Will smart balloons change design?

At the 2009 ACADIA (Assoc. for CAD In Architecture) conference, I was blown away by all the radical design ideas brought forth. Of them, the most intriguing ideas imagined how new technologies could be used to create responsive structures - buildings that could change shape and function in reaction to external stimuli. Ideas like this are more familiar in the robotics field, but it turns out that simple mechanisms can be utilized to bring our buildings alive.

Mehran Gharleghi and his colleagues at Studio Integrate in London have been exploring the field of responsive structures. Their motivation was to apply simple light weight technologies to provide naturally ventilated and cooled spaces in hot sunny locations. The following is a short description of their research on an Adaptive Pneus in their own words:

"This research focuses on the performative capacities of a pneumatic material system in regard to the specific environmental conditions. It explores a new approach that integrates form generation, material behavior and capacity, manufacturing, and assembly to deliver a modulated environment suitable for occupation.

The focus of the design process and research was the use of Adaptation as a mechanism to modulate environmental performance. Here, adaptability relates to the responsive action that affects the performance of the whole building and, therefore, holds a much closer relationship to the biological and natural ideas of responsiveness.

Location of the sun during the day acts as a trigger to adapt the system, allowing the system to augment passively the environmental conditions. Detection and reaction are embedded in each cell, and responses take place locally and independently. These responses at the regional and global scales allow for the distribution of intelligence across the whole system."

Will a catenary span 600 ft?

The Chameleon is a design concept for linking Chicago’s Northerly Island to the shore near Soldier field. In the second part of my series exploring the potential structure of this design, I applied basic load and deflection principles to estimate a steel quantity. Unsatisfied with the brute force approach, I explored other structural forms and became intrigued by the concept of the catenary.

A catenary is the theoretical shape that a hanging chain or cable will assume when acted on only by its own weight. Such a member experiences only tension forces and is very efficient for spanning a distance. The inverse would be the classical arch, a design feature that ideally only experiences compression. Both structural concepts were widely implemented until the advent of steel beams. In fact, the Catalan architect Antoni Gaudi was known to utilize catenary models in his most famous works. A series of strings was used to construct the complex arch and vault system he desired - just upside down. Gaudi realized the relationship between strings in pure tension and stones in pure compression, a law most eloquently described by Newton. “To every action there is an equal and opposite reaction.”

The arc of the catenary is defined by a fairly simple mathematical relationship. y=a*cosh(x/a) The key constant in the equation, “a,” represents a relationship between the tensile force in the member and the applied gravitational force. By tuning the axial stiffness, or resistance to elongation, and strength of the members the arc can be adjusted. Even within fairly rigid confines, such as those set by the need to allow boats to pass beneath the bridge, a satisfactory geometry can be achieved.

Recently building engineers have begun to revisit the potential of catenary action. Many of the most recent reports have dealt with the capacity for floor systems to apply catenary effects to prevent progressive collapse. If properly detailed, the floor beams on several floors can actually form a catenary that will support a column despite the removal of a column support. These recent reports still caution that the method is only effective when large deformations occur and the system has a substantial span to depth ratio. Fortunately, both of these conditions may be permitted in our long span bridge design.

Several bridge forms that utilize this structural technique. Simple rope bridges, like those creaky death traps featured on Indiana Jones, are the most elementary catenary structure. Unlike a conventional suspension bridge, these parabolic structures follow a true catenary curve, because the flexible deck follows the free hang of the cable. The longest such rope bridge, located near Vancouver, is an incredible 450 ft. long. Of course, the problem with these true catenary structures is the bounce and sway experienced by the brave souls that cross them.

Hybrid applications of the catenary shape have been applied in more static conditions. While the cable of a suspension bridge may initially follow a catenary arc, once the deck cables are attached, the form becomes a parabola carefully computed by the designers. Nor is it essential to use cables to achieve the purpose. Tower Bridge, in London, is known as a suspension bridge, but the “cables” are actually riveted steel plate sections. Therefore, we can assume that a catenary form can be applied to a solid static form.

