Steel in Construction - Case Study Example

Introduction Careful selection of environmentally sustainable building materials is the easiest way for architects to begin incorporating sustainable design principles in buildings. Traditionally, price has been the foremost consideration when comparing similar materials or materials designated for the same function. However, the "off-the-shelf" price of a building component represents only the manufacturing and transportation costs, not social or environmental costs. The Romans were the first to use metal as a major building material. The Pantheon had a bronze roof, parts of which survived until the middle of this century; Hagia Sophia originally had a lead roof that lasted 1400 years. Because of their malleability and relative ease of working, copper and lead became synonymous with the complexities of Gothic architecture. Endowed with the rich green patina of age, weathered copper spires and roofs still enliven the skylines of northern European cities. Improved techniques of pre-patination can now bestow an instant, uniform illusion of maturity; Jean Nouvel's new cultural centre in Lucerne (p38) is crowned by a vast, overhanging roof clad in sheets of prepatinated copper. Sheltering a new urban square in its oversailing embrace, the emerald green structure forms a powerful horizontal datum in the lakeside landscape Metals have useful properties such as tensile strength, ductility, hardness, electrical conductivity, and high melting points. They are widely used for electrical and structural applications. Understanding the physical and chemical properties of metals allows for improved technological advances. Since metals are so widely used in today's modern world, corrosion is all around us and affects our lives in many ways. Corrosion has many serious consequences to our society such as, economic, health, safety, technological, and cultural. Cast iron Cast iron played a pre-eminent role in the industrial development of our country during the 19th century.. As an architectural metal, it made possible bold new advances in architectural designs and building technology, while providing a richness in ornamentation. cast iron in the form of slender, nonflammable pillars, was introduced in the 1790s in English cotton mills, where fires were endemic In 1849 Bogardus created something uniquely American when he erected the first structure with self-supporting, multi-storied exterior walls of iron. Known as the Edgar Laing Stores, this corner row of small four-story warehouses that looked like one building was constructed in lower Manhattan in only two months. Its rear, side, and interior bearing walls were of brick; the floor framing consisted of timber joists and girders. One of the cast-iron walls was load-bearing, supporting the wood floor joists. The innovation was its two street facades of self-supporting cast iron, consisting of multiples of only a few pieces--Doric-style engaged columns, panels, sills, and plates, along with some applied ornaments. Each component of the facades had been cast individually in a sand mold in a foundry, machined smooth, tested for fit, and finally trundled on horse-drawn drays to the building site. There they were hoisted into position, then bolted together and fastened to the conventional structure of timber and brick with iron spikes and straps. The second iron-front building erected was a quantum leap beyond the Laing Stores in size and complexity. Begun in April 1850 by Bogardus, with architect Robert Hatfield, the five-story Sun newspaper building in Baltimore was both cast-iron-fronted and cast-iron-framed. In Philadelphia, several iron-fronts were begun in 1850: The Inquirer Building, the Brock Stores, and the Penn Mutuai Building (all three have been demolished). The St. Charles Hotel of 1851 at 60 N. Third Street is the oldest iron-front in America. Framing with cast-iron columns and wrought-iron beams and trusses was visible on a vast scale in the New York Crystal Palace of 1853. Wrought iron can be distinguished from cast iron in several ways. Wrought-iron elements generally are simpler in form and less uniform in appearance than cast-iron elements, and contain evidence of rolling or hand working. Cast iron often contains mold lines, flashing, casting flaws, and air holes. Cast-iron elements are very uniform in appearance and are frequently used repetitively. Cast-iron elements are often bolted or screwed together, whereas wrought-iron pieces are either riveted or forge-molded (heat welded) together. Example Cast iron was the metal of choice throughout the second half of the 19th century. Not only was it a fire-resistant material in a period of major urban fires, but also large facades could be produced with cast iron at less cost than comparable stone fronts, and iron buildings could be erected with speed and efficiency. The largest standing example of framing with cast-iron columns and wrought-iron beams is Chicago's sixteen-story Manhattan Building, the world's tallest skyscraper when built in 1890 by William LeBaron Jenney. By this time, however, steel was becoming available nationally, and was structurally more versatile and cost-competitive. Its increased use is one reason why building with cast iron diminished around the turn of the century after having been so eagerly adopted only fifty years before. Nonetheless, cast iron continued to be used in substantial quantities for many other