建筑木材的安全性英文文献和中文翻译(5)
Construction timber can be readily supplied by imports China continues to import increasing volumes of wood products for construction and other end uses. Fortunately, there are many softwood producing regions in the world with the capacity to supply growing Chinese markets with quality structural wood products from forest reserves certified for sustainable development.Importing softwood timber complies with WTO rules and Chinese government policies, which reduced the tariff rates for importing industrial roundwood and sawn timber to zero in 1999. The government particularly encourages imports of wood products from sustainable forest resources.This is partly to reduce carbon emissions. Research has shown that carbon emissions from transport are small relative to the carbon stored in wood, and in comparison with the potential carbon emissions from using fossil fuel-intensive materials for construction.
The importance of using wood from sustainably managed forests
Credible independent third-party forest certification is becoming an important tool for forest companies, governments and buyers around the world. Certification provides assurance that wood products are legally sourced, environmentally-friendly and from a sustainably managed forest.There is co-operation between China, Canada, and Europe in the exchange of information on modern forest practices, including certification and sustainable forest development. Canada has 91 per cent of its original forest cover, and more protected forest (over 40 million hectares) than any other country. It accounts for over 40 per cent of the world’s certified forests. Its deforestation rate has been virtually zero for decades.European forests are the most intensively managed forests in the world, providing about 25 per cent of the current world industrial production of forest products. Europe’s forests are expanding at an annual net rate of 661,000 hectares.There are four systems which are accepted internationally to provide certification as credible evidence of legal and sustainable forest management. The four systems are The Forest Stewardship Council (FSC), The Programme for the Endorsement of Forest Certification (PEFC), The Sustainable Forestry Initiative (SFI) and The Canadian Standards Association (CSA). The SFI and CSA also work in conjunction with PEFC.
It is never easy to compare the costs of building with different materials and systems. So many factors are involved. For example, the relative costs of different materials change according to supply and demand as well as currency fluctuations. Local conditions vary significantly. And there are many different ways to build in different materials. Building with wood could involve anything from traditional wood frame, to technologically advanced engineered systems, or even hybrid construction. And building efficiencies vary, depending on the regulatory system, scale of development, knowledge and skills, the extent of off-site construction, and how adept and experienced the construction company is at planning and managing the building process.It is worth noting, however, that wood frame systems account for around 70 per cent of residential construction in the developed world. And 90 per cent in North America. One of the reasons for its popularity is its cost-effectiveness, which includes a much shorter construction time and less waste than other systems.
Codes and standards
China has an extensive system of national and regional building codes and standards. The Ministry of Housing and Urban-Rural Development (MOHURD) publishes a range of:
• National building codes, generally designated GB or GB/T
• National sector or industry standards, generally designated JGJ or JGJ/T
The Municipal Urban-Rural Development and Transportation Commission publishes building codes and standards that address regional requirements. Regional codes are generally designated DBG or DGJ.Enterprise standards (designated ‘QB’) are published by industry.These are for manufactured products which are not covered by national standards.Provincial and regional jurisdictions enforce mandatory national building codes and standards as minimum requirements. Regional codes cannot set requirements below those required by national codes. Both national and regional codes can include the T-designation which may affect the level of penalties for non-compliance with certain clauses. In China, wood buildings are subject to the same regulatory requirements as all other types of construction. They address health,safety, fire safety, structural safety, protection of persons and property,durability, environmental protection and the public interest. Chinese building codes are continuously under review, expanding in coverage and evolving to meet China’s housing and construction needs.Since the introduction of wood structures into the Chinese code system a decade ago, a comprehensive set of codes and standards has been developed specifically for wood construction and wood products. A number of more broadly based national building codes also set minimum requirements for wood construction. Some of the more important codes impacting the design, construction and inspection of wood buildings are described as follows.
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