Engineering construction with steel in accordance with the engineering people’s “tactility” is divided into light round steel bar and ribbed steel bar (rebar), smooth surface of light round bar. The ribbed steel bar feels uneven, commonly known as rebar.
There’s a code on each bar. From left to right is a four-part combination of a number + a letter + one or two letters + two numbers.
- The numbers in the first section are one of the “3, 4 and 5,” representing the strength levels of the steel bars with yield strength of 300 MPa, 400 MPa and 500 MPa respectively.
- The second part of the letter is the description of the type of steel, if the position of the empty letter, for hot rolled steel bar, K heat treatment of steel; C stands for fine-grained rebar; E stands for seismic reinforcement; W stands for weldable rebar.
- One or two letters in the third section denote the steel mills that produce the steel. For example, AY is Anyang Iron & Steel, CG is Chengdu Iron and Steel and T is Tangshan Iron, X is Xuanhua Iron andsteel, and HG is Handan Steel. The “JY” in the picture above is the code of Hebei Dedicated Iron and Steel.
- The two digits in the fourth section represent the diameter of the rebar, 6 to 50 mm.
After the initial understanding of steel, we also need to master the steel should have several hard indicators, yield strength, tensile strength, elongation, cold bending elongation, weight deviation.
- Yield strength B means that the steel bar enters the stage of plastic deformation from elastic deformation, at which point the deformation of the bar is not recoverable (before reaching this point, the deformation caused by the force on the bar can be completely restored after the stress is relieved). Tensile strength D indicates the limit value that the steel bar can bear during plastic deformation. If there is a stress in excess of this limit value, the steel will break down. The values of the above two special points lead to the concepts of strong yield ratio and super yield ratio.
- Elongation at stretch. It is a characteristic parameter of steel bar ductility, the greater the elongation, the better the ductility of steel, can bear more deformation. In reinforced concrete, the better the ductility of the reinforcement, the longer the time between the cracks and the collapse, the greater the chance for people in the building to escape.
- Cold bending elongation. It is used to examine the plastic index of reinforcing steel bar, and it is also one of the indexes required for reinforcing steel processing. Cold bending performance of steel bar generally decreases with the increase of strength grade, cold bending elongation of round steel bar should not exceed 4% and that of ribbed steel bar shouldn’t exceed 1%.
- Weight deviation, whether the rebar manufacturer is cutting corners in the production process can be judged by the comparison between actual weighing and theoretical weight. The weight deviation of rebar is more intuitive and easier to get data.
There are two points that need special attention:
- First, in order to eliminate the chance of the change of the weight of a single steel bar, the total weight of three steel bars is compared.
- Second, the result of steel deviation measurement is a percentage, but also a negative deviation, that is, the weight of the deviation is set a lower limit, steel manufacturers can make steel unlimited weight, but the magnitude of light can only be less than 10%. Like a stock trader in the acceptance of investor funds at the same time, was told that the principal loss of only 10%, otherwise all forced to cut meat common; But if the profit percentage is not capped.
Engineering construction cannot do without steel, here are 8 kinds of steel:
- Force bar
Refers to the arrangement in the lower part of the beam or slab. The part of steel to bear tension and shear bending reinforcement, hanging reinforcement.
How to distinguish the force of the plate with the distribution of reinforcement?
According to the width and depth of the plate, if it is a single plate, the reinforcement parallel to the direction of short span is the stress reinforcement, and the reinforcing bars parallel to long span are the frame reinforcement. If it is a two-way slab, then the long span, short span direction of the reinforcement is all the force reinforcement.
