The Essential Guide to Bridge Maintenance
Spectacular bridges create incredible sights to behold. Then there are simple, elegant bridges too. Apart from their beauty, bridges have great significance for the economy and culture of the areas they connect; hence their upkeep becomes extremely important. In this article, we’ll take an in-depth look at bridge maintenance.
Why bridge maintenance is important
India, being a country with vast geographical diversities, has numerous bridges to extend road and railway connectivities across rivers, valleys, seas, ravines, etc. Many of these bridges were designed for less traffic, smaller and slower vehicles, and lighter loads. While these old bridges require regular inspections for timely upgrades, natural deterioration factors affect both old and new bridges.
Bridge construction is an expensive project that is undertaken only when necessary. Once built, bridges become strategic links of the transportation system, and the events of failure or collapse of the bridges not only cripple transport and supply chains but also lead to disastrous situations with the loss of lives more often than not.
The primary objective of bridge maintenance is to ensure the safety and long-term conservation of the bridge structure. Regular and comprehensive bridge inspections help in planning and undertaking maintenance works with minimal traffic disruption. It is especially required for historic bridges that were not intended to meet modern loading standards and whose building materials have deteriorated due to weathering.
How does regular inspection help bridge maintenance?
- By determining whether the bridge is structurally safe and deciding the best course of action to ensure its safety.
- Identifying real and potential sources of trouble soon after it occurs.
- Maintaining a systematic and periodic record of the structure’s state.
- Imposing a speed restriction on the bridge if needed, until the bridge is repaired.
- Determining and reporting on whether the bridge requires extensive rehabilitation to deal with the natural environment and traffic travelling over it.
- Provide feedback to designers and construction engineers on some parts and features that need maintenance.
What are the different types of inspections carried out for bridge maintenance?
Bridge inspections may be divided into three types:
(i) Routine inspection,
(ii) in-depth inspection, and
(iii) special inspection.
Routine inspection
The routine examination is especially useful for short-span bridges. It often entails a routine evaluation of the building to look for clear visible physical indicators of distress that may want repair or maintenance care.
In-depth inspection
In-depth inspections necessitate a thorough visual examination of all superstructure and substructure components. This is especially important in the case of ageing bridges and large structures, where structural failure could have disastrous repercussions.
An in-depth inspection may be scheduled every three to five years. major inspections are conducted following major events such as earthquakes, cyclones, or the passage of extremely heavy loads.
Special Inspection
Bridges subjected to the ongoing action of natural forces, such as heavy wind, excessive rain, or ravages of a river, require periodic special inspections by experts.
To be reliable, an inspection must be thorough and done by an expert crew.
Anatomy of Bridge maintenance
Before getting deeper, here are some basics of bridge structure to help understand better. A bridge structure has the following two main functional parts:
1. Superstructure
2. Substructure
All the components of the bridge that are supported by bearings on abutments or piers form the superstructure (e.g.- bridge girders, bridge deck, bridge flooring system etc.).
Sub-structure comprises all components of the bridge that transfers loads from the bridge span to the earth (e.g – piers, foundations, bed blocks, abutments, etc.)
Applying the right bridge maintenance action depends a great deal on experience. The situation would determine the best course of action to take at a given moment for a specific bridge.
For example, implementing preventive maintenance to avoid corrosion would therefore only be necessary for a bridge where corrosion has not yet begun. Also, If the bridge’s reinforcement is corroding, a mix of techniques would be required, including fixing the damage, stopping the corrosion, and putting in place a preventive measure to stop future corrosion.
There are two broad types of bridge maintenance works:
- Preventive maintenance
- Repairs (may involve strengthening/replacement).
Preventive maintenance
The purpose of preventive maintenance is to avert spending of large amounts of money and also avoid long traffic closures, etc. due to major repairs during the lifetime of the bridge asset. Strong preventive measures have always been proven to be the most economical course of action.
Preventive maintenance of bridges is further divided into two types: Routine checkups and responsive actions
Routine checkup :- This includes tasks that need to be carried out at regular intervals, such as
- cleaning decks, seats, caps, and salt splash zones;
- cleaning bridge drainage systems;
- cleaning and lubricating expansion-bearing assemblies
- sealing concrete decks or substructure elements.
- Vegetation control around the bridge
Responsive actions: This includes resetting things, doing minor repairs, etc., reported during the routine checkup and are performed on an as-needed basis, such as:
- resealing expansion joints
- painting structural steel members
- removing debris from waterway channels
- replacing wearing surfaces
- extending or enlarging deck drains
Preventive maintenance for bridges is based on the tenet that timely maintenance and little repairs help keep the bridge in good shape and avert costly major rehabilitation or replacement..
Bridge Repair
Bridge repair involves repairing structural parts that have been damaged or deteriorated so that the structure regains the strength and serviceability that is considered acceptable.
The types of defects or damages that are generally developed in bridges and require repairing are as follows:
1. Defects in substructure and foundation – This includes masonry cracks and scours. Masonry cracks can be filled by grouting under pressure using epoxy or cement grout. Boulders can be used to fill up scoured areas. Scoured aprons can also be applied if needed.
If the substructure exhibits spalling of concrete, it can be reinforced by applying cement and sand mixture on the affected areas or by jacketing it with extra concrete thickness and 20 dowel bars spaced roughly 450 mm apart both vertically and horizontally to bond with the existing structure.
2. Defects in concrete decks – To effectively repair concrete decks, one must comprehend the reason for degradation. The most common cause is the corrosion of the reinforcement, which is impacted by the environment, the concrete’s quality, and the cover.
Repair interventions may include crack sealing, structural crack repair, and mortar repair.
The purpose of filling in cracks is to keep chemicals or water from seeping into the concrete and also to restore the original strength of the structure Cracks in R.C.C decks can be filled with cement grout for cracks larger than 0.25 mm and filled with epoxy grout under pressure for cracks less than that.
3. Unusual tremors and deflections in decks made of prestressed concrete – This problem typically implies loss of prestress in concrete and can be fixed by adding external prestressing,
4. Cracks and corrosion in steelwork in the superstructure – If the cracks appear discreetly, cover plates can be added via welding or riveting.
In the event of more cracks found in clusters throughout every span in a multi-span bridge, the design needs to be examined. If a girder exhibits localized corrosion, patch repair may be tried. When it’s convenient, the damaged member may be replaced with a new member.
If the cracks are located in isolated places, cover plates may be added by riveting or welding. If similar cracks are noted in identical locations in all the spans in a multi-span bridge, the design should be checked.
Patch repair may be attempted when corrosion is local al in a girder. The defective member may be replaced by a new member when convenient.
5. Deterioration of Curbs and Railings – Curbs and railings are damaged owing to automobile collisions, cracking and spalling, rust, and poor construction. Collision-related damage should be addressed soon following the event.
Repairs for degradation caused by cracking and corrosion should be used in the same way as they are for similar flaws in the superstructure.