Main contents of reinforcement design

The reinforcement and retrofitting design of the building includes the checking calculation of the bearing capacity and deformation of the strengthened members, the processing of the members and the drawing of the construction drawings, and the guidance of the construction process.

In the calculation of bearing capacity, special attention should be paid to the synergy between the new part and the original structural member. Generally speaking, the stress of the new part lags behind the stress of the original structure. When dealing with the structure of the reinforced structure, we should not only meet the structural requirements of the new member itself, but also consider its connection with the original structural member. Reinforcement construction is more complicated than normal new construction, the main reason is that the original structure is not fully understood, so the design of reinforcement construction guidance is particularly important.

Importance of reinforcement scheme selection

It is very important to choose the reinforcement and transformation scheme of existing buildings. The reinforcement and transformation scheme not only affects the investment of funds, but also affects the quality of reinforcement. For example, it is not advisable to add longitudinal reinforcement to a member with excessive cracks and sufficient bearing capacity, because increasing longitudinal reinforcement will not reduce existing cracks. The effective method is to apply prestressed reinforcement, or additional prestressed support, or to change the force system. For example, when the bearing capacity of structural members is enough, but the stiffness is insufficient, it is preferable to increase the section size of beam-slab structural members to improve their stiffness. For example, if the bearing capacity of the structural members is insufficient and the actual reinforcement has reached the bar, it will not play a reinforcing role if the reinforcement or steel plate is still added in the tension zone. Therefore, the reasonable reinforcement scheme should be good reinforcement effect, less impact on the use of function, reliable technology, simple construction, economical and reasonable, without affecting the appearance.

Externally bonded steel plate and steel jacketing

External bonding steel plate or steel jacketing reinforcement method is a kind of reinforcement method of wrapping steel around reinforced concrete beams and columns. Generally, angle steel is set along the length of members or a certain section at the four corners of the section, and the angle steel is connected into a whole by hoop plate or bolt hoop. This reinforcement method can greatly improve the bearing capacity of the original member on the basis of increasing the section size of few members.

1. problems that should be paid attention to in design of steel jacketing

(1) Modified epoxy steel plate bonding adhesives should be used to pour into commercial concrete structural members when they are strengthened with externally bonded or wrapped profiled steel.

(2) When calculating, it is necessary to consider the influence of section steel on members. The new section steel strength utilization coefficient alpha a (alpha a = 1.0 in aseismic design and alpha A = 0.9 in design code for strengthening commercial concrete structures) is added to the calculation formula. We should pay special attention to it when calculating.

(3) When beams are strengthened with externally bonded profiled steel, angle steel should be attached to the strengthened positions, or to the corners of the bottom of the beams, or to the top of the beams, but hoops should be installed. When there is a floor, the U-shaped hoop plate or its additional screw shall pass through the floor, welded with additional strip steel plate, or embedded in the floor after the glue anchor.

(4) When strengthening the column, the lower end of the angle steel should be anchored in the foundation; the middle should pass through the floor, and the upper end should extend to the upper floor or the bottom of the roof.

2. problems to be noted in construction of steel jacketing

(1) Attention should be paid to the surface treatment of commercial concrete and steel plates. For the bonding surfaces of old and dirty commercial concrete components, a hard brush should be used to stain the detergent, clean the surface after removing the dirt, rinse with clean water, and grind the bonding surface to remove the surface layer of coarse aggregate, and remove the dust. For the better surface of commercial concrete, the bonding surface is directly grinded to remove the surface of 1-2 mm, make it smooth, remove dust, and wipe the surface with acetone. For the surface of the steel plate should choose a newer steel plate, the surface of the steel plate using abrasive cloth or grinding wheel for grinding, so that the steel plate appears metallic luster, grinding must pay attention to the grinding of the lines must be perpendicular to the direction of force, and then wipe clean with acetone. If the surface of the structure is relatively wet, manual drying is necessary. The bigger the roughness is, the better the grinding texture should be perpendicular to the stress direction of the steel plate.

(2) Selection of adhesives should be in accordance with the design requirements, carefully select high-quality products with high visibility, strictly prohibit the use of unqualified products. Structural adhesive in the mixing process should avoid rainwater and other impurities into the container, and ensure that mixing in the same direction in the mixing, containers should not contain oil and other impurities.

(3) The selected adhesive should be prepared strictly according to the proportion in the instructions, especially the amount of curing agent. The prepared adhesive must be uniform and full and compact in the range of the adhesive surface. When the bonding area is large, the exhaust holes should be reserved on the steel plate to avoid bubble and void between the steel plate and the commercial concrete structure.

(4) The protection of finished products should be strengthened after the completion of bonding construction, and there should be no disturbance to the steel plate and its related support during the curing stage of the adhesive.

(5) The system composed of jack, backing plate and Jack pole is suitable for compression fixation during reinforcement, which can not only produce greater pressure, but also unload the load of some reinforcement members, so that the post-bonded steel plate and the original member can bear force simultaneously, and the reinforcement effect is better.

(6) When strengthening commercial concrete members, high strength cement mortar with a thickness of not less than 25 mm should be applied on the surface of the profiled steel as a protective layer, and other decorative materials with anti-corrosion and fire-proof properties can be used to protect the profiled steel.