To distinguish the diameter of rebar: the larger diameter rebar is the stress rebar; the smaller diameter rebars are the distributed rebars;
To the layout to distinguish: positive bending moment reinforcement arranged in the lower reinforcement for stress reinforcement, The vertical distribution of reinforcement above is the distributed reinforcement, the negative moment reinforcement (such as cantilever plate) contrary, the reinforcement below is the distribution reinforcement, above the reinforcement is the stress reinforcement. - Distributed reinforcement
The steel bar appears in the plate and is arranged on the upper part of the stressed steel bar and is perpendicular to the stressing steel bar. The function is to fix the position of the reinforcing steel bar and disperse the load on the plate to the stressing steel bar. At the same time, it can prevent the cracks in the direction perpendicular to the bearing steel bar because of the concrete shrinkage and temperature change. (To meet the structural requirements, for various factors that are not easy to calculate and not taken into account, the steel bar set is a structural steel bar). - Hoop
Used to meet the shear strength of the oblique section, and connect the tension main steel bar and compression zone concrete to make them work together, in addition, used to fix the location of the major steel bar so that the beam of various steel bars constitute a steel bar skeleton. Is a beam and column shear resistant configuration of ring (of course there are circular and rectangular) reinforcement, is the mouth shape, the upper and lower reinforcement fixed, while shear resistance. - Erecting tendons
It is the steel bar on the upper part of the beam. It only plays a structural role and has no real meaning. But at both ends of the girder, the upper frame bars resist the negative bending moment and cannot be missing. The erecting steel bars are arranged on both sides of the outer edge of the compression zone of the beam to fix the stirrups and form the steel bar skeleton. If the compression area is provided with longitudinal compression reinforcement, the vertical reinforcement may not be provided. The diameter of the erecting bar is related to the span of the beam. ) - Perforated bar
A steel bar that runs through the entire length of a member, such as a beam, without bending or breaking in the middle. When the steel bar is too long, it can be lapped or welded without changing the diameter.
What is the difference between erecting and penetrating tendons?
In the arrangement of rebar, the erecting rebar is 1 / 3 of this span. The span beam has left and right supporting rebar. The long rebar is the full-length arrangement, the erecting rebar can be known from the literal, such as a beam only need to cloth tensile reinforcement and shear stirrups, The compressive area of concrete strength is enough, without reinforcement, then do steel skeleton, the upper beam there is no longitudinal reinforcement, stirrups on the corner can not be fixed.
Therefore, two 14 or 16 bars are generally distributed in the upper two corners, which is the erecting bar. There is no force in calculation, but in fact there is pressure. For the positioning of the later can not be, without calculation, and the structure is to be calculated. The bearing capacity of the beam can be improved to some extent because of the compression of the erecting bar.
These are two intersecting concepts.
Through bars are steel bars that run through the whole length of a member (such as a beam) without bending or breaking in the middle. When the bars are too long, they can be lapped or welded without changing the diameter. The through-bar can be a force reinforcing bar or a frame reinforcing bar.
The erecting bar is a kind of non-stressed steel bar which is usually arranged in the compression area of the beam and has a smaller diameter. When there is a negative bending moment steel bar in the upper part of the support of the beam, the frame reinforcement can only be arranged in the middle of the span, and the two ends are overlapped or welded with the negative moment steel bars. Lapping should also meet the lap length requirements and should be tied. Frame reinforcement is also through, such as the specification in the upper beam on both sides of the frame reinforcement must be through, then frame reinforcement in support can also bear part of the negative moment. - Negative tendon
Is the negative bending moment reinforcement, bending moment is defined as the lower tension is positive, and the beam plate position of the upper reinforcement in support position according to the force is generally the upper tension, which is to bear the negative moment, so called negative bending moments. The support has negative reinforcement, is relatively speaking, generally should refer to the support part of the beam to offset the negative bending moment of steel, commonly known as Dan Dan reinforcement.
General structural members are divided into positive bending moment and negative bending moment, resistance to negative bending moments with the reinforcement called negative reinforcement, generally fingerboard, beam upper reinforcement, some upper configuration of structural reinforcement is also known as negative reinforcement. When the beam, plate of the upper reinforced Tong Long, we are also accustomed to call the upper reinforcement, beam or board gluten is negative reinforcement). - Tie-in
A steel bar reserved between two or more members that cannot be constructed simultaneously is a tie bar. - Waist tendon
Also known as the “abdominal tendons,” his name is because his position is generally located in the middle of the beam on both sides of the middle. It is the middle of the beam structure reinforcement, mainly because some beams are too high, need to add a connecting bar in the central stirrup (beam side of the longitudinal structure reinforcement is actually called waist reinforcement).
At the height of 450mm, waist tendons should be set along both sides of the beam, so the number of not less than 2. The minimum diameter of the waist tendons is 10mm, the spacing should not be more than 200mm, and the area reinforcement ratio should be not less than 0.3%, in the beam on both sides of the longitudinal structure reinforcement (waist reinforcement) between the deployment of tie reinforcement.