The steel bar binding is barbaric, and the site personnel ignore it and directly pour concrete, which will bring irreparable serious consequences. Is it really invisible to take pictures of the cover works and hide them?

0 1, slimming steel bar

After the formed steel bars enter the site, the test pieces shall be selected for yield strength, tensile strength, elongation and weight deviation inspection, and the inspection results must conform to the provisions of relevant standards. Slimming steel bar is a steel bar whose diameter deviation does not meet the requirements. The tensile strength of these steel bars is lower than the requirements of codes and standards. Once used in engineering, the bearing capacity of concrete members will be reduced. Round steel needs to be straightened after entering the site. In the process of straightening, some straightening machines will pull out fine steel bars while straightening steel bars, which also belongs to slimming steel bars.

02, wall (column) reinforcement deviation.

Rebar deviation refers to the position deviation of rebar. As shown in the above figure, the rebar offset of a column is150 mm. According to the design requirements, there are ***8 rebar, and 5 rebar will be located outside the column! The seriousness can be imagined! There are many reasons for the deviation. Construction errors, drawing errors and deformation during concrete pouring will all cause the deviation of steel bars. Before concrete pouring, various measures should be taken to ensure and check carefully. Once the facts are formed, the consequences can be imagined. After rebar deviation occurs, different treatment schemes must be adopted according to the size and severity of the deviation. If necessary, ask the design unit to adjust the design, and it is absolutely impossible to cut it off.

03. The reinforced end face of straight thread joint is uneven.

The straight thread connection of steel bar is simple in processing, convenient in connection, and does not need electricity at the connection site, so it is widely used in construction sites. The force acting on the straight thread steel bar connection depends entirely on the mechanical bite force of the thread. If the end face is uneven, it means that the number of effective thread heads screwed into the sleeve is reduced, which reduces the bearing capacity of the steel bar connection.

04, steel anchor is not enough.

Connections between members, such as beams and columns, are established by anchorage. For example, beam reinforcement needs to meet a certain length when entering the column. According to the requirements of the code, the beam reinforcement must pass through the center line of the column with 5 times the diameter of the reinforcement. If the anchorage is too short, the reinforcement may be pulled out during the stress process of the component. Therefore, it is necessary to specify the anchorage length of all kinds of steel bars according to the requirements of standard atlas and meet the requirements.

05, steel bending with electric welding.

The bending of steel bars must adopt the method of cold bending, and cannot be bent repeatedly. We take a thin wire in our hand and bend it several times repeatedly, which can be broken without pliers. The same is true of repeated bending of steel bars. Hot bending is to heat the steel bar with oxygen flame and then bend it. Under normal circumstances, steel bars are rectified if they are tied wrong. For example, the steel bar union has thought of such a time-saving and labor-saving method. But as we all know, steel will be tempered after heating and then cooling, and the strength of steel bars will be greatly reduced.

06. Lack of stirrup

The requirements for stirrups are as follows: when the column meets the beam, there must be stirrups in the column, and when the main beam meets the secondary beam, there must be stirrups in the main beam. Lack of stirrups will greatly reduce the shear capacity and bearing capacity of this part.

07. The exposed thread of straight thread is too long.

Straight thread again. I don't need to elaborate on the reasons. The thread leakage is too long, indicating that the screw-in length is not enough. This reinforced connection is like kissing, only touching the edge. Can you do that?

08. The weld length of steel bar is not enough.

The rebar welding length specification requires that one-sided welding should meet 10 times the rebar diameter, and double-sided welding should meet 5 times the rebar diameter. When the welding length is insufficient, the strength of the steel bar connection area will decrease. In addition, the distance between the welding place and the bending place of the steel bar is more than 10 times of the diameter of the steel bar, which is the same as the reason for the hot bending of the steel bar mentioned in Article 5.

09. The thickness of concrete protective layer is not enough.

Steel bars will rust when exposed to air for a long time. Rust will reduce the diameter of steel bars and endanger the life of buildings. Therefore, the reinforcement needs to enter the concrete to a certain thickness, which is the protective layer. If the protective layer is too small or the reinforcement leaks, the service life of the building will be shortened.

10, concrete pouring is unattended.

When pouring concrete, the steel bar needs special care to avoid being trampled and deformed when pouring concrete. Some steel bars are well bound, and the position and size meet the requirements. When pouring concrete, it changed, and the final result was not good. As shown in the picture above, the steel bars on the original floor are divided into upper and lower layers, all of which are crowded together and inseparable. How to give them appropriate pressure?

Second, the template project

0 1, the stud spacing decreases and then decreases.

