STRUCTURAL ENGINEERING FOR SUSTAINABLE BUILDINGS

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1 STRUCTURAL ENGINEERING FOR SUSTAINABLE BUILDINGS K K CHOY REUBEN CHU M F HUI The Hong Kong Institution of Engineers 9/F Island Beverley, No 1 Great George Street, Causeway Bay, Hong Kong China Tel: Fax: hkie-sec@hkie.org.hk The global environment has been seriously affected by the growth of population and the continuous development of urban areas. As building professionals, we bear important responsibilities for the sustainability of building developments such that the problem of pollution may be reduced in the course of construction as well as in the operation stage of the buildings. This paper attempts to illustrate how structural engineering can contribute in the planning, design, demolition, construction and operation stage for sustainable buildings. Keyword: Sustainability, green buildings, holistic life cycle, pre-design stage, green features, recycled materials, waste management, operation stage. 1. Introduction The continuous growth of population in Hong Kong has caused high demand for new building developments which in turn lead to the consumption of a significant amount of energy and resources, and the production of considerable amount of waste, and thus would seriously affect the environment. This paper attempts to present a brief introduction of the sustainable strategies, design and practices adopted in a variety of building projects in Hong Kong. It provides an account of the effort that the construction industry has offered in the direction of sustainable development. It will also illustrate the contributions that structural engineering can be offered in the planning, design, demolition, construction, and operation stage of the buildings for achieving sustainability. 2. Structural Engineer s Role in Building Developments Structural engineers bear significant responsibilities for the achievement of sustainability in building developments, which include adopting a holistic life cycle approach from planning, design, demolition, construction and operation of the buildings. Any decision made during a particular stage of a building project may have crucial implications on the remaining stages. The choice of materials, design and construction method have a major bearing on the buildability, resources consumption and maintenance requirements, which structural engineers should carefully consider from sustainability point of view. 3. Pre-Design Stage Before the design of a building development project is commenced, it is necessary to coordinate among building professionals for the consideration of various aspects regarding the environmental performance of the project from demolition, construction to actual operation. Based on the environmental potentials of the development and the limitations of the project site, the project team should formulate the sustainable policies and the major direction of the development scheme, aiming at low pollution and low energy consumption. During this stage, the structural engineer may contribute in deciding suitable sustainable elements to be used in the building development such as targeting the achievement of a particular grading of environmental assessment; the use of environmental and recycled construction materials; specifying the use of timber from sustainable forest; adoption of stringent and economical design standards; conducting relevant laboratory tests including microclimate studies and wind tunnel tests to enhance the understanding of the effects of the development on the surrounding environment and optimizing the building orientation; 1

2 2 providing more natural lighting and better ventilation for energy conservation; and introducing more green features for the development. 4. Design Stage In the design stage, the strategies developed for the adoption of suitable structural supporting system, building materials and design standards would affect the environmental performance of the building. It is also essential to consider the construction details as well as the operational and maintenance needs of the finished building at the design stage. For instance, the structural support system chosen should have considered buildability to facilitate the adoption of sustainable construction methods, and access and facilities for maintenance should be provided for at this stage to enable efficient maintenance as well as establishing a balance between the capital and long-term maintenance costs Engineering Studies for Sustainable Building Design and Construction It is always encouraged to conduct relevant engineering studies to assist the overall design of the building development for achieving better environmental performance during construction and after completion of the project. These studies may include microclimate studies for the nearby region, wind tunnel tests for assessment of wind effect on the building and environment. Other engineering studies such as use of recycled aggregates for structural concrete, and fire engineering tests on structural elements are also beneficial in terms of economical and environmental design Adoption of Updated Design Standards While the authority should take the lead to review and update existing design standards and building regulations towards sustainability, building professionals should always be alert of the availability of new and innovative materials and the use of performance based design standards. In this respect, the Buildings Department of the Hong Kong Special Administrative Region Government has carried out a major review on a number of practice notes and codes of practice incorporating the latest technological findings, good practices and local experience. In recent years, the Department has issued a series of new standards including the Code of Practice for Foundations, Code of Practice on Wind Effects, Code of Practice for Structural Use of Concrete, Code of Practice for Structural Use of Steel and Code of Practice for Precast Concrete Construction. Apart from providing more comprehensive and updated guidelines on design requirements, these codes of practice also allow the use of performance based design concept and the optimization of use of materials Incorporation of Green Features and Facilities in the Design Green features and facilities such as energy efficient air handling unit, solar panels, natural ventilation and lighting, waste sorting and recycling system, green roof and green walls may be adopted in a building development. The engineer should consider to incorporate them as far as possible in the design, based on the site-specific requirements and limitations. The Hong Kong Government has been promoting green buildings for many years. The Buildings Department together with the Lands Department and the Planning Department have issued two Joint Practice Notes in 2001 and 2002, providing incentives in the form of exemptions from the gross floor area and/or site coverage calculations for eleven types of green features in new buildings. These features include balconies, wider common corridors and lift lobbies, communal sky gardens, communal podium gardens, acoustic fins, sunshades and reflectors, wind catchers and funnels, non-structural prefabricated external walls, utility platforms, mail delivery rooms, and noise barriers. For the benefits of the development as well as the environment, the engineer should incorporate as many as possible of these green features to their building projects Choices of Structural System Tall buildings generally entails a high ratio of height to building width, thus the efficiency of a building structure may be significantly affected by the structural system chosen. For the selection of structural form, a comparison can generally be made for various systems, such as tube-in-tube, perimeter frame with central core wall, and outriggers. Consideration should be given for both the structural performance at the ultimate limit state and the serviceability limit state. Moreover,

