Development and Prospect of Masonry Structure in China?

China is a big country of masonry, with the world-famous Great Wall of Wan Li in history. This is one of the greatest masonry projects in the world built with "Qin Zhuan Hanwa" more than 20 million years ago. Dujiangyan Water Conservancy Project, built by Li Bing and his son in Qin Dynasty, was built in the Spring and Autumn Period and the Warring States Period and still plays an irrigation role. There is an existing Anji Bridge in Zhao County, Hebei Province, which was built with stones 1400 years ago. It is the earliest open-shouldered arch bridge in the world. The bridge has been selected as 12 world civil engineering milestone by American Civil Engineering Society. These are worthy of our pride and inheritance, and also play a positive role in promoting our cultural heritage. After liberation, the masonry structure in China has developed greatly, which is briefly introduced from three aspects.

Masonry structures have a large number and a wide range.

Since liberation, the output of bricks in China has increased year by year. According to statistics? 1980, the national annual output was160 billion bricks, and 1996 increased to 620 billion bricks, which is the sum of the annual output of other countries in the world. Masonry, as a wall material in national capital construction, accounts for about 90%. Brick walls are widely used in civil buildings such as offices and houses. In 1950s, this kind of house was usually 3-4 storeys, but now it is 5-6 storeys, and many cities are usually built to 7-8 storeys. Today, the annual urban residential construction area is as high as 654.38+0 billion m2. According to Chongqing 1980 ~ 1983, the construction area of newly-built houses is 5.03 million m2, of which 98% are brick branches and 50% are 7 ~ 7 floors or more. 1972, a house with 12 floors was built.

Brick walls and columns are widely used in small and medium-sized single-storey industrial workshops and multi-storey light industrial workshops, as well as theaters, canteens, warehouses and other buildings.

Masonry structures are also used to build various structures. For example, a brick chimney with an outer diameter of 2. 18m at the top, an outer diameter of 4.78m at the bottom and a height of 60m built in Zhenjiang; 80m stone exhaust tower; Brick granary built in Hunan with a height of12.4m, a diameter of 6.3m and a wall thickness of 240mm; Xiangdong Canal is a large-scale water diversion project built by rubble in Fujian, which spans Xiao Yun and Dongshan counties. It has a total length of 4,400 m and a height of 20m, and has 258 piers. The project scale is huge. In addition, on the basis of ancient bridge-building technology, China built a stone arch bridge with a span of 60m and a height of 52m in 1959, and then built an open-shouldered modern highway bridge with a maximum span of 120m-Wuchaohe Bridge in Hunan. China has built 10 stone arch bridges 10 meters above (including Wuchaohe Bridge), and each stone arch bridge has made new development and set a world record.

China has also accumulated valuable experience in building masonry buildings in earthquake areas. The vast majority of large and medium-sized cities in China are in seismic fortification zones above 6 degrees. Masonry structures with earthquake intensity ≤6 degrees have withstood the test of earthquake. After the improvement and treatment of design and structure, a large number of masonry houses were built in the 7-degree zone and 8-degree zone. According to incomplete statistics, since the early 1980s, the construction area of multi-storey masonry houses built in major cities in China has reached 7-8 billion m2 [4].

Research and application of new materials, new technologies and new structures

Since the 1960s, the production and application of clay hollow brick (perforated brick) in China have made great progress, and a 6-8 storey hollow brick bearing hotel has been built in Nanjing. At that time, the void ratio of hollow brick was 22%, which was equivalent to the strength of solid brick, but it could reduce its own weight 17%, wall thickness by 20%, mortar by 20-30%, masonry time by 20-25% and wall cost by 19-23%. According to the further requirements of energy saving, in recent years, on the basis of digesting and absorbing foreign advanced technology, China has manufactured sintered thermal insulation hollow bricks (blocks) with specifications of 380×240× 190 and porosity of 40%. The density of the insulation brick is 10 12kg/m3, and the compressive strength is 10.5Mpa. The main mechanical and thermal performance indexes are close to or reach the international level of similar products [5]. The industry standard "Technical Specification for Design and Construction of Porous Brick Masonry" has created conditions for the popularization of this kind of brick.

