Abstract: Steel is an important component of construction engineering structures. The quality of steel has a direct impact on the reliability and durability of house structures and components. So, what are the common construction steel materials? What kind of steel is best for building a house? Below, let’s take a look and find out more! Classification and use of construction steel rebar The general lengths of rebar are 9m and 12m. The 9m long thread is mainly used for road construction, and the 12m long thread is mainly used for bridge construction. The specification range of threads is generally 6-50mm, and the country allows deviations. Rebar has three types: HRB335, HRB400, and HRB500 according to strength.
Round steel, as the name suggests, is a solid long steel bar with a circular cross-section. It is divided into three types: hot-rolled, forged and cold-drawn.
Panluo Panluo is rebar that is coiled together like wire rods and is a type of steel used in construction. Rebar is widely used in various building structures. The advantage of coiled screws compared to rebar is that the rebar is only 9-12, while coiled screws can be cut at will according to the needs of use.
There are only two types of wire rods for wire construction steel: Q215 and Q235. The commonly used specifications are 6.5mm in diameter, 8.0mm in diameter, and 10mm in diameter. At present, the largest wire rod in my country can reach a diameter of 30mm. In addition to being used as reinforcement for building reinforced concrete, wire rods can also be used as wire rods for wire drawing and mesh.
Steel materials for steel structures Types of steel materials for steel structures (1) H-shaped steel
H-shaped steel is a new type of economical steel for construction. H-shaped steel has an economical and reasonable cross-section shape and good mechanical properties. During rolling, the extension of each point on the cross-section is relatively uniform and the internal stress is small. Compared with ordinary I-beam steel, it has the advantages of large section modulus, light weight and metal saving, which can make buildings The structure is reduced by 30-40%; and because the inner and outer sides of the legs are parallel and the leg ends are at right angles, they can be assembled into components, which can save up to 25% of the welding and riveting workload. It is often used in large buildings (such as factories, high-rise buildings, etc.) that require large interception capacity and good cross-sectional stability, as well as bridges, ships, lifting and transportation machinery, equipment foundations, brackets, foundation piles, etc. H-shaped steel is divided into two types: hot-rolled H-shaped steel and welded H-shaped steel.
(2) I-beam
I-beam, also called steel beam, is a long steel material with an I-shaped cross-section. I-beams are divided into ordinary I-beams and light I-beams. I-beams are widely used in various building structures, bridges, vehicles, supports, machinery, etc. The flanges of ordinary I-beams and light I-beams gradually become thinner from the root to the edge and have a certain angle. The models of ordinary I-beams and light I-beams are represented by Arabic numerals in centimeters of waist height.
(3) Z-shaped steel
Z-shaped steel is a common cold-formed thin-walled steel. The thickness is generally between 1.6-3.0mm, and the cross-section height is mostly between 120-350mm. between. The processing materials are hot rolled (painted) and galvanized. Z-shaped steel is usually used in large steel structure factories. The processing length and holes are produced according to the processing requirements. Supporting products of Z-shaped steel: color steel tiles; rock wool sandwich panels; floor decking, etc.
(4) C-shaped steel
The types of C-shaped steel are: galvanized C-shaped steel, hot-dip galvanized C-shaped steel, inner beveled C-shaped steel, roof purlin C-shaped steel, automobile profile C Type formwork supports C-shaped steel, precision C-shaped steel for equipment, etc. It is processed by cold bending of hot rolled plate. It has thin wall, light weight, excellent cross-sectional performance and high strength. Compared with traditional channel steel, the same strength can save 30% of material. It is widely used in purlins and wall beams of steel structure buildings, and can also be assembled into lightweight roof trusses, brackets and other building components. In addition, it can also be used for columns, beams and arms in mechanical light manufacturing.
Amount of steel used per square meter of steel structure (1) The light steel structure has a crane beam of 35-40_/_.
(2) Light steel structure with crane and no beams 25-30_/_.
(3) The heavy steel structure has a crane beam of 80-100_/_.
(4) Heavy steel structure without crane beam 60-80_/_.
Tips for purchasing steel for steel structures The selection of steel materials for steel structures follows the following principles:
(1) Selection of quality grade
①If it is a general non- Welded steel structure, grade A steel is used for the front pit.
