PFEIFER leave its mark on SoFi Stadium roof
Memmingen (Germany)-headquartered PFEIFER is an internationally operative group of companies. The company’s business purpose leads them along the value creation chain of rope and lifting technology, connecting and lifting systems and cable structures – directly to the customers’ application tasks.
The 70,000-capacity SoFi Stadium is a stadium and entertainment complex in Inglewood, California, United States. The stadium stands out for its spectacular architecture and is the cynosure of all eyes.
For PFEIFER, while being engaged in the roof work of SoFi Stadium, time was at a premium and looming deadlines are a common factor in almost all construction projects. However, the SoFi stage goes beyond that. Twenty-three kilometers of pre-assembled steel cables had to be on site 12 months after the contract was inked. Shipping alone took 28 days. This meant that quantities of rope and weight had to be channeled through production in record time that would otherwise not have been manageable in a normal business year. To enable this, production ran in three shifts.
For the 302 ethylene tetraflurorethylene (ETFE) panels, PFEIFER procured 60 tonnes of ETFE membrane, printed it and, after printing, cut, assembled and welded it.
PFEIFER landing the SoFi Stadium deal was not a business/cost decision, but full credit goes to its Design Assist factor as well as the company’s wide span of services.
Jassen Mihaylov, Head of Tension Members and Head of Lightweight Architecture, PFEIFER Structures, Germany, stated that two important factors led to PFEIFER becoming part of the SoFi Dream-Team – “First, the Design Assist, our support to engineers and architects in making the structure doable in engineering – the right material in the right place and having in mind the budget. It pays always in such a complex project to involve a one-stop-shop company from the very beginning on a consulting fee basis: This is a common way of working in the United States but not yet established in Europe.”
Added Mihaylov, “Secondly, with our wide span of services – Tension Members Fabrication, Membranes and Foils Fabrication, Retractables development, engineering and design, PFEIFER was the sole construction company to have in-house all elements of the most critical elements in the stadium structure: The long span cable net, the unique single layer roof skin and the movable pictures frame to support the climate engineering, and last but not the least, and very important for the business case of Stan Kroenke was the integration of LED in the transparent roof skin and transforming the roof to the biggest media display in the world . As a single point of contact for these challenges, only PFEIFER could give answers to all this different open points.”
PFEIFER played a very key role within the planning and construction team involved in building the spectacular SoFi Stadium.
Informed the PFEIFER top official, “We were the Designer, Producer, Builder, Installer, Project Manager of all related to the transparent illumination building skin of the biggest indoor-outdoor stadium of the world. In the construction team, we were the expert for long-span big displacements structures, with kinematic and movable elements, enabler for the energy concept and media show on the roof.”
Assembly of the cable net:
Step by step:
After the ropes were delivered on reels, they were laid out for assembly on the construction site. A reel platform was used, i.e., a frame with a drive that was hung on a crane. The crane moved down the grandstand, the reel moving slowly and the rope extending. First, the lower rope net was laid out followed by the upper rope net, to which 158 supports were attached.
At the joints, i.e., the connection points of the two-part ropes, the ropes were pulled together using strand jacks like a zipper. Then, in the first step, the upper rope net was pulled up, then the lower rope net, which was also connected to the supports in this step. By pretensioning the lower cable network, the upper cable network was pushed above the horizontal zero point, which gave it its characteristic curvature.
When working with the double ropes (120 mm diameter), tension forces of over 800 tons occurred. Accordingly, lifting devices had to be used that can handle such forces.
Once the complete roof of SoFi Stadium was erected, the steel frames for the ETFE foils were lifted and the drive technology installed.
The biggest challenges for PFEIFER during planning and construction were, according to Mihaylov, the timeline! – “Problems come and pandemic situation comes, but the deadline and the opening stays! Due to the time constraints, from a certain point onwards, several tasks were carried out parallel. It was also necessary to make up for the delay in the earthworks. With a project like this, the deadline had to be met, no matter what.”
He added, “PFEIFER came to the rescue with its engineering idea: Thanks to the structure of the multipart cable network, other trades could already start their work after the installation on the East side of the stadium, during the installation on the West side. To do this, all schedules and shift divisions had to be adjusted. The support with the assembly and hanging of the video board (Oculus) in the stadium, which ran parallel to the assembly of the roof on the West side, proved to be an additional challenge.”
