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5 C H A P T E R 2 Literature Review and Survey Literature Review Synthesis Mr. Jim Phillips of Hardesty and Hanover led the effort of gathering references relevant to the project objectives. The references gathered included code specifications (including both local and federal domestic as well as international), technical literature and industry publications related to RBM and probabilistic- based design. The approach taken to review the literature began with identification of relevant sources/documents and then providing a general description of each document. Information gathered from codes/standards and technical reports from professional societies or government entities was synthesized. Gaps and shortcomings were identified. A listing of the literature reviewed is included in this report in the References section preceding the Appendices. The detailed literature reviews can be found in Appendix A. Of particular importance is the Dutch Movable Bridge Design Code BS 6786-1. Many of the goals of this study have already been addressed or progressed to varying degrees in this Dutch standard. The RT borrowed from the methodologies and factors imbedded throughout to determine how they may be appropriately applied to the MHBDS. To this end, our Auburn team members made contact with original contributors to the Dutch standard and obtained background information that was utilized in its development. Background This task involved review of relevant standards from other jurisdictions and those from similar industries to determine the extent of RBM in current practice as related to movable bridge design. The process involved the following for each document reviewed: a) Identified the producing agency, initial date of publication, date of publication reviewed and date of latest publication if different from that reviewed. b) Provided a general description of the document relative to this task. c) Scanned the document for key words or phrases related to and used in the context of RBM. d) Determined what systems or components covered under the standard are similar to or applicable to movable bridge design. e) Determined the extent of RBM used or referenced in the document. f) Identified elements of the standard that had direct or indirect relevance to the use of RBM in the AASHTO LRFD MHBDS. g) Identified areas for further research, as appropriate.
6 h) Identified AASHTO LRFD provisions that could be adapted for RBM design. Summary The documents reviewed that are based on RBM or a similar concept and offer the most information relevant to NCHRP 12-112 are American Gear Manufacturers Association (AGMA) 2001-D04, American Bearing Manufacturers Association (ABMA) 14:2014, BS (NEN) 6786-1, IEEE 493, and NFPA T2.12.11- 2. IEEE 352, although geared toward the nuclear industry offered similar information as IEEE 493 as well as a discussion of additional methods to differentiate the significance of failure. BS EN 1090-2 is reliability based but offered little information for movable bridges. The other documents offered little regarding development of an AASHTO RBM movable bridge specification. The origins of the Dutch Movable Bridge Code BS (NEN) 6786 were researched to identify the source of the wind load provisions and to determine the target reliability indices presented in the current version. The results are presented in the document review included herein. This information was used by the research team in comparing proposed methodologies with current European practice. Reliability-Based Methodologies A key aspect of the literature review was to identify standards that had addressed RBM for movable bridges or components of movable bridges. Table 1 summarized the use of RBM in the various documents reviewed. The level of use of RBM was categorized as follows: RBM: the document presented a design methodology based on reliability or presents methodologies for determining reliability. Limited-RBM: the document was reliability based, but did not extend RBM to machinery, hydraulic, and electrical systems or only addressed RBM for limited scenarios. Minimum-RBM: the document did not explicitly identify RBM or present specific information on methodologies to achieve reliability, however, the document referenced standards based on reliability for some design elements. Non-RBM: the document was not based on a reliability-based methodology. Table 1. Use of RBM Document Level of RBM Usage Comments AASHTO LRFD Movable Highway Bridge Design Specifications Limited-RBM Current provisions for mechanical, hydraulic and electrical systems are not reliability based with minor exceptions ANSI/ABMA 11:2014, Load Ratings and Fatigue Life for Roller Bearings RBM Bearing ratings are based on 90% reliability; limited to roller bearings AGMA 2001-D04 Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth RBM Limited to gearing BS 6786-1 Requirements for the Design of Movable Parts of Structures â Part 1: Movable Bridges RBM Dutch RBM code for design of movable bridges, including mechanical, hydraulic and electrical systems
7 Document Level of RBM Usage Comments BS EN 1090-2: Execution of steel structures and aluminum structures, Part 2: Technical requirements of steel structures RBM Limited to structures Canadian Highway Bridge Design Code CSA S6-14, Chapter 13 Limited-RBM Refers to reliability for fatigue design; refers to B10 and L10 life for bearings and bearings in speed reducers CMAA Specification No. 70-2004 Specifications for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes Minimum-RBM Includes provisions for load factors, but design is based on allowable stress and/or fatigue DIN 19704: 1998. Hydraulic Steel Structures, Part 1. German Standard, 1998 Non-RBM Unlike the 2014 version, this version is not RBM DIN 19704-1: 2014, Hydraulic Steel Structures, Part 1. German Standard, 2014 (machine translated from German to English) Limited-RBM Through reference to BS EN 1090-2 RBM is applied for structures; machinery includes limited references to design life and reliability European Material Handling Federation (FEM) 1.001, Rules for the Design of Hoisting Appliances Minimum-RBM Uses factored loads and allowable stresses for design. Some modifiers are applied, including a safety coefficient; class of utilization and load spectrum relate load characteristics IEEE 493-2007 - Institute of Electrical and Electronics Engineers (IEEE) Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems (commonly referred to as the IEEE "Gold Book") RBM Limited to nuclear power systems IEEE 352-2016 - IEEE General Principles of Reliability Analysis of Nuclear Power Generating Systems and Other Nuclear Facilities RBM Limited to electrical systems; includes component reliability data collected