As a crucial component of bridge structures, the reinforcement and maintenance of municipal bridge pier columns are vital to the safety and durability of bridges. Currently, various construction techniques are applied to pier reinforcement and maintenance, each with different adaptability to specific scenarios. Therefore, construction units should thoroughly analyze these techniques to select the most appropriate one, ensuring effective reinforcement and maintenance. This article introduces specific reinforcement and maintenance techniques to provide support for bridge pier column reinforcement. 

1. Section Enlargement Reinforcement Method 

The section enlargement reinforcement method is a commonly used technique to enhance load-bearing capacity by expanding the cross-sectional area of existing bridge pier columns. Its core involves adding supplementary steel bars and pouring new concrete around the pier, thereby altering the pier’s cross-sectional dimensions to improve its shear and bending resistance. This method is widely adopted in many municipal bridge projects, especially for scenarios where load requirements are increased or original components are damaged. 

In the application of the section enlargement method, the function of new concrete varies according to the stress demands of different pier regions. For example, in compression zones, new concrete primarily provides necessary bonding force and protects supplementary steel bars; in tension zones, besides protective effects, it significantly enhances the overall stiffness of the pier, enabling it to better resist external tensile and bending stresses. This dual functionality makes the method highly adaptable to complex stress conditions. 

The construction process of the section enlargement method includes the following steps: 

- First, setting out and positioning to ensure the location and dimensions of new components align with design requirements. 

- Next, roughening the pier surface to enhance bonding between old and new concrete, while cleaning residual debris and impurities. 

- Then, implanting steel bars outside the pier and ensuring secure connections. External skeleton steel bars are typically welded using double-sided welding, with weld lengths complying with design specifications to ensure frame stability. 

- Subsequently, installing external formwork and conducting concrete pouring. During pouring, strict control of concrete mix ratio and mixing quality is required; for piers no taller than 15 meters, one-time pouring is usually specified. To ensure structural density, layered vibration is performed, with thorough checks on vibration quality for each layer. 

The section enlargement method offers significant technical advantages, most notably reliable reinforcement effects, which greatly improve the pier’s load-bearing capacity and structural stiffness. Additionally, it has wide applicability, capable of both repairing existing defects and supporting increased bridge load capacity. However, it has limitations: complex construction processes and long durations often require traffic suspension for safety; added components increase the overall weight of the bridge structure, imposing higher demands on the bridge foundation; enlarged sections reduce under-bridge space, affecting functionality or traffic conditions; and the bonding interface between old and new concrete is a weak point in durability and corrosion resistance, requiring additional protective measures.

2. Bonded Steel Plate Reinforcement Method 

The bonded steel plate reinforcement method enhances structural load-bearing capacity by attaching steel plates to the pier surface using structural adhesives. The steel plates and pier form an integrated load-bearing system, sharing external forces while effectively improving the pier’s bending and shear resistance. This method is particularly suitable for reinforced concrete components under bending or with large eccentric loads. Its relatively simple construction and minimal impact on the original structure make it widely used in municipal bridge pier reinforcement. 

The construction process of the bonded steel plate method includes: 

- Setting out and positioning to determine the exact location and size of steel plates according to design requirements, ensuring full contact with the pier surface during construction. 

- Surface treatment: Removing laitance, loose concrete, and other attachments, then filling cracks or uneven areas with high-strength resin mortar to create a smooth base surface. 

- Steel plate treatment: Polishing to remove rust using grinders, followed by wiping with acetone or xylene-soaked degreasing cotton to thoroughly remove oil and impurities, ensuring surface cleanliness. 

- Unloading after surface treatment: Using temporary supports to unload live loads on the pier, reducing the impact of steel plate strain lag and ensuring the full effectiveness of the bonded steel plates. 

- Pre-attachment and formal bonding: Ensuring steel plate dimensions match the design profile and fit tightly to the pier surface. Applying pre-mixed structural adhesive evenly to both the steel plate and pier surface, then using specialized pressing equipment to compress the steel plate for optimal bonding. 

- Curing after bonding to allow the structural adhesive to reach its optimal performance. 

The bonded steel plate method advantages include simple construction, convenient operation, short construction periods, no damage to the original structure, and moderate improvements in overall pier stiffness. However, it has limitations: high material costs for steel plates and structural adhesives; increased overall pier weight after reinforcement; relatively poor corrosion and fatigue resistance of steel plates, requiring additional protection in humid or chemically corrosive environments; low fire resistance of steel plates, which may compromise structural safety under high temperatures; and limited effectiveness in improving ultimate load capacity due to the performance constraints of bonding materials. 

