BRIDGE MAINTENANCE LEVEL-OF-SERVICE OPTIMIZATION. Tommy K. Morrow Graduate Research Assistant. and. David W. Johnston Professor of Civil Engineering

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1 BRIDGE MAINTENANE LEVEL-OF-SERVIE OPTIMIZATION by Tommy K. Morrow Graduate Research Assistant and David W. Johnston Professor of ivil Engineering Research Project 93-8 Final Report in cooperation with the North arolina Department of Transportation and the United States Department of Transportation Federal Highway Administration ENTER FOR TRANSPORTATION ENGINEERING STUDIES Department of ivil Engineering North arolina State University Raleigh, North arolina July 1993 i

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3 The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the North arolina Department of Transportation or the Federal Highway Administration. The report does not constitute a standard, specification, or regulation. iii

4 AKNOWLEDGEMENTS The research documented in this report has been sponsored by the North arolina Department of Transportation in cooperation with the United States Department of Transportation, Federal Highway Administration through the enter for Transportation Engineering Studies. The authors express sincere appreciation to Mr. Jimmy D. Lee of the North arolina Department of Transportation for sharing his expertise in the field of bridge management and his support throughout the project. Many others within NDOT and FHWA provided guidance and information which made the project possible. For their efforts, gratitude is extended to Mr. Pat Strong, Mr. Paul Simon, Mr. George Phillips, Mr. Vance Wrenn, Mr. John Jefferies, Mr. Jim Barnhill, Mr. Ron orter, Mr. Dan Holderman, Mr. Jack Edgeton, Mr. Lin Wiggins, Mr. Larry ordell, and Mr. Bobby Spence. iv

5 TABLE OF ONTENTS Page LIST OF TABLES... vii LIST OF FIGURES... viii 1. INTRODUTION Bridge Management Systems NDOT Need for Routine and Preventive Maintenance Strategy urrent Practice oncerning Routine and Preventive Maintenance Proposed Method of Strategy Development REVIEW OF LITERATURE AASHTO BMS Recommendations for Maintenance Approaches Taken by Others Algorithm for Selection of Optimum Policy (ASOP) Previous Work with ASOP OPTIMIZATION METHODOLOGY MAINTBRG / ASOP Analysis Bridge Maintenance Model Elements onsiderations onditions Alternate Levels of Service Resource Requirements Value Tradeoff Assessment Algorithm omputations Analysis Output Program Modifications EVALUATION OF ANALYSIS RESULTS Selected Strategy Discussion of Results...38 v

6 5. ONLUSIONS AND REOMMENDATIONS onclusions Recommendations LIST OF REFERENES APPENDIES Definition of Special Terms Used in the MAINTBRG Analysis Maintenance Work Function ode Descriptions Maintenance Level of Service Descriptions RESNEEDS Users Manual RESNEEDS Program ode Listing RESNEEDS Output Example Typical Maintenance Work and ondition Rating Improvements Assessed Desirability for Each Level of Each Attribute MAINTBRG User Information and Input Example MAINTBRG Program ode Listing MAINTBRG Output Example vi

7 LIST OF TABLES Table Page 3.1 MAINTBRG Model Inputs Annual Resource Requirements to Achieve Each Level of Service alculation of Each Attribute Relative Weight for ase alculation of Each Attribute Relative Weight for ase Attribute Best, Midvalue, and Worst Values for Each Element Selected Maintenance Strategy for ase Selected Maintenance Strategy for ase Bridge Element Maintenance Work Function ode Descriptions Descriptions of the Alternate Levels of Service Equations for Estimated Average Unit ost (EAU) of Bridge Maintenance Estimated Average Unit ost (EAU) of Bridge Maintenance Average Time Elements Remain at ondition Ratings Without Maintenance Average ondition Rating Improvement due to Maintenance NDOT Bridge Maintenance Unit Annual Expenditures by Element Input Data ard Summary for DETRIMPR Data File Input Data ard Summary for UNITOST Data File Average Element ondition Rating with Maintenance Work Assessed Desirability for Each Level of Each Attribute vii

8 LIST OF FIGURES Figure Page 3.1 RESNEEDS Methodology Overview Mid-Value Attribute Level Overview of the MAINTBRG Algorithm RESNEEDS Methodology Overview EAU vs ondition Rating...93 viii

9 1. INTRODUTION 1.1 Bridge Management Systems The purpose of a Bridge Management System (BMS) is to help transportation agencies evaluate current and future conditions and needs and determine the best mix of maintenance and improvement work on a road network over time with and without budget limitations (Hyman and Thompson, 1992). The development of the BMS has come about through necessity, as replacement and repair needs continue to grow and out pace resources available for these tasks, bridge managers must use limited funds in the best possible way. The BMS provides assistance to managers in making the complex decisions concerning maintenance, rehabilitation, replacement, and improvement of bridges. 1.2 NDOT Need for Routine and Preventive Maintenance Strategy The North arolina Department of Transportation (NDOT), Bridge Maintenance Unit has developed and implemented a BMS (Johnston, 1992) with the objective of meeting AASHTO Guidelines for Bridge Management Systems (1992). One part of this is continuing development of a tool to assist in the formation of a strategy for routine and preventive maintenance of bridges. This would complement OPBRIDGE, a tool in the existing analysis system which is focused at rehabilitation and replacement decision support (Al-Subhi, Johnston, and Farid, 1989). Within the NDOT Bridge Maintenance Unit, the Area Maintenance Supervisors are charged with the task of developing work plans for the routine and preventive 1

