Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information (2022)

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33   During the survey process, agencies were asked to provide load rating examples for bridges that are missing as-built information. In response, 13 agencies described a total of 24 examples of various bridge types with a wide range of ages, condition states, and load rating methodolo- gies. The report team selected seven of these instances as case examples, summarized in this chapter. The case examples offer a detailed insight into the diversity of approaches across the nation and the differing levels of effort and resources required by each approach. Each case example describes the bridge, its condition, the history of the bridge and traffic on the bridge, and its current load rating. The case example then explains how the load rating was performed. As shown in previous chapters, most bridges with missing as-built information are simpler structure types, but even a simple bridge can require a complex effort to reach a load rating that gives the owner confidence while trying to avoid overconservatism when essential pieces of information (e.g., material properties and reinforcement spacing) are not available. Table 11 briefly overviews the seven case examples, which are then presented in more detail, illustrating the differences in approach, depending on agency policy and any special circumstances affecting the load rating. Case Example #1 Bridge Type: Reinforced Concrete Box Culvert Year Built: 1967 Controlling Span Length: 29 feet 11 inches Number of Spans: 1 Location: Colorado Bridge No./Name: B-16-AR Bridge Procedure: EB Posted Bridge: No NBI Code, Item 63: Field Eval/Eng Judge (0) NBI Code, Item 65: Field Eval/Eng Judge (0) Bridge Description Located on the east side of Fort Collins, CO, the structure is a single-cell reinforced concrete box culvert (18 feet by 5 feet) built in 1967, with a skewed span measuring 29 feet 11 inches. No plans exist for this structure. The culvert is topped with fill and riding overlay (4 feet 6 inches) and carries State Highway 14 as well as a local access road over a tributary creek of the Cache la Poudre River (Ditch #2). The culvert totals 319 feet long on a 53 degree skew with the six lanes of traffic that it carries. As of 2011, the ADT for this structure was estimated at 33,000, with 5% truck traffic. The culvert condition rating has been set at 6 since November 1990. At the time of the pro- vided load rating example (September 2, 2011), no essential repairs were necessary, and no damage significant enough to affect the load rating was noted. In September 2011, the culvert received a permit operating rating of 96 tons. C H A P T E R 4 Case Examples

34 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Load Rating Methodology and Summary The Colorado Department of Transportation publishes its own CDOT Bridge Rating Manual [61], and the agency provided a copy of its April 2011 publication, in effect when this example of load rating was performed in September 2011. A review of the April 2019 version of the manual indicates that the process for culverts remains largely unchanged. For a concrete box culvert with no plans on file, the numerical rating is determined by a professional engineer registered in the State of Colorado, who bases the rating on the live load history and current condition rating of the bridge. Following the guidance of the CDOT Bridge Rating Manual [61], the agency comprehensively inspected the entire length of the culvert, which had no plans on file. The inspection did not find any signs of distress because of loading, reconfirming the condition rating of 6. Using the results of the inspection and noting that the condition rating was a 5 or higher and that the culvert had been supporting traffic for 44 years without signs of distress, the load rating engineer designated the maximum allowable inventory rating of 36 tons and an operating rating of 40 tons for the HS-20-44. The bridge also received a Colorado permit rating of 96 tons, setting its overload color code to white (per Subsection 1.16 of the manual), meaning that any level of permit vehicles could be routed over the bridge. The Colorado Load Factor Rating Summary form that must be completed for these bridges is illus- trated in Figure 10 for this specific bridge. Case Example #2 Bridge Type: Prestressed Concrete Slab Year Built: 1968 Controlling Span Length: 48 feet Number of Spans: 2 Location: California Bridge No./Name: 34 0105 Rating Procedure: DL Posted Bridge: No NBI Code, Item 63: Field Eval/Eng Judge (0) NBI Code, Item 65: Field Eval/Eng Judge (0) Case Example Location (State) Procedure Category Bridge Type Rating Approach 1 CO EB RC Culvert Combine visual field evaluation with a long history of the structure carrying all traffic. 2 CA DL Prestressed Concrete Slab Confirm no signs of deterioration with a field visit and consider the bridge’s history of carrying traffic. Assume a design load and set the inventory rating for this load to 1.0. Establish rating factors for all other vehicles by calculating the ratio of the moment they create divided by the moment created by the assumed design truck. 3 OR DL Concrete Channel Beam Confirm condition rating of the bridge. If the bridge has a service history of more than 20 years, assume a capacity equal to the highest load effect caused by legal vehicles (up to an SU4). Then, calculate rating factors for all other vehicles based on a ratio of the moment they produce and the moment of the worst legal vehicle. If the condition rating is low, reduce all rating factors. 4 ID RE Reclaimed T-Beam Perform field evaluation, with particular focus on the condition rating of the superstructure from the last inspection, which is used to set inventory and operating ratings for an HS-20 truck, applying a table of established values. Then, compare these ratings to ratings of similar bridges that are about the same age, producing adjustment factors for calculating the operating ratings for legal loads. 5 RI FH Masonry Arch Combine measurements from a field evaluation with material properties from the AASHTO MBE. Create a finite element model to calculate all dead load effects and then use influence lines to run all legal and design vehicles across the bridge to receive a rating per the allowable stress method. 6 MA FT RC Culvert Use detailed field measurements and nondestructive test methods to essentially create a set of plans for analyzing the bridge. Enter the information gathered into the AASHTO Culvert LFR, producing load ratings for the design vehicle and all legal vehicles. 7 FL FT Prestressed Slab Unit Perform proof test with two incrementally loaded test trucks and with strain and deflection gauges monitored in real time. Compute load ratings for all Florida legal loads by using the field testing procedure outlined in the AASHTO MBE [2], generating load rating factors that all exceeded 1.0. Table 11. Case example summary.