Design and installation of ETFE membrane:
Skin of envy
The indoor-outdoor stadium is called the SoFi Stadium, partly because of its transparent, thin outer skin. To achieve transparency, glass, ETFE or, as a cost-effective solution, polycarbonate can be used. In a building the size of the SoFi Stadium, the main advantage of ETFE foil is but apparent: While glass has to be calculated with a weight of 18 kg/m2, the weight of ETFE including installation material is 1 kg/m2. The structure can be made leaner, done with less expense and also more sustainable. At the same time, it is a facility where air gets well-circulated because a load-bearing steel construction for panes of glass overhead, which must meet the appropriate security requirements, would be comparable to a prison bar. When it comes to safety, ETFE is much more reliable than glass, especially in an earthquake-prone area – because ETFE is deformed, but there is no risk of breakage.
The challenge to set up ETFE membranes is generally based on the fact that the light foil moves upward in the wind suction. In order to compensate for this suction, an ETFE structure must always have a counterweight that ensures a pull downwards. In SoFi Stadium, steel cables were pulled in at defined points. In addition, a pocket containing a supporting rope was welded into each individual ETFE membrane. The background: At a size of 18 meters by 18 meters, wind suction would have become a problem even within a membrane. Such a modification poses special challenges for the film engineering, because each film is produced slightly smaller than the panel. During assembly, the film is pulled until the tension is right. That alone is very demanding for very large ETFE membranes. In addition, the pulling had to be planned so accurately so that the rope pockets with the supporting rope get in the right place and the stiff weld seam does not tear.
The UV radiation from the sun is particularly important for the lawn in the stadium to grow. ETFE film is permeable to this UV radiation. In order to reduce solar radiation and thus heating to a reasonable level, the ETFE film for the SoFi stage was printed with silver dots that reflect part of the sunlight. The energy transmission value (G value) was calculated in such a manner so that the UV radiation is still sufficient for the lawn to grow.
Tasks cut out
The core of every project is the structure/process organization with all functions and the associated structure plan with scheduling. Even with a project of this size, it is a matter of defining all tasks down to the granular level, defining work packages and finding out who is available for which task. In addition to pure technology, this includes issues such as export, import, contact management, billing, and numerous other functions.
The SoFi Stadium development was divided into six sub-projects, each of which originally had its own calculation for administrative tasks. In order to work more efficiently, a separate, seventh sub-project was defined, which took over the administrative tasks for all the others. This included the management of travel expenses, local transport, the vehicle fleet for the employees as well as the procurement and furnishing of 20 apartments. The volume for this alone was around EUR 2.5 million.
Receiving supplements in the project means that trust has been built in the collaboration. Nevertheless, there are additional expenses behind it that need to be traded. In parallel to the assembly of the stadium roof, a request was made to PFEIFER to help with the installation of the video board. It weighs 1,000 tons and is fixed to 14 suspension points. First, a steel frame was built in front, which was lifted at 14 points with strand jacks. The screens were then mounted in a floating state, whereby the steel frame had to be kept in the water by leveling and readjusting the strand jacks. Then the video board was pulled up and hung on the roof.
Six months prior to the stadium getting completed came the request to carry out the steel installation for the sponsorship signage. In the final spurt, the secondary steel construction and the ETFE panels had to be modified at two points on the outer skin in order to enable the attachment.
A long-discussed sub-project that was implemented shortly before the end was the development and installation of the video surface on the roof, which consists of 28,000 V-Pix LEDs. As a precaution, PFEIFER had the necessary pockets and cable guides integrated into the ETFE membrane during production. Together with the LED manufacturer, PFEIFER developed a surface model of the roof as a 3D simulation in order to calculate the perfect position for each individual LED for a coherent overall picture. In the final phase of integrating the LEDs, the drive concept also had to be adjusted in order not to cause any inconsistencies when the ETFE panels were driven and stopped.
The SoFi Stadium project threw up challenges as far as the engineering facet was concerned, and it was not ‘business as usual’.
Asserted Mihaylov, “In the field of outstanding lightweight structures, wide span, integrated solutions there is no such thing as “business as usual” and every project is a new exceptional challenge. For this reason, it is important to work early in the team of the developer, architect, engineer, and local Manager.”
The economic power:
In order to be considered as a partner for a project of this dimension, financial reliability plays a major role. PFEIFER is economically positioned in such a way that large construction projects can be implemented without problems through equity and financing. The company boasts the credit rating to receive the necessary payment security from banks. For this purpose, the internal cash flow reporting is designed in such a manner that the economic viability of a project can be shown. In-house and external work with manpower is calculated in such a way that a positive result can be achieved at the end despite the changing schedules and tasks. In addition to the company’s own competence centers for rope, steel, membrane, and drive technology within the company, PFEIFER also has a network of subcontractors and suppliers who also have the financial wherewithal to carry out projects of any size.
