Tensile cover turns an ordinary parking shelter into
a focal point for a Mexico City supermarket.
By Julie Swiler
The Santa Fe area of Mexico City is a booming business district with high rises and dramatic contemporary architecture, a modern contrast to many of the neighborhoods in the historic city. A fairly new development on the western edge of town, the area was previously a landfill. Now it is home to multinational corporations, upscale condos, shops and restaurants.
One of the flagship properties in Sante Fe is Centro Santa Fe, the largest shopping mall in Mexico. It features more than 300 shops, restaurants, a hotel, movie theaters and office space.
It also features a Chedraui supermarket built by the Chedraui Group, one of Mexico’s largest grocery store and department store chains. Chedraui wanted to launch a different kind of store, one that reflected the company’s commitment to sustainability and was attractive to the area’s sophisticated residents.
In an effort to take customers who live and work in this sprawling urban area back to the land and connect them with how their food is grown, Chedraui brought the farm to the city by creating a rooftop vegetable garden adjacent to the store. There, shoppers can find a bit of pastoral serenity while wandering through a green space among rows of vegetables and herbs. It’s a market, too—they can buy produce right on-site.
The rooftop also features a 250-car parking shelter built for Chedraui customers. It was designed by Michel Rojkind of Rojkind Arquitectos, a Mexico City-based firm known for testing the boundaries of architecture with innovative shape, color and form.
Rojkind wanted to create a cover over the parking area and walkways that would be an iconic element for the store as well as provide protection from sun, wind and rain. His firm worked with Lonas Lorenzo S.A. de C.V., a Guadalajara, Mexico-based maker of fabric coverings and metal constructions, to create and install the cover and the steel structure that supported it.
“For the cover, the architects were looking for a material that could provide translucency,” says Cesar Eloy Perez, Lonas Lorenzo’s architect on the project. “They considered a number of materials including fiberglass, aluminum, glass and architectural membrane. When they looked at tensile and saw that they could make the roof glow with different colors at night, they decided this fabric was the right choice.”
Tension fabric fit Rojkind’s other requirements for a material to make the membrane—it was lightweight and easy to install with minimal structural elements. It also offered flexibility and durability, and could easily be fashioned and formed, which was important because the concept for the covering was an amorphous shape with four large inverted cones over a frame-supported structure. The four sections look as though they are suspended midair.
The tensile membrane, which spans 4,865 square meters, is made of Precontraint® 1202 S2 by Serge Ferrari. Lonas Lorenzo began by performing a structural analysis using STAAD and RAM Elements from Bentley AutoCAD for initial lines and TechNet Easy Services Ltd. for formfinding to determine the stress capacity that could be loaded on the structure. Solid Works was used for fluid flow analysis, a wind tunnel simulation to gauge the effects of pressure and suction over the surface of the membrane in order to determine the size of pipe and weight of tensile fabric needed.
The tests confirmed that the membrane met local codes for wind, rain and ice loads, and international codes for reinforcement, detailing and design of the steel structure. This information was used to determine the anchor details to the building.
The tensile membrane was patterned and cut using the TechNet Easy program. The process consisted of first printing the pattern pieces on paper, then cutting and assembling the paper pieces into sections that were used to cut the membrane. Those sections were welded together using hot air. The final shapes, which accommodate the inverted cones in the final design, looked like a giant spider’s net.
The steel structure supporting the membrane needed to be constructed so as to keep the parking area as open as possible. Bridges were built between the parking shelter columns to achieve this. Curved pipes create a spine around the inverted cones and connect to a tube suspended from the floor, creating a sense that the entire cover is lightweight and airy. The bridges also line the exterior pathways to the garden, providing a unique walkway for customers.
Assembling the cover structure had its challenges. For one thing, the design phase of the project took longer than originally expected and the deadline, which was to complete the parking shelter in time for the supermarket opening, could not be changed.
For Lonas Lorenzo, that meant constructing the 200-ton steel framework and the tensile membrane in just five months. The problem? It could not use a crane for assembly. “All the work had to be done by hand, and that made it much more time consuming,” explains Perez. “There is a four-level parking garage underneath the rooftop, and that structure could not support a crane. Instead we had 80 people build the entire cover.” It took four months to construct the steel frame and one month to construct the tensile membrane. The sections of the inverted cones were assembled piece-by-piece and welded together as they were put up.
The design required a very short bending radius for the pipes that arc throughout the steel structure, which proved to be another challenge for Lonas Lorenzo. The pipe comes in 6mm lengths and is welded together and bent to the proper radius. The pressure put on the pipes to achieve this often causes unsightly marks. The architect insisted that the pipes could not be marked up since they are exposed to the public. “We made mockups and tested for the right shape and curvature without creating marks. We tested until we got the shape and look that the client wanted,” says Perez.
The tensile canopy with its translucent quality provides a protected, yet airy space by day. At night it glows and shines with LED lights, creating a luminous beacon to attract customers.
There has been a change to the cover since the parking shelter opened in August 2013. The Chedraui supermarket needed more space for parking, so another level of parking was built above half of the original shelter. To do this, half of the cover had to be removed because the structure would not support another parking level and the membrane. Half of the cover, with two of the inverted cones, remains.