According to the specification, a special construction scheme should be prepared for formwork support erection, and the structural design and calculation should be carried out, and the approval should be carried out according to the regulations; However, it is not uncommon that the construction is not carried out as planned when it is erected on site. Poles spacing requirements of 900mm, 900mm poling spacing requirements 1000 mm, a strict, point down to the second floor. After the third floor, all the managers were on the road and the inspection was relaxed. Later, the vertical bar spacing gradually decreased. In some projects, even as high as 100.

The most serious consequence: collapse.

02, horizontal bar can be saved.

According to the specification requirements, the horizontal bar is required to be pulled vertically and horizontally. Some people are too troublesome. If they lose one or two, there will be no problem in the back. There are not a few construction sites where horizontal poles are reduced. One direction has taken root, and what about the other? Some pull one every other, some pull one every two, and even some pull one every three to four. This will cut corners and reduce the overall stiffness of the formwork support.

The most serious consequence: collapse.

03, backfill soil directly removed from the template support, without tamping.

Backfill above the formwork support, backfilling earthwork is no different from the foundation of formwork support, and some engineering earthwork backfilling is to rob the construction period. Directly loose filling, no tamping, large tamping on the surface. Actually, it's all empty underneath. After the formwork support is supported, the foundation soil will sink when it rains. How can it stand the weight of concrete?

The most serious consequence: collapse.

04. The formwork support lacks a sweeping rod.

According to the specification, sweeping poles are set along the vertical and horizontal directions at a height of 200mm from the bottom of the column to the ground. Some construction sites just don't set up or set up less.

The most serious consequence: collapse.

05, tall template construction by experience.

Document Jian Zhi [2009] No.254, issued by the Ministry of Housing and Urban-Rural Development, stipulates that the construction scheme of tall formwork support system must be prepared, and it needs expert argumentation if it exceeds a certain scale. The system fundamentally ensures the construction safety of tall formwork. However, there are also experienced people.

The most serious consequence: collapse.

06. The square section is too small and the spacing is too large.

In recent years, the unit price of wood cubic meters has been on the rise. In order to save money and compete at low prices, dealers reduce the cross section of the square wood once and then. Now the smallest square cross section is 35mm×65mm. Can it be redeemed again?

The most serious consequence: collapse.

07, steel pipe wall thickness is getting smaller and smaller.

The earliest steel pipe wall thickness was 3.6mm；; Then dropped to 3.0mm；; Later, 2.8mm appeared, and the common specification in previous years was 2.75mm；; At present, the thinnest steel pipe is 2.6mm, and it is said that there is still 2.4mm, so it is impossible to measure the steel pipe sent from the rental station when recycling. If the steel pipes of several rental stations imported from a construction site are mixed with different wall thicknesses, some rental stations themselves can't tell what their current steel pipe wall thickness is.

The most serious consequence: collapse.

08, direct demolition of post-cast strip.

Before the pouring of post-cast strip is completed, the beam is disconnected, and the formwork support below plays an important supporting role. Many workers don't know that the support system of post-cast strip needs to be set up separately, and it must be kept separately when it is demolished. Some people know that they are afraid of trouble and directly build it into a whole. Wait till they tear it down, or tear it down and build it again. Don't take the rest off at all.

The most serious consequence: structural damage.

09. After the scaffold is dismantled, dismantle the template.

The reason is that after dismantling the formwork support, the steel pipe can be picked out first, and then people can stand below or take movable scaffolding to dismantle the formwork, so that the formwork and the square wood will not be pressed under the steel pipe, so that the material loss will be smaller. However, whose head is made of iron? What if a piece of the template falls off?

The most serious consequence: fatal injury.

10, the waste of hand saw processing is amazing and the quality is poor.

Since the portable saw appeared, the wooden shed has lost its function. As long as you allow the hand saw to go upstairs, the cross-sectional size and flat-fell seam of that template can't be guaranteed. The waste of square timber formwork is amazing. A 30-story residential building consumes 300 million cubic meters of wood? Cutting down 56 mu of forest can make150,000 pairs of chopsticks.

The most serious consequences: serious consumption of wood resources and environmental deterioration.

Third, the concrete engineering

According to article 6.6. 14 of GB 50164-201Concrete Quality Control Standard, the duration of concrete mixture from mixing by mixer to pouring shall not exceed the provisions in Table 6.6. 14. That is, when the temperature is ≤25℃, the duration should not exceed150min; ; When the temperature is higher than 25℃, the duration should not exceed 120 minutes.