structural and ornamental purposes well into the 20th century: storefronts; marquees; bays and large window frames for steel-framed, masonry-clad buildings; and street and landscape furnishings, including subway kiosks Cast Iron in Buildings With all buildings, fire was a recurring problem with timber structures. It was almost certainly the reason for one very early application of cast iron, the columns supporting the vast cooker hood and chimney of 1752 at the Monastery of Alcobaca in Portugal. In Britain, cast iron was used in the early 1770s in churches, partly for the cheap reproduction of Gothic ornament, but also for structural columns. In Russia architectural cast iron was used extensively throughout the 18th Century but it is not clear to what extent it was also used to support floors and roofs. It is hard to see any trend arising from these early applications of iron to buildings. It was in the multi-storey textile mills in Britain in the 1790s that cast iron was first shown to have a major future in building structures. The disastrous fire at Albion Mill in 1791 was perhaps the biggest incentive for change. Bage and Strutt were the great pioneers. Between them, they developed totally incombustible interiors in cast iron and brick but with floor spans still of only about 2,5 to 3,0 metres in each direction, as had been the case with timber interiors. Later, this iron mill construction spread to warehouses with a gradual increase of spans. It is tantalising how little is known about who actually fixed the size and shape of the beams used by Nash, Barry and other architects of this period. Thomas Tredgold's book on cast iron of 1824 was undoubtedly influential but dangerously in error in some respects. In most cases, it is probable that proof-loading of beams, which was widely used, provided the main safeguard against misconceptions and poor workmanship. Apart from the mills and the long span floors, there was a whole range of new uses of cast iron between 1810 and 1840, sometimes on its own for complete structures as in Hungerford Market of 1836, or Bunning's highly decorated Coal Exchange of 1847-49. In Russia, there was also a considerable quantity of cast iron building construction in the first half of the 19th Century, as in the Alexandrinsky theatre of 1829-32 and the Dome of St Isaacs Cathedral (1837-41). Towards the close of the 1840s, cast iron had lost much of its golden image and was being seen as an unreliable material, especially for beams. The progressive collapse of five storeys of Radcliffe's Mill in Oldham in 1844 and the failure of the Dee Bridge in 1847 were both highly damaging to its image. But it is iron and steel that have had the most radical influence on architecture. The skeletal structural frame effectively liberated buildings from the inhibitions of the loadbearing wall and trabeated construction. Cast iron, the great material of the Industrial Revolution, revolutionized Georgian and Victorian buildings. Ideally suited to repetition and standardization, the metal's ubiquity defined the British Empire; cast iron bandstands, ornamental gates, fountains, and entire prefabricated buildings (Victorian 'tin tabernacles') were simply plucked from manufacturers' pattern books and energetically exported around the Imperial world, from Durban to Bombay Wrought Iron in Buildings In buildings the scope for drama in the use of iron was generally more modest, the largest outlet being in flooring systems both in Britain and in other parts of Europe. It was almost certainly the development of these flooring systems in France in the late 1840s and early 1850s which provided the impetus for the commercial development of rolled joists, regardless of whether the first ones of all were rolled there or in Britain. The size of the joist sections gradually increased but until liquid steel took over, size was limited by the problems of handling large quantities of puddled iron. Cast iron continued to be used extensively for columns well after 1850. In America there was a great vogue for cast iron facades which lasted for several decades. Bogardus and Badger were the two main suppliers. Internally, the structures vary, with iron, masonry and timber all represented. Apart from these useful, but often unseen, applications of iron to traditional buildings, some spectacular iron build structures, mainly long span roofs, were built in all countries. Most commonly, but far from exclusively, they were over railway stations. They included the ribbed iron dome of the British Museum Reading Room (1854-57), the 73 metre wrought iron arches at St Pancras Station (1868) and the dome of the Albert Hall (1867-71). These buildings were matched in France, for instance, by the Bibliotheque National (1868), Les Halles (1854-68) and the Bon Marche Department Store (1867-78); and in America by the dome of the Capitol in Washington (1856-64). Throughout this period most buildings, particularly those of more than one storey, depended on masonry walls for stability, whether or not the floors and roof were of iron. The route to full structural framing in iron or steel is uncertain. It is often stated that the Home Insurance Building in Chicago of 1884-85 was the first fully framed tall building which formed part of a continuing development. Perhaps the earliest example of a stiff-jointed frame was Godfrey Greene's four-storey Boat Store at Sheerness of 1858-60. The Great Exhibition Building in