-mile trip from the fabrication facility the site.

• Once at the site, additional police patrols were needed to stop traffic and help with maneuvering.

• One beam was delivered each day and lifted into place with an 800-ton crane, one of the biggest in the country, for eight days.

• Transportation process followed a meticulously engineered sequence for raising and setting the beams due to concerns overloading a portion of the building if the beams didn’t balance each other out.

Installation Innovations and Accomplishments

The site was open so there were few obstacles. There was good coordination throughout the process of delivering and erecting the pieces ensure installation went as planned.

• Each beam had to be lifted over the steel columns, which were stubbed up 5 ft over the top of the roofline to accommodate the beam being slid onto it.

• The beams were set into the steel cradle, which helped line up the connection points on the ground to match with those on the columns. A robotic arm was used to weld in connectors, after which the beam was lifted over the roofline and lowered onto the stubbed column, with the capitals weaved over the drain.

• Plates embedded in the beams were welded to the columns, after which the vaulted panels were set onto bearing ledges cast into the edges of the beams to support them. The vaults closest to the edges were erected first, followed by the interior vaults. With all the pieces in place, reinforcing bar was placed over the top of the entire roof in a basket-weave configuration and a concrete layer was poured over the surface, locking it all together.

• To eliminate any installation surprises, the construction team did some practice runs with the rigging sequence at the precaster’s plant using mock-ups and test beams, which made the actual installation, run smoothly. With multiple shapes, each had to be rigged differently so the study at the plant paid off at the site.

Photos via Forster + Partners and GATE Precast Company