The major implicit challenges are tuning the member sizes to achieve the final elongated position and constructing given the daily changing member orientations (as construction load is applied). Such a non-linear analysis and sequencing model is beyond the scope of this speculative blog. However, if we overlay a tension catenary (blue) and a compression arch (red) on the elevation of the bridge, we can see potential in the architectural form. Two more parabolic lines (green) appear to close the gaps, facilitating a continuous structure. Even if the intent of the exterior surface is to be undulating and unpredictable, we could envision facet lines that follow the main structural form or find ways to embed that within the structure. I believe this is a concept that brings structural harmony and simplification to a chaotic form that is more visually indicative of the sense of turbulent times.

Taking the catenary concept one step further, I would further propose that the interior pedestrian paths be supported by the means of one massive catenary bridge. Spanning 600 ft., it would be the longest “rope bridge” in the world. Far from typical, this catenary bridge would be comprised of dual layers with a depth of 16 ft. between. Ramps would connect the two layers and provide exit from the top down to dry land. The original programming called for entertainment and snack bar venues. Providing a stable surface, not wildly influenced by passing pedestrians would be challenging. Perhaps, the catenary pedestrian bridge could be connected to the exterior structure via a system of dampers, to modulate the movement and sway.

Though the initial design suggests that the pedestrian walks be suspended from the super structure, the incorporation of a pedestrian catenary bridge might provide the necessary construction platform to facilitate the building of the shell structure. At times during construction, might the shell actually be suspended from the pedestrian bridge. This might be a significant design consideration that has greater bearing in determining the size of the catenary bridge members than the actual person load.

Though this analysis has been brief, I hope it has accurately represented the thought process of an engineer presented with a design challenge. Use of catenary and arch forms is far from new technology, but they may be appropriate for this project. Even within an apparently static form, there might be potential to implement a bridge form known in the popular mindset as awkwardly unstable. From a structural dreamer’s standpoint the irony of the design is quite satisfying. Delivering a record setting structure goes even further in achieving the goal of a landmark bridge.

What other examples of catenary bridges are out there? Does the catenary concept have merit? Do you think the pedestrian platform would be steady enough to be comfortable? How might contractors cope with the gradual change in shape that will occur in the structure throughout construction? Comment below.

Will a bridge link Northerly Island?

The Chameleon pedestrian bridge would link Soldier Field to Northery Island. But, will it stand? In this blog, I will apply basic structural principles and equations to estimate the material requirements of such a bridge. To the greatest extent possible, I have tried to remain true to the original design intent, but early schematic evaluations require lots of approximation.

My first caveat is that I’m a building engineer. The layman would be surprised at the differences between the thought processes and building codes that apply to bridges and buildings. However, given the functional intent of this pedestrian bridge, it might is some senses be better treated as a building. To that end, I’ve used the Chicago Building Code (CBC) as a baseline for determining load conditions and general requirements. As we proceed, though, you may find that more elements of common vehicle bridges will find their way into the concept by way of seeking the most efficient forms.

As a building engineer, my first inclination was to evaluate the bridge concept as a beam. In the classic, simply supported beam, the greatest bulk of the structure would necessarily need to be located in the center of the span. However, the architectural intent is to minimize the mass of the structure where it most influences the efficiency of the design. That runs counter to the simple approach. Instead, I thought of the bridge as a system of two cantilevering beams. This type of layout places the greatest cross-section size over the abutments.

Cantilever bridges were once very common, owing to the ability to construct out from the piers until meeting in the middle. This reduced or eliminated the need for temporary piers or barges located in the deepest part of the body of water below. Employing such a construction method would be advantageous in this example as well, so that the marina below could remain in operation to the fullest extent possible.

Before I could run some preliminary numbers, I needed to make several estimates about the size and scope of the project. From Google maps, I estimated a free span of 600 ft. Taking all of the abutment requirements into account the real span might be a fair distance larger, but this estimate provides a baseline for exploring the concepts. Secondly, I estimated from the architectural sections, the dimensions of the superstructure. The platforms looked to be about 25 ft wide. The total height might be 45 ft. at the maximum depth. Since the exterior shape was to be comprised of many jagged surfaces, I applied a 33% reduction of the height to approximate the relative location of the main structural elements, treated as two lumps of steel - one representing the top chord of a truss, and the other the bottom chord.

