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Architectural practice
According to the arrangement of the school, I went to xxxx Project Department of Wuhan xX Construction Company on xx, XX, XX.
Construction practice, this is a good opportunity for me to understand the construction site and let me know more.
The difference between theory and practice.
1. Project introduction
This project is an apartment building developed by Wuhan xxxx State-owned Investment Company, and the contractor is Wu.
Handi xxx Construction Company is Building No.5 and Building No.6 respectively, and there is also a golf fitness building, and the foundation is XXX No.4..
It was built by pile foundation company and designed by Beijing xxxx Design Institute. Frame shear wall structure is adopted, and the columns are anisotropic columns.
Column. A commercial and residential building, with an area of 65,438+03,000 square meters, consists of three buildings, with cast-in-place reinforced concrete and six-story frame-shear joints.
Structure.
Second, the internship content
1: Woodworking
1) Types and manufacturing methods of templates;
2) Quality standards for formwork installation of various structures;
3) Quality standard for formwork installation of cast-in-place structure;
4) Time and sequence of dismantling the cast-in-place structure template;
5) Precautions for template removal;
6) Methods and requirements for template cleaning, stacking and maintenance;
2. Reinforcement worker
1) Types and appearance characteristics of reinforcement;
2) Welding methods and quality requirements of steel bars;
3) Method and technology of cold working of steel bar;
4) Binding method and quality requirements of reinforcement;
5) lap length requirements for steel binding;
6) Control method of protective layer thickness of various components;
7) Master the recording methods and main contents of concealed works;
3. Concrete workers
1) Types, specifications and mixing principles of mixers;
2) Type and scope of application of vibrator;
3) Conversion of construction mixture ratio and mark content;
4) Design and treatment of construction joints;
5) Concrete curing methods and requirements;
6) Causes of concrete surface defects and preventive treatment methods;
7) Quality inspection content of concrete engineering;
Three points of harvest and experience
First of all, internship is a familiar and unfamiliar word to me, because I have been a student for more than ten years.
Ya has also experienced many internships, but this time it is so different. He will comprehensively test each of us.
Ability: study, life, psychology, body, thought, etc. It is like a touchstone.
Whether I can apply the theoretical knowledge I have learned to practice is related to whether I can stand here smoothly in the future.
A challenging society is also the key to building my confidence, and so is my investment in it.
100%! The intense one-month internship life is over, and I still have some problems for more than a month.
The harvest is very small. It is necessary to sum up after the internship. First of all, through more than one month's internship,
I learned a lot of practical knowledge through practice. The so-called practice is the only criterion for testing truth.
After passing the side station, I observed the whole construction process at close range and learned a lot of applicable tools.
Knowledge of body structure, which I seldom touch and pay attention to at school, is ten.
Important basic knowledge.
For example, the cause and treatment of concrete cracks is a very complicated problem, so I will talk about mine.
Viewpoint:
1 Causes of cracks
There are many reasons for concrete cracks, mainly the change of temperature and humidity, the brittleness of concrete and the shortage of concrete.
Uniformity, unreasonable structure, unqualified raw materials (such as alkali aggregate reaction), template deformation, foundation
Uneven settlement and so on.
In the process of concrete hardening, cement releases a lot of hydration heat, and the internal temperature rises continuously, resulting in tensile stress on the surface.
In the later cooling process, it will appear in the concrete due to the constraint of foundation or old concrete.
Tensile stress. The decrease of air temperature will also produce great tensile stress on the concrete surface. When these tensile stresses exceed
Cracks will appear when the crack resistance of concrete is high. The internal humidity of many concretes has little or no change.
Slow, but the surface humidity may change greatly or greatly. If the maintenance is not good, it will alternate between dry and wet, as shown in the table.
Surface shrinkage deformation is constrained by internal concrete, which often leads to cracks. Concrete is a brittle material.
The tensile strength is about110 of the compressive strength. The ultimate tensile deformation under short-term loading is only (0.6 ~ 1.0) × 104, and that under long-term loading is only (1.2 ~ 2.0) × 14. In the same piece of concrete, its tensile strength is uneven, and there are many weak parts with low tensile capacity, which are prone to cracks. In reinforced concrete, tensile stress is mainly borne by steel bars, and concrete only bears compressive stress. If the tensile stress appears in plain concrete or the edge of reinforced concrete structure, it must be borne by the concrete itself. Generally, there is no tensile stress or only a small tensile stress. However, when the concrete is cooled from the highest temperature to a stable temperature during operation, considerable tensile stress often occurs inside the concrete. Sometimes the temperature stress will exceed the stress caused by other external loads, so it is extremely important to master the variation law of temperature stress for reasonable structural design and construction.
2 temperature stress analysis
According to the formation process of temperature stress, it can be divided into the following three stages:
(1) Early stage: generally, it takes about 30 days from the beginning of concrete pouring to the end of cement exothermic.
Two characteristics, one is that cement releases a lot of hydration heat, and the other is the sharp change of elastic modulus to coagulation.
With the change of elastic modulus, residual stress is formed in concrete during this period.
