WHAT IS PREVENTIVE MAINTENANCE?
Preventive maintenance can be defined as the act of keeping a structure in its as-built condition and/or protecting it from inevitable deterioration due to environment, traffic vibration and deicing chemicals. In some cases, structures are built with flaws such as cracks in concrete which require action to prevent moisture and chlorides from infiltrating the micro-structure and causing early deterioration. One fact remains, however; a structure starts to deteriorate the day its construction is completed, and it is the duty of the person in charge to slow the deterioration as much as practical using methods and materials that are considered best practices. It is the intent of this Manual to present best practices that have proven themselves to work in Ohioís environment and with the type of construction and materials most commonly found in Ohio. This is not to say that other materials and methods do not have merit, and in fact an open mind should be kept for trying new materials as they are developed.
It is always more cost-effective in the long run to perform preventive maintenance activities than to allow a known condition get progressively worse until the entire member or structure has to be replaced. This methodology is similar to keeping your carís finish waxed and/or touching up minor scratches or stone chips before the next stage of deterioration which is rust perforation. Similarly, at your home, it is always cheaper to repair a minor leak in your roof as soon as it is noticed rather than waiting until the underlying roof sheeting is rotted.
Many times on a bridge, there are numerous visual defects which may be overwhelming as to what should be fixed now and what can be deferred. Usually a bridge deteriorates from the top (deck) down. The deck is the first element of a bridge that is impacted by traffic. It also is in the worst environment due to deicing chemicals and temperature variations. The deck acts as a roof over the other elements of the bridge and as such protects the superstructure (beams or girders) and substructure (piers and abutments). A deck that remains dry on the bottom side with no (or very minor) cracks can protect the rest of the bridge indefinitely from most top-down deterioration.
Another factor in the deterioration of a bridge is caused by drainage or splash. Deck expansion joints that leak cause deterioration of end cross frames, tops of bottom flanges, freezing of movable bearings and deterioration of pier and abutment seats located directly under the leaking joints. Overpass-type bridges are affected by splash from traffic passing underneath. The elements most usually affected by splash are piers/columns within the "splash zone" (usually shoulder piers), and the lower portion of beam webs due to salt spray collecting on top of the bottom flange directly over passing traffic.
One of the most predominate causes of bridge failure nationwide is the loss of substructure stability due to scour or streambed migration. The undermining of footers/foundations is caused by water action eroding away the supporting soil. Usually this undermining can be detected visually, and corrected relatively easily, if caught in its early stages.
This Preventive Maintenance document addresses the various above-mentioned issues in the same way a bridge usually deteriorates: from the top down. The types of bridges and culverts most common to Ohio are discussed.