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26 CHAPTER FOUR INSPECTION TYPES AND INTERVALS U.S. INSPECTIONS · Access for inspections and policy for close-up and hands-on inspection. U.S. federal regulations define eight types of bridge inspec- · Application of methods of testing and/or measurement tions (Table 34). Three of these, fracture-critical member including NDT methods. inspection, routine inspection, and underwater inspection · Personnel requirements for complex structures, com- occur at intervals set by regulation. plex inspection methods, and/or complex access. For routine inspection and underwater inspection, U.S. This section presents practices at U.S. state DOTs related federal regulations cite three intervals: A standard interval; a to routine inspections. Information was collected from 34 longer interval applied to specific bridges and with the DOTs. Not all DOTs have information on every topic related approval of the FHWA; and any interval, shorter than stan- to routine inspection. dard, that may be needed at a bridge. For fracture-critical member inspections, a standard interval and shorter interval, Routine Inspection--U.S. State Department if needed, are stated in regulation (Table 35). of Transportation Practice NBI data from 2005 (2) show that state DOTs use standard Full routine inspection of bridges occurs at 24-month intervals intervals for 85% of routine inspections, 34% of underwater at most state DOTs and for the majority of bridges. Two states, inspections, and 67% of fracture-critical member inspections Minnesota and Ohio, require routine inspection at 12-month (Table 36). Inspection intervals from NBI data are listed intervals. Minnesota allows a 24-month inspection interval for for routine inspections (see Tables 37 and F1), underwater specific bridges with the approval of the DOT. As a result, rou- inspections (see Tables 38 and F2), and fracture-critical tine inspection intervals are 24 months for approximately 63% inspections (see Tables 39 and F3). Throughout this chapter and 12 months for 28% of bridges in Minnesota. In Ohio, more more detailed responses to the questions on inspection types than 99% of all bridges have routine inspections at 12-month and intervals can be found in the tables in Appendix F. intervals. Routine Inspection--U.S. Federal Regulations Specific Tasks in Routine Inspections U.S. federal regulations define four aspects of routine in- Seven DOTs reported policies on specific inspection meth- spection of bridges: ods or measurements that must be collected at set intervals (see Table F4). Tasks include measurement of vertical clear- · Structures--regulations define the bridges and struc- ances, measurement of channel cross section, fathometer tures that must be inspected. surveys at substructures, mandatory wading at substructures, · Frequency--regulations set maximum intervals for and mandatory boring of timber members. For bridges in inspections. good condition, intervals for tasks range from 60 to 144 · Inspectors--regulations set minimum qualifications months. Intervals become progressively shorter as bridge for inspection program managers and inspection team condition becomes poorer, as scour hazard is more severe, or leaders. as vertical clearances are more limited. · Procedures--regulations include, by reference, the Bridge Inspector's Reference Manual (4) and the AASHTO Access Policies for Routine inspections Manual for Condition Evaluation of Bridges (5). Ten DOTs and Eastern Federal Lands reported policies Aspects of routine inspection that are determined by state regarding access to bridge components for routine inspection DOTs, other bridge owners, and their inspection staff include: (see Table F5). Access can include climbing, rigging, UBIVs, and entry of confined spaces. Idaho, Iowa, Oregon, · Short-interval inspections of some structures. Interim and Eastern Federal Lands set maximum intervals for close- inspections of structures or critical components of up inspection, ranging from 48 to 120 months. The Oregon structures. DOT requires entry of box girders during every routine
