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2 In this chapter, bridge preservation and bridge components are defined, actions in bridge preservation are listed, bases for preservation actions are identified, and a method for evaluation of the benefits of bridge preservation is outlined. Definition of Bridge Preservation Bridge preservation applies actions in maintenance and repair to existing bridges that are adequate for continued service. Preservation is one part of the overall management of highway bridges. Overall management addresses bridge construction, maintenance, repair, improve- ment, and replacement. Preservation is the maintenance and repair of bridges that are not currently candidates for improvement or replacement. Bridge preservation programs select, deliver, and evaluate work in maintenance and repair of highway bridges. The programs examine the performance of actions applied to bridges and adjust policies on the selection of actions to improve program performance. They also evaluate the benefits of actions. Benefits are expressed as savings of agency costs. Preservation programs can use new materials and methods in maintenance and repair and can provide evaluations of performance of new materials and methods. Preservation programs report on accomplishments and benefits of preservation. Bridge preservation, as the term is used in NCHRP Project 14-36, is distinct from historical preservation. The Guides developed during NCHRP Project 14-36 are intended for preservation of bridges at all ages without specific relation to the historical importance of bridges. Table 1 contains AASHTOâs definition of bridge preservation (4). U.S. DOTâs Federal Highway Administration (FHWA) uses a similar definition (20). The AASHTO definition establishes criteria for candidates of preservation. Preservation candidates are existing bridges in good or fair condition. The AASHTO definition limits the actions that are considered preservation. Preservation restores function and extends service life. The Bridge Guide addresses preservation candidates and preservation actions. Programs for bridge preservation are limited in scope to candidate bridges and admissible actions. The limited scope allows programs to deliver actions to protect bridges before defects appear and to deliver repairs for minor defects before larger defects appear. The Bridge Guide defines a set of terms (articles in the Bridge Guide are shown in parentheses) as follows: â¢ Preservation (Bridge Guide 2.2). Preservation is a program of bridge maintenance to extend service life. â¢ Preservation Candidates (Bridge Guide 2.2.1). Preservation candidates are existing bridges that have acceptable condition, capacity, robustness, and durability. C H A P T E R 2 Bridge Preservation
Bridge Preservation 3 â¢ Preservation Actions (Bridge Guide 2.4.1). Preservation actions maintain or repair major components of bridges. Major components are decks, superstructures, substructures, and culverts. Preservation actions also repair, replace, or retrofit other components of bridges. Other components are approaches, channel protection, joints, bearings, drains, and railings. â¢ Preservation Plan (Bridge Guide 2.6). A preservation plan is a statement of actions and time intervals for actions necessary to preserve a bridge. â¢ Preservation Program (Bridge Guide 2.7). A preservation program is the policies, staff, and resources applied to preservation of bridges. Bridge Components Bridge components are objects of preservation actions (see Table 2). Components have quan- tity and condition. Components may need maintenance, repair, or replacement. Preservation actions can improve the condition of components and extend the service life of components. Preservation Actions In the Bridge Guide, preservation actions are named by bridge component and activity. Most actions are further identified by detail. Preservation activities are clean, overlay, paint, rehabilitate, repair, replace, retrofit, and seal (see Table 3). Detail attaches to individual combinations of component and activity. Detail identifies a method, material, or device employed in the preservation activity. The system of naming provides distinct names for distinct preservation materials and methods. The system allows group- ing of actions of the same activity or the same component. The naming of actions as component, activity, or detail supports a database of actions, and their costs, time intervals, and outcomes. Source Definition of Bridge Preservation AASHTO Actions or strategies that prevent, delay, or reduce deterioration of bridges or bridge elements, restore the function of existing bridges, keep bridges in good condition and extend their useful life. Preservation actions may be preventive or condition-driven. Table 1. Definition of bridge preservation. Bridge Component Parts of Bridges Approach Approach pavements, slabs, wearing surfaces, pressure relief joints, embankments, and slope protection for embankments Bearing Fixed and movable bearing devices Bridge All components of a bridge, collectively Channel Banks, bank protection, protection at substructures in water, stream diverters, channel cross- section, and profile Culvert Culverts subject to U.S. National Bridge Inspection Standards (21) Deck Structural decks, slabs, wearing surfaces, and waterproofing membranes Drain Grates, scuppers, downspouts, pipes, supports, outlets, and splash blocks Joint Fixed and movable joints in decks Railing Parapets, railings, and guardrails Substructure Abutments, wingwalls, bents, footings, pier walls, pier columns, and pier caps Superstructure Beams, girders, stringers, arches, cables, and trusses Table 2. Bridge components.