COVID no hindrance
The SoFi Stadium development was a project of unprecedented proportions and the coronavirus storm could not bring the project to a standstill. When the pandemic broke out in California in March 2020, the venue construction work was on because the stadium was defined as “essential work”. However, the strict COVID-19 protocols in place put up several stumbling blocks. While up to 15 workers took the elevator to work on the roof pre-COVID-19, the same had come down to two post-pandemic. If the team worked with no social distancing up until then, in the coronavirus world, a new work concept had to be implemented ensuring maximum physical distancing. Positive COVID-19 cases were reported and workers did go into quarantine several times. Nevertheless, the project was completed on time, thanks to the strong motivation and perseverance of all employees.
The coronavirus menace did have a impact on PFEIFER as Mihaylov puts it, “We had a huge impact: Delivery chains were interrupted, and delivery times did not work. But, PFEIFER has a very experienced Logistics Department and reacted properly to this challenge. Our processes are redundant and we could switch to other places in our international net where the pandemic was not that strong at the given moment. Being PFEIFER, the client buys flexibility too, even for a pandemic.”
SoFi Stadium is the most expensive stadium of all times. Being part of such a prestigious project was a reason for PFEIFER to rejoice, but it was a huge load of responsibility too for this top-notch company as he continued, “On the one side you are happy to be part of this exceptional project, but sure this is a big responsibility too. PFEIFER grew up along these increasing responsibilities, and then at the end the COVID pandemic came on top. But, we were successful. So, we are now ready and self-confident for the next challenges!”
PFEIFER did learn lessons from the magnanimous SoFi Stadium project for future stadia as Mihaylov remarked, “We need to keep being and getting more flexible in design, production and execution for our customers. More fields, like Media Façades, LED integration are becoming part of the structure and we need to manage and deliver this integrated product. Media solutions, sustainability and adaptable changing constructions are the big topics of the future and PFEIFER is working very hard on this future setup.”
Brains behind the project
Christian Schlögl, Head of Division Structures, PFEIFER, stated, “In my point of view, the team is extremely important. Regardless of whether you are a Project Manager or a Technician – at PFEIFER we have engineers who are empathetic, who are focused on their goal. You can also feel this spirit when working with other companies. If, as with SoFi, our partners are open to Design Assist, then our employees show that they have the right instinct. The feeling for project management, for financial feasibility, the feeling for teamwork.”
Remarked Bill Schmidt, COO, PFEIFER Structures North America, “When I look back at SoFi, I feel immense pride and an intense sense of accomplishment. The appreciation for this is due solely to the strength of our entire team. In total, more than 100 of our employees were fully committed to the SoFi stage at peak times. There were also specialists from the group of companies. We had colleagues from the Czech Republic, Poland, Germany, Switzerland, Austria, plus the Americans and Mexican-Americans from Los Angeles. At first, we didn’t know how it would go on the construction site. Would the skilled workers here respect all the bright minds from abroad? The concern was unfounded, we experienced great interpersonal openness and a deep bonding developed.”
Asserted Schmidt, “With SoFi, we saw what we as PFEIFER can achieve in the company. With this experience behind me, I would say there is no project that we cannot manage. There is just so much knowledge in the company and such a great team spirit that we will achieve every goal together, also in the future.”
Mihaylov informed about future projects – “We are working on a very innovative future technology project for an Energy Storage Tower in Heidelberg Germany, this is part of the green deal and our contribution to future innovative technologies. We want to implement our expertise as regards bridges in the US too, like in the Redmond Technology Station Pedestrian Bridge in Washington, US.
He added, “On the sports front we are working on the refurbishment of the Olympic Stadium in Sevilla, Spain, and on the most modern closed sports arena of Spain in Valencia.”
Mihaylov named few of his favorite PFEIFER project, “I love the Dubai Expo Entrance Art Shading structure with perforated aluminum panels, LED and stainless Steel Tension Members, it is amazing how real becomes the rendering of Hopkins Architects.
Another one is the Canyon at Salt Lake City International Airport at Utah in the United States. I like the interface to art, interior, engineering and new technology.”
He concluded by stating, “My favorite Sports PFEIFER Structures Project is the Allianz Field in Minnesota (US) due to the interaction of light, material, lightness and changeable, transformable skin and the innovative use for the first time in this scale of this membrane material.”
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