In our daily study and work life, everyone has written a paper. With the help of papers, we can discuss problems and conduct academic research. I believe that writing papers is a headache for many people. The following is a paper on the ductility of short columns in architectural structure design, which is for your reference only and I hope it will help you.
For short columns, their flexural capacity and shear capacity are much larger, so under the earthquake, if the shear capacity is damaged, the flexural strength will not be exerted.
abstract:
With the development of social economy, many high-rise buildings have appeared in urban construction. When designing high-rise buildings, most of the designs can be designed with calculation software, which reduces the workload of designers, but there are still some tasks that designers need to operate, that is, to calculate the stress state of buildings according to the results of software calculation and design the structural measures of buildings. This paper mainly analyzes and studies the popularization of ductility design of short columns in facade buildings.
Key words:
High-rise building; Structural design; Ductility of short columns; analyse
In the construction of high-rise buildings, short columns are widely used. In order to improve the ductility of buildings, it is necessary to increase the cross-sectional area of columns and reduce the axial compression ratio. The smaller the axial compression ratio, the larger the cross-sectional area of the column. Therefore, in the structural design of high-rise buildings, in order to meet the limitation of axial compression ratio, it is often necessary to increase the cross-sectional area of columns, resulting in short column structures or even ultra-short column structures. Under the requirement of seismic performance, short columns are required to have sufficient seismic performance, and the ductility of short columns needs to be improved. This paper also analyzes the methods to improve ductility in building structure design.
1, the method of determining short columns
According to relevant requirements, a short column is defined as the ratio of the clear height (h) of the column to the section height (h), that is, when h/h is less than or equal to 4, it is called a short column. In building construction, most construction technicians determine short columns according to this judgment method. The parameters used in this method are only the relationship between the story height and the column section, not the internal force relationship of the column itself. According to the theory of material mechanics and structural mechanics, the shear span ratio (λ) can also be used as the basis for measuring short columns, that is, when λ=M/Vh≤2, the column is also short columns. However, compared with the method for judging short columns with H/h≤4 under the relationship between story height and column section, λ may not be less than 2 under this condition, that is, it may not be a short column. In most designs, designers use H/h≤4 to judge short columns, mainly according to the following principles: first, λ = m/VH ≤ 2; Secondly, because most of the bending points of frame columns have intersected near the midpoint of the columns, the value of m is 0. 5VH, then at this time λ≤2, that is, H/h≤4. However, in high-rise buildings, because the linear stiffness of columns and beams is relatively small, especially at the bottom of the building, the influence of column embedding is relatively great, and the columns are constrained by beams with small bending moments, and the height of the anti-bending point is more than half of the height of the columns, or even there is no anti-bending point. At this time, if it is unreasonable to judge short columns by H/h≤4, λ=M/Vh≤2 should be used. If the inflection point is not in the center of the column, the bending moment values of the upper and lower sections of the column are different, that is, MH ≠ mt
Therefore, the shear span ratio of the upper and lower parts is also different, that is, λh = Mh/Vh≦λt = Mt/Vt. At this time, when judging short columns, which section shear span ratio is used to judge is a key problem. Through analysis and research, it is considered that the larger value of the two is the basis for judging short columns, that is, λ=max(λh, λt). The reasons include the following aspects: First, frame columns can be regarded as continuous beams, and the column height (Hn) is similar to the shear span ratio of continuous beams under constant axial compression. Relevant experimental research shows that when the shear-span ratio of continuous beam is constant, the same longitudinal reinforcement is arranged above and below the section, and the bending moment is large. Secondly, in frame columns, critical oblique cracks will also appear in sections with large bending moments. In fact, in the range of shear span ratio of continuous beam or column height, the maximum shear span ratio will appear in the section with large bending moment.
With the increase of shear span ratio, the shear bearing capacity of reinforced concrete members will decrease. Therefore, under the same conditions, the shear bearing capacity of the section with smaller bending moment is greater than that of the section with larger bending moment. Under load, the possibility of shear failure of the section with large bending moment is greater than that of the section with small bending moment. Therefore, it is in line with the requirements to take the larger shear span ratio in the upper and lower sections as the shear span ratio of short columns. Generally speaking, the bending points of frame columns located at the bottom foundation of high-rise buildings are located at the upper part of the columns, that is, MB >；; Mt .