② If it is welded structural steel and it is subject to static load, then grade B steel should be selected; if it is subject to dynamic load, then C, D or grade steel should be selected according to the ambient temperature where the structure is located. E-grade steel structure, or special grade steel. In this way, the brittleness transition temperature of the steel can be lower than the ambient temperature of the structure.
③If there are structural parts that are subject to lamellar tearing, and the steel plate is thick, it needs to be able to resist lamellar tearing.
④ For node structures or heavy-duty welded steel structures with complex conditions and harsh working environment conditions, it is necessary to improve the standard requirements for steel quality.
(2) Selection of strength grade
① If it is ordinary steel structure steel, the strength grade is generally Q235 or Q345.
② If it is heavy-duty or super-heavy steel structural steel, its strength grade is Q345, Q390 or Q420, or higher.
③If it is a cold-formed thin-walled lightweight steel structure, you can choose grade A when not welded and grade B when welded.
Steel structure construction technology (1) Single-layer steel structure installation and construction technology
Single-layer steel structure installation projects are represented by single-layer industrial factory building structures. Single-story factory buildings generally consist of columns, crane beams, roof trusses, skylight frames, purlins, wall frames and various supports. Due to the different forms, sizes, weights, installation elevations, etc. of components, different lifting equipment and hoisting methods should be used, and sufficient preparations should be made to lay the foundation for the installation project.
①Technical preparation work
Preparation of construction organization design:
The content includes: project overview and characteristics; construction organization and deployment; construction preparation plan; construction procedures and Process design; hoisting plan; construction progress plan; construction site floor plan; supply plan for labor, mechanical equipment, materials and components; quality measures and safety measures; component transportation methods, stacking and site management; environmental protection, etc.
Before installing the steel structure, the relevant drawings and technical documents should be carefully read and reviewed. If any problems are found, the owner and the design unit should be contacted promptly to solve the hidden dangers in a timely manner.
Preparation of steel column foundation and supporting surface: Before installation, the strength of the foundation concrete must meet the design requirements.
Steel structure maintenance (1) Regular anti-corrosion treatment
Generally, the designed service life of steel structures is 50 years. During the use of steel structures, they are damaged due to overload use. The probability is very small. Most steel structure damage is caused by corrosion that reduces the mechanical and physical properties of the structure. The "Steel Structure Design Code" has certain requirements for the anti-corrosion of steel structures that have been used for more than 25 years. Therefore, it is required that the external coating protection of the steel structure should meet the usage requirements of the steel structure. Generally, the steel structure needs to be maintained for three years (dust, rust and other dirt in the steel structure should be cleaned before painting). The type and specifications of the paint should be the same as the original paint. Otherwise, the incompatibility of the two paints will cause greater harm. Users must perform planned and regular maintenance.
(2) Methods to prevent steel structures from rusting
There are many methods to prevent steel structures from rusting, and the following are usually used.
①Use alloy steel that is not easy to rust to make steel structures
②Chemical oxide layer protection method
③Use metal plating protection method
④Non-metallic coating protection method
In the later maintenance and maintenance process, non-metallic coating protection method is particularly commonly used. The surface of the component is protected with paint and plastic to prevent it from coming into contact with the surrounding corrosive media, so as to achieve the purpose of anti-corrosion. This method is effective, low-priced, has many types of coatings, a wide range of options, and strong applicability. It is not limited by the shape and size of the component. It can form a film with any shape on the surface of the component, adheres firmly, and can change with the temperature when the temperature changes. The components are telescopic and easy to use. You can also give components a beautiful color appearance.
(3) Requirements for daily maintenance of coatings
For maintenance personnel, the first step in daily maintenance of steel structures is to maintain the surface coating of components.
The quality of coating maintenance directly affects the service life of the steel structure. Therefore, in order to do daily maintenance, the surface of the steel structure must be kept clean and dry. Places where dust is likely to accumulate on the steel structure (such as steel column feet and gusset plates) should be cleaned regularly.
Regularly check the intact condition of the steel structure protective coating. If any of the following occurs, timely maintenance should be carried out:
① It is found that the area of ??the coating surface that has lost its luster reaches 90%;
②The area of ??rough, weathered, and cracked coating surface reaches 25%;
③The area of ??paint film bulges and slight corrosion of components reaches 40%;
④ Protective plates should be added to steel structure parts affected by high temperatures and temperatures to protect the coating from high temperature damage.
