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Publication Number:  FHWA-HRT-16-072    Date:  December 2016
Publication Number: FHWA-HRT-16-072
Date: December 2016

 

FHWA LTPP Guidelines For Measuring Bridge Approach Transitions Using Inertial Profilers

Chapter 3. Data Analysis and Reporting

The profile data collected with the LTPP inertial profiler is used to evaluate the smoothness of the transition between the pavement, approaches, and bridge deck. The profile data is also used to determine whether settlement has occurred at the deck approaches, which may or may not be evident through cracking or steps/faulting at the interface between the different structures. In addition, the profile data is used to evaluate various bridge systems to determine factors and recommendations that will lead to the meeting of smoothness specifications from initial construction and over time.

Three profile passes are collected in each direction at all bridge locations. Unless there are issues identified with certain profile runs by the data analyst, the profiles from run 2 will be analyzed and presented as part of the reporting.



Profile Graphs

As part of the pilot project, procedures were developed to graphically present the profiles from the bridge survey that showed the elevation profile for the length of the survey section (the bridge plus 200 ft (61 m) either side of the bridge). The procedure used is as follows:

  1. Load raw (.ARD) data into ProQual 2012 software.

  2. Generate ERD files using ProXport software using .ARD data and ProQual 2012 sectioning information.

  3. Reverse elevations for opposite lane. (Microsoft® Excel was used.)

  4. Load ERD files into ProVAL software.

Since the pilot project, the ability to load .ARD files has been developed into ProVAL, so it is expected that steps 1 through 4 can be combined into a single step.

Photocell events are used to identify the start and end of the bridge. Using these events, it is possible to isolate the location of the bridge approach structures to determine whether there are bumps, dips, or settlement associated with the bridge approach. Figure 13 through figure 18 are examples of the graphical presentation for a GRS-Integrated Bridge System (IBS) bridge and conventional bridge structure, respectively. These were collected as part of a pilot project in St. Lawrence County, NY. Other than the application of a 300-ft (91-m) upper wavelength filter, no corrections have been made. Applying normalization at various spans yielded insignificant results. As mentioned previously, the opposite direction data have been reversed in order to line up the data. The edge-of-bridge locations in figure 13 vary because the bridge is on a curve. A photo of this bridge is shown in figure 19. A photo of the conventional bridge is also shown in figure 20. The procedure developed and presented in these figures will be produced for all bridge profile sections as part of the bridge profile study.



This graph shows the profile elevations for a geosynthetic reinforced soil integrated bridge system (GRS-IBS) bridge in the eastbound direction. Elevation is on the y-axis and ranges from -4 to 4 inches (-102 to 102 mm), and distance is on the x-axis and ranges from 0 to 460 ft. (0 to 140 m). The date is October 9, 2013, the time is 5:34 p.m., and temperature is 64.5 °F (18.1 °C). The left and right elevations are plotted from both the east and west directions. In the east direction, the transitions are located at 199.1 and 242.8 ft (60.69 and 74.01 m). In the west direction, the transitions are located at 197.8 and 243.3 ft (60.29 and 74.16 m). No discernable bump can be identified.

1 inch = 25.4 mm.

1 ft = 0.305 m.

1 °F = 1.8° C +32.

Figure 13. Chart. Example of a GRS-IBS bridge profile in St. Lawrence County, NY (eastbound direction).



This graph shows an example of a geosynthetic reinforced soil integrated bridge system (GRS-IBS) bridge at the first interface in the eastbound direction. It is a sub chart of figure 13 with a rescaled area of the first deck interface location. Elevation is on the y-axis and ranges from -2 to 1 inches (-51 to 25 mm), and distance is on the x-axis and ranges from 160 to 218 ft (48.77 to 66.45 m). The left and right elevations are plotted from both the east and west directions. In the east direction, the first transition is located at 199.1 ft (60.69 m). In the west direction, the first transition is located at 197.8 ft (60.29 m). No discernable bump can be identified.

1 inch = 25.4 mm.

1 ft = 0.305 m.

Figure 14. Chart. Example of a GRS-IBS bridge profile in St. Lawrence County, NY, at first interface (eastbound direction).