At this time, the short column can be judged according to the following formula (1): Hn/H ≤ 2/yn, where Hn represents the clear height of N-layer column. Yn represents the height ratio of the anti-bending point of the N-layer column. According to the geometric relationship, yn= 1/( 1+ψ), where ψ=Mt/Mb, 0≤ψ≤Hn. If the inflection point appears at the midpoint of the column, then ψ= 1 and yn=0.5, then the formula (1): HN/h ≤ 4; If the inflection point is at the upper end of the column, ψ=0, yn= 1, and the formula (1): HN/h ≤ 2; If there is no inflection point, it can be judged directly according to the shear span ratio λ=M/Vh≤2. Generally speaking, in the calculation process, the height ratio yn of the reverse bending point can be determined according to the D-value method, and then whether it belongs to a short column can be preliminarily judged according to the formula (1).
2. Measures to improve the ductility of short columns
2. 1 Concrete-filled steel tubular column is adopted.
Thin-walled concrete-filled circular steel tube is a concrete-filled steel tube structure. The steel tube exerts lateral binding force on concrete, and the concrete is in compression, which improves the compressive strength and ultimate compressive strain capacity of concrete, especially the ductility of high-strength concrete. In addition, the steel tube in the structure not only plays the role of transverse stirrup, but also plays the role of longitudinal reinforcement. The ratio of pipe diameter to pipe wall thickness is less than 90, which is similar to the concrete reinforcement ratio of more than 4.6%, and obviously exceeds the requirement of concrete reinforcement ratio in seismic requirements.
Because this kind of structure has excellent compressive strength and deformation resistance, even under high axial compression ratio, the compression zone will not be destroyed first, and compared with steel columns, there will be no buckling instability. Therefore, there is no need to limit the axial compression ratio in order to control the rotational capacity of the section. The bearing capacity of concrete-filled steel tubular single column can be calculated according to formula (2), that is, the bearing capacity is ≤ φ 1 φ en θ, where θ represents the hoop index, and the value range is. According to Formula (2), when the hoop index is properly selected, the bearing capacity of columns can be greatly improved by using high-strength concrete, and the section of columns can be greatly reduced by at least half compared with ordinary reinforced concrete columns, eliminating short columns and greatly improving the seismic performance.
2.2 the use of steel reinforced concrete columns
Steel reinforced concrete columns can be formed by wrapping concrete around steel ribs. In half cases, the types of steel skeleton include cross, open and I-shaped. Compared with steel structure, steel structure members may buckle locally, while steel reinforced concrete columns will not buckle because the steel members are wrapped in concrete, so the overall strength of the column is strengthened and the strength of steel can be effectively exerted. Moreover, the steel reinforced concrete structure can reduce the steel consumption by more than half compared with ordinary steel structure columns. Compared with the concrete structure, the bearing capacity of the column is greatly improved and the cross-sectional area of the column is effectively reduced due to the existence of steel ribs. Because the concrete is restrained by steel skeleton and stirrup, the ductility of concrete is improved, and the ductility and energy dissipation capacity of columns are enhanced. In this type of structure, the advantages of concrete and steel have been brought into full play. It has the advantages of good ductility, small section and light weight. The application in high-rise buildings can effectively improve the seismic performance.
2.3 using a separation column
For short columns, their flexural capacity and shear capacity are much larger, so under the earthquake, if the shear capacity is damaged, the flexural strength will not be exerted. Therefore, the bending strength of short columns can be artificially reduced to slightly lower than the shear strength. Under the earthquake condition, the bending strength of the column is exerted, which shows ductile failure. In order to reduce the bending strength, a notch can be vertically arranged in the column, and the short column can be divided into two or four parts to form a split column. Each split column is reinforced separately, and connecting nodes are arranged between the split columns to increase the initial stiffness of the split columns. Relevant research shows that compared with the whole column, the shear bearing capacity of the split column is basically the same, and the bending bearing capacity is reduced, which improves the deformation capacity and ductility of the column, from the original shear failure form to the bending failure form, and also cancels the short column and becomes a split long column, which effectively improves the seismic performance when the shear span ratio λ≤2.
3. Conclusion
When judging short columns, the shear span ratio λ≤2 should be taken as the judgment basis, the section size of short columns should be reduced as much as possible to improve the bearing capacity of short columns, and the ductility of short columns should be improved by various methods to effectively improve the seismic performance of short columns. In practice, concrete filled steel tube, steel reinforced concrete and other structural types have a very significant effect on improving the bearing capacity of short columns, while split columns have a very good effect on improving the seismic performance of short columns. The application in high-rise buildings also effectively reduces the appearance of short columns and ultra-short columns at the bottom of buildings, and avoids the problem that the brittle failure of short columns leads to the decline of seismic performance of buildings.