over a 35-year period NEN 6787 The Design of Movable Bridges â Safety Non-RBM Limited to safety considerations on movable bridges NFPA/T2.12.11-2-2007, Hydraulic fluid power components â Assessment of reliability by testing Limited-RBM Limited to hydraulic components; RBM is not explicit, but standards are presented for determining component reliability through testing NAS 149/09, NCHRP 20-07/348, Review of the AASHTO LRFD MHBDS - Final Synthesis Report RBM General Definitions Document describes the general principles of RBM Failure Significance Several of the documents reviewed discussed means of differentiating the significance of a failure. This is a concept identified as important to movable bridges as failures can have various impacts on operations and resulting interruptions in service (e.g., a 5-minute delay vs a lengthy delay). Similarly, operational disruptions can vary in significance based on the bridge function in the transportation grid (e.g., heavy traffic vs light traffic or commercial vs recreational marine use). IEEE 352 used ranking scales in Failure
8 Modes and Effects Analysis (FMEA) applying the concept of severity ranking on a scale of 1 to 10, with 1 indicating no loss of function and 10 representing the loss of human life. Two other ranking scales were also introduced; probability of occurrence and detectability. Discipline Matrix Table 2 identifies the disciplines and general movable bridge components addressed within the documents reviewed. Table 2. Discipline / Component Matrix Document Disciplines Included Movable Bridge Components Included AASHTO LRFD Movable Highway Bridge Design Specifications Loads, Structures, Mechanical, Hydraulic, Electrical All movable bridge components ANSI/ABMA 11:2014, Load Ratings and Fatigue Life for Roller Bearings Mechanical Roller bearings, including the typical sizes and types used in movable bridges AGMA 2001-D04 Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth Mechanical Gearing BS 6786-1 Requirements for the Design of Movable Parts of Structures â Part 1: Movable Bridges Loads, Structures, Mechanical, Hydraulic All movable bridge components except electrical systems (except for drive motors) BS EN 1090-2: Execution of steel structures and aluminum structures, Part 2: Technical requirements of steel structures Structures Fixed bridge structures only Canadian Highway Bridge Design Code CSA S6-14 (Chapter 13) Loads, Structures, Mechanical, Hydraulic, Electrical All movable bridge components CMAA Specification No. 70-2004 Specifications for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes Loads, Structural, Mechanical, Electrical Hoisting ropes, sheaves, drums, gearing, bearings, brakes, bridge drives, shafting, couplings, wheels, motors, brakes, controllers, resisters, protective features, limit switches DIN 19704: 1998. Hydraulic Steel Structures, Part 1. German Standard, 1998 Loads, Structures, Machinery, Hydraulic All machinery, hydraulic cylinders DIN 19704-1: 2014, Hydraulic Steel Structures, Part 1. German Standard, 2014 Loads, Structures, Machinery, Hydraulic All machinery, hydraulic cylinders European Material Handling Federation (FEM) 1.001, Rules for the Design of Hoisting Appliances Structural, Mechanical, Electrical Wire ropes, drums, sheaves, shafts, bearings, gearing, wheels, electrical power and control systems and components IEEE 493-2007 - IEEE Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems (commonly referred to as the IEEE "Gold Book") Electrical Electrical power and control systems and components
9 Document Disciplines Included Movable Bridge Components Included IEEE 352-2016 - IEEE General Principles of Reliability Analysis of Nuclear Power Generating Systems and Other Nuclear Facilities Electrical Electrical power systems NEN 6787 The Design of Movable Bridges â Safety Structural, Mechanical, Hydraulic, Electrical Focus on hazards (OSHA-type) and operational guidelines (e.g., visibility, sequence, etc.) NFPA/T2.12.11-2-2007, Hydraulic fluid power components â Assessment of reliability by testing Hydraulic Accumulators, cylinders, filters, pumps, motors & valves Relevant Document Summaries The following briefly discusses the literature and elements of the literature that were most relevant in terms of providing information or reference for an updated RBM movable bridge design code. ANSI/ABMA 11:2014, Load Ratings and Fatigue Life for Roller Bearings, American Bearing Manufacturers Association: Roller bearings are an important machinery element in movable bridges, both as individual components and as elements of a larger assembly (e.g., speed reducer). This standard sets criterion for establishing the relationship between loading, use (hours) and reliability. A method for rating roller bearings for static (non-rotating condition) loading, as would be the case for trunnion bearings on a bascule bridge is included although it is based on a factor of safety against limitations on distortions. The methodology for rating roller manufactured bearings is standardized for all users. The current approach for use with movable bridges maintains the industry-standard approach (with a few unique modifiers). Integration with movable bridge RBM was not warranted, as it would likely cause confusion and possible conflict. AGMA 2001-D04 Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth, AGMA â Technical Standards. Gears are a critical element in movable bridge drive systems and auxiliary systems. Both open gearing and enclosed gearing (speed reducers) are currently designed based on AGMA standards. AGMA utilizes a Service Factor in design and application requires MHBDS load factors to be unity so that the two standards donât conflict. Integration with movable bridge RBM was not warranted, as it would likely cause confusion and possible conflict. BS 6786-1 Requirements for the Design of Movable Parts of Structures â Part 1: Movable Bridges. Dutch Standard, 2017 (machine translated from Dutch to English with supplemental manual translation) (Formerly NEN6786). This Dutch code for design of movable bridges is the closest companion of the AASHTO LRFD Movable that is RBM based. Detailed review of this document on a system and component level was performed to determine areas that were used as a guide or reference in updating the AASHTO LRFD Movable. Particularly helpful areas included the following: â¢ "Bridge Availability", including the importance of the waterway and nominal bridge clearance. â¢ Wind design specifically developed for individual movable bridges including consideration of locality and bridge height. â¢ Partial Factors â partial factors presented for dead loads, variable deck weight, wind loads, resistance of sections, resistance of materials, fatigue, sliding resistance, high strength bolts.