This graph shows an example of a geosynthetic reinforced soil integrated bridge system (GRS-IBS) bridge at the second interface in the eastbound direction. It is a sub chart of figure 13 with a rescaled area of the second deck interface location. Elevation is on the y-axis and ranges from 1 to 4 inches (25 to 102 mm), and distance is on the x-axis and ranges from 224 to 262 ft (68.3 to 79.9 m). The left and right elevations are plotted from both the east and west directions. In the east direction, the second transition is located at 242.8 ft (74.01 m). In the west direction, the second transition is located at 243.3 ft (74.16 m). No discernable bump can be identified.

1 inch = 25.4 mm.

1 ft = 0.305 m.

Figure 15. Chart. Example of a GRS-IBS bridge profile in St. Lawrence County, NY, at second interface (eastbound direction).



This graph shows the profile elevations for a conventional bridge in the northbound direction. Elevation is on the y-axis and ranges from -4 to 2 inches (-102 to 51 mm), and distance is on the x-axis and ranges from 0 to 480 ft (0 to 146 m). The date is October 10, 2013, the time is 11:46 a.m., and temperature is 64.9 degrees °F (18.3 degrees °C). The left and right elevations are plotted from both the north and south directions. In the north direction, the transitions are located at 200.6 and 269.7 ft (61.14 and 82.20 m). In the south direction, the transitions are located at 200.5 and 269.3 ft (61.11 and 82.08 m). A bump is noticeable at both transitions.

1 inch = 25.4 mm.

1 ft = 0.305 m.

1 °F = 1.8° C +32.

Figure 16. Chart. Example of a conventional bridge profile in St. Lawrence County, NY (northbound direction).



This graphs shows the profile elevations for a conventional bridge at the first interface in the northbound direction. It is a sub chart of figure 16 with a rescaled area of the first deck interface location. Elevation is on the y-axis and ranges from -2 to 1 inches (-51 to 25 mm), and distance is on the x-axis and ranges from 182 to 218 ft (55.5 to 66.4 m). The left and right elevations are plotted from both the east and west directions. In the east direction, the first transition is located at 200.5 ft (61.11 m). In the west direction, the first transition is located at 200.6 ft (61.14 m). A bump is noticeable at both the transitions.

1 inch = 25.4 mm.

1 ft = 0.305 m.

Figure 17. Chart. Example of a conventional bridge profile in St. Lawrence County, NY, at first interface (northbound direction).



This graph shows the profile elevations for a conventional bridge at the second interface in the northbound direction. It is a sub chart of figure 16 with a rescaled area of the second deck interface location. Elevation is on the y-axis and ranges from -1 to 1 inch (-25 to 25 mm), and distance is on the x-axis and ranges from 252 to 290 ft (76.81 to 88.39 m). The left and right elevations are plotted from both the east and west directions. In the east direction, the second transition is located at 269.3 ft (82.08 m). In the west direction, the second transition is located at 269.7 ft (82.2 m). A bump is noticeable at both the transitions.

1 inch = 25.4 mm.

1 ft = 0.305 m.

Figure 18. Chart. Example of a conventional bridge profile in St. Lawrence County, NY, at second interface (northbound direction).



This photo shows the approach to a geosynthetic reinforced soil integrated bridge system (GRS-IBS) bridge in the eastbound direction. This bridge is a two-way one-lane road and is on a curve that turns to the left and is located on County Road 12 over Malterna Creek in Lawrence County, NY.

Figure 19. Photo. A GRS-IBS bridge in St. Lawrence County, NY (eastbound direction).



This photo shows the approach to a conventional bridge in the northbound direction. This bridge is a two-way one-lane road and is straight and is located on County Road 31 over Brandy Brook in Lawrence County, NY.

Figure 20. Photo. A conventional bridge in St. Lawrence County, NY
(northbound direction).



IRI

IRI is a statistic used to estimate the amount of roughness in a measured longitudinal profile. IRI is computed from a single longitudinal profile using a quarter-car simulation as described in the report “On the Calculation of IRI from Longitudinal Road Profile.”(9) The standard for most State transportation departments is to collect two profiles (one in each wheelpath) and average the IRI calculated for each wheelpath to represent the roughness for a section of roadway. Appendix E in the Highway Performance Monitoring System Field Manual lists the following advantages of using IRI to document pavement performance:(10)

FHWA has determined ranges of IRI that fit particular categories (from very good to very poor) of road roughness. Those ranges are as follows:

Many State transportation departments have replaced the Profile Index (PI) collected from RSE with IRI from lightweight or high-speed inertial profilers as part of pavement smoothness specification for construction quality control. IRI has proven to be a better indicator of pavement smoothness than PI and also provides an advantage in that the initial profiles are relevant in monitoring long-term performance. IRI is the standard by which most State transportation departments manage pavements and determine the time frame for maintenance or
rehabilitation interventions.