(2) Mid-term: from the end of the exothermic effect of cement to the cooling of concrete to a stable temperature, which
During this period, the temperature stress is mainly caused by the cooling of concrete and the change of external temperature. These pressures
Superimposed with the residual stress formed in the early stage, the solidification elastic modulus changed little during this period.
(3) Late stage: the operation period after the concrete is completely cooled. Temperature stress is mainly caused by the change of external temperature.
These stresses are superimposed with the residual stresses of the first two.
According to the causes of temperature stress, it can be divided into two categories:
(1) Self-generated stress: A structure without any constraint on the boundary or completely at rest, if the internal temperature is nonlinear.
Sexual distribution, because the structure itself is about each other
Temperature stress caused by beam. Such as piers and structural rulers.
When the concrete is cooled, the surface temperature is low and the internal temperature is high, and the surface tensile stress appears.
Occasionally, compressive stress occurs.
(2) Constraint stress: All or part of the boundary of the structure is constrained by the outside world and cannot be deformed freely.
Stress, such as box girder roof concrete and guardrail concrete.
These two kinds of temperature stress often interact with the stress caused by concrete drying shrinkage.
It is a complicated work to accurately analyze the distribution of temperature stress according to the known temperature.
In most cases, it depends on model test or numerical calculation. The creep of concrete will cause temperature stress.
Considerable relaxation, when calculating temperature stress, the influence of creep must be considered, and the specific calculation is not here.
Explain in detail.
3 temperature control and measures to prevent cracks
In order to prevent cracks and reduce temperature stress, we can control temperature and improve constraints.
Measures to control the temperature are as follows:
(1) Improve aggregate gradation, use hard concrete, mix mixture, add air entraining agent or plasticizer, etc.
Measures to reduce the amount of cement in concrete;
(2) When mixing concrete, add water or water to cool the crushed stone to reduce the pouring temperature of concrete;
(3) When pouring concrete in hot weather, reduce the pouring thickness and use the pouring layer to dissipate heat;
(4) embedding water pipes in concrete and introducing cold water for cooling;
(5) Provide a reasonable time for form removal, and conduct surface insulation when the temperature drops suddenly to avoid freezing of the concrete surface.
Sharp temperature gradient;
(6) The surface of concrete pouring blocks or thin-walled structures exposed for a long time during construction shall be insulated in cold season.
Measures;
Measures to improve the constraint conditions are:
(1) Reasonable jointing and plugging;
(2) Avoid excessive fluctuation of foundation;
(3) Reasonable arrangement of construction procedures to avoid excessive height difference and long-term exposure of the side;
In addition, improve the performance of concrete, improve crack resistance, strengthen maintenance, and prevent surface drying shrinkage, especially
It is very important to ensure the quality of concrete and prevent cracks, and special attention should be paid to avoid through cracks and cracks.
At present, it is difficult to restore its structural integrity, so measures should be taken to prevent through cracks in construction.
Occurrence is the main factor.
In concrete construction, in order to improve the turnover rate of formwork, it is often required to dismantle the newly poured concrete as soon as possible.
Template. When the concrete temperature is higher than the air temperature, the formwork removal time should be properly considered to avoid premature concrete surface.
Early cracks. The surface tensile stress is great due to premature formwork removal after fresh pouring, resulting in "temperature shock" phenomenon.
At the early stage of concrete pouring, due to hydration heat, the surface causes considerable tensile stress, and at this time, the surface
The temperature is also higher than the air temperature. At this point, when the template is removed, the surface temperature suddenly drops, which will inevitably cause a temperature gradient, so
A tensile stress is added to the surface, which is superimposed with the thermal stress of hydration, plus the shrinkage of concrete and the tensile stress on the surface.
If it reaches a large value, there is a risk of cracks, but if it is covered on the surface in time after formwork removal.
Lightweight thermal insulation materials, such as foam sponge, are very important to prevent excessive tensile stress on the concrete surface.
The effect is remarkable.
Steel bars have little effect on the temperature stress of mass concrete, because the reinforcement ratio of mass concrete is extremely low.
It only affects ordinary reinforced concrete. Under the condition that the temperature is not too high and the stress is lower than the yield limit,
The properties of steel are stable and are not affected by stress state, time and temperature. Linear expansion coefficient of steel and mixture
The difference of linear expansion coefficient of concrete is very small, and only a small internal stress is generated between them when the temperature changes.
The elastic modulus is 7~ 15 times that of concrete. When the stress of internal concrete reaches the tensile strength and cracks appear,
The stress of steel bars will not exceed 100 ~ 200 kg/cm2 ... so steel bars should be used to prevent it in concrete.
It is difficult to produce tiny cracks, but after reinforcement, the cracks in the structure will generally become more and the spacing will be smaller.
The width and depth are small, and the crack resistance of concrete will be improved if the steel bars are thin in diameter and closely spaced.
Small and shallow cracks often appear on the surface of concrete and reinforced concrete structures, among which
Most of them belong to shrinkage cracks. Although these cracks are generally shallow, they are harmful to the strength and durability of the structure.
It still has some influence.
In order to ensure the quality of concrete engineering, prevent cracking and improve the durability of concrete, it is also necessary to use additives correctly.