/kloc-in the past 0/0 years, great progress has been made in China in making cement cinder concrete blocks or autoclaved lime-sand bricks, fly ash silicate bricks and blocks by using concrete, lightweight aggregate concrete or aerated concrete, as well as river sand, various industrial wastes, fly ash and coal dry stone. The block wall building was built in 1958. After more than 40 years of practice, block wall has become one of the effective ways of wall innovation in China. There are many types and specifications of blocks, among which medium and small blocks are common, and various strength grades of load-bearing blocks and decorative blocks have been developed in small blocks. According to incomplete statistics [6], the total output of blocks in China from 65438 to 0996 was about 25 million m3, and all kinds of block buildings

About 50 million m2, the annual growth rate of concrete blocks and block buildings in recent ten years is about 20%, especially in large and medium-sized cities. Taking the building blocks in Shanghai as an example, 1994, 1995, 1996 and 1500 are about 500,000 m2. Most of the buildings in these blocks are multi-storey. For medium and high-rise block buildings, China began to carry out pilot projects in the 1980s, such as the Guangxi Science and Technology Commission 10-story block residential test building built in 1982, and the Guangxi Construction Second Company 1 1 0-story small block test building built in 1986, [7 Since the early 1990s, on the basis of summarizing the experimental research experience of reinforced concrete blocks at home and abroad, China has made a breakthrough in the research of supporting materials and supporting application technologies for reinforced concrete block structures, and on this basis, it has carried out more representative and targeted pilot work [10], such as Panjin State Taxation Bureau 15-storey block residence completed in 1997. The pilot project practice shows that the middle and high-rise reinforced block building has obvious social and economic benefits: the original 15-story block building saves 45% steel and reduces the civil construction cost18%; Shanghai 18 building saves 25% steel and reduces the civil construction cost by 7.4%. Therefore, it is natural to incorporate the middle and high-rise reinforced block structure system into the design code of masonry structure in China. It can be seen that as the main substitute of clay bricks and some blocks with stronger functions than clay bricks, the development prospect is very good.

From 1950s to 1970s, China used prefabricated large-scale wall panels to build multi-storey houses, such as vibrating brick wall panels, slag and slag concrete wall panels to build hundreds of thousands of square meters of buildings. In recent 10 years, Beijing and other places have adopted the mixed structure of internal pouring (concrete) and external masonry to build middle and high-rise buildings, and achieved good economic benefits. In recent years, Tsinghua University has carried out experimental research and small-scale pilot projects on the mixed structure of multi-storey large-bay concrete core tube and masonry exterior wall, which has made beneficial exploration in improving and expanding the performance and application scope of masonry structure. [ 12、 13]

The application research of reinforced masonry in China started late. In 1960s, some walls and columns of some houses in Hengyang and Zhuzhou were supported by reticulated reinforced masonry, which saved steel and cement. 1958 to 1972 were built in Xuzhou 12-24m, and the crane lifting capacity was 50-200t, which was in good use. Since the 1970s, especially after the 1975 Haicheng-Yingkou earthquake and the 1976 Tangshan earthquake, a series of experimental studies have been carried out on structural columns and ring beam confined masonry, and the results have been introduced into China's seismic design code. On this basis, the research on the so-called high-rise masonry structure with strong constraints formed by adding dense structural columns in brick walls has achieved gratifying results. For example, Shenyang City, Liaoning Province, Xuzhou City, Jiangsu Province, Changsha City, Hunan Province, Lanzhou and other places have successively built such buildings with 8 ~ 9 floors and a million m2, and achieved good economic benefits. Some of the research results have been incorporated into local standards or national standards [14, 15, 16]. This is the contribution made by Chinese researchers to middle and high-rise buildings under the condition of low strength of clay brick masonry materials. Only China can build such a tall building in the earthquake zone with such low masonry materials!

Corresponding to the restrained reinforced masonry is the so-called uniformly reinforced masonry, which is a reinforced concrete block shear wall structure widely used abroad. This kind of masonry, like reinforced concrete shear wall, has minimum reinforcement ratio requirements for horizontal and vertical reinforcement, and is similar to concrete shear wall structure in stress mode. It uses reinforced block shear wall to bear the vertical and horizontal functions of the structure, and is a load-bearing and lateral force-resisting member of the structure. Reinforced masonry has high strength and good ductility, which is very similar to reinforced concrete shear wall and can be used for large bay and high-rise building structures [6]. According to American seismic code, the application scope of reinforced masonry is the same as that of reinforced concrete structure. In the early 1980s, China presided over the compilation of the international standard "Code for Design of Reinforced Masonry" [1 1], and has carried out systematic experimental research on it [7, 8 and 9], indicating that reinforced masonry can be used to build a building structure with a certain height of economic security, such as10//in Guangxi. At present, the reinforced block high-rise buildings under construction include Shougang 18 storey reinforced block residential project (8-degree fortification), 6 buildings in Fushun, Liaoning 16 storey block residential building, and 2 buildings in Harbin 18 storey block residential building. It can be seen that the research and application of reinforced masonry in middle and high-rise buildings has a very broad prospect.