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27 TABLE 34 U.S. FEDERAL INSPECTION TYPES Inspection Description Damage An unscheduled inspection to assess structural damage resulting from environmental Inspection factors or human actions. Fracture-Critical A hands-on inspection of a fracture-critical member or member components that may Member include visual and other nondestructive evaluation. Inspection Hands-On Inspection within arms length of the component. Inspection uses visual techniques that Inspection may be supplemented by NDT. In-Depth A close-up inspection of one or more members above or below the water level to Inspection identify any deficiencies not readily detectable using routine inspection procedures; hands-on inspection may be necessary at some locations. Initial Inspection First inspection of a bridge as it becomes a part of the bridge inventory to provide all Structure Inventory and Appraisal data and other relevant data and to determine baseline structural conditions. Routine Regularly scheduled inspection consisting of observations and/or measurements Inspection needed to determine the physical and functional condition of the bridge, to identify any changes from initial or previously recorded conditions, and to ensure that the structure continues to satisfy present service requirements. Special An inspection scheduled at the discretion of the bridge owner, used to monitor a Inspection particular known or suspected deficiency. Underwater Inspection of the underwater portion of a bridge substructure and the surrounding Inspection channel that cannot be inspected visually at low water by wading or probing, generally requiring diving or other appropriate techniques. Source: Code of Federal Regulations (1). inspection if deterioration is known to exist. DOTs in other range from general advice to making hands-on inspections as states track the need for access equipment at some bridges as needed, to requirements for hands-on inspection at specific a part of planning and scheduling for inspections. details or in response to specific defects (see Table F7). The Pennsylvania DOT sets a maximum 72-month interval for Routine Inspections for Specific Structures hands-on inspection of each component of a bridge. or Details In-Depth Inspection Nineteen DOTs set intervals for inspection of specific bridge types and detail types (see Table F6). Intervals are set for Eight DOTs set maximum intervals for in-depth inspection inspection of pin and hanger details and fatigue-prone details on of bridges (see Table F8). For bridges in good condition, redundant bridges, for pontoons of floating bridges, for cables in intervals range from 10 to 15 years. DOT policy may require cable-supported spans, and for segmental superstructures. specific measurements, specific reports, and the use of spe- cific personnel for in-depth inspection. Long-interval in- Hands-On Inspection depth inspections are thorough, detailed inspections of entire bridges. Short-interval in-depth inspections are applied to Thirty DOTs and Eastern Federal Lands reported policies for specific components such as nonredundant members or con- hands-on inspection during routine inspections. Policies nections, and equipment for movable bridges. TABLE 35 INSPECTION INTERVALS: U.S. FEDERAL REGULATIONS Underwater Inspection Inspection Standard Interval Maximum Interval NBI data (2) indicate that although 84% of NBI-length Fracture-Critical Member 24 months -- Routine 24 months 48 months bridges and culverts are water crossings, only 6% require in- Underwater 60 months 72 months TABLE 37 INSPECTION INTERVALS--ROUTINE TABLE 36 INSPECTION--SUMMARY U.S. INSPECTION INTERVALS IN PRACTICE Bridges and Culverts Short Standard Long Routine Inspection Interval, Months Inspection Interval Interval Interval <12 12 24 36 48 Total Fracture-Critical Member 26% 67% 7% 1,629 60,363 504,413 19 28,275 595,149 Routine 11% 84% 5% (0.3%) (10.1%) (84.8%) (0.003%) (4.8%) (100%) Underwater 66% 34% <1% Source: 2005 NBI data (2). Source: 2005 NBI data (2). Note: Not all inspection intervals are shown.