10 maintenance of bridges within their area. The maintenance needs identified and recorded during inspections far exceed the available resources provided for this type of work. At the time of this study, the recorded maintenance needs backlog for bridge elements exceeded $100,000,000 while the average annual expenditures for these same elements was approximately $8,500,000. The managers and Area Maintenance Supervisors within NDOT realize the need to allocate the available resources to the maintenance activities which will provide the most benefit considering the budget constraints and the bridge network as a whole. This need is the driving force behind development of a decision assistance tool to help form a maintenance strategy. 1.3 urrent Practice oncerning Routine and Preventive Maintenance Decisions regarding maintenance are generally made by maintenance personnel in an informal, intuitive manner, based on experience (Kulkarni and Van Til, 1984). This general trend has also been prevalent within the NDOT Bridge Maintenance Unit. While individual experience is invaluable in making bridge maintenance decisions, the NDOT Bridge Maintenance Unit recognizes that a more formal, systematic, and defendable procedure to assist in the development of bridge maintenance strategy is needed. 1.4 Proposed Method of Strategy Development In a previous research effort (Nash and Johnston, 1985) sponsored by NDOT, the Algorithm for Selection of Optimum Policy (ASOP) was explored for use in bridge 2

11 maintenance. Although the analysis was conducted using approximate data, the study concluded that it was feasible to apply ASOP to the bridge maintenance problem. The recommendations resulting from the study included an expanded list of maintenance elements for which condition ratings and maintenance needs are recorded. These recommendations have been carried out to allow for a more structured and detailed analysis herein. The proposed methodology, MAINTBRG, includes a modified and expanded version of the ASOP program as developed by Kulkarni, Finn, Golabi, Johnson, and Alviti (1980). ASOP utilizes a level of service approach in the determination of optimum maintenance strategy. A maintenance level of service is defined as a threshold level of maintenance condition that should trigger an appropriate maintenance activity (Kulkarni and Van Til, 1984). The analysis procedure considers the assessed value tradeoffs of maintaining certain bridge elements at higher levels of service while other elements must be maintained at lower levels when operating under a constrained budget. An optimum maintenance level of service strategy may be determined for various budget levels. The analysis utilizes bridge inspection and maintenance cost data in the form currently available within NDOT. 3

12 2. REVIEW OF LITERATURE 2.1 AASHTO BMS Recommendations for Maintenance AASHTO Guidelines for Bridge Management Systems (Hyman and Thompson, 1992) recommends minimum requirements for an effective BMS and suggests various approaches to meet these requirements. Several features concerning routine and preventive maintenance, which are considered essential for an effective BMS, are discussed in this section. The AASHTO guidelines classify bridge maintenance in two categories, maintenance, repair, and rehabilitation (MR&R) actions and improvement actions. MR&R actions are primarily a response to deterioration and include small actions such as bearing repair, spot-painting, and deck patching, as well as large actions such as replacement of large structural elements. Improvement actions are primarily a response to user demands and include widening, strengthening, and raising. The type of work considered in this research is defined as routine and preventive maintenance and generally corresponds to MR&R actions. However, the definition of routine and preventive maintenance does not include replacement of large structural elements or complete bridges which, in the North arolina BMS, is addressed by OPBRIDGE. An effective BMS should provide for an expanded database which contains more detailed information on element types, quantities, and condition than is required for the national bridge inventory. Typical elements should include deck, joints, railings, girders, bearings, abutments, and piers. The detailed element level information is essential for development of strategy concerning routine and preventive maintenance work of bridge 4

13 elements. This information can be used to identify the quantity of elements at deficient condition levels which require maintenance work. The ability to identify funding requirements to bring bridges from their current condition to desired service levels is identified as a requirement for an effective BMS. This necessitates the identification of both quantities of maintenance work required and the cost of performing the work. Data concerning quantity and cost of maintenance work completed should be recorded for use in determining the cost of performing future maintenance work. The quantities of maintenance work required should be identified during bridge inspections. The AASHTO guidelines state that a BMS should include a computerized database and decision support tool that supplies analyses and provides means by which alternative policies may be considered. The database and decision support tool play a very important role in the development of routine and preventive maintenance strategy. The decision support tool should provide for compilation of bridge element condition and maintenance needs data in a form useful to bridge managers. 2.2 Approaches Taken by Others Various approaches have been taken by others in BMS development to achieve optimization of bridge maintenance work expenditures. Two of the systems reviewed as a part of this research include the Pennsylvania DOT BMS and PONTIS. Prioritization of maintenance work is accomplished by the Pennsylvania DOT system through the use of deficiency point assignment to individual bridges based on 5

