Strengthening Bridge Pier and Girder

Project Overview

Silaga Bridge is a multi-span reinforced concrete highway bridge supported on cylindrical concrete piers founded in a riverbed. The superstructure consists of cast-in-place concrete T-girders supporting a composite deck slab. The bridge crosses a river in a tropical environment with seasonal high-flow conditions and is located in a seismically active region of the Philippines.

Problem

After years of service, the bridge exhibited progressive structural deterioration under continuous traffic loading and the harsh tropical humid river environment. The structural evaluation identified two primary deficiency areas:

Pier Deficiencies:

• Long-term exposure to the humid tropical river environment has caused concrete deterioration and corrosion of the internal reinforcement within the pier columns

• Corrosion-induced section loss of transverse reinforcement (ties/hoops) has compromised the confinement capacity of the pier columns, reducing their ability to resist shear forces

• Concrete surface degradation and loss of cover in multiple pier columns indicated advanced deterioration beyond routine repair

• Original reinforcement detailing, adequate at the time of construction, no longer provides sufficient structural capacity after years of material degradation

Girder Deficiencies:

• Years of sustained traffic loading have resulted in progressive flexural deterioration of the T-girder soffits

• Long-term environmental exposure has contributed to concrete cover deterioration and accelerated reinforcement corrosion

• Existing longitudinal reinforcement has effectively lost a portion of its original cross-sectional area due to corrosion, reducing the flexural capacity of the girders below their original design capacity

• Progressive crack development at mid-span regions indicated that the degraded girders can no longer reliably carry their intended service loads

Solution

For Piers (CFRP Confinement Wrapping):

Restore lateral confinement capacity lost due to reinforcement corrosion and concrete deterioration

Enhance shear capacity of degraded pier columns to compensate for the loss of corroded transverse reinforcement

Improve ductility and energy dissipation capacity under seismic loading, which has been compromised by years of material degradation

Provide a corrosion-immune protective layer around the pier to prevent further environmental deterioration

Comply with NSCP 2015 seismic zone requirements for bridge structures

For T-Girders (CFRP Flexural Strengthening):

Restore flexural capacity of degraded T-girder soffits to meet the bridge's original design requirements

Compensate for the loss of effective reinforcement area due to years of corrosion-induced section loss

Limit further crack propagation and control service-level deflections

Ensure composite action between CFRP and existing concrete through adequate bond design per ACI 440.2R-17

The CFRP solution was selected over conventional strengthening methods (such as concrete jacketing of piers or steel plate bonding to girders) because:

• Minimal dead load addition — CFRP adds negligible weight to the existing structure, critical for bridge foundations in river environments

• Rapid installation — wet lay-up CFRP can be applied with basic scaffolding access, minimizing traffic closure duration

• Corrosion immunity — carbon fiber does not corrode in the humid tropical river environment, unlike steel jacketing solutions

• Confinement efficiency — full-wrap CFRP provides superior confinement-to-weight ratio compared to concrete or steel jacketing for cylindrical piers

• Seismic performance — the increased ductility from CFRP confinement directly addresses the seismic deficiency identified in the assessment

Materials Supplied by Horse Construction

For this project, Horse Construction supplied:

Unidirectional Carbon Fiber Fabric — for both pier confinement wrapping and girder soffit flexural strengthening

Structural Epoxy Saturant — two-part epoxy resin system for wet lay-up application and concrete bonding