I could estimate the weight of the bridge by taking the lumped mass of steel plus another 50% to account for connections, web members and cladding. Depending on the type of façade and the interior build-out, that number could be substantially larger. For the live load, due to pedestrians and amenities, I applied the 100 PSF load stipulated by the CBC for corridors, lobbies and other public space. Notably missing from my quick calculations were allowances for the effects of mother nature. Snow accumulation and lateral wind pressures would place a particularly large demand on any actual structure.

Nevertheless, I proceeded with a basic cantilever model. With the inputs described above, I was able to use pre-derived equations (taken from the AISC Steel Manual) to estimate the deflection of the beam at it’s cantilevered end and the amount of moment accumulated above the piers. As expected for such a long span, the deflections were large. Use of the spreadsheet allowed me to incrementally increase the amount of structural steel until arriving at quantity that seemed to meet the criteria. Again using my building background, I sought a deflection of no more than the length of the span divided by 360 (an arbitrary, but typically justifiable criteria). A deflection due to live loads up to 20 in. would be acceptable.

I also experimented with the length of the back-span. Intuitively, I figured that the longer the back-span, the smaller the end displacements. However, since my simple equation assumed the same stiffness throughout the length of the beam, when the back-span length increased too much, it became too flexible to provide a steady prop for the cantilever. This suggests that the architectural concept, which shows a short but deep section behind the forward pier, conceptually meets the structural demand.

After iterating through my calculations to meet deflection and strength criteria, I arrived at a design that called for about 1200 tons of structural steel. In more graphic terms, the bridge truss superstructure would consist of thirteen 14 in. wide flange beams (I-shaped) each weighing about 120 pounds per foot. Considering the other factors left out of my analysis, this seemed like an expensive brute force way to achieve the design.

I thought back to the original intent to minimize structural mass where not required by strength demands. The simple model assumed that the entire length of the bridge consisted of the same size section. However, because we chose a cantilevered design, the forces in the members would decrease as we approached the end of the cantilever. The structural shape could also taper with that demand. I used RISA 2D, a simple finite element analysis program, to compare the effect of tapered versus constant sections. In the tapered model, I reduced the weight of the section by 60% from the pier to the free end. As a baseline to see if I was still meeting the strength and stiffness minimums, I computed the deflection due to a constant live load first. The results showed an almost negligible difference. The effect on the dead load deflection, however, was a significant 50% reduction.

These results indicated that the original design had been conceived with sound structural principles in mind. Of course, many issues still remain to be addressed. One such concern is whether the multi-faceted shell will be stable. The jagged exterior form seems to call for some type of internal space frame or self-bracing mechanism to prevent the perimeter from buckling. Surely solutions exist, but a what cost to the overall project.

Without even addressing many additional design considerations, the steel quantities that I had arrived at still seemed heavy. Perhaps more efficiencies could be realized without compromising the architecture. Looking for inspiration, I would turn to other bridge examples. In the form of suspension bridges, I remembered the principles of catenary structures. To be continued in the next post…

How would you have conducted this schematic evaluation? Do you agree with the load applied? Would you have used the full section depth to estimate the building stiffness? What other important considerations were ignored in this evaluation?

Will new faces deliver landmarks?

Early in 2009, Chicago’s architecture community was a buzz about the opportunity to design spaces for the 2016 Olympics. They looked to showcase the city’s rich architectural history and implement new modern forms being explored by a new generation of architects. Adina Balasu was one such enterprising designer completing her graduate degree. As part of her studies, she devised a landmark bridge to allow pedestrians access Olympic venues on Northerly Island, just across the marina from Soldier Field.

The concept, christened Chameleon, was to create a functional bridge that would be a destination in itself. Two levels of walkway would be suspended within a futuristic space frame shell. The large interior space might also be used as a multi-purpose venue for entertainment, retail and relaxation. After the Olympics left, the structure would be a necessary link to further the planned development of the little-used island park. An inspirational form and engineering feat, visitors would make a visit to the Chameleon part of their itinerary, expanding the traditional Chicago tourist district several blocks south.