4 Proposed AASHTO Guides for Bridge Preservation Actions Treatments in the Deck Guide are named by activity and material. All treatments affect the same component, that is, the deck. Actions in the Bridge Guide are listed in Table 4. Treatments in the Deck Guide are listed in Table 5. Basis of Preservation Action A basis triggers the use of an action (Bridge Guide 3.2.1). Preservation actions are selected to meet specific intervals in time or selected in response to specific defects in bridges. The Bridge Guide defines two bases: 1. Cyclic: Actions taken at regular intervals. 2. Condition-driven: Actions performed in response to conditions or defects. Cyclic actions apply and renew protections for bridges, bridge components, or bridge elements. Actions to clean, seal, paint, or apply wearing surfaces are cyclic actions. Cyclic actions are performed at intervals set in policy. Cyclic actions may make slight or no improve- ment to condition. Condition-driven actions are repairs, replacements, and retrofits. Condition-driven actions usually improve condition. Condition-driven actions do not have intervals in policy, but they will exhibit intervals in actuality. The normal deterioration of bridges in a population generates a steady need for repairs. The rate of the appearance of these needs reveals intervals for condition-driven actions. Durability is improved by retrofits, a type of condition-driven action. The Deck Guide identifies repairs and protections. Protections are cyclic; repairs are condition- driven. Benefits of Preservation Bridge preservation is cost-effective if preservation reduces agency costs for bridge service. Agency costs for bridge service are the costs of preservation actions at bridges plus the costs of eventual replacement of bridges. The Guides present methods to evaluate costs of bridge preservation and to compute benefits. Preservation-Cycle Cost Analysis Cost evaluations are made using preservation-cycle cost analysis (PCCA). PCCA computes the costs of keeping existing bridges in fair or good condition and in service at current capacities. Activity Work Items Clean Sweep, flush, and wash bridge elements. Clear vegetation. Clear sediment and debris in waterways and culverts. Overlay Concrete or polymer overlay. Asphalt wearing surface with or without waterproofing membrane. Paint Full, zone, or spot paint. Paint steel elements. Coat concrete elements. Rehabilitate Repair and/or replacement of portions of bridges to restore fair or good condition or to restore original load capacity. Repair Work to correct defects in bridge components or elements. Replacement of a portion of a component or element is a repair. Replace Complete provision of new bridge components or elements. Retrofit Modify bridge components or elements to improve robustness or durability. Seal Apply materials to provide waterproofing to surfaces. Table 3. Bridge preservation activities.
Bridge Preservation 5 Component Cyclic Condition-Driven Approach Overlay, Asphalt Overlay, Polymer Seal Rehabilitate, Reinforced Concrete Repair, Asphalt Wearing Surface Repair, Embankment Repair, Settlement, Mudjack Repair, Reinforced Concrete Repair, Slope Paving Repair, Voids under Slab Replace, Reinforced Concrete Slab Replace, Slope Paving Retrofit, Relief Joint in Approach Bearing Clean Clean, Lubricate Paint Rehabilitate Repair Repair, Reset Replace Retrofit, Change to Elastomeric Bridge Clean Clean, Graffiti Paint, Full Paint, Spot Paint, Zone Rehabilitate Repair, Patch Concrete Channel Clean Repair, Channel Protection Repair, Scour Hole Retrofit, Channel Protection Retrofit, Modify Channel Retrofit, Stream Deflector Culvert Clean, Vegetation, Silt Rehabilitate, Reinforced Concrete Repair, Concrete Barrel Repair, Concrete Headwall Repair, Concrete Spalls Repair, Concrete Wingwall Repair Joints in Walls, Floor Repair, Voids Beyond Walls, Floor Replace, Apron Replace, Concrete Headwall Replace, Concrete Wingwall Retrofit, Streambed Paving Deck Clean Overlay, General Overlay, Asphalt + Membrane Overlay, Concrete or Modified Concrete Overlay, Polymer Concrete Seal Repair, Asphalt Wearing Surface Rehabilitate, Reinforced Concrete Repair, Concrete Crack Repair, Concrete Crack, Healer/Sealer Repair, Concrete, Full Depth Repair, Concrete, Partial Depth Repair, Timber Replace, Grid Plate Replace, Precast Panel Drain Clean Repair Replace Retrofit, Drains Through Parapet Retrofit, Extend Scuppers Retrofit, Install Drain Joint Clean Replace, Seal/Filler Rehabilitate Repair, All Types Replace Retrofit, Change Type of Joint Retrofit, Eliminate Expansion Joint (continued on next page) Table 4. Preservation actions and bases: Bridge Guide.