10 â¢ Loads that impact the sizing of the prime mover, including partial factors. â¢ Loads used to design drive machinery for both mechanical and hydraulic systems, including partial factors. Detailed review of BS 6786-required translation from Dutch, as it was not available in English. The machine-translated version was often difficult to follow, especially regarding the translation of some of the technical terms. Our team obtained an accurately translated version of the 1995 DRAFT version of BS 6786. The overall content was very similar to the latest version. This was of great importance to update our current translation, and to help verify concepts that have evolved. BS EN 1090-2: Execution of steel structures and aluminum structures, Part 2: Technical requirements of steel structures, British Standard published under the authority of the Standards Policy and Strategy Committee, 2008: This document was of little use for further research as it applies to design of fixed structures. No further review was recommended. Canadian Highway Bridge Design Code Canadian Standards Association (CSA) S6-14 with emphasis on Section 13-Movable Bridges: This document was essentially an equivalent of the current AASHTO LRFD Movable and did not offer much for further research. No further review was recommended. CMAA Specification No. 70-2004, Crane Manufacturers Association of America, Inc., Specifications for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes: The specifications contained a vast amount of information related to cranes. However, the specifications applied to top running and gantry type multiple girder electric traveling cranes, which are not common on movable bridges. No further review was warranted. DIN 19704: 1998, Hydraulic Steel Structures, Part 1. German Standard, 1998: This document was superseded by the 2014 edition, see below. No further review was recommended. DIN 19704-1:2014, Hydraulic Steel Structures, Part 1. German Standard, 2014 (machine translated from German to English): This specification included design service life for several elements that are used in movable bridges. Article 10:14 addressed factors for using manufacturer ratings for spherical plain bearings, an element not defined in the current AASHTO LRFD Movable. Both of these topics were found to be beyond the scope of the current project but are recommended for future research in Chapter 4 herein. European Material Handling Federation (FEM) 1.001, Rules for the Design of Hoisting Appliances: The document contained a detailed discussion of the factor of safety for wire ropes. Included was the âclass of utilization and load spectrumâ method of evaluation. This methodology is quite different than the RBM ultimately used. However, because wire rope selection remains mostly isolated, it is recommended (in Chapter 4 herein), that this should be a topic of future research. IEEE 493-2007 - Institute of Electrical and Electronics Engineers (IEEE) Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems (commonly referred to as the IEEE "Gold Book"): With regard to electrical systems, this document offered the most potential. It included data tables summarizing 35-years of reliability data for electrical systems. Relative to movable bridges, the data included transformers, motors, circuit breakers, motor starters, generators, disconnect switches, and cable. HVAC component reliability data is also presented, including accumulators, switches, UPS, and valves. Ultimately, our RBM approach steered away from considering âabsolute reliabilityâ due to the multitude of environmental and usage variables in movable bridges.
11 IEEE 352-2016 - Institute of Electrical and Electronics Engineers (IEEE) General Principles of Reliability Analysis of Nuclear Power Generating Systems and Other Nuclear Facilities: There was not much information in this standard relative to movable bridges that was not covered in IEEE 493-2007. One item that underwent a more detail look is the FMEA ranking scales, a severity ranking scale as a means of differentiating the significance of failure. Some basic concepts of the FMEA approach were utilized by Auburn in developing the RBM with data mined from the owner surveys. NEN 6787 The Design of Movable Bridges â Safety. Dutch Standard, 2003 (machine translated from Dutch to English): This standard focused primarily on âOHSA-typeâ safety and hazard identifications. There was little application of this standard regarding RBM design. No further review was recommended. NFPA/T2.12.11-2-2007, Hydraulic fluid power components â Assessment of reliability by testing: This standard established testing methods and procedures for determining the reliability of typical hydraulic system components, including the most common major components used in movable bridge applications. The defined failure thresholds for various components were also helpful. Discussions with major hydraulic system suppliers indicated that, although they performed similar testing, they did not use this standard. Ultimately, our RBM approach steered away from considering âabsolute reliabilityâ due to abundant environmental and usage variables in movable bridges. The NAS 149/09, NCHRP 20-07/348 Final Synthesis Report: This project included the following tasks which are presented in the report: Task 1: Review relevant literature and practices Task 2: Synthesize the various types of 1) Mechanical systems and 2) Electrical drives and controls Task 3: Discuss the application of reliability-based design to mechanical, electrical, and traffic/marine safety systems for movable bridges Task 4: Outline of proposed areas of AASHTO LRFD Movable Bridge Design Specifications for future modification, addition, and deletion Task 5: Revise the outline per NCHRP project panel comments Task 6: Present to the AASHTO HSCOBS Technical Committee T-8 Movable Bridges; Revise outline Task 7: Develop research problem statement Task 8: Synthesis Report â including draft, incorporation of comments, and final report, while setting the background for this project, offers little information Task 3 of the NAS 149/09, NCHRP 20-07/348 Final Synthesis Report included discussions of reliability- based design and identified redundancy as an element of reliability for movable bridge systems. This information was included in the scoping for the project. Task 4 of this same report provided a useful overview of the existing AASHTO MHBDS with suggested areas of change or modification in a future update. The information was summarized in a listing by article in the AASHTO MHBDS. This information was utilized in our Task 4 Outline of Specification Modifications.
