trb paper: design & full scale testing of retrofit …docs.trb.org/prp/16-6053.pdf · william...

William F. Williams 1

TRB PAPER: DESIGN & FULL SCALE TESTING OF RETROFIT BRIDGE RAIL FOR 1 24.8 MILES LONG SOUTHBOUND CAUSEWAY BRIDGE, NEW ORLEANS, 2

LOUISIANA 3 By: 4 5 William F. Williams, P.E. 6 Associate Research Engineer 7 Safety & Structural Systems Division 8 Texas Transportation Institute 9 3135 TAMUS 10 College Station, Texas 77843-3135 11 Phone: 979-862-2297 12 Email: [email protected] 13 14 15 Date: August 1, 2015 16 17 Word Count: 2,467 words + (20 Figures @ 250 words each) = 7,467 words 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46


47 48 49 ABSTRACT 50

51 The purpose of this project was to design and test a retrofit bridge rail for the Southbound 52

Lake Ponchartrain Causeway Bridge in New Orleans, Louisiana. This bridge is approximately 53 24.8 miles in length and was constructed in the late 1950’s. When the bridge opened, it carried 54 two-way traffic from New Orleans to the north shore of Lake Pontchartrain. The existing bridge 55 railing consists of a 15-inch high concrete parapet mounted on top a 10 inches high by 28 inches 56 wide concrete curb. Several retrofit options were developed for this project. A few retrofit 57 designs were selected for full-scale testing. The purpose of the testing reported herein was to 58 assess the performance of the Lake Pontchartrain Causeway Single Rail Bridge Rail Design 59 Option A (25-inch tall concrete parapet, with steel posts and a single steel railing standing 14 60 inches above the parapet, atop a 10-inch curb, for a total height of 39 inches) according to the 61 safety-performance evaluation guidelines included in AASHTO MASH Specifications (1). 62 Three crash tests were required to evaluate the bridge rail’s performance for Test Level 4 (TL-4) 63 of MASH. These tests involved a 10000S vehicle (22,000-lb single unit truck), a 2270P vehicle 64 (a 5000-lb (½-ton) Quad Cab Pickup), and a smaller 1100C vehicle (2420-lb small car). The 65 Lake Pontchartrain Causeway 39-inch tall Option A single rail bridge rail design performed 66 acceptably for MASH TL-4 criteria. 67 68

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INTRODUCTION 94 95

The Greater New Orleans Expressway Commission desired to improve the railings on the 96 Lake Pontchartrain Causeway Bridge, particularly the southbound lanes where 13 vehicles have 97 gone over the side since 1994. The main focus of improvement has been on the southbound 98 lanes, where the concrete bridge railing stands 25 inches above the roadway. An aluminum rail 99 tops the concrete, but is not designed to resist vehicular impact. The concrete parapet on the 100 northbound lane stands 31 inches above the roadway. Most of the vehicular accidents involved 101 taller vehicles, such as pickups and SUVs. 102

103 The southbound causeway's bridge was built in the early 1950s. The bridge opened in 104

1956. The vehicle fleet since the 1950s has changed considerably. The taller and heavier 105 vehicles of today have a greater propensity to go over the existing southbound bridge rail. 106 Photos of the current bridge rail are shown in Figures 1 to 3. Details of the existing Bridge rail 107 are shown in Figure 4. 108 109

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FIGURE 1 Photo of Southbound Causeway Bridge. 112 113


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FIGURE 2 Photo of Southbound Causeway Bridge Rail. 116 117


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FIGURE 3 Photo of Southbound Causeway Bridge Rail. 120 121


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FIGURE 4 Details of Concrete Curb and Parapet. 124 125 DESIGN & STRENGTH ANALYSES OF RETROFIT OPTION A BRIDGE RAIL 126 127

Several retrofit options were developed for this project. A few were selected for analyses 128 and full-scale static strength testing. Option A which consisted of a single steel post and tube rail 129 section was selected as Option A. The steel posts were fabricated from steel plate and anchored 130 to the top of the concrete parapet using ¾-inch diameter HAS-e Rods anchored using Hilti 131 RE500 Epoxy Anchoring System. The steel bridge rail element consisted of a HSS8x6x3/8 tube 132 section. The steel tube section met the requirements of ASTM A500 Grade B Material. Details 133 of Option A are shown in Figures 5 to 7. 134 135