⑤ Try to avoid contact between components and corrosive substances, and any contact should be cleaned up in time.
(4) Rust removal on the surface of steel structures
For steel structure projects that have been used for a period of time, there are inevitably some attachments on the surface, such as rust, Dirt, dust; old paint film, etc. If these attachments are not completely removed before painting the surface of the steel structure, although they can be temporarily covered after painting, due to their isolation effect, the adhesion between the coating and the component matrix will be reduced. If the paint film is seriously reduced, the paint film will fall off prematurely, which will eventually lead to a reduction in the surface coating's ability to resist rust and will not be able to play its due protective role. Therefore, before painting the surface of the components, the attachments on the surface of the steel structure should be thoroughly cleaned.
In the construction of steel structure maintenance projects, surface cleaning work mainly includes the removal of old paint films. In the process of rust removal, due to limitations of construction conditions, the main methods generally used are:
① Manual rust removal
This method uses scrapers, shovels, and hand hammers , wire brushes and other steel tools, rely on manual shoveling, and manual grinding with emery cloth, sandpaper and grinding wheels to remove dirt, so that the surface of the components is basically free of oil, rust, and burrs. This method is a rust removal method often used in steel structure maintenance projects because it is convenient and easy to implement, requires simple equipment, has low labor costs, and is not limited by the conditions and dimensions of the construction site. Its main disadvantages are poor working conditions, low work efficiency, incomplete rust removal, and difficult to determine quality. Therefore, when using this method to remove rust, managers should emphasize quality requirements.
②Mechanical rust removal
In order to improve the quality and work efficiency of rust removal. To improve the working conditions of construction workers, pneumatic or electric small equipment has been widely used in steel structure rust removal work.
③Sandblasting and rust removal
In projects that can stop production for construction and maintenance, sandblasting and rust removal can be used. Use a sandblasting machine to remove the rust on the surface of the steel structure components to reveal the true color of the metal. A better sandblasting machine can automatically screen out the fine powder of limestone, iron sand or iron pellets, prevent dust from flying, and reduce the impact on the health of the operator. This method removes rust thoroughly. The efficiency is also high and has been widely used in developed countries. It is a better rust removal method.
④ Use pickling paste to remove rust
Special pickling paste for rust removal can be purchased on the market. The method of use is to apply the pickling paste on the surface of the components under the quilt. , its thickness is about 1~2mm. After soaking and rolling for an appropriate period of time, peel off a small piece of pickling paste to check the rust removal. If the true metal color is exposed on the surface of the component, peel off the pickling paste, rinse it with water, and completely remove the residue. of acid. Except for some special circumstances, this rust removal method is rarely used now.
(5) Cleaning of old paint molds on the surface of steel structures
① If the old paint film is strong and complete and the component surface is well adhered, soapy water or dilute alkaline water can be used to clean the old paint film. Remove all impurities on the surface, rinse and wipe dry with clean water, and then apply paint after polishing.
② If most of the old paint film is well adhered to the components and part of it needs to be removed, in addition to cleaning it according to the above method, it should also go through processes such as puttying, polishing, and touch-up paint to strive to achieve the desired result. It is smooth and consistent with the old paint film and has the same color.
(6) Regular fire protection treatment
Steel has poor temperature resistance, and many of its properties change with temperature rise and fall. When the temperature reaches between 430-540℃, the steel’s The yield point, tensile strength and elastic modulus will drop sharply and the load-bearing capacity will be lost. Necessary maintenance of steel structures must be carried out with refractory materials. Fire retardant coatings or fire retardant paint treatments have not been used previously. The fire resistance of a building depends on the fire resistance of the building components. When a fire occurs, its load-bearing capacity should last for a certain period of time, so that people can safely evacuate, rescue materials and put out the fire.
(7) Regular monitoring
The damage to components caused by rust in steel structures is not only the thinning of the effective section of the components, but also the "rust pits" produced on the surface of the components. The former reduces the bearing capacity of components, leading to a decrease in the overall bearing capacity of the steel structure, which is especially serious for thin-walled steel and light steel structures. The latter causes "stress concentration" in the steel structure. When the steel structure is under impact load or alternating load, brittle fracture may occur suddenly. There are no signs of deformation when this phenomenon occurs, and it is difficult to detect and prevent in advance. For this reason, it is important to monitor stress, deformation and cracks in steel structures and major components.