6 Proposed AASHTO Guides for Bridge Preservation Actions Railing Clean Paint Seal Repair, Concrete Repair, Metal Replace Retrofit, Eliminate Deflection Joint Substructure Clean Seal Rehabilitate Rehabilitate, Pier Cap Repair, Cathodic Protection Repair, Concrete Repair, Epoxy-Inject Reinforced Concrete Cracks Repair, Masonry, Repoint Repair Pile, Reinforced Concrete Jacket Repair, Steel Pile Repair, Timber Repair, Underpin in Stream Repair, Wingwall Replace, Panel, MSE Wall Replace, Reinforced Concrete Substructure Replace, Timber Retrofit, Timber Retrofit, Weepholes in MSE Wall Retrofit, Widen Reinforced Concrete Cap/Bearing Seat Component Cyclic Condition-Driven Superstructure Clean Seal Paint Paint, Spot or Zone Rehabilitate Repair Repair, Concrete Repair, Concrete Beam End Repair, Concrete Crack Seal, Inject Repair, Prestressed Concrete Beam Repair, Steel Repair, Steel Beam End Repair, Steel, Crack, Repair/Arrest Repair, Timber Replace, Reinforced Concrete Replace, Steel Replace, Timber Retrofit, Steel Truss Retrofit, Strengthen, Concrete Retrofit, Strengthen, Steel Table 4. (Continued). The period from initiation of preservation at a bridge to the time of replacement of a bridge is the analysis period for PCCA. This period is the preservation cycle. When a bridge is replaced, a new preservation cycle begins. PCCA follows the events and costs associated with bridge preservation. The preservation cycle has three general events: 1. Bridges are added to the preservation population. 2. Preservation actions are performed. 3. Bridges are replaced. 1. Bridges are added to the preservation population. A preservation program operates on a population of bridges that a bridge owner elects to keep in service, that is, bridges not programmed for replacement. These bridges are in fair
Bridge Preservation 7 Activity Detail Abbreviation Inspection Inspection and evaluation in support of selection of treatment for bridge deck I&E Pr ot ec tio n Surface sealer Silane, Siloxane SeSi Methyl methacrylate SeMm Epoxy SeEp Thin polymer overlay Epoxy OvThEp Polyester OvThPe Methyl methacrylate OvThMm Polymer overlay Polyester concrete OvPpc Hot mix asphalt (HMA) plus membrane Preformed membrane OvHma+MLiquid membrane Portland cement overlay Portland cement concrete (PCC), dense OvPccD PCC, latex-modified OvPccLm PCC, microsilica or fly ash OvPccSm Re pa ir Patch T0 - Shallow spall T1 - Spall above top mat of reinforcing steel RpPcT1 T2 - Spall below top mat of reinforcing steel RpPcT2 T3 - Full-depth spall RpPcT3 Cracks Injection of binder RpCrEp Gravity-feed or floodcoat of binder SeMm SeEp Timber Local repairs in timber decks RpTm Steel Local repairs in steel grid decks RpSt Table 5. Actions and bases: Deck Guide. or good condition with adequate traffic capacity and load capacity. These bridges are the preservation population. Each bridge in the preservation population is an asset put into the preservation program. Each bridge was built to meet demands for service along a route. The costs of construction of the bridge are not costs to the preservation program. In PCCA, the cost of initial construction of a bridge is a sunk cost. 2. Preservation actions are performed. Actions are taken to preserve fair or good condition. To plan for bridge preservation, actions are anticipated, and costs are estimated. To assess ongoing bridge preservation, histories of actions and actual costs are used. 3. Bridges are replaced. A preservation program returns the asset it received. The value of the asset is returned intact. This will usually require bridge replacement. The cost to replace a bridge in-kind is a preser- vation cost. Determining Benefits of Bridge Preservation To determine the benefits of bridge preservation, compare the cost of bridge service without preservation with the cost of bridge service with preservation. Without preservation, there is a single cost, bridge replacement. With preservation, there is a cost for bridge replacement plus costs for preservation actions during service. Without preservation, service life is shorter. With preservation, service life is longer. Longer service life can offset the costs of preservation actions. The benefit of bridge preservation is computed as the difference in cost of service. Costs can be compared as present-value costs or as annualized costs.
