Detailed explanation of various structural forms
Masonry structure
masonry concept
A structure built with brick masonry, stone masonry or block masonry, also known as a masonry structure. Due to the high compressive strength of masonry and low tensile strength, masonry structural members mainly bear axial or small eccentric pressure, but are rarely pulled or bent. Generally, walls, columns and foundations of civil and industrial buildings can use masonry structures. In buildings with reinforced concrete frames and other structures, brick walls are often used as enclosure structures, such as infill walls for space frame structures
Advantages and disadvantages of masonry structure
The main advantages of masonry structures are:
1. It is easy to obtain local materials. Bricks are mainly fired with clay; the raw material of stone is natural stone; blocks can be made of industrial waste ─ ─ slag, the source is convenient and the price is low.
2. Brick, stone or block masonry has good fire resistance and good durability.
3. Formwork and special construction equipment are not required for masonry masonry. In cold areas, the freezing method can be used for masonry in winter, and no special insulation measures are required.
4. Brick walls and block walls can insulate and keep warm, so they are not only better load-bearing structures, but also better enclosure structures.
The disadvantages of masonry structure are:
1. Compared with steel and concrete, the strength of masonry is lower, so the cross-sectional size of the components is larger, the amount of materials is large, and the weight is heavy.
2. Masonry masonry is basically manual, and the construction labor is heavy.
3. The tensile and shear strength of masonry is very low, so the seismic performance is poor, and its use is limited; the compressive strength of bricks and stones cannot be fully utilized.
4. Clay bricks need to be made of clay, which occupies too much farmland in some areas and affects agricultural production.
Applicable fields of masonry structure
Masonry load-bearing is widely used in residential buildings, office buildings and other civil buildings.
The number of floors of the built houses has increased. It is very common for 5–6 storey houses to adopt a mixed structure with brick masonry as load-bearing. Many cities have built up to 7–8 storeys; Chongqing City built up to 12-storey masonry load-bearing houses in the 1970s; in some stone-producing areas, houses with rubble masonry as load-bearing walls are as high as 6 storeys;
In industrial plant construction, masonry is usually used to build enclosure walls;
The load-bearing structure of medium and small factory buildings and multi-storey light industrial factory buildings, as well as theaters, canteens, warehouses and other buildings;
Buildings with masonry structures can be built in earthquake fortified areas — reasonable design, construction quality assurance, and structural measures. The investigation and research on earthquake damage shows that: in areas with an earthquake intensity below six degrees, general masonry structures can withstand the test of earthquakes; according to the requirements of seismic design, it is possible to build masonry structures in fortified areas of seven and eight degrees.
Reinforced block buildings have shown good seismic performance and have been applied and developed in earthquake areas. The United States is the country where reinforced blocks are most widely used. After the earthquake in 1933, the reinforced concrete block (reinforced masonry) structural system was introduced, and a large number of multi-storey and high-rise reinforced masonry buildings were built. Most of these buildings have experienced the test of strong earthquakes. For example: 26 6–13-story U.S. veterans hospitals built in 1952; the 8-story Heiner Hotel (located in the 9-degree area) and the 19-story apartment in Los Angeles built in San Diego in 1966; in May 1990, four 28-story reinforced block hotels were built in Las Vegas, Nevada (7-degree area). Using reinforced blocks, many masonry high-rise buildings have been built in various places in my country: in 1983 and 1986, Nanning has built 10-story residential buildings and 11-story office buildings with reinforced blocks. MU20 high-strength blocks were used and vibrated twice manually, so mass production was impossible; in 1988, Benxi built a batch of 10-story residential buildings with gangue concrete block reinforcement; in 1997, according to the research results of Harbin Architecture University and Liaoning Academy of Construction Sciences, Northeast Design Institute designed and built a 15-story reinforced block shear wall point-type residential building in Panjin, Liaoning; in 1998, Shanghai Residential Corporation built an 18-story reinforced block shear wall in Shanghai The tower building is the highest 18-story block high-rise building in China, and it was built in an area with 7-degree earthquake resistance; in 2000, a 6.6-meter-wide 12-story reinforced block shear wall panel residential building was built in Fushun; in 2001, a 12-story reinforced block building was built in Harbin Aji Science and Technology Park, and then an 18-story block high-rise building was also built.
