First, the basic principles of structural design or review
It conforms to the specifications, is safe, reliable, reasonable and economical, and is convenient for construction.
1, structural system, structural layout, load, strength, stiffness, structure, calculation, etc. , should meet the requirements of the specification (the words "easy" and "possible" in the specification should be implemented as much as possible, and many designers think that it is wrong not to implement them), not only not to violate the mandatory provisions of the specification. "Regulations on Quality Management of Construction Projects" and "Regulations on Management of Survey and Design of Construction Projects" both stipulate that "if the design unit fails to design according to the mandatory standards of engineering construction", it shall be ordered to make corrections and be fined between 654.38 million yuan and 300,000 yuan ". China's national design standards are mandatory.
2. Structural systems that are not included in the code (such as special-shaped column frame structures, except for existing local regulations) and super-high and over-limit buildings should be specially examined.
3, to be safe and reliable, but not too wasteful and conservative, to be reasonable and economical, under normal construction conditions, according to China's standard design can ensure the safety of the project. A five-story brick-concrete office building is designed, which is not seismic and has a stone foundation. The steel consumption is only 4.6kg/m2, which is still in good condition.
4. Construction should be convenient: for example, there should not be too many kinds of concrete strength grades (commercial concrete has 1 strength grade, and the price difference is about 10 yuan /m3, which will affect the project cost of 2 yuan /m2, and the steel bars in a member should not be too complicated (the diameter and quantity of steel bars should not be too many).
5. Construction quality and other factors should be considered in the design, such as the quality of migrant workers, competitive price reduction, bribery and gifts, cutting corners, fake and shoddy building materials (such as strip steel), verticality deviation and thickness deviation of concrete protective layer. There is a big gap between the construction results and the theoretical conditions of design, so don't be too idealistic.
2. Prerequisites for design or audit.
1, "three basics": basic knowledge, basic theory and basic skills. We should master the concept, transmission mode and basic calculation formula of force.
1) Should transverse reinforcement be added when the column is hoisted off the beam? [1] can be omitted.
2) There is a stair calculation program that takes M=qL2/24 when calculating the negative bending moment of stair slab, which is unfounded.
3) Calculation of eccentric compression foundation: In addition to the bending moment at the column foot, the additional bending moment generated by horizontal shear force V at the column foot should also be considered, which is ignored by many designers, making the foundation area and reinforcement smaller.
2, familiar with the specification, and should correctly understand the meaning and intention of the specification.
(for example, the function and setting of additional transverse reinforcement for beams), there are also many shortcomings in the code, and there are also contradictions between the codes. If the code is high, it will be low. It is a "big code" rather than a "small code".
Chief engineer, chief engineer, approver and construction drawing reviewer must be familiar with the specifications, and it is easy for a small unit to be familiar with the specifications.
3. The structural scheme should be the crystallization of collective wisdom, and it should be discussed, brainstormed and finalized.
4. Before the start of construction drawing design, the professional director shall jointly determine the design technical conditions or measures with the reviewer and approver.
5. Management system and post responsibility system: designers, cartographers, auditors, professional leaders, auditors and approvers should all be professionals, and the signature of registered engineers should be professional leaders, at least those who have participated in the project. Drawings and calculations must be signed at least three times, and the signature cannot be filled in (if the project has been audited, the structural auditor shall be a construction professional. There are also chief engineers of large professional design institutes who sign examiners of architecture, structure, water supply and drainage, electricity and communication. The draftsman even signed it as "CAD". What's the point of such a signature? ); Some design units do not set up the post of "professional director", which is inappropriate.
6, work responsibility, meticulous work attitude, strive for perfection, and be responsible for your signature (name). The designer's self-calibration is the most important.
7. Design experience is very important: young and old, mentoring; Learn from the experience of others and predecessors (including subscribing to magazines); Chief engineer, chief engineer and construction drawing reviewer must have rich design experience; Examiners, auditors and construction drawing examiners are unfamiliar with specifications and lack design experience. How to examine other people's designs?
8. Self-protection consciousness: You can't allow the unreasonable demands of the construction profession and the owners to carry out illegal design.
9, the building (civil) engineering design is a high-risk industry should have a full understanding.