References:
[1] Kang, Wang Xingyang. Solutions to short columns in seismic design of high-rise buildings [J]. Science and Technology Information, 2013 (12): 412.
[2] Xie Guo. On the Ductility Design of Frame Structure of High-rise Building [J]. Henan Science and Technology, 2013 (13):166+170.
Extended content
Practice report of building structure
My architectural structure practice is roughly divided into two parts: one is to visit various buildings that have been put into use, so as to understand the classification and different characteristics of various structures, and the other is to visit the construction site to understand how to make design drawings into solid buildings through construction. Through visiting and studying, we have a preliminary understanding of the structure and structure of the building, which has played a guiding role in our future study and practice. Now I will summarize the two parts of the internship respectively.
First, visit and understand the structures of various buildings.
Architectural laboratory is an old-fashioned industrial workshop with bent structure. Through the teacher's explanation, we know that building structures can be classified by different classification standards, such as concrete structure, masonry structure, steel structure, wood structure, bamboo structure and so on. According to the different forces, it can be divided into bent, frame, grid, arch, truss and other structures. The bent structure used in the laboratory has the advantage of convenient construction. Generally, prefabricated components are used to build a one-story factory building.
Precast reinforced concrete movable beams and concrete slabs are used at the top of the laboratory. This structure is heavy, which limits the span of the beam. Now it has been replaced by widely used steel trusses and steel plates. We can see that in order to reduce the weight of precast concrete structures, I-beams are made in the middle of the beams in the laboratory, and excess concrete is dug out to reduce the weight.
The columns on both sides are typical columns of industrial buildings, and there are brackets on the upper part for installing the rails of cranes. The middle is also made into an I-shape. In order to increase stability, inter-column supports are arranged at intervals between the two columns. In addition, on the side of the crane track, the transverse connection between the crane track and the column is added, because the horizontal movement of the crane will produce horizontal load during the use of the crane.
Two wind-resistant columns are also designed on the wide side of the laboratory. These wind-resistant columns and beams arranged at intervals make the wall rigid enough to resist the load of strong wind.
Then there is the building energy-saving laboratory, which is a brick-concrete structure and a frame structure.
Frame structure is a single-storey and multi-storey building composed of foundation, column, beam and slab, and a high-rise building composed of frame and shear wall or frame and tube. The connection between them is fixed or rigid. Different from the bent structure of the building laboratory, the optimal floor of the frame structure building is about 15- 16, and the frame structure is mostly cast-in-place construction rather than prefabricated hoisting. In addition, I know that the frame structure is composed of beams and columns, and the cross section of the members is small, so the bearing capacity and stiffness of the frame structure are low. Its mechanical properties are similar to those of vertical cantilever shear beams. The higher the floor, the slower the horizontal displacement, and the high-rise frame bears great horizontal force in both vertical and horizontal directions. At this time, the cast-in-place floor slab is also used as a beam, regardless of the role of assembling the whole floor slab. The wall of the frame structure is a infilled wall, which plays the role of enclosure and protection.
The frame of the house is divided into single span and multi-span according to the number of spans; According to the number of layers, there are single layer and multi-layer; According to the facade, there are symmetry and asymmetry; Depending on the materials used, there are steel frames, reinforced concrete frames, prestressed concrete frames, glued wood frames or mixed frames of steel and reinforced concrete.
The floor of the building energy-saving laboratory is a precast reinforced concrete slab, which is a one-way slab. Through the teacher's explanation, we know that various boards can be divided into one-way boards and two-way boards according to their length-width ratio, but the value of length-width ratio is different in elastic theory and plastic theory. The elastic theory is that one-way slabs can only be supported in one direction, while two-way slabs are the opposite.
Next, we visit the automobile laboratory, which is a steel structure building. Steel is characterized by high strength, light weight and high rigidity, so it is especially suitable for building long-span, ultra-high and overweight buildings. The material has good uniformity and isotropy, and is an ideal elastomer, which is most in line with the basic assumptions of general engineering mechanics. The material has good plasticity and toughness, can deform greatly and can bear dynamic load well; Short construction period; High degree of industrialization, which can be used for specialized production with high degree of mechanization; High machining precision, high efficiency and good sealing performance. Its disadvantages are poor fire resistance and corrosion resistance.