Reinforced masonry has become a structural system with similar performance and application range to reinforced concrete structures.
Brick-concrete structure
Concept of brick-concrete structure
Brick-concrete structure means that the walls and columns of the vertical load-bearing structure in the building are built with bricks or blocks, and the horizontal load-bearing beams, floor slabs, roof panels, etc. are reinforced concrete structures. That is to say, the brick-concrete structure is a load-bearing structure with a small part of reinforced concrete and most of the brick walls. The brick-concrete structure is a kind of mixed structure, which is a mixed structure system composed of brick walls for load bearing, reinforced concrete beams, columns and slabs. It is suitable for buildings with small bay depth, small room area, multi-storey or low-rise buildings. The load-bearing walls cannot be changed, while the space frame structure can change most of the walls.
Features of brick-concrete structure
The load-bearing structure of a space frame structure house is beams, slabs, and columns, while the load-bearing structure of a brick-concrete structure house is floor and wall.
In terms of firmness, theoretically, space frame structures can achieve greater firmness than brick-concrete structures. Therefore, when designing brick-concrete structures, the building height cannot exceed 6 floors, while space frame structures can achieve dozens of floors. However, in the actual construction process, the state stipulates the earthquake resistance level that buildings must achieve. Whether it is brick-concrete or frame, it must meet this level. Even if the developer builds a house with a space frame structure, he will not increase the investment to improve the strength of the building, as long as it meets the earthquake resistance level.
In terms of sound insulation effect, the sound insulation effect of brick-concrete houses is moderate, and the sound insulation effect of space frame structures depends on the choice of partition materials. The sound insulation effect of some advanced partition materials is better than that of brick-concrete buildings, while ordinary partition materials, such as cement hollow boards, have poor sound insulation effects.
If you want to renovate the interior space, most of the walls of the space frame structure are not load-bearing, so the renovation is relatively simple. Just knock down the wall. However, many walls in the brick-concrete structure are load-bearing structures and are not allowed to be demolished. You can only make a fuss about a few non-load-bearing walls. A simple way to distinguish between a load-bearing wall and a non-load-bearing wall is to look at the original structural drawing. Usually, a wall with a thickness of 240mm is load-bearing, and a wall with a thickness of 120mm or less is non-load-bearing.
The form of brick-concrete structure
The layout of the walls of the brick-concrete structure building is as follows:
1. The horizontal wall is load-bearing. Support the floors with transverse walls parallel to the gables. It is often used in buildings with small rooms such as residences, dormitories, hotels, and office buildings with regular layouts. The transverse wall is also used as a partition wall and a load-bearing wall, and the spacing is 3–4m.
2. The vertical wall is load-bearing. The floor is supported by the cornice wall and the longitudinal wall parallel to the cornice wall, and the bays can be flexibly arranged, but the building rigidity is poor, and large-area doors and windows cannot be opened on the facade.
3. Vertical and horizontal walls mixed load-bearing. Some use horizontal walls and some use vertical walls to support floors. It is mostly used in buildings with complex planes and diverse internal space divisions.
4. Brick wall and inner frame mixed load bearing. Internally, beams and columns are used instead of walls to bear the load, and the outer parapet also plays the role of load-bearing. This arrangement can obtain a large internal space and a flexible layout, but the rigidity of the building is not enough. It is often used in large halls.
5. The bottom layer is a reinforced concrete frame, and the upper part is a brick wall load-bearing structure. It is often used for shops along the street, or a large space for public activities on the ground floor, and buildings such as residences, offices or dormitories above.
Key points of brick-concrete structure design
For brick-concrete structure buildings with load-bearing brick walls as the main body, attention should be paid to the design: the openings of doors and windows should not be too large, and they should be arranged in an orderly manner; the distance between internal horizontal walls should not be too large; the shape of brick walls should be regular and flexible. The selection and arrangement of components should consider the strength and stability requirements of the structure, as well as durability, fire resistance and other structural requirements, such as thermal insulation, moisture resistance, surface decoration, opening of doors and windows, and special functional requirements for external walls. Houses built in the earthquake zone shall take anti-seismic measures according to the anti-seismic code, such as reinforcement, setting up structural columns, ring beams, etc. Brick-concrete buildings can create a simple, friendly and rural style in terms of texture, color, line pattern, scale, etc. In the design, the layout of the auxiliary buildings and the garden environment can also be considered in a unified way to achieve a harmonious artistic effect.