Case Examples 35   Bridge Description is prestressed concrete slab bridge is located on the east side of San Francisco, CA, and carries Mariposa Street over two lines of railroad tracks, with I-280 crossing overhead. Built in 1968, this bridge is 106 feet long, with two simple rated spans, each 48 feet long. As of May 2018, the ADT for this structure was estimated at 6,000, with 3% truck trac. e NBI component condition rating was set at 7 for both the superstructure and sub- structure. At the time of the provided load rating example, no essential repairs were necessary, and no damage signicant enough to aect the load rating was noted. In March 2019, the bridge received an inventory rating of 1.0, assuming an HS-20 design load. Load Rating Methodology and Summary e California Department of Transportation (Caltrans) issues guidance for load rating bridges in its internal Structures Maintenance and Inspection (SM&I) Procedures Manual; Caltrans provided a copy of the September 2018 internal publication in use at the time of this example of load rating. SM&I Section 5.10.3 specifically addresses concrete bridges with unknown reinforcement. is SM&I section references language from the AASHTO MBE [2] regarding bridges carrying unrestricted trac for an appreciable length of time but showing no signs of distress. e SM&I manual then lays out a six-step procedure to load rate concrete bridges with unknown reinforcement. No plans for this bridge existed, leaving the bridge load rating to be based on the bridge inspec- tion performed on September 24, 2018. Upon conrming no signs of structural deterioration Figure 10. Load Factor Rating Summary for Colorado Culvert B-16-AR.

36 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Figure 11. Design load per year of design in California. Figure 12. Live load moment table in Section 5.10 of Caltrans internal SM&I manual. aer carrying unrestricted trac for 50 years, the load rating engineer turned to the procedures for determining the load rating. e procedure began by referencing Table 1 (reproduced in Figure 11) in SM&I Section 5.10 to establish the design vehicle based on the design year of the structure. e measured span length from the inspection report and the design vehicle were then entered into the Live Load Moment Table (Figure 12) to extract the moments that the legal load and permit load vehicles will induce in the structure. ese moments were used in the le side of the Assigned Load Rating Data Sheet, provided in Attachment A of SM&I Section 5.10. e inventory rating was set at 1.0, and the other rating factors for the legal and permit vehicles were established by the ratio of the moment generated by the design truck divided by the moment generated by the truck in question, as shown in Figure 13. e Assigned Load Rating Data Sheet must be signed, sealed, and archived just like other rating calculations usually would be, thereby completing the load rating for the bridge. Case Example #3 Bridge Type: Concrete Channel Beam Year Built: 1957 Controlling Span Length: 19 feet Number of Spans: 3 Location: Oregon Bridge No./Name: 01253 180 01470 Rating Procedure: DL Posted Bridge: No NBI Code, Item 63: Field Eval/Eng Judge (0) NBI Code, Item 65: Field Eval/Eng Judge (0) Bridge Description is concrete channel beam bridge carries Highway 180 over the Marys River, approximately halfway between Corvallis and Newport, OR. Built in 1957, this three-span bridge, 57 feet long overall, has a rated span of 19 feet. As of October 2017, the ADT for this structure was estimated at 560, with 20% truck trac.

Case Examples 37   The NBI superstructure condition rating was set at 6. At the time of the provided load rating example, no essential repairs were necessary, and no damage signicant enough to aect the load rating was noted. In June 2018, the bridge received an inventory rating of 0.75 for the HL-93 truck. Load Rating Methodology and Summary e Oregon DOT (ODOT) publishes its ODOT LRFR Manual for load rating bridges in the state [67]. ODOT provided a copy of its June 2018 publication, in use when this example of load rating was performed. Section 15 covers load rating concrete bridges without existing plans. Despite the title of the load rating manual, both the introduction of Section 15 and the load rating report make it clear that load ratings of structures with missing information are not the same as LRFR load ratings. For bridges lacking as-built information, ODOT instead uses the service history, span conguration, and member condition of the bridge to designate an operating and inventory rating. Figure 13. Completed Caltrans assigned load rating data sheet for the case example.