London of 1851 and the Chocolat Menier Factory outside Paris of 1870-71 have also been claimed for this 'first', but they both had diagonal bracing and, anyway, had no apparently direct influence on the multi-storey steel construction of today STEEL Designers and builders have long recognized and lauded steel for its strength, durability, and functionality. Increasingly, however, architects are recognizing steel's important environmental attributes- especially its high recycled content and high reclamation rate. Although it is often believed that "durable" structural materials such as steel and concrete will provide the longest service lives for their buildings, our results suggest there is no significant relationship between the structural system and the actual useful life of the building. The assumption that wood can't offer the same durability as steel and concrete excludes it from building applications where longevity is important. In addition, the environmental profile of wood is hurt by this durability image. A short service life has a negative effect on life-cycle environmental analysis results, as the impact of a replacement building will be included in the calculation. The use of cold-formed steel in the structural system of residential construction has taken hold in some site building markets but potentially offers far more value to the manufactured home industry. The Manufactured Housing Research Alliance (MHRA) is coordinating an effort to develop a market competitive structural design, based on cold-formed structural steel technology and suitable for the home manufacturing environment. This report summarizes findings of the first phases of the research. The effort is a cooperative undertaking of MHRA, the Manufactured Housing Institute (MHI), several home manufacturers, the North American Steel Framing Alliance (NASFA) and the US Department of Housing and Urban Development (HUD). CHARCTERTICS OF STEEL Flexibility IN DESIGN - IT and software. - Steel's excellent strength to weight ratio creates an attractive and economic use of space when beams and columns have small profile areas. - New rolled and prefabricated section shapes. - Economic methods for shaping and curving. - Standardised solutions for floor systems and connections. - Opportunities to integrate large openings, for doors and windows - Fire engineering. DURING CONSTRUCTION - Complementary structural components can easily be accommodated - curtain walling readily and efficiently connected to the structure, and other modularised elements such as toilet pods, dry-casing, M&E items easily fitted. - Easy adaptation - during the construction period the client may wish to alter installations and this can readily and rapidly be achieved. - Steelwork connections, particularly bolted ones, can easily be released or re-made in whatever form necessary. IN USE - The client may need to extend, to change the use of the building, to absorb changes in loading requirements, and to incorporate new installations. - Should an increase in loading requirements occur, then the structural elements can easily be individually strengthened, or additional members introduced or altered to suit. - Steel's relative lightness in weight allows adaptation in the future to be easily accomplished. - New connections can easily be introduced by bolting or welding - enabling alterations for services or changes of use. Steel Formulation Structural design of steel structures has long been based upon the assumption that structural steels have the same general strength characteristics at elevated temperatures. Failure has been described based upon standardized tests that more-or-less ignore the specific thermal and mechanical properties of different steels. This is largely because, at least in the US, a very limited range of structural steels is used. Generally speaking, these basic steel formulations have performed well for decades. The past ten years have seen the emergence of new steel formulations resulting from innovative research and improved production practices. These new steels have seen limited use in Japan and other Asian countries, although they have not yet made their way to the United States. Referred to as fire-resistant steels, these materials have caught the attention of some within the industry. Advocates of fire-resistant steels note that the characteristics of these materials at elevated temperatures provide for decreased loss of strength at elevated temperatures when compared to more traditional steel formulations28. The same advocates caution that fire resistant steels cannot replace passive protection measures, but rather can provide a structure with additional time to failure and can allow a structure to survive for a longer time after the failure of protection materials. Examples of the use of fire-resistant steel exist in Japan, China and Germany. These include a car park, a sports arena, a rail station, and an office building, among limited others. While some data exists regarding the performance and material properties of fire-resistant steel, additional research is needed to determine the benefits (or lack thereof) and cost impacts associated with application in the US. Additionally, research is necessary to understand how and when such steels can be appropriately applied in structural design practice. Facts - This headquarters building was the first major structure in the Chicago Loop in more than twenty years. - A wire