12 Summary and Knowledge Gaps The documents reviewed that were based on RBM or a similar concept and offered the most information relevant to NCHRP 12-112 are AGMA 2001-D04, ABMA 14:2014, BS (NEN) 6786-1, IEEE 493, and NFPA T2.12.11-2. Most of these documents were utilized for manufacturing standards for commercial products and it was not useful to deconstruct these standards for selecting commercial components. Therefore, they were of only limited value for original design, but helped with applying proper load/resistance factors in selection of commercial products in the overall system design. IEEE 352, although geared toward the nuclear industry offered similar information as IEEE 493 as well as a discussion of additional methods to differentiate the significance of failure. BS EN 1090-2 was reliability based but offered little information for movable bridges. The other documents offered little regarding development of an AASHTO RBM movable bridge specification. The origins of the Dutch Movable Bridge Code BS (NEN) 6786 were researched to identify the source of the wind load provisions and to determine the target reliability indices presented in the current version. The results are presented in the document review included herein. This information was used by the research team in comparing proposed methodologies with current European practice. Survey of Bridge Owners In order to obtain relevant data regarding movable bridges that could be effectively utilized, the RT found that our original perception of required data needed to be re-focused. As initial research developed, the RT determined the need to focus on the following topics: â¢ Bridge Availability / Importance â¢ Operating Conditions / Restrictions (design loading, particularly operating wind speed) â¢ Failure Modes (to develop Target Reliability Indices - related to the probability of not achieving the goal, i.e., failure) The RT had originally developed questionnaires for owners and suppliers, but it was determined that the questionnaires were too lengthy and should be scrapped. The RP suggested that we perform phone interviews with movable bridge owners. Prior to the interviews, the owners were provided an abbreviated preparation survey. Owner interviews were then conducted using the surveys as a guide but allowed the RT the opportunity to ask follow-up questions to fully extract desired data. Bridge owners in diverse parts of the country were selected to provide a more comprehensive data set. Especially important was obtaining feedback from bridge owners in varied climates and different environments (e.g., urban and rural). The data collected was substantial (267 different movables from eight different owners). This represents a little over 1/4 of the entire movable highway bridge inventory in the US. The interviews were organized into three parts: 1) Importance / Availability 2) Existing Bridge Reliability
13 3) Supplemental / Follow-up Condensed results of the interviews are presented with descriptive commentary, graphs, and tables. The preparation surveys and interview results are included and contain all the raw data. The survey results are summarized in this chapter, and the raw responses are provided in Appendix B of this report. Importance / Availability Part 1 of the interview deals with the actual use of the bridge for navigation and highway transit, factors that could be considered for determining bridge âimportanceâ, and existing restrictions to operation. All of these considerations are utilized by the Dutch code to develop the appropriate design wind speed for each bridge. 1. Can the waterways crossed by movable bridges be classified within the following categories? Check acceptable classifications. Are there other categories you recommend considering? ï¨ Port Entry ï¨ Commercial ï¨ Mixed Use ï¨ Recreational All respondents indicated the four classifications provided were acceptable and no other classifications were suggested (Figure 1). A summary of classifications that were applicable to the ownersâ inventories is shown in Figure 2, with approximately half falling in the âCommercialâ category. Figure 1. Waterway Classification Figure 2. Applicable Waterway Categories 2. The following factors are being considered as potential modifiers in establishing design wind pressure. Check acceptable factors. Do you have any other factors you believe should be considered? ï¨ Evacuation Route ï¨ Strategic or Military Route ï¨ Detour Length (miles) ï¨ Vehicle and/or Truck Usage (ADT / ADTT) 8 0 ALL LISTED CATEGORIES ACCEPTABLE? ANY ADDITIONAL CATEGORIES? 1. Waterway Classification 21 129 105 12 PORT OF ENTRYCOMMERCIAL MIXED USE RECREATIONAL 1.1 Applicable Categories (Waterway)