3. Bonded Carbon Fiber Sheet Reinforcement Method 

The bonded carbon fiber sheet reinforcement method uses high-performance composite materials to enhance bridge pier load-bearing capacity. Its construction principle is similar to the bonded steel plate method, but carbon fiber materials offer significant advantages such as light weight, high strength, corrosion resistance, and strong fatigue resistance. By bonding carbon fiber sheets to the pier surface, this method effectively improves concrete deformation performance and enhances the pier's seismic resistance, making it a key choice in bridge seismic reinforcement projects. 

The construction process of carbon fiber sheet reinforcement includes: 

- Setting out and positioning to define the bonding area of carbon fiber sheets. 

- Surface treatment: Cleaning laitance, loose concrete, and contaminants from the concrete surface, then repairing cracks with resin mortar to achieve a smooth finish. The treated surface is wiped with a cleaning agent to ensure tight bonding between the carbon fiber sheet and the substrate. 

- Applying specialized structural adhesive to affix the carbon fiber sheet to the pier surface, followed by uniform pressing to eliminate air bubbles or gaps during bonding. 

- Curing to allow the structural adhesive to reach full design strength, ensuring bonding effectiveness and material performance. 

Compared to traditional methods, bonded carbon fiber sheets offer high construction efficiency and simple operation, improving load-bearing capacity and ductility without significantly increasing pier weight. However, it has limitations: the flexibility of carbon fiber sheets limits their effectiveness in enhancing pier stiffness, making them unsuitable for structures with high stiffness requirements; their performance is significantly reduced when concrete strength is low or cracking is present; poor fire resistance of carbon fiber materials threatens structural safety under high temperatures; and construction quality is easily affected by on-site environmental factors such as humidity, temperature, and substrate treatment precision, demanding stricter construction management. 

4. External Prestressing Reinforcement Method 

The external prestressing reinforcement method enhances structural performance by installing prestressed components outside bridge piers. Its core principle involves placing external prestressed steel struts or tie rods around the pier and applying prestress through tensioning, thereby improving the pier’s load-bearing capacity and stiffness while partially offsetting internal forces from dead loads. This method is widely used in the reinforcement of long-span and large-scale bridges but is unsuitable for structures with significant concrete shrinkage/creep or long-term exposure to high temperatures, as durability and material performance degrade under such conditions. 

The construction process of external prestressing includes preparation and tensioning control phases: 

- In the preparation phase, prestressed steel strands meeting standards are selected according to design requirements, processed to the required length, and threaded to ensure precise installation of prestressed components. Steel strands must be embedded accurately to avoid affecting subsequent prestress application. 

- The tensioning control phase is typically conducted when concrete strength reaches over 95% of the design value and the age exceeds 7 days. Tensioning follows a graded control principle: starting from zero, tension is gradually increased to 10%, 20%, 50%, and finally 100% of the design control stress. After reaching full tension, the stress is maintained for 2 minutes to stabilize the system, and prestress is fixed using anchoring devices to ensure uniform distribution in the pier structure, meeting design expectations.  

The external prestressing method significantly enhances the pier’s load-bearing capacity and stiffness while effectively controlling the expansion of vertical bridge cracks. Moreover, its external nature avoids internal damage to the original structure and prevents long-term performance degradation due to fatigue. However, it has limitations: complex construction techniques demand experienced technical teams and strict on-site management, with significant influence from construction environments and original bridge structures; anchorage ends are critical weak points in the system, requiring special attention to design and construction quality; high material and equipment costs, combined with long construction periods, result in relatively low economic efficiency; and prestressed components lack protection in high-temperature environments, leading to rapid performance degradation and reduced service life.  

Conclusion 

Reinforcement and maintenance techniques for municipal bridge pier columns are essential for bridge maintenance. By analyzing the applicable conditions, advantages, and disadvantages of the section enlargement method, bonded steel plate method, carbon fiber sheet method, and external prestressing method, targeted construction techniques can be provided for bridge piers under different conditions, thereby enhancing their load-bearing capacity. In the future, construction units should further research construction techniques, focus on improving the adaptability of reinforcement methods to pier conditions, and maximize reinforcement quality to ensure the long-term safe operation of bridges.