For most State transportation departments, the smoothness of the pavement excludes the area of the bridge approach and bridge. Departments have monitored smoothness at bridge locations using IRI, but there does not appear to be a widely accepted standard based on IRI covering the bridge area.(11) In general, it can be expected that the roughness at a bridge will be greater than the road surface as a result of the transition zones and variance in construction. This does not appear to be the situation for the GRS-IBS structures because the travelling public response has been that the bridge area is undetectable from the roadway pavement. When evaluating the bridge location performance based on IRI, a tolerance limit of 80 inches/mi (1,263 mm/km) would apply for postconstruction surveys, and a value of 170 inches/mi (2,683 mm/km) would separate smooth from rough bridge locations.

The Smoothness Assurance Module within ProVAL can be used to plot IRI profiles and identify locations where the IRI exceeds a tolerable limit. This process can be used to identify a location where grinding could be considered to correct a portion of pavement that does not meet an acceptance criteria. The grinding module within ProVAL can also be used to determine the improvement that can result from the grinding process. For the bridge study plotting, the IRI locations based on a tolerable limit would allow identifying any smoothness issues that could be associated with the bridge transition zones.

An IRI graph (showing areas that are acceptable and out of tolerance for an approach structure) is shown in figure 21. The plot range is 20 ft (6 m) before and after the bump. By plotting IRI in this manner, it is easy to determine whether there are smoothness issues at the approach structure. The graph should be produced based on an IRI tolerance limit of 170 inches/mi (2,683 mm/km) for both the approach and exit from the bridge. For the newly constructed bridges, a tighter tolerance limit of 80 inches/mi (1,263 mm/km) should also be generated. The results can also be tabulated and presented in a histogram.



This line graph shows localized International Roughness Index (IRI) at a deck interface location. IRI is on the y-axis and ranges from 0 to 1,800 inches/mi (0 to 28,409 mm/km), and distance is on the x-axis and ranges from 180 to 222 ft (54.9 to 67.7 m). A transition takes place at approximately 200 ft (60.96 m), where a significant bump is shown.

1 inch/mi = 15.8 mm/km.

1 ft = 0.305 m.

Figure 21. Chart. IRI plot using ProVAL software of conventional bridge profile in
St. Lawrence County, NY.



RSE

Traditional smoothness specifications for newly constructed pavements for most State transportation departments have been based on the output from an RSE. The process requires pushing a rubber tire wheeled device of that is 10 ft (3.1 m) long along the wheelpath of the pavement to obtain the deviation at the midpoint of the profiling device. An acceptable tolerance for this deviation, which varies from department to department, is used to calculate the percentage of defective length and located areas that require improvement.

Profiles collected using inertial profilers can be used to simulate the RSE measurement by determining the vertical deviation between the center of the straight edge and the profile for every increment in the profile data. To simulate the straight edge, the length of the straight edge and the deviation threshold value is required to determine out-of-spec locations. For this study, it was suggested to use a specification of 0.125 inch (3.2 mm) in 10 ft (3.1 m) RSE requirement.(2)

A module in ProVAL allows for the processing and reporting of the RSE results from inertial profile data. The outputs can include a plot of the surface deviations (see figure 22), surface deviations with shaded thresholds, and a defective segments table (i.e., hot spots or out-of-spec areas and maximum surface deviations). The peak deformation value can be used to quantify the bump/dip height at the approach transition.

This line graph shows rolling straight edge surface deviations at a deck interface location. Surface deviation is on the y-axis and ranges from -1 to 0.8 inch (-25 to 20 mm), and distance is on the x-axis and ranges from 178 to 220 ft (54.3 to 67.1 m). A transition takes place at approximately 200 ft (60.96 m), where a change in deviation is shown. Large deviations indicate the existence of a bump.

Figure 22. Chart. RSE surface deviations plot using ProVAL software of conventional bridge profile in St. Lawrence County, NY.

 

 

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