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28 TABLE 38 INSPECTION INTERVALS--UNDERWATER INSPECTION--SUMMARY Bridges and Culverts Underwater Inspection Interval, Months Inspections 72 (total) 37,735 2,209 1,114 11,092 636 9,835 12,796 4 0 (100.00%) (5.9%) (3.0%) (29.4%) (1.7%) (26.1%) (34.0%) (0.01%) (0.0%) Source: 2005 NBI data (2). Note: Not all inspection intervals are shown. spection by diving. Thirty-eight percent of dive inspections Complex Bridges are performed at intervals of 24 months or less, 26% are done at 48-month intervals, and 34% are done at 60-month inter- U.S. federal regulations identify movable bridges and cable- vals. Less than 1% of dive inspections are performed at the supported bridges as examples of complex bridges. Inspec- maximum 72-month interval currently permitted by U.S. tion of complex bridges may require special procedures or federal regulations. specially trained inspectors. Dive inspections are applied when inspection by wading Twenty-four DOTs identified some structures and inspec- and probing is not adequate (see Table F9). Seven DOTs tion types as complex or as needing special methods reported a maximum depth of water for inspections by wad- (Table 40). These are in addition to fracture-critical inspection ing or from boats. Maximum depths range from 30 in. to 6 ft. and underwater inspections. Twenty-two DOTs require spe- In deeper water, inspection must be by diving. Eight DOTs cific training or experience in personnel for these inspections. reported policies for short-interval underwater inspection. The Connecticut DOT identifies bridge complexity in three Inspection intervals are shorter for bridges with poor scour levels and specifies inspection team size and technical grades ratings and where scour protection is absent or inadequate. of team members for each level of complexity. The Ohio Five DOTs identified two or three intensity levels for dive DOT identifies major bridges by structural type and span inspections that differ in the extent of cleaning of submerged length. Bridge types and inspection types that require specific components. Channel cross sections may be measured during training of personnel are listed in Table F11. dive inspections. Movable Bridges Fracture-Critical Inspection At movable bridges, additional inspections are made of motion Inspection of fracture-critical members is required every 24 equipment, motion operation, and signals and gates (see Table months by federal regulation. Three DOTs reported annual F12). Cursory inspections and trial operation of movable spans inspections of fracture-critical members, and four DOTs are made once each year at four DOTs. One DOT performs perform increased intensity inspections of fracture-critical trial operations once each month. In-depth inspections of members using intervals that range from 48 to 120 months. motion equipment are done at 72-month interval at two DOTs. The shorter intervals are applied to older bridges, bridges with a greater volume of truck traffic, and bridges having Routine Interim Inspection specific design details. Longer intervals for increased inten- sity inspections are applied to newer bridges in good condi- Short-interval inspections, usually called interim inspec- tion with (relatively) robust design details (see Table F10). tions, are performed in response to poor conditions, posting The Oregon DOT, for example, employs a Level 1 fracture- for load, scour vulnerability, fracture vulnerability, and for critical inspection that is done with every routine inspection, and a more intense Level 2 fracture-critical inspection at a TABLE 40 longer interval. Level 2 inspections can include use of NDT U.S. COMPLEX BRIDGES methods. Complex Bridge No. of DOTs Suspension 19 (59%) TABLE 39 Cable-Stayed 17 (53%) INSPECTION INTERVALS--FRACTURE-CRITICAL Movable Bridge 14 (44%) INSPECTION--SUMMARY Tied-Arch 13 (41%) Eyebar Bridge 8 (25%) Bridges and Culverts Box Girder with External Post-Tensioning 8 (25%) Fracture Inspection Interval, Months Single Concrete Box Girder 7 (22%) Critical Two-Girder 6 (19%) (total) 48 Single Steel Box Girder 6 (19%) 21,668 384 5,292 14,616 16 288 1,023 Bridges with Pins and Hangers 6 (19%) (100.0%) (1.8%) (24.5%) (67.6%) (0.1%) (1.3%) (4.7%) Note: Percentage refers to how many of the 32 agencies that Source: 2005 NBI data (2). responded to the question mentioned inspecting this type of Note: Not all inspection intervals are shown. complex bridge.
