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From page 22... ... 22 Discussion of Proposed LRFD Bridge Design Pier Protection Guidelines Appendix A: Proposed LRFD Bridge Design Pier Protection Specifications provides preliminary proposed guidelines for bridge pier protection for consideration in a future edition of the AASHTO LRFD Bridge Design Specifications. The text has been based on the eighth edition of the AASHTO LRFD Bridge Design Specifications [AASHTO 2017] Read the entire page →
From page 23... ... 23 rather than ignore both. In this research, failure is defined as the inability of the superstructure to support its design dead load and permanent-lane live load. Read the entire page →
From page 24... ... 24 Column-cap connection failure Column-foundation failure Column shear failures Figure 9. Examples of pier system failure models [Buth 2010] Read the entire page →
From page 25... ... 25 simple-hinge method described in Appendix E: Nominal Resistance to Lateral Impact Loads on Pier Columns is an inelastic analysis method, so using a value of 1.00 or slightly greater would be appropriate and consistent with the seismic provisions if that method were used to calculate the pier column hinge capacity. Given this general background, the basic LRFD design equation can be rewritten explicitly for piers subjected to Extreme Event II lateral vehicle collision forces as: η η η γ ≤ φCT CT CPC CPCQ RD R I where hD = 1.00 = ductility load modification factor for Extreme Event II vehicle collision forces (AASHTO 2012, Article 1.3.3) Read the entire page →
From page 26... ... 26 barrier design experience it is known that a 10-in. thick TL-5 vertical concrete wall properly reinforced and with proper foundation will contain and redirect an 80,000-lb tractortrailer truck [AASHTO 1994a] Read the entire page →
From page 27... ... 27 critical impact is the end-on impact scenario since, for circular or square columns, the cross-section is the same at every orientation. The leading column is also the most at-risk column since it can be struck from a variety of orientations, whereas the interior columns are shielded by the leading columns, and the impact angle is limited. Read the entire page →
From page 28... ... 28 non redundant piers up to about 1.05 for redundant pier systems [Ghosn 2014, Appendix A, Article 1.3.6.2] Read the entire page →
From page 29... ... 29 Since the eighth edition of the LRFD Bridge Design Specifications uses a value of 0.0001 for essential bridges and 0.001 for typical bridges in both the vessel collision provisions in Article 3.14 as well as the heavy-vehicle collisions in Article 3.6.5, there appears to be some history of using these values for the critical acceptance annual risk for bridge collapse. These values are retained in this research, although they can be modified by AASHTO should it want to make the acceptance criteria either more or less conservative. Read the entire page →
From page 30... ... 30 where We = effective weight of engine (lb) , Wf = effective weight of structure in front of the engine (lb) Read the entire page →
From page 31... ... 31 Figure 15. Cumulative distribution of expected impact force – rural Interstates/primaries. Read the entire page →
From page 32... ... 32 28 Figure 16. Cumulative distribution of expected impact force – rural collectors. Read the entire page →
From page 33... ... 33 Figure 17. Cumulative distribution of expected impact force – urban Interstates/primaries. Read the entire page →
From page 34... ... 34 32 Figure 18. Cumulative distribution of expected impact force – urban collectors. Read the entire page →
From page 35... ... 35 These figures indicate that large impact forces are primarily associated with tractor trailers, as expected. This is also confirmed by Table 3 and Table 4, where all but two of the 24 realworld crashes found in the literature involved tractor trailers. Read the entire page →
