January 28, 2014
Tall Building Trends in 2013
Tall building design and construction is alive and well. 2013 had the second-highest ever rate of completion of buildings 200 m (650 ft) or taller. Since the year 2000, the number of completed 200-m-plus buildings has increased from 261 to 830.
Trends in tall building design over the last several decades are also interesting. Considering the worlds 100 tallest buildings in 1990:
- 80 percent were located in North America.
- Almost 90 percent were exclusively office use.
- More than half were constructed of steel.
In 2013, for the world's 100 tallest buildings:
- The largest share (43 percent) are now in Asia. (Only one new 200-m-plus building was built in North America in 2013, compared to 54 in Asia.)
- Less than 50 percent are exclusively office use. Almost a quarter are mixed-use and 14 percent are residential.
- Almost half were constructed of reinforced concrete and only 14 percent of steel. (The remainder are composite or mixed structural materials.)
Change in regional distribution of tall buildings is a direct reflection of changing world economies. Change in structural materials is a reflection of regional availability of different materials. For example, concrete is the predominate structural material in China, where many of the world's new tall buildings are being constructed. Change in material also relates to change in building use, with residential and hotel buildings favoring the thinner floor plates and lesser floor-to-floor heights possible with concrete in comparison to steel.
November 01, 2013
Creative Shipping Container Architecture
Outside the box: Celebrating the shipping container in architecture (Gizmag.com, 9/5/13) showcases 10 innovative shipping container structures for single- and multifamily housing, portable hotels, temporary theater, orphanage, Antarctic research station, and drive through coffe shop.
August 02, 2013
Can a 200-floor highrise be constructed in 7 months?
China Firm Plans To Erect World's Tallest Building in Seven Months (enr.com, 07/30/2013) reports on the Changsha-based Broad Group's plans to erect an 838 meter (2750 foot) high-rise tower. Using prefabrication techniques, construction is planned to take just 7 months.
Broad Group has proven experience building prefabricated tall buildings. The 15-story New Ark Hotel prototype was constructed in one week, and the 30-story T30 Hotel in just 15 days. For a video of the T30 Hotel construction process, see here.
March 09, 2011
Sustainable Very Tall Buildings
Newton Suites and other endeavors (video, Council On Tall Buildings and Urban Habitat) is an interesting lecture given to the Council at their October 2009, Chicago conferance. WOHA founding partner Mun Summ Wong's disusses sustainable tall buildings. Some of the idea discussed include:
March 02, 2011
Tall Buildings and The City
How Skyscrapers Can Save the City, Atlantic Magazine, March 2011, is a provocative analysis of the role of tall buildings and density in the development of cities and the fostering of social equity. Some additional interesting features are also included, such as a interactive graphic of the historical development of tall building structures, an interview with article author Edward Glaeser, an historical gallery of architecture by Louis Sullivan, articles on the world's most dynamic cities, and more.
July 28, 2006
Structural Innovations In Seattle Highrise
Banking On A Museum (ENR, July 17, 2006) describes the construction of Seattle's Washington Mutual Center-Seattle Art Museum Downtown highrise, a 42-story office tower/museum expansion with innovative structural design and construction, including:
The building is the tallest to date in the US to use performance-based methods for its seismic design. Rather than adhere to the prescriptive seismic design requirements of the building code, structural engineers Magnusson Klemencic Associates performed a more complex and lengthy analysis of the building structure to prove that their alternative design could perform to the same levels. The result is structure with fewer architecturally intrusive elements.
The building is also the first in the US to use buckling restrained braces (BRBs). In this case, 44 BRBs within the first thirteen levels of the structure link the relatively slender concrete core to a pair of outlying concrete-filled steel pipe columns. This linked composite structure increases the core's effective depth, thereby increasing its stiffness and reducing overturning forces.
Where the main structural core is located eccentrically relative to the lower, larger floor plates, additional braced and moment frame structures provide balanced lateral force resistance to these portions of the structure.
Steel reinforcing in the "ductile concrete" core was so densly placed that it was cast with self-consolidating 10,000 psi concrete. In addition, the concrete mat foundation, constructed 95 feet below grade, ranged from 7 to 14 feet thick.
Apart from the structural design, other interesting aspects of this project include unusual financial and development relationships between the building's two banking and museum tenants, provisions for structural changes in floor configurations as occupancy between these two tenants changes over time, and a variety of innovative techniques applied to the construction process.
This article is good case study in the real-world interaction of the many forces that shape buildings and the interesting designs that can result.
Tall, skinny ... stable: Using novel technology, S.F. tower should resist quakes, gales (SFGate.com, July 2, 2006) discusses another innovative tall building designed by engineers Magnusson Klemencic Associates, this one in San Francisco. The companion Back Story also links to video and a podcast, in which engineer Ron Klemencic discusses the building's design.
November 01, 2005
Buckling Resistant Braced Frames
Technology Triumphs (Modern Steel Construction, September 2005) describes the use of "buckling restrained braces" in steel frame construction. These composite steel members are used as diagonal, lateral force resisting members in a steel braced frame. In comparison to conventional steel members, BRBs have significantly greater energy absorbing capacity and result in a structure better able to resist extreme seismic events.
BRBs are comprised of three main parts:
1) An inner steel member acts as the primary loadbearing component. This element is intended to resist the axial forces--both tension and compression--that are generated in the brace when the structure is subjected to lateral forces.
2) An outer steel tube surrounds the inner member.
3) Mortar fills the space between the outer tube and inner member. A coating on the inner member prevents bonding between the inner member and the mortar so that the inner member remains free to slide within the mortar.
