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The Souk Okaz

December 1st, 2013 / By: / Case Studies, Exteriors, Feature

Tensile membrane design recalls rich cultural history.

Located in the Mecca Province, on the slopes of the Sarawat Mountains in the Kingdom of Saudi Arabia, lies the city of Taif. With fresh mountain air and beautiful scenery, the city of 500,000 is a popular getaway from the intense heat in the region.

For hundreds of years, it was home to the Souk Okaz, a famous bazaar that served as a cultural center where people gathered to hear poets exchange and challenge each other with their writings. The annual poetry festival was revived in 2008. To accommodate the festival and other cultural activities, a new 3,000-seat theater was built at the site, a modern facility that pays tribute to the cultural history of the city. The theater, designed and built by the architecture firm Saudi Diyar Consultants SDC, features a center arena surrounded by stone towers that make a dramatic visual statement as well as provide support to the structure’s roof.

To create that roof, Saudi Diyar contracted with Taiyo Middle East LLC, the Middle East division of MakMax (also part of the Taiyo Kogyo Group), an international company that designs, builds and installs membrane projects worldwide. Taiyo Middle East managed the project, while MakMax Australia designed the structure and Shanghai Taiyo Kogyo Co. Ltd. fabricated it.

“They wanted a tent-like structure that would embody traditional Arabic design and maintain a natural appearance in its desert location,” says Martin Eddleston, the project engineer with MakMax Australia who designed the structure. “It also needed to allow for the transmission of natural light, and serve as a landmark for the theater and event center.”

The extremes of the location shaped additional requirements for the covering: It needed to provide shade from harsh sunlight, be watertight and include a porte-cochere (a covered carriage entrance). The material had to protect visitors from wind, the extremely high UV environment and the inevitable sandstorms for which the area is known.

Modern tradition

Eddleston and his team designed a tensile membrane structure made from PVC-coated polyester fabric. It is reminiscent of a bedouin tent placed atop the theater, with a central spine and draping sidewalls. Tent-like details such as masts and cable stays were used wherever possible.

To expand on the traditional Arabic motif, MakMax took great care in creating a pattern of geometric shapes and forms provided by the client that are used commonly in mosaic art. However, printing the pattern on the fabric presented challenges of its own. One concern was how the coating would hold up under the harsh sun.

“We used accelerated aging testing to investigate different methods of printing the pattern onto the fabric,” says Eddleston. “Ultimately, we determined that laser printing would provide the longest life span.” Japanese company Hiraoka & Co. Ltd. manufactured the fabric.

Another issue was the laborious process required to accurately align the intricate pattern on the individual sections of fabric. Using form-finding finite-element software and detailed design calculations, a 3-D form was created and then flattened and cut into segments to plot on 2-meter-wide fabric rolls that were already printed with the desired geometrical patterns.

The individual segments of fabric were welded together into 20- and 30-meter panels while maintaining the continuity of the printed pattern. The fabric segments were cut using computer-controlled plotting machines that aligned the segments onto printed rolls with the careful placement of the operator. During the process, pattern alignment was double-checked on a computer screen.

Assembled, the tensile membrane structure features 11,000 square meters of fabric, 130 metric tons of steelwork and 2.5 kilometers of structural cables between 20 and 40 millimeters in diameter. “It is actually quite light for its size, as well as very durable,” says Eddleston.

Making spaces

The large public space required an internal clear span measuring approximately 60 meters x 65 meters. The central roof truss spans about 65 meters and is anchored to four of the towers. The minimum under-canopy clearance was 12 meters with full integration of the structure with the main seating, stage and tower construction.

To accommodate for thermal expansion and wind, a system of slide bearing pots was used. This allows the central truss to constantly shift and move by a few millimeters, reducing the large lateral forces that would impose too heavy a load on the four towers.

With a structure this size, careful consideration was needed designing joints, allowing for adjustment at connections to ensure that any fabrication and construction inaccuracies could be easily dealt with on-site. Many base plates were designed as two-piece plates, connected with long threaded rods to enable adjustment on-site before being welded together with cover plates.

The main connections at the porte-cochere are fixed with 89 millimeter bow shackles to steel CHS beams hidden inside the main tower. Here a complex sleeving system was used to jack the fixing CHS against the wall of the tower using hydraulic rams to achieve the design location of the front membrane plates with the ability to adjust as required.

There were unique challenges on-site during installation, according to Ahmad Dalain, Taiyo Middle East project director, including the realization midway through the project that the site contained a large rock measuring 100 meters long by 30 meters wide that could not be disturbed. “This rock had great historic value,” says Dalain. “It was the site of the most famous poetry competition held hundreds of years ago and also a site for sporting competitions for the entire Arabian Peninsula.”

Two of the concrete towers to which the membrane was to be anchored could not be built, and it was too late to consider any changes to the design of the fabric structure. Instead they used vertical trusses fixed into the ground with rock anchors.

Meeting challenges

The location of the rock also proved difficult for installation. Originally, the central truss was to be built on-site and put in position with a crane. However, there simply wasn’t the space to build it or to maneuver a crane.

Another problem was wind, for which the city of Taif is well known. “Wind is simply the enemy of any fabric installer and forms 99 percent of constraints,” says Dalain. These two complications caused delays in approval of MakMax’s plans, leaving just 60 days to complete the project before the start of the poetry festival. According to Dalain, “Installing such a large, complex structure safely and accurately within 60 days was quite a challenge knowing that the weather conditions would not work in our favor. Fortunately, we had already started erecting the steel truss structure two months earlier.”

They built the truss in two sections and constructed scaffold towers in the arena from which they could erect the sections. The membrane panels were also installed from the scaffolding, and the work was done in two 16-hour-a-day shifts.

Safety nets were used to enable workers to interconnect the panels and to enable other work to take place on the ground. Workers were properly trained on how to walk and work on the nets.

To make the festival deadline, 80 workers were employed for the last 45 days. Says Dalain, “That is a lot of manpower when you consider that typically, you build a soccer stadium with 35 to 40 workers.”

The Souk Okaz Public Theatre did open on time and to great reviews. The use of modern materials and construction techniques helped achieve the goal of fitting in with the surroundings and serving as a cultural landmark and an attraction for visitors.

Julie Swiler is a freelance writer based in St. Paul, Minn.

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