Structural design bears most of the responsibility for housing safety; Lifelong responsibility system; Full claim; Serious criminal responsibility. But many designers don't really know this. We should treat it correctly: not afraid, carefully designed. Implement design insurance.
1) Construction (civil) engineering accidents will cause mass casualties and huge property losses. There are accidents, big and small, in China every year, and there are many accidents abroad. In addition to the construction party's particularly malicious serious Jerry-building, the collapse of the house can be said to be caused by improper design.
2) The house is inclined, and cracks often appear in the wall and ground.
3) The designer cannot control the construction quality regardless of the construction.
4) The structural design is subject to the architectural specialty and the owner; Most building professionals and owners don't understand the structure; For example, the Code for Seismic Design of Buildings stipulates: "Architectural design shall meet the requirements of seismic conceptual design, and serious irregular design schemes shall not be adopted." The plane, elevation and longitudinal section of the building should be regular. Who will check it? Is the building in charge? The structure is in charge? The design scheme of buildings (especially high-rise buildings) should be finally determined by the structural specialty, but it is often impossible to implement it in China.
The Managua Bank of America designed by Lin Tongyan, an international architect, adopted a symmetrical shear wall core tube structure. 1in the earthquake of magnitude 6.5 (9 degrees) on February 23rd, 972, only the coupling beam of the core tube in layer 8- 17 had slight oblique cracks, and the others were intact. However, the15th floor central bank, which is very close to each other, adopts a double-column frame structure (the span of the frame beam reaches 12.50m), and one end is offset by two elevator shafts, which is seriously damaged and the repair cost is as high as 80% of the construction cost, which fully proves the importance of structural conceptual design.
5) Construction quality problems involving design and survey units. For example, if a project in Shanghai dies in the span pouring of floor formwork 13, the license of the construction, design and survey unit will be revoked.
6) The standard safety of China is much lower than that of developed countries.
7) There is too much knowledge for structural majors to learn and master. There are hundreds of codes (regulations) about structural design and construction acceptance in China, which are neither detailed nor detailed, and are not easy to be familiar with, and there are many contradictions. People have different understandings of these standards, and their implementation is also very different.
8) Spot check of design quality by the competent department and penalties for design units and employees in case of quality accidents: fines, suspension of business for rectification, and revocation of licenses.
9) Fire-fighting: Fire-fighting is mainly responsible for building and water and electricity design, but the structural specialty may also be implicated, as can be seen from the collapse of buildings in Hengyang fire.
10, correctly understand the role of computer and design calculation software. Today's design or calculation software is far from intelligent. It is just a design or calculation tool (equivalent to ancient abacus and slide rule). No matter what kind of structure system and structure arrangement you input (including violation of regulations), it can calculate whether the total information of your computer is wrong or not, or it depends on the human brain to judge whether it is correct or not. Especially the younger generation of designers, many people blindly trust computers and do not pay attention to conceptual design, so it is impossible to make qualified structural design.
Three. About computer problems
1, the value of total information: the prerequisite is very important, otherwise the calculation is meaningless. Although all kinds of computer programs have detailed descriptions or regulations on the value of total information, many designers do not fully understand its meaning, and improper values sometimes occur.
1) The bulk density of concrete should be 27 ~ 30: the bulk density of beams, columns and shear walls. After painting or decorating the surface, it should be greater than 25kN/m3. If the powder surface is 20 thick mortar, the column should be 400× 400: γ = (4402-4002 )× 20/4002+25 = 4.2+25. Column 600× 600: γ = (6402-6002 )× 20/6002+25 = 2.7555+25 = 27.8, column1000×1000: γ = (1. Beam 250×500 (thickness calculated by 100mm): γ = (290× 420-250× 400 )× 20/(250× 500)+25 = 3.488+25 = 28.5, beam 300×800 (.