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29 specific defects such as damage resulting from high-load hits, Special Inspections loss of bearing, the presence of temporary supports, and incipient buckling of members (see Table F13). DOT policy Eleven DOTs identified as "special" a variety of inspections guidelines to interim inspections recognize: directed at particular types of structures, addressing specific defects or performing specific tasks. Table F15 lists inspec- · Bridges posted for load (five DOTs); tions that collect specific quantitative data, but might not be · Bridges with low NBI condition ratings (seven DOTs)-- periodic. These inspections include measurement of joint This usually means condition ratings for deck, super- opening, crack extent, substructure settlement, vertical structure, substructure, and culvert; however, some DOTs clearance after overlays are placed, and inspection of sub- include ratings for channel and approach roadway as well; structures and channels after storms or other high-flow · High-load hits, unrepaired critical findings, severe section events. loss, or other known significant defects (seven DOTs); and · Temporary bridges and bridges with temporary sup- Minor Bridges and Non-Bridges ports or temporary repairs (three DOTs). Information on routine inspection of minor bridges, non- Interim inspections focus on the specific defect, specific poor highway bridges, and non-bridges was collected from 13 condition, or specific cause of load posting. state DOTs (see Table F16). Tennessee and Washington State DOTs inspect roadway bridge spans as short as 4 ft. Intervals for interim inspections range from 6 to 24 The Virginia DOT inspects all structures with openings of months, with shorter intervals for more severe deficiencies. 36 square feet or greater. DOTs inspect or require the in- Note that interim inspections at 24 months alternate with rou- spection of pedestrian bridges, railroad bridges, utility tine inspections also at 24 months. In this way, defects are bridges, and private bridges that cross public roads. Inspec- inspected every 12 months. tion may be limited to the highway environs, and may focus on potential hazards to road traffic. DOTs also inspect sign Forty-Eight-Month Routine Inspection structures, high-mast lights, retaining walls, noise barriers, tunnels, and ferry slips. Intervals for routine inspection gen- DOTs in Arizona, Illinois, and New Mexico apply a 48-month erally range from 24 to 72 months. At ferry terminals, vehi- interval for routine inspection at more than one-third of their cle transfer spans and equipment for hoists may be inspected bridges (2) (Table 41). Five other DOTs, Colorado, Kentucky, annually. Montana, North Dakota, and West Virginia use a 48-month interval for at least 10% of their bridges. Thirty-six DOTs use Informal Inspections a 48-month interval for less than 1% of their bridges. U.S. DOTs responding to the questionnaire all indicated that Forty-eight-month inspection intervals are applied only to external reports of problems at bridges are investigated by bridges in good condition. Some DOTs set bounds on bridge bridge inspectors (see Table F17). Thirteen DOTs preserve length, bridge age, load capacity, or vertical clearance to external reports as hardcopy in bridge files. Twelve DOTs qualify for a 48-month inspection interval (see Table F14). routinely receive problem reports from state maintenance crews. In North Carolina, findings from annual highway TABLE 41 reviews (ride-bys) performed by maintenance crews are PREVALENCE OF 48-MONTH IN- SPECTION INTERVAL shared with bridge inspectors. In Vermont, annual reports of the DOT's Operation Division are shared. In Iowa, there is Percentage of Routine frequent, informal contact among inspectors and mainte- Inspections at DOT 48-Month Interval nance crews, and frequent exchange of information. Arizona 44 Illinois 42 Monitoring of Bridges New Mexico 35 West Virginia 24 Kentucky 17 Table F18 presents bridge monitoring methods for 31 U.S. Montana 16 DOTs and Eastern Federal Lands. Methods of monitoring are Colorado 14 identified as visual monitoring, measurement, and instrumen- North Dakota 10 tation. Visual monitoring (15 DOTs) is often not periodic, is Texas 9 directed at one or very few defects, might be performed by South Dakota 7 Connecticut 6 maintenance crews or others, and is not recorded as an indi- Washington 6 vidual inspection. Measurement (22 DOTs) is the collection, Arkansas 5 usually by hand methods, of quantitative values during rou- Virginia 5 tine inspections. Instrumentation (10 DOTs) is the application Mississippi 1 of acoustic detectors, strain gages, or other devices for precise Oklahoma 1 and/or remote collection of quantitative data.