38 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information ODOT is more descriptive when considering the long service history of a bridge carrying legal loads without distress, dening a long history of service as 20 years or more. If a bridge satises this criterion, the assumption is that the safe capacity equals the worst load eect of the legal loads (up to the SU4 vehicle). e inventory rating for the HL-93 design truck is then evaluated by a ratio of the highest moment produced by the legal trucks divided by the moment produced by the HL-93 loading. is same ratio methodology is then applied to all other legal loads and to emergency vehicles, producing all required rating factors. In addition, the NBI condition rating is taken into consideration: if the bridge inspection reports the superstructure or substructure condition rating as lower than a 5, then all rating factors are reduced by the condition factor listed in Table 8.2.2-1 of the ODOT LRFR Manual [67]. For bridges with condition ratings of 2 or 3, further engineering judgment must be applied to determine whether more extreme measures are needed (such as restricting the bridge to one lane of trac, posting the bridge for a maximum of 3 tons, or opting for a complete closure). In this case example, the inspection report came back with condition ratings of 6 and 5 for the superstructure and substructure, respectively, and no signs of distress from loading. Using the lowest condition rating and referencing the table in Figure 14, the condition factor for this bridge was set at 1.0 (i.e., no reduction in the calculated rating factors). Next, following guidance from Section 15.2.5 in its LRFR manual, ODOT calculated the live load moments produced from all legal loads and the design loadings at every 10th point along the span length of the bridge and also at a point equal to 0.45 times the span length of the bridge. ODOT then com- puted the maximum moments generated by the legal loads and design loadings based on the equations in Figure 15. Furthermore, ODOT estimated the inventory and operating rating factors for all design and legal loads, as dened in Figure 16. Figure 14. Rating factor reduction per condition rating in Oregon. Figure 15. Equations for maximum legal load and design moments in Oregon.

Case Examples 39   Case Example #4 Bridge Type: Reclaimed Concrete T-Beam Year Built: 1960 Controlling Span Length: 34 feet 6 inches Number of Spans: 1 Location: Idaho Bridge No./Name: X996260 100.30 Rating Procedure: RE Posted Bridge: Yes NBI Code, Item 63: Field Eval/Eng Judge (0) NBI Code, Item 65: Field Eval/Eng Judge (0) Bridge Description is concrete T-beam bridge carries E 421 North Road over the Lewisville Canal, approxi- mately 16 miles northeast of Idaho Falls, ID. e state built this 39-foot-long bridge in 1960, using girders salvaged from another bridge. e estimated ADT for this structure was 50 in 2016, with no truck trac. e NBI component condition ratings for the superstructure and deck were set at 4 and 5, respectively, during the November 2018 inspection. e state completed the initial bridge inspection in November 2014; the state coded the superstructure with a condition rating of 4 at that time because of signicant damage to the girder anges. e bridge is scheduled for annual inspections. is bridge had no previous load rating. In January 2019, the bridge received an inventory rating of 0.33 for an HS-20 design truck. Load Rating Methodology and Summary e Idaho Transportation Department (ITD) publishes its Idaho Manual for Bridge Evalu- ation (IMBE) for load rating bridges in the state [66]. ITD provided a copy of its June 2020 publication. Section 6.1.4 covers load rating concrete bridges with unknown structural compo- nents and requires an exhaustive search for plans and shop drawings, which must be conducted Figure 16. Rating factors for some of the design and legal loads required by ODOT.

40 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information and documented. If the required details to perform a load rating cannot be acquired, a load rating by engineering judgment is performed for an HS truck, with particular focus on the NBI condition ratings issued during inspection reports. Table 6.1.4-1 in the IMBE (Figure 5) lists the recommended values for inventory rating and operating rating factors as well as tonnages for a given condition rating. Note that the IMBE recommends the reduction of rating factors for condition ratings below 8 for the superstructure. Condition ratings for the bridge deck and substructure are only considered case by case when they are aected by live load. Aer an exhaustive search for plans, a eld sketch dated November 11, 2014, was the only documentation oering any details about the bridge. is eld sketch showed general bridge layout and dimensions but did not detail the reinforcement in the girders. Unable to analyze the structure by traditional methods, ITD used rating factors from Table 6.1.4-1 in the IMBE based on the lowest condition rating of the superstructure, 4, and then established the inventory rating factor as 0.33 and the tonnage as 12 tons. Per IMBE Section 6.1.4, because the condition rating was 4 or less, the operating rating factors had to be established for state legal loads (Type 3, Type 3S2, Type 3-3, and Notional Rating Load). e IMBE includes further guidance on establishing weight restrictions for bridges in poor condition by comparing the bridge with two similar bridges that have calculated load ratings based on available design plans, shop drawings, or both. If possible, the bridges utilized for comparison should be constructed around the same time as the bridge subject to engineering judgment rating. e operating tonnage for a legal load for the bridge being rated is derived by multiplying the operating rating tonnage for the HS-20 (taken from Figure 5) by the ratio of the operating rating for the legal load for the two similar bridges. e ITD load rating in this case example went a bit further and compared 10 other similar bridges, as detailed in Figure 17. ITD calculated the proportions, averages, and standard deviations for the operating ratings listed in Figure 17 to produce the table in Figure 18. e load rating engineer chose this method, stating that 95% of bridges would be covered if two standard deviations were subtracted from the averages. ITD applied these adjustment factors (in the bottom row of Figure 18) to the HS-20 operating tonnage obtained from Figure 5 to determine the tonnages for all legal loads and specialized hauling vehicles (SHVs). When applying the adjustment factors, the calculated tonnage was rounded down to a whole number. For example, the operating rating tonnage for the Type 3-3 truck for this case example would be 1.33 × 20 tons = 26.6 tons, but the reported operating rating tonnage would be 26 tons. All of the computed operating rating tonnages and rating factors are shown in Figure 19. Because the condition rating of the superstructure of this bridge was a 4 or less, ITD determined that it was necessary to post the bridge as recommended in Figure 20. Figure 17. Operating ratings in tons for Idaho bridges similar to the case example bridge, with span lengths of 25 feet to 55 feet.