(8) Inspection and treatment of engineering deformation of steel structures
If the steel structure undergoes excessive deformation during use, it indicates that the load-bearing capacity or stability of the steel structure cannot be met. Use required. At this time, the owner should pay enough attention and quickly organize relevant industry insiders to analyze the cause of the deformation. Propose a treatment plan and implement it immediately to prevent greater damage to the steel structure project.
(9) Steel structure crack repair method
① First drill a round hole with a diameter equal to the thickness of the steel plate at both ends of the crack, and let the tip of the crack fall into the hole , the purpose of this and is to prevent cracks from continuing to expand.
② The crack between the two drilled holes must be welded. During welding, the edge of the crack can be gas-cut into different types of grooves according to the thickness of the component to determine the quality of the welding. When the thickness is less than 6mm, use the 1-shaped groove (that is, no bevel). When the thickness is greater than 6mm and less than 14mm, use the V-shaped bevel; when the thickness is greater than 14mm, use the X-shaped bevel.
③ After heating the metal around the crack to 200_C, use E43 type (steel plate material is low carbon steel or) E55 type (steel plate material is manganese steel) welding rod to weld the crack.
④ If the crack is large and has a great impact on the strength of the component, in addition to welding the crack, the metal cover plate should also be reinforced with high-strength bolts.
Classification of steel bars for reinforced concrete structures (1) Stress-bearing bars
Stress-bearing bars are also called main bars, which refer to the resistance to bending, compression, and stress in concrete structures. Tension and other basic components are configured with steel bars that are mainly used to withstand the tensile stress or compressive stress caused by the load. Their function is to ensure that the bearing capacity of the component meets the structural functional requirements.
(2) Stirrups
Stirrups refer to the steel bars used to meet the shear strength of the oblique section and connect the main stress-bearing bars and the mixed-reinforcement skeleton in the compression zone. They are divided into single-limb stirrups, open rectangular stirrups, closed rectangular stirrups, diamond stirrups, polygonal stirrups, tic-shaped stirrups and circular stirrups. The stirrups should be determined based on calculation. The minimum diameter of the stirrups is related to the beam height h. When h_800mm, it should not be less than 6mm; when hgt; 800mm, it should not be less than 8mm. The stirrups at the beam support are generally set 50mm from the beam edge (or wall edge). For independent reinforced concrete beams supported on masonry structures, no less than two stirrups should be provided within the anchorage length Las of the longitudinal stress-bearing steel bars. When the beam is integrally connected to a concrete beam or column, no stirrups are required in the support. Muscles.
(3) Erecting bars
Erecting bars refer to the longitudinal structural steel bars that penetrate the corners of the stirrups required to erect the stirrups. If the stirrup of the beam is a "two-limb stirrup" beam, it is enough to mark the full-length bars of the middle and upper longitudinal bars together, for example: 2Фd1.
However, when the stirrups of the beam are "limb stirrups", the centrally marked upper steel bars cannot all be marked as full-length bars, and the "erected bars" must also be marked. At this time, the upper longitudinal bars should be Mark the form "s1Фd1 (s2Фd2)", and the steel bars in parentheses are erecting bars.
(4) Distribution bars
Most of them appear on the floor. The distribution bars are located at 90 degrees above the stress-bearing bars and play a role in fixing the position of the stress-bearing steel bars. , and distribute the load on the plate to the stressed steel bars, and at the same time, it can also prevent cracks in the direction perpendicular to the stressed steel bars due to shrinkage and temperature changes of the concrete. In shear walls, the longitudinal and transverse reinforcements of the wall other than the wall beams and wall columns are also called distributed reinforcements.
(5) Others
Structural reinforcements configured due to component structure requirements or construction and installation needs. Such as waist bars, embedded anchor bars, rings, etc.
Principles for selecting steel bars for concrete structures. First of all, in reinforced concrete structures, steel bars are the main stress-bearing components (tension, compression, bending, shear and torsion). They mainly bear the tension and partial shear caused by bending moments, so they must be determined. The area of ??the steel bars must be sufficient, that is, it must be safe, and it must also take into account the principles of applicability and economy. Structural design is actually seeking a healthy balance between conservatism and appropriateness.
