Section 3: AASHTO Inspection ManualsAnchor: #i1003284
1970 and 1974 AASHTO Manuals
The first AASHTO Manual issued in 19705 (the small grey book) and subsequently modified slightly in 19746 (the small green book) described the minimum information considered necessary for inspection, records, rating, and check of bridge load capacities. Primary subjects with their major items were:
- Frequency of two years
- Waterway, debris, and channel profile observed
- Investigate evidence of scour and undercutting
- Deterioration of main structural members, deck, superstructure, and bents
- Fatigue details of steel girders to be considered (little guidance given)
- Abnormal cracking in concrete members
- Bridge railings to have only visual inspection, no strength requirements
- Trusses inspected for damage, bracing, condition of paint
- Timber structures to be inspected for decay, overloading
- Written Structural Inventory and Appraisal (SI&A) sheet (little similarity to current SI&A sheet)
- Condition Ratings given as 9 to 0 as now, but little guidance on selection of ratings
- At least two photos to be taken
- All normal identifications, widths, clearances, etc. to be recorded
- Painting record to be kept
- Stress calculations to be kept
- All spans should be listed by length (this is not currently done except indirectly in the bridge plans)
- Operating and Inventory Ratings to be H- or HS-equivalents
- Calculations in accordance with current AASHTO bridge specifications
- Higher safety factor allowed for heavily traveled routes
- Dimensions from as-built or field measurements if necessary
- Pictorial posting signs recommended (not used by Texas at that time)
Load Capacity of Bridges
- Consider two lanes loaded with rating trucks if bridge is 18-ft clear or wider
- Allow fewer lanes if warranted by judgment of Engineer
- “Train” of lighter-weight trucks to be considered, spaced at 30-ft headway when at H-12 or less
- Load distribution and allowable stresses as given by AASHTO Bridge Specifications
- Sample calculations given in Appendix B of AASHTO Manual
- Unique nomographs for live load rating in Appendix B
- Load Factor Rating introduced as an acceptable method
1978 AASHTO Manual
The third AASHTO Manual was issued in 19787 (the small yellow book), and it included all the same information and requirements as the first two AASHTO Manuals, with some re-ordering of contents. In addition, the following major additions and modifications were made as compared to the 1974 AASHTO Manual:
- Recommendations modified for repair, maintenance, and posting
- Definition of Inventory Rating changed to omit the equivalency to the original design load
- Typical load and speed posting signs omitted and reference made to the Manual for Uniform Traffic Control Devices8 (MUTCD)
Load Capacity of Bridges
- The “Secant Formula” was added for steel column strength calculations (this formula is believed to be out-of-date and should not be used by a rater)
- Allowable Inventory Rating stresses listed for A36, A572, A441, and other steel types
- Increased allowable bearing stresses on rivets and bolts
1983 AASHTO Manual
The fourth AASHTO Manual was issued in 1983 in loose-leaf form9 (the large yellow book) and contained essentially the same requirements as the first three AASHTO Manuals. The Records and Ratings requirements were essentially unchanged from the 1978 AASHTO Manual. The following list summarizes the major additions and modifications since the 1978 AASHTO Manual:
Load Capacity of Bridges
- Allowable Inventory Rating stresses became more detailed
- Allowable bearing stresses on rivets and bolts for Operating Ratings was again increased to be consistent with the increases made in 1974 for Inventory Rating
- Allowable Inventory stresses for A7 bolts and rivets clarified
- Allowable Operating Rating stresses for high-strength bolts detailed for all conditions
- Comparative chart for fastener bearing stresses added
- Maximum Operating Rating concrete stresses in bending clarified
AASHTO Interim Specifications
The AASHTO Interim Specifications10 of 1984 through 1990 included some re-ordering and editing of various sections of the 1983 AASHTO Manual. In addition, there were significant changes and additions were made in certain sections. These changes are summarized as follows:
- In 1984 the inspection frequency could be increased to more than two years for certain types of bridges if properly documented. An example in Texas is reinforced concrete box culverts.