Features of the space frame structure
The main advantages of the frame building are: flexible space separation, light weight, good for earthquake resistance, and material saving; it has the advantage of being able to flexibly match the building layout, which is good for arranging building structures that require a larger space;
The disadvantages of the space frame structure system are: the stress concentration of the frame joints is significant; the lateral stiffness of the space frame structure is small, and it is a flexible structural frame. Under the action of a strong earthquake, the horizontal displacement of the structure is relatively large, which is likely to cause serious non-structural damage; the amount of steel and cement is large, the total number of components is large, the number of hoisting is large, the joint workload is large, the process is many, wastes manpower, and the construction is greatly affected by the season and environment; it is not suitable for building high-rise buildings. (Even if it can be considered that the cast-in-place floor and beams work together to increase the horizontal stiffness of the floor, it is also limited). Its stress characteristics are similar to vertical cantilever shear beams. The bending moment and the overall lateral movement also increase significantly, resulting in an increase in cross-sectional size and reinforcement, which may cause difficulties in building layout and space processing, affecting the rational use of building space, and tends to be unreasonable in terms of material consumption and cost, so it is generally suitable for building houses with no more than 15 floors.
Advantages of space frame structure
The biggest advantage of the space frame structure is that the layout of the building space is flexible, and the arbitrariness is relatively flexible. Because the main stress components of the space frame structure are columns and beams, and the walls are all filled with light materials, the layout of the building space is flexible.
Suspension-cable structure
Definition of suspension cable structure
A load-bearing structure formed by flexible tension cables and their edge members. The material of cable can adopt steel wire bundle, steel wire rope, steel hinge line, chain, round steel, and other wire rods with good tensile properties.
Plane Suspension Cable Structure
A planar structure that is mainly stressed in one plane, and is mostly used for suspension bridges and overhead pipelines. According to the structural form, it is divided into: 1. Single-layer suspension cable structure. It can be used as a flexible suspension bridge, and can also be used for roofs. The structure has low rigidity and large deformation under variable loads. It is suitable to lay heavy roofs on cables. 2. Stiffened single-layer suspension cable structure. Stiffening trusses (or stiffening beams) are hung by several suspenders under the cables to enhance the rigidity of the structure. 3. Double-layer suspension cable structure. The curvature of the upper cable and the lower cable is opposite, and it has better rigidity by applying prestress in the tension diagonal rod between them.
Spatial Suspension Cable Structure
A structure in a state of space stress, mostly used in long-span roof structures. Divided by structure:
1. Circular single-layer suspension cable structure. For the roof of the circular plane, the cables are arranged radially, and the entire roof forms a concave surface of revolution. The outer end of each cable is fixed on the surrounding reinforced concrete ring beam, and the inner end is fixed on the pull ring near the center of the circle. When a column is allowed at the center of the circle, an umbrella-shaped suspension cable structure can be formed. 2. Circular double-layer suspension cable structure. Its shape is similar to the above-mentioned structure, except that there are two layers of cables up and down, so that prestressed tie rods in different arrangements can be arranged to enhance rigidity. The roof of the competition hall with a diameter of 94 meters in Beijing Workers’ Gymnasium in China adopts this structural form. The pull ring near the center of the circle bears pressure in the vertical direction in addition to bearing hoop tension. 3. Two-way orthogonal cable network structure. It consists of two sets of cables that are orthogonal to each other. The concave group is load-bearing cables, the convex group is stable cables, and the two groups of cables form a surface with negative Gaussian curvature. When prestressing is applied to one group of cables, the other group of cables also obtains the effect of prestressing at the same time. By applying prestress, the two sets of cables can always be tightly attached under the action of the roof load, and good rigidity can be obtained. This cable net can be used for oval plan, rectangular plan, rhombus plan or other plan roofs. The roof of the Gymnasium in Milan, Italy adopts a saddle-shaped cable-net structure with a circular plane, with a diameter of 140 meters, which is currently the largest cable-net structure in the world. The roof of the People’s Gymnasium in Zhejiang Province, China uses a saddle-shaped cable net with an elliptical plane of 80 x 60 meters, and its cable ends are fixed on a curved beam in space. In order to reduce the bending moment in the curved beam, a layer of horizontal stay cables is also set up under the cable net.