8 Proposed AASHTO Guides for Bridge Preservation Actions Eq. 1 PV Benefit PV Cost PV Cost Annual Benefit Annual Cost Annual Cost No Preservation Preservation No Preservation Preservation = â = â where: PV Benefit is the difference in present-value costs. A positive benefit indicates that preservation yields a lower present-value cost to the bridge owner. PV CostNo Preservation is the present value of the cost of bridge service without preservation. PV CostPreservation is the present value of the cost of bridge service with preservation. Annual Benefit is the difference in annualized costs. A positive benefit indicates that preservation yields a lower annualized cost to the bridge owner. Annual CostNo Preservation is the annualized cost of bridge service without preservation. Annual CostPreservation is the annualized cost of bridge service with preservation. PCCA Scope Costs may be evaluated for an entire bridge or for a major component of a bridge. The bridge as a whole or a bridge component is the subject of cost evaluation. The actions included in PCCA correspond to an entire bridge or to bridge components as appropriate to the evalua- tion (see Table 6). Total Costs There are total costs for each alternative: Eq. 2 Preservation Cost Cost Cost No Preservation Cost Cost Preservation Replace Action i No Preservation Replace â( )= + = where: CostPreservation is the total cost of service with preservation. CostReplace is the cost of future replacement of a bridge or bridge component. Î£(CostAction)i is the total cost of preservation actions. Each action, i, has a cost. These are summed for all actions applied in service. CostNo Preservation is the total cost of service without preservation. Actions with Preservation Action Without Preservation Deck ( Superstructure ( Substructure ( Bridge (entire) ( Table 6. Alternatives: actions.
Bridge Preservation 9 Present-Value Costs Present-value costs for preservation actions and future replacement of bridges or bridge com- ponents are computed. Present-value costs are obtained for bridge service with preservation and bridge service without preservation. The years of future actions and eventual replacement of bridges or bridge components are estimated. 1 1 1 Eq. 3 Preservation PV Cost Cost r Cost r No Preservation PV Cost Cost r Preservation Replace T Action i T No Preservation Replace T P i B â( ) ( ) ( ) ( ) = + + + = + where: r is the discount rate. TP is the service life in years of a bridge or bridge component with preservation. Ti is the year of application of preservation action i. TB is the service life in years of a bridge or bridge component without preservation. This is called basic service life. The Bridge Guide presents examples of PCCA applied to bridge preservation. These examples are as follows: â¢ Preservation plan and PCCA for a prestressed concrete multibeam bridge â¢ Preservation plan and PCCA for a painted steel multibeam bridge â¢ Annual budget for preservation of candidate bridges â¢ Subset PCCA to compare alternatives in preservation of reinforced concrete deck â¢ Subset PCCA to compare alternatives in preservation of painted steel superstructure â¢ Sensitivity of outcomes of PCCA The Deck Guide presents examples of PCCA applied to deck treatments. These examples are as follows: â¢ Use of thin polymer overlay on a bridge deck in good condition â¢ Re-application of thin polymer overlay on a bridge deck in good condition â¢ Use of a PCC overlay on a deck in fair condition â¢ Use of a PCC overlay on a deck in poor condition