From page 36... ... 36 RCPC ≤45 50 55 60 65 70 75 ≤45 50 55 60 65 70 ≥75 100 0.9999 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 150 0.9939 0.9989 0.9999 1.0000 1.0000 1.0000 1.0000 0.9817 0.9969 0.9993 1.0000 1.0000 1.0000 1.0000 200 0.9063 0.9629 0.9890 0.9966 0.9992 0.9996 0.9999 0.6980 0.8826 0.9609 0.9892 0.9960 0.9994 0.9998 250 0.8058 0.8422 0.9049 0.9565 0.9824 0.9935 0.9974 0.3710 0.5055 0.7018 0.8602 0.9431 0.9792 0.9930 300 0.7931 0.7928 0.8125 0.8566 0.9116 0.9533 0.9771 0.3322 0.3429 0.4023 0.5462 0.7134 0.8523 0.9283 350 0.7892 0.7884 0.7907 0.7996 0.8279 0.8684 0.9142 0.3302 0.3315 0.3350 0.3657 0.4455 0.5800 0.7291 400 0.7584 0.7832 0.7886 0.7902 0.7978 0.8079 0.8370 0.3179 0.3294 0.3300 0.3374 0.3464 0.3897 0.4873 450 0.6440 0.7550 0.7820 0.7887 0.7931 0.7914 0.7990 0.2720 0.3177 0.3280 0.3358 0.3327 0.3357 0.3622 500 0.4232 0.6620 0.7552 0.7817 0.7912 0.7894 0.7901 0.1797 0.2770 0.3163 0.3328 0.3313 0.3296 0.3360 550 0.1964 0.4754 0.6731 0.7570 0.7843 0.7879 0.7888 0.0817 0.1993 0.2837 0.3213 0.3290 0.3285 0.3323 600 0.0597 0.2628 0.5216 0.6903 0.7602 0.7810 0.7870 0.0254 0.1086 0.2163 0.2895 0.3183 0.3261 0.3313 650 0.0125 0.1054 0.3292 0.5582 0.6999 0.7584 0.7790 0.0056 0.0432 0.1397 0.2356 0.2942 0.3174 0.3287 700 0.0016 0.0312 0.1614 0.3816 0.5883 0.7076 0.7586 0.0008 0.0130 0.0657 0.1645 0.2463 0.2956 0.3193 750 0.0002 0.0067 0.0584 0.2132 0.4338 0.6144 0.7095 0.0000 0.0028 0.0253 0.0916 0.1833 0.2550 0.2998 800 0.0000 0.0008 0.0177 0.0958 0.2706 0.4781 0.6263 0.0000 0.0005 0.0070 0.0429 0.1129 0.1975 0.2666 850 0.0000 0.0001 0.0048 0.0361 0.1390 0.3246 0.5072 0.0000 0.0001 0.0016 0.0158 0.0610 0.1343 0.2167 900 0.0000 0.0000 0.0007 0.0098 0.0594 0.1934 0.3692 0.0000 0.0000 0.0003 0.0048 0.0269 0.0796 0.1571 950 0.0000 0.0000 0.0001 0.0024 0.0224 0.0988 0.2362 0.0000 0.0000 0.0001 0.0012 0.0107 0.0400 0.0998 1,000 0.0000 0.0000 0.0000 0.0006 0.0065 0.0431 0.1363 0.0000 0.0000 0.0001 0.0002 0.0033 0.0165 0.0559 1,050 0.0000 0.0000 0.0000 0.0000 0.0018 0.0155 0.0670 0.0000 0.0000 0.0000 0.0000 0.0010 0.0063 0.0260 1,100 0.0000 0.0000 0.0000 0.0000 0.0006 0.0054 0.0285 0.0000 0.0000 0.0000 0.0000 0.0002 0.0018 0.0117 1,150 0.0000 0.0000 0.0000 0.0000 0.0001 0.0015 0.0102 0.0000 0.0000 0.0000 0.0000 0.0000 0.0005 0.0042 1,200 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0034 0.0000 0.0000 0.0000 0.0000 0.0000 0.0002 0.0014 1,250 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0011 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 0.0004 1,300 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0002 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0001 Rural CollectorsRural Interstates and Primaries Posted Speed Limit (mi/hr) Posted Speed Limit (mi/hr) Read the entire page →
From page 37... ... 37 3.3 Design Choice Is Shielding with a Barrier If the design choice is to shield the bridge pier system, the bridge engineer should evaluate whether a shielding barrier is necessary given the traffic, site, and structural characteristics of the pier system. The procedure suggested for evaluating bridge piers for protection is outlined in Table 8 and involves finding the following four values: HVEi = The expected annual number of heavyvehicle encroachments in direction i is found using Table 13 using the highway type, traffic volume, and percentage of trucks. Read the entire page →
From page 38... ... 38 of 65 mph. In addition, if the highway is a divided highway, it is assumed that there are two lanes in each direction, whereas if it is an undivided highway, it is assumed there is one lane in each direction. Read the entire page →
From page 39... ... 39 is 300 ft. For fixed-point hazards like bridge piers, only trajectories that depart within 300 ft upstream of the pier are likely to strike the leading component of the pier, so the segment length is 300 ft; the encroachment frequency should therefore be multiplied by 300/5,280 = 0.0568. Read the entire page →
