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MASH Railing Load Requirements for Bridge Deck Overhang (2023)

Chapter: Chapter 3 - Physical Testing and Instrumentation Procedures

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Suggested Citation:"Chapter 3 - Physical Testing and Instrumentation Procedures." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Suggested Citation:"Chapter 3 - Physical Testing and Instrumentation Procedures." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Suggested Citation:"Chapter 3 - Physical Testing and Instrumentation Procedures." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
×
Page 15
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Suggested Citation:"Chapter 3 - Physical Testing and Instrumentation Procedures." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
×
Page 16
Page 17
Suggested Citation:"Chapter 3 - Physical Testing and Instrumentation Procedures." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
×
Page 17
Page 18
Suggested Citation:"Chapter 3 - Physical Testing and Instrumentation Procedures." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
×
Page 18

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13   Physical Testing and Instrumentation Procedures In this chapter, the test specimen construction and testing sequence are described, and specimen instrumentation processes are briefly discussed. Additionally, the surrogate bogie vehicle used to load physical test specimens is described. Construction Sequence Tested specimens included overhangs supporting barriers, concrete posts, deck-mounted steel posts, and curb-mounted steel posts. In total, six tests were performed. The concrete-post test was performed on a dual-purpose specimen that was also used in a full-scale crash testing series. The remaining five tests were performed on a 70-ft overhang specimen constructed for NCHRP Project 12-119. The first test was performed on a concrete post, which was originally part of a MASH TL-4 crash-test specimen. Before specimen construction, analytical modeling was performed to pre- dict which post region would sustain the least amount of damage in the crash testing series. The post region selected in that modeling effort was instrumented with linear strain gages on transverse slab bars throughout the region of expected load distribution. The specimen was then cast and subjected to MASH test designation numbers 4-10, 4-11, and 4-12. In the crash testing series, the selected post expectedly sustained minimal damage. The post was sawcut from the beam and subjected to a bogie impact test. This test specimen is shown in Figure 13. The remaining five tests, which included two barrier tests, one deck-mounted steel-post test, and two curb-mounted steel-post tests, were performed on a 70-ft overhang specimen. Follow- ing the concrete-post test described above, the overhang and railing were removed, and the new overhang was constructed on the existing grade beam. Analytical models were used to determine test locations and instrumentation schedules. Test locations, which are shown in Figure 14, were carefully selected such that damage in one test would not interfere with the nominal behavior of subsequent tests. To maximize the utility of the limited specimen length, the deck-mounted steel-post test was performed first, prior to pouring the barrier and curb. Testing was performed prior to casting these elements, as their edge-stiffening effect was shown in preliminary analytical modeling to interfere with the deck-mounted steel-post test. The deck-mounted steel post is shown in Figure 15. After the deck-mounted steel-post test was performed, the barrier and curb were cast. The interior and end-region barrier tests were then performed. The interior barrier test location was selected such that a rough interior behavior could be developed without the cracking pattern extending into the cracking pattern of the end-region test. Locations of bogie impact tests C H A P T E R 3

14 MASH Railing Load Requirements for Bridge Deck Overhang Figure 13. Concrete-post test specimen. Figure 14. Barrier and steel-post test locations. Figure 15. Deck-mounted steel-post test specimen.

Physical Testing and Instrumentation Procedures 15   performed on the barrier are shown in Figure 16. Curb-mounted steel-post tests were performed aer barrier testing. Test locations were selected such that their expected damage patterns did not interact. Curb-mounted steel-post specimens are shown in Figure 17. Specimen Instrumentation Physical test specimens were instrumented with strain gages and linear potentiometers to record global deformations and internal bar strains. Instrumentation plans for each specimen are shown in their respective chapters. Additionally, tests were recorded with high-speed digital cameras to track the progression of damage throughout the impact events. End-region test Interior test Interior specimen End-region specimen Figure 16. Barrier test specimen. Figure 17. Curb-mounted steel-post specimens.

