Presentation on theme: "Mn/DOT Bridges Legislative Staff Briefing"— Presentation transcript:
1 Mn/DOT Bridges Legislative Staff Briefing February 5, 2008Bridge Design and Bridge TypesBridge Inspection ProgramBridge TerminologyBridge Crews and Contract WorkCurrent Bridge Structural Condition and TrendsBridge Preservation Investments
2 Bridges Are Designed According to a National Code American Association of State Highway and Transportation Officials (AASHTO) “LRFD Bridge Design Specification” is the governing code.All 50 states participate in code development and annual updating.Development of the first national bridge design code began in the 1920’s and was published in 1931.Reflects the combined experience of 50 states.
6 Concrete slab for shorter spans. Prestressed beams for intermediate spans with straight alignment.Steel beams for intermediate/long spans or curved alignment.
7 Steel or concrete box girders for major spans. Other types for very long spans and “signature” bridges.ArchSuspensionCable-stayedExtradosed
8 Safety Factors in Bridge Design Bridges are intentionally over-designed to provide a safety factor for many issues including the following:With a year service life, traffic may increase in frequency or weight.Materials may have slight imperfections from specificationsTolerances in construction or fabrication may cause a bridge component to be slightly different than designed.Steel will corrode during the bridge lifetime and loose some thicknessDeterioration of concrete, steel, timber
9 Who Designs TH Bridges?Mn/DOT Bridge Office (in Oakdale) has a preliminary design unit, hydraulic unit, cost estimating unit and five final design units to design bridges across the state.In-house, Mn/DOT is staffed to design for about $40 M-$50 M bridge program/year.Program above this annual amount is sent out to consultants.
13 Bridge Inspections, general Bridge Inspection Cycles – Bridges are inspected once every two years per National bridge Inventory System. In Minnesota, if the condition of the deck, superstructure or substructure is rated “4” or less, bridges are inspected annually.Fracture critical bridges get an in-depth inspection at least once every two years.Mn/DOT Bridge Inspectors – Mn/DOT has 75 certified inspection team leaders. These inspection team leaders have taken three weeks of FHWA approved Bridge Inspector training.
14 Bridge Inspections, cont’d Equipment used for inspection - inspection equipment can include snooper trucks, aerial manlifts, ladders, measuring devices and various tools.In-depth inspections use ultrasonic testing, die penetrant, and magnetic particle test methods and a video scope in order to detect cracks and/or corrosion.Critical Deficiency – any condition discovered during a scheduled bridge inspection that threatens public safety and, if not promptly corrected, could result in collapse or partial collapse of the structure. When inspectors report critical findings, immediate actions are taken to further assess the situation and to repair or close the bridge.
15 What Are Inspectors Looking For? Deterioration of bridge members such as:- cracked or spalled concrete- corrosion of steel such that thickness is lost- corrosion that is causing distortion in a jointAssess condition of paint systemsDistortion of members such as bowing not aligned as originally builtScour from water flow around foundationsLeaking jointsSupport piers that are tilting or moving
19 Governor’s Inspection Program TH System:3,875 Routine and FC Inspections270 By ConsultantsLocal System141 FC inspections43 By ConsultantsAs of December 20th all State Bridge inspections are up to date.
20 Bridge TerminologyCondition rating – overall assessment of the physical condition of the deck, superstructure or substructure, range from 0 to 9.Sufficiency rating (SR) — Sufficiency rating is a computed numerical value that is used to determine eligibility of a bridge for Federal funding. The sufficiency rating formula result varies from 0 to 100. The formula includes factors for structural condition rating, bridge geometry, and traffic considerations.
21 National Bridge Inventory Condition Ratings 9 – Excellent8 – Very Good7 – Good - No problems noted.6 – Satisfactory – Some minor problems.5 – Fair – All primary structural elements are sound but may have minor section loss, cracking, spalling, or scour.
22 National Bridge Inventory Condition Ratings, cont’d 4 – Poor – Advanced section loss, deterioration, spalling or scour.3 – Serious – Loss of section, deterioration, spalling or scour have seriously affected the primary structural components.2 – Critical – Advanced deterioration of primary structural elements.1 – Imminent Failure – Major deterioration or section loss in critical structural components. Bridge is closed to traffic, but corrective action may put it back in light service.0 – Failed – Out of service, beyond corrective action.