I was introduced to the project at a meeting of the AIA Young Architects Forum. Following Ms. Balasu’s presentation, we had the opportunity to discuss the details of the project. I was intrigued by the structural challenge and impressed with her desire to express the structural form in the bridge’s appearance to reflect the technology of the times.

I delayed in my review for several months before picking up the concept with a fresh perspective. Unfortunately, in that time, Chicago was passed over for the Olympic bid. Despite this missed opportunity, I started wondering who deliver the trend-setting designs of the future. The current recession seems to have stalled several major projects, and missing out on the Olympics further deflated the local architecture community. When the economy turns around again, who will be at the forefront. I suspect that many of the innovative architects that I met at the YAF will lead the charge.

The Chameleon appeals to me as one of those great next-generation architectural concepts. Over the next few blogs I will outline my thought process and presents some potential strategies for making the Chameleon stand.

What do you think, when will we escape the current economic downturn? Will their be a new generation of architects leading the way at that time? Where should enterprising structural engineers look to network with these future partners? Please comment below.

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.

pollcode.com free polls

Matrix Gateway Complex, will it stand?

Yes No

Will it stand in crystaline form?

If a tectonic shift in an undersea geological formation sent giant crystals thrusting up through the water’s surface, it might look something like this dramatic arts center prototype positioned in a lake or harbor. Eleven jutting, crystalline structures of varying size—with cantilevers of up to 230 feet over the water—are joined at a base largely concealed beneath the surface.


Inside the structures, the cantilevers create stunning interior spaces from which occupants will enjoy extraordinary views while experiencing a sense of being suspended above the water. The cantilevered roofs also allow the building to shade itself in a hot climate, which in turn allows for greater transparency in the glass curtain walls beneath.

Despite the challenging geometry, a rational framing plan using standard members is anticipated. The intent is to support the cantilevering point of the structure with a prop extending down to the foundation. Chord members (top or bottom members of a truss) would run along the major facets forming a shell-like structure that defined the top of the tapering shape. Several rows of columns would be hung from the exterior truss, while other columns extending to the foundation would lean up to meet the superstructure.


Lateral wind and earthquake forces could affect the general stability of the structure and induce unacceptable amounts of movement at the point of the form. The level of uncomfortable sway was estimated by first computing the period of the structure, or the time it would take for one complete cycle of swaying movement. A damper would be required in the structure to mitigate the motion.


Working within the basic architectural form, top exterior facets would include steel trusses. At lower levels in the building, an internal braced frame (x-braces) would link the floor diaphragms to the exterior trusses as well as to assist in torsional resistance. These systems compliment a unique inclining concrete core.

The design is by Adrian Smith + Gordon Gill Architects. Thornton Tomasetti provided schematic structural consulting.

pollcode.com free polls

Crystal Center, Will it Stand?

Yes No

ACADIA 09: reForm()

This past week, I attended the annual conference for the Association for Computer Aided Design in Architecture (ACADIA). It was held in Chicago at the Art Institute. This setting provided the perfect backdrop for the conference, which annually provides a forum for the examination of emerging research and application of technologies in the building and design professions.


New Modern Wing of the Art Institute of Chicago I attended sessions covering a very broad range of topics from self actuating pneumatic structures to kinetic tensegrity grids. However, the most immediately applicable ideas were, imho, related to parametric strategies for design optimization.

Needle Tower at the Kröller-Müller Museum, a tensegrity structure
One paper, by designers at Aedas & Arup, focused on optimizing energy and life cycle costs in tall buildings. They considered an optimized structural shape with adaptation for reducing HVAC loads induced by the environment. The most visually rich presentation about parametric tools was given by an architect from NBBJ. He specifically discussed the parametric generation of the Hangzhou Stadium using Grasshopper algorithms in association with Rhino. On the final day of the conference, SOM shared some of the results of their structural optimization research. They discussed the application of Michell Frames (optimized cantilever shapes) in high rises, principal stress trajectories in diagrids, and shape optimization.