sculpture by Richard Lippold titled "Radiant I" is the centerpiece of the lobby. The artwork spans a shallow reflecting pool. - The office floors are supported entirely by 7 columns on the east and west sides. These are set outside the building's perimeter, so the office spaces are completely open across the whole floor. - Like the columns, the 25-story service core (holding elevators and utilities) is set outside the main building envelope. - Designated as an architectural landmark in 1999. - The building occupies sixty-six percent of its site, with the attached service tower on the east side leaving room for loading areas and a small plaza. - The structural steel framing includes sixty-foot girders spanning the office floors and supporting the beams and steel decking. - The facade consists of stainless steel and dual glazed green tinted windows with a vertical accentuation. - The steel piling foundation is an unusual exception for Chicago skyscrapers, which normally use concrete caissons Steel framing is also a strong candidate for reuse. In today's economy, however, steel is hardly ever salvaged, but rather separated from other materials and recycled. Salvaging is a better option environmentally than recycling, and, when designing for deconstruction, the engineer should seek out ways to improve the deconstruction cost equation. Steel Framed Construction There are several different methods of framing used in light construction. The most common used in the construction of residential construction is wall-bearing framing. This type of construction allows the weight of the building to be carried on the exterior walls or a combination of the interior and exterior walls. This allows the builder and designer the advantage of wide-open spaces within a residence with fewer interior walls required for construction. It also provides the future potential of easier remodeling or updating of the residence if desired. The basic joining method used in steel frame construction is the joining of pieces by welding, bolting or riveting. This method provides a distinct advantage to the joining of pieces by nailing as is used in wood framed construction. The steel connections are less susceptible to vibration, movement of the base material and weather induced loads. The Advantages of Steel Strength Steel has the highest strength to weight ratio of any building material, twenty-five times greater than wood. (The Steel Alliance, Building to Battle Earthquakes.) Because of this strength, and the inorganic nature of steel, it does not warp split or twist. Also because the steel member is an inorganic material, it will not swell or shrink in reaction to moisture content. This allows an architect to use true dimensions when designing without the need to compensate for the wood's shrinkage. Additionally, because steel is dimensionally stable and will not "settle" as wood does in new construction dry wall cracks or shifting walls over time including the induced strain put on other structural members is non-existent. The inherent strength of steel makes it a natural choice for construction in earthquake prone regions of the country. The manufacturing process insures the consistent strength of steel from piece to piece as opposed to wood that can vary within lumber grade and species. The characteristics of steel include a higher ductility than wood. Allowing it to bend. In an earthquake, the steel would absorb more of the stresses and be less prone to cracks or breakage. As stated previously, the connections within a steel frame structure are less susceptible to pull out or failure and will not weaken over time because of material shrinkage or the decrease in strength of the base material due to age. Fire Safety The largest fire safety selling point of steel framing in comparison to wood is that the steel framing is non-combustible. It does not burn and will not provide additional fuel to the fire. The structural members will deform and will reach a critical point where eventual failure will occur but they do not provide additional fuel, nor perpetuate the fire growth. Residential construction regulations are the least restrictive of the building codes. However, all major structural members and materials of a new construction are required to be fire rated. The fire rating is based on standardized tests and calculations conducted by the American Society for Testing and Materials (ASTM). Additional information regarding the fire rating of structural members can be found under the ASTM Standard E-119 or within the National Fire Protection Association SFPE Fire Protection Handbook. Because of the standardized production methods of steel, the fire resistance rating provided by the structural members is consistent throughout the structure and does not fluctuate from piece to piece. That can often be a problem in wood construction with different quality of wood members. The insulation materials used in steel construction are a vital concern to the builder and consumer because of their cost and their necessity in steel construction due to the conductive properties of steel. In addition to the main structural members, materials used for insulation of these members are also put through standardized tests and fire rated under ASTM E-119. As discussed in the NFPA SFPE Fire Protection Handbook: The basic intent of the various methods of protection is to reduce the rate of heat transfer to the structural steel. This