How to calculate the steel content of concrete (1) Calculate the concrete volume V of a certain structure and the amount of steel bars in the volume G. Then, the steel content of the structure is G/V (kg/m3) .
(2) Calculate the total steel consumption G and the total building area S of a certain project, then the steel content of the building is G/S (kg/m2).
Round steel bars vs rebar (1) Definition of rebar
Rebar is the common name for hot-rolled ribbed steel bars. It is a small-shaped steel material and is mainly used for reinforced concrete building components. skeleton. It requires certain mechanical strength, bending deformation performance and process welding performance during use.
(2) Definition of round steel bars
Round steel bars are finished steel bars that have been hot rolled and naturally cooled. They are made of low carbon steel and ordinary alloy steel pressed at high temperatures. , mainly used for reinforcement of reinforced concrete and prestressed concrete structures, and is one of the most commonly used steel types in civil construction projects.
(3) The difference between rebar and round steel bars
① Round steel refers to a solid long steel bar with a circular cross-section. The specifications are expressed in millimeters of diameter. For example, "50" means round steel with a diameter of 50 mm. Round steel is divided into three types: hot rolling, forging and cold drawing. The specifications of hot-rolled round steel are 5.5-250 mm. Among them: small round steel of 5.5-25 mm is mostly supplied in straight strips and bundles, and is often used as steel bars, bolts and various mechanical parts; round steel larger than 25 mm is mainly used to manufacture mechanical parts or seamless steel pipe blanks.
② Rebar is a small steel material and is mainly used for the skeleton of reinforced concrete building components. It requires certain mechanical strength, bending deformation performance and process welding performance during use. The raw material billet for the production of rebar is carbon structural steel or low alloy structural steel that has been killed and smelted. The finished steel bar is delivered in a hot-rolled, normalized or hot-rolled state.
Building steel bar construction specifications (1) Key points of steel bar entry control
①Check whether the brand of steel bars meets the contract requirements;
②Check the product certificate, Whether the factory inspection report meets the national standards;
③ Determine whether the quality of the steel bars meets the national standards through observation (the steel bars should be straight and undamaged, and there should be no cracks, oil stains, granular or flaky rust on the surface) ;
④After the steel bars enter the site for acceptance, fill in the "Material Entry Acceptance Record Form" and keep the image data;
⑤Conduct sampling re-inspection according to the product sampling plan, and issue the steel bar The inspection report can only be used after it is qualified.
(2) Key points for controlling the stacking of steel bars
①The stacking area of ??steel bars should be hardened and ensure smooth drainage;
②The steel bars should be stored according to grade, variety, diameter, The manufacturer stacks them in piles and puts up signboards, indicating the place of origin, specifications, varieties, quantity, and quality inspection status (pending inspection, qualified, unqualified);
③ To prevent steel bars from rusting, they cannot be used in time The steel bars should be covered with colored strips of cloth, and the steel bars should be placed on ridge walls or square timbers.
(3) Control points for steel bar processing
① Cutting of steel bars: Ensure the cutting length, check the quality of the cut steel bars, and cut off the parts that are split, shrunken or severely bent. Steel bars used for mechanical connections must be cut with a toothless saw, with straight ends and no bevels, horseshoes or flat ends at the top.
② Steel bar bending: When the first-grade (plain round) steel bar is tensile, the end is made into a 1800 hook, and the length of the straight section after bending is ≥ 3d; the ends of the stirrups and tension hooks are made into 1350 hooks, and they are flat after bending. The length of the straight section is ≥10d and ≥75mm (not less than 5d when there is no earthquake resistance requirement); the end of the steel bar is made into a 90° hook, and the length of the straight section after bending is ≥12d (or meets the design requirements).
③Thread processing: The length of the thread is one thread longer than 1/2 the length of the sleeve; the thread head has a full tooth shape, no missing teeth, broken teeth, and no twisted ribs. The steel bars must be fully tied, skipping or missing is strictly prohibited; steel bars with a diameter ≤ф14 must be tied and connected, and electroslag pressure welding is prohibited; formwork positioning bars must be reserved before concrete pouring, and are strictly prohibited from being welded directly to the main bars. Steel bar connection templates, including lashing, mechanical, and welded connections.
