Detailed design for widening a pontoon bridge in Fonte de Oleiro

SMAS of Leiria

Introduction

We highlight the rehabilitation project of the Fonte do Oleiro bridge, located over the Ribeira dos Murtórios stream, in the municipality of Leiria. This intervention focuses on preserving the heritage value of the existing structure, combining it with modern engineering solutions to ensure the safety and functionality of the road between Boavista and Fonte do Oleiro.

Context and Need

The project, promoted by SMAS Leiria, arose from the need to recover and reinforce the existing bridge, prioritizing the preservation of its original geometry. The intervention aimed to straighten the roadway to allow for the inclusion of side walkways and ensure that the structure could withstand contemporary road demands, as well as public service infrastructure. One of the central technical challenges involved integrating supports dimensioned for water and sewage pipes that cross the deck, in addition to the need to implement an effective drainage system to direct rainwater to the stream.

Summary of the Project Completed

The solution adopted prioritized the preservation of the original masonry structure, reinforcing it with a new reinforced concrete structure. The project details the following technical components:

• Structure and Deck: Implementation of a solid reinforced concrete slab, 8 meters long and 60 cm thick, supported on a beamed foundation. The foundations were constructed using cyclopean concrete blocks 5 meters deep, ensuring stability without adding critical stresses to the soil.
• Materials and Durability: Use of C30/37 (B35) class concrete and A500NR steel. Given the environmental exposure class (XC3 and XS1), the structure was designed to withstand moderately aggressive environments, with 3 cm reinforcement layers to ensure longevity against carbonation and chlorides.
• Finishes and Aesthetics: The project maintained the stone masonry side finish, while the new structural elements were executed in exposed concrete. Metal elements, such as railings, received a galvanized finish for corrosion protection.
• Structural Analysis: The modeling rigorously followed RSA and REBAP, including dynamic analyses for seismic actions and verifications of serviceability limit states (deformation and cracking). Four strategically positioned culverts were also installed at the pier entrance for road drainage.

The final solution resulted in a balance between economic viability, ease of implementation, and respect for the heritage requirements of the Leiria region.

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