Will a floating donut design stand?

In 2007, I spent six months living and working in Copenhagen. There were many cultural differences to overcome, and a lot of new construction methods to learn. Scandinavian design is renown for being modern and forward thinking. Danish architects are leaders in long span structures, sustainable design and creative use of space. I learned to approach projects more creatively in order to achieve the design goals.

One conceptual project that I was involved with was sited adjacent to Parken, the National Football Stadium. The proposed program included a multipurpose arena, a theatre stage, parking, office space, a fitness center and an extensive green roof. Locating all of these services on the constrained site was a challenge for the architectural team. Parking was located below grade, the arena at ground level and everything else above.

In that scenario, the major challenge was finding an economical way of supporting multiple floors of occupied space above the arena. To ensure unobstructed views in the arena, a 50m (160 ft) free span was required. The first scheme was

The first concept explored a conventional box design, topped with tennis courts and a crown-like perimeter wall. However, when the long span loading concerns were shared, the architects relieved weight by removing structure above the mid-span. The resulting design featured a floating square donut above the box. Developing a structure that retained the visual intent would be difficult, but more economical than the original, more conventional, approach.

Structural design proceeded in two steps: first setting the design of the arena enclosure and secondly supporting the ancillary levels above. The intent was to have both systems vertically supported by the same set of columns, thus avoiding a transfer situation in the arena roof. In one scenario, we considered supporting the entire donut on just four corner super-columns.

The truss supporting the donut would need to be three stories tall in order to span the length of the arena. However, this was aesthetically possible, because the truss would be located along the interior face of the building. The design of the truss members depended on the loads, materials, and architectural requirements.

The layout of the diagonals can be chosen so that they are in compression or tension. Eventually, all loads find their way to the top or bottom members, called chords. The design of these members is critical, since they usually see the greatest amount of load. Different design consequences apply if a member is in tension or compression. For a member in compression, the length is especially critical, since this most determines the susceptibility to buckling. Therefore, we would prefer the longest members to be in tension. However, dealing with strange load conditions and providing room for walkways through the truss can disrupt the best laid plans.

In the end, our design mixed a Warren layout (alternating diagonal directions) with a Pratt (diagonals only in tension). The combination was due selected so that the 3-story tall truss would be stable during construction. The one-story warren truss could be erected on the ground and lifted all at once. Then the other two stories would be erected above, using the first floor as an erection platform.
We later looked at several more schemes for the proposed arena. Ultimately, the project was canceled before construction commenced. Nevertheless it presented an interesting exercise in combining universal principles with local preferences.

Will it stand into space?

Earlier this week CNN ran an article on its front page about the prospects of a space elevator. The idea, first seriously proposed by author Richard C. Clarke 30 years ago, has gained some momentum because of a series of prizes offered to pioneering inventors. NASA offers a $2 million prize to anyone who can design a suitably powered lift to crawl up a 1 km high tether. Another contest challenges teams to design a tether twice as long and strong as what currently available on the market.


Why all the enthusiasm for pursuing such science fiction? In this case, geeky altruism gives way to corporate opportunism. Offering a low cost solution to lifting satellites and research modules into geosynchronous orbit could result in a major pay day. Consider sending tourists into space at $1,000 a trip or the potential for solar energy generation free from cloud cover and other environmental restrictions.

But will it stand? Experts and enthusiasts believe that the space elevator will happen within our lifetimes. But for now, two major hurdles stand in the way: 1) finding a suitable material for the tether and 2) developing an efficient propulsion system.



The experts quoted in CNN's article estimated that a chord 25 times stronger than most advanced industrially available materials would be required. On first glance, that seemed extreme, so I ran some of my own numbers. To simply things, I assumed that the cable would pretty much just hang the whole way - the real design is certain to be more complex.

First up, the length of the tether must extend into geosynchronous orbit, so that the space platform remains directly above the base. That's over 22,000 miles up. At that elevation the force of gravity from the Earth is almost 60% smaller. That helps, but a steel cable like those used in suspension bridges would still be around 950 times over capacity. Using Kevlar represents a 10-fold improvement, but we're still not in the ballpark. At least my numbers arrived within an order of magnitude of the expert. The web is a buzz with the potential for carbon nano-tube technologies. Still in their infancy, they provide the hope for a suitable tether material.

Construction a climbing vehicle is proving to be as difficult a challenge. To date, no teams have achieved the goals of NASA's competition. The latest attempts drive a small electric motor with solar power. Try finding a 22,000 mile long extension chord. Carrying fuel on board also heavy and detracts from payload capacity. Looking ahead, many experts believe that laser propulsion holds the key, at least as an energy supply for on-board motors.

The challenges seem very exciting. Science and technology geeks like myself believe that the new technology being developed along the way is worth the cost and may be more valuable than the actual working elevator. However, the viewpoints shared by non-technical contributors to the CNN comment board are very disheartening. "Solve world hunger and stop all wars first," decries one writer. Another thinks NASA is a sham and that all monies should be directed toward the recovering economy. Certainly, there needs to be a balance to funding policy, but I for one believe that such scientific exploration return much more than the initial investment.

Where do you stand on this question? Is prize money well spent on incentives to create a space elevator? How would you approach the problem? What other materials might offer a solution? Have you heard of an innovative new energy solution? Comment below or participate on at www.spaceelevator.com

Note: I had not ever considered the possibilities of a space elevator until earlier this week. It's an intriguing and compelling technical challenge to structural engineers.