From page 40... ... 40 develop the values of HVEi for various traffic volumes, percentage of trucks, and highway types, as shown in Table 13. 3.3.2 Site-Specific Adjustment Factor: Ni The second value needed to assess the need for pier protection in Table 14 is the site-specific adjustment factor, Ni. Read the entire page →
From page 41... ... 41 2012] and the forthcoming final reports for NCHRP Project 22-12(03) Read the entire page →
From page 42... ... 42 3.3.3 Probability of a Collision Given a Heavy-Vehicle Encroachment: P(C \| HVEi) The third value needed to assess the need for pier protection in Table 8 is the probability of a collision given a heavyvehicle encroachment has occurred [P(C \| HVEi) Read the entire page →
From page 43... ... 43 vehicles encroaching will avoid the crash and no more than 100% of the encroachment vehicles will have a crash. A logistic curve reaches asymptotes of 0 and unity; therefore, it prevents the model from fitting negative proportions and proportions greater than unity. Read the entire page →
From page 44... ... 44 Figure 22 is a plot of the observed probability of a crash for each simulated diameter and offset with an overlay of the predicted probability of a crash. The predicted probabilities closely track the observed probabilities; therefore, this model is a reasonable representation of the observed data. Read the entire page →
From page 45... ... 45 suggestions for placement and layout of barriers used for pier protection generally conform to the RDG guidance. 3.3.5.1 Shielding Barrier Type The barrier options for shielding bridge piers to minimize the chance of bridge collapse will only include barriers that meet the MASH crash-testing guidelines [AASHTO 2016] Read the entire page →
From page 46... ... 46 NCHRP Report 350 TL-5 conditions, but an official equivalence has not yet been established by either AASHTO or the FHWA. NCHRP Project 20-07/Task 395 investigated NCHRP Report 350 bridge railings to determine MASH equivalency [Dobrovolny 2017] Read the entire page →
From page 47... ... 47 the impact with the front of the truck. The box of the truck contacting the pier is only a concern if the box of the truck is carrying a rigid load and traveling at a high speed. Read the entire page →
From page 48... ... T yp e W ei gh t (l bs ) Read the entire page →
From page 49... ... 49 so the results in Figure 25 are not directly transferable to the development of these guidelines. Table 22 shows a summary of the 24 single-unit and tractor- trailer crash tests that were found in the crash-testing literature. Read the entire page →
From page 50... ... 50 The resulting ZOI of the trailer behind the barrier during impact is shown Figure 27. The intrusion is measured from the top traffic-face of the barrier to the point on the trailer with the greatest lateral extent behind the barrier. Read the entire page →
From page 51... ... 51 54-inch Barrier48-inch Barrier 50-inch Barrier 46-inch Barrier42-inch Barrier 44-inch Barrier 22" 20" 13" 15" 11" 14" Figure 28. Images from analyses at time of maximum lateral intrusion of trailer behind barrier for each barrier-height case. Read the entire page →
From page 52... ... 52 Test 490025-2-1 involved a 79,945-lb tractor trailer striking a 42-in.-tall concrete post and beam bridge rail at 50.5 mph and 14.1 degrees [Williams 2017] Read the entire page →
From page 53... ... 53 4. The tangent length (L1) Read the entire page →

From page 22...

... 22 Discussion of Proposed LRFD Bridge Design Pier Protection Guidelines Appendix A: Proposed LRFD Bridge Design Pier Protection Specifications provides preliminary proposed guidelines for bridge pier protection for consideration in a future edition of the AASHTO LRFD Bridge Design Specifications. The text has been based on the eighth edition of the AASHTO LRFD Bridge Design Specifications [AASHTO 2017]