is accomplished by using insulation, membranes, flame shielding, and/or heat sinks. Insulation of the steel is achieved by surrounding the steel with materials that preferably have the following characteristics: Non-combustibility and the added attribute of not producing smoke or toxic gases when subjected to elevated temperatures; Thermal protective capability when tested in accordance with the standard fire test, ASTM E-119; Product reliability giving positive assurance of consistent uniform protection characteristics; Availability in a form that permits efficient and uniform application; Sufficient bond strength and durability to prevent either dislodgment or surface damage during normal construction operations; and Resistance to weathering or erosion resulting from atmospheric conditions. Resistance to Termite Infestation Approximately 1.1 billion dollars a year in damage is caused by termites within American residences. This damage is devastating to homeowners and is not usually covered in typical home insurance policies. Termite infestation is common in warm wet regions of the country and can cost a homeowner thousands of dollars even before it causes major structural damage. The steel-framed construction is impervious to infestation. The main cost to the homeowner is when the main structural members of the home are effected by infestation. So in steel homes the auxiliary or aesthetic structure may be damaged, but the main structural members will remain unaffected saving the homeowner substantial financial impact. (The Steel Alliance) Environmental Benefits Steel is North America's most recycled material. More than 67 million tons of scrapped steel, approximately 64%, are recycled every year, more than all other recycled materials combined. The steel framing production process uses a minimum of 25% recycled steel, and all new steel that is produced contains recycled steel. (Steel the Clear Cut Alternative for Building Homes) A recent study conducted by Baylor University assessed the benefits of using steel framing in residential construction. The study determined that steel should be recognized as a "green" building material based on economic and environmental criteria: The study concludes that the steel industry is increasingly producing materials for the residential market that are cost competitive, performance enhancing, and environmentally advantageous. These products should be viewed by environmentalists as more environmentally compatible than they have been viewed historically because the steel industry has actively improved its environmental record in mining, processing and recycling steel. In comparison the timber industry, while emphasizing its "green" image, has problems associated with the environmental impacts of growing harvesting and replanting operations, which do not show true evidence of sustainability. Plantation style lumber production and pest management policies have tarnished the timber industry image. Another major hurdle to cross is to convince the builders and architects that steel framing is economically viable. This includes the consideration of time, labor, the effect of availability to the price, and the long-term concern of cost to operate the home as a secure and comfortable home. This concern is mainly the concern held by builders and architects that the thermal performance of steel will result in substantial costs to the consumer. It is a well-known fact that steel is a much better conductor of heat than wood, on the average of 400 times more conducive. This could in some applications, translate into substantial costs for heating and cooling the home. The industry asserts that this concern can be quickly nullified by the proper application of high level insulation and the design of thermal breaks within the original design. As discussed in the report from Baylor University, "Designing for efficiency may be more costly than using the lower priced building material; however, from a life cycle perspective, total costs will usually be lower because the long term benefits will continue over the life of the home." In the long-term comparison this cost is balanced by the other benefits of steel over wood and will not impact the end user. Five years ago the steel industry entered into the residential framing market; initial predictions by industry members had hoped for an optimistic 25 percent of the new home market to be framed in steel by 1998. While the current numbers fall far below their initial projections, approximately 3-6 percent, the numbers are increasing. The industry has developed a clear-cut agenda of where they want to be in the future, and what hurdles they need to clear to get there. In a recent newsletter of the NASFA the Major Barriers and Strategic Objectives of the organization were outlined: Major Barriers Cost of construction Lack of Infrastructure Industry standards Thermal performance Consumer Preference Strategic Objectives Maximize Current Opportunities Reduced Cost Of Construction Develop Infrastructure Implement Standards Improve Thermal Performance Create Consumer Preference Develop Government Support Develop and Maintain Liaisons with Stakeholders and Influencers It is obvious that steel framing provides numerous advantages to the standard residential wood framed construction. While there are several concessions to these advantages with the constant effort of the industry to minimize the costs and to develop new methods