Language: English
Beam cracks repair
300g carbon fiber wrap. 0.167mm
Carbon fiber wrap is flexible and can be cut freely according to the shape of the structure. Most of them are manually operated and can be constructed in narrow spaces. The strength is high, and the strength is higher than that of the steel plate. No rust and good waterproof performance. The time limit is short.
1 Project overview
A reinforced concrete structure of an industrial factory building with a plane size of 48m *30m and a total number of four stories is found to have cracks in one beam in each of the second and third stories six months after the main structure is completed and used. The crack characteristics of the two beams are the same. A transverse crack appears at the bottom of the beam span and extends along both sides of the beam. The height of the crack extends to 150 mm, and the protective layer slightly falls off on the top of the beam. A transverse crack appears on the top of the beam support (column edge) and extends downward with a length of 180 mm. The width of the crack is more than 0.3 mm, the shape is triangular, the outer edge is wide, and the crack extends inward short and gradually fines, which runs through the cross-section of the beam. From the analysis of the crack shape of the beam, it is preliminarily judged that the crack caused by the insufficient bearing capacity of the concrete beam. In order to be safe, it is necessary to analyze and recalculate the causes of cracks in order to confirm that strengthening measures should be taken to reinforce the beams.
2 Cause analysis of cracks
In the drawings, there are no walls on the beams. However, due to the change of use function, Party A has not obtained the consent of the designer to build 180 walls more than 2 m high on the beams without authorization.
3 Reinforcement scheme
3.1 scheme 1: increasing cross section reinforcement method
By amplitude modulation, the reinforced concrete structure is reinforced at the bottom of the beam. The new concrete strength grade is C25, slightly higher than that of the original concrete (C20), as shown in figure 1. reinforcement design and construction requirements:
(1) Interface treatment of the original concrete structure interface: chisel 10-25 mm deep and rinse clean, new poured concrete surface of the original concrete with interface agent treatment.
(2) The reinforcing steel bar at the bottom of the beam is 4 25. The short reinforcing steel bar of 25 is welded to the stress reinforcing steel bar of the original member. The length of the short reinforcing steel bar is 125 mm and the middle distance of each short reinforcing steel bar is 500 mm. Through the above connection, the new and old stress reinforcing steel bars work together.
(3) U reinforcement should be installed when reinforcing. U-type stirrups should be welded on the original stirrups, with a single weld of 10 days. The diameter of U-type stirrups is the same as that of the original stirrups.
(4) the reinforcing bar is anchored by planting steel bar and the depth of the implanted column is 200mm.
3.2 scheme two: sticking carbon fiber reinforcement method
The working principle of carbon fiber reinforcement method is to use resin materials to bond carbon fibers to the surface of the structure to form composite CFRP. Through the shear resistance and anchorage ability of high-strength binder, it can work in coordination with structural members, give full play to the tensile properties of carbon fibers, and achieve the purpose of strengthening structural members.
When carbon fiber is used to strengthen the beam, the carbon fiber sheet can only bear the tensile force and can not bear the pressure. In this project, when the beam support is strengthened by bending, carbon fibers are pasted around the column on both sides of the beam. The width of each side is 250 mm, and the length of the edge of the support is 3300 mm. The beam is bypassed and anchored to the bottom of the plate. When the bottom of the beam is strengthened by bending, the bottom of the beam is pasted along the longitudinal direction of the beam, the width is 250mm, and the thickness is four layers, to the edge of the support.
The U-shaped hoop of carbon fibre sheet is set on both sides of the action point of concentrated load and at both ends of the support. The width of the hoop is 125 mm, which can increase the anchorage of carbon fibre at the bottom of the beam.
3.3 Comparison of comprehensive effects of reinforcement schemes
| Plan | Advantage | Shortcoming | Time limit for a project |
Enlargement section | The technology is simple, wide in application and reliable in reinforcement effect. | The amount of wet work done at the site is large, the increase of section will reduce the use of space, and the weight of structure will increase. | 28 days |
Carbon fiber reinforcement | It is flexible and can be cut freely according to the shape of the structure. Most of them are manually operated and can be constructed in narrow spaces. The strength is high, and the strength is higher than that of the steel plate. No rust and good waterproof performance. The time limit is short. | Carbon fiber sheet is expensive, and the cost of maintenance and repair is high. The requirements for construction technology are relatively high and generally should be constructed by professional teams. | 4 days |
Finally, choose carbon fiber for the beam reinforcement.
4. Concluding remarks
The building has been put into use after being reinforced. From the construction condition, the carbon fiber and the beam surface are well bonded. The thickest place is the U-shaped hoop (five layers) at the bottom of the beam, and the thickness of each layer is 0.167 mm. It basically does not increase the cross-section size and self-weight of the beam. It meets the requirements of the owner in terms of construction period, use space, durability of materials and construction quality, and achieves satisfactory reinforcement effect.
