FLOOD DEBRIS BUILD-UP LOADING AND ASSESSMENT OF ADEQUACY OF ALDOT BRIDGE PILE BENTS DURING EXTREME FLOOD/SCOUR EVENTS. Joslyn B.

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1 FLOOD DEBRIS BUILD-UP LOADING AND ASSESSMENT OF ADEQUACY OF ALDOT BRIDGE PILE BENTS DURING EXTREME FLOOD/SCOUR EVENTS Except where reference is made to the work of others, the work described in this thesis is my own or was done in coaboration with my advisory committee. This Thesis does not incude proprietary or cassified information. Josyn B. Danies Certificate of Approva: Robert W. Barnes Assistant Professor Civi Engineering G. Ed Ramey, Chair Professor Civi Engineering Chai H. Yoo Professor Civi Engineering Stephen L. McFarand Dean Graduate Schoo

2 FLOOD DEBRIS BUILD-UP LOADING AND ASSESSMENT OF ADEQUACY OF ALDOT BRIDGE PILE BENTS DURING EXTREME FLOOD/SCOUR EVENTS Josyn B. Danies A Thesis Submitted to the Graduate Facuty of Auburn University In Partia Fufiment of the Requirements for the Master of Science Auburn, Aabama August 8, 25

3 FLOOD DEBRIS BUILD-UP LOADING AND ASSESSMENT OF ADEQUACY OF ALDOT BRIDGE PILE BENTS DURING EXTREME FLOOD/SCOUR EVENTS Josyn Backburn Danies Permission is granted to Auburn University to make copies of this dissertation, at its discretion, upon request of individuas or institutions and at their expense. The author reserves a pubication rights. Signature of Author Date Copy to: Date: iii

4 VITA Josyn Tres Backburn Danies, daughter of Lynn Davis and Joan (Davis) Backburn, was born October 3, 198, in Montgomery, Aabama. She graduated High Schoo from Lowndes Academy in May of She entered Auburn University in August of 1998 and graduated Auburn University with her Bacheor of Civi Engineering Degree in December of 21. She then entered Graduate Schoo at Auburn University in January of 22. She married Jack Washington Danies Jr., son of Mr. and Mrs. Jack Washington Danies Sr. of Montgomery, Aabama on August 9, 23 in Lowndesboro, Aabama. iv

5 THESIS ABSTRACT FLOOD DEBRIS BUILD-UP LOADING AND ASSESSMENT OF ADEQUACY OF ALDOT BRIDGE PILE BENTS DURING EXTREME FLOOD/SCOUR EVENTS Josyn Backburn Danies Master of Science, August 8, 25 (B.C.E., Auburn University, 21) 359 Typed Pages Directed by Dr. G. Ed Ramey A description of a food debris buid-up oading and an assessment of the adequacy of a chosen group of typica ALDOT bridge pie bents having various oading conditions and under various amounts of scour are presented in this thesis. Many of Aabama s existing bridges were not designed for scour, and this report is to aid in determination of the suitabiity and condition of these bridges when subjected to atera food water oadings (atera to the bridge or in the pane of the bent). Pushover anayses were performed on numerous bridge pie bents having a range of oading and scour conditions present. The pushover anayses performed make up part of a screening too that is presented in this report to evauate the existing fied bridges. Finay, concusions and recommendations are made based on the research and anayses of the bridge pie bents having food debris buid-up oadings during extreme food/scour events. v

6 ACKNOWLEDGEMENTS The author woud ike to thank the Aabama Department of Transportation (ALDOT) for funding this project. Aso, the author woud ike to thank Dr. G. Ed Ramey for assistance with academic guidance and assistance in competing this thesis. Aso, thanks are due to Dr. Dan A. Brown, for his contributions to the Phase I and Phase II reports to ALDOT on Stabiity of Highway Bridges Subject to Scour. The author woud aso ike to acknowedge the advisory committee Dr. Barnes and Dr. Yoo. Thanks are in order to Jack Danies Jr. for his support during the course of my graduate studies. vi

7 Stye manua used: The Chicago Manua of Stye Computer software used: Microsoft Word, Microsoft Exce, GT STRUDL vii

8 TABLE OF CONTENTS LIST OF TABLES...x LIST OF FIGURES.....xiv CHAPTER 1: INTRODUCTION 1.1 Introduction Objectives Work Pan Scope...3 CHAPTER 2: BACKGROUND AND LITERATURE REVIEW 2.1 Background Literature Review....7 CHAPTER 3: DESCRIPTION OF BRIDGE PILE BENT DEBRIS BUILD-UP AND LOADING MODEL FOR EXTREME FLOOD/SCOUR EVENTS 3.1 Genera Description of Debris Buid-Up Mode Description of Loading Mode...34 CHAPTER 4: POTENTIAL MODES OF PILE BENT FAILURE DURING FLOOD DEBRIS BUILD-UP AND SCOUR EVENTS 4.1 Genera Pie Bent Pushover Faiure Pie Bent Kick-Out Faiure.45 CHAPTER 5: ANALYSES OF ALDOT PILE BENTS SUBJECT TO SCOUR AND GRAVITY AND FLOOD WATER LOADINGS 5.1 Genera Pie HP1x42 Bent without X-Bracing Pie One-Story HP1x42 X-Braced Bent Pie Two-Story HP1x42 X-Braced Bent Pie HP1x42 Bent without X-Bracing Pie One-Story HP1x42 X-Braced Bent Pie Two-Story HP1x42 X-Braced Bent Pie HP1x42 Bent without X-Bracing Pie One-Story HP1x42 X-Braced Bent...61 viii