The general lesson I’ve come away with is that many architects are applying very complex digital and mechanical tools to innovate solutions to common building problems. They are prepared to engage engineers on a highly technical level. This leads me to ponder the question, are structural engineers content to watch from a distance as forward thinking architects take on the seminal building design challenges?

Certainly, engineering colleges believe that they are on the cutting edge of innovation. Engineering journals are filled with complex dissertations, but are these papers pushing forward design innovation? Or are we just continually reinventing the buildings codes and shaving off nominal quantities of steel reinforcement. If structural engineers are little more than efficiency experts, they offer little value to their clients, and the profession becomes an outsourceable commodity.

We ought not to ask will it stand today? Rather, how will we make it stand tomorrow?

Engineers Gone Wild

Structural engineers can also be fun, clever and creative. A case in point is the ‘Engineers Gone Wild’ Youtube video produced to encourage attendance at a regional structural engineering conference. The video makes a tongue-in-cheek comparison between the business of engineering and Girls Gone Wild. It is well produced, and the result is hilarious.

Even the stodgiest PE can recognize the appeal of such a video to the younger generation. However, for too long, public outreach has been guided by out-of-touch grey-haired men. Although they typically recognize this fact, due to interaction with young employees and grandchildren, this is hardly enough to convince those who consider themselves experts in all fields. The resulting promotional materials have been conservative, highly technical, and reinforce nerdy stereotypes that turn-off creative individuals to engineering careers.

Fortunately, the last few years have witnessed a major change in how engineering professions are representing themselves to the public. It’s debatable whether this was caused by demographic changes in marketing committees or in recognition of previous failed efforts. Both are true. In my five-year experience on various outreach committees, I have noticed more women and younger members gravitating to such service to the profession. This comes not a moment too soon, as the number of engineering degrees granted annually remains below the peak set in the late 1970s (reference).

The National Academy of Engineering has recently taken charge of the re-branding campaign for engineers. A recent report called “Changing the Conversation” sets forth some guidelines for marketing engineering. Instead of emphasizing the static educational requirements of math and science, engineers must highlight the innovative people-serving aspects of their profession. “turning ideas into reality” was found to be the most appealing (and accurate) tagline for summarizing the role of engineers in society.

Civil and structural engineers have been at the forefront of this shift in public perception. The American Society of Civil Engineers (ASCE) has worked extensively with media outlets, like WGBH in Boston, to produce programming, outreach guides and web resources for pre-college students. Asceville is the latest targeted effort to provide a portal for kids looking to explore civil engineering. Meanwhile the National Council of Structural Engineering Associations (NCSEA) and the Structural Engineering Institute (SEI) have teamed to publish an inspirational poster featuring the Beijing Olympics’ Birds’ Nest stadium.

Nevertheless, engineers have a long way to go in correcting the image of pocket-protector wearing cubical-dwelling number-crunchers. Embracing new media outlets and viral marketing might be the next step in communicating with the next generation of engineers. On that front, PR committees are stumbling, too concerned about liabilities and fearing misrepresentation. We ought to be encouraging more viral videos, like Engineers Gone Wild, and promoting discussions on social networks. There are certainly enough silly things in our vernacular (free body diagrams, erection and shrinkage to name a few) to go wild on Youtube and fuel an online buzz about structural engineering.

What did you think of Engineers gone wild? Do structural engineers deserve their stereotypes? Should new media (Youtube, Facebook, Twitter) be use to promote the profession? Are there dangers to doing so? Do you have a great idea for a viral video about engineering? Please comment below.

Ken Maschke is chair of ASCE’s Committee for Pre-college Outreach and a member of NCSEA advocacy subcommittees on public relations & the media and students & educators.

NCSEA Annual Conference

The National Council of Structural Engineering Associations (NCSEA) serves to advance the practice of structural engineering and, as the national voice for practicing structural engineers, protect the public’s right to safe, sustainable and cost effective buildings, bridges and other structures. The group's annual convention kicks off this Thursday, October 15 in Phoenix, AZ.