Case Examples 41   Figure 20. Recommended load posting in Idaho case example. Figure 18. Tonnage adjustment factors for legal loads and SHVs for Idaho bridges similar to the case example bridge. Figure 19. Operating ratings considering condition rating in Idaho case example.

42 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Case Example #5 Bridge Type: Masonry Arch Year Built: 1901 Controlling Span Length: 20 feet Number of Spans: 3 Location: Rhode Island Bridge No./Name: 38801 Rating Procedure: FH Posted Bridge: No NBI Code, Item 63: Allowable Stress (2) NBI Code, Item 65: Allowable Stress (2) Bridge Description is three-barrel stone masonry arch culvert carries Manville Road over the Manville Mill Trench, located on the north side of Manville, RI. Built in 1901, this 1,050-foot-long culvert, pictured in Figure 21, carries a total roadway distance of 70 feet. As of 2014, the estimated ADT for this structure was 8,200, with 10% truck trac. e NBI component condition rating for the culvert was set at 4. At the inlet end, the center barrel (#2) is exposed while the west barrel (#1) is almost com- pletely buried, as shown in Figure 22. No spandrel walls are in place at the inlet end. Investiga- tion of a manhole to the east of the center barrel (#2) near the inlet revealed that the manhole Figure 21. Aerial view of the extent of the culvert in Rhode Island case example.

Case Examples 43   is set on top of an arch structure. is arch structure appears to be the east barrel (#3), which is completely buried at the inlet and not visible. Field observations indicated that the arches are constructed of mortared naturally shaped and split stones. Field measurements of the arch thickness of the center barrel produced a consistent 22 inches along its entire length. e center- to-center spacing between adjacent arches measured 25 feet, with the clear span of the arch at 20 feet with a rise of 7 feet. e center arch has mortared granite block thrust walls measuring approximately 40 inches in height below the spring lines to the existing grade. From the outlet end of the structure, three barrels are visible in the vicinity of the river, as pictured in Figure 23. e state believed that these three barrels compose the Manville Mill Trench structure. Figure 22. Exposed Center Barrel #2 at inlet end of culvert in Rhode Island case example. Figure 23. Exposed barrels at outlet end of culvert in Rhode Island case example.

44 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Load Rating Methodology and Summary e Rhode Island Department of Transportation (RIDOT) publishes its Bridge Load Rating Guidelines for load rating bridges in the state [70]. RIDOT provided a summary of its November 2019 publication. Section 1.10.1 (Review of Existing Bridge Plans and Documents) requires that if no plans exist for a bridge, complete eld measurements must be gathered to perform a load rating. If material properties are unknown, a review of RIDOT construction and materials specications must be performed to nd applicable material properties from the era when the bridge was constructed. As a last resort, the AASHTO MBE [2] can be consulted to approximate material properties. Key observations from the eld evaluation included the following: • e limited visible portions of the west and east arch barrels (#1 and #3) indicated that the geometry and condition of these two barrels were similar to those of the accessible center barrel (#2). erefore, the assumption was that the three barrels were in the same condition, so the rating was based on an analysis of the center barrel (#2). • e measurements of size, shape, and spacing of the three separate barrels were compiled as shown in Figure 24. • e measurement of the arch thickness of the center barrel was a consistent 22 inches along its entire length. • e arches were composed of a mix of split granite and naturally shaped stones. e mortar was in good condition and showed no signs of distress. • e height of the ll above each arch barrel was measured, as shown in Figure 24. • e arches appeared to be level, both transversely and longitudinally. • No settlements were observed in the roadway along Manville Hill Road above the arch location. Figure 24. Dimensions of Manville Mill Trench culvert in Rhode Island.