14 All respondents indicated that the six factors presented were acceptable, and no other factors were suggested (Figure 3). The distribution of these factors for the inventory bridges is presented in Figure 4. Note that all six factors are well represented. Figure 3. Modifying Factors â for Wind Figure 4. Modifying Factors â for Wind 3. Does your agency place movable bridges in lockdown or otherwise render them inoperable, under specific warnings of impending high winds (e.g., gale force winds, tropical storm warning, etc.)? If so, provide specifics of the conditions that initiate bridge closure including wind speed. Also include time of advance warning in the table below (âODâ for on demand). All respondents had operating (wind speed) restrictions. All but one of the restrictions applied to sustained wind speeds. The singular exception was for wind gust speed (see Figure 5). 8 0 ALL LISTED FACTORS ACCEPTABLE? ANY ADDITIONAL FACTORS? 2. Modifying Factors for Wind 8 5 7 8 8 5 2.1 Applicable Factors (Wind)
15 Figure 5. Operating Wind Restrictions Figure 6. Operating Wind Restrictions (avg. sustained / gust) A condensed summary of the data from Part 1 of the interview is included below in Table 3 for additional reference. 40 50 35 30 40 40 35 40 0 10 20 30 40 50 60 1 2 3 4 5 6 7 8 Operating Wind Restrictions (mph) Sustained Wind Limit (mph) Wind Gust Limit (mph) 38.6 40.0 AVG. SUSTAINED WIND LIMIT (MPH) WIND GUST LIMIT (MPH) 3. Operating Restriction - Wind (mph)
16 Table 3. Condensed Summary of Part 1 Data Reliability Survey Part 2 of the interview deals with the reliability that the bridge owners have experienced with the various bridge types, systems, and components required for operation. This information was utilized to identify adequacy of the existing design code. This was useful for establishing Target Reliability Indices for the various limit states (part of Phase II work). The questions in this part of the interview typically require a ârankingâ for which the respondents were given the following description: The attached Existing Movable Bridge Reliability Survey has been prepared by the research team to collect data from bridge owners to assist in evaluating the reliability of existing movable bridge components. Please use the following guidelines for reliability rating0: ï¨ Excellent Failures/Service are very rare and at well beyond expected design/service life ï¨ Good Failures/Service are rare and at beyond expected design/service life ï¨ Satisfactory Failures/Service occur at about the expected design/service life ï¨ Fair Failures/Service occur at less than the expected design/service life ï¨ Poor Failures/Service are common and at well below expected design/service life i Design service life for machinery, other than components designed to wear (e.g., bushings), has traditionally been 50 years. This includes machinery designed in accordance with the AASHTO LRFD MHBDS (first edition 2000) and the Standard Specification for Movable Highway Bridges (first edition 1938). Design service life for electrical and hydraulic equipment is generally accepted to be in the 15 to 25 year range depending upon the equipment. a - P al m B ea ch Co un ty , F L b - N ew Yo rk C ity DO T c - M ich iga n DO T d - N or th Ca ro lin a DO T e - M ul tn om ah Co un ty , O R f - Fl or id a D O T D4 g - F lo rid a D O T D1 & D 7 h -L ou isi an a DO TD TO TA L AV ER AG E Importance / Avaliability 1 Waterway Classification (yes = 1, no = 0) All listed categories acceptable? 1 1 1 1 1 1 1 1 8 Any additional categories? 0 0 0 0 0 0 0 0 0 1.1 Applicable Categories (number of bridges in each category) Port of Entry 2 2 8 2 0 0 0 7 21 Commercial 0 21 0 8 2 30 3 65 129 Mixed use 7 0 3 1 2 7 20 65 105 Recreational 0 0 1 1 0 0 3 7 12 2 Modifying Factors for Wind (yes = 1, no = 0) All listed factors acceptable? 1 1 1 1 1 1 1 1 8 Any additional factors? 0 0 0 0 0 0 0 0 0 2.1 Applicable Factors (yes = 1, no = 0) Evacuation Route 1 1 1 1 1 1 1 1 8 Strategic or Military Route 0 1 0 1 0 1 1 1 5 Detour Length 1 1 1 1 0 1 1 1 7 ADT / ADTT 1 1 1 1 1 1 1 1 8 Number of Openings 1 1 1 1 1 1 1 1 8 Combined Hwy/Rail Use 0 1 0 1 1 1 0 1 5 3 Operating Restrictions Avg. Sustained Wind Limit (mph) 40 50 35 30 40 40 35 38.6 Wind Gust Limit (mph) 40 40.0
17 This rating scale along with typical design service life of various systems was reviewed at the time of interview to emphasize a consistent understanding of the ranking. The results of Part 2 of the interviews follow. 1. How would you rate the reliability of movable bridge support machinery systems and components (trunnions, rolling lift track/tread, center bearings, etc.) on your movable bridges? Note: Support Machinery refers to mechanical elements subjected to span dead load in both static and dynamic conditions and vehicular live load such as trunnions and rolling lift track and tread. Figure 7. Reliability of Support Machinery Rated reliability of support machinery was extremely high and ranged from 4 to 5 with an average of 4.3. This was the highest average rating of any of the categories. 0 1 2 3 4 5 1 2 3 4 5 6 7 8 Re lia bi lit y Ra tin g Respondent Reliability - Support Machinery
