In the house safety appraisal, it is necessary to appraise the safety of the structural members of the whole house. First, the appearance inspection through site reconnaissance may cause problems.

At present, there are various quality problems in reinforced concrete structural members, among which cracks are one of the most common phenomena. There are various reasons for cracks, including design errors and original problems.

Material performance defects, poor construction quality, changes in environmental conditions, improper use, uneven settlement of foundation, etc. And the destruction of buildings often begins with cracks.

Therefore, how to identify cracks, analyze cracks and control cracks is one of the important contents of safety appraisal.

Keywords: concrete; Structural members; Cracks; analyse

1 Introduction

In the house safety appraisal, it is necessary to analyze the structure of the whole house.

Safety appraisal, first of all, through on-site reconnaissance for appearance inspection.

During inspection, various quality problems of reinforced concrete structural members may be found.

Among them, crack is one of the most common phenomena. Cracks are everywhere.

Everything happens for a reason, including design errors, performance defects of raw materials, and construction

Poor quality, changing environmental conditions, improper use and uneven foundation.

Even settlement, etc., and the destruction of buildings often begins with cracks. because

Therefore, how to identify cracks, analyze cracks and control cracks is safe.

One of the important contents of appraisal work. Accord to that causes and characteristic of cracks,

Judge the working condition of the structure and evaluate the safety and applicability of the structure.

Sex and durability. This identification method is simple, intuitive and fast.

And other advantages, widely used in housing safety appraisal. Its disadvantage is that

It is only a qualitative analysis method, not a quantitative analysis method.

Security of the structure. To this end, the suspicious structural members should be strength,

Stiffness and crack resistance calculation, if necessary, should also pass the load test, but

After making a safety appraisal opinion.

2 crack analysis of reinforced concrete structural members

Identifying structural cracks or non-structural cracks: reinforced concrete

There are many reasons for cracks in concrete structures, and their effects on the structures are also different.

It is also very big, just to understand the stress state of the structure and the influence of cracks on the structure

On the basis of this, the structural members are qualitative. structural cracks

Most of the structural stress reaches the limit value, resulting in insufficient bearing capacity.

Yes, it is the characteristic of the beginning of structural failure, or the lack of structural strength.

Signs are dangerous and cracks must be further divided.

Analysis. Unstructured cracks are often formed by their own stress, such as temperature.

Cracks and shrinkage cracks have little effect on the bearing capacity of the structure, which can be rooted.

According to the structural durability, impermeability, earthquake resistance and use requirements, etc.

Remedial measures.

(1) Identify the mechanical properties of structural cracks; According to mechanical properties and failure forms; Structural cracks are further divided into two types:

One is brittle failure, and the other is plastic failure. brittle fracture

It is characterized by sudden occurrence without obvious warning in advance. Once it appears,

Cracks are signs of structural failure and have a great influence on structural strength.

Cracks of this nature include cracks in compression members (including central bearing)

Compression (small eccentric compression and large eccentric compression), flexural members

Compression zone, inclined section, punching surface, post-tensioned crack.

Local compression cracks at the end of prestressed members, etc. Brittle fracture is dangerous.

, should cause enough attention, must take security measures such as reinforcement.

Comprehensive measures. Plastic failure is characterized by obvious deformation and crack in advance.

Omen, people can take timely measures to remedy the danger.

Yeah, it's a little small. Cracks in stressed members belong to this type of failure: tension

The cracks on the normal stress surface of members, flexural members and large eccentric compression members are in the normal stress state.

Surface tension zone cracks, etc. Whether this kind of crack affects the safety of the structure,

According to the location, length, depth and development of cracks

Settings. If the crack has stabilized and the maximum crack does not exceed the specified value.

Allowable value, which belongs to allowable cracks and does not need to be reinforced.

For example, an office building is a four-story two-span frame structure with a span of 5m.

7m, completed in 1998, and cracks appeared in some beams shortly after use.

Need identification. Through field investigation, it is found that the cracks in the beam all appear in

At both ends of the beam, there are about 45 inclined cracks, which are related to the quality of concrete.

Poor, the strength of some beam concrete is the lowest after coring test.

The degree grade is about C 12, and the average strength grade is C 15. Drawing design.

The strength grade of concrete is C20, which is quite different. Due to the load

Increase and concrete strength is low, after recalculation, the beam is super-reinforced.

State, belongs to the brittle fracture, should be reinforced immediately.

(2) Find out the width, length and depth of cracks: reinforced concrete.

Cracks in soil structural members can be divided into three types according to their characteristics: First, the surface is thin.

Small cracks, that is, small width and short and shallow length; The second is moderate cracking.

Seam, its width is about 0.2mm, and its length is limited to the tension zone.

Cracks have penetrated into the structure to a certain depth; The third type is penetrating crack, which is wider.

More than 0.3mm, the length extends to the compression zone, and the crack has penetrated the whole section.

A surface or partial section. Structural cracks not only represent the stress state of the structure

Conditions, it will also affect the durability of the structure. The greater the crack width, the more reinforcement.