However, it often takes more than 180min or even more than 300min when pouring constructional columns or secondary structures at the construction site. Especially in summer, it is not easy to pour concrete for more than 3 hours. You'd better dilute it with additives before pouring. In some construction sites, continuous pouring after direct dilution with water will inevitably lead to insufficient concrete strength.

In article 6.6.9 of GB 50164-201Concrete Quality Control Standard, it is clearly stipulated that "when pouring a structure with a large vertical size, it should be poured in layers, and the pouring thickness of each layer should be controlled at 300 ~ 350mm；; And more vibrating rods can be arranged, and they should be vibrated while pouring concrete, and they should be continuously formed. "

Ultra-high pouring is easy to cause die expansion. If you can't vibrate with the pouring, it is easy to form cavities, exposed tendons and honeycomb pits due to false vibration. When the wall within 3m is poured, it can be divided into two layers. If the workability of pumped concrete is good and it is easy to vibrate and compact, the layering height can be increased to 1000 ~ 1500mm. When the vibrating speed can't keep up with the pouring speed, stop pouring immediately, and then start pouring after the vibrating personnel catch up.

Article 7.5.2 of GB/T 14902-20 12 "Ready-mixed Concrete" clearly stipulates: "The mixer truck should drain the accumulated water in the mixing tank before loading, and it is forbidden to add water to the concrete in the mixing tank after loading". Some construction workers ignored this regulation, in order to facilitate pumping and reduce leveling resistance, they used water pipes to add water to the pump barrel or water tank privately; What's more, it seems that the material is not thin. Drain the hose first, and pour it while adding water.

Adding water to concrete mixture will increase the water-binder ratio of concrete. The greater the water-binder ratio, the lower the final strength of concrete. Too much water, concrete strength can not meet the design requirements, and the acceptance is unqualified. In the end, it will be remedied by strengthening, or even reinvented. This has caused great losses to construction enterprises. Therefore, the national standard clearly stipulates that it is forbidden to add water to concrete mixture. When the slump of concrete mixture is small, the tanker driver can be required to add appropriate additives to adjust the slump according to the technical disclosure of his company, so as to facilitate pumping construction.

It is common for workers on site to sprinkle raw water for the convenience of collecting noodles, and technicians on site will not stop it, which will seriously affect the quality of concrete. Spraying raw water on the concrete surface increases the water-cement ratio of the concrete surface, increases the gap of hardened slurry, makes the concrete surface loose, reduces the strength and carbonation resistance of the concrete surface, and makes the concrete surface ash, sand return and crack.

In the process of construction, often due to ideological and technical defects, the construction unit produces various defects on concrete components, such as honeycomb, pits, cracks, exposed tendons, holes and so on. But without reinforcement, it will cause lifelong defects in concrete engineering and affect the service life of buildings, and affect the true judgment of concrete performance when detecting concrete entities.

Due to the low strength of concrete and the poor working ability of concrete and steel bars, it is easy to cause steel bars to slide in concrete under the vibration of component weight and construction load, thus reducing the holding power of steel bars; Early formwork removal leads to premature water loss on the concrete surface, and accelerated carbonation on the concrete surface reduces the durability of concrete.

When the strength of concrete is lower than that of formwork removal, it is easy to crack in the tension zone, or even destroy the compression zone, resulting in safety accidents; Early concrete formwork removal will increase the creep of concrete and lead to structural deformation; Early formwork removal, due to the low strength of concrete, is prone to collapse or local collapse in the process of formwork removal, which weakens the section of members and affects the bearing capacity and appearance quality.

In some construction sites, in order to catch up with the construction period, the concrete poured the night before was demolished the next morning. It is ok when the temperature is normal, but in case of cooling weather, it will be too early to dismantle the formwork the next morning, because the concrete has not yet been finally set. Early formwork removal will lead to formwork sticking or horizontal cracks along stirrups (horizontal bars). This is caused by the self-weight sinking of concrete. Therefore, before dismantling the formwork, it is necessary to check whether the concrete is finally set, and it is advisable to scrape the top surface of the concrete with nails without loose mortar, otherwise the formwork cannot be dismantled.

When pouring concrete, if the reinforced concrete column and wall poured from the top are too high, the coarse aggregate in the concrete will be separated from the concrete and rolled to the outside or bottom of the concrete pile, or in the pouring process, the coarse aggregate will fall first and the mortar will fall behind, resulting in the segregation of the concrete, which will make the coarse aggregate squeeze into the corners of the floor slab and easily form "honeycomb", "pockmarked surface", "rotten root" or sand and gravel. Moreover, if the height of the free fall is too high, the concrete will have a great impact force, which will bend the steel bars and dislocate the stirrups of the vertical members, thus affecting the mechanical properties of the members.