- In 1984 the two lanes of live loading for roadways between 18 to 20 feet was clarified. For roadways over 20 feet in width, the spacing between trucks became 4.0 feet, which is the same as the AASHTO bridge specifications.11 This corrected a long time disparity between the bridge specifications and the AASHTO Manual.
- In 1986 there was a major change in the qualification of inspection personnel required that the individual in charge must be a Registered Professional Engineer. Prior to this time, the individual in charge could be qualified by experience.
- In 1986 scour was specifically identified as an item requiring more intense inspection.
- In 1986 nonredundant structures were identified as requiring the initiation of special inspection procedures.
- In 1986 concrete bridges with no plans were allowed to be rated by simple physical inspection and evaluation by a qualified engineer.
- In 1987 underwater inspection was identified as an important inspection requirement. This was a direct result of the failure of the Schoharie Creek Bridge in New York in April 1987, which also resulted in a 1988 FHWA technical advisory.12
- In 1987 hangers and pins were identified as features to be properly inspected.
- In 1987 new sections entitled Evaluation and Limiting Vehicle Weights were added. Higher safety factors could be considered for structures with large volumes of traffic. In addition, the agency responsible for maintenance of a structure could use stress levels higher than Inventory Ratings to post a bridge if inspection levels exceeded the minimum.
- In 1987 speed postings were allowed in certain cases to reduce impact loads and thus reduce the need for lowering weight limits. This procedure is not believed to have been applied to any structures in Texas, either on- or off-system.
- In 1988 the requirement that all inspections be done by a Registered Professional Engineer was re-interpreted to allow an inspection team leader to be qualified by experience. However, the person in responsible charge must be an Engineer.
- In 1988 emphasis was placed on underwater inspection of pilings, particularly those exposed to salt water or salt spray, and any foundation member in contact with brackish or chemically contaminated waters.
- In 1989 the minimum weight limit for posting was clarified to be three tons at the Operating Rating stress level. Texas’ minimum capacity for bridges to remain open is HS-3 instead of 3 tons.
- In 1989 a new Appendix B was added that described the
five basic Inspection Types:
- The categories and description of each Inspection Type were relatively broad. However, clarifications were made that the first Inventory Inspection was to determine all the Structure Inventory and Appraisal data required by the FHWA and that Routine Inspections were defined as those done at regularly scheduled intervals.
- In 1990 only minor editorial changes were made.
1994 Rewrite of AASHTO Manual
The AASHTO Manual was in the process of a complete rewrite during the period of about 1989 to 1992 under a research contract through the National Cooperative Highway Research Program (NCHRP). Since the rewrite was anticipated to be first presented to the AASHTO Bridge Committee in about 1991, no major changes were made to the 1983 loose-leaf version of the AASHTO Manual in 1991 or 1992. However, the rewrite was not completed for review until 1993. In 1994, AASHTO adopted the revised version (loose-leaf, dark blue) of the AASHTO Manual, which is now called the AASHTO Manual for Condition Evaluation of Bridges13.
Major additions and changes since the 1983 AASHTO Manual are:
- Total bridge width is to be recorded. Prior to this time, the total was implied by the summation of the deck width, sidewalk or curb width, and railing type.
- Critical features such as special details, scour susceptibility, fatigue-prone details, etc. are now to be recorded.
- Flood records are to be kept if known. This information is not entered in the Coding Guide but should be kept in the Bridge Folder described in Chapter 8.
- Qualifications of the Inspection Program Manager are changed again to allow the person to be qualified by experience. The qualifications are listed the same as first introduced in 1983. The changes of 1986 and 1988, which did not allow qualification by experience, were therefore rescinded. This conforms to State and Federal Regulations, which allow qualification by experience.
- Qualifications of the Inspection Program Manager are modified to allow the person to be qualified by experience. This conforms to state and federal regulations, which are summarized in Appendix A: State and Federal Regulations and allow qualification by experience.