14 activity ranking, activity urgency, bridge criticality, and bridge adequacy. Activity ranking is related to the importance of the maintenance need, such as stringer repair versus application of protective coatings. Activity urgency relates to the severity of a deficiency. The importance of the bridge in the road network is represented by the bridge criticality. The bridge adequacy is a measure of the condition of the bridge as well as it's ability to carry loads necessary for the route. After deficiency points are assigned to each bridge, prioritization of maintenance work is accomplished by ranking bridges and their corresponding maintenance needs according to their assigned deficiency points. The PONTIS system (Golabi, Thompson, and Hyman, 1992) includes a maintenance, repair, and rehabilitation (MR&R) optimization model which determines, for each bridge element, the policy which minimizes the long-term maintenance funding requirements while keeping the element out of risk of failure. The optimization of MR&R is based on a Markov decision model for each element type. A probalistic deterioration model must be defined for each element type. The optimal maintenance work policy is taken to the project level and all bridges selected for MR&R are identified. When budget constraints exist, a set of bridges needing MR&R are identified with total cost within a specified budget. The selection of bridges for MR&R, under a constrained budget, is based on a benefit to cost ratio of performing maintenance work on the bridge elements. The benefit of performing maintenance work is considered to be the savings of future expenditures compared to the alternative of not performing the maintenance work during the current budget period. 6

15 2.3 Algorithm for Selection of Optimum Policy (ASOP) The ASOP analysis, as developed by Kulkarni, Finn, Golabi, Johnson, and Alviti (1980) has as its purpose the optimization of maintenance levels of service for various highway elements (such as pavement, shoulder, vegetation, drainage structures). Alternate maintenance levels of service define a maintenance effort for each of the elements and this effort must be considered in the preparation of budgets and work plans. The determination of optimal policy may take into account such considerations as safety, riding comfort, economics, environmental impact, preservation of investment, and aesthetics. onstraints on available resources are also recognized in the analysis. Resource constraints may prevent maintenance of all elements at the most desirable condition, therefore tradeoffs between different elements become necessary. The tradeoffs recognize which maintenance elements are to be allowed to deteriorate to less than desirable conditions while others are maintained at higher levels when funding is not adequate to obtain desirable maintenance levels for all elements. This research recognizes that maintenance decisions are generally made by maintenance personnel in an informal manner and may be less than optimal considering the complex issues involved and the possibility of inconsistent decisions. ASOP provides a systematic and objective method to establish maintenance levels of service guidelines for maintenance elements of a highway system. This type of strategy development is a tool that can be used to ensure uniformity of maintenance levels within a statewide system. 7

16 2.4 Previous Work with ASOP Nash and Johnston (1985) explored the possibility of using a level of service approach for the determination of optimum strategy for routine and preventive maintenance of bridges under constrained funding. In this work, the Algorithm for Selection of Optimum Policy (ASOP) (Kulkarni and Van Til, 1984) was modified for use by NDOT in the bridge maintenance strategy selection problem. The study concluded that it was feasible to apply ASOP to the bridge maintenance problem. However, in this research, the ASOP analysis was limited to a maximum of 10 elements. It was recognized that in order to achieve the desired results increased data on the maintenance condition of each bridge would be needed as well as some improvements to the program. In 1989, NDOT revised the bridge inventory data base to accommodate FHWA required changes. At the same time, the data collection and storage for each bridge was modified to include the condition rating of over 40 bridge elements. Also bridge maintenance needs are now recorded for 37 different maintenance work activities which correspond with the bridge elements considered in the analysis. The cost and quantity of work performed is recorded by the same function codes allowing the prediction of future cost for maintenance work. 8

17 3. OPTIMIZATION METHODOLOGY 3.1 MAINTBRG / ASOP Analysis The methodology used in the determination of optimum maintenance levels of service for bridge elements is based on the methodology developed for optimizing maintenance levels of service for highway elements by Kulkarni, Finn, Golabi, Johnson, and Alviti (1980) and coded in the computer program ASOP. Many of the same difficulties arise when considering the maintenance levels of service for bridges as for the highway system as a whole. Personnel within state highway agencies responsible for maintenance of bridges must make decisions concerning the levels of service for the bridge elements (such as deck, rail, expansion joint, superstructure, substructure). These decisions must be made under budget constraints and with consideration of performance measures such as preservation of investment and safety. The analysis utilized with the ASOP program has been modified and applied to the bridge maintenance problem. The modified analysis and program are titled MAINTBRG. 3.2 Bridge Maintenance Model The model developed for optimization of maintenance strategy for bridge elements is structured in a format very similar to that detailed in NHRP Report 273, Manual for the Selection of Optimal Maintenance Levels of Service (1984). The NHRP 273 report provides a detailed, step by step, process by which the ASOP analysis should be structured for a highway system. The remainder of this section outlines the 9

18 development of the bridge maintenance model in a similar manner. The information used in the analysis was acquired through group discussions and interviews with NDOT bridge maintenance personnel involved with both inspection and performance of bridge maintenance. The input development and terminology for the bridge maintenance model follow the NHRP Report 273 guidelines very closely and these guidelines may be used to supplement this documentation. Some simplification of the model was possible for the bridge element analysis because the problem concerns fewer considerations than are identified with the highway system as a whole. Some simplification of the model was also required because of the information available to structure the model. A defined objective of the research was to develop a system capable of using information currently available to the NDOT Bridge Maintenance Unit within the North arolina Bridge Inventory (NBI) data base or through the accounting system. Appendix 7.1 provides a reference for definitions of special terms used in the MAINTBRG analysis Elements The selection of bridge elements considered in the analysis was based on identification of physical bridge elements which require a substantial maintenance effort and for which condition and maintenance cost information is available. ondition information is available for bridge elements within the NBI data base and is recorded for approximately 40 bridge elements during routine inspections. The condition information is recorded in the form of a condition rating, which ranges from 0 to 9, 10

