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Maine Demonstration Project: Reconstruction of Lamson and Boom Birch Bridges
DATA ACQUISITION & ANALYSIS
During construction of the Lamson and Boom Birch projects, there were no worker injuries or motorist incidents. Since the completion of the projects, and as of the date of this report, no motorist or highway user safety incidents have been reported.
Using cast-in-place bridge construction for this type and scope of project typically would require between 24 and 36 weeks. The Boom Birch project was completed in 6.5 weeks, a reduction of between 73 and 82 percent, and the Lamson project was completed in 8 weeks, a reduction of between 67 and 78 percent.
Lamson "On-board" Sound Intensity
On-board sound intensity (OBSI) testing was conducted prior to the Lamson project construction on July 2, 2007, and after rehabilitation on November 15, 2007. Testing included the approach to the bridge as well as the bridge itself, and was conducted at 35 mph.
OBSI measurements were made using the latest accepted technique, which included dual vertical sound intensity probes and an ASTM Standard Reference Test Tire (SRTT). The sound measurements were recorded using the Bruel and Kjaer PULSE software and data collection system. A minimum of three runs were made in the right wheel path of each traffic direction. The two microphone probes simultaneously collected noise from the leading and trailing tire/pavement contact areas. Figure 19 shows the dual probe instrumentation and the tread pattern of the SRTT.
The average of the front and rear SI values was then computed with the Bruel & Kjaer PULSE software, which utilizes Fourier transform to analyze the raw data signals over the full length of the project to produce sound intensity values. Raw noise data were normalized for the ambient air temperature and barometric pressure at the time of testing. The resulting mean SI levels are A-weighted to produce the noise-frequency spectra in 1/3rd octave bands, as shown in figure 20.
Global noise levels were calculated by averaging values from the northbound and southbound lanes and then using logarithmic addition of the 1/3 octave band frequencies between 315 and 4000 Hz. The global noise levels are 94.8 and 95.8 dB(A) for pre- and post-rehabilitation, respectively. Even though the original project surface was distressed and weathered, the newly constructed asphalt overlay is 1.0 decibel higher than the original construction. The slight increase in noise is in the upper frequencies (1000 Hz and higher) and is not as noticeable to the human ear as lower frequencies. For reference, a 3.0 decibel difference in noise is considered noticeable. Both the pre- and post-test results met the project goal of 96 dB(A) or less.
Lamson Smoothness Testing
Smoothness testing at Lamson was done in conjunction with noise testing utilizing a laser profiler manufactured by International Cybernetics Corporation built into the noise test vehicle. Figure 21 is an image of the test vehicle showing the laser positioned in-line with the right rear wheel. A minimum of three test runs were performed in each wheel path in each direction. The northbound and southbound test runs are averaged to produce a singe IRI value with units of in/mile.
The overall IRI values are 301 and 389 in/mi for pre- and post-construction, respectively. Figure 22 shows large peak values north of the bridge in the general location as distresses in the original pavement. Irregularities in the new overlay at the location of the original distressed pavement contributed substantially to an increased IRI. Figure 23 is an image of the post-construction pavement showing irregularity in the surface located where the highest IRI values occur.
Boom Birch "On-board" Sound Intensity
OBSI testing was performed prior to the Boom Birch construction on July 3, 2007, and after rehabilitation on November 17, 2007. Testing included the approach to the bridge as well as the bridge itself, and was conducted at 45 mph. The test equipment and procedures were the same as used on the Lamson project. The Boom Birch resulting mean SI levels are A-weighted to produce the noise-frequency spectra in 1/3rd octave bands as shown in figure 24.
The global noise levels are 102.3 and 98.7 dB(A) for pre- and post-rehabilitation, respectively. There has been a significant 3.6 dB(A) reduction in noise with the new construction due to the relatively smooth pavement and bridge deck improvements, even though the project goal of 96dB(A) or less was not attained. The decrease in noise is mostly in the lower frequencies (1000 Hz and lower), which means the traffic noise will not carry as far.
Boom Birch Smoothness
Smoothness testing at Boom Birch was done in conjunction with noise testing utilizing the same equipment and procedures as Lamson. The overall IRI values are 262 and 137 in/mi for pre- and post-construction, respectively. Post-construction IRI was remarkably and significantly smoother. Figure 25 shows peak values corresponding to bridge abutments and center pier locations where slight humps occur. Figure 26 shows the finished pavement.
For these two bridge replacement projects, Maine DOT elected to use prefabricated concrete bridge elements for their superior quality and durability over cast-in-place concrete. The existing timber pile foundations were replaced with concrete on the Lamson Bridge, and steel piles with a two-layer corrosion protection system were used on the Boom Birch Bridge. Both bridges used a concrete deck system, waterproof membrane, and a 3-inch hot-mixed asphalt (HMA) concrete wearing surface. As a result, these new bridges will likely last longer and perform better than the previous bridges.
The Maine DOT sent a survey letter to local agencies and residents in Addison and Old Town. The Old Town/Boom Birch project letter asked two questions:
The Addison/Lamson project asked two questions:
Three responses were received for the Boom Birch project and nine for the Lamson project. All responses indicated complete satisfaction with the reconstructed bridge and roadway. Regarding the second questions, the replies were generally satisfied or very satisfied. However, a few did note concern over the added cost of the lengthy detours and the potential for increased response time to respond to an incident. Appendix A contains all of the original responses to the surveys.
This page last modified on 04/04/11