Case Examples 45   Because of the age, construction method, and materials associated with this bridge, several reference documents were consulted during the development of a load rating method, including the following critical references: • AASHTO MBE, 2nd Edition, 2010 (with 2011 interim revisions and revisions to Article 6A.4 per the 2012 AASHTO Bridge Committee Agenda Item 1) • AASHTO Manual for Condition Evaluation of Bridges (MCEB), 2nd Edition, 1994 (with 2003 interim revisions) • AASHTO Standard Specifications for Highway Bridges, 17th Edition, 2002 • State of Rhode Island Department of Transportation Guidelines for Load and Resistance Factor Rating of Highway Bridges, March 2009 Revised January 2011 The RIDOT review of these references produced the following few discoveries that heavily influenced the load rating effort: • MBE Sections 6A.9.1.2 and 6B.5.2.6 and MCEB Section  6.6.2.6 indicate that the evaluation of unreinforced masonry arches should be performed using the ASR method. These sections also state that masonry components should be evaluated at the inventory level. Allowable operating level stresses for the masonry are not provided. • Per AASHTO Standard Specifications for Highway Bridges 3.8.2.3, culverts with more than 3 feet of fill will not be subjected to a live load impact factor. To perform the load rating, a determination of material properties was required. Per the field observations and MBE Table 6B.5.2.6-1, the following stone types and allowable compressive stresses were determined: • Stone ashlar masonry (granite) with Type N mortar = 640 psi • Rubble stone masonry (coarse, rough, or random) with Type N mortar = 100 psi Because the arch stones are a combination of split granite and naturally shaped stones, an average allowable inventory compressive stress for the two types was used to estimate the arch capacity. This result was an allowable compressive stress of 370 psi. The remaining parameter to be set before analysis was the fill height. Based on field measure- ments, the depth of cover above the arch crowns ranged from 4.7 feet to 5.1 feet. An average depth of 4.9 feet was the fill height used in the rating calculations. An analysis of four locations along the arch determined the controlling truck placement. These locations were the spring line, crown, quarter-point, and region of maximum negative moment (tension along the extrados). The location of maximum negative moment corresponds to Node 2 of the analysis model, where the spring lines are assumed to be pinned and therefore subject to thrust only; the other three analysis locations are subject to a moment-thrust interac- tion. The rating calculations utilized one-quarter of the available passive earth pressure along the lower arch segments of the analytical model, with active earth pressure applied against the remainder of the arch. To aid in analysis of the arch, the cross-section was divided into 20 segments, each measuring 13.1 inches along the horizontal. As depicted in Figure 25, with this discretization set, the earth pressure, self-weight, and asphalt wearing surface were applied to the arch to calculate all dead load effects. A model was created in GT Strudl to calculate the moments and thrust attributable to dead load. The dead load moment diagram is illustrated in Figure 26. With the dead load effects determined, the analysis of live load effects on the culvert followed, starting with the application of a 1 kip unit load to all points along the GT Strudl model to con- struct live load thrust and moment influence lines. Each of the rating vehicles was then tracked across the live load influence lines to determine the maximum thrust and moment produced

46 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Figure 25. Earth pressures on culvert in Rhode Island case example. Figure 26. Moment diagram due to dead load for Rhode Island case example.

Case Examples 47   by each truck. Once the live load and dead load eects were both quantied for a given truck, these values were compared to the capacity of the arch segments by using a simple stress block analysis, nding that no posting was needed. Figure 27 lists the inventory rating factors for all Rhode Island legal loads. Case Example #6 Bridge Type: ree-Sided RC Rigid Frame Year Built: 1991 Controlling Span Length: 16  feet Number of Spans: 2 Location: Massachusetts Bridge No./Name: L-16-027 Rating Procedure: FT Posted Bridge: No NBI Code, Item 63: Load Factor Rating (1) NBI Code, Item 65: Load Factor Rating (1) Bridge Description is reinforced concrete frame bridge carries Genovevo Drive over Minechoag Brook in a residential area northeast of central Ludlow, MA (Figure 28). Built in 1991, this bridge is 32 feet 10 inches long, has an overall width of 25 feet 4 inches and a curb-to-curb roadway width of 21 feet 8 inches, and is supported on concrete footings. e transverse cross-section of the bridge is composed of ve adjacent three-sided frames, each 5 feet wide with 4 feet of headspace (Figure 29). e bridge is topped by 11 inches to 13 inches of compacted gravel backll, followed by a 3.5-inch-thick to 5-inch-thick bituminous wearing surface. e NBI component condition ratings for the superstructure, deck, and substructure were all set at 6 during the August 2018 inspection. e estimated ADT for this structure was 100 in 2018, with 0% truck trac. Load Rating Methodology and Summary e Massachusetts Department of Transportation (MassDOT) publishes its bridge load rating guidelines as a chapter in its LRFD Bridge Manual [76]. MassDOT provided the pertinent Figure 27. Manville Mill Trench culvert inventory rating in Rhode Island case example.

