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Basic Knowledge of Steel Reinforcement in Construction Engineering

According to different functions, rebar can be divided into:

  1. The force of steel: reinforced concrete structure, according to the structure calculation, bear tension or pressure of steel, is the main part of the configuration of steel.
  2. Erecting steel: to meet the structural or construction requirements and set the positioning of steel. The function is to fix the main reinforcing bars (such as the main reinforcement, stirrups, etc.) in the correct position, and the main bar into a reinforced skeleton, so as to give full play to their mechanical characteristics.
  3. Distributed reinforcement: structural reinforcement perpendicular to the bearing direction of the plate or beam. Its role is to act on the plate or beam load more evenly to the reinforcement, while in the construction of the main reinforcement can be fixed by binding or spot welding, and used to resist temperature stress and concrete shrinkage stress.
  4. Structural reinforcement: because of the structural requirements of the components and the construction and installation of the need to configure the reinforcement. Erecting reinforcement and distributing reinforcement also belong to structural reinforcement.

Processing of steel bars

The processing of rebar includes rust removal, straightening, cutting and bending. The shape and size of rebar processed shall meet the design requirements.

1. Straighten
The straightening of rebar should be mechanical or cold drawing. The local twists and turns, bending or into a plate of steel should be straightened before use.
The cold drawing rate of HPB235 is less than 4%, HRB335 、HEB400 、RRB400 ≦1%
2. Rust removal
Steel rust can be generally through the following two ways:
(1) A large number of steel rust can be completed by cold drawing or straightening machine;
(2) A small amount of local steel rust can be removed by electric rust remover or manual steel wire brush, sand plate, sand blasting and pickling methods.
3. Cut off
Before cutting, the length of rebar should be matched with the same specification, overall arrangement, generally breaking long material first, then breaking short material, in order to reduce short head and loss.
Steel bar cutting machine or manual shear can be used. Steel bars larger than 40 mm in diameter should be cut by oxyacetylene flame or electric arc.
4. Bending forming
The order of steel bar bending is drawing line, bending test, bending forming.
Line drawing mainly according to the different bending angle in the steel bar marked the bending of the site, in accordance with the size of the package, the deduction of bending measurement difference.
There are manual bending and mechanical bending.
The connection methods of reinforcing steel bar include welding connection, mechanical connection and binding connection.

Principles of connection

The joint of the reinforcing steel bar should be set in the smaller stress, the same longitudinal reinforcing bar should not set two or more joints, the distance from the end of the joint to the beginning of the bending of the reinforcement should not be less than 10 times of the diameter of reinforcement.
The longitudinal direction of axial tension and small eccentric tension members (such as the tension members of trusses and arches) shall not be lashed lap joints.
When the diameter of the tension steel bar is more than 28 mm and the diameters of the compression steel bar are more than 32 mm, the lapping joint should not be used.

Commonly used connection method of steel bar

  1. Welding connection
    (1) Flash welding: the use of the welding machine to make the two sections of steel contact, through the low voltage of strong current, to be heated to a certain temperature after the steel is softened, axial compression forging, forming welding joints.
    (2) Arc welding
    Arc welding is to use arc welding machine to produce high temperature arc between the electrode and the welding pieces, so that the welding rod and the arc within the range of combustion melting, and to be solidified to form a weld or joint.
    Arc welding is widely used in steel joint and steel frame welding, fabricated structure joint welding, steel and steel plate welding and all kinds of steel structure welding.
    (3) Resistance spot welding
    The use of spot welding machine crisscross steel mesh welding, mostly used for small precast steel mesh molding.
    (4) Electroslag pressure welding
    Electroslag pressure welding is the use of electric current through the slag pool produced by the resistance of the end of the steel melting, and then apply pressure to make steel welding.
    Electroslag pressure welding of rebar is divided into manual operation and automatic control. When automatic electroslag pressure welding is adopted, the main equipment is automatic electro-slag welding machine. Generally used for the vertical reinforcement in the structural members, the application is more extensive.
    (5) Submerged arc pressure welding
    Submerged arc pressure welding is to use the arc under the flux layer to melt the adjacent parts of the two welds, and then pressure upset to make the two welded. It has the characteristics of small deformation and high tensile strength after welding.
    (6) Barometric welding of rebar
    Gas pressure welding of rebar is the use of acetylene, oxygen mixed gas combustion of high temperature flame, heating the end of the steel bar, do not wait for steel melting to make its high temperature pressure joint. Gas pressure welding equipment includes gas supply device, heater, pressurizer and crimping device.
  2. Mechanical connection
    The mechanical connection of reinforcing steel bar is a connection method that the two reinforcing bars can transfer force through the mechanical occluding function of the connecting pieces or the bearing function of steel bar end face.
    Commonly used mechanical joints: extrusion sleeve joints, taper thread sleeve joints and straight thread sleeve joint.
  3. Binding connection
    Steel bar binding requirements:
    1) The intersection of rebar should be fastened with wire.
    2) The stirrups of columns and beams should be perpendicular to the reinforcing bars except for special design requirements; Stirrup hook overlap, should be staggered along the direction of the reinforcement.
    3) when the vertical reinforcement is overlapped in the column, the angle between the hook plane of the corner reinforcement and the formwork should be 45 ° for the rectangular column and the bisector angle for the polygon column.
    4) the plate, the second beam and the main beam intersection, the steel plate in the upper, the secondary beam in the middle, the main girder under the steel; When there is a ring beam or pad beam, the main beam reinforcement should be placed on the ring beam. The shelving length at both ends of the main reinforcement shall be uniform.