Wood structure building refers to the use of wood as the main load-bearing component of the building, in all building materials, wood is the only kind of renewable green materials, in the recycling, energy conservation and environmental protection, earthquake and disaster reduction, assembly prefabrication, construction efficiency and other aspects of the unique advantages of other building materials. Moreover, wood structures can play an excellent role in carbon sequestration, by increasing the use of wood in buildings, increasing the carbon sequestration in them, and mitigating climate change.
By applying to buildings, the carbon sequestration cycle of trees can be achieved with the same life cycle as the building or even longer, and even if the building is demolished, the wooden building material can still be reused.
Therefore, the development and promotion of wood structure buildings is conducive to the development of forest products industry, which can increase the added value of forestry production and achieve better economic and social benefits.
Relevant experts proposed to the State Forestry and Grassland Administration the "Thoughts and Suggestions on Promoting Timber Structure Houses in the Seismic Zone" (hereinafter referred to as the "Proposal"), pointing out that wood structure buildings have unique advantages in earthquake resistance, and analyzing the feasibility of application, and suggesting that the government formulate policies to promote wood structure buildings in seismic belts to better realize the ecological, economic and social benefits of wood structure buildings.
China's seismic belt is closely related to the trend of mountain ranges, mainly concentrated in the Pacific Plate, the Indian Plate, the Philippine Sea Plate and the Eurasian Plate interaction area. At present, the main building of China's seismic belt is a brick-concrete structure of the house, such a house building due to the use of brittle materials of clay bricks and mortar masonry, in the absence of reasonable seismic measures, its seismic performance is generally poor, the need for special design and treatment to meet the seismic requirements. Some buildings in the seismic zone also use frame structures, which have better seismic performance than brick-concrete structures. Due to the level of economic development and demographic and environmental conditions, single-storey and multi-storey brick houses are still the main structural form of urban residential buildings in the seismic zone, especially in the economically underdeveloped rural areas of the seismic zone.
1. About the construction of rural areas in China
China's rural areas are widely distributed in various regions of the country, with changeable terrain, diverse architectural types, and obvious differences in architectural styles. The traditional residential buildings in the northern countryside are mostly bungalows with symmetrical layout, generally known as "courtyards" or "courtyards", and newly built houses mostly use asymmetrical layouts. The traditional residential buildings in the southern countryside have both bungalows and buildings, with symmetrical and asymmetrical layout forms, and the newly built houses are mostly buildings. Rural houses located in mountainous areas, hills and water towns are located in the mountains and rivers, using the terrain, using the combination of bungalows and buildings, and the layout form is more flexible. Others, such as cave dwellings on the Loess Plateau, bucket-shaped timber structures in the southwestern mountains, and civil engineering houses in the northwest region, have their own characteristics in combining topography, adapting to natural conditions and using indigenous materials. The building materials are mainly clay bricks and concrete, using traditional structural forms such as wood structures, earth structures, brick-concrete structures, etc. Bamboo and stone are also commonly used to build buildings in rural areas where bamboo resources are abundant and quarrying is convenient.
2. Construction market capacity in seismic zones and rural areas
According to the national standard GB 50011-2010 "Building Seismic Design Code", buildings with seismic fortification intensity in areas of 6 degrees and above must be seismically fortified. According to the 2015 "Zoning Map of China's Seismic Parameters", 41% of China's land and more than 50% of cities are located in areas with a basic earthquake intensity of 7 degrees or above, and the area of 6 degrees and above accounts for 79% of the total land area. As of 2020, 30 provinces across the country have experienced earthquakes of magnitude 6 or above, 19 provinces have had earthquakes of magnitude 7 or above, and 12 provinces have had earthquakes of magnitude 8 or above.
At present, the area of China's earthquake fortification area accounts for about 60% of the total land area, and the national housing construction area in 2019 is about 3.532 billion m2, and the rough estimate of the housing construction area in the earthquake defense area is about 2.119 billion m2.
According to the survey data of the National Bureau of Statistics, in 2019, China's urban population was 850 million, with a per capita housing construction area of 39.8 m2; the rural population was 550 million, with a per capita housing construction area of 48.9 m2, and in 2019, the rural housing construction area was 695 million m2 and the completed area was 600 million m2.
The Guiding Opinions on Vigorously Developing Prefabricated Buildings issued by the General Office of the State Council in 2016 requires that "prefabricated concrete structures, steel structures and modern wooden structures be developed according to local conditions, and strive to use about 10 years to make prefabricated buildings account for 30% of the new construction area".
According to the above statistics, it is estimated that modern wooden structure buildings account for 10% to 15% of prefabricated buildings (that is, modern wooden structure buildings account for 3% to 4.5% of new buildings), by 2025, it is conservatively estimated that the construction area of modern wooden structure buildings in the national seismic fortification area will reach 0.7 to 100 million m2, and the construction area of wooden structure houses in rural areas of the country will reach 0.2 to 0.3 billion m2.
It can be seen that wooden structure buildings have a huge potential market capacity in China's seismic belt and rural areas.
3. Wooden structures in seismic zones and rural areas
China has thousands of years of wood structure architecture history, at present, there are still dozens of wooden structure buildings preserved for about a thousand years. At the end of the 20th century, the state began to implement natural forest protection projects, advocating the use of metal, plastic and other alternative wood, and the development of wood structure buildings was once seriously restricted. Since the 21st century, with the sustainable development of the economy and the improvement of people's living standards, the state has begun to pay attention to energy conservation and environmental protection, encourage the use of renewable materials, and modern wooden structure buildings in Europe and the United States have begun to enter the domestic market, and a number of exemplary modern wooden structure buildings have been built successively.
