National Bridge Inspection Program

National Bridge Inspection Program Why? 1967 Silver Bridge collapse (fracture of an eyebar at a pin connection) 1968 National bridge inspection (NBI) program initiated (requiring regular and periodic inspections) 1971 National bridge inspection standards (NBIS) adopted (prescribe how, with what frequency, and by whom bridge inspections must be completed) 1987 Schoharie Creek collapse (scour) 2007 Minnesota I-35W collapse (undersized gusset plate design)

National Bridge Inspection Standards How? When? Who? Visual assessment Collection of 116 standards NBI fields of data collected 75 supplemental state data fields Every 24 months unless otherwise warranted by conditions For non-nbi structures, inspected at least every 60 months Qualified and trained inspectors each having a minimum of 5 years bridge inspection experience Comprehensive two-week inspector training course Fracture critical inspection course

VTrans Inspection Program 2,688 bridges (span length greater than 20 feet) 313 interstate highway 764 state highway 1,606 town highway 5 private or railroad 1,294 bridges (span length greater than or equal to 6 feet and less than or equal to 20 feet) 223 interstate highway 1,071 state highway

VTrans Inspection Program 219 rail bridges (state owned railroads) 253 retaining wall (along state highways having a height greater than 3 feet) 108 recreational path structures (span length greater than 6 feet) 156 overhead sign support structures

Inspection Terms Bridges are considered STRUCTURALLY DEFICIENT if significant load-carrying elements are found to be in poor or worse condition due to deterioration and/or damage, or the adequacy of the waterway opening provided is determined to be extremely insufficient. The fact that a bridge is structurally deficient does not immediate imply that it is likely to collapse or that it is unsafe. Bridges are considered FUNCTIONALLY OBSOLETE when the geometry of the roadway no longer meets today s minimum design standards for width or vertical clearance for that roadway classifications, or the adequacy of the waterway opening provided is determined to be insufficient. The fact that a bridge is functionally obsolete does not imply that it is unsafe.

Inspection Terms The SUFFICIENCY RATING of a bridge is a single number from 0 (low) to 100 (high) taking into account, bridge condition, geometry, traffic, and how well the waterway passes underneath the bridge. Sufficiency rating is used to determine funding eligibility. A low sufficiency rating does not necessarily mean the bridge is unsafe or in need or immediate repair. A FRACTURE CRITICAL MEMBER is a steel member in tension that does not have enough additional, structural members to sufficiently redistribute load in the bridge if one member loses capacity, thus resulting in a portion of or entire bridge collapse. FATIGUE is a material response that describes the tendency of a material to break when subjected to repeated loading.

Structural Deficiencies in Vermont Bridge Age and Structural Deficient Trends 500 100 450 400 350 300 250 200 150 100 50 0 147 0.00 187 236 2.67 1.69 392 6.38 437 15.56 200 20.00 266 23.31 343 349 28.86 34.67 47.06 34 55.56 99 90 < 10 10 and < 20 20 and < 30 30 and < 40 40 and < 50 50 and < 60 60 and < 70 70 and < 80 80 and < 90 90 and < 100 100 Number of Bridges Percent Structurally Deficient in Age Group 80 70 60 50 40 30 20 10 0 Count SD Age

Types of Inspections Initial The first inspection of a bridge to determine baseline structural conditions Routine Regularly scheduled inspection consisting of observations and/or measurements needed to determine the physical and function condition of the bridge In-Depth A close-up inspection of one or more members to identify deficiencies Special An inspection scheduled at the discretion of the inspector used to monitor a known or suspected deficiency

Types of Inspections Damage Unscheduled inspection to assess structural damage resulting from environmental factors or human actions Fracture critical A hands-on inspection of a fracture critical member Underwater Inspection of the underwater portion of the bridge substructure

National Bridge Inspection Ratings Condition ratings Deck Directly carries traffic Superstructure Supports the deck and connects one substructure element to another Substructure Supports the superstructure and distributes all bridge loads to below-ground bridge footings Culvert A pipe or small structure used for drainage under a highway or railroad