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FIGURE 5 Details of Retrofit Option A. 138 139 140


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FIGURE 6 Rail Section Details of Retrofit Option A. 143 144


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FIGURE 7 Details of Steel Post Retrofit Option A. 147 148 Strength analyses and full-scale static strength testing was performed on Option A. The 149

calculated post strength was approximately 28 kips. Full-scale static strength testing was 150 performed on the actual bridge structure in New Orleans in July 2014. The average strength of 151 the Option A post was approximately 27 kips. The post was designed to maximize the strength 152 of the post anchorage in the concrete parapet. In addition the post anchorage was designed to 153 minimize the interferences with existing reinforcing steel in the concrete parapet. Also, the post 154 anchorage design minimized the post installation construction time. A photo of the full-scale 155 testing of the post is shown in Figure 8. 156

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158 159 FIGURE 8 Photo of Full-Scale Testing of Steel Post Retrofit Option A. 160 161 Strength analyses were performed on the retrofit Option A Design with respect to the 162

American Association of State Highway and Transportation Officials (ASSHTO) Load 163 Resistance Factor Design (LRFD) Design Specifications (Section 13) (2). Considering the 164 strength of the existing concrete parapet and the new retrofit steel post and beam system, the 165 calculate strength of the new retrofit rail system was approximately 85 kips @ 32 inches. The 166 strength of the new design met the strength requirements for MASH Test Level 4. 167 168 FULL-SCALE TEST INSTALLATION DETAILS 169

A full scale test installation for the Option A Lake Pontchartrain Causeway Single-Rail 170 Bridge Rail was constructed for three full scale crash tests. The test installation was a 160-ft 6¾-171 inch long single steel rail on a concrete parapet comprised of four 40-ft long rail segments with 2¼-172 inch gaps at spliced expansion joints between each segment. The single bridge rail measured 39 173 inches in height above the bridge deck. The rail was anchored to the top of a 25-inch tall steel 174 reinforced concrete curb and parapet that replicated the existing structure on the subject Lake 175 Pontchartrain Causeway bridge deck. Additionally, the parapet had a 2¼-inch wide expansion joint 176 gap every 40 feet along the length of the installation, which coincided with the expansion splice 177 between adjacent spliced rail segments. 178

Fabricated steel posts, 8 inches tall, supported the rail atop the parapet. Each post’s base 179 was a 20-inch long × 9½-inch wide × 1-inch thick plate containing four 1-inch wide × 1½-inch long 180 slots located on the longitudinal centerline and symmetrically centered about the lateral centerline at 181


2½ inches and 7¾ inches. Each post’s top was a 12½-inch long × 5½-inch wide × ¾-inch thick 182 plate containing two ⅞-inch wide × 2-inch long slots located ¾-inch off of the longitudinal 183 centerline and symmetrically centered about the lateral centerline at 3-inches. Two 1-inch thick 184 side gusset plates, each tapered upward from 6 inches to 4½ inches wide × 6¼ inches tall and 185 symmetrically located on 10¼-inch centers, were welded to the base with a continuous ½-inch fillet 186 weld, and to the top with a continuous ⅜-inch fillet weld such that the top plate holes were offset 187 2½ inches to the traffic side relative to the base plate holes. The traffic-side face of the rail 188 extended towards the traffic approximately ½ inch beyond the traffic-side face of the parapet. All 189 post material was ASTM A572 Grade 50. 190

The ends of each adjacent rail element, which were separated by a 2½-inch gap, were 191 internally spliced (at three locations in the total installation) with a 38-inch long insert made from 192 7-inch × 5-inch × ½-inch thick wall hollow structural section (HSS) of ASTM A500 Grade B 193 material. Two sets of two ⅞-inch diameter bolt holes were located on the 7-inch face’s centerline 194 and longitudinally spaced at 6 inches beginning 2 inches from one end of the HSS. 195

