Comparison of Environmental Effects of Steel and Concrete Framed Buildings - Assignment Example

Introduction Designing and constructing sustainable buildings revolves around balancing social, environmental as well as economic considerations simultaneously. The current building (Brunel University’s Lecture Centre) is in large part constructed using a concrete frame. The building is envisaged for reconstruction and this presents a number of options to designers such as timber frame, steel frame and composites. However, the final say on the matter can only be arrived at after balancing social, environmental and economic considerations for these differentiated methods of construction. 1.1. Social Buildings have to comply with social considerations of sustainability so that they must provide safe, comfortable and healthy interiors. In order to meet these objectives the major considerations are ensuring structural integrity, dealing with vibration levels, adequate weather protection, fire resistance and acoustic performance. 1.2. Economic Economic considerations play a major and often deciding role in determining what kinds of materials to use for construction purposes. The major considerations are that buildings ought to be durable, reusable, require low maintenance and energy efficient. These considerations need to be satisfied both during the building phase as well as during the operation phase. Some other considerations include the construction costs, net lettable area, building reuse value, construction programmes and whole of life value. 1.3. Environmental Environmental considerations mandate that buildings ought to be constructed in a manner that their whole-of-life energy use as well as their greenhouse gas emissions produce a small ecological footprint. The major considerations are the life cycle assessment (LCA), cooling of urban areas, thermal mass and recycling. Appendix ‘A’ shows the mutually common area that social, environmental and economic factors share to produce a truly sustainable design. 2. Sustainability of Current Lecture Centre Building Concrete has been in extensive use around the globe as a preferred construction material for residential and commercial applications alike (Goodchild, 1997). When put in perspective of sustainability, concrete has a number of advantages to offer including (but not limited to) economic considerations, durability, acoustic performance, recyclability, thermal mass, fire resistance and adaptability. The factors listed above can be optimised to achieve maximised sustainability from concrete construction based on construction techniques and other considerations. The current Lecture Centre Building at Brunel University is made out of concrete in large part and offers a sustainable outlook based on social, economic and environmental considerations. These are discussed below in detail. 2.1. Social Concrete buildings are able to offer structural integrity along with structural requirements that are well understood by designers and builders alike. This leads to the construction of safer structures that are able to stand up to risks such as snow, earthquakes, wind base loading etc. The large mass involved in concrete construction ensures that these structures provide excellent damping characteristics that are required for minimising vibration. In addition, concrete provides exceptional fire resistance given that it does not burn at all and does not emit toxic fumes when exposed to fire (Ching, 1995). For most cases concrete structures can be described as fire proof. Similarly, concrete structures are able to offer excellent acoustic damping characteristics as well which mandates the lowest possible use of insulation materials. 2.2. Economic Concrete buildings are the most economical solution when it comes to multi-storey buildings (please see Appendix ‘C’ for a comparison). The large amount of benefits that are provided by concrete such as fire resistance, large thermal mass and durability ensure that concrete buildings have lower operating costs and maintenance requirements. Building reuse is also more common for concrete structure for example old warehouses are converted into office space at little cost (Sezen, 2011). 2.3. Environmental LCA cannot be under stressed for any building under consideration. Estimates reveal that concrete buildings with a 50-year life cycle use only 10% of their total energy requirements when being built and instead the largest energy requirements stem from the operational phase of the building (please see Appendix ‘B’ for a comparison) (Cement Concrete & Aggregates Australia, 2010). Furthermore, the energy consumption for a concrete structure and a steel structure are nearly the same during the construction phase. Thermal mass describes the building’s ability to store thermal energy and release it a few hours later and serves an important part in determining the heating and cooling loads for comfortable residence (Cement Concrete & Aggregates Australia, 2010). Portland cement used for concrete construction offers an albedo between 0.35 and 0.8 leading to greater reflection of incoming electromagnetic radiation (Geem, 2002). This in turn leads to cooler urban areas. When a concrete building is recycled, the resulting aggregate cannot be used for rebuilding but instead gets used for landfill and road base building purposes. 3. Re-Selecting Construction Materials Governmental regulations require that most buildings meet a net zero carbon emissions stipulation by 2019. In this respect, alternative construction materials are being considered for the Lecture Building at Brunel University. The materials under consideration include concrete, steel, timber and composites. A comparison of these materials is provided below to select a preferable material for construction. 