④ Binding connection: The overlap length meets the specification requirements (1.2Lae, Lae length: third-grade steel, first-grade earthquake resistance, C30: 40d, C35: 37d, C40: 33d), and the tying is no less than Three ways.
⑤ Mechanical connection: The number of exposed threads after connection shall not exceed 1.
(4) Key points for batch processing control of steel bars
①Check the steel bar processing blanking list
Check the type, spacing, size and installation of the steel bars in the blanking sheet Whether the method, etc. are consistent with the drawings and specification requirements.
②Rust removal of steel bars
The oil stains, paint stains, floating skin, rust, etc. on the surface of the steel bars must be removed.
③Steel bar straightening
Steel bar straightening must be done mechanically (cold stretching is prohibited).
④ Steel bar cutting, steel bar bending and thread processing are all controlled in accordance with sample standards.
(5) Control points for steel bar installation
① Overlap of steel bars: Set according to 50 overlap percentage at the reinforced part, and the overlap length is 1.2Lae (Lae length: third-grade steel, first-class steel) Level seismic resistance, C30: 40d, C35: 37d, C40: 33d), staggered by 500mm; in non-reinforced parts, the overlap rate can reach 100, but the overlap length is not less than 1.2Lae.
② Spacing of steel bars: The spacing of steel bars is arranged strictly in accordance with the requirements of the drawing, with a deviation of ≤10mm;
③ Number of hooks: Set in strict accordance with the requirements of the drawings and specifications, there must be no missing bindings, and the binding is firm And the bending direction needs to be staggered;
④ Positioning of steel bars: Vertical ladder bars on the wall: arranged at a distance of 1.2m, which can replace the vertical steel bars on the wall, but one size larger than the design diameter; horizontal ladders Rebar: control the spacing and position of the vertical bars, set up a horizontal ladder bar, the height from the plate is no more than 300mm, and use it as the upper positioning bar turnover; double F card, plastic spacer: control the wall steel bar section and steel bar protective layer thickness, double F Cards are arranged in a plum blossom shape with a spacing of 800mm and must be firmly tied to the steel bars. Plastic spacers are arranged in a plum blossom shape with a spacing of 400mm. The spacing between wall steel bars shall not be greater than 10mm, and the thickness deviation of the protective layer shall not exceed ±5mm.
⑤Stirrup settings: When the longitudinal stress-bearing steel bars are overlapped, a stirrup density area is set within the overlap range of the main bars. The stirrup spacing in the density area is 100mm and 5d (d is the larger number of overlapped steel bars. Small diameter); stirrups at beam-column nodes must be set as required; when shear wall steel bars replace stirrups, the column bars surrounded by the original stirrups must be surrounded, and tension hooks and curved hooks should be set at the intersection with the column longitudinal bars. The angles are all 135°.
⑥Connection setting: The connection part of the longitudinal stress-bearing reinforcement of the column must be set above 1/3 of the clear height and more than 500mm from the bottom of the beam plate. The welding connection position of adjacent longitudinal reinforcements must be staggered by a distance of ≥35d and ≥500mm. , the mechanical connection position is staggered by a distance of ≥35d.
⑦Beam steel bar binding sample: the length of the straight anchor is not less than Lae; when the anchor is bent, the horizontal section is not less than 0.4Lae, and the bending section of the bent anchor is not less than 15d. When the anchor is anchored into the frame column, the horizontal section needs to extend to The longitudinal bars on the outside of the column are on the inside; when the beam height is greater than 450mm, horizontal structural bars are set with a spacing of ≤200mm; stirrups should be configured according to the design requirements. When there are no specific requirements in the design, a stirrup density area is set at the beam-column node. If the length is 500mm or 1.5 times the beam height, whichever is greater, the distance between the first stirrup and the node is less than 50mm; when the beam steel bars are arranged in double rows, the upper and lower rows of steel bars The spacing is the larger of the steel bar diameter d and 25mm.