9 5.1 5-Pie Two-Story HP1x42 X-Braced Bent Pie HP1x42 Bent without X-Bracing Pie One-Story HP1x42 Singe X-Braced Bent Pie One-Story HP1x42 Doube X-Braced Bent Pie Two-Story HP1x42 Singe X-Braced Bent Pie Two-Story HP1x42 Doube X-Braced Bent Pie HP1x42 Bent without X-Bracing Pie One-Story HP12x53 X-Braced Bent Pie Two-Story HP12x53 X-Braced Bent Pie HP12x53 Bent without X-Bracing Pie One-Story HP12x53 X-Braced Bent Pie Two-Story HP12x53 X-Braced Bent Pie HP12x53 Bent without X-Bracing Pie One-Story HP12x53 X-Braced Bent Pie Two-Story HP12x53 X-Braced Bent Pie HP12x53 Bent without X-Bracing Pie One-Story HP12x53 Singe X-Braced Bent Pie One-Story HP12x53 Doube X-Braced Bent Pie Two-Story HP12x53 Singe X-Braced Bent Pie Two-Story HP12x53 Doube X-Braced Bent Summary of Pushover Capacities for Pie Bents of Varying Pie Size, Numbers and Configurations.87 CHAPTER 6: SCREENING TEST AND PROCEDURE TO ASSESS ADEQUACY OF BRIDGE PILE BENTS FOR EXTREME FLOOD/SCOUR EVENTS 6.1 Genera Assessing Bent Adequacy via a Screening Too Step 4 Bent Pushover Evauation.16 CHAPTER 7: CONCLUSIONS AND RECOMENDATIONS 7.1 Genera Concusions Recommendations 112 BIBLIOGRAPHY 114 APPENDIX A..115 APPENDIX B..228 ix

10 TABLES Tabe 2.1 Tabe 2.2 Tabe 2.3 Tabe 4.3 Drag Coefficients. 9 Latera Drag Coefficients...17 Soi and Other Parameter Vaues Used in FB-Pier Modeing of Probems Shown in Figure Estimates of Maximum Food Water Latera Pressures on Pie Bent for V Design = 6 mph...48 Tabe 4.4 Appied F Tip vaues for HP1x42 and HP12x53 Pies for Θ Vaues of 2 and 3 for a Range of H + S Vaues for V Design of 6 mph.49 Tabe 4.5 Tabe 5.1 Tabe 5.2 Tabe 5.3 Tabe 5.4 Tabe 5.5 Tabe 5.6 Estimated Pie Embedment Required After Scour for Various Tip Geoogica Settings to Have Adequate Latera Capacity for the Magnitudes of F Shown in Tabe appied t Pushover Capacities of a HP1x42 3-Pie Bent without X-Bracing with H=1 and H= Pushover Capacities of a HP1x42 3-Pie X-Braced Bent with H=13 and H=17 54 Pushover Capacities of a HP1x42 3-Pie Two-Story X-Braced Bent with H=21 and H= Pushover Capacities of a HP1x42 4-Pie Bent without X-Bracing with H=1 and H= Pushover Capacities of a HP1x42 4 Pie One-Story X-Braced Bent H=13 58 Pushover Capacities of a HP1x42 4-Pie Two-Story X-Braced Bent with H=21 and H=25.59 Tabe 5.7 Pushover Capacities of a HP1x42 5-Pie One-Story Bent without X- Bracing with H=1 and H=13'. 61 x

11 Tabe 5.8 Tabe 5.9 Pushover Capacities of an HP1x42 5-Pie One-Story X-Braced Bent with H=13 and H= Pushover Capacities of a HP1x42 5-Pie Two-Story X-Braced Bent with H=21 and H= Tabe 5.1 Pushover Capacities of a HP1x42 6-Pie One-Story Bent without X- Bracing with H=1 and H=13'.. 64 Tabe 5.11 Tabe 5.12 Tabe 5.13 Tabe 5.14 Tabe 5.15 Tabe 5.16 Tabe 5.17 Tabe 5.18 Tabe 5.19 Tabe 5.2 Tabe 5.21 Tabe 5.22 Pushover Capacities of an HP1x42 6-Pie One-Story Singe X-Braced Bent H=13 and H= Pushover Capacities of an HP1x42 6-Pie One-Story Doube X-Braced Bent H=13 and H= Pushover Capacities of an HP1x42 6-Pie Two-Story Singe X-Braced Pie Bent H=21 and H= Pushover Capacities of an HP1x42 6-Pie Two-Story Doube X-Braced Bent H=21 and H= Pushover Capacities of a HP12x53 3-Pie Bent without X-bracing with H=1 and H= Pushover Capacities of a HP12x53 3-Pie X-braced Bent with H=13 and H=17.71 Pushover Capacities of a HP12x53 3-Pie Two-Story X-braced Bent with H=21 and H= Pushover Capacities of a HP12x53 4-Pie Bent without X-bracing with H=1 and H= Pushover Capacities of a HP12x53 4 Pie One-Story X-braced Bent H=13 and H= Pushover Capacities of a HP12x53 4-Pie Two-Story X-braced Bent with H=21 and H= Pushover Capacities of a HP12x53 5-Pie Bent without X-bracing with H=1 and H=13'..77 Pushover Capacities of an HP12x53 5-Pie One-Story X-braced Pie Bent H=13 and H= xi

12 Tabe 5.23 Tabe 5.24 Tabe 5.25 Tabe 5.26 Tabe 5.27 Tabe 5.28 Tabe 5.29 Tabe 5.3 Tabe 5.31 Tabe 5.32