23 Summary of Sufficiency Rating (SR) Factors 1. Structural Adequacy & Safety (55% max)2. Serviceability & Functional Obsolescence (30% max)3. Essentiality for Public Use (15% max)
24 Summary of Sufficiency Rating (SR) Factors 1. Structural Adequacy & Safety (55% max) – includes superstructure, substructure, culverts, and inventory rating.2. Serviceability & Functional Obsolescense (30% max) – includes number of lanes on the structure, Average Daily Traffic (ADT), approach roadway width, structure type, bridge roadway width, vertical clearance over deck, deck condition, structural evaluation, deck geometry, under-clearances, waterway adequacy, approach roadway alignment, STRAHNET highway designation.3. Essentiality for Public Use (15% max) – includes detour length, ADT, and STRAHNET highway designation.
25 Bridge Terminology, cont’d Structurally deficient (SD) — Bridges are classified as “structurally deficient” if they have a general condition rating for the deck, superstructure, substructure or culvert as 4 or less or if the road approaches regularly overtop due to flooding. The fact that a bridge is structurally deficient does not imply that it is unsafe.Functionally obsolete (FO) — a functionally obsolete bridge is one that was built to standards that do not meet the minimum federal clearance requirements for a new bridge. These bridges are not automatically rated as structurally deficient, nor are they inherently unsafe.
26 Federal Funding Eligibility A bridge that is Structurally Deficient or Functionally Obsolete and has a SR of 80 or less is eligible for federal rehabilitation funding.A bridge that is Structurally Deficient (has a condition code of 4) or Functionally Obsolete and has a SR of less than 50 is eligible for federal replacement funding.
39 2007 Performance Summary for TH Bridge Structural Condition (20’ and over) Statewide average of bridges in Poor condition dropped from 3.6% to 3.1% reflecting a steady improvement in condition since 2003.Bridges in Poor and Fair condition dropped slightly from 11.3 to 11.1%.Statewide average bridges in “Good” structural condition moved above the 55% target to 55.2% this year as a result of the increased level of system expansion and bridge preservation investments that began in 2002.Statewide there are fewer bridges in poor condition than there were last year.The bridges in either fair or poor condition remained the same as last year,And the number of good bridges increased about 6/10sWe believe the overall improved condition of bridges across the state can be attributed to the increased preservation investments made available under the Bond Accelerated Program that ends this year.
40 Principal Arterial = 85% of TH Bridge Area Fair & Poor Condition Target – 16%11.1%STATEWIDE Trunk Highway Principal Arterial Bridges (Over 20’) Structural Condition Performance Target (Percentage by Area)3.1%Poor Condition Target – 2%The yellow line at the top of this graph shows the how the percentage of bridges in either fair or poor condition has varied since We are beginning to emphasize these bridges because these bridges are primarily where we spend our preservation dollars.Conditions have been improving since about 2002 and we are well below our target set at 16% last year. But we do anticipate seeing some increase of bridges in fair condition due to the age profile of out State highway bridge.Bridges in Poor condition continue to remain steady at 4 percent and have been less than 4% for a couple of years now.Bridges in good condition continue to improve since 2003, largely as result of bridge replacement and expansion funding from the BAP and other bonding programs.Good Condition Target – 55%55.2%Principal Arterial = 85% of TH Bridge AreaJanuary 2008
41 Minnesota Deficient & Functionally Obsolete Bridges – how we compare* Interstate and State Bridges (20’ and over)Total F.O. – 6% MN : 14.6% NationallyTotal S.D. – 3% MN : 6.6% NationallyCity/County/Township Bridges (20’ and over)Total F.O. – 3% MN : 11.6% NationallyTotal S.D. – 11% MN : 14.9% Nationally* Source: “Better Bridges” Better Roads 2007 Bridge Inventory, November 2007; 42 states reporting.