48 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Chapter 7 of its 2019 publication. Section 7.2.5.5 addresses bridges with missing information, stating that engineering judgment alone is not acceptable for rating superstructure elements. It requires execution of detailed field measurements, NDT, and a material testing program to gather the information needed to perform a load rating. In these situations, the materials sampling and testing program must be submitted to the state bridge engineer for approval before any testing is performed. MassDOT hired CME Associates, Inc., to measure the bridge and conduct the load rating and NDT Corporation to determine the material properties and location of reinforcing steel. e NDT methods utilized on the structure were (1) sonic and ultrasonic impact-echo methods to determine the mechanical properties of the concrete and (2) GPR to calculate the location, depth, and spacing of reinforcement in the slab and walls. With the information compiled from the eld evaluation and testing, CME Associates devel- oped the schematics of the bridge, as depicted in Figure 30 and Figure 31. e impact-echo testing computed the concrete compressive strength as 6,000 psi and found the strength to be Figure 28. North elevation view of bridge in Massachusetts case example. Figure 29. Adjacent concrete frames in Massachusetts case example.

Case Examples 49   uniform throughout the walls and slab. e GPR testing was useful on several fronts. On top of the bridge, the GPR testing ascertained the thickness of both the asphalt and compacted gravel backll. Underneath the bridge, GPR testing established the layout of the reinforcing steel and cover depth for the dierent layers in both the walls and the top slab, as illustrated in Figure 32 and Figure 33. NDT Corporation also collected GPR data at a spacing of 6 inches and 18 inches from the corners to detect whether corner tie-in bars were in place and where they might ter- minate, but no tie-in bars were detected. It is important to note that GPR cannot determine the size of the reinforcing steel. To verify the diameter of the reinforcement, the consultant removed a small bit of concrete from a few locations (Figure 34) to expose the steel so that it could be measured directly. Once the consultants established the reinforcement layout and material properties, MassDOT could combine this information with eld observations to run a load rating analysis. MassDOT rates its bridges per the provisions of the current AASHTO MBE [2] and the AASHTO specica- tions used in designing the bridge. us, CME Associates analyzed Bridge L-16-027 according to the following reference materials: • AASHTO Standard Specications for Highway Bridges, 17th Edition, 2002 • AASHTO MBE, 3rd Edition, 2018 • MassDOT 2019 LRFD Dra Bridge Manual Figure 30. Transverse cross-section of Massachusetts Bridge L-16-027. Figure 31. Longitudinal cross-section of Massachusetts Bridge L-16-027.

50 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information CME Associates performed an initial load rating, using AASHTOWare Bridge Rating Ver- sion 6.8 and considering the bridge as a rigid frame structure. Under this assumption, the walls of the structure fared poorly, with a rating factor of 0.37, while the top slab rating factor was 3.44 when considering an HS-20 loading. After reviewing the field observations, CME Asso- ciates noted the lack of chamfer in the top corners, and GPR did not detect any indication of additional reinforcement at those locations. CME Associates also observed that the two spans are separate from each other, as seen in Figure 35. With these observations in mind, a second load rating analysis treated the structure as two adjacent box culverts with pin supports at the ends of the top slab. Other important assumptions included the following: 1. Because of the lack of evidence of functioning shear keys along the longitudinal joints, the assumption was that the barrier loads were carried entirely by the exterior frames of the struc- ture. Figure 36 shows a typical joint between frames. 2. Because of lack of access during testing, the consultants could not measure the sizes of the top bars in the top slab. Therefore, a conservative assumption of #3 size rebar was made for this reinforcement. Concrete compressive strength was set at 5,500 psi. NDT testing determined the compressive strength as 6,000 psi, but the accuracy of that figure is verified at ±500 psi. 3. The assumption was that reinforcing steel strength (Fy = 60,000 psi) is based on the year of bridge construction. 4. The compacted gravel fill unit weight (120 pcf) was taken from AASHTO Standard Specifica- tions for Highway Bridges, Section 3.3.6. Figure 32. Top slab reinforcement layout detected by using GPR in Massachusetts case example.

Case Examples 51   Figure 34. Exposed reinforcement measured for diameter in Massachusetts case example. Figure 33. Side wall reinforcement layout detected by using GPR in Massachusetts case example.

52 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Figure 36. Typical open joint between frames in Massachusetts case example. Figure 35. Open joint between box culverts in Massachusetts case example.

Case Examples 53   All of these assumptions, plus the dimensions of the bridge, were entered into AASHTO Culvert LFR Engine Version 6.8.2, which analyzed the bridge for carrying all legal loads, the design load, and the EV and SHV loads, producing the satisfactory load ratings for vehicles listed in Figure 37. Case Example #7 Bridge Type: Prestressed Concrete Slab Units Year Built: Mid-1960s Span Length: 25 feet Number of Spans: 3 Location: Florida Bridge No./Name: Hillsboro Canal Bridge Rating Procedure: FT Posted Bridge: No NBI Code, Item 63: Field Testing (4) NBI Code, Item 65: Field Testing (4) Bridge Description e slab unit bridge pictured in Figure 38 is located in southern Palm Beach County, FL. e exact year of its construction was unknown, but the best estimate was the mid-1960s. e total Figure 37. Inventory and operating rating tonnage for Massachusetts Bridge L-16-027. Figure 38. Prestressed slab unit bridge over Hillsboro Canal in Florida.

