...on a parking garage?

The Fairbanks at Cityfront Center in Chicago was built on top of an existing parking garage. In order to support the new football-shaped tower on the center of the garage, a 6-foot deep concrete transfer mat was used to distribute load to the stronger perimeter columns.
Crystal Center

...in crystaline form?

If a tectonic shift sent giant crystals thrusting up through the water’s surface, it might look something like this dramatic arts center prototype by AS+GG. Crystal structures with cantilevers of up to 230 feet are joined at a base beneath the water.
Matrix Gateway Complex

...as a cube?

The Matrix Gateway Complex by AS+GG 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.

...like a big "W?"

Walter Towers are Danish architects Bjarke Ingels Group’s latest project in Prague, Czech Republic. Cool design, but will it stand?

Monday, October 26, 2009

Will it stand in crystaline form?

Posted by Will it stand? at 7:15 PM 0 comments
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.

print_33x33_W03

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.

Crystal - Floor Plan - Isometric

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.

Hood Columns

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.

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ACADIA 09: reForm()

Posted by Will it stand? at 6:04 PM 0 comments
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.

IMG_3990
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
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?

Monday, October 19, 2009

Engineers Gone Wild

Posted by Will it stand? at 7:37 AM 2 comments
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.



Tuesday, October 13, 2009

NCSEA Annual Conference

Posted by Will it stand? at 6:00 AM 1 comments
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?
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Friday, October 9, 2009

Will it stand as a "W"?

Posted by Will it stand? at 4:48 AM 0 comments
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.


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Thursday, October 8, 2009

Will it stand on a parking garage?

Posted by Will it stand? at 6:23 AM 0 comments
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.

metal deck

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.

CityFrony_top

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.

pouring concrete

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
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