The rail elements were vertically bolted to each post with two ¾-inch diameter × 8-inch 196 long ASTM A325hex bolts, SAE washers, flat washers, and heavy hex nuts (on the bottom of the 197 post top). The posts were attached to the parapet with four Hilti ¾-inch diameter × 10-inch long 198 HAS-E threaded rods, USS flat washers, and heavy hex nuts (on top of the base plate). The Hilti 199 rods were secured a minimum of 8 inches deep in drilled holes in the parapet with Hilti RE500 200 epoxy anchoring system per Hilti instructions. 201

An exemplar curb and parapet was installed to match that of the Lake Pontchartrain 202 Causeway Bridge. The curb was 28 inches wide × 10 inches tall (nominal) with a 2-inch deep 203 backwards sloping traffic side face (2/10, or 11.3 degrees) and a 2-inch radius shoulder. Each 204 40-ft curb section contained five 4-inch high water and debris drainage slots cast into the bottom 205 of the curb at deck level. The top of the parapet extended 15 inches above the top of the curb for 206 a height of 25 inches above the bridge deck. The parapet’s upper section profile was a 12-inch 207 wide × 10-inch tall rectangle with 1-inch chamfers on the top edges. The upper section 208 symmetrically reduced to an 8-inch wide by 5-inch tall web atop the curb via 2-inch tapers on the 209 bottom edges. The upper face of the parapet was 18 inches from the traffic side of the curb. 210

Curb reinforcing steel consisted of eight ½-inch diameter longitudinal reinforcing bars 211 (#4 rebar); four upper bars spaced on approximately 6-inch lateral centers with approximately 212 2 inches of concrete cover on top, and four lower bars spaced at approximated 8-inch, 8-inch, 213 and 2-inch centers. For each section, these eight longitudinal bars were contained within #3 214 closed stirrups (‘P’-bars) spaced at 12 inches. 215

Parapet reinforcing steel consisted of four ½-inch diameter longitudinal reinforcing bars 216 (#4 rebar) spaced rectangular on approximately 7-inch on centers. For each section, these four 217 parapet longitudinal bars, and three of the ‘field’ side curb longitudinal bars, were contained 218 within 46 vertical 16-inch × 4½-inch rectangular closed #3 stirrups (‘N’-Bars ). The ‘N’ bars 219 were tied to the curb reinforcing steel prior to pouring the curb. Concrete cover was 220 approximately 3½ inches at the top of the parapet and 1¾ at the thinnest side section of the 221 parapet. Details of the test installation are shown in Figures 9. Photos of the completed 222 installation are shown in Figures 10. 223


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FIGURE 9 – Details of the Overall Test Installation 227 228 229 230 231 232 233 234 235 236 237


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FIGURE 10 – Photos of Full Scale test Installation 242 243

FULL-SCALE MASH TL-2 CRASH TESTING OF T631 BRIDGE RAILS 244 245 Full scale crash testing was performed on the retrofit bridge rail in accordance with 246 MASH TL-4 specifications. The tests performed on the Option A Bridge rail design are as 247 follows: 248 249

MASH Test 4-10 with a 2420-lb small passenger vehicle (1100C) impacting the 250 critical impact point (CIP) of the length-of-need (LON) of the bridge rail while 251 traveling at an impact speed and angle of 62 mi/h and 25 degrees. The purpose of 252


this test is to evaluate the overall performance of the LON section, in general, and 253 occupant risks, in particular. 254 255 MASH Test 4-11 with a 5000-lb pickup truck (2270P) impacting the CIP of the 256 LON while traveling at an impact speed and angle of 62 mi/h and 25 degrees. 257 The test is intended to evaluate strength of the section in containing and 258 redirecting the 2270P vehicle. 259 260 MASH Test 4-12 with a 22,000-lb single-unit box-van truck (10000S) impacting 261 the CIP of the LON while traveling at an impact speed and angle of 56 mi/h and 262 15 degrees. This test is intended to evaluate the strength of the LON in containing 263 and redirecting the heavy test vehicle. 264

265 All three tests were performed on the Lake Pontchartrain Causeway retrofit bridge rail. 266 The target CIP for each test was determined according to the information provided in MASH, 267 and are shown in Figure 11. All tests targeted joints in the rail and parapet. 268 269

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FIGURE 11 – Critical Impact Points (Locations) For Full-Scale Crash Tests. 272 273 MASH Test 4-12 274