of framing unique to the residential market these concessions can be compensated for. From an engineering, safety, and long term financial standpoint steel should become the best choice for architect, builder, and consumer when it comes to new home construction Conclusion One of the most noticeable moves in construction in the last ten years, in Britain certainly, but it seems elsewhere in Europe as well, has been towards a revival of structural steel for bridges and buildings. Fashions change in constructions, as in clothing, and so do needs and costs. It is, thus, interesting to look at some of the recent variants on normal structural steel and at rival materials to see how they have fared and to speculate on what may happen in the future. Weathering steel (unpainted with stabilised corrosion) and exposed steelwork fire-proofed by water in hollow sections are both innovations of the 1960s but neither shows signs of wide adoption. On the other hand, stainless steel, although in itself much more expensive than mild steel or even high tensile steel, is being found to be increasingly worthwhile when the cost of maintenance is considered. Plastics have yet to make any significant impact except as a protective coating or for architectural trim. Aluminium was once thought to be a dangerous rival to structural steel but, so far, it has made little impact in bridge or building structures. Reinforced concrete - still dependent on steel - has been a strong and growing competitor of fabricated steelwork since the 1890s, largely because of its in-built fire resistance, helped in the 1950s and 1960s by an architectural desire to 'expose the structure'. This trend is now being reversed and, since 1980, there has been a vigorous rebirth of structural steel. The increasing use of structural steel has been encouraged by the pursuit of 'fast-track' construction and the realisation that reinforced concrete is not a maintenance-free material. There has also been a swing in taste from visually expressed concrete to 'high tech' styling or to the complete wrapping of buildings in glass or masonry. Future developments with structural steel in buildings are likely to be associated with fire protection. Thin intumescent coatings which froth up when heated and form a protective layer, are becoming still thinner - more like paint - but the need for such protection may be substantially reduced by the development of fire engineering. This development could lead to a new era of exposed steelwork with increasing attention to the shape and form of members and the appearance of joints. Castings of steel or ductile iron could well be in demand once more. . CONCLUDING SUMMARY The use of iron and steel in structures evolved through development in the production and properties of the three ferrous metals, cast iron, wrought iron and steel. Cast iron is formed into its final shape from molten metal a liquid which is poured into a mould and solidifies. Wrought iron never reaches a fully molten state and is shaped by rolling and forging. Mild steel can be cast as well as rolled but has a lower resistance to corrosion than wrought iron. Iron has been known and used for more than three thousand years but it is only in the last 250 years that new production methods have allowed the large scale use, first of cast iron, then wrought iron and finally steel. Cast iron was widely used in bridges and buildings in the period between 1750 - 1850. Wrought iron became popular during 1850 - 1900 allowing the construction of many novel bridges and building structures of increasing size and span. Steel came into increasing use from about 1880, and being stronger than wrought iron, has been used to build even larger structures. The introduction of welding of steel was a major innovation in connection techniques which facilitates the wider use of steel. For the future, stainless steel is being found to be increasingly attractive despite its greater cost. The development of fire engineering may lead to a new era of exposed steelwork together with a wider use of coatings of steel or ductile iron. References 1. Autoclaved Aerated Concrete - An Overview, AzPATH, Del E. Webb School of Construction, Arizona State University, Tempe, AZ, October 2001. 2. Buchanan, Andrew, H. Structural Design For Fire Safety, John Wiley & Sons, LTD, New York. 3. Milke, J.A., 'Analytical methods for determining fire resistance of steel members', Chapter 4-9, SFPE Handbook of Fire Protection Engineering, Third Edition, Society of Fire Protection Engineers, 2002. 4. Uniform Building Code (1997), International Conference of Building Officials, Whittier California, USA. 5. Fire Resistance Directory. Volume 1. Underwriters Laboratories, Inc., 2003. 6. Jackman, P. E, Intumescent Materials - Ancient Technology, Modern Application, Part I The Technology, Fire Engineers Journal, May 1998. 7. Swindlehurst, J. Fire Proofing Steel Structures - Decorative Intumescent Coatings are Becoming a Viable Option for Manufacturing Plants, July, 2001, www.plantservices.com/web_first/ps.nsf/articleid/hcok- 4xvvbn 8. Fire resistance of Steel framed Buildings, Corus, www.corusconstruction.com 9. Off-Site Fire Protection Application for Commercial Buildings: Cost Benefit Analysis. Report RT433, Prepared by the Steel Construction Institute. 10. Twilt, L and Witteveen, J, 'The fire resistance of wood-clad steel columns.', Fire Prevention Science and Technology, No. 11, 1974. Read More