China has rich experience in building arches and vouchers with bricks. Since liberation, it has developed into a new structural form and a large span. In the 1950s and 1960s, a large number of arched brick roofs and floors were built, and flat spherical brick roofs of10.5×1.3m, hyperbolic flat spherical brick thin shells of 16× 16m and spherical brick shells of 40m diameter were also built. In 1960s, Nanjing built 14× 10m hyperbolic flat shell roof warehouse and 10m diameter round shell roof oil depot with hook hollow bricks, and built 24m hyperbolic flat shell roof in Anjian. In 1970s, China also built an 88m-span (concrete-assisted) hyperbolic brick arch bridge on Meixi Bridge in Minqing.

Theoretical research and calculation method of three-story masonry structure

Before liberation, there was no structural design theory in China until 1950. 1956, the state construction Committee approved the popularization and application of the Soviet union's "design standards and technical specifications for masonry and reinforced masonry structures" NUTY 120-55 until the 1960s. From the 1960s to the early 1970s, under the leadership and organization of the relevant departments in China, a large-scale experimental research and investigation on masonry structures were carried out nationwide, and a set of advanced masonry structure theories, calculation methods and experiences in line with China's reality were summarized. It has China characteristics in the calculation formula of masonry strength, the calculation of bearing capacity of compression members of unreinforced masonry, the consideration of building space work according to rigid-elastic scheme and related structural measures. On this basis, 1973 promulgated the national standard "Code for Design of Masonry Structures" GBJ3-73. This is the first code for design of masonry structures in China. Since then, the design of masonry structure in China has entered a new stage. From the mid-1970s to the end of 1980s, in order to revise GBJ3-73 code, China conducted the second large-scale experimental study on masonry structure, and collected 4,023 masonry strength data tested all over the country over the years, supplemented by nearly 200 long column compression specimens, 100 local compression specimens, more than 200 wall beam specimens and more than 2,000 finite element analysis data, and conducted/kloc. In this way, new achievements have been made in the design method of masonry structure, the spatial working performance of multi-storey houses, the coordination of walls and beams, the mechanical properties of blocks, the design of block houses and so on. In addition, a large number of experimental studies have been carried out on the seismic performance of reinforced masonry, structural columns and masonry houses. Code for Design and Construction of Medium-sized Block Buildings (JGJ5-80), Code for Design and Construction of Small Concrete Hollow Block Buildings (JJ14-82), Code for Design of Reinforced Concrete Wall Beams in Metallurgical Industry Buildings (YS07-79) and Code for Seismic Design and Construction of Reinforced Concrete Structural Columns in Multi-storey Brick Houses (JJ/KLOC-0) For the space work of multi-storey masonry buildings, the research results of considering the work of wall beam and the design method of local compression of wall beam are in a leading position in the world. 10 years, especially after GBJ3-88 Code for Design of Masonry Structures was promulgated, it entered the third large-scale revision period. For example, "Technical Specification for Small Concrete Hollow Block Building" (JJ/T14-95) issued by 1995, the original specification (JJ14-82) can be added with one story through the test, which strengthens the seismic structural measures and expands the application scope of the earthquake area. 1GB50203-98 Code for Construction and Acceptance of Masonry Engineering issued in June 1999 replaced GB203-83 Code for Construction and Acceptance of Masonry Engineering. It mainly supplements the construction technology and construction quality control grade of new materials and reinforced masonry in recent years. GBJ3-88, which is currently being revised, mainly adjusts and supplements the reliability of masonry structures and the seismic performance of reinforced concrete block masonry and wall beams. According to China's current national conditions, the reliability of masonry structure has been appropriately improved. This is mainly to promote the use of higher-grade masonry materials, improve durability, and appropriately improve the ability to resist risks. Reinforced masonry, especially the middle and high-rise reinforced concrete blocks, makes the theory of reinforced masonry in China more perfect. According to the international standard Code for Design of Reinforced Masonry Structures edited by China and the experience of large-scale experimental research and pilot buildings in recent years, its application scope and limitations have been greatly expanded and broken through. As far as its application scope is concerned, it has reached the application scope of reinforced concrete shear wall. As a system, reinforced concrete block masonry has been brought into the masonry code, and its future implementation will play an important role in promoting the development of block structure in China to a high level.