In addition to the above-mentioned suspension structures, cable-stayed structures are also commonly used in engineering, such as cable-stayed bridges and cable-stayed roofs. This kind of stay cable is mainly used to reduce the span of roof or bridge deck structural components, so as to meet the large span requirement of the whole structure and achieve the purpose of saving materials.
With the development of coiled and thin steel plates, in recent years, some countries have adopted suspended strip structures. For example, the roof of the hangar at the Frankfurt Airport in the Federal Republic of Germany has a plane size of 270×100 meters and is divided into two spans. Each span is composed of 10 strips with a length of 13 meters and a width of 7.5 meters. The strips are separated by a 3-meter-wide lighting strip.
In addition to the above-mentioned suspension cables, there is another structure that uses steel cables to hang concrete roofs. This structure is called a suspended structure. Its characteristics are: making full use of the tensile characteristics of steel cables to reduce the bending force on reinforced concrete roofs. For example, the Yoyogi Gymnasium in Japan uses high-tension cables as the main suspension roof structure to create a large inner space with a sense of tension and dynamics.
In various forms of suspension cable structures, the rationality and reliability of cable edge members and ground anchors are extremely important, and determine the technical and economic indicators and safety of the structure to a certain extent.
arch structure
Definition of arch structure
The arch structure is a curved or broken line member that mainly bears axial pressure and is balanced by thrust at both ends.
The arch structure is composed of the arch ring and its support. The support can be made into a buttress that can bear vertical force, horizontal thrust and bending moment; it can also be used to bear vertical force with wall, column or foundation and horizontal thrust with tie rod. The arch ring mainly bears axial pressure, which is smaller than the bending moment and shear force of beams with the same span, so that it can save materials, increase stiffness, and span a large space. It can be used as a large-span roof load-bearing structure for auditoriums, exhibition halls, gymnasiums, railway stations, hangars, etc.; it is conducive to the use of cheap building materials with high compressive strength and low tensile strength such as bricks, stones, and concrete. Arches can be used for load-bearing structures such as general roofs, crane beams, lintels, retaining walls, and bulk material warehouses, as well as load-bearing structures for underground buildings, bridges, dams, and docks.
Advantages and disadvantages of arch structure
Under the action of external load, the arch mainly produces pressure, which makes the component get rid of bending deformation. If materials with better compressive properties (such as masonry or reinforced concrete) are used to make arches, the properties of materials can be brought into full play. But the arch structure support (arch foot) can produce horizontal thrust, and this thrust is also big when the span is big, and it is still a troublesome and material-consuming thing to deal with this thrust. Due to this shortcoming of the arch structure, trusses are still more commonly used than arches in practical engineering applications.
Membrane structure
Definition of Membrane Structure
Membrane structure (Membrane) is a new type of architectural structure developed in the middle of the 20th century. It is a form of space structure that is made of a variety of high-strength film materials (PVC or Teflon) and reinforcing components (steel frames, steel columns or steel cables) in a certain way to generate a certain pre-tensioned stress inside to form a certain space shape, as a covering structure, and can withstand certain external loads. Membrane structures can be divided into two categories: inflatable membrane structures and tensioned membrane structures. Pressure difference (generally between 10㎜～30㎜ water column), the indoor and outdoor pressure difference makes the roof membrane cloth receive a certain upward buoyancy, so as to achieve a larger span. The tensioned membrane structure is formed by column and steel frame support or steel cable tension, and its shape is very beautiful and flexible.