54 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information length of the bridge was 78 feet 6 inches, and it carried a private access road over the Hillsboro Canal. e slab units were almost identical in length from one span to the next, measuring (from south to north) 26 feet 2 inches, 26 feet 1 inch, and 26 feet 3 inches, respectively (Figure 39). Eight adjacent 12-inch-deep prestressed concrete at slab units formed the cross-section of the bridge, with a total width of 27 feet 6 inches. e layout of the slab units was symmetrical across the width of the bridge, with each fascia unit 4 feet wide and the other six slab units 3 feet wide, but the center measured 1 foot 6 inches and was a cast-in-place non-prestressed closure pour in the middle. e slab unit construction relied on simply supported spans sitting on felt pads (6 inches wide) atop the pile caps. At the outside edges of both fascia units, a curb (1 foot 8 inches wide by 8 inches high) was topped by a 2-foot-tall aluminum railing. e actual road width (between inside to inside of the curbs) was 24 feet 2 inches, topped with an asphalt wearing surface (1 inch thick). Load Rating Methodology and Summary e Florida Department of Transportation (FDOT) issues guidance on a proper bridge load rating methodology through the publication of its Florida Department of Transportation Bridge Load Rating Manual [64]. e state also follows the guidance of the 2018 MBE. FDOT provided a copy of its January 2020 publication for reference. e pertinent information for this case example lies in Section 6.1.4 (Load Rating Analysis for Bridges with Unknown Structural Com- ponents), and Chapter 8 (Load Rating of Bridges through Load Testing). For bridges that lack as-built information, eld measurements must be taken, including, at a minimum, the use of a measuring tape, calipers, and a pachometer. FDOT has used more advanced NDT methods (e.g., GPR and 3D laser scanners) when exceptional circumstances require them. FDOT can approxi- mate the reinforcement inside concrete by using plans from similar bridges of the same era or by applying era-appropriate code. If the reinforcement cannot be estimated and if the bridge shows no signs of distress, an assigned load rating is acceptable. If a bridge either restricts the ow of trucks or cannot be analyzed by traditional means, FDOT performs NDT as necessary and analyzes or proof tests the bridge. FDOT has the loading equipment, instrumentation, and expertise to self-perform both the physical load testing of a bridge and the analysis of the data, leading to a load rating. is equip- ment and expertise reside at the Structures Research Center (SRC), part of the FDOT central oce. e expectation is that the SRC will perform a minimum of three load tests per year. e state load rating engineer confers with district structures maintenance engineers, the permitting oce, and the SRC to develop the list of bridges to be load tested. For the bridge in this case example, District 4 requested the load test on the basis that no plans existed for the bridge. e Figure 39. Prestressed slab unit bridge dimensioned elevation view in Florida case example.

Case Examples 55   goal of the test was verifying that the bridge could safely carry all Florida legal loads and the specied crane load shown in Figure 40. Because no plans existed for the bridge, the state required an initial eld visit to measure the dimensions of the bridge to develop a test setup, with the intent of proof testing the bridge. FDOT employed the measurements from this initial visit to create the prole and cross-section drawings reproduced in Figure 39 and Figure 41. With known bridge dimensions, FDOT ran a preliminary live load analysis to calculate the maximum moment that each legal load, design load, and crane load would produce in the bridge. e bridge span lengths used for these max- imum moments were 24 feet 9.25 inches, 24 feet 9.5 inches, and 24 feet 11.125 inches for Spans 1, 2, and 3, respectively. FDOT adjusted these span lengths by adding 10 inches to the distance between pier cap faces to account for the chamfer and the distance to the bearing, which was based on visual inspection. During the proof test, FDOT incrementally loaded its test trucks with concrete blocks, each weighing approximately 1 ton, in sets of six blocks until the moment they produced encom- passed all of the vehicles to be rated. Figure 42 depicts the dimensions and rear block layout of the test trucks. Figure 43 lists the maximum live load moments that each vehicle produced in each span of the bridge. Note that the 1.33 multiplier for dynamic load allowance was applied to all legal loads and to the crane load. For each load increment, the test trucks pulled onto the bridge slowly and parked before the data were recorded; therefore, the dynamic load allowance was not applied to the test truck moments because the test trucks are intended simply to stati- cally proof all dynamic legal loads driving across the bridge. Based on the live load analysis, the SU4 generated the largest moment of the required rating vehicles. According to MBE Section 8.8.3.3, the test truck was required to impose the following required moment on the bridge: [ ]( )× × + = × =• • •1.4 271.6 1 0.33 1.4 361.2 505.7 .kip ft kip ft kip ft Figure 40. Specied crane load needing to cross the bridge in Florida case example. Figure 41. Bridge cross-section produced from eld measurements in Florida case example.