Water is a necessary condition for cement hydration reaction, so environmental humidity has a great influence on the normal development of concrete strength. If the humidity is not enough, concrete will lose water and dry, which will affect the normal hydration of cement and even stop hydration. The earlier the drying time, the more serious the drying shrinkage and cracking, the looser the structure, the greater the strength loss, the greater the carbonation of the concrete surface and the lower the durability.

Improper pouring sequence and distribution will cause uneven sand and gravel in concrete members, affect the strength of concrete members, produce defects such as honeycomb, pits and holes, cause hidden dangers to engineering quality, and may also constitute a major quality accident.

Article 7.4.2 of JGJ 55-201+0 Code for Design of Mix Proportion of Ordinary Concrete stipulates: "The dosage of cementing material for pumping concrete should not be less than 300㎏/m?" . However, in order to reduce the production cost, some mixing stations design the cementing material in the mix proportion of low-grade concrete as 280㎏/m? What's more, the cementing material of C 15 fine stone concrete mixture ratio is also designed to be 280㎏/m? Results A truck of C 15 fine stone concrete blocked the pump many times and finally had to be dumped, and the cementing material was adjusted to 340? ㎏/m？ Only in this way can the pumping construction be carried out normally.

Fourth, masonry engineering

0 1

Cement plant for more than 3 months.

According to the specification, cement that has been shipped for more than 3 months must be rechecked, because the strength of wet and caked cement will be reduced.

02

Mortar mixing is not measured.

One of the biggest factors affecting masonry strength is mortar strength. How much cement and sand should be used for mortar mixing should be carried out according to the mixture ratio. If the mixture ratio is not measured, it will be inaccurate and the mortar strength cannot be guaranteed.

03

Anchor lacing bar is unqualified

The end of the anchor brace must have a 90-degree hook, and it must be made of first-class steel, and the length must meet the requirements. In the process of pouring, leakage, insufficient length, substitution of three-grade steel and so on often occur. Pulling anchor is an important measure to prevent cracks in infilled wall, and irregular practices will inevitably increase cracks in masonry.

04

Artificial vibration of secondary structure concrete

The vibrating of secondary structure concrete such as ring beam and constructional column is completed by machinery (vibrator). Artificial vibrating concrete is not dense enough, and concrete defects increase, which often affects the integrity and strength of concrete. The wall must be built first, then the constructional column is poured, and the horse teeth must be retired first. Irregular retention will reduce the biting force between the wall and the constructional column and increase the cracks in the masonry.

05

The rest length of lintel is not enough.

According to the specification, the static length of the lintel should be greater than 240 mm If the static length is not enough, the local compression of the masonry under the lintel is insufficient or the lintel falls, endangering safety.

06

One-step jacking of inclined brick

The specification stipulates that the inclined brick at the top of the infilled wall masonry should wait 14 days after the completion of the masonry below. In some construction sites, in order to save trouble, the horizontal cracks in masonry will be greatly increased if the masonry is built to the top at one time.

07

No mounting holes are reserved.

In the installation project, reserved holes are fire box, distribution box, air conditioning tuyere, etc. Should be set in advance, and precast lintels should be added if the width exceeds 300. Later, opening a hole and hitting the wall will bring cracks to the masonry and produce a lot of construction waste.

08

Masonry with different masonry angles

The corner and junction of brick masonry should be built at the same time. In areas where the seismic fortification intensity is 8 degrees or above, the temporary breaks that cannot be laid at the same time should be laid into oblique rubs, in which the horizontal projection length of the oblique rubs of ordinary brick masonry should not be less than 2/3 of the height (h), and the oblique rubs ratio of porous brick masonry should not be less than 1/2. The height of diagonal rubbing shall not exceed the height of scaffold. The quality of masonry and jointing at the corner and junction of brick masonry is one of the keys to ensure the overall performance and seismic performance of brick masonry structure. The lessons of Tangshan and Wenchuan earthquakes have fully proved this point.

09

Before leaving the factory, the blocks will be pasted on the wall.

Autoclaved aerated concrete blocks can not be put on the wall until more than 28 days after leaving the factory. Block under age has low strength and is easy to be damaged. After laying, they continue to deform and increase cracks.

10

Replace the water stop in the bathroom with cement bricks.

The toilet should be made of concrete water stop platform with a height of 150mm, instead of cement bricks, so as to avoid the resurgence of the wall caused by leakage of the bathroom and water absorption of the masonry.