⑧Top plate steel bar binding sample: the spacing between the upper and lower rows of steel bars meets the design requirements; the hook length of the upper layer of steel bars is not less than the plate thickness h-30mm; the length of the lower layer of steel bars anchored into the beam is not less than 5d, and at least to The center line of the beam; when the upper and lower steel bars are anchored into the shear wall, the length of the steel bars extending into the shear wall is 0.35La or 5d, whichever is greater, and at least passes the center line of the wall. In addition, the upper steel bars are anchored downward in the shear wall for 15d; The upper steel bars are supported by horse stool iron, and erecting bars are used to control the thickness of the steel protective layer. The lower steel bars are supported by concrete pads with a spacing of 800mm-1000mm. At the lifting plate, the intersection length of the steel bars at the variable cross-section is at least La.
⑨ Stair steel bar binding sample: The spacing between the upper and lower rows of steel bars meets the design requirements; the upper longitudinal bars are anchored into the ladder beam, and the length of the extension into the ladder beam is not less than 0.35La, and it extends at least to the opposite side of the beam before it can be directed towards the back. The length of the straight section of the hook should be no less than 15d and the length of the straight section of the hook should be no less than 15d; the lower longitudinal bar should be anchored into the ladder beam, extend into the ladder beam for no less than 5d, and at least extend past the center line of the beam; the upper longitudinal bar of the ladder plate should be set as a non-through bar (set at both ends of the ladder), the length of the longitudinal reinforcement in the ladder is at least 1/4Ln (Ln is the length of the ladder).
(6) Control points of steel bar binding sample section
① Beam: The length of the upper row of additional steel bars should be configured according to the design requirements. When there are no specific requirements in the design, it is 1/ 3 beam span, the reinforcement length of the second row of steel bars is 1/4 of the beam span, and the span is the larger span of the adjacent beams.
②Slab: When there is no beam below the slab and there is masonry on the upper part, additional reinforcements need to be set directly below the masonry. The diameter of the additional reinforcements shall not be less than 14mm, and the extension length after intersection shall not be less than La.
(7) Key points for protection and control of finished steel bars
①Protection of finished steel bars after processing
Put protective caps on the wire ends that have passed the inspection to prevent If there is any corrosion or pollution, they should be sorted and stacked neatly according to specifications, ready to be transported to the construction site for use.
②Protection of finished products during the binding process
Temporary shelves should be set up when binding wall bars. It is not allowed to step on the steel bars. Deformed steel bars should be rectified before the formwork is supported.
③Protection of finished products during concrete pouring
Before pouring concrete, wrap the vertical bars of walls and columns tightly with colored strips of cloth and plastic strips, and immediately use cotton silk after pouring concrete. Or use a wire brush to clean the contaminated steel bars.
④ Finished product protection of slab steel bars
After the slab steel bars are tied, a dedicated person will be assigned to watch them, and construction workers are strictly prohibited from stepping on the steel bars. When pouring concrete, use steel springboards to set up temporary passages or lay wooden springboards on the steel mesh. During the pouring, assign a special person to supervise, control the evacuation time of the springboard, and promptly restore the deformed and displaced steel bars. The horse springs are as shown on the right.
When pouring concrete, if machines such as placing machines are used, it is strictly prohibited to place them directly on the roof steel bars. It is required to make separate brackets and place them on the brackets to avoid damage to the tied steel bars. .
Tips for maintenance of steel bars in buildings (1) Choose appropriate sites and warehouses
The sites or warehouses where steel materials are kept should be chosen in a clean and well-drained place away from harmful gases or Dust factories and mines. Weeds and all debris should be removed from the site and the steel should be kept clean. The warehouse is required to be ventilated on sunny days, closed to prevent moisture on rainy days, and a suitable storage environment must be maintained at all times.
(2) Reasonable stacking, first-in-first-out
The principle requirement of stacking is to stack according to varieties and specifications under the conditions of stable stacking and ensuring safety. Different types of materials should be stacked separately to prevent confusion and mutual corrosion.
(3) Packaging and protective layer of protective materials
Steel should be coated with various preservatives or other plating and packaging before leaving the factory. This is an important measure to prevent material corrosion , which can extend the storage period of the materials. Care must be taken to protect it from damage during transportation, loading and unloading.
(4) Keep the warehouse clean and strengthen the maintenance of materials
Be careful to prevent the materials from being exposed to rain or mixed with impurities before entering the warehouse. Materials that have been exposed to rain or soiled must be removed. Use different methods to clean according to their properties; check the materials frequently after they are put into storage to ensure that the rust layer is removed in time.