When designing steel structures, we should pay special attention to the instability of materials. Therefore, in the steel of automobile laboratory, we can see that a rib will be added to the web of I-beam every short distance to solve the stability problem. The construction of steel structure is generally to prefabricate various components in the factory and then assemble them in the construction site. There are three assembly methods: welding, bolt and riveting. Among them, welding is easy to rust, and the strength of bolt connection is the highest, so the joints with high shear load requirements, such as the joints between beams and columns, are strengthened by bolts.
Finally, we visited the gymnasium and learned about the characteristics of truss structure, which is a geometric structure composed of many members connected by pins. Trusses with all members in the same plane are called plane trusses, otherwise they are called space trusses. Because the materials used in the truss structure are relatively economical, the truss itself is light in weight, and each member of the truss is only in tension or compression, so the role of materials can be fully exerted. For a large building like a gymnasium, truss structure can not only save costs, but also meet the load requirements.
Second, visit the construction site
We visited the fourteen-story science and technology building under construction in our school. When we arrived at the meeting place, I saw all the students wearing engineering hats; At the same time, the doors of the living area and construction area of the construction site also read: those who do not wear safety helmets are not allowed to enter the construction site; Of course, the slogan is also written on the protective net outside the main structure of the science and technology building: safety responsibility is more important than Mount Tai; This shows that the first thing to pay attention to in building construction is safety. In the past, many work-related injuries and deaths were caused by the fact that production enterprises did not pay attention to the safety of migrant workers, which brought great harm to workers and enterprises! At the same time, in order to ensure the smooth progress of the construction and the safety of the construction, the construction site should be surrounded by brick walls, and only vehicles and internal personnel under construction can enter and leave, and our internship should also be approved by them!
Entering the construction area, you can see the main structure of the science and technology building at a glance. At that time, the main structure didn't feel like architecture and was not beautiful. This may be because it is different from the buildings I have seen that have been built and put into use. There is a large area in front of the main body for stacking building materials. It can be seen that the building materials piled up are mainly steel bars, and there are no building materials such as cement and sandstone. This is because the finished concrete has been used for pouring structures. This can ensure the quality of concrete, reduce construction waste and reduce production costs. In the steel bar stacking area, you can see that different types of steel bars are placed separately, and the type and entry time of steel bars are also marked in front.
We followed the site manager upstairs. We stepped on a ladder made of steel pipes and iron nets and began to feel dangerous. There are steel pipes or iron bars sticking out everywhere. The formwork and supports on the second and third floors have been removed, and it can be clearly seen that the pillars supporting the upper weight are so big that we all feel that the height of the floors has become smaller. There are many constructional columns around the load-bearing columns to increase the strength of the wall and avoid the collapse of the wall because of its long length. Along the way, we saw that the supports of the upper floors were not removed. These supports are made of steel pipes and templates. Steel pipes are very dense, and obviously need a lot of support to bear concrete slabs and beams with no strength at all.
Up to the tenth floor, we saw that the workers were still binding steel bars, and the steel bars of columns and beams had been tied and put into the reserved slots of the formwork. I observed several beams and columns, as the teacher said: the lower part of the beam is the first rib, with nine main beams and six secondary beams; Not a stud, the main beam is different from the secondary beam; Stirrups are used to bind the reinforced bar and the reinforced bar of the frame. Columns are different. If there are three or four beams in the column, it is necessary to let the steel bars of the beams pass through the column, which makes the steel bars of the stigma very dense, and at the same time, we should pay attention to the compactness when pouring concrete. In general, the reinforcement of the slab is composed of stressed steel bars and frame steel bars, with the stressed steel bars below, which are divided into two ways: vertical and horizontal; The supporting ribs are at the top, which are also placed vertically and horizontally. The laid steel bars should be tied with wire. In order to ensure that the gluten is not trampled down, it should be heightened with horseshoe tendons. When we looked at the steel bars, we found that there were wire tubes and steel bars laid together, which was a manifestation of the cooperation between electrical and structural specialties.
Our on-site visit time is very limited. We only saw the workers arranging steel bars, but didn't see the construction scenes such as pouring column beams and slabs and laying brick walls, so our understanding was also very one-sided. This can only be regarded as our perceptual knowledge of architecture!