Engineers representing societies from across the nation will be in attendance. I'm making my first trip to the conference, because I recently accepted a nomination to the NCSEA advocacy committee. I hope to make a contribution on Media, Education and Outreach topics.

While many structural engineers hope to grow the prestige of the profession, they face a public that is increasingly unaware of what it is exactly that they do. On the other hand, people seem to attribute many of the structural engineer's roles to architects. Over the past 75 years, these two professions have begun to separate in a way that the public has just not kept up with. The challenge for structural engineers is to educate the public about the added value they provide to building projects. We also ought to highlight how better designs result from the complimentary application of two quite different skill sets.

In an early assignment for the Media sub-committee, I attempted to research non-traditional media outlets discussing the building industry. I quickly arrived at dozens of architectural blogs, but only a handful of sites touched on structural topics. Many of those were published by material suppliers or manufacturers of proprietary products. There we very few independent opinions about engineering. View my list on Google Docs.

This discovery led in part to my desire to launch Will It Stand? I hope that this blog will fill that noticeable void in cyberspace and address those questions highlighted above. The NCSEA conference will be my first opportunity to pitch Will It Stand to a group of highly regarded structural design professionals. Wish me luck.

Ken Maschke, P.E., S.E., LEED A.P. is editor of Will It Stand? Do you agree with his view of the difference between architects and engineers? To what extent should the engineering community utilize 'new media' outlets like blogs to educate the public about the profession?

Will it stand as a "W"?

The opinion below was provided by Ken Maschke, editor of willitstand.com and structural engineer. He is NOT a member of the Walter Towers design team. Concept and images by BIG | Bjarke Ingels Group.


Will the Walter Towers stand? Sure. There are lots of leaning towers, employing a wide variety of materials and structural systems. Frequently, the most influential element of their construction is the foundation. Nevertheless, leaning towers like the famous one in Pisa stand to this day. A more compelling argument against the Walter Towers can be made on the basis of economics. But even here, smart engineering decisions can be made to lessen the cost impact.

The renderings of the development seem to show four adjacent leaning towers. It’s not clear if each is independent or conjoined where they brush by each other. In either case, the two end towers provide the greatest structural challenge, because they do not appear able to lean against anything. What prevents them from falling over?


In engineering circles, we prefer to call this overturning. All tall buildings must resist this force, but typically it’s caused by the wind. Let’s assume that the total force of the wind hits the building just above half the building’s height. The force multiplied by that distance is called overturning moment. Moment has a lot of physical meaning, but just assume for now that it provides a measurement for comparing overturning to the resistance. Then, take a portion of the building’s weight and multiply it by the distance between the extremes of the building’s lateral-force-resisting-system to compute the resistance to overturning. If the resistance is greater, you’re on your way to a stable building. If otherwise, you have three options: socket your foundations into bedrock, add weight to the building or spread apart the structural system. Each option negatively impacts the economics of the project.

Leaning towers are even more greatly influenced by overturning. That’s because the building’s weight now works against you – more lean, more overturning moment.

To resist the increased overturning, the building’s lateral force resisting system must be chosen carefully. However, most beams and columns are not engaged in the system and do not help resist overturning. That effort is typically left up to structural concrete walls and braced frames (X-braces, diagonals, chevrons, etc.). Buildings with a structural outer face, like the Hancock Tower in Chicago, are very stable in part because the lateral system is maximally spread out. However, this system typically introduces large outer braces or otherwise reduces the light entering through the façade. Most designers would prefer to locate this part of the structure within the building around windowless elevator and stair shafts.

The Walter Towers renderings seem to imply a very open façade, precluding the use of exterior braces. One way to extend the reach of the lateral system is to engage the outer columns through the use of outriggers. These are similar in concept to the outer pontoons that stabilize a trimaran sailboat. Every ten floor or so, a stiff truss connects the interior core with the exterior columns. Frequently this truss is hidden in areas intended for mechanical equipment or storage, so to minimally disrupt the programming of the building. Using a composite structural system with a central core linked to exterior outrigger columns maximizes the resistance to overturning moment while minimizing the aesthetic impact.