The material of the membrane structure
The membrane material used in the membrane structure is composed of base cloth and coating. The base cloth is mainly made of polyester fiber and glass fiber materials; the coating material is mainly polyvinyl chloride and polytetrafluoroethylene. Common membrane materials are polyester fiber covered polyvinyl chloride (PVC) and glass fiber covered polytetrafluoroethylene (Teflon). The main characteristics of PVC material are low strength, high elasticity, easy aging, large creep, and poor self-cleaning property, but it is cheap, easy to process and produce, rich in color, and has good folding resistance. In order to improve its performance, a layer of polytetrafluoroethylene coating can be coated on its surface to improve its anti-aging and self-cleaning ability, and its service life can reach about 15 years. Teflon material has high strength, large elastic modulus, self-cleaning, durability and fire resistance, etc., but it is more expensive, not easy to fold, requires high precision in cutting and manufacturing, and its service life is generally more than 30 years. It is suitable for permanent buildings.
Features of Membrane Structure
Light weight, high strength, fire and flame retardant, good self-cleaning, not affected by ultraviolet rays, anti-fatigue,
Resistant to twisting, aging and long service life. It has high light transmittance and little heat absorption. It is precisely because of the invention of this cross-age membrane material that the membrane structure building has become a modern permanent building.
Superior performance: self-cleaning, light-transmitting and energy-saving, economical, artistic, fireproof and earthquake-resistant, and diverse shapes; in addition, it also has the advantages of wide application fields, covering large-span spaces and short construction periods.
Fields of application of membrane structures
Cultural facilities — exhibition centers, theaters, conference halls, museums, botanical gardens, aquariums and other sports facilities — stadiums, gymnasiums, fitness centers, swimming pools, tennis courts, basketball courts, etc. Commercial facilities — shopping malls, shopping centers, hotels, restaurants, store fronts (overhanging eaves), commercial streets and other transportation facilities — airports, railway stations, bus stations, toll stations, wharves, gas stations, bridge corridors, etc. Industrial facilities — factories, warehouses, scientific research centers, processing centers, greenhouses, logistics centers and other landscape facilities — building entrances, landmarks, pedestrian streets, parking lots, etc. The cable-membrane structure originated from the tents that humans lived in in ancient times. After the 1970s, with the emergence of high-strength, waterproof, light-transmitting, smooth-surfaced, easy-to-clean, and anti-aging architectural membrane materials, coupled with the rapid development of contemporary electronics, machinery, and chemical technology, cable-membrane architectural structures have been widely used in public buildings with large spaces such as coastal tourism, expositions, art, and sports. The Millennium Dome on the banks of the River Thames in the UK is a landmark building of the membrane structure system and has attracted worldwide attention. The cable-membrane structure has the advantages of being easy to build, easy to dismantle, easy to move, easy to renew, making full use of sunlight and air, and integrating with the natural environment. It is the darling of the green building system in the 21st century. At present, the cable-membrane structure is in an upsurge both in the engineering field and in the scientific research field all over the world. In recent years, the demand for cable-membrane construction technology in my country’s construction market has obviously increased significantly. Major foreign famous cable-membrane technology companies have landed in my country, stimulating the development of my country’s cable-membrane construction industry. With the further development of modern science and technology, human beings are faced with the mission of protecting the natural environment. Therefore, natural materials and traditional ancient building materials will be replaced by light and thin high-strength and lightweight materials with good thermal insulation properties. Cable-membrane construction technology will play an important role in this transformation, and its wider application in the field of construction is foreseeable, and it can be said that the future is bright.
Properties of Membrane Structure
The characteristics of the membrane structure as a building system mainly depend on its unique shape and the performance of the membrane itself. Because of this, membrane structures can be used to create designs that cannot be realized with traditional building systems.
1. Lightweight: The reason why the tension structure has a small self-weight is that it relies on the prestressed form rather than the material to maintain the stability of the structure. Therefore, its self-weight is much smaller than that of traditional building structures, but it has good stability. Architects can take advantage of its lightweight and long-span characteristics to design and organize structural detail components, and organically unify its light and stable structural characteristics.
2. Light transmission: Light transmission is one of the most widely recognized characteristics of modern membrane structures. The light transmittance of the membrane can provide the required illuminance for the building, which is very important for building energy saving. It is especially important for some commercial buildings that require a lot of light and high brightness. Through the comprehensive utilization of natural lighting and artificial lighting, the light transmittance of membrane materials can provide greater space for aesthetic creation in architectural design. At night, the translucency turns the membrane structure into a sculpture of light.