19 representing conditions from failed to excellent. Maintenance needs and cost of work performed data is recorded by the use of approximately 37 function codes which identify types of maintenance work. Many of the function codes correspond to the various bridge elements thus providing for a system to track maintenance expenditures and needs to element types. Twenty one bridge elements were selected for the analysis. See Table 3.1 for a listing of the elements selected and other model inputs discussed in subsequent sections. A listing of the function codes and maintenance work descriptions corresponding to the elements considered in the analysis are in Appendix onsiderations A consideration is defined as a factor that is used to evaluate the performance of a bridge maintenance element and to establish a level of service. The consideration chosen for each of the bridge maintenance elements consists of two parts. Preservation of investment and safety were both identified as important factors in measuring performance and establishing levels of service for each of the bridge elements. The ASOP analysis provides the ability to apply multiple considerations to each of the maintenance elements. The MAINTBRG analysis is structured with only a single consideration for each bridge element because condition and resource requirement data available for the alternate levels of service did not support a more detailed analysis. With the existing system, it is not possible to determine if maintenance work expenditures for an element were attributable to preservation of investment or safety. For most elements, the maintenance consideration at the lower levels of service is safety while the consideration is preservation of investment at the higher levels. ondition information for the elements is 11

20 based on types of deterioration which may affect preservation of investment, safety, or a combination of both. 12

21 Table 3.1 MAINTBRG Model Inputs Bridge Maintenance Element Maintenance Element onsideration 1. oncrete Deck Preservation of - Safety Attribute of the onsideration 1. Extended Service Life Maintenance ondition Variables Affecting Attribute 1. racking, Scaling, Spalling, Efflorescence, Delamination, orrosion of Reinforcing Steel Parameters for Defining Maintenance ondition rack Type, Area Affected, Number of Occurrences Alternate Maintenance Levels of Service R = 7 R = 6 R = 5 R = 4 R = 3 2. Timber Deck Preservation of - Safety 2. Extended Service Life 2. Loose Floor Boards, Split and Broken Floorboards, Decayed Floorboards and Nailers Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = 3 3. Steel Plank Deck Preservation of - Safety 3. Extended Service Life 3. orrosion of Steel Planks, Loose Steel Planks or Broken Welds, Asphalt Deterioration Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = 3 4. Open Grid Steel Deck Preservation of - Safety 4. Extended Service Life 4. Deterioration of Galvanic oating or Paint, Worn or Missing Studs, racked or Broken Welds, Grid Deterioration, Debris Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = 3 13

22 Table 3.1 ontinued. Bridge Maintenance Element Maintenance Element onsideration 5. oncrete Rail Preservation of - Safety Attribute of the onsideration 5. Extended Service Life Maintenance ondition Variables Affecting Attribute 5. racking, Scaling, Spalling, Efflorescence, Delamination, orrosion of Reinforcing Steel, Loose or Missing Sections Parameters for Defining Maintenance ondition rack Type, Length Affected, Number of Occurrences Alternate Maintenance Levels of Service R = 7 R = 6 R = 5 R = 4 R = 3 6. Timber Rail Preservation of - Safety 6. Extended Service Life 6. racking, Decay, Loose or Broken Boards or Posts, Timber Dried Out Length Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = 3 7. Aluminum Rail Preservation of - Safety 7. Extended Service Life 7. Oxidation, Accident Damage, Loose or Missing Anchors, Broken Rail or Posts, Misalignment Length Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = 3 8. Steel Rail Preservation of - Safety 8. Extended Service Life 8. orrosion, Accident Damage, Loose or Missing Anchors, Broken Rail or Posts, Misalignment Length Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = 3 14

23 Table 3.1 ontinued. Bridge Maintenance Element Maintenance Element onsideration 9. Steel Plate or Finger Type Exp. Jnt. Preservation of - Safety Attribute of the onsideration 9. Extended Service Life Maintenance ondition Variables Affecting Attribute 9. Presence of Debris, Loose or Broken Anchors, Loose or racked Plates, Misalignment, Frozen Joints, Missing Fingers Parameters for Defining Maintenance ondition Length Affected, Number of Occurrences Alternate Maintenance Levels of Service R = 7 R = 6 R = 5 R = 4 R = Misc. Prefabricated Exp. Jnt. Preservation of - Safety 10. Extended Service Life 10. Presence of Debris, Loose or racked Anchors, Leakage, Torn or Missing Seal Membrane, Misalignment Length Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = ompression Seal Exp. Jnt. Preservation of 11. Extended Service Life 11. Presence of Debris, racking of Adjacent oncrete, Loose or Torn Seal, Leakage, Misalignment Length Affected R = 7 R = 6 R = 5 R = 4 R = Standard Deck Exp. Jnt. Preservation of 12. Extended Service Life 12. Presence of Debris, racked or Loose Seal, Leakage Length Affected R = 7 R = 6 R = 5 R = 4 R = 3 15