16 MASH Railing Load Requirements for Bridge Deck Overhang Strain Gages To directly measure load distributions in the slab as well as to provide internal strain data by which LS-DYNA models could be calibrated, linear strain gages were installed on reinforcing bars at the cross section of locations deemed critical in the analytical program. Typically, strain gages were installed on transverse slab bars at the critical sections directly below the barrier or post specimen (Design Region A-A) or above the field edge of the grade beam supporting the overhang (Design Region B-B). Longitudinal positioning of strain gages was determined via analytical modeling. In total, the first specimen, which included the concrete post, was instru- mented with 29 strain gages; the second specimen, which included the barrier and steel posts, was instrumented with 180 strain gages. Of the installed strain gages, 16 of the 29 gages survived the construction process on the first specimen, and 166 of the 180 gages survived the construc- tion process on the second specimen. The number of strain gages operational in each test was sufficient to adequately characterize load distributions and provide calibration data for the corresponding LS-DYNA models. Strain gage application and protection materials, as well as the gages themselves, were varied between the two test specimens due to vendor material availability. For the first test specimen on which the concrete post was tested, Micro-Measurements C4A-06-235SL-350/39P strain gages were used. These strain gages had a roughly 0.25-in. gage length and 350-ohm resistance. For the second specimen, Tokyo Measurement Laboratories (TML) FLAB-5-350-11-3LJC-F strain gages were used. These strain gages had a 0.2-in. gage length and 350-ohm resistance. To install the gages on reinforcing bars, ribs were first removed with an angle die grinder, and the surface was smoothed using abrasive pads of increasing grit. Gages were typically installed on the sides of bars to negate the potential for local bending strains to affect recorded mea- surements. The surface was then treated with Micro-Measurements degreaser (CSM-3), acid conditioner (MCA-2), and neutralizer (MN5A-2). Gages were adhered to the prepared surface using M-Bond 200 catalyst and adhesive, and a waterproof M-Coat A coating was applied. Gages installed on the first specimen were coated with M-Coat JA polysulfide coating for mechanical protection (Figure 18). Due to material availability limitations, gages installed on the second specimen were protected using TML heat-activated coating tape (Figure 19). Gages installed on vertical barrier bars were protected using a generic protection system consisting of 3M adhesive pads, thread tape, electrical tape, and spray-on rubber (Figure 20). For the concrete-post test, gage lead wires were fed through PVC conduit and out the bottom of forms. For other tests, wires were routed along the bottom of noncritical slab bars to provide protection during the concrete pour. Wires were then funneled out of the top of the slab over the grade beam through PVC conduit to avoid wire damage during surface finishing. Although wires could have exited through the field edge of the slab, the top surface was chosen as the exit point to avoid wire clusters in critical regions and wire damage during formwork removal. Examples Figure 18. Gage coated with Micro-Measurements M-Coat JA.

Physical Testing and Instrumentation Procedures 17   of wire routing and exit channels for the deck-mounted steel-post test specimen in Figure 15 are shown in Figure 21. Leads were connected to shielded signal wire using gel splices and fed into a National Instru- ments Data Acquisition (DAQ) System. Data was recorded at 10,000 Hz during each test. Surrogate Bogie Vehicle Test specimens were impacted by the 5,378-lb surrogate bogie vehicle shown in Figure 22. The bogie vehicle was instrumented with two onboard accelerometers near its center of gravity in each test to measure vehicle accelerations (and by extension, impact loads). Retroreflective tape and a laser speed trap were used to measure bogie impact speeds. To lengthen the impact event and reduce data noise in the initial contact phase, the bogie was fitted with a crushable head typically consisting of a 6-in.-deep, 8-in.-tall, 5-ft-long wood post backed by three circular 12- × ¼-in. hollow structural section (HSS) tubes. The center of the wood post was mounted 29 in. above the deck surface. The length and quantity of crush tubes used in each test depended on the anticipated stiffness of the test specimen. The bogie impact head is shown in Figure 23. A similar crushable head was used by Williams et al. in bogie testing of concrete barriers and concrete post-and-beam railings (11). Figure 19. Gage protected with TML coating tape. Figure 20. Generic coating system on gages on vertical barrier bars.

18 MASH Railing Load Requirements for Bridge Deck Overhang Figure 21. Gage lead wire routing and slab exit channels. Figure 22. Surrogate bogie vehicle used in specimen impact testing. Figure 23. Bogie impact head with wood post and steel crush tubes.

Next: Chapter 4 - Overhangs Supporting Concrete Barriers »
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State highway agencies across the country are upgrading standards, policies, and processes to satisfy the 2016 AASHTO/FHWA Joint Implementation Agreement for MASH.

NCHRP Research Report 1078: MASH Railing Load Requirements for Bridge Deck Overhang, from TRB's National Cooperative Highway Research Program, presents an evaluation of the structural demand and load distribution in concrete bridge deck overhangs supporting barriers subjected to vehicle impact loads.

Supplemental to the report are Appendices B through E, which provide design examples for concrete barriers, open concrete railing post on deck, deck-mounted steel-post, and curb-mounted steel-post.

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