In addition, this revision supplements the design method of wall beam in earthquake area, and further expands the application scope of this structural form. In addition, according to the serious temperature cracks and dry shrinkage cracks in masonry structures, especially in new wall materials, more effective anti-crack structural measures have been added after in-depth research.

In recent years, the theory of masonry structure in China has made great progress, which is reflected in the promulgation of GBJ3-88, Code for Design of Masonry Structure. Ding Dajun's Masonry Structure, Shi Chuxian's Theory and Design of Masonry Structure, Essays on Masonry Structure, Masonry Structure Design Manual and other textbooks and works have been published successively. These have a certain role in promoting the development of masonry structure in China.

Four prospects

Masonry is made of many materials, among which masonry is the oldest building material. For thousands of years, because of its good physical and mechanical properties, easy access to materials, convenient production and construction, and low cost, it has become the leading building material in China. However, the masonry materials in China generally have some shortcomings, such as heavy weight, low strength, high energy consumption, serious site damage, low level of construction mechanization, poor durability and seismic performance. Therefore, I think the following work should be carried out to solve these problems.

1, actively develop new energy-saving and environmental protection building materials [3]

The concept of "green building materials" was first put forward at 1988, the first international conference on materials research. 1In June, 1992, the World Summit on Environment and Development held in Rio de Janeiro, Brazil, adopted the Agenda Declaration of 2 1 century, which defined the strategic policy of "sustainable development", and its goal was to regenerate and coordinate life according to the environment. Protect the ecological environment and ensure the sustainable development of human society.

In recent years, developed countries have made great progress in implementing the "green building materials" plan. China took the opportunity of the 1992 United Nations Summit on Environment and Development, followed Comrade Jiang Zemin's instruction that "economic development must be considered with population, environment and resources as a whole, and we must never take the old road of wasting resources first, polluting first and then treating them, let alone eating ancestral rice and killing future generations ...", acted quickly and extensively developed "green building materials" products, and achieved initial results.

1) Improve the productivity of products with high energy consumption, high resource consumption, high pollution and low efficiency. For example, clay bricks (according to 1996, the price of producing 600 billion bricks is to destroy more than 654.38 million mu of land and consume 60 million tons of standard coal), and the state has long introduced a policy of reduction and restriction. In recent years, restrictions have become more and more severe. For example, cities such as Beijing and Shanghai are not allowed to use clay solid bricks in buildings, which indirectly promotes the development of other new materials.

2) Vigorously develop autoclaved lime-sand waste products. This includes steel slag brick, fly ash brick, slag brick and its hollow block, fly ash aerated concrete wallboard, etc. Before the 1980s, the output of these products in China reached 250 million pieces, consuming millions of tons of industrial waste residue. However, due to various reasons, most manufacturers stopped production, which led to the resurgence of clay brick production. In the future, we should increase investment in scientific research, improve technology, improve product performance and strength grade, reduce cost and develop into multi-function.

3) Using shale to produce porous brick. China is rich in shale resources and widely distributed. Sintered shale brick has the advantages of low energy consumption, high strength and regular appearance. Its strength grade can reach MU 15 ~ MU 30, and it can be used to build drywall and middle and high-rise buildings. Shale brick has been applied in Sichuan, Hubei and Dalian. For example, this kind of brick is used in the building of 65,438+600,000 square meters in Chengdu Mianchengyuan Community.

4) Vigorously develop waste residue lightweight concrete wallboard. This lightweight board uses fly ash to replace part of cement, and the aggregate is ceramsite, slag or slag, and glass fiber or other fibers are added. And the industrialization level of masonry construction technology is improved.

Improvement and improvement of GRC board. This kind of board is light in weight, fireproof, waterproof and convenient in construction and installation. GRC hollow lath is a kind of wall product which is developing vigorously, and it needs advanced production technology and assembly to improve the output and quality of plate.

6) Autoclaved fiber cement board. China is the third largest producer of fly ash in the world. The power industry alone emits hundreds of millions of tons of fly ash every year, and the current utilization rate is only 38%. In fact, after treatment, fly ash can produce wall materials with higher value. Such as high performance concrete block, autoclaved fiber reinforced fly ash wallboard, etc. It has the characteristics of low bulk density, low thermal conductivity, strong machinability and white color. At present, the national output has reached 7 million square meters.

7) Vigorously promote composite wallboard and composite block. At present, there is no single material at home and abroad, which can meet the technical requirements of building energy saving, thermal insulation, waterproof and strength of external walls. Therefore, composite technology can only be used to meet the multi-functional requirements of walls. Such as steel wire mesh cement sandwich panel. At present, it seems that the cracking phenomenon that is difficult to overcome after plastering in wet operation on site needs to be improved.