Summary:
In the internship, we did come into contact with many practical things, but there is still a big gap between higher production mode and more advanced technology. I found that all the production techniques we saw were not advanced, just like the shutter method of watching videos was useless in the science and technology building, but people began to use it in the early 1980 s. This may be because the construction unit lacks materials, but advanced production technology can really improve the construction progress and production quality.
From the development trend of architecture, people pay more and more attention to and affirm steel structure, so it is an urgent task to study the stress of steel structure and enhance its fire resistance.
Of course, based on the study of reinforced concrete structure, we should have a deeper understanding of the structure of the building through study and practice, and we can't ignore some possible hidden dangers to ensure that the high-rise buildings we build can really deal with all kinds of emergencies.
Experience of building structure training
Internship purpose:
Through this week's internship, we learned about some structures and components mentioned in the course. Understand some practical knowledge, realize some problems encountered in practical engineering and their solutions. Let's put the blunt knowledge in the textbook into practice and lay a certain foundation for future design courses.
Internship content:
When I visited the public building, I learned some problems involving the interior of the building and the public parking lot. Because the building doesn't need much open space, the shear wall structure is adopted. The columns in the basement are thick but not dense, so the space is not crowded. The accompanying designer explained to us the layout and classification of the bottom pipes, and explained how the fire pipes, domestic water pipes and other pipes were arranged. The formation and treatment methods of expansion joints, construction joints and settlement joints are expounded.
For example, the causes of concrete cracks: there are many reasons for concrete cracks, mainly the change of temperature and humidity, the brittleness and unevenness of concrete, as well as unreasonable structure, unqualified raw materials, template deformation, uneven settlement of foundation and so on. In the process of concrete hardening, cement releases a lot of hydration heat, the internal temperature rises continuously, and the surface produces tensile stress. In the later cooling process, due to the constraint of foundation or old concrete, tensile stress will appear in concrete. The decrease of air temperature will also produce great tensile stress on the concrete surface.
When these tensile stresses exceed the crack resistance of concrete, cracks will appear. The internal humidity of many concrete changes little or slowly, but the surface humidity may change greatly or greatly. Such as poor maintenance, sometimes dry and sometimes wet, surface shrinkage and deformation are constrained by internal concrete, which often leads to cracks. Some of our problems were explained in detail through explanations. At the same time, the teacher also pointed out the irrationality of the external design of this building, such as: the equipment platform is too narrow, and the patchwork balcony design is easy to cause sewage infiltration, reminding us of the places that need attention in future design.
Entering the interior of the house, we visited the functional partition of the interior house, accompanied by the staff, telling us the misunderstandings and mistakes in architectural design, so that we can pay attention to the treatment of elevator room and bathroom stairs in future architectural design. There, first of all, we watched the excavation process of the foundation by the builders, and learned the reasons that affected the foundation depth, as well as some problems that should be paid attention to in laying the foundation in Guizhou. Then I visited the second phase project there. This project adopts frame-shear wall structure, which is a combination of frame structure and shear wall structure, and absorbs their respective advantages, which not only provides more space for building layout, but also has good lateral force resistance. This kind of structure is to arrange a certain number of shear walls in the frame structure to form flexible and free use space to meet the requirements of different building functions. It also has enough shear walls and considerable rigidity. The stress characteristics of frame-shear wall structure are new stress forms composed of two different lateral force resisting structures, namely frame and shear wall structure, so its frame is different from pure frame structure, and the shear wall in frame-shear wall structure is also different from the shear wall in shear wall structure. In this project, we have a detailed understanding of the construction methods of beams and columns and the problems that should be paid attention to when building frame structures.
The constructors explained to us the different construction methods of beams and columns, the binding of steel bars and the connection of broken steel bars. For example, the binding of steel bars and the binding of bottom foundation steel bars should be laid out first, and the number of joints per span of steel bars is only 25%, that is, there is only one joint for four steel bars. In addition, the joint should be located in the compression zone as far as possible.
In the process of building walls, if there are corners or intersections between walls, the two walls should be built together. In the process of leaving a gap, you can leave an oblique gap. If you want to leave a straight seam, you must leave a straight seam, with Rachel bars, but not a negative seam. This knowledge is often something I seldom touch and pay attention to at school, but it is very important and basic knowledge. Let us benefit a lot. I worked as an intern outside for a month. Through personal experience these days, the theoretical knowledge I learned in school has been well practiced. But also provides great help for the actual design work and realistic data for the graduation design. So as to avoid the phenomenon that the design is out of touch with the actual construction in the design process.
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