3 3 factors such as method of construction, buildability, cost, layout, flexibility and useful floor areas should also be taken into account to ensure efficient design. Optimisation of a structural system can significantly improve its efficiency, thus resulting in saving in materials and associated cost, and increase in usable floor area. Conventionally, optimisation involves engineering judgement and reiteration to obtain the most optimum and efficient design. There are computer softwares available in the industry, which can take into account the efficiency of material use, cost, layout, usable floor areas and method of construction, and provide the engineer with an optimum and efficient design for the project. A number of skyscrapers in Hong Kong have adopted such computer programmes to optimize the structures of the buildings and in certain cases, a saving of up to 15% in construction materials has been achieved comparing with the original design Use of Materials Reinforced concrete is the most common type of construction material used in Hong Kong for structural elements. There are choices of different types of reinforced concrete that may be adopted to enhance its strength and quality. For example, high strength concrete may reduce the amount of material use and minimize the size of structural elements; self compacting concrete can ensure quality and durability of the concrete for locations where there is difficulty in compaction; the use of pulverized fuel ash as a partial replacement for ordinary Portland cement can be beneficial technically and environmentally. On the other hand, where possible, environmentally friendly, reusable and recycled materials should be chosen. There are a number of green construction materials that have been commonly used in Hong Kong. These include reusable safety fences that can be easily installed and reused many times. Recyclable system formwork was also adopted in lieu of the traditional timber formwork for many projects. These have reduced the amount of timber used on site and provided high quality finishes. Road paving made from trash and paint of low volatility are also available. In addition, a number of tailor-made facilities can be used for the collection and recycling of wastewater on site. 5. Construction Stage The choice of construction method, the handling of construction waste and the effectiveness of construction management have significant implication on the environment. During construction stage, it is always focused on the control of noise, air and water in view of the statutory requirements on the environmental legislation. However, sustainable construction methods, proper handling of construction and demolition wastes, and effective construction management can contribute to a large extent in the environmental performance of a project Effective Construction Management It is essential to ensure effective management during the construction stage. Each step of the construction process as agreed by the engineer should be properly followed. It is always recommended that the contractor should make detailed records and carry out accurate assessment of each construction process, including consumptions in electricity, water, fuel, paper and timber, and the amount of waste produced. These data would enable further strengthening of the control and management of construction cost and energy conservation. Some sustainability conscious contractors in Hong Kong have good experience in managing the construction site and making valuable achievement in minimizing the disturbance to the environment Construction Waste Management It is of major concern in Hong Kong that a great portion (about 40%) of the total solid waste disposed of in landfills is generated from the construction industry. The problem is aggravated by the impending crisis of the remaining short life of only a few years for landfill sites and the limited number of reclamation sites available. Measures should be taken by the construction industry to arrest this acute problem by way of reducing the amount of waste generated, increasing the overall recovery rate and reducing disposal in landfills. For site formation works, the engineer should adopt the balanced cut and fill principle where possible. A Waste Management Plan prepared at the beginning of the construction works, is a useful tool to ensure that adequate measures are taken during the

