A Marketing Approach to Bridge Longevity

All about being specifically wrong … while being generally rightPresented by: Heinrich O. Bonstedt

Executive DirectorPrestressed Concrete Association of

Pennsylvania

The Engineering Approach

Examines Each Specific CriteriaTherefore, Every Bridge is Different in a Thousand Ways Design Construction Climate Weather Traffic Etc, etc

The Engineering Goal

To be Specifically Right

The Marketing Approach

Examines Only Basic Criteria

To Draw Conclusions To Make Decisions To Create Forecasts

The Marketing Goal

To be generally right

(While often being specifically wrong)

Data Analysis for Insights

Bridges are Important to Us

They even directly support education!

But Bridges Don’t Last Forever

Data Source

The National Bridge InventoryDecember 2000

Prepared according to a Standard Recording and Coding Guide that covers over 115 items

“By having a complete and thorough inventory, an accurate report can be made to Congress” and it provides the data necessary to “produce Defense Bridge and Federal Emergency Management Agency (FEMA) reports.”

Evaluation Objectives

Determine deficiency rates for bridgesEvaluate deficiency trendsCompare bridge material alternativesEstablish a basis for projections of service life expectancy

Limitations of our NBI Analysis

A continuation of past practices was assumed to continue into the futureIn view of the scope of the sample factors such as location, uniformity of rating were assumed to hold true over the period studied

Constraints Applied to Data

Constructed or reconstructed after 1950No railroad bridges or buildings and plazasNo CulvertsDistance between back-walls of abutments >20 feetConsider only structural deficiencies from Appraisal Ratings (2 or less) Condition Ratings (4 or less)

Deck Super-structure Sub-structure

Elimination of Coding Errors

Blank or improperly coded records in the following fields were discarded: Inventory route Type of service Structure length Bridge width Year built and/or reconstructed Structure use Materials used Condition rating

Sample for the Trend Analysis

683,861 structures in the National Bridge Inventory

459,286 bridges remained for analysis

369,985 of which have been built or reconstructed since 1950

Deficiencies Reported (all thru 1998)

Road System

Inventory Units

Rated Structurally Deficient

Units %

Interstate 46,464 2,920 6.3

US Highways

36,932 3,865 10.5

State Routes

101,220 15,698 15.5

County Roads

214,489 54,847 25.6

Other 60,181 12,787 21.2

Total 459,286 90,117 19.6

Deficiencies Reported (1950 thru 1998)

Road System

Inventory Units

Rated Structurally Deficient

Units %

Interstate 46,113 2,835 6.1

US Highways

30,672 2,128 6.9

State Routes

84,011 9,473 11.3

County Roads

161,794 28,166 17.4

Other 47,395 6,663 14.1

Total 369,985 49,265 13.3

Plotting Limitation

When plotting ratios (deficiency rates), those based on fewer than 275 units per year were omitted from plotting – but not from later computations.

Sources of Deficiencies

Super-structure conditionSub-structure conditionDeck conditionAppraisal Rating

Deficiencies by Road System

Interstate HighwaysUS Numbered RoutesState HighwaysCounty RoadsOther RoadsAll Highways, Routes and Roads

Trend Evaluation

Statistical analysis of deficiencies on the identified roads systems indicates a parabolic trend, following the general algorithm:

Y = a + bx + cx2 where,

Y = the percentage of bridges rated deficientx = the number of years since the bridge was constructed and/or reconstructed

Conclusions

While engineering standards and specifications aim to create solutions of equal performance across all materials, actual results indicate that concrete bridges outperform their competitive materials

Conclusions - continued

Individual service life expectancy projections are:

Type of Road System Carried by Bridge

Bridge Type Interstate

Highways

US Numbere

dHighway

s

State Routes

CountyRoads

Prestressed Concrete

83 75 69 73

Reinforced Concrete

102 93 78 66

Structural Steel 67 68 63 55

Timber N/A N/A 53 50

Conclusions - continued

The most reliable, simply because there is more data, would be a projection for all road systems combined:Bridge Type Central

Estimate

Prestressed Concrete 73

Reinforced Concrete 72

Structural Steel 58

Timber 50

Conclusions - continued

To account for these differences in service life expectancy, “first costs” of a bridge would have to factored by the following to reflect performance parity: Prestressed Concrete 1.00 Reinforced Concrete 1.01 Structural Steel 1.26 Timber 1.44

Thank you for your attention!

Questions?