The light transmittance of the film is determined by its base fiber, coating and its color. The spectral transmittance of standard film materials is between 10% and 20%, and the spectral transmittance of some film materials can reach 40%, while some film materials are opaque. The light transmittance of the film and the choice of light color can be adjusted by the color of the coating or the color of the surface layer.
Through the proper combination of film material and light-transmitting thermal insulation material, the multi-layer film with thermal insulation layer can be made transparent. Even if the spectral transmission is only a few percent, the membrane roof is still shiny and transparent to the human eye, giving the appearance of a light roof.
3. Flexibility: The tensile membrane structure is not rigid, and it will deform under the action of wind load or snow load. The membrane structure adapts to the external load by deforming, during which the radius of curvature of the membrane surface in the direction of the load decreases until it can more effectively resist the load.
The flexibility of tensile structures allows them to undergo large displacements without permanent deformation. The elastic properties of the membrane material and the level of prestress determine the deformation and response of the membrane structure. The flexible features adapted to nature can inspire people’s architectural design inspiration.
Different membrane materials have different flexibility procedures. Some membrane materials have excellent flexibility and will not be brittle or damaged due to folding. Such materials are the basis and premise for effectively realizing movable and expandable structures.
4. Sculptural sense: The unique curved shape of the tensioned membrane structure gives it a strong sense of sculpture. The membrane surface achieves self-balance through tension. The balance of the ups and downs of the negative Gaussian membrane surface makes the larger structure seem to float lightly between the sky and the earth as if it has escaped the shackles of gravity. This sculptural quality is exciting both indoors and out.
The tensioned membrane structure enables architects to design various self-balancing, complex and vivid spatial forms. As the light changes throughout the day, the sculptural membrane structure takes on different forms through light and shadow. At sunrise and sunset, light from a low angle of incidence will accentuate the curvature and relief of the roof, and when the sun is at apogee, the streamlined boundaries of the membrane structure cast sinuous shadows on the ground. Utilizing the translucency and reflectivity of the membrane, the designed artificial light can also make the membrane structure a sculpture of light.
5. Safety: The light tensile membrane structure designed according to the existing national codes and guidelines has sufficient safety. Lightweight structures can maintain good stability under horizontal loads such as earthquakes.
Due to the light weight of the light structure, even if an accidental collapse occurs, its danger is less than that of the traditional building structure. When the membrane structure is torn, if the structural arrangement can ensure that rigid supporting members such as masts and beams do not collapse, the danger will be smaller.
The flexibility of the membrane structure makes it bear in the most favorable shape under any load. Of course, the arrangement and shape of the structure should be designed and adjusted according to the load situation. The design must ensure that the membrane surface and its auxiliary structure work in harmony, so as to prevent the force from concentrating on the membrane surface or the auxiliary structure and reaching the critical value of structural damage.
Prefabricated structure
Definition of assembled structure
Prefabricated building refers to a building assembled on site with prefabricated components. The advantage of this kind of building is that the construction speed is fast, it is less restricted by climatic conditions, it saves labor and can improve the construction quality.
Advantages and disadvantages of prefabricated structure
advantage:
1. The components can be industrialized in the factory, and can be installed directly on the construction site, which is convenient and fast, and can shorten the construction period.
2. The components are mechanized in the factory, and the product quality is more easily controlled effectively.
3. The input of revolving materials and tools is reduced, and the rental cost of materials and tools is reduced.
4. Reduce the amount of wet work on the construction site, which is conducive to environmental protection.
5. Due to the reduced workload on the construction site, material waste can be reduced to a certain extent.
6. The mechanization of components is high, which can greatly reduce the construction personnel on site.
shortcoming:
1. Because the current domestic design and acceptance specifications are too lagging behind the development of construction technology, prefabricated buildings have relatively large restrictions on the total height and floor height of buildings.
2. The use of embedded parts and bolts in buildings has increased significantly.
3. Due to the limitations of molds and transportation (horizontal and vertical) restrictions in the factory production of components, the size of the components cannot be too large.
4. The requirements for vertical transport machinery on site are relatively high, and larger hoisting machinery is required.
5. Components are prefabricated in factories, and the prefabrication factory should not be too far away from the construction site.