24 Table 3.1 ontinued. Bridge Maintenance Element Maintenance Element onsideration 13. oncrete Superstructure Preservation of - Safety Attribute of the onsideration 13. Extended Service Life Maintenance ondition Variables Affecting Attribute 13. racking, Scaling, Spalling, Efflorescence, Delamination, orrosion of Reinforcing Steel Parameters for Defining Maintenance ondition rack Type, Area Affected, Number of Occurrences Alternate Maintenance Levels of Service R = 7 R = 6 R = 5 R = 4 R = Steel Superstructure Preservation of - Safety 14. Extended Service Life 14. orrosion, Section Loss, Traffic Damage Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = P/S oncrete Superstructure Preservation of - Safety 15. Extended Service Life 15. racking, Spalling, Efflorescence, Delamination, orrosion of Reinforcing Steel rack Type, Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = Timber Superstructure Preservation of - Safety 16. Extended Service Life 16. Decay, Splitting, racking, Insect Infestation Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = 3 16

25 Table 3.1 ontinued. Bridge Maintenance Element Maintenance Element onsideration 17. Timber Substructure Preservation of - Safety Attribute of the onsideration 17. Extended Service Life Maintenance ondition Variables Affecting Attribute 17. Weather racking, Decay, Delamination, Settlement, Timber Dried Out Parameters for Defining Maintenance ondition Area Affected, Number of Occurrences Alternate Maintenance Levels of Service R = 7 R = 6 R = 5 R = 4 R = oncrete Pile Substructure Preservation of - Safety 18. Extended Service Life 18. Scaling, racking, Spalling, Delamination, Settlement rack type, Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = Steel Pile Substructure Preservation of - Safety 19. Extended Service Life 19. orrosion, racks in Welds, Bends or Tears in Flanges, Settlement, Misalignment Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = oncrete Piers and Abutments Preservation of - Safety 20. Extended Service Life 20. Scaling, racking, Spalling, Delamination, Settlement rack Type, Area Affected, Number of Occurrences R = 7 R = 6 R = 5 R = 4 R = 3 17

26 Table 3.1 ontinued. Bridge Maintenance Element Maintenance Element onsideration 21. Paint System (Structural Steel) Preservation of Attribute of the onsideration 21. Extended Service Life Maintenance ondition Variables Affecting Attribute Parameters for Defining Maintenance ondition 21. orrosion Area Affected Alternate Maintenance Levels of Service R = 7 R = 6 R = 5 R = 4 R = 3 18

27 Although the cost of maintenance is an important consideration in the usual sense, it is not included in the considerations chosen for analysis because maintenance costs are viewed as constraints on the system rather than user related considerations. The cost of maintenance is accounted for in a subsequent optimization part of the model. An attribute is defined as a descriptor that is capable of expressing the level of a consideration. The attribute identified for each of the bridge maintenance elements is extended service life. The selection of this attribute is based on the premise that bridge elements that are maintained at higher levels continue to perform in an acceptable manner longer than elements maintained at lower levels. Extended service life may be due to a reduced rate of deterioration caused by preventive maintenance work or the ability of an element to remain in service at acceptable performance levels because of improvements due to maintenance work onditions The condition of a bridge element is measured through the use of a condition rating. For each bridge maintenance element, several different types of deterioration may be present. The different types of deterioration are identified and are noted as condition variables. The condition rating takes into account the several different types of deterioration and provides the maintenance condition by which the maintenance levels of service are determined. Parameters are a measure for defining, in numerical or descriptive terms, the alternate levels of service of a maintenance condition. Due to the nature of condition rating data recorded for bridge elements, the parameters are generally identified in broad terms. The condition ratings of bridge elements encompass several factors. A condition 19

28 rating must take into account the type of deterioration, the extent to which the element is effected, and the severity of the deterioration. ombining these factors into one number precludes the use of detailed parameter measurements Alternate Levels of Service The alternate levels of service chosen for each bridge maintenance element are the conditions corresponding to condition ratings 3 through 7 and are referred to as level of service 3 through 7. ondition descriptions of each level of service for each element may be found in Appendix 7.3. These descriptions were developed in conjunction with bridge inspection personnel within the NDOT Bridge Maintenance Unit. The condition rating descriptions are intended to generally correspond with the descriptions provided in the Recording and oding Guide for the Structure Inventory and Appraisal of the Nation's Bridges (1988) for general condition ratings used as a guide in evaluating deck, superstructure, and substructure items. The effect each alternate level of service has on the consideration of the corresponding element must be defined. This effect is estimated in terms of the attribute of the element consideration. Due to the structure of the model, only one consideration was established for each element. Also only one condition is applicable to each element. Therefore the effect of the alternate levels of service in terms of the attribute were defined in a one to one manner. Five attribute levels are defined and the five levels of service directly correspond to the five attribute levels. For example, the effect level of service 7 (highest level of service) has on the consideration is attribute 1 (highest attribute level). 20

