The steel plate is bonded to the tensile edge or weak part of reinforced concrete structure with epoxy resin series adhesive, which forms an integral force with the original structure, thus improving its stiffness, improving the stress state of the original structure steel bar and concrete, and limiting the further development of cracks. So as to increase the reinforcement and improve the bearing capacity of the bridge, which is the purpose of the steel plate reinforcement method.
Bond strength between steel and concrete
Bond shear test of 1. 1
Two steel plates with the same size were bonded with structural adhesive on C40 concrete cubes, and after the structural adhesive was completely cured. The shear test shows that the shear failure occurs inside the concrete, not on the bonding surface, and the failure surface of the concrete is larger than the bonding surface. It can be seen that the shear strength of bond is greater than that of concrete.
1.2 bond tensile test
Two steel plates are symmetrically bonded on a C40 concrete cube for tensile test. The results show that the tensile section occurs on the concrete block. However, the bonding surface is intact, and the failure surface of concrete is greater than the bonding surface. It can be seen that the bond tensile strength is greater than that of concrete.
The above tests show that the failure of steel plate and concrete bonded with structural adhesive occurs in concrete, and the bond strength depends on the strength of concrete itself, regardless of its bond shear capacity or bond tension. Therefore, the bond shear strength and bond tensile strength between steel plate and concrete can be equal to the shear strength and axial tensile strength of concrete.
2. Bonding steel reinforcement design
(1) In order to improve the bending capacity of bridge structures, steel plates are usually pasted on the tensile edge surfaces of members, so that the steel plates and the original structures form a whole to bear the force. At this time, the local shear strength of concrete at the joint between steel plate and concrete is used for control design. Reasonable and safe design should control the shear failure of concrete at the bond before the yield deformation of steel plate occurs.
(2) When the diagonal bars in the main tensile stress area of the bridge structure are insufficient, the shear strength of the structure is increased for reinforcement. Steel plates can be pasted on the side of the structure and obliquely pasted perpendicular to the direction of shear cracks (the slope is generally 45-46) to bear the principal tensile stress.
(3) In the reinforcement design, the steel plate can be regarded as the section of reinforcement. Steel plates are converted into steel bars, and the original components bear the dead load and live load, and the added steel plates bear the live load that the original components cannot bear.
(4) When designing members, the steel plates for reinforcement can adopt different shapes according to actual needs, but the thickness of the steel plates must be greater than the calculated thickness. The steel plate used to strengthen the bending capacity should be as thin and wide as possible, and the thickness is generally 4 ~ 6 mm The thinner steel plate can have enough elasticity to adapt to the surface shape of the component. The thickness of steel plate used to improve the shear capacity should be thicker, depending on the design, and 10 ~ 15 mm is generally used.
(5) When designing the length of the steel plate, both ends of the steel plate should extend to the low stress area, so as to reduce the bond stress concentration at the clamping end of the steel plate, and prevent the components at the bond site from cracking or the bonded steel plate from being pulled off.
(6) How to ensure that the steel plate and external reinforcement members form an integral force is the key to the success of reinforcement. Therefore, in the reinforcement design, in addition to considering that the steel plate has sufficient anchoring length and the adhesive has sufficient bonding strength and durability, in order to avoid the steel plate from falling off at the free end, clamping bolts can be used to fix the end, or U-shaped hoop plates and horizontal anchoring plates can be set and bolted to the steel plate at a certain distance to ensure the bonding force between the steel plate and concrete.
3. Materials and construction requirements
(1) Binders for steel bars must have high bonding strength, good durability and certain elasticity.
(2) The steel plate used for reinforcement is generally No.3 steel or 16 manganese steel. The strength design values of steel plates, connecting bolts and welds shall be adopted according to the current national standard Code for Design of Steel Structures.
(3) The bond strength of the bonded steel reinforced connection table depends mainly on the concrete strength of the reinforced member besides the strength of the adhesive itself. Therefore, the concrete strength grade of bonded steel reinforced base should not be lower than C 15.
(4) For the compression-bonded steel reinforcement, when steel is bonded to the beam side, the width of the steel plate should not be greater than 1/3 of the beam height.
(5) The anchorage length of bonded steel plate outside the reinforcement point should meet certain structural requirements in addition to the calculated value; The tensile area is not less than 200t(t is the thickness of steel plate) and not less than 600mm；; The compression zone should not be less than 160t and 480mm；; At the same time, additional anchorage measures should be added in the anchorage zone, such as U-shaped hoop plates or bolts.
(6) In order to prevent the steel plate from rusting and delay the aging of adhesive, the surface of the steel plate should be sealed, waterproof and anticorrosive.
4. The characteristics of the method of pasting steel bars
When the tensile strength of bridge structure is insufficient and cracks appear in the tensile part, the reinforcement method of sticking steel bars is generally used to strengthen the bridge to enhance the tensile capacity of fibers outside the curved part of the bridge. Bonding steel reinforcement has the characteristics of good bonding with the structure, easy processing and molding, less steel consumption, firm and convenient anchorage and obvious reinforcement effect. Generally, epoxy mortar is used to paste steel bars, and the thickness of epoxy mortar shall be subject to not exposing steel bars. In order to facilitate construction and reinforcement, and better form a whole with the original structure, short steel bar anchors can be set on the original structure at a certain distance.
5. Key points of reinforcement construction technology
(1) A bracket is provided with a supporting beam and a forming template.
(2) Treat the concrete surface of the original structural reinforcement to ensure a better bonding effect. Broken parts should be removed from the concrete surface, aggregate should be chiseled and brushed, and floating dust should be removed with wire brush or compressed air.
(3) Install anchor rod and arrange reinforcement. Before laying the steel bar, the shape of the steel bar should be cut, cleaned with acetone after rust removal, and then placed on the template to form rows of grids, or welded in place under the bridge. Before putting in place, coat a layer of epoxy resin mucilage on the surface of the steel grid, and then fix it on the bottom of the component with anchor rods.
(4) bonding. In order to facilitate demoulding, a layer of plastic film is spread on the formwork before the reinforcement is pasted, and then epoxy mortar is evenly spread on the formwork, and the thickness is slightly greater than the design value. When pasting, knock the wooden wedge between the template and the supporting beam, jack up the template and press it on the steel bar at the bottom of the component, so that the epoxy mortar is pressed into the gap of the steel bar and bonded with the concrete of the original structure.
(5) Remove the template after the epoxy mortar is cured, and immediately check the paste quality. If defects such as holes are found, repair them with epoxy mortar in time.
(6) Protect the surface of the steel bar. Generally, the rust spots and dust on the surface of the steel bar are removed first, and then a protective layer of epoxy resin grouting is coated, and then two layers of antirust paint are coated on it for protection. You can also spray a concrete protective layer on the surface of the steel bar to prevent the steel bar from rusting.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd