ONE THOUSAND MUSEUM

Background

A new architectural landmark This 707ft high-rise, designed by a Pritzker awarded architect, offers its occupants a high-end living experience at the heart of Miami. The 62 stories house 84 premium residences, a multimedia theater, aquatic center, and rooftop helipad. The most prominent architectural feature, the exoskeleton, reflects the architect’s signature fluid design but also acts as an integral component of the structural system. The curvature is elegant and has bracing properties that help resist lateral loads exerted by high winds in the area. As the exterior columns split and rejoin, intertwining around the building, their cross-section, location, and inclination change from floor to floor. The original cast in situ design would have required very complex formwork that is both expensive and time-consuming to erect.

Building Block’s insight, as value engineering consultants, was to re-design the current in situ façade to precast GFRC permanent formwork. This solution decreased the complexity associated with the original proposal. The simple assembly and minimal finishing work contributed to the reduction of labor requirements and sped up the construction process. GFRC was chosen for its lightweight and high performance that enabled its use in thin sections. Despite that, thickness still ranged from 4”-8” to resist wind loads and concrete pressure. This would have been added thickness to the existing exoskeleton design. Structurally redesigning the entire building allowed for the additional permanent formwork thickness while still conforming to architecture. Using permanent formwork alone without the redesign would have increased the size of the columns hence a GFRC pre-caster would not have been able to implement this solution alone.

The project’s co-developer publicly stated on Engineering News-Record that “[Precast permanent formwork] saved more than six months in schedule and improved the overall product”. The quick turnaround time between floors is attributed to the reduced labor requirements, formwork installations, and finishing work. Permanent formwork was tested to endure both high wind loads in the hurricane-prone area and the pressure exerted by fresh concrete. FEM software (Midas Gen) was used to simulate the behavior of the panels, internal ties, and ring support under loaded conditions. Full-scale testing was also carried out to verify the proposed sections, rib sizes, anchors, and fabrication precision. This was critical to ensure this solution is both safe and effective with no risk of leakage. The architectural design of the exoskeleton made it so no two sections are the same. This burden was taken off-site and provided an easy to install permanent formwork solution which was better than casting the complex shapes on site. A “storybook” was provided that acted as detailed method statements to visually describe the systematic and correct approach to installing the panels. This helped prevent panel mishandling and delays caused by having to refabricate and ship replacement parts.

Design Challenges

The main construction challenge was the need for a very complicated formwork system to cast the exoskeleton. The original design included bulky climbing formwork that used custom shaping elements to accommodate the geometric variations. The labor-intensive process of assembling and dissembling the forms after each cast made this option very time-consuming and resource-demanding. The original design also required additional finishing work and painting after casting. The exoskeleton is a defining architectural feature of the façade, it was crucial that the surface was impeccable. By using precast as permanent formwork, the designers were able to eliminate the exoskeleton formwork system from the 15th to 62nd floor. The precast panels, once on site, would be lifted into position then secured using simple props and straps while concrete is poured inside. After the concrete sets, the props and straps are removed, and the next panels are erected creating a quick and efficient workflow. The controlled environment of precast manufacturing allowed us to closely monitor geometric accuracy and finish quality. This allowed every panel to seamlessly fit one another and eliminated extra painting on site. By using tension straps and external propping the team avoided invasive tie-rods and any finishing work associated with them.

Innovations/Accomplishments

During the structural redesign of the building, the team was able to reduce quantities of concrete and steel by 20% and 9% respectively without changing the original architectural geometry. The design team achieved these major savings by utilizing value engineering methods. By running multiple design iterations while using techniques such as wall tapering the team not only achieved the necessary 4”-8” of circumferential reduction but resulted in additional savings as well. Using GFRC as cladding on the first 15 floors allowed us to attain the desired exterior while simplifying and reducing the size of structural components. After the 15th floor, GFRC was used as permanent formwork to cast the rest of the floors. 3508 distinct GFRC panels had to be individually fabricated in their own molds, so the team developed a parametric tool to help automate the process. Using Grasshopper, the precaster extracted individual panel pieces straight from the Rhino model. The script would provide the outline as well as sections at different elevations of each panel. These geometric details could then be exported and turned into shop drawings. The script sped up the drafting process and allowed us to very accurately match the desired façade. The designer tested the use of tension/ratchet straps to further optimize the construction process due to the tight schedule. Our initial proposal used steel frames to keep the panels in place while concrete sets. Straps could more easily be installed and would work for all cross-sections without modification reducing erection time. The precaster successfully tested the method on sample panels at 1.5 times the actual height. Despite the additional pressure, the straps prevented leakage and panel deformation. GFRC is both lightweight and strong enough to withstand the pressure exerted by fresh concrete as well as high wind loads in the region. It was a priority to keep panel thickness low; permanent formwork remains on the outside of the column creating additional thickness which is architecturally unacceptable. The properties of GFRC make it ideal for casting thin high-quality sections.