18 2. How would you rate the reliability of movable bridge drive machinery systems and components on your movable bridges? Figure 8. Reliability of Drive Machinery Rated reliability of the Drive Machinery was fairly high and ranged from 3 to 5 with an average of 3.7. In the expanded notes section (Appendix B), it can be seen that some respondents provided separate ratings for hydraulic operating machinery that was slightly lower than electro-mechanical drive machinery. The results herein are a combined scoring. 3. How would you rate the reliability of movable bridge locking (live load transfer) devices (center locks, tail locks, end/center wedges, etc.) machinery on your movable bridges? Note: Locking devices are mechanical systems subject to vehicular live load. These may also support some dead load, but not the weight of the moving span. Figure 9. Reliability of Locking / Live Load Transfer Machinery Rated reliability of the Locking and Live Load Transfer Machinery had the highest variation in ranking and ranged from 2 to 5 with the lowest average of 3.1. This is consistent with the detailed responses gathered and presented in Appendix B. 0 1 2 3 4 5 1 2 3 4 5 6 7 8 Re lia bi lit y Ra tin g Respondent Reliability - Drive Machinery 0 1 2 3 4 5 1 2 3 4 5 6 7 8 Re lia bi lit y Ra tin g Respondent Reliability - Locking / Live Load Transfer
19 4. How would you rate the reliability of movable bridge electrical power and control systems on your movable bridges? Figure 10. Reliability of Electrical Power and Control Systems Rated reliability of the Electrical Power and Controls ranged from 2 to 4 with the second lowest average of 3.3. This is consistent with the detailed responses gathered and presented in Appendix B. Also, the detailed responses would indicate that if controls were queried separately from power, it would be the lowest ranking category. 5. How would you rate the reliability of movable bridge traffic control (gates, signals) systems on your movable bridges? Figure 11. Reliability of Traffic Control (gates / signals) Rated reliability of the Traffic Controls (gates / signals) ranged from 3 to 4 with an average of 3.7. Digging deeper into the responses seems to indicate that a common underlying problem is traffic gate limit switches. 0 1 2 3 4 5 1 2 3 4 5 6 7 8 Re lia bi lit y Ra tin g Respondent Reliability - Electrical Power / Control 0 1 2 3 4 5 1 2 3 4 5 6 7 8 Re lia bi lit y Ra tin g Respondent Reliability - Traffic Control (gates / signals)
20 6. Approximately how many movable bridges are included in the assessment? Figure 12. Number of Bridges per Respondent 7. How would you rate the routine maintenance these bridges have received over their service life? Figure 13. Routine Maintenance (over service life of bridge) Rating for routine maintenance over the life of the bridge inventory ranged from 3 to 5 with an average of 3.4. Most respondent were relatively satisfied with the current level of maintenance, but also acknowledged that prior maintenance practices may have been lacking. 9 23 12 12 4 37 26 144 1 2 3 4 5 6 7 8 Respondent Number of Movable Bridges 0 1 2 3 4 5 1 2 3 4 5 6 7 8 Re lia bi lit y Ra tin g Respondent Reliability - Routine Maintenance (for service life)
21 The following two graphs present a condensed summary of the Part 2 reliability data. The grouping below in Figure 14 indicates that there may be some minor respondent scoring bias. Figure 14. Condensed Reliability Data â by Respondent The grouping below in Figure 15 shows the overall consistency of responses. Figure 15. Condensed Reliability Data â by System / Component 0 1 2 3 4 5 1 2 3 4 5 6 7 8 Re lia bi lit y Ra tin g Respondent Reliability - Routine Mainenance Support Machinery Drive Machinery Locking / Live Load Transfer Electrical Power / Control Traffic Control (gates / signals) Routine Maintenance (over life) 0 1 2 3 4 5 Support Machinery Drive Machinery Locking / Live Load Transfer Electrical Power / Control Traffic Control (gates / signals) Routine Maintenance (over life) Re lia bi lit y Ra tin g System / Component Reliability - Routine Maintenance
22 A condensed summary of the data from Part 2 of the interview is included below in Table 4 for additional reference. For more detailed information, see Appendix B. Table 4. Condensed Summary of Part 2 Data Supplemental / Follow-up Questions Part 3 of the interview contains follow-up questions that are intended to provide more information. Some of the additional information is fairly basic, such as statistical breakdown of their inventory. Many of the questions attempt to better define operational problem areas. This data may also be useful in revealing dependencies that may not be readily apparent. 1. What is your inventory of bridges? Figure 16. Inventory by Owner Existing Movable Bridge Reliability Survey (Excellent = 5, Good = 4, Satisfactory = 3, Fair = 2, Poor = 1) a - P alm B ea ch Co un ty , F L b - N ew Yo rk C ity DO T c - M ich iga n DO T d - N or th C ar ol in a DO T e - M ul tn om ah Co un ty , O R f - Fl or id a DO T D4 g - F lo rid a D OT D 1 & D7 h - L ou isi an a DO TD TO TA L AV ER AG E 1 Support Machinery 5 4 4 4 4 4 5 4 4.3 2 Drive Machinery 5 4 4 3 4 3 3 4 3.8 3 Locking / Live Load Transfer 5 3 4 2 2 3 3 3 3.1 4 Electrical Power / Control 4 4 3 3 2 3 4 4 3.4 5 Traffic Control (gates / signals) 4 4 4 3 3 4 4 3 3.6 7 Routine Maintenance (over life) 5 3 3 3 3 3 4 3 3.4 6 Number of Movable Bridges 9 23 12 12 4 37 26 144 267 0% 20% 40% 60% 80% 100% 1 2 3 4 5 6 7 8 Respondent Inventory by Owner Trunnion Bascule Rolling Lift Bascule Other Bascule Vertical Lift Swing Retractable