Under the influence of lateral forces, a building frame naturally distorts, with columns tending toward out of plumb, and normally rectangular column/beam bays becoming parallelogram shapes. In the case of a braced frame structure, this distortion is resisted by diagonal braces within the frame which experience axial tension or compression under these conditions. Under the extreme loading that may accompany a major seismic event, such braces may be subjected to repeated cycles of stress reversals, well beyond the elastic limits of the material.
In the case of conventional steel bracing, the ability of the bracing members to to resist seismic forces under such conditions is limited by the tendency of the member to fail in buckling. Once buckling occurs, the member's load resisting capacity becomes compromised, and it may no longer be able to effectively resist additional stress cycles.
In contrast, with buckling restrained braces--as the name suggestions--the combined effect of the outer steel tube and the mortar infill is to restrain the brace against buckling failure. Under high compressive forces, the BRB will yield plastically, but not undergo gross geometric instability. In this way the brace remains intact and capable of absorbing additional cycles of stresses.
First developed in Japan, BRBs are gaining acceptance in North America as well. In comparison to conventional structural steel bracing members, the major benefit of using BRBs in a braced frame are its greater strength and energy absorbing capacity with less weight. Additional benefits may include simplification of bracing member connections, and reduced foundation loads.
Seismic framing technology and smart siting aid a California community college (Tech Brief, Architecture Record, 08.05) describes the use of buckling restrained braces in the San Bernadino Vallue College of California.
November 09, 2004
Calatrava's Turtle Bay Sundial Bridge
What price beauty? According to Metropolis Magazine (Buying The Bridge, November 2004) the final cost for Santiago Calatrava's footbridge over the Sacramento River for the town of Redding, California was $23.5 million, far above the original $3 to $5 million budgeted for the project.
The bridge connects the city's Turtle Bay Museum with parkland on the river's opposite shore. The bridge's 700 foot long by 23 foot wide deck is supported by a sculptural, inclined steel pylon and 14 cable stays. The steel pylon was fabricated in Vancouver, Washington and shipped to the site in sections weighing 30 to 40 tons each. In order to minimize the bridge's environmental impact, it avoids setting foot in the river or even casting shadows into the river's sensitive salmon spawning grounds. Yet the pylon does function as a sun dial, casting its shadow onto the large plaza formed at its base.
According to Modern Steel Construction's Sun Sculpture (October 2004), the project was not just a financial challenge for the client, but also a constructional challenge. The project required approximately 500 construction drawings to be completed by the construction team based on preliminary design drawings provided by Calatrava. This documentation work included:
- 3-d modeling of the original design
- Sophisticated mathematical adjustment of the 3-d model providing cambering to counteract dead and live loads on the structure
- Development of detailed descriptions of each of more than 1200 steel plates, including different angle cuts on each edge in preparation for full-penetration welding to adjacent plates
- Preparation of several scale models and an animation to assist with visualization of the bridge and its construction sequencing
Complicating this work was the fact that the pylon is a double-walled structure, with the non-parallel inner and outer walls. Detailing took almost 2 years to complete.
June 21, 2004
Recent News In Structural Steel Design
Steel Connection Design
30 Good Rules for Connection Design, Modern Steel Construction, May 2004, discusses principles of economical steel connection design. Some examples:
- Limit the number of bolt diameters used (to reduce errors in fabrication or the field).
- Avoid different grade bolts with the same diameter.
- Avoid overhead welding.
- Limit maximum fillet weld size to 5/16-inch (the maximum size that can be completed in a single pass). Longer, smaller thickness welds are preferred over shorter, thicker welds.
For structural designers and others interested in gaining a better appreciation of steel connection design friendly to fabricators and erectors, this article is a good reference.
Architectural Exposed Structural Steel
Architecturally Exposed Structural Steel, Modern Steel Construction, May 2003, discusses guidelines for the design and specification of exposed steel structure. This lengthy article includes extensive sample specification language, commentary, color photographs, and detailed cost data. This article is recommended reading for architects and specifiers concerned with this type of construction.
The information contained in this article is also available on the American Institute of Steel Construction web site's AESS Guide Specification page. This information has also appeared as a continuing eductation series article in the 06.04 issue of Architecture Record magazine.
Propriety Steel Connection for Seismic Load Conditions
SOM receives patent for novel seismic structural joint, Building Design & Construction, describes a new structural steel joint system designed and patented by architecture/engineering firm Skidmore, Owings & Merrill. The "Pin-Fuse" joint is a hinged connection that remains rigid under moderate structural loads. However under extreme seismic load conditions, the joint may rotate while dissapating the dynamic energy of the seismic forces. According to the article, the Pin-Fuse joint can be used with either steel or concrete structural frames, and should allow reduced structural frame member sizes in comparison to alternative design strategies for such extreme loadings. (At the time of this writing, this article could be viewed online here.)
For more on the fundamentals of steel connection details, see pages 386 - 395 in the textbook.
March 01, 2004
Chicago's Millenium Park
Chicago Team Struggles To Impose Order On Chaos, ENR, February 9, 2004, describes the challenges faced in the construction of Chicago's $475 million music amphitheater designed by Frank Gehry. According to the article, success of the project depended on "computer enhanced" techniques such as three-dimensional solid object modeling, "net" meetings conducted over the World Wide Web, high-tech surveying of in-place construction, and computer aided fabrication.
The article describes some of the positives and challanges of working on a structure with complex geometry. On the plus side, steel system RFIs were reduced to 125, from an estimated 10,000 if computerized modeling had not been employed. On the other hand, misalignments in fabricated supports required as built modeling of the in-place structure so that it could be tested against the original design model, and then descrepencies identified and corrected.
The article continues on at some length regarding structural design and analysis, constructability issues, temperature- and load-related movements, steel erection strategies, panel fabrication, and more. For those interested in the new digitally driven design and construction methods, this article is a good reference.