The extreme bend in the Walter Towers introduces complications toward providing stability in other ways too. Wind hitting the building on the face perpendicular to the lean will cause a twisting of the building. This can be countered by a strong central core, but the shape of the walls are important. To resist twisting, a closed square shape is better than an open C-shape. The extent of the tower’s bend will also influence the location of the core. Instead of placing the core in the center at the base, it should be located at a point where it can rise as high in the building as possible without itself leaning.

In order to further reduce the effect of the lean, lightweight building materials should be used in the upper half of the tower. Steel beams and columns can provide the freedom to frame the gradually changing floors at minimum weight. The need for mass and stiffness in the core, however, probably makes concrete a preferable alternative for that element.

Will the Walter Towers stand in Prague one day? I hope so. Within the design there are many opportunities to illustrate the potential of structural design practices.

What’s missing from this discussion? Are there any other design technologies that could be employed to make these buildings stand? How would you do it? Vote, comment below or contribute to the willitstand wiki.

Will it stand on a parking garage?

Constructing a new building on top of existing structure can sometimes feel like trying to fit a square peg into a round hole. That’s the problem that designers faced in the construction of a 25-story residential tower on top of an existing 8-story concrete garage. In an effort to respond to market changes, the developer abandoned the plans for a square hotel tower with a large light core. Instead a football-shaped condo building that maximized window space was desired.

The immediate problem faced by the design engineers was how to support the new tower on the existing base. The tower columns did not align with the existing grid, and the structure itself was centered over columns and foundations that were not designed for such loading. In addition, the podium’s lateral system was primarily located outside of the envelope of the planned tower.

Remembering their approach to a similar problem in which a new building planned to reuse existing drilled-pier foundations, the engineers envisioned a 6’-0” deep transfer mat on top of the parking garage. In addition a 16’-0” deep transfer girder was introduced along the center of the mat to further alleviate load from the smaller interior columns. Computer analysis helped determine the required size and reinforcing of the structural members. About 500 tons of steel reinforcing were required for the transfer mat.

However, in order to make the transfer mat and girder system economical, the residential tower needed to be as light as possible. A steel framing system was found to be the best option. A wind tunnel test revealed that the local wind environment funneled winds off of Lake Michigan and could excite the tower in a twisting motion. Although the building was sufficiently strong to resist these winds, the particular motion had the potential to upset the occupants.

The design engineers immediately began discussing options with the architect and developers. Stiffness of the tower played the biggest role in reducing the uncomfortable wind-induced accelerations. The engineers proposed changing the lateral system to a stiff cast-in-place concrete shear wall system. Large openings in the wall were required to accommodate the condominium units’ floor plans. And for even greater stiffness in the east-west direction, a hat truss was added at the 31st floor to link the cores located at either end of the tower.

The construction team likewise faced challenges with the site. The first major construction challenge was figuring out how to support six feet of wet concrete from a series of lightweight post-tensioned parking decks. The supermarket on the 1st floor would have to remain open throughout construction, so it was not possible to shore down to grade. Moreover, the existing parking floors could not support all six feet of wet concrete. Instead, the transfer mat was constructed in two lifts. The first 3’-6” lift included additional shear transfer reinforcement and was designed to support the full wet weight of the remaining mat layer. In this way, the parking decks were actually re-opened ahead of schedule.

With some engineering, the square peg can be fit into the round hole. In this case, a 25-story residential tower was engineered to fit on an existing podium. Creative solutions for distributing gravity load and resisting lateral forces enabled the developers to create a building that could succeed in the current economic environment – even if that meant a drastic departure from the originally designed program.

In what other ways might the design team have addressed these challenges? Could the need to pump so much wet concrete 8-stories above ground have been avoided? Comment below or contribute to the willitstand wiki.

Acknowledgements:
Destefano & Partners, 330 North Wabash, Suite 3200, Chicago, Illinois
Linn –Mathes Inc., 309 South Green Street, Chicago, Illinois
Thornton Tomasetti, 330 North Wabash, Suite 1500, Chicago, Illinois