Beam Strengthening

In recent years, with the development of science and technology and the application of new materials, a new type of fast and efficient strengthening method has emerged, that is, the carbon fiber strengthening method.

The method is to paste one or more layers of carbon fiber cloth on the surface of the component to reinforce or improve the bearing capacity, thereby meeting the requirements of structural safety. The strengthening principle of this method is basically the same as the original bonding steel strengthening method. Only a carbon fiber with higher strength, thinner thickness and lighter weight replaces the steel plate, which has its corresponding advantages, such as less impact on building clearance, no damage to the original structure, no increase in structural weight, etc. Moreover, carbon fiber has excellent physical and mechanical properties, high tensile strength and strong corrosion resistance. These characteristics make it very suitable for the strengthening of concrete structures.

Project Overview

A teaching building in Guanghua No. 1 Middle School is under construction. A beam located on the first floor of the stairs due to a design error, the longitudinally stressed steel strengthening configuration is insufficient, and its bearing capacity cannot meet the requirements of normal use, and structural strengthening is required to improve its flexural bearing capacity. The owner has relatively tight requirements for the construction period, and the strengthening shall not affect the appearance after decoration. From the field point of view, the effective use of the building space is insufficient, and there are certain restrictions on the clear height. Combining these factors, the method of sticking carbon fiber strengthening was chosen for convenient and rapid construction.

Strengthening plan

The strengthening material adopts HM-20 12K T700 carbon fiber fabric and supporting structural adhesive HM carbon fiber adhesive series

Based on calculation analysis and previous experimental research results, it was decided to stick two layers of carbon fiber cloth on the bottom surface of the beam, and use the U-shaped hoop for anchoring.

Strengthening construction technology

1) Surface treatment: Before pasting, chip off and level the surface of the concrete component pre-bonded with carbon fiber cloth to remove dust and oil, and then clean it with acetone.

2) Apply base glue: Configure HM-180 base glue according to the specified ratio, mix evenly, and evenly apply to the surface of the concrete.

3) Apply leveling glue: After the base rubber is dry to the touch, configure the HM-180CE leveling glue according to the specified ratio and mix it evenly, and apply to the uneven surface of the component for leveling.

4) Apply penetrating glue: After the base glue and leveling glue are cured, configure HM-180C3P penetrating glue according to the specified ratio and stir evenly, and apply to the part where carbon fiber cloth needs to be pasted.

5) Paste the carbon fiber cloth: Paste the carbon fiber cloth on the surface of the concrete beam coated with glue, and use a roller to roll in one direction and flatten it to expel air bubbles, so that the carbon fiber cloth and the beam surface are bonded tightly.

Strengthening effect

According to the calculation of the relevant formula of the "Technical Specification for Carbon Fiber Sheet Reinforced Concrete Structures", after the beam is strengthened, its flexural bearing capacity has increased by 12.8kN·m, which is about 35% higher than the original foundation, which satisfies the bearing capacity. Power requirements. After strengthening, the carbon fiber and the surface of the original component are pasted intact and integrated. The thickest part of the paste is the U-shaped hoop at the bottom of the beam (4 layers), and its thickness is less than 0,5mm, which basically does not increase the weight and section size of the structural member. Moreover, the strengthening construction period is short, the area is small, and the decoration effect is not affected after strengthening, which fully meets the requirements of the owner. In addition, the carbon fiber material has strong durability and corrosion resistance and does not require regular maintenance in the future. In short, this strengthening has achieved satisfactory results.