29 3.2.5 Resource Requirements The resource requirements to achieve each level of service for each of the elements is a required input. During the previous ASOP application by Nash and Johnston (1985), a need was identified for a tool to develop an estimate of these resource requirements. A computer program titled RESNEEDS was developed herein to meet this need. The RESNEEDS program uses condition, maintenance needs, and other element data available in the NBI data base along with supplemental information concerning element deterioration rates and condition improvements due to maintenance work to calculate estimates of resource requirements to achieve each level of service for each element. The following discussion provides an overview of the methodology utilized by the RESNEEDS program. Figure 3.1 illustrates a model and example for discussion of the program methodology. In the determination of annual resource requirements, the analysis considers annual maintenance work which must be performed to eliminate the maintenance needs backlog and maintenance work for element units which cross the level of service threshold each year. The maintenance needs backlog is defined as maintenance work to be performed on element units which have a condition rating less than or equal to the subject level of service. Each container in the model represents the amount of units an element has at each condition rating in a year during the analysis period. The variable container widths are used to simulate the variable time element units remain at each condition rating. 21

30 Figure 3.1 RESNEEDS Methodology Overview The analysis calculates the amount of element units which transition from one condition rating to another due to deterioration during a year and this is represented by the small arrows leading from one condition rating to another and the variable ELUNTRDN. The amount of units which transition is determined by the amount of element units with a condition rating and the deterioration rate for the element at the condition rating. The element units which transition through the level of service threshold in a year require maintenance work. For this example, the subject level of service is 4. Therefore all element units which transition from condition rating 5 to condition rating 4 require maintenance work in the year of transition. Maintenance work generally provides for an improvement in condition rating and in the example the element units receiving this maintenance work are improved from a condition rating of 4 to a condition rating of 8. These units are represented by the variable QDELN. The annual maintenance work requirement due to 22

31 backlog removal is determined by calculating the total amount of element units with a condition rating equal to or less than the subject level of service at the beginning of the analysis period and then performing maintenance work for an equal amount of these element units each year over the defined backlog period. The quantity of units receiving annual maintenance work in the backlog is represented by the variable QBKLOG and in this example the improvement is from a condition rating of 3 to 9. The backlog removal period is a user defined variable within the program and for the current analysis equals 5 years for each of the expansion joint types and 10 years for all other elements. The annual cost of performing work is determined by multiplying the annual quantity of work by an average unit cost of performing maintenance work for the element at the condition rating before maintenance work is performed. The RESNEEDS program calculates this average unit cost of performing maintenance work based on inspectors estimates of maintenance needs which are recorded in the NBI data base. In this analysis, the maintenance work requirement will change from year to year as progress is made in achieving a level of service. As the maintenance backlog is reduced a shift of element units to the higher condition ratings will occur. This will result in a larger amount of element units passing through the level of service threshold each year, thus requiring more maintenance work at the level of service condition rating. The backlog removal maintenance work is performed on the elements units remaining in the backlog with the lowest condition rating each year. As time passes, the units remaining in the backlog have a higher condition rating and require work at a lower cost. Due to the year to year change in annual resource requirements to perform maintenance work, the analysis is performed over a defined time horizon and an average cost of 23

32 maintenance work is calculated. The following provides a summary of the analysis process. The analysis begins with the element unit distribution as currently represented in the NBI data base. Element unit transition due to deterioration and maintenance work is calculated for the first year of the analysis period. The resource requirement to perform identified maintenance work is calculated for the year. A new element unit distribution is calculated for the beginning of the next year based on the element unit transition and unit distribution in the previous year. The process is repeated for a defined analysis period and the average resource requirements are calculated. The resource requirements as determined by the RESNEEDS program and modified as required are shown in Table 3.2. The RESNEEDS analysis uses the unit costs of maintenance work contained within the NBI data base. These costs are updated annually, therefore the resource requirements are in current dollars. Appendix 7.4 is a program users manual for RESNEEDS and contains a detailed description of the methodology utilized and user information. 24

33 Table 3.2 Annual Resource Requirements to Achieve Each Level of Service. Bridge Maintenance Element Annual Resource Requirements to Achieve Each Levelof-Service (Thousands) oncrete Deck $1,295 $2,482 $4,367 $5,787 $7,323 Timber Deck $1,067 $1,360 $1,859 $2,103 $2,499 Steel Plank Deck $133 $172 $278 $320 $352 Open Grid Steel Deck $4 $8 $17 $23 $30 oncrete Rail $21 $56 $138 $189 $248 Timber Rail $206 $360 $721 $953 $1,210 Aluminum Rail $3 $5 $7 $13 $26 Steel Rail $17 $35 $95 $129 $173 Steel Plate or Finger Type Exp. Jnt. $44 $56 $67 $72 $84 Miscellaneous Prefabricated Exp. Jnt. $101 $154 $206 $275 $328 ompression Seal Exp. Jnt. $75 $112 $179 $226 $278 Standard Deck Exp. Jnt. $380 $696 $1,025 $1,492 $1,814 oncrete Superstructure $130 $321 $566 $775 $993 Steel Superstructure $315 $558 $1,105 $1,449 $1,844 P/S oncrete Superstructure $94 $97 $141 $158 $182 Timber Superstructure $403 $565 $706 $861 $1,013 Timber Substructure $1,192 $1,908 $2,798 $3,572 $4,375 oncrete Pile Substructure $121 $140 $191 $221 $256 Steel Pile Substructure $51 $63 $82 $96 $112 oncrete Piers and Abutments $461 $997 $1,693 $2,282 $2,898 Paint System (Structural Steel) $2,906 $4,019 $5,264 $6,221 $7,400 Total $9,019 $14,164 $21,505 $27,217 $33,438 The resource requirements determined by the RESNEEDS program should be reviewed and compared with recent annual expenditures for the elements. Adjustments based on past expenditures and experience may be required. The RESNEEDS program uses maintenance needs estimates to develop the resource requirements. However the actual expenditures for several maintenance elements considerably exceed what might be expected based on the inspector estimated maintenance needs. Thus, the RESNEEDS 25

