Concrete Beam Strengthening

Project Overview

A construction project in Suzhou has a five-story frame, an independent foundation under the column, and a strip foundation under the partial column. The size of the foundation beam is 1100mmx800mm. In the second construction section of the foundation beam rebar lap welding process, due to engineering management reasons, HRB40025 rebar was welded with E43 type welding rod, which caused brittle fracture in the lap welding test and failed the welded joint test. 

Due to the large number of foundation beams involved, the cost of reconstruction is relatively high. After multi-party consultation, it was agreed that the design institute would issue the same plan. After research and analysis, designers put forward a carbon fiber reinforcement scheme based on the current technical specifications for concrete structure reinforcement. Achieve advanced technology, safe and applicable, economical and reasonable, and guarantee quality.

Design calculation and structural reinforcement method

Design Calculation

According to the construction drawing of the original structure, the main reinforcement at the bottom of the foundation beam is 8025 and the main reinforcement on the beam surface is 16 in size. According to the joint consultation of the owner, design, supervision, and construction, the design strength of the steel bar whose welding quality does not meet the design requirements is reduced to 210MPa, and considering the favorable factor that the welding position is a position with less stress, the reinforcement is only welded to the top surface of the beam. At the joint, the reinforcement is equivalent to 8 25 steel bars with a strength of 150MPa. The same material uses carbon fiber cloth, the ultimate tensile strength is 3550MPa, the thickness t is 0.167mm/layer, and the elastic modulus is 2.35x10⁵MPa.

Structural reinforcement plan

According to the design calculation, considering the actual construction situation on site, if it is pasted in two layers, the length of the paste is 2000mm, the bottom layer is 900mm, and the surface layer is 750mm carbon fiber cloth. If it is pasted in three layers, the length of the pasting is 2700mm. The bottom layer is 600mm, the second layer is 600mm, and the surface layer is 450mm carbon fiber cloth.

Carbon fiber construction procedures and process requirements

Before the carbon fiber reinforcement construction, part of the load should be removed as much as possible to minimize the load on the structure or components during the carbon fiber paste construction. The reinforcement construction process is: concrete base treatment, primer coating, defect repair with epoxy putty, carbon fiber sheet, curing and acceptance.

Conclusion

From the example of this project, carbon fiber reinforcement has the characteristics of high strength, convenient construction, reliable reinforcement technology, and good reinforcement effect, and the project has been used for 3 years and is in good condition. Therefore, we believe that the use of carbon fiber to strengthen reinforced concrete beams with insufficient tensile strength due to longitudinal reinforcement welding is successful.