275 MASH Test 4-12 was performed on December 12, 2014. MASH Test 4-12 involves a 276

10000S vehicle weighing 22,000 lbs. ±660 lbs. and impacting the bridge rail at an impact speed 277 of 56 mi/h ±2.5 mi/h and an angle of 15 degrees ±1.5 degrees. The target impact point on the 278 curb was 10 ft. 2½ inches upstream of the joint between posts 6 and 7 and on the rail was 60 279 inches upstream of the joint between posts 6 and 7. Target impact severity (IS) was 154.5 kip/ft., 280 and actual IS was 166.5 kip-ft. (+8%). Based on the results from the crash test, the Option A 281 Retrofit Bridge Rail performed acceptably with respect to all the evaluation criteria in MASH 282 Test Level 4-12 Specifications. Photos of the crash test before and after are shown in Figures 12 283 and 13. Photos of the test vehicle are shown in Figure 14. 284 285 286

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FIGURE 12 MASH Test 4-12 Before Test Photos. 292 293 294

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FIGURE 13 MASH Test 4-12 After Test Photos. 299 300


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FIGURE 14 Photos of the MASH Test 4-12 Test Vehicle. 303 304

MASH Test 4-11 305 306

MASH Test 4-11 was performed on December 15, 2014. MASH test 4-11 involves a 307 2270P vehicle weighing 5000 lbs. ±100 lbs. and impacting the bridge rail at an impact speed of 308 62 mi/h ±2.5 mi/h and an angle of 25 degrees ±1.5 degrees. The target impact point on the curb 309 was 87½ inches upstream of the joint between posts 12 and 13 and on the rail was 51⅝ inches 310 upstream of the joint between posts 12 and 13 (@ joint). Target IS was 115.5 kip/ft., and actual 311 IS was 120.5 kip-ft. (+4%). Based on the results from the crash test, the Option A Retrofit 312 Bridge Rail performed acceptably with respect to all the evaluation criteria in MASH Test Level 313 4-11 Specifications. Photos of the crash test before and after are shown in Figures 15 and 16. 314 Photos of the test vehicle are shown in Figure 17. 315

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FIGURE 15 MASH Test 4-11 Before Test Photos. 319 320


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FIGURE 16 MASH Test 4-11 After Test Photos. 324 325 326

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FIGURE 17 Photos of the MASH Test 4-11 Test Vehicle. 329 330 MASH Test 4-10 331 332

MASH Test 4-10 was performed on December 16, 2014. MASH test 4-10 involves a 333 1100C vehicle weighing 2420 lbs. ±55 lbs. and impacting the bridge rail at an impact speed of 62 334 mi/h ±2.5 mi/h and an angle of 25 degrees ±1.5 degrees. The target impact point on the curb was 335 79 inches upstream of the joint between posts 18 and 19, or on the rail at 433/16 inches upstream 336


of the joint between posts 18 and 19. Target IS was 55.9 kip/ft., and actual IS was 54.6 kip-ft. (-337 2%). Based on the results from the crash test, the Option A Retrofit Bridge Rail performed 338 acceptably with respect to all the evaluation criteria in MASH Test Level 4-10 Specifications. 339 Photos of the crash test before and after are shown in Figures 18 and 19. Photos of the test 340 vehicle are shown in Figure 20. 341 342

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FIGURE 18 MASH Test 4-10 Before Test Photos. 345 346 347

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FIGURE 19 MASH Test 4-10 After Test Photos. 351 352


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FIGURE 20 Photos of the MASH Test 4-10 Test Vehicle. 356 357 SUMMARY AND CONCLUSIONS 358 359

The Option A Retrofit Bridge Rail as presented herein met all the strength and safety 360 performance criteria of MASH TL-4. The Greater New Orleans Expressway Commission is 361 currently planning to construct the retrofit option on the Southbound Causeway Bridge over 362 Lake Pontchartrain in New Orleans, Louisiana. 363 364 REFERENCES 365 366 1. AASHTO, Manual for Assessing Safety Hardware, American Association of State 367

Highway and Transportation Officials, Washington, D.C., 2009. 368 369 2. AASHTO LRFD Specifications, American Association of State Highway and 370

Transportation Officials, Washington, D.C., 2010. 371 372

trb paper: design & full scale testing of retrofit …docs.trb.org/prp/16-6053.pdf · william...

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