34 resource requirement estimates are sometimes lower than actual historical work action data. For example, at the time of analysis, total estimated maintenance needs for timber rails was approximately $110,000 while the recent average annual expenditure for this element was approximately $720,000. The large annual expenditure compared to the estimated maintenance needs is at least partly attributed to painting. The inspectors do not record painting as a maintenance need, but the cost of painting is charged to the function code for this element. In this case, either the resource requirements for timber rails must be adjusted upward to more closely reflect what expenditures might be expected for this element or the inspection data collection must be modified Value Tradeoff Assessment The relative desirability or value of the different levels of each element attribute must be determined for use in the analysis. This tradeoff information is used in the analysis to determine which elements are maintained at higher levels of service while other elements are maintained at lower levels when budget constraints exist. The desirability of each attribute level was assessed for each element through formal group discussion with NDOT bridge maintenance personnel. Attribute level desirability may be defined as how much better or worse one level of an attribute is relative to another level of the same attribute concerning performance of the related consideration. The desirability of each attribute level was measured through assessment of willingness to pay to achieve each attribute level. The participants of the work group were provided with information concerning current element conditions, which correspond to attribute levels, and the percent of the current budget expended on each of 26

35 the elements. The work group members were then asked what percentage of the budget they would be willing to pay to achieve each of the alternate attribute levels. The work group members were encouraged to engage in discussion concerning why they consider alternate attribute levels to be better or worse than other levels. Discussion continued until a consensus was reached by the group about the percent of the budget the group members would be willing to pay to achieve each of the attribute levels for each of the elements. The assessment data is contained in Appendix 7.8. This data must be further processed for use in the MAINTBRG program. The relative weight of each attribute is determined by the difference between the assessed percentage of the budget work group members were willing to pay for the lowest and the highest level of each attribute and provides a measure of importance of each element attribute relative to all others. Two sets of relative weight values were developed to provide alternate case analyses and ascertain the affect of changes in the relative weight values on the selected strategy. The ranking of the element attribute relative weights remains approximately the same for both cases. For example, paint system and standard deck expansion joints still have the highest relative weight and open grid steel deck and aluminum rail have the lowest relative weight. The relative weight values for case 2 vary in range to a much larger degree than those developed for case 1. The range of the relative weight values for case 2 are intended to more closely parallel the range of values for resource requirements to actually achieve the attribute levels. Larger relative weights are applied to attributes which have greater resource requirements to go from the lowest to the highest attribute levels, while smaller relative weights are applied to attributes which have smaller resource requirements to go from the lowest to the highest attribute 27

36 levels. Each of the attribute relative weights are calculated for case 1 as shown in Table 3.3 and case 2 as shown in Table 3.4. Individual values provide information concerning the value of each attribute level relative to other levels of the same attribute. Information concerning individual attribute values must be developed for use in the program by determining the high, midvalue, and low attribute levels. The high and low attribute levels for this model are always 1 and 5 respectively. The determination of the midvalue level requires the calculation of a relative value for each level of each attribute. The relative values are calculated using the following equation: RelativeValue ( i, j) % Budget( i, j) % Budget( i,5) (3.1) % Budget % Budget ( i,1) ( i,5) where: Relative Value (i,j) = Relative Value of level j for attribute i. % Budget (i,j) = "Maximum % of Budget Willing to Pay" to achieve level j for attribute i. % Budget (i,1) = "Maximum % of Budget Willing to Pay" to achieve level 1 (highest level) of attribute i. % Budget (i,5) = "Maximum % of Budget Willing to Pay" to achieve level 5 (lowest level) of attribute i. The midvalue level is found by plotting the relative value versus attribute levels as shown in Figure 3.2. The attribute level corresponding to the relative value of 0.5 is selected from the plot and used as the midvalue attribute level. The individual values for each of the element attributes are shown in Table 3.5. The same individual values are used in both cases. The calculated relative values are within Appendix

37 Table 3.3 alculation of Each Attribute Relative Weight for ase 1. Bridge Maintenance Element Increase in the Maximum Percent of Total Available Budget to go from the Least to the Most Desirable Level Relative Weight of the Attribute oncrete Deck P 1 = 5.4 P 1 /P = Timber Deck P 2 = 4.0 P 2 /P = Steel Plank Deck P 3 = 2.0 P 3 /P = Open Grid Steel Deck P 4 = 0.2 P 4 /P = oncrete Rail P 5 = 0.7 P 5 /P = Timber Rail P 6 = 3.0 P 6 /P = Aluminum Rail P 7 = 0.2 P 7 /P = Steel Rail P 8 = 1.0 P 8 /P = Steel Plate or Finger Type Exp. Jnt. P 9 = 2.5 P 9 /P = Miscellaneous Prefabricated Exp. Jnt. P 10 = 2.2 P 10 /P = ompression Seal Exp. Jnt. P 11 = 1.0 P 11 /P = Standard Deck Exp. Jnt. P 12 = 6.0 P 12 /P = oncrete Superstructure P 13 = 1.7 P 13 /P = Steel Superstructure P 14 = 3.0 P 14 /P = P/S oncrete Superstructure P 15 = 0.9 P 15 /P = Timber Superstructure P 16 = 3.5 P 16 /P = Timber Substructure P 17 = 4.0 P 17 /P = oncrete Pile Substructure P 18 = 1.4 P 18 /P = Steel Pile Substructure P 19 = 0.7 P 19 /P = oncrete Piers and Abutments P 20 = 3.0 P 20 /P = Paint System (Structural Steel) P 21 = 6.0 P 21 /P = P = 3P i = P i /P = 1 29

