By rights, the terrorist attack on New York's World Trade Center on Sept. 11, 2001, should have made the world, and the international construction industry, skittish about society's ongoing fascination with skyscrapers and mega high-rise buildings.
This clearly proves not the case, as seen by May’s CIB World Building Congress 2004 in Toronto. Members of the CIB, the Conseil International du Bâtiment, based in Rotterdam, Holland, explored two themes during the conclave: trends in high-rise building and the need to encourage sustainable construction methods.
The events of 9-11 may have made the public feel, briefly at least, more vulnerable about society’s most iconic building typology, the skyscraper. But the engineers, architects and construction professionals at the meeting—co-hosted by the Institute for Research in Construction, National Research Council of Canada in Ottawa—focused on ways of making high-rise buildings––indeed, buildings of all types––safer, more energy efficient, more productive and “greener” through constant innovation in design and construction processes.
Abdul-Rahmin Sabouni, adjunct professor at Ryerson University in Toronto, in his discussion about global versus local trends in high-rise building, noted that the desire to build “towering monuments” dates to ancient Egypt and the pyramids. Indeed, as Sabouni observed, it wasn't until 1907 that Egypt's largest pyramid was trumped in height by New York City's first skyscraper, at 47 stories. Ever since, competition to possess the world's highest building has been intense and ongoing, and a seismic shift in the “skyscraper wars” occurred in 1998 when the title migrated across the Pacific from the United States, with the opening of the Petronas Towers in Kuala Lumpur, Malaysia.
Since then, Asian, and especially Chinese, developers have been building higher and higher. But this may be shifting: In March 2003, officials in the city of Dubai, in the Persian Gulf, announced their intention to build the world's tallest building.
The author is a Toronto freelance writer.
Thin Skins
Massachusetts Institute of Technology professor Oral Buyukozturk sees the demand for mega- structures as fueled by three phenomena: the human aspiration to build higher; the demand for business and residential space in highly populated urban areas; and the extraordinary advances in construction technology, making tall buildings possible. As Buyukozturk noted, “Advances in the structural systems from the 1960s onwards revolutionized the building of high-rise buildings by leaving the sheer frame systems behind and recognizing a hierarchy of new structural forms such as interacting systems, partial tubular systems, tubular systems and hybrid systems.” But, as he also noted, “The increase in the height of buildings leads to greater challenges including structural safety, control of deflections, human comfort, fire safety, exit strategies, crowd control and security.”
Still, most experts in Toronto seemed sanguine about the industry's ability to meet such challenges because of ongoing innovations in construction techniques and building materials. Nowhere are the challenges more striking than in the glass industry because, as conference speakers underscored, glass remains the preferred external cladding material of the modern “transparent” skyscraper. And numerous experts in Toronto explored specific challenges facing glass professionals in contemporary construction.
Double-Glazed Facades
Among the papers tabled was “Advanced Façades and Environmental Systems” by Massimo Colombari and Marc Zobec, researchers with Milanese Permasteelisa R&E. They explore how advanced double-skin façades can resolve the sometimes competing demands for low-energy architecture with a transparent curtain-glass wall aesthetic. To Colombari and Zobec, the double-glazed façade best resolves the problem. “Whereas external shading devices are the most efficient in terms of solar control, they pose a series of problems related to wind resistance as well as costly installation and maintenance. The principle of the ventilated double-skin façade is to position the shading device between the two layers of glazing [the double skin], capturing the energy trapped in the cavity. The energy can be expelled in periods with high solar gains and cooling demands, or recovered in periods with heating demands.” By regulating such façades with advanced “building management systems,” Colombari and Zombec find it possible to achieve significant reductions in power for both heating and cooling.
Double Walled in Warmer Climates
Another study, presented by Amado Guzman, a researcher from the Department of Construction Engineering at Catalonia Polytechnic University in Barcelona, explores the viability and practicality of the double glass skin façade in Mediterranean- climate countries. As Guzman admitted upfront, issues other than thermal efficiency explain the popularity of this type of building aesthetic in hot-weather climates, saying, “Such buildings evoke status and prestige.”
An initial premise of the Barcelona study: Double glass skin façades have worked well in northern climates combining “transparency with reasonable energy use.” But could they perform a similar function in southern climates, he asked. Though the study remains a work in progress, Guzman and his five-person team remain tentative about the effectiveness of double glazing, concluding, “The simple application of the double glass skin façade typology in the Mediterranean climate zones, without taking into account the particular characteristics of this climate, is not a prudent action for sustainable construction.”
Still, other studies defer to the primacy of glass as a contemporary building material and explore ways to make its application as efficient as possible. As researcher Adrian Panait, from France's Université de Marne-la-Vallée, noted, “to take full advantage of its principal qualities [transparency, aestheticism, durability], architects are pushing the conception of glass structural elements towards the adoption of more slender elements.” But such “effects” are achieved by employing “bolted connections” between the glass plates and metallic splice plates with aluminum pads used as inserts between them. As Panait suggested, “A precise characterization of the friction between an aluminum pad and a glass plate is the key to both the design and the safety of such assembly systems.” Using numerical simulations, he attempted to determine “the maximum principal stress” that glass could withstand and as Panait noted, the increase, a phenomenal 350 percent in the examined case, likely explained the glass break and failure of the joint. As a result, the French group plans to further explore “the problem of optimizing the geometry of joints.”
Which Way?
A Swedish study, “Window Size and Orientation in a Low-Energy House,” attempted to debunk the theory that the ideal house has large windows facing south for solar heat gain and small windows facing north to minimize heat loss in winter. According to one of the authors, professor Mari-Louise Persson of Uppsala University in Sweden, “Solar heat in well-insulated houses is not a major source of heat [in the winter] or cooling in the summer.” To Persson, thermal issues are less relevant than daylight. And she suggested that it would be possible to reorient the house [in her study] 180 degrees without noticing any significant change in the “energy balance.” “If the tenants [in the project under examination] prefer having larger windows to the north, for instance, this would cost very little extra energy for heating.”
At the opening of the conference, Arthur Carty, national scientific advisor to the prime minister of Canada, challenged the attendees with a quote from the science fiction writer Arthur C. Clarke, “The world needs uninhibited thinkers who are not afraid of far-out speculation. It also needs hardheaded conservatives to make those dreams come true.” Both genres of people seemed abundant that first week of May in Toronto. To order the $36.71 proceedings on compact disc, call NRC at 613/993-0435. To see “Advanced Facades,” visit www.permasteelisa.com, click on “blue technology” and “publications.”