56 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Vehicle Type Maximum Moment (kip-feet) Span 1 Span 2 Span 3 HS-20 271.2 271.7 274.3 Tandem 348.0 348.3 350.5 FL SU2* 185.8 186.1 187.5 FL SU3* 326.2 326.7 329.6 FL SU4* 358.3 358.7 361.2 FL C3* 205.9 206.1 207.5 FL C4* 303.9 304.3 306.3 FL C5* 289.7 290.0 292.4 FL ST5* 258.3 258.7 261.1 Crane* 326.9 327.0 329.3 Test Truck with 12 Blocks 199.6 199. 201.1 Test Truck with 18 Blocks 269.7 270.0 271.8 Test Truck with 24 Blocks 324.1 324.4 326.5 Test Truck with 30 Blocks 376.5 376.8 379.4 Test Truck with 36 Blocks 443.2 443.7 446.6 Test Truck with 42 Blocks 495.9 496.3 499.7 * Moment increased because of the dynamic load allowance (MBE 6A.4.4.3). Figure 43. Maximum live load moments for a single truck in Florida case example. Figure 42. Test truck dimensions and load block layout in Florida case example.

Case Examples 57   The test truck with 42 load blocks produced a moment of 499.7 kip-feet, which is 98.8% of the required moment. This test load was sufficient because the live load factor (Xp = 1.4) was reduced by 10% because the ADTT for this bridge was less than 1,000, per MBE Section 8.8.3.3.1. This adjustment reduced the live load factor to XpA = 1.26. Per the MBE, XpA cannot be less than 1.3. This reduced live load factor lowered the proof test moment to 469.6 kip-feet. With the loading satisfied, FDOT finalized the test setup and procedures. Before placing the test trucks on the bridge, the test setup involved installing strain and displacement gauges at the locations noted in Figure 44 and Figure 45. FDOT placed the displacement gauges in Span 3 and the strain gauges in Span 2 along the location of the maximum moment for the corre- sponding truck positions, Position 2 and Position 3, depicted in Figure 46. The strain gauges were primarily located to monitor both distribution between panels and bridge linearity. FDOT set displacement gauges (D10 and D11) to check movement of the pier. Gauge Lines 1 and 4 monitored shear distribution attributable to trucks sited at Position 1. The transverse location of the test trucks (Figure 47) imposed the maximum loads on the interior slab panels. The test trucks were incrementally loaded with concrete blocks, starting with 12 blocks and progressing in 6-block increments to 42 blocks. As test truck weight increased, the data recorded by the strain and displacement gauges were plotted in real time, allowing engineers to monitor the linearity of the bridge behavior. The test pro- cedure used the following steps: 1. Record gauge readings with no live load. 2. Place one test truck (west truck) with 12 blocks in Position 1, and record gauge readings. 3. Place second test truck (east truck) with 12 blocks adjacent to first truck in Position 1, and record gauge readings. 4. Remove east truck, move the west truck to Position 2, and record gauge readings. Figure 44. Gauge layout plan view in Florida case example.

58 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information 5. Place east truck adjacent to west truck in Position 2, and record gauge readings. 6. Place west truck in Position 3, and record gauge readings. 7. Place east truck adjacent to west truck in Position 3, and record gauge readings. 8. Remove trucks from the bridge, and record gauge readings. 9. Repeat steps 2 through 8, incrementally increasing the loads by 6 blocks until either 42 blocks or nonlinearity is reached. Figure 48 plots bridge deflection along its transverse width and displays the individual slab units, which are spreading the load well from one adjacent unit to the next. Figure 49 graphs the strain versus the applied moment for Gauge Line 2, showing that linear bridge behavior was maintained throughout the entire load test. The results of the proof test confirmed that the bridge had adequate capacity to carry all Florida legal loads as well as the specified crane load. The operating ratings for the Florida legal loads and the crane load are listed in Figure 50. FDOT computed the operating ratings by applying the equation (taken from the 2008 MBE) RF k L X L IM o p pA R 1 0 ( )= × × × + where RFo = rating factor at the operating level Lp = actual applied proof live road ko = factor for how the proof load test was terminated, 1.0 Figure 45. Transverse gauge layout in Florida case example.

Case Examples 59   Figure 46. Longitudinal test truck positioning in Florida case example.

60 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Figure 47. Transverse test truck positioning in Florida case example. Figure 48. Deflection vs. transverse location for both trucks positioned along Line 2 for each block load level in Florida case example.

Case Examples 61   Truck Type Rating Factor Rating (tons) HS-20 1.30 46.8 Tandem 1.02 25.5 SU2 1.90 32.3 SU3 1.08 35.7 SU4 1.00 35.0 C3 1.72 48.1 C4 1.17 42.7 C5 1.22 48.8 ST5 1.37 54.7 Crane 1.08 47.5 Figure 50. Operating rating in Florida case example. Figure 49. Strain vs. applied moment for both trucks positioned along Line 2 in Florida case example.

62 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information Summary The survey asked DOTs whether they could provide examples of load rating BCMI, and 13 agencies described a total of 24 case examples. The survey team selected seven case examples, presented here to illustrate the varying methods for load rating these structures, from a simple experience-based rating to the more complex field testing approach. This collection of case examples illustrates the wide range of tools and techniques that owner agencies are currently utilizing to arrive at load ratings for this subset of bridges and culverts (i.e., those with missing or incomplete as-built information) in their inventories.