A brief look into some overseas precast concrete projects that are making news.
By Kirk Stelsel
Precast concrete has long been a staple building material in North America for everything from infrastructure and utility products to architectural building materials. Beyond our shores, though, a thriving and innovative global precast concrete industry can lend ideas to designers and builders here at home.
Check out these exciting projects from around the world.
Tel Aviv, Israel
A stunning example of how precast concrete can be used to define a design, not just support it, can be found at a recent expansion to the Tel Aviv Museum of Art in Tel Aviv, Israel. The structure was designed by Preston Scott Cohen, owner of Preston Scott Cohen Inc. in Cambridge, Mass. Cohen also serves as chair of the Department of Architecture and the Gerald M. McCue Professor of Architecture at the Harvard University Graduate School of Design.
The expansion includes an exterior shell made of 460 precast concrete panels. Each panel has four sides, but no two have the same shape or size. The panels, some as large as 30 ft on one edge, were cast using flexible-edge molds that were adjusted to create the individual angles and dimensions. With so many different shapes, the need to drill holes in the casting table to bolt down the forms for pouring was eliminated by using powerful magnets to keep the sides in place.
In Stockholm, Sweden, one of the newest additions to the skyline brings to mind an iconic structure in New York City. That’s because the wedge-shaped building is a sort of 21st century reboot of the famous Flat Iron Building. While the Swedish version may share a name and some design cues, that’s where the similarities end.
The Swedish exterior has a distinct modern feel that stands in stark contrast to the New York version, which is punctuated by lions’ heads, faces and terra cotta – a look that New York Magazine described as reminiscent of “an Italian Renaissance palazzo.” The modern facade of the Swedish version is wrapped in precast concrete panels, which added a number of attributes to the building. In addition to the exterior panels, the contractor used hollow-core slabs and interior wall panels throughout the building.
With a short construction timeline, the use of precast allowed Skanska, the building contractor, to achieve the desired look while increasing job-site efficiency to get the building to the rental market as quickly as possible. The precast facade panels also eliminated a lot of potential construction issues due to the site being in the heart of Stockholm, bordered by a railway and a busy street with cars, pedestrians and bicycles.
The panels were delivered to the site with preinstalled windows, which eliminated the need for bulky, expensive scaffolding during construction. With the urban location, space for building material storage was also limited, making the just-in-time delivery of the precast elements an absolute necessity for the contractor. According to Skanska, the precast also provided a high range of architectural and design options and will offer reduced management and maintenance issues throughout the building’s life cycle.
Designed with sustainability in mind, the building, which contains 129,167 sq ft of office space, earned a LEED Gold certification as well. The inherent thermal mass of the precast panels allows for more efficient heating and cooling of the building, contributing to the eco-friendly attributes of the building. The concrete also acts as a sound barrier between a rail depot bordering one side of the building and a residential area on the other.
At the 2014 Commonwealth Games, which will take place in Glasgow, Scotland, precast concrete will be on full display. Decomo UK Ltd. was awarded a contract to provide 32,292 sq ft of architectural precast cladding for the Emirates Arena and Sir Chris Hoy Velodrome.
The precast, which features a black exposed granite aggregate finish achieved through acid etching, creates a look that evokes the heritage of the region’s coal mining past. The 398 panels were used on the external facade of the two buildings and the interconnecting hub between them. Precast was specified for its durability and design flexibility, as well as inherent acoustic and thermal qualities.
Decomo was contacted by the project architect early on for general advice about the panels. Among the pieces provided by the precaster, the most unique were curved units and circular columns with a shiplap pattern. The panels were poured with a mix that included a super plasticizer additive to help reduce the water-cement ratio and enhance early strength for next-day stripping.
The panels were cast over a six-week time period after approximately four months of design work. Once on site, the precaster faced inclement weather and had to install the panels after the insulation and waterproofing had been completed, which required extra caution to not damage those materials during installing of the precast panels. The end product was well received by the client, who is working on another project with Decomo.
In addition, SCC Ltd., also located in the United Kingdom, contributed precast for a 1,600-space parking garage. The garage utilizes SCC Ltd.’s newly developed inverted frames, named IPCs (Integrate Precast Components), and its PFV (Precast Finished Voided) flooring system. Two semicircular ramps on the north end of the garage are also made of precast manufactured by SCC Ltd., and are thought to be the first of their type to be constructed in this way.
SCC Ltd. has been using the innovative system, which includes U frames consisting of floor beams and columns with infill beams between the frames, for roughly five years. Those units, along with triple-tee flooring units, make up the precast structure. The design is lighter and cost effective – 33% lighter than a typical hollowcore structure. The ramps are similar to the frames for the garage, with warped slabs and integral vehicle barriers.
All precast components were poured over a six-month period using self-compacting concrete, and the tee-shaped flooring units were poured using steel forms from AKB in conjunction with Spiroll. All other forms were wood and manufactured in-house.
Wind turbines are nothing new in the United States, but one precaster located in Bilbao, Vizcaya, Northern Spain is offering its own take on the construction of the towers. Norten PH has engineered a precast concrete tower produced in segments and assembled on the job site. The company began investigating the towers in 2002 after reading some technical magazines about precast towers for wind turbines. Since that time, the company has designed and certified concrete towers for turbines ranging from 1.6 MW to 4.6 MW.
The towers vary in height from 361 ft to 396 ft, and incorporate anywhere from 20 to 42 post-tensioned units, depending on height and diameter. Due to the stress the wind can exert on a tower at this height, the finished product must be strong. This means a high-strength mix and plenty of reinforcement. To start, Norten PH has worked to develop a mix that achieves 8,000 to 10,000 psi at 28 days.
The mix design, a self-consolidating concrete using a superplasticizer in order to make the concrete more fluid, contains a standard aggregate, CEM I 52 R cement and no supplemental cementicious materials (SCMs). By using this mix, the company is able to achieve a high initial strength of more than 80% of final strength by the end of the first week and ensure the concrete will flow with ease over the dense cages of rebar.
Rebar weights alone range from 30 to 70 metric tons per tower, meaning a reinforcement density of 5-10 lb/ft3 and the finished units vary from 45 tons for the largest down to 15 metric tons. The walls of the units, which may include horizontal and vertical ribs, are 5 to 9 in. thick.
To date, Norten PH has installed nine towers in Spain, with the plans for 100-200 more down the road. The company feels its concrete towers are more versatile than steel towers from a diameter point of view, and in many cases the dynamic behavior is better than that of steel towers. Each tower is tailor-made as well. As the wind turbine industry trends toward larger and larger towers, steel towers also become heavy and impossible to transport in several tube segments.
The company is currently producing its precast towers in Europe, including Spain, Germany and Finland, as well as Brazil as a shareholder in Eolicabras, a company formed in order to supply towers to the Brazilian and South American market. It has also conducted a study in the United States. With an eye to the future, Norten PH is also seeking new opportunities in other markets.
For companies in North America looking to diversify into emerging markets, a look overseas can often offer insights into products and practices that have yet to take shape here. Although the information can be harder to come by, the precast community is just as friendly and willing to share advice as it is here, and the international trade associations can provide a wealth of information as well.
Kirk Stelsel is NPCA’s director of Communication.