2) Periodic reduction coefficient Tc: it must be reduced, otherwise the earthquake action will be small, and the value of the periodic reduction coefficient should be determined according to the number of infilled walls in this project, with the infilled walls taking more small values and the infilled walls taking less large values. Article 3.3. 16 of Technical Specification for Concrete Structures of High-rise Buildings stipulates that "the natural vibration period of the structure used to calculate the seismic influence coefficient of each mode should be reduced by considering the stiffness influence of non-bearing walls" as a mandatory provision, which is 0.6 ~ 0.9 for general frame structures, 0.9 ~ 0.99 for shear wall structures and 0.7 ~ 0.9 for frame-shear wall structures. However, if it is a full shear wall structure (that is, no load-bearing wall), it should be possible to take the periodic reduction factor of 1.
3) When calculating the period, displacement and story stiffness ratio of the structure, the assumption of rigid floor should be adopted. If there is a big hole in the floor or the floor is discontinuous, the internal force of the structure should be calculated according to the elastic floor.
4) Number of vibration modes: assuming rigid floor, translation ≤ calculated number of floors, coupling ≤ calculated number of floors× 3. For the frame structure with 10 story, the assumption of rigid floor is adopted, and the coupling analysis is not considered. The periods of output vibration modes with vibration modes of 12,1and 12 reach 146.5 and 56.6 seconds, indicating that the vibration mode is 12. When calculated by elastic floor, the number of vibration modes can exceed the above limit.
5) Beam stiffness increase coefficient: middle beam 2 and side beam 1.5 (1.3 ~ 2.0 specified in Article 5.2.2 of Technical Specification for Concrete Structures of High-rise Buildings), otherwise, the earthquake action will be small.
6) Beam end moment amplitude modulation coefficient: 0.8 ~ 0.9 (Article 5.2.2 of Technical Specification for Concrete Structures of Tall Buildings (JGJ 3-2002)), generally 0.85 can be filled in. It is inappropriate for some designers (including the technical director of a large Grade A design institute) to stipulate that the bending moment at the beam end is not modulated, because it is more likely to cause too many negative bending moment steel bars at the beam end, which will affect concrete pouring, and the reinforcement ratio is more likely to exceed 2.5% (mandatory provisions), and the ratio of steel bars at the lower part of the beam to negative bending moment steel bars at the beam end does not meet the specification requirements (mandatory provisions). Moreover, the negative bending moment at the beam end is generally much greater than the bending moment at the middle and lower part of the beam. For example, the negative bending moment at the beam end is 800kN.m, and the bending moment at the middle of the beam is 400 kn. M. If the amplitude modulation coefficient of the beam end bending moment is 0.85, the bending moment in the middle of the beam should be 400+800× 0.15 = 400+420 = 520kn. M. If the amplitude modulation of the bending moment at the end of the beam is not considered, the bending moment in the middle of the beam will increase by 65438.
7) Symbol of the influence of column width on the bending moment at the beam end: When the amplitude modulation coefficient of the bending moment at the beam end has been filled, the column width should not be regarded as the reduction of the negative bending moment at the beam end in the rigid domain.
8) The bending moment increase coefficient in the middle of the beam: 1 ~ 1.4, which can be filled in generally, and will be increased by 1 .2 ~1.4 times as appropriate during reinforcement. If the program is set to "beam bending moment increase coefficient", that is, both positive and negative bending moments increase, 1 should be filled in. It is unreasonable to increase negative bending moment after considering negative bending moment modulation in program setting.
9) Torque reduction coefficient of beam: 0.4, and the reduction of filling torque stiffness has little effect on beam torque reduction.
10) Coupling beam stiffness reduction coefficient: 0.5 ~ 0.55 (Code for Seismic Design of Buildings GB 50011-20013, Technical Specification for Concrete Structures of High-rise Buildings JGJ 3-2002) 5.
1 1)0.2Q0 force adjustment: the frame column must be adjusted for the frame-shear structure.
12) amplification factor of small tower earthquake action: SATWE, TAT: 3rd-5th order mode in translation: ≤3, 6th-9th order mode: ≤ 1.5, and 9th-order mode in coupling: ≤ 3,1. TBSA: No amplification.
13) Basic wind pressure: once every 50 years, for structures with height ≥60m and wind sensitivity 100 years. See load specification for basic wind pressure values. Note: The basic wind pressure is not revised in the new code (that is, the basic wind pressure of high-rise buildings is 1. 1 times).