National Bridge Inspection Ratings Appraisal ratings Waterway adequacy (frequency of overtopping) Structural evaluation (load rating) Approach roadway alignment Deck geometry (roadway width) Under clearances (vertical and lateral)

NBI Condition Ratings (scale 9 to 0) 9 Excellent condition 8 Very good condition no problems noted 7 Good condition some minor problems

NBI Condition Ratings (scale 9 to 0) 6 Satisfactory condition structural elements show some minor deterioration. 5 Fair condition all primary structural elements are sound but may have minor section loss, cracking, spalling or scour.

NBI Condition Ratings (scale 9 to 0) 4 Poor condition advanced section loss, deterioration or scour Serious condition loss of section, deterioration, spalling or scour have seriously affected primary structural components. Local failures are possible.

NBI Condition Ratings (scale 9 to 0) 2 Critical condition advanced deterioration of primary structural elements. Unless closely monitored it may be necessary to close the bridge until corrective action is taken

NBI Condition Ratings (scale 9 to 0) 1 Imminent failure condition major deterioration or section loss present in critical structural components or obvious vertical or horizontal movement affecting structure stability. Bridge is closed to traffic but corrective action may out back in light service. 0 Failed condition out or service beyond corrective action.

NBI Appraisal Ratings (scale 9 to 0) 9 Superior to present desirable criteria 8 Equal to present desirable criteria 7 Better than present minimum criteria 6 Equal to present minimum criteria 5 Somewhat better than minimum adequacy to tolerate being left in place as is

NBI Appraisal Ratings (scale 9 to 0) 4 Meets minimum tolerable limits to be left in place as is 3 Basically intolerable requiring high priority of corrective action 2 Basically intolerable requiring high priority of replacement 1 Not used 0 Bridge closed

VTrans Bridge Inspection Charge Four teams consisting of at least one individual meeting the minimum qualifications specified with the National Bridge Inspection Standards http://www.fhwa.dot.gov/bridge/nbis.htm Inspection records and bridge inventories are prepared and maintained in accordance with the standards http://www.fhwa.dot.gov/bridge/nbi.htm Each structure required to be inspected shall be rated as to its safe load carrying capacity Why aren t all structures rated? Missing information or lack of record plans

VTrans Bridge Inspection Charge Provide technical assistance to bridge owners Provide recommendations to DMV for oversize / overweight movements and routing on interstate and state highways Prepare inspection results and summaries for bridge owners Conduct and develop, with a multidisciplinary team, scour determination and plans of action (POA)

Inspection Results and Summaries For each bridge inspected, a structure inspection, inventory and appraisal sheet will be created and sent to the respective bridge owner (DTA or Selectboard chair) To get a sense of the immediate and future needs, the inspection summary and needs section is key these are the inspectors comments. Don t wait for a special letter.

Preventative Maintenance Why? 1987 Inspection

Rate of Deterioration? 2001 Inspection

Preventative Maintenance What? Smooth approaches and wearing surface to reduce impact damages Plug wind slots in concrete curbs and drain off ends of the deck Maintain runner planks on timber decks Maintain a crash worthy rail system on and off the bridge Wash bridges in the spring of every year Apply water repellent every other year on all exposed concrete surfaces

Preventative Maintenance What? Spot paint steel members or grease to protect the steel Keep the bearing areas clean and take measures to reduce debris buildup or moisture on and around the bearings Maintain protective rip-rap countermeasures Monitor for scour after high water events and place concrete sub-footings as needed Maintain leak free roofs and sideboards on covered bridges Maintain deck joints and ensure that they do not leak Remove debris from steel or timber members

Questions? Pamela Maza Thurber, P.E. Bridge Management and Inspection Engineer 1 National Life Drive Structures Section Montpelier, Vermont 05633 Telephone: 828-0041 Fax number: 828-3566 Email: pam.thurber@state.vt.us Thank you