38 Table 3.4 alculation of Each Attribute Relative Weight for ase 2. Bridge Maintenance Element Increase in the Maximum Percent of Total Available Budget to go from the Least to the Most Desirable Level Relative Weight of the Attribute oncrete Deck P 1 = P 1 /P = Timber Deck P 2 = 3.00 P 2 /P = Steel Plank Deck P 3 = 0.21 P 3 /P = Open Grid Steel Deck P 4 = 0.01 P 4 /P = oncrete Rail P 5 = 0.08 P 5 /P = Timber Rail P 6 = 1.50 P 6 /P = Aluminum Rail P 7 = 0.01 P 7 /P = Steel Rail P 8 = 0.08 P 8 /P = Steel Plate or Finger Type Exp. Jnt. P 9 = 0.05 P 9 /P = Miscellaneous Prefabricated Exp. Jnt. P 10 = 0.25 P 10 /P = ompression Seal Exp. Jnt. P 11 = 0.10 P 11 /P = Standard Deck Exp. Jnt. P 12 = 4.25 P 12 /P = oncrete Superstructure P 13 = 0.75 P 13 /P = Steel Superstructure P 14 = 2.25 P 14 /P = P/S oncrete Superstructure P 15 = 0.05 P 15 /P = Timber Superstructure P 16 = 1.00 P 16 /P = Timber Substructure P 17 = 6.25 P 17 /P = oncrete Pile Substructure P 18 = 0.10 P 18 /P = Steel Pile Substructure P 19 = 0.02 P 19 /P = oncrete Piers and Abutments P 20 = 3.50 P 20 /P = Paint System (Structural Steel) P 21 = P 21 /P = P = 3P i = P i /P = 1 30

39 Attribute Level Figure 3.2 Mid-Value Attribute Level. 3.3 Algorithm omputations This section provides an overview of the algorithm utilized in the MAINTBRG analysis to determine the optimum maintenance strategy. A nonlinear integer programming algorithm is used to solve the optimization problem. The method of implicit enumeration is utilized to perform a branch and bound search for the optimal solution. A simplified overview of this process follows. The algorithm identifies all combinations of alternative levels of service for the maintenance conditions and determines which of these combinations satisfy the constraints on available resources. For each combination identified, the attribute level of each consideration is quantified and the individual value of the attribute level is 31

40 Table 3.5 Attribute Best, Midvalue, and Worst Values for Each Element. Bridge Maintenance Element Best Midvalue Worst oncrete Deck Timber Deck Steel Plank Deck Open Grid Steel Deck oncrete Rail Timber Rail Aluminum Rail Steel Rail Steel Plate or Finger Type Exp. Jnt Miscellaneous Prefabricated Exp. Jnt ompression Seal Exp. Jnt Standard Deck Exp. Jnt oncrete Superstructure Steel Superstructure P/S oncrete Superstructure Timber Superstructure Timber Substructure oncrete Pile Substructure Steel Pile Substructure oncrete Piers and Abutments Paint System (Structural Steel) assessed on a scale of 0 (worst attribute level) to 1 (best attribute level). The relative weights of the various attributes are determined based on assessed tradeoffs between attributes. An overall weighted value of each combination is calculated ranging from 0 (all worst attribute levels) to 1 (all best attribute levels). The final stage of the analysis identifies the combination of alternative levels of service with maximum overall value. This is the optimum combination of levels of service in the sense that it maximizes overall value subject to the constraints of available resources. Figure 3.3 illustrates the algorithm process. 32

41 0 Figure 3.3 Overview of the MAINTBRG Algorithm 33

42 3.4 Analysis Output The MAINTBRG program output consists of a summary of input data and the selected maintenance strategy for the base case analysis and any sensitivity analysis options which are selected. The selected strategy output consists of a listing of each bridge maintenance element, the selected level of service, and the estimated cost to achieve the level of service. The total cost of the selected strategy, an evaluation of the attributes, and the value of the strategy are printed. A sample output listing can be found in Appendix Program Modifications The ASOP program, as previously explored by Nash and Johnston (1985) for bridge maintenance optimization, had a maximum limit of 10 maintenance elements and 100 alternate levels of service. These variable limitations presented a problem because 21 elements were identified to be included in the subject analysis and each of these elements have 5 associated levels of service for a total of 105 levels of service. The FORTRAN source code for the program has been altered to allow for the use of up to 40 elements and 200 levels of service. The program is capable of solving in a reasonable time (a few minutes) the problem as modeled. If a problem were analyzed which approached the new upper limits for the modified variables then excessive computer run times might be experienced. 34