Section 3: AASHTO Inspection Manuals
Anchor: #i10032841970 and 1974 AASHTO Manuals
The first AASHTO Manual issued in 19706 (the small grey book) and subsequently modified slightly in 19747 (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:
Inspections
- 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
Records
- 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)
Ratings
- 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 19788 (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:
Records
- Recommendations modified for repair, maintenance, and posting
Ratings
- 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 Devices9 (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 form10 (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 Specifications11 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 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.12 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.13
- 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.
- In 1989 a new Appendix B was added that described the
five basic Inspection Types:
- inventory
- routine
- damage
- in-depth
- interim
- 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 Bridges14 and is considered current at this time (2001).
Major additions and changes since the 1983 AASHTO Manual are:
Records:
- 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.
Inspections:
- 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:
- Initial,
- Routine
- Damage
- In-depth
- Special.
- 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 bridges in Texas considered to be susceptible to earthquake forces except for a minor area in the Big Bend region.
- 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.
Material Testing:
- 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.
Ratings:
- 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.15
- The AASHTO Manual now states 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 1994 AASHTO Manual
As of this time (2001), no significant changes or additions have been made to the AASHTO Manual since 1994 except for minor changes to bolt stresses in 1995, shear analysis provisions for pre-stressed concrete in 1996, and the formulas for load-factor analysis in Appendix C of the Manual in 1998. Some of the information now in the AASHTO Manual contains recommendations on proper inspection techniques and items to look for during an inspection. These are all covered in similar or greater detail in the Bridge Inspector’s Training Manual 90.16
Anchor: #i10039481994 AASHTO Manual Omissions and Inconsistencies
The various editions of the AASHTO Manual have contained a number of errors and inconsistencies over the years. Many have been clarified in the 1994 version of the AASHTO Manual. However, significant omissions and incomplete discussions remain in the AASHTO Manual, which are listed below. All of these will be addressed in later chapters along with recommended interpretations.
- The Inventory and Inspection
Data to be recorded do not require the following three specific items:
- Date of investigation. The date of investigation is implied since all reports must be periodically made. Any proper inspection or data recording of any type must have a date. Therefore this is believed to be a simple omission in the current AASHTO Manual.
- Paint Record. This item was originally intended to allow records to be kept on the painting of the structure for corrosion protection. However, the painting record is described later in the AASHTO Manual as an item that should be maintained in the Bridge File. Therefore, its omission from the list of requirements may simply be another error in the AASHTO Manual.
- Signature. It is unclear why the requirement for Signature is now omitted from the AASHTO Manual. Since all inspections and ratings are to be done by qualified individuals, it is appropriate that their work continue to be identified by name. TxDOT requires that all calculations and inspection reports be signed and sealed by a licensed engineer. This requirement is specifically contained in the current inspection requirements described in Chapter 8, Bridge Records.
- Methods of inspection and requirements for bridge railing and other traffic safety features are minimally presented in the AASHTO Manual. A list of bridge railings is presented in the Bridge Railing Manual.
- A list of bridge railings will be presented in the Bridge Division Railing Manual, to be published in late 2001.
- No clear explanation is made of the difference between rating calculations using two trucks side-by-side, usually used for Inventory Ratings, and rating calculations using a single truck, often used for Operating Ratings. This is an important point in understanding the relationship between the two types of load ratings, and also the methods used for permit load analysis. This subject will be covered in detail in Chapter 5, Legal Loads and Load Posting.
- The AASHTO Manual states when a redundant bridge has details not available from plans, then a physical inspection and evaluation may be sufficient to approximate the Operating and Inventory Ratings. It is not clear why non-redundant bridges are excluded from this procedure.
- The tables of allowable steel stresses for Inventory Ratings exclude A36 as a listed material. This omission is believed to be an error in the AASHTO Manual. A36 is listed for Operating Rating stresses.
- An out-of-date formula, commonly called the “Secant Formula,” is retained in Appendix A of the AASHTO Manual as an alternate to the more widely accepted column formulas listed in the allowable stress tables. The Secant Formula was introduced in the 1979 AASHTO Manual, four years after being eliminated as acceptable by the AASHTO Bridge Specifications.17 Its continued use is not recommended since it is inaccurate and not conservative for some column lengths.
- The AASHTO Manual does not explain why the Operating Rating should be considered when full truck and sidewalk loads act simultaneously. It is surmised that the logic assumes the odds are remote that all design truck loads will occur at the same time as full sidewalk loading.
- The AASHTO Manual is unclear on use of a train of trucks for spans over 200 feet. Why this criterion is limited only to spans and not to continuous units is not explained, nor has it been properly explained in the past. A more logical assumption is that a train of trucks should be used not only for any spans exceeding 200 feet but also for continuous units exceeding 200 feet.
- The AASHTO Manual now contains some detailed examples. However, the examples do not give the necessary guidance on proper distribution of live loads for the various ratings. Distribution recommendations will be given in Chapter 5, Ratings and Load Posting.
6. Manual for Maintenance Inspection of Bridges, AASHTO, 1970.
7. Manual for Maintenance Inspection of Bridges, AASHTO, 1974.
8. Manual for Maintenance Inspection of Bridges, AASHTO, 1978.
9. “Scour at Bridges,” Technical Advisory, FHWA, 1988.
10. Manual for Maintenance Inspection of Bridges, AASHTO, 1983.
11. “Interim Specifications for Bridges,” AASHTO, 1984, 1986, 1987, 1988, 1989, 1990.
12. Standard Specifications for Highway Bridges, AASHTO, 1994.
13. “Scour at Bridges,” Technical Advisory, FHWA, 1988.
14. Manual for Condition Evaluation of Bridges, AASHTO, 1994.
15. Load and Resistance Factor Design Specifications, AASHTO, 1994.
16. Bridge Inspector’s Training Manual 90, FHWA, 1991.
17. Standard Specifications for Highway Bridges, AASHTO, 1994.