23 Figure 17. Distribution of Single and Double Leaf Figure 18. Movable Bridge Type â Totals by Type in Survey 0 5 10 15 20 25 30 35 1 2 3 4 5 6 7 8 Bascule Bridges - Single and Double Leaf Single Leaf Bascule Double Leaf Bascule 92 22 2 53 83 15 Movable Bridge Type - Totals Trunnion Bascule Rolling Lift Bascule Other Bascule Vertical Lift Swing Retractable
24 2. How frequently do your bridges open? Figure 19. Busiest and Least Busy Bridge Operations per Year 3. How often do you experience failures that prevent operation? Figure 20. Failures per Year that Prevent Operation Data was provided by only three respondents. Data gaps will need to be filled for meaningful analysis. 120 24 500 400 6,000 60 12 14,400 2,000 1,500 1,000 14,600 3,420 11,400 1 2 3 4 5 6 7 8 Respondent Frequency of Operation per Year (busiest and least busy bridges in inventory) Operations per Year (low) Operations per Year (high) 18 60 30 1 2 3 4 5 6 7 Respondent Failures per Year (that prevent operation) Failures per year (prevent operation)
25 4. What causes more of your disruptions in operation, electrical or mechanical issues? Figure 21. Most Common Failures This chart shows that 6 of 7 respondents indicate the electrical failures are more likely than mechanical. However, ALL respondents indicated that the most likely cause of failure is limit switches. 5. What is the average time to restore operation with electrical issues? Mechanical Issues? Figure 22. Average Operational Restoration Time (M/E) 1 2 3 4 5 6 7 8 Respondent Most Common Failures More likely mechanical More likely electrical Most often Limit Switch / Control Sys 1 7 2 24 48 8 8 10 1 2 1 0.5 2 2 1 1.5 1 2 3 4 5 6 7 8 Respondent Average Time to Restore Operation (hours) Mechanical issue Electrical issue
26 Note that typical electrical restoration times are much less than mechanical. On average, mechanical time was 14 hours, while the electrical was 1.4 hours. Most respondents indicated that it is not uncommon to require an hour or more just to get to the bridge, which escalates all repair times. 6. Span Locks â how often to you service span locks? In general, only three respondents indicated a typical maintenance frequency other than normal lubrication. The three respondents are those owners with much higher average annual operations. Servicing of span locks was typically referenced relative to adjusting alignment and shims. The frequencies reported varied from once per year to once every 3 years. 7. Do your bridges have PLC or Relay System Controls? Which do you see as more reliable? Figure 23. Control System Makeup %PLC and % Relay Most respondents indicated that a very high percentage of their movables are controlled with PLCs. However, it is interesting that most respondents also indicated that the relay controls are more reliable than PLC. 8. Do your bridges have generators for backup power? All but one respondent indicated that nearly all their bridges have backup generators. One respondent indicated that about half had on-site generators and the others had redundant power. 9. Do you have bridges with redundant systems, such as: dual power supply and/or dual motor/drives? See response to 8 for redundant power. Responses regarding redundant motors/drives ranged from 30% to 60% of bridges. The general trend seems to be that newer bridges are including these redundancies. 10. Are there any movable bridge systems that are inherently problematic that you donât recommend? The most common response cited problems with span locks. Many respondents indicated the desire for more substantial and trouble-free locks. One owner indicated a preference for âjaw-typeâ span locks. 90 70 25 90 100 60 80 3 10 30 75 10 0 40 20 97 Relay Relay PLC Relay Relay 25 1 2 3 4 5 6 7 8 Respondent %PLC and %Relay Control PLC (%) Relay (%) Most Reliable (PLC=25, Relay=50)
27 11. Are there any bridge types you think are more or less reliable than others? There were no discernible trends in the responses obtained. There is some missing data for this question that once obtained, may add clarity. 12. Any suggestions for changing movable bridge design requirements? Respondents had several suggestions, and the most common was the desire for redundancy for: incoming power, motors, and backup power (generators). Other items that were mentioned by at least two owners included better locking systems and adequate access for maintenance personnel. A condensed summary of the data from Part 3 of the interview is included below in Table 5 for additional reference. Blue cells indicate missing information. For more detailed information, see Appendix B. Table 5. Condensed Summary of Part 3 â Supplemental / Follow-up Questions a - Palm Beach County, FL b - New York City DOT c - Michigan DOT d - North Carolina DOT e - Multnomah County, OR f - Florida DOT D4 g - Florida DOT D1 & D7 h -Louisiana DOTD TOTAL AVERAGE Supplemental Questions 1 Inventory of Movables Trunnion Bascule 5 8 0 6 1 35 24 13 79 64% Rolling Lift Bascule 3 3 11 0 0 2 1 2 20 16% Other Bascule 0 0 0 0 2 0 0 0 2 2% Vertical Lift 0 3 1 1 1 0 1 46 6 5% Swing 1 7 0 5 0 0 0 70 13 11% Retractable 0 2 0 