42 MN/DOT BRIDGE CONSTRUCTION Let or Programmed Includes Bridge Expansion, Replacement, Preservation, and Culverts January 4, 200857.144.846.574.586.345.844.9133.9110.4113.0192.5174.220406080100120140160180200979899'00'01'02030405060708DOLLARS IN MILLIONSFiscal YearACTUAL BRIDGE & CULVERTS ESTIMATED BRIDGE & CULVERTSCost is for bridge portion of contract, does not include approach roadway cost. Yearly total is the sum of all bridge contract let that fiscal year FY 2008 does not include I-35W Emergency Replacement Bridge Costs.
43 MN/DOT BRIDGE CONSTRUCTION Let or Programmed Includes Bridge Replacement, Preservation and Culverts January 4, 2008Fiscal YearACTUAL BRIDGE & CULVERTS ESTIMATED BRIDGE & CULVERTSCost is for bridge portion of contract, does not include approach roadway cost. Yearly total is the sum of all bridge contract let that fiscal year FY 2008 does not include I-35W Emergency Replacement Bridge Costs.
46 Planned Investments vs. Bridge Needs (Including Inflation) ( )250Bridge Needs (STIP & Model)Add’l Major Bridges:42Planned Investments200Annual Bridge ProjectNeedsin Millions(Including Inflation)200+/-Add’l Major Bridges:98Add’l Major Bridges:29150130+/-Gap = 20M/yr10080This graph is broken down to the three planning periods that will be used in updating the districts’ long-range plans. The first time period is the STIP years. The blue bars show bridge funding needs during these time periods. In the STIP years, we also show the planned investments for that time period. There is an average of approximately $80 million of needs in the sTIP years, for which we have planned $60 million of projects.This graph is showing overall project construction costs, not just structure costs. Also, this does not reflect budget buster bridges. If it did it would, for instance, need to include the Lafayette bridge project in the STIP years – that is $143 million in 2011, therefore it would increase both the needs and the investments by $36 million averaged annually.The last couple slides of pie charts in your handout were added as an attachment to indicate the approximate distribution of these needs across the eight districts.6050STIP01/31/08
47 Targeting the Right TH Bridges Goal is to Fund the Replacement/Renovation in the STIP years or time period of the current:3.1% Poor Condition (Structurally Deficient) &8% Fair Condition Bridges
48 Fracture Critical Bridges Fracture-critical (FC) — a fracture-critical bridge typically has a steel superstructure with load (tension) carrying members arranged in a manner in which if one fails, the bridge could collapse. Examples of fracture critical bridges are two girder bridges or truss bridges. The classification of fracture critical does not mean the bridge is inherently unsafe
49 Fracture Critical Bridges, cont’d Not all fracture critical bridges are planned for replacement in the next 20 years. The right work planned for some FC bridges is painting, overlays and/or other repairs.Three bridges are planned for replacement in the STIP years ( ):– TH 11 Bridge in Drayton, ND/Robin, MN– Bridge 5388 TH 24 in Meeker County– TH 52 Lafayette Bridge in St. PaulAnother 13 bridges are planned for replacement in
50 Statewide Bridge Preservation Fund 2009-2024 Fund Large Bridge Preservation Projects Where Project Cost Exceeds 50% of an ATP’s Annual Federal Funds.100% of Bridge Costs Eligible for Funding (does not include grading, R/W)Fund is Capitalized with up to $80 Million Annual in FiscalDistrictBridgeFYBridge Cost in Construction FY2TH 11 /Red River at Robbin200914*MTH 52/Mississippi River – Lafayette20111306I-90/Mississippi River – Dresbach201458*TH 43/Mississippi River – Winona2017903TH 23/Mississippi River – St Cloud201538TH 61/Mississippi River – Hastings120TH 36/St Croix River2024218*TOTAL668 MillionThis shows our current Statewide Bridge Preservation Program. We originally had bridge projects in this program out to 2018, but now with updating costs and long-range plans we are looking out into the middle time period as well.This fund was set up to…(see slide)These bridges aren’t necessarily programmed in a priority order, but rather scheduled in the time frame in which they are deliverable.The St. Croix River Crossing bridge is shown here as planned in That year is simply the early years of Metro’s current TSP- last funding time period. However, at $40 million/year it is difficult to fit funding for that bridge in sooner. (Note:2004 cost estimate for the bridge was $83 million).The spending plan on this fund assumes 30% of the cost in the 1st year, 50% in the second year and 20% in the 3rd year.* Mn/DOT Share of Border Bridge