- Qualifications for Inspection Team Leader allow training to be based on a National Institute for Certification in Engineering Technologies (NICET) Level III or IV certification in Bridge Safety Inspection.
- The five basic Inspection Types are now called:
- The categories and description of each Inspection Type are essentially the same as described for the 1983 AASHTO Manual as modified by the 1989 Interim.
- Detailed sections are added on methods of inspection including equipment, safety, advance planning, and preparation for inspections.
- Sections are added to describe inspection procedures, including organized and systematic field notes and procedures.
- Emphasis is placed on obtaining uniformity in condition ratings by different field inspection teams by developing an objective system of evaluation and training.
- New emphasis is placed on inspection of substructures including susceptibility to earthquake damage. There are no areas in Texas with bridges considered to be susceptible to earthquake forces except for a small portion of the El Paso district.
- More emphasis is placed on various types of substructure inspection.
- Detailed inspection recommendations are given for each of the various types of bridge superstructure including new superstructure types such as cable-stayed and prestressed concrete segmental bridges and new component types such as prestressed deck panels.
- Fracture-critical members are to be properly identified.
- More detail is required on description of timber components.
- Greater detail is added on inspection of trusses.
- Extensive new material is added on field testing of materials for concrete, steel, and timber including reference to the various newer methods such as acoustic emission for steel and pull-off and thermographic tests for concrete.
- Sampling techniques are described in detail.
- Interpretation and evaluation of field and laboratory material tests is discussed.
Non-Destructive Load Testing:
- This is a new section in the AASHTO Manual. However, very little useful information on actual load testing procedures is given.
- Methods of determining equivalent standard ratings from load tests are complex and costly, and are not used at the present time in Texas.
- The rating section of the AASHTO Manual is much more extensive than corresponding sections in previous editions.
- The description of the safety factors for the Load Factor Rating method are similar to the factors in the new AASHTO Load and Resistance Factor Design (LRFD) Specifications.14
- The AASHTO Manual stated when a redundant bridge has details not available from plans, then a physical inspection and evaluation may be sufficient to approximate the ratings. An interpretation on applying this criterion to redundant bridges will be presented in Chapter 5, Ratings and Load Posting.
- Structural grade of reinforcing steel is listed separately in the Load Factor Method of rating but is combined with all the older unknown grades for the Allowable Stress Rating Methods. Texas allowed the use of structural grade of reinforcing until about 1962 which was described in the TxDOT Construction Specifications of 1951 and 1962. This will be discussed in more detail in Chapter 5, Ratings and Load Posting.
- The AASHTO Manual now contains detailed examples of allowable stress, load factor, and load and resistance factor (LRFR) ratings for a simple-span, I-beam structure and for a simple-span, concrete structure. An example of an allowable stress rating is also given for a simple-span timber structure.
- An expanded index of subjects is now included in the AASHTO Manual.
Current Status of AASHTO Manual
The Manual for Bridge Evaluation, First Edition (MBE) was adopted by the AASHTO Highways Subcommittee on Bridges and Structures in 2005. The MBE combines the Manual for Condition Evaluation of Bridges, Second Edition (2000) and its 2001 and 2003 Interim Revisions with the Guide Manual for Condition Evaluation and Load and Resistance Factor Rating (LRFR) of Highway Bridges, First Edition and its 2005 Interim Revisions. Revisions based on approved agenda items from annual Subcommittee meetings in 2007 and 2008 are also incorporated into the MBE.
The Manual for Bridge Evaluation, First Edition, with 2010 Interim Revisions supersedes the Manual for Condition Evaluation of Bridges, Second Edition and any revisions made in previous Interim Revisions. With the 2008 publication of the MBE, the Subcommittee conferred archive status on the Manual for Condition Evaluation of Bridges, the Guide Manual for Condition Evaluation and Load and Resistance Factor Rating (LRFR) of Highway Bridges, and all Interim Revisions of both prior bridge evaluation titles.