3.1. Structural Integrity Structural integrity is the core most requirement for any construction based outcome. When the structural integrity of the selected construction materials is compared it becomes obvious that concrete and steel are able to offer the greatest structural integrity especially for high rise buildings. In contrast, composites offer greater structural integrity than timber but it is still low when compared to concrete and steel. Given that the Central Lecture Building is not a high rise it can be surmised then that concrete, steel and composites could be used because timber would be unable to support the multi-storey structure. 3.2. Social In terms of social aspects, the first thing to consider is fire resistance. Concrete is able to offer the greatest fire resistance followed by steel and composites. Unfortunately, timber is itself combustible and is unable to offer any fire resistance even with large amounts of fire resistance cladding. Concrete has the greatest resistance to fire as it is not affected by high temperatures because of its non-combustible nature and because it cannot be melted. In contrast, steel can offer decent fire resistance with fire proof claddings but it cannot withstand heat for prolonged periods. Any extended fires can damage steel structures to a large degree though it is rare that steel structures are damaged beyond repair. When considering composites it is necessary to see what the composite in question is made out of. For high steel composites the same fire resistance issues may emerge as well. In addition, concrete structures offer the best vibration protection as well as acoustical performance. Steel structures can match these characteristics only with a large amount of cladding that often increases the size of the structure required to support it. Consequently, when a steel structure needs to be fire proofed and its acoustic performance needs to be improved then its cost rises dramatically. Furthermore, all available construction material options provide suitable weather protection as long as thermal mass considerations are not taken into account (Froeschle, 1999). 3.3. Environmental In terms of environmental considerations, the first thing to look into is the LCA for the selected materials. Concrete and steel offer nearly the same amount of energy consumption during the construction phase (Guggemos & Horvarth, 2005) making them bear an equal environmental footprint. In contrast, composites lie close to steel and concrete in terms of energy usage in the construction phase while timber has the lowest energy consumption during construction. However, when the operational costs of these materials are considered it becomes obvious that concrete has the lowest operational costs followed by steel, composites and finally timber. Concrete provides a large thermal mass that offers lowering of energy input for heating and cooling purposes. In contrast, steel has a low thermal mass and bolstering the thermal mass requires upgrading the structure to bear the additional weight. Timber requires extensive insulation to make it more environmentally friendly while composites lie between timber and steel for their operational costs. However, when the issue of urban cooling is considered it becomes obvious that concrete and timber have relatively low albedos leading to distortion in cooling patterns. On the other hand, steel structures offer better albedos due to the extensive use of glass which is similar to composite based structures (NHBC Foundation, 2007). As for recycling, steel offers the greatest advantage at recycling because it is totally recyclable which is not true for any of the other materials being considered. 3.4. Economic The construction costs for concrete and steel are near equal (as steel prices have shot up in recent years). However, these costs are large when compared to timber construction while composite construction requires the greatest cost largely due to few contractors handling such materials and their construction. The whole-of-life value for concrete is the highest followed by steel, composites and then timber. Moreover, concrete and steel building reuse is far higher when compared to composites and timber. 4. Conclusion Overall, concrete offers the best possible choice in terms of structural integrity and sustainability although its construction costs are higher than timber. Steel structures offer close competition but fail to deliver the required LCA and whole-of-life value that would make them just as or more sustainable. 5. References Cement Concrete & Aggregates Australia. (2010). CCCA Comparison of LCA. Retrieved March 8, 2012, from Cement Concrete & Aggregates Australia: http://www.ccaa.com.au/LCA Cement Concrete & Aggregates Australia. (2010). Thermal Mass Benefits for Housing. Perth: Cement Concrete & Aggregates Australia. Ching, F. (1995). A Visual Dictionary of Architecture. Amsterdam: Van Nostrand Reinhold Company. Froeschle, L. (1999). Environmental Assessment and Specification of Green Building Materials. The Construction Specifier , 53. Geem, V. (2002). Albedo of Concrete and Selected Other Materials. Retrieved March 7, 2012, from Construction Technologies: http://www.lehigcement.com/Education Goodchild, C. (1997). Economic Concrete Frame Elements. 1st ed. . Berkshire: British Cement Association. Guggemos, A. A., & Horvarth, A. (2005). Comparison of Environmental Effects of Steel and Concrete Framed Buildings. Journal of Infrastructure Systems ASCE . NHBC Foundation. (2007). Climate Change and Innovation in House Building: Designing out Risk. Retrieved March 7, 2012, from NHBC Foundation: http://www.nhbcfoundation.org/LinkClick.aspx?fileticket=viZ9mWU9cqQ%3D&tabid=339&mid=774&language=en-GB Sezen, H. (2011). Reinforced Concrete Frame and Wall Buildings. Retrieved March 7, 2012, from http://nisee.berkeley.edu/turkey/Fturkch3.pdf 6. Appendix ‘A’ 7. Appendix ‘B’ Figure 1 - Energy used on three CCAA warehouse life cycle examples studied (Cement Concrete & Aggregates Australia, 2010) 8. Appendix ‘C’ Figure 2 - Total cost of medium-rise commercial building structural frames by location (8.4 x 8.4 m grid) (Cement Concrete & Aggregates Australia, 2010) Read More