4 4 construction stage to reduce waste materials. Many civil engineering projects in Hong Kong have adopted the Waste Management Plan Scheme and the objective of reducing waste can be achieved. A measure to discourage the production of excessive waste from construction sites has been implemented since January This is the Construction Waste Disposal Charging Scheme, in which disposal of construction waste to landfills is subject to a charge of HK$125 per tonne, whereas, illegal dumping is subject to a maximum penalty of HK$500,000 and 6 months imprisonment. Therefore, effective waste sorting and treatment not only allow reusing and recycling, but also reduce disposal charges Precast Concrete Construction Precast concrete construction is considered as a green construction method. Its benefits to the environment include the reduction in noise and air pollution, efficient use of materials and faster construction cycle. Therefore, precast concrete construction has been widely adopted in many public housing projects and private developments. Since 2002, the Hong Kong Government provides incentives in the form of gross floor area exemption for non-structural prefabricated external walls. As a result, more and more private developments have adopted this construction method. In addition to using precast concrete facades, these developments also introduce other prefabricated units such as precast stairs, semiprecast slabs and precast structural columns and beams in the buildings although these do not attract any gross floor area exemption Demolition In Hong Kong, it is very common that staged demolition is carried out in a systematic manner. This enables efficient sorting and recycling of demolition waste. In general, non-structural elements including window frames, pipes, metal elements and timber such as doors and wooden floorboards are removed in sequence, then followed by structural elements. Sorting, selection and screening of materials are usually done at source for easy recycling or reuse of materials. In the adoption of demolition method, more environmental friendly tools should be used, such as hydraulic crasher, wire saw. Regarding environmental precautions, and debris and waste handling in demolition of buildings, the Code of Practice for Demolition of Buildings issued by the Buildings Department has provided detailed guidelines. 6. Operation Stage Comparatively, the operation stage of a building is much longer than its other stages of planning, design and construction. Therefore, systematic and proper building management and maintenance are particularly important. The engineer should incorporate his concept of sustainability during the planning, design and construction regarding the buildings inherent quality, durability and maintainability, into the operation stage by providing a concise manual for the maintenance and repair of building facilities to the users including the management team and the occupants. 7. Conclusion With increasing awareness in sustainability, it is positive to note that the construction industry and the Hong Kong Government are making contributions to sustainable building developments. However, we consider that it is still only a small step in the direction of a sustainable city. As structural engineers, we should be aware that we have an important role to play in the whole life cycle of a building. We need to offer our best effort for the achievement of sustainable building developments. It is important for us to continue our mission with an open mind and instill a sense of responsibility for the protection of the environment, into all the stakeholders as well as the younger generation such that a proactive attitude will be taken in achieving sustainability in the long run. References 1. Joint Practice Note No. 1 issued by the Buildings Department, Lands Department, and Planning Department of the Hong Kong SAR Government 2. Joint Practice Note No. 2 issued by the Buildings Department, Lands Department, and Planning Department of the Hong Kong SAR Government 3. Code of Practice on Wind Effects in Hong Kong 2004, published by the Buildings Department of the Hong Kong SAR Government 4. Code of Practice for Structural Use of Concrete 2004, published by the Buildings Department of the Hong Kong SAR Government

5 5 5. Code of Practice for Demolition of Buildings, published by the Buildings Department of the Hong Kong SAR Government 6. Code of Practice for Foundations, published by the Buildings Department of the Hong Kong SAR Government 7. Code of Practice for Precast Concrete Construction, published by the Buildings Department of the Hong Kong SAR Government 8. Code of Practice for the Structural Use of Steel 2005, published by the Buildings Department of the Hong Kong SAR Government Presenters background Ir CHOY Kin Kuen Vice President, The Hong Kong Institution of Engineers Vice Chairman, Professional Green Building Council Ir CHOY Kin Kuen was graduated in 1975 at the Hong Kong Polytechnic with an Associateship in Structural Engineering. Ir CHOY is a Chartered Civil and Structural Engineer, a Fellow of the Institution of Structural Engineers and the Hong Kong Institution of Engineers, and a Class 1 Registered Structural Engineer of the People s Republic of China. He is a Council Member of the Institution of Structural Engineers, United Kingdom. He also serves the Hong Kong Institution of Engineers as a Vice President and the Hong Kong Professional Green Building Council as a Vice Chairman and the Chairman of the Board of Education and Research. Presently, Ir CHOY is an Assistant Director of the Buildings Department responsible for all structural engineering and related matters. He has been appointed as an Adjunct Professor of the University of Hong Kong and the Hong Kong Polytechnic University since Ir Prof CHU Pui Kwan Reuben Vice President, The Hong Kong Institution of Engineers Managing Director, Meinhardt (C&S) Ltd and Meinhardt Infrastructure and Environment Ltd Ir Prof Reuben CHU is the Managing Director of Meinhardt (C&S) Ltd and Meinhardt Infrastructure and Environment Ltd consisting of over 300 staff covering civil, structural, geotechnical, infrastructural and environmental engineering. He has over 30 years experience in consulting engineering and has delivered services to Private Sectors, Government Departments, MTRC, KCRC and London Underground in Hong Kong, Macau, Mainland, and the UK. His involvement in major projects including projects of Hong Kong International Airport, Hong Kong Disneyland, MTRC Airport Rail Link, MTRC Shenzhen Metro, KCRC Kowloon Southern Link, KCRC East Rail Extension, Eastern Harbour Crossing, Tate s Cairn Tunnel and London Underground Jubilee Line Extension etc. He was also a part-time Lecturer in Civil Engineering with Hong Kong Baptist University and The Polytechnic University of Hong Kong. Ir Prof CHU is also the Vice President of Hong Kong Institution of Engineers, Past Chairman of the Professional Green Building Council and Past Chairman of the Hong Kong Association of Consulting Engineers.

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