This is one of the measures to reduce cracking. For example, the author summarizes his main works in practice.
Used as:
There are many capillary channels in (1) concrete. After water evaporates, capillary tension is generated in capillaries, which leads to blood coagulation.
Soil shrinkage and deformation. Increasing the pore size of capillary can reduce the surface tension of capillary, but it will reduce the strength of concrete.
This theory of surface tension was confirmed internationally as early as 1960s.
(2) The water-cement ratio is an important factor affecting the shrinkage of concrete, and the use of water reducing agent and anti-cracking agent can reduce the water consumption of concrete.
Reduce by 25%.
(3) The amount of cement is also an important factor of concrete shrinkage, and the curing of concrete mixed with water reducer and anti-cracking agent.
Under the condition of concrete strength, the dosage of cement can be reduced by 15%, and its volume can be supplemented by increasing the dosage of aggregate.
(4) Water reducing and anti-cracking agent can improve the consistency of cement slurry, reduce concrete bleeding and reduce shrinkage and deformation.
(5) Improve the bond between cement slurry and aggregate, and improve the crack resistance of concrete.
(6) When the concrete shrinks, it is restrained to produce tensile stress, and when the tensile stress is greater than the tensile strength of the concrete, it produces cracks.
There will be cracks. Water reducing agent and anti-cracking agent can effectively improve the tensile strength of concrete and greatly improve concrete.
Crack resistance.
(7) Adding admixtures can make concrete have good compactness, effectively improve the carbonation resistance of concrete and reduce.
Carbonization shrinkage.
(8) Appropriate retarding time of concrete after adding water reducing agent and anti-cracking agent can effectively prevent the rapid hydration and heat release of cement.
In fact, it avoids the increase of plastic shrinkage caused by long-term non-coagulation of cement.
(9) The concrete mixed with admixture has good workability, and the surface is easy to level off, forming a micro-membrane, reducing water evaporation, reducing
Drying shrinkage.
Many additives have the functions of retarding setting, increasing workability and improving plasticity, so more efforts should be made in engineering practice.
Compared with simply improving external conditions, it may be simpler and more economical to carry out experimental comparison and research in this area.
4 Early curing of concrete
Practice has proved that the most common cracks in concrete are surface cracks with different depths, and the main reason is temperature.
The sudden drop of temperature in cold areas caused by temperature gradient is also easy to form cracks. Therefore, the thermal insulation of concrete is very important to prevent the surface
Early surface cracks are particularly important.
From the point of view of temperature stress, thermal insulation shall meet the following requirements:
1) to prevent concrete temperature difference between inside and outside and concrete surface gradient, to prevent surface cracks.
2) In order to prevent concrete from freezing, the lowest temperature of concrete during construction should be not lower than the lowest temperature of concrete.
Stable service life and temperature.
3) Prevent the old concrete from supercooling, so as to reduce the constraint between the new and old concrete.
The main purpose of early curing of concrete is to maintain suitable temperature and humidity conditions, so as to achieve two effects.
On the one hand, it protects concrete from adverse temperature and humidity deformation and prevents harmful cold shrinkage and dry shrinkage. On the other hand,
The surface makes the cement hydrate smoothly to achieve the design strength and crack resistance.
Appropriate temperature and humidity conditions are interrelated, and thermal insulation measures for blood coagulation often have moisturizing effect.
Theoretically, the water content of fresh concrete can completely meet the requirements of cement hydration, but
Due to evaporation and other reasons, it often causes water loss, delays or hinders the hydration of cement, and the surface concrete is the most resistant.
It is easy to be directly affected by this kind of bad influence. Therefore, the first few days after concrete pouring is the key period of maintenance.
Attention should be paid in construction.
Therefore, we should handle these incidents carefully in the construction process and deal with them according to different situations.
These problems should be paid attention to in the construction, and what kind of cement and dosage should be paid attention to in the construction.
Yes, and early curing of concrete.
And template design:
Basic work before template installation:
1) Setting-out: First, measure the axes of the side columns and walls of the building, and take this axis as the starting point to lead out all the lines.
Axis. Template lofting, according to the construction drawing with chalk line pop up the center line and edge of the template, and play the wall template.
Release the template sideline and external control line to facilitate template installation and correction.
2) According to the actual elevation requirements, the horizontal elevation of the building is directly putright to the formwork installation with a level gauge.
Location.
3) The bottom of the template should be leveled in advance, and the sundries should be cleaned up to ensure the template position is correct.
After concrete molding, the bottom of the formwork leaks slurry or roots rot.
4) The foreman determines the assembly design scheme of the template in advance, and implements the technology, quality and safety of the construction team.
Full disclosure.
5) Template shall be coated with release agent. There are many matters needing attention, so I won't list them here.
I firmly believe that the practical experience gained through this period of internship will benefit me for life.
I will continue to verify it in practical work in the future, and I will continue to understand and experience the knowledge I have learned in my internship.
In the future work, I will apply the theoretical knowledge and practical experience I have learned to practical work.
Give full play to your personal value and life value, and strive to realize your ideal and bright future.
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/Zhang Wen/Upload file _ 2417/200809/2008090421551899.doc.