14) Ground roughness: Grade D(4) (Dense high-rise urban area) Use with caution. Class D (4) can only be filled in when there are buildings around this project that are higher than this project.
15) number of wind carrier types: to be divided into sections, it can be divided into 1 section every three floors or so. If only 1 section is filled in multi-storey and high-rise buildings, the wind load will be too large. Some computer programs (such as SATWE and TAT) stipulate that it can only be divided into three segments at most. The 1 floor of 12 is divided into 1 section, with a maximum of 8 floors. There is no wind load on the upper 4 floors, which is unsafe.
16) Thickness of concrete protective layer: beam 25 (30 when concrete C20) and column 30.
17) P-Delta effect: high-rise buildings should be considered (technical specification for concrete structures of high-rise buildings. Multi-storey buildings should be considered and should be possible.
18) Accidental eccentricity: Accidental eccentricity should be considered when calculating unidirectional earthquakes in high-rise buildings (technical specification for concrete structures of high-rise buildings, and it is not necessary to consider accidental eccentricity when calculating bidirectional earthquakes.
19) unfavorable combination should be considered for live load.
20) Calculation principle of column calculation length (SATWE and other programs are aimed at steel columns): As the frame structure, shear wall structure and frame-shear wall structure all have lateral displacement, it is appropriate to fill in "with lateral displacement", but it seems unreasonable to fill in "without lateral displacement".
2 1) Translation and coupling: Generally, coupling is adopted, but sometimes translation may be worse than coupling.
22) Calculation principle of column reinforcement: sometimes the calculation results of single deflection and double deflection are quite different, so it should be calculated twice according to single deflection and double deflection respectively, and the reinforcement shall be subject to the larger value.
23) When the seismic fortification category is Class B, the calculated seismic intensity is not increased, but the seismic measures 1 degree should be increased. For example, the seismic grade should be increased by 1 degree, the limit value of axial compression ratio should be reduced, and the seismic structural measures should be improved, such as the reinforcement length of masonry walls should be increased, and so on.
24) The basements are all connected together, and the joints are divided into several independent structural units, which are not calculated according to the multi-tower structure. There are several buildings and elevators on the roof of a house, not to mention the multi-tower structure.
2. Formal parameters: the plane layout of beams and columns.
1) shall be reasonably simplified and shall be consistent with the construction drawing (structure layout and section size). The staggered floor of elevator machine room shall be calculated as 2 floors.
2) The foundation beam can be used as the input computer of 1 floor (the basement of 1 floor should be filled up, otherwise the wind load is too large), or it can be calculated separately.
3) Basement wall: transportable wall or transportable deep beam (the beam height is higher than the floor height).
4) Floor height: it should be taken from floor surface to floor surface (independent foundation: it should be counted as the top surface of foundation).
5) The concrete structure with steel frame on it should participate in the overall analysis, rather than just input the weight, and the results are quite different (especially in the earthquake area, the edge effect has a greater impact).
3. Loading (compulsory):
1) static and dynamic force, surface load, linear load and concentrated force.
2) The load should be reasonable: too large is unnecessary, and too small is even worse. Ground decoration surface (except leveling layer and bottom plastering) 1 ~ 1.5kN/m2, fire staircase 3.5kN/m2. Is 0.5kn/m2 too small for non-human roofs? Code for Load of Building Structures (Mandatory Provisions)
Note 1:
When the construction or maintenance load is heavy, the empty roof should be adopted according to the actual situation, and the suggested construction load is 1.5 ~ 2kn/m2. The rigid frame of light steel structure is greater than 60m2, and the purlin is still 0.3kN/m2 (mandatory provision). Note to Article 3.2. 1 of Code for Design of Steel Structures (Mandatory Provisions): "Members or structures supporting light roofs (20)
4, computer results print:
1) General information, period, period ratio, displacement, shear-weight ratio, stiffness ratio, over-limit reinforcement, bottom axial force and other information.
2) Formal parameter planning.
3) Load input plan (intermediate results of load need not be printed).
4) Plan of reinforcement results.
5) Shear V envelope diagram (used to configure additional transverse reinforcement of beam), and data files such as bending moment m are not printed.