ASCE Annual Conference

This year’s ASCE Annual Convention was held in Kansas City. The event provided an excellent opportunity to network with industry leaders, learn about the direction of the profession and learn new skills for improving your business acumen. My favorite part of the conference was meeting old friends from previous ASCE commitments.

The formal conference began with several inspirational speeches. Outgoing ASCE President, Wayne Klotz, declared, “modern society cannot exist without infrastructure.” He urged the incoming leadership and all in attendance to embrace the ABCs of ASCE: advocate for, believe in and commit to advancing the profession and protecting the nation’s infrastructure. The importance of advocacy was driven home by Jim Suttle, professional engineer and mayor Omaha. In short, we all lose when engineers shy away from advocacy and the public debate.

Throughout the conference many sessions were offered to promote the profession through better management practices. These included: Negotiating Better Engineering Contracts, Maximizing Your Bottom Line - Flexible Work Arrangements, The Economic Crisis - Leveraging Infrastructure Development for Recovery, Making the Most of Generational Differences, and more. Technical tracks on sustainability and Building Information Modeling were also among the conference offerings. Students and Younger members also attended symposiums specifically tailored to their interests. There was something for everyone.

Ben Stein was the final speaker at the conference. Far from the monotone sleep inducing lectures attended by the Wonder Years’ kids, his talk was very entertaining. He woke everyone up by starting, “I like you guys because your job’s not B.S.” As opposed to the entertainers with which he frequently works, he expressed thanks that engineers work “real jobs with exactitude.” The connection between his various stories and civil engineering was subtle but important. People from all walks of life are seeking answers to the complex questions of our day. Engineers are viewed as an elite team of problem solvers with the education and creativity to solve these problems. It is a lofty charge but one we can achieve if we accept this vision for the profession.

Sunday was perhaps the most fun day of the trip. Traditionally, a service day is planned following the conclusion of the conference. This year ASCE members volunteered to make improvements to the Heartland Therapeutic Riding Ranch. This facility provides equine-assisted therapy to children and adults with disabilities through human interaction with horses. The day’s events also included outreach activities that introduced engineering principles to over 50 local children.

In addition to the typical conference events, I was busy working behind the scenes on many tasks. On the Wednesday before the conference, I attended the Committee on Younger Members meeting. There, I learned about proposed changes to the organization to adapt to the needs of upcoming generations of engineers. I also met with members of ASCE’s media relations staff to discuss the blog I write for Student and Younger members, http://blogs.asce.org/bridgingthegap/. The Committee on Pre-College Outreach, which I chair, also met informally. We brainstormed some good new ideas and sought to gain support immediately by fanning out into the afternoon ice breaker reception and talking with ASCE leaders. Friday night, I had dinner with the editor of the Journal of Leadership and Management in Engineering. He asked me to contribute a column to their next edition. What a week!

Will it stand as a Cube?

Architects and engineers are often creatively constrained by the perception of economy in conventional designs. Generations of efficient refinement of building form have led toward standard boxy structures. However, creativity and function driven design can be encapsulated within a traditional cube. The Matrix Gateway Complex would be an exception to the rule of monotony in rectilinear buildings. It would provide residents a full 3-D city experience, featuring suspended platforms linking modular housing and community venues.

Designed as both an urban gateway and a self-sustaining city, this 42-story, 180m cube prototype would be one of the greenest, most aesthetically striking and technologically innovative mixed-use buildings in the world. The Matrix Gateway Complex would contain many of the amenities of a great urban center: a hotel with fitness and conference centers, retail and office spaces, cultural and religious facilities, and waterfalls surrounded by lush green terraces. Each component would take the form of a moveable module, connected to one of five central cores, all of which would be visible from the outside through a semi-transparent exterior skin.


Will it stand?

Based on conventional beam and column floor support, the structure would appear obvious. However, the initial concept dictated that the entire structure be supported only on four central concrete cores. Columns on the grid would not extend down to a foundation. There would be potential economy in this design requirement, given that the entire building is sited over water

Early expectations were that the entire structure could act as a gravity load-resisting moment frame. This concept relies on the stiffness of the columns, beams, and their connections, similar to the concept of a Vierendeel truss. However in this case, the structure would instead cantilever away from the cores. Computer analysis indicated that the 18m span of the beams was too great to satisfy the load demand.

Alternately, large hat trusses could be constructed in the top stories of the structure (intended for mechanical and energy generation equipment). The majority of the columns would then hang from these trusses. This idea has been put to practice in the Boeing building, in Chicago. A full bay is hung over the train lines that run along side the Chicago River.

In order to preserve vast interior atria while providing links between the core clusters, a combination of moment frames, hat trusses, and inter-story trusses would need to be implemented. These elements would facilitate a stable load path for floor plates of varying size and shape. The final structural hurdle involves the asymmetrical layout of the cores. To preserve the economy of the structure, it is likely that an additional steel core, or large column, would be required to support one corner of the cube from below.

The Matrix Gateway Complex was the named the Best New Global Design for 2009 by the Chicago Athenaeum Museum of Architecture and Design. The design is by Adrian Smith + Gordon Gill Architects. Thornton Tomasetti provided schematic structural consulting.

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