Section 2: Condition Ratings
Anchor: #i1005218Definition of Condition Ratings
Condition ratings based on field inspections are snapshots in time and cannot be used to predict future conditions or behavior of the structure. However, condition ratings based on inspections along with written comments by a field inspector act as the major source of information on the status of a bridge. Condition ratings also help planning for necessary repairs or modifications. In addition, the condition ratings are used as flags when performing over-weight permit evaluations.
Condition ratings are one-digit numbers given by the field inspector to the various components of a bridge. They are objective and not opinions. The current AASHTO Manual for Condition Evaluation of Bridges1 emphasizes the need to have more consistent condition ratings between inspectors given the same deficiency of structural component.
Condition ratings reflect deterioration or damage and do measure design deficiency. For instance, an old bridge designed to a low load capacity but with little or no deterioration may have excellent condition ratings while a newer bridge designed to modern loads but with deterioration will have lower condition ratings.
Channel, waterway, riprap, and other channel protection components under and directly upstream and downstream of the bridge are often related in assignment of a condition rating for the channel.
Anchor: #i1005254Recording Condition Ratings
Condition ratings are entered on the Bridge Inspection Record, (Old Form 1085). Six component items are covered on the form, and each lists four to 11 elements. The Item Numbers relate to the entry of the data in the electronic Bridge Inventory Files, the detailed instructions for which are contained in the instructions of the file titled “coding_guide”:
- Deck (Item 58)
- Superstructure (Item 59)
- Substructure (Item 60)
- Channel (Item 61)
- Culverts (Item 62)
- Approaches (Item 65)
- Miscellaneous (used for information, but not entered in the Bridge Inventory File. Still important as part of the Bridge Folder).
Elements for each component have minimum values (shown to the left of the element description on Form 1085) that the rating must equal or exceed. Each element is rated based on independent consideration. For instance, poor or deficient secondary members (bracing, diaphragms, etc.) in a superstructure may cause the Superstructure (Item 59) component to have a poor rating even though the main members show no significant deterioration. The summary Component Rating must be the least of the element ratings comprising that component.
However, Deck (Item 58) component is independent of its associated element ratings such as joints, railings, wearing surface, etc.
The known presence of chlorides in the deck, superstructure, or substructure concrete or low compressive strengths from core samples should not influence condition ratings. The condition rating is determined solely on the observed, materials-related, physical condition of the component at the time of the inspection.
Form 1085 has space for fully supportive written comments for each of the above features. These comments are required for any condition rating of 7 or less. The form includes a brief summary of the description of each level of rating. More detail on the condition rating for each item number is given in the instructions for file titled “coding_guide.”
Anchor: #i1005321Assigning Condition Ratings
General considerations for assignment of the ten levels of condition ratings require that each element be evaluated separately. However, other deficiencies may affect the condition if they are directly related. For instance, instability of an approach embankment may reduce the abutment condition rating but not reduce the Superstructure condition rating.
Only permanently installed repairs are considered when assigning condition ratings. Permanent implies that the repair has returned the damaged or deteriorated element to a condition as good as or better than the remainder of the bridge. For instance, a steel beam damaged by an over-height load that reduced the load capacity of the beam is considered permanently repaired when a section is replaced or a bent section is straightened by proper techniques and no residual cracks can be found. The strength of the repaired member is the primary concern. Modifications and repairs that simply improve the appearance of a damaged member are not considered to improve the condition rating.
Components with temporary repairs, even though functioning, are not considered for condition rating. For instance, a support or brace to a partially undermined column could be susceptible to damage from another flood; therefore, the condition rating must be made on the basis that the support is not present. Temporary repairs must not be considered in determining condition ratings because they directly affect the calculations of the sufficiency ratings described in Chapter 7.
Condition ratings are still a matter of judgment, which should be made based on experience, knowledge, and consistency with other structures with the same deterioration.