Composite block wall materials are also the future development direction. For example, any one of slag hollow brick, lime sand block and concrete hollow block can meet the requirements of external wall by compounding with thermal insulation materials, and a small amount of production has been made at present. China has a certain foundation in the application of composite wall materials, and it is necessary to further improve and perfect the supporting technology and vigorously promote it, which is the main way out for the "green" wall materials.

2. Develop high-strength masonry materials

At present, compared with developed countries, masonry materials in China have low strength and poor durability. For example, the compressive strength of clay brick is generally 7.5 ~ 15 MPa, and the porosity of load-bearing hollow brick is ≤25%. In developed countries, the compressive strength is generally 30 ~ 60 MPa, which can reach 100Mpa. The porosity of load-bearing hollow brick can reach 40%, and the bulk density is generally 13KN/m3, and the lightest can reach 0.6KN/m3. According to foreign experience and China's national conditions, the strength and quality of sintered bricks can be significantly improved as long as the batching, molding and sintering processes are improved. For example, Dalian Pacific Brick Factory, a Sino-US joint venture, can produce shale bricks of 20 MPa ~ 100 MPa. Because of its high strength, good durability, wear resistance and unique color, it can be used as drywall and decorative material, and has been exported and widely used in high-grade buildings. High strength block has much higher price advantage than low strength material.

According to China's restrictive policy on clay bricks, we can use local materials and plant them according to local conditions, and develop high-strength clay products, high-porosity thermal insulation bricks, decorative bricks and external wall blocks in areas with more clay, such as the Northwest Plateau. Develop high-strength concrete blocks, load-bearing decorative blocks and waste blocks in areas with little clay.

While developing high-strength blocks, develop high-strength masonry mortar. At present, the highest strength grade of mortar is M 15. It is necessary to develop high-performance mortar larger than M 15 when it is matched with high-strength block. In the industry standard of concrete small hollow block mortar and grouting concrete being drafted in China, the strength grade of mortar is M5 ~ M30, and that of grouting concrete is C20~C40. This is an important progress of concrete block supporting materials and plays an important role in promoting the development of high-strength masonry materials.

According to the development trend, in order to ensure the quality, the development of dry-mixed mortar and commercial mortar has a good prospect. The former is that all ingredients are mixed and packaged in a dry state and then supplied to the site, and water is added to stir as needed. Tianjin Shubuluoke Cement Block Company has supplied this dry-mixed mortar, and its price is about 20% higher. The advantages of commercial mortar are the same as those of commercial concrete. Once the development of this mortar replaces the traditional mortar, what a great change it will be!

3. Continue to strengthen the research on reinforced masonry and prestressed masonry.

Although the reinforced masonry structure system has been initially established in China, the machines and tools for producing block building construction, such as mortar paver, small diameter vibrator (Ф ≤ 25), small pouring pump for pouring concrete into holes, small steel bar welder and pouring concrete detector, need to be developed and finalized. These machines are very important to the quality of reinforced block structures.

The principle of prestressed masonry is the same as that of prestressed concrete, which can obviously improve the mechanical properties and seismic capacity of masonry. Foreign countries, especially Britain, have a high level in reinforced masonry and prestressed masonry. China did research in the early 1980s, but only recently did a few experts study it. For example, Professor Luo from chongqing jianzhu university made suggestions on the seismic design of prestressed brick walls. [ 17]

4. Strengthen the research of masonry structure theory.

Through physical and mathematical models, it is a topic of concern to further study the failure mechanism and mechanical properties of masonry structure and establish an accurate and complete theory of masonry structure. China's research in this field has a good foundation, and some topics have a certain depth. [18] It is very beneficial to continue to strengthen this work, and it is also of far-reaching significance to promote the development of masonry structures. Therefore, it is necessary to strengthen the research on the test technology and data processing of masonry structure, so as to realize the automation of the test and get more accurate test results.

As senior scholars of masonry structure, E, A and James pointed out that "masonry structure experienced a Renaissance in medieval Europe, and its attractive functional characteristics and economy are the key to its rebirth. We can't stay here. We are further giving new concepts and uses to masonry structures. " We are full of confidence in the future of masonry structure. Under the correct guidance of the Party's principles and policies, we adhere to a scientific attitude, be brave in innovation and make continuous efforts to make greater contributions to the development of masonry structures in China and the world.

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