The easier it is to rust, it means that the bonding force between steel bar and concrete has ended.

Completely destroyed, the service life is coming to an end. General indoor structure, horizontal

The risk of corrosion caused by cracks is small, and cracks will not affect the appearance.

The visual requirement is degree, but in wet environment, cracks will cause steel bars to rust.

Corrosion, crack width should be less than 0.2mm, but longitudinal joints are easy to cause reinforcement.

Corrosion, and lead to peeling off the protective layer, affecting the durability of the structure, should be

Deal with it. When the crack is long and deep, it will seriously affect the structure.

The integrity of a work is often a sign of destruction. Such as that normal section of a flexural memb.

Cracks appear at the bottom of the face beam, and the crack length develops to the compression zone and reaches

Or exceed the neutral axis, which is more dangerous if the seam length is short and local.

In tense areas, the danger is generally less. Fracture depth is also a feature.

First, surface cracks are usually unstructured cracks and penetrating cracks.

Most of them are structural cracks, which are easy to corrode steel bars and are more dangerous.

We should find out the reasons and take necessary reinforcement measures according to the dangerous situation.

(3) Determine whether cracks develop or stabilize: reinforced concrete.

According to its spreading nature, cracks in soil structural members are usually divided into three types: one is

Stable cracks, that is, the width and length of cracks remain unchanged; sequence

The other is active crack, whose width and length increase with the increase of load.

State and surrounding temperature and humidity changes; The third is development.

Cracks, the width and length of cracks increase with time. steel

Under various loads, reinforced concrete structures are generally allowed to be in tension zone.

It is allowed to work with cracks, which means that cracks are inevitable.

As long as the crack is stable, its width is not large, which conforms to the specification.

By the way, there is not much danger, and it is a safe ingredient. But cracks do not change with time.

Fracture propagation indicates that the stress of reinforcement may approach or reach the flow limit, contrary to the bearing.

The load impact is serious and dangerous, so measures should be taken in time.

Stone. Whether the crack will expand again depends on the stable structure of the crack.

Whether the environment is stable, the environment has changed, and the old cracks may still exist.

Expansion, there will be new cracks, should be combined with the specific situation.

Analysis. For example, a teaching building with a three-story frame structure has a shallow foundation because of the attached

There are cracks in some roof girders near piling, which need to be identified. get through

There is no big problem in checking the design and construction data. This teaching

The school building has been built for many years and no cracks have been found. After field investigation

The investigation found that the ground soil swelled seriously, and the cracks in the roof girder only appeared in

There are oblique fine cracks on both sides of the beam end, and the preliminary opinions should be followed.

Keep watching. After piling, after three months of observation, no cracks appeared.

Keep developing. It is considered that the foundation movement is caused by piling and soil squeezing.

It leads to cracks in the local stress redistribution of the superstructure, which affects the structure.

Not loud.

3 deformation analysis of reinforced concrete structural members

Structure in long-term use, due to the load, temperature, humidity

And foundation settlement, which will lead to structural deformation and displacement and deformation.

It not only has an impact on aesthetics and use, but also has an impact on the stress and stability of the structure.

There must be an impact. Large deformation often changes the stress bar of the structure.

Parts, increase stress eccentricity, in the component section, connecting nodes.

Generate new additional stress, thus reducing the bearing capacity of the component, resulting in

The lifting member breaks or even collapses. The measurement items of structural deformation should be pointed out.

Suspicious signs should be selected according to the determined requirements and purposes, but

The maximum deflection and displacement must be detected. Deformation measurement should be related to cracks.

Combined with measurement, excessive deformation of the structure will produce corresponding cracks.

Cracks, too large cracks will expand the deformation of the structure. Therefore, the structure

Deformation often reflects whether the structure works normally.

Important signs are an important part of safety appraisal of structural members. another

It also depends on whether the deformation is stable or developing. It is normal for the deformation to develop slowly or basically stably. If the deformation develops rapidly, the deformation speed will be fast.

A gradual or sudden increase in degree, that is, an abnormal phenomenon, should cause

Note that it usually means that the structure may be damaged and measures should be taken immediately.

Make sure the house is safe. Excessive deformation of the structure means that the stiffness of the structure is insufficient or unstable.

The sign of insufficient quality does not directly reflect the strength of the structure. shadow

The main factors of structural deformation, such as section size, span and load.

Load, bearing form and material quality also affect the strength of the structure.

Degree. Therefore, when conducting safety appraisal, cracks and structural members should also be combined.

Stability and other considerations.

4 conclusion

The safety appraisal of reinforced concrete members should also consider the structure and mixing.

Concrete carbonation and other factors. Housing safety appraisal is a technology and policy.

There are many factors to consider, such as combination, combination of part and whole.

The technical work mentioned in this paper is only a partial analysis.

This is just a little experience in personal study and peacetime work, including Xu.

Many problems need to be discussed and studied in depth, and colleagues are expected to criticize them.

Positive.