Typical representatives include:
The "Mengjiayuan" exhibition center built in Shanghai in 2005, the Dujiangyan Xiang'e Primary School, Mianyang Special Education School, Beichuan Hongfeng Elderly Home, etc. built by Canada after the Wenchuan earthquake in 2008, the modern light wooden structure "Huaxia Star" Chuxin Library built in Changsha in 2010, the China-Canada Low-carbon energy-saving Building Technology Exchange Center built in Shijiazhuang in 2012, the Nankang Home Characteristic Town Wooden House Complex built in Ganzhou in 2018, and the Xijiao Hotel Yijing Park built in Shanghai in 2018. The implementation of these projects marks the entry of timber-framed architecture into a new stage of development in China.
However, in terms of the recognition of timber-framed buildings, the situation is still not optimistic.
Compared with concrete buildings, wood structure buildings are generally considered to have poor fire performance and better environmental protection performance, and their seismic resistance, heat preservation and cost are comparable to concrete buildings. It reflects that a considerable number of groups in China still have misunderstandings about wood structure buildings, especially in the application of seismic belt areas, the advantages of wood structure buildings with better seismic performance than concrete buildings have not been understood and recognized by the public.
Respondents who have a positive attitude towards the future market development of wooden structure buildings in the seismic zone and rural areas generally believe that wood structure buildings have the advantages of environmental protection, living comfort, energy conservation and emission reduction; the strong support of the government, the further development of rural tourism, the further improvement of rural income, and the progress of wood structure construction technology provide opportunities and conditions for the development of wood structure buildings.
At present, a considerable number of consumers still have a negative and solidified concept of wood-framed buildings, which restricts the promotion in seismic zones and rural areas to a certain extent.
Respondents who have a negative view of the future market development of timber-framed buildings in seismic zones and rural areas generally believe that:
The fire performance of wood structure buildings is worse than that of concrete buildings; with the acceleration of urbanization, the rural population will be greatly reduced in the future, and land will be more scarce; wood structure buildings are not practical, not durable, high cost of raw materials, and lack of professional designers; concrete buildings are widely popularized, easy to build, and form an inherent concept that is difficult to change. At present, domestic wooden structure buildings in the design, structure, construction, policies, regulations and other aspects can not fully meet and adapt to the needs of seismic zones and rural areas, it is necessary to further study the characteristics of the demand for building forms in these areas, so as to optimize and improve the wood structure buildings, so that they can better meet the actual needs of different regions.
Due to the above problems, the following difficulties have occurred in the promotion of wood structure buildings:
Some respondents still have doubts about the fireproof, waterproof, durability and safety of wood structure buildings; the technical specifications of wood structures are relatively backward, and the strong competition for concrete buildings is the main difficulties and obstacles faced by the promotion of wood structure buildings in rural areas and seismic belts. Among them, the biggest obstacle is the inherent concept of consumers, the lack of understanding of modern wood structure buildings, and the low degree of market recognition and acceptance.
In view of the above difficulties and problems, changes can be made from the following aspects:
The market is guided by the government's guided policies. As a low-carbon, energy-saving and renewable building material and construction technology, modern wooden structure buildings conform to China's national policy of building energy conservation and emission reduction, and are also an effective way to help achieve China's "carbon neutrality" goal.
On the one hand, it is necessary to vigorously promote the announcement of relevant policies to support wood structure buildings and encourage the use of wood in construction; on the other hand, to improve the relevant standards for wood structure buildings in earthquake zones and rural areas, and expand the development space of the wood structure market.
Do a good job in the publicity and popularization of wood structure buildings. Through this survey, it is found that the biggest obstacle to the promotion of wood structure buildings in seismic belts and rural areas is the inherent concept of consumers, the lack of understanding of modern wood structure buildings, and the low degree of market recognition and acceptance.
Therefore, we should increase the publicity and promotion of modern wood structure buildings, so that consumers can correctly understand the characteristics of modern wood structure buildings, understand more about the advantages of wood structures, and jointly create a good environment for the development of wood structure buildings.
Develop different types of wooden structure buildings according to local conditions. At present, from the perspective of regional distribution, there are relatively many wood structure projects in North China and East China, followed by the southwest region, northeast china and southern region, which reflects the good thermal insulation and seismic performance of wood structures, and is suitable for use in areas with low temperatures and frequent earthquakes.
According to previous estimates, the market for wooden structure buildings in China's seismic belt and rural areas has great potential, and different forms of wood structure buildings can be developed according to local conditions, such as the use of combined wooden structure buildings in the construction of township houses in economically developed areas of the eastern and southern coasts; the priority development of low-rise earthquake-resistant wooden structure buildings in earthquake-prone zones such as southwest mountainous areas.
Realize the localization of wood structure buildings and reduce construction costs. China's wood structure industry chain is not yet complete, most of the wood and some accessories used in modern wood structure buildings need to be imported, therefore, the overall cost is higher than the concrete structure by a certain proportion. If the promotion of wood structure buildings in the seismic zone and rural areas, we must take into account the local economic level and consumer demand, building design, materials, equipment, accessories, technical standards and specifications and installation technology should be based on the actual situation of our country, gradually realize localization, paving the way for wood structure buildings to enter the public life.
Cultivate professional and technical personnel of wood structure. At present, domestic wood structure construction enterprises generally lack professional and technical personnel in design, material production, processing and production, construction and installation, which seriously restricts the development of enterprises. It is recommended to start cultivating undergraduate professionals in colleges and universities with relevant majors, and carry out training in coordination with associations and social teams, encourage industry-university-research cooperation between universities, scientific research institutions and enterprises, promote the orderly development and benign interaction of talent training, and provide talent support for the development of wood structure buildings.