Widening of Monistrol Bridge over the Llobregat River

Project Description

The widening of this historic masonry arch bridge over the Llobregat River was successfully completed in April 2017, four months ahead of schedule. The bridge was originally built in the 13th century and was partially blown up during the Spanish Civil War in 1939. The structure consists of four masonry arches of lengths: 13+17.5+27.1+38.7 m.

In 2014, the owner Diputació de Barcelona, decided to widen the bridge to enlarge the capacity and to enhance the safety for both vehicles and pedestrians. Pedelta provided design engineering and contract administration services for this project. Some of the tasks completed during this project include, among others: site inspection of the existing bridge, special inspection and preliminary reports of existing damage, identification and cause of cracks and fissures, core-sample extraction and material testing, bridge load rating analysis, rehabilitation procedure approach, methods of construction, structural report of the new widening structure, and construction and post-construction engineering services.

Design/Construction Approach

The key project challenge was how to widen the platform from 7.9 to 11.3 m while keeping the visual appearance of the bridge. The proposed solution was to implement a minimal intervention by widening the platform with a concrete slab sitting on the fill between the spandrel walls. The concrete deck consists of partial depth precast concrete slabs topped with a continuous concrete layer. Safety barriers and pedestrian railings were designed with minimal and clearly differentiated elements to visually lighten the intervention. Ultimate equilibrium analysis was used to assess the structural safety of existing arches.

The widening and rehabilitation project preserves the existing historic arches, masonry walls and exterior wall supports. Several elements of the existing masonry bridge were repaired, including the arches, the spandrel walls, the abutments and the wing walls.