0 0 0 0 13 2 2% Single Leaf Bascule 2 2 1 1 0 4 3 5 13 13% Double Leaf Bascule 6 9 10 5 3 33 22 10 88 87% 2 Operations per Year (low) 120 24 500 400 6,000 60 12 1,184 Operations per Year (high) 14,400 2,000 1,500 1,000 14,600 3,420 11,400 6,153 3 Failures per year (prevent operation) 18 60 30 36 4 Operational disruptions (yes=1, no=0) More likely mechanical 0 1 0 0 0 0 0 0 More likely electrical 1 0 1 1 1 1 1 1 Most often Limit Switch / Control Sys 1 1 1 1 1 1 1 1 5 Average time to restore operation (hours) Mechanical issue 1 7 2 24 48 8 8 10 14.0 Electrical issue 1 2 1 0.5 2 2 1 1.5 1.4 6 Span lock service frequency (per year) 0.5 1 0.4 12 0.6 7 Control system 0 PLC (%) 90 70 25 90 100 60 80 3 73.6 Relay (%) 10 30 75 10 0 40 20 97 26.4 Most Reliable (PLC=25, Relay=50) 50 50 25 50 50 25 0 8 Generator backup (%) 100 100 50 100 100 96 96 50 91.7 9 Redundancy 0 0 0 0 0 0 0 0 0 Dual Power Feed ( %) 60 50 55.0 Dual Motors / Drives (%) 30 60 30 30 50 30 38.3 10 Inherently Problematic Systems (yes=1) Rolling Treads 1 Span / Tail Locks 1 1 1 Hydraulic Cylinders 1 Hopkins Frames 1 1 0 11 Bridge Types with Lower Reliability (yes=1) Trunnion Bascule 1 Rolling Lift Bascule 1 Hopkins Bascule 1 0 Vertical Lift 1 Swing 12 Suggested Design Code Changes (yes=1) Better Locking Systems 1 1 Redundant Power / Motors / Backup 1 1 1 Standard Components 1 Adequate Miantenance Access 1 1 Higher Reliability Elec Equipment 1 Operator Line of Sight / Ped Safety 1 0 No Changes Recommended 1
28 Summary of Findings The results of the interviews confirmed the experience of those on the RT that have been working in the movable bridge industry for decades. The overall reliability of movable bridges is providing acceptable service. The existing design requirements have required at least base service that is acceptable in nearly all cases for which data has been obtained. In Part 1 of the interview results pertaining to Bridge Importance and Availability, there was unanimous agreement regarding classification of waterways and suggested factors for determining Bridge Importance. Finally, restricted operation wind speeds were relatively consistent and averaged approximately 40 mph. This is consistent with the existing design requirements that have a singular wind loading for all movable bridges. This data provided the basis to confirm the traditional (default) wind loading and development of the optional site-specific approach for determining design wind speeds for individual bridges. Part 2 of the interview results related to reliability of bridges, systems, subsystems and components. The results did not indicate a particularly favored nor problematic type of movable bridge. The final sampling of bridges represented nearly Â¼ of all highway movables in the US inventory. Machinery support items such as trunnions, track/treads, counterweight sheaves, and center bearings have the highest cost and life-safety implications. This category of items had the highest reliability ratings, which indicates that the existing code utilizes appropriate design factors for these items. For bridge operation, the electrical system is more prone to failure than the mechanical. However, mechanical failures are typically much more costly in time and expense to address. The elements that are the root cause of nearly all âfailuresâ are: â¢ Electrical: Limit Switches â¢ Mechanical: Span Locks The data seemed to indicate that there may be reason to adjust the calibration of load and resistance factors related to locking devices. However, follow-up questioning revealed that most issues with span lock failures were related to a combination of maintenance practices and environmental conditions. The high failure rate of limit switches was typically dependent on environment and effective protection from roadway debris. Even for the components with the highest failure rate, the existing design requirements were not the root problem. Overall, the data revealed that the existing specifications were providing acceptable outcomes. Part 3 results from the interviews provided clarification on several topics, including: inventory data, operational frequency, failure types and frequency, repair time, existing redundancies, etc. This data was used in Phase II to help in calibrating target reliability indices. Another important finding that was a bit perplexing was that most owners have converted to PLC control or were in the process of doing so. However, the respondent data overwhelmingly indicated that relay-based control is more reliable. One possible reason for the continued PLC migration is that many respondents indicated that once the âbugsâ are eliminated, the PLC controls provide better trouble-shooting tools. Also, PLC control allows owners to monitor, diagnose, and sometimes resolve control system problems remotely. The respondents also provided guidance regarding suggested modifications to the existing design specifications. Not surprisingly, the most frequent suggestions were to address the major deficiencies identified from the other data. The remainder of this report provides the approach utilized to update the specifications with a uniform RBM.