6) Calculation results of 6)JCCAD: Not all column feet can be printed, and the calculation results corresponding to J 1 J2, ... should be selected, and three combinations of Nmax, Mmax and Vmax should be considered. For example, printing all the combined calculation results calculated by JCCAD is simply a "heavenly book". The calculation result of JCCAD does not show whether the column foot shear force V is read. If the shear force v of column foot is not considered, the foundation area and foundation reinforcement are small. If the foundation beam is not input into the computer as 1 layer, JCCAD cannot be used to calculate the foundation, because the load from the foundation beam (including the partition wall) should also be considered.
7) The computer calculation results of steel structure and grid structure are not all data files, but graphic files.
5, to analyze the computer results, can't ignore.
Four. basic design
1, correctly use the geological exploration report, and choose the foundation by yourself. You cannot use any foundation type recommended by the geological exploration report. Generally speaking, structural designers are better at basic design than geological prospecting personnel.
2. Beware of impact vibration of cast-in-place pile: necking is common.
3. Manual digging pile: it is more likely to construct (especially reaming) cross-hole in sandy gravel layer, and the construction risk is greater. If the pile is too short (less than 6m), it cannot be counted as a pile, but only as a pier.
4. Foundation treatment: replacement, vibroflotation, CFG pile (settlement should be included, article 9. 1.3 of the code for foundation treatment).
5. The basement floor is not designed according to the raft, but the so-called "waterproof board", and its thickness should not be less than 300. In addition to the buoyancy of groundwater, there is also the reaction of foundation, and its reinforcement and crack width should be calculated to be no more than 0.2mm (Technical Specification for Waterproofing of Underground Engineering).
6. Settlement joints are not required for expansion joints and seismic joints. A 6-story masonry structure building is equipped with 100mm wide seismic joints and settlement joints, so the strip foundations on both sides of the seismic joints are large eccentric foundations, which is extremely inappropriate.
7. C 15 concrete should be adopted for the cushion under the basement floor (Article 4. 1.5 of Technical Specification for Waterproofing of Underground Engineering).
8, the basement wall vertical reinforcement and horizontal reinforcement should pay attention to the minimum reinforcement ratio ρmin.
9. The basement exterior wall should have horizontal construction joints.
10, leaving only the post-cast strip in the super-long basement can't solve the problems of temperature and concrete shrinkage during use, so measures should be taken to strengthen steel bars, add anti-cracking agents and adopt prestressed concrete. The reinforcement spacing of basement exterior walls, floors and roofs should not be greater than150 mm.
1 1, the layout of settlement observation points should have observation details, and the observation methods should be explained, not just according to a certain specification.
12. Checking calculation of soft substratum of foundation: the design code of foundation can be adopted, but when ES 1/ES2 < 3, θ cannot be found, and it can also be calculated by the foundation stress formula.
13, pile foundation (including pile quality, single pile bearing capacity) testing, testing methods, testing quantity and other instructions, not just according to a certain specification.
14. Should the pure basement without superstructure be subjected to seismic design in the earthquake area? This problem has been clearly stated in the original code. For example, the Code for Seismic Design of Buildings stipulates that "the part of the basement without superstructure can be rated as Grade III or below according to the specific circumstances", and the Technical Specification for Concrete Structures of High-rise Buildings also stipulates that "the part of the basement beyond the scope of the upper main building without superstructure can be rated as Grade III or IV according to the specific circumstances. In the 9-degree seismic design, the seismic grade of the basement structure should not be lower than the second level. "
15, the rest, discussion of reinforced concrete structure (5).
Verb (abbreviation of verb) On the Design of Frame Structure
1. The section of column and beam should be reasonable: controlled by displacement, axial compression ratio and reinforcement ratio. Large cross-section should be adopted for large span and small cross-section for small span, and the cross-section width of continuous beam should be the same. The cross section of the column should be reduced every three stories or so to save investment. In order to facilitate shuttering, each side should be closed for one hour not less than 50 mm and not more than 200 mm to avoid sudden stiffness change. The top section (top floor) can be 300mm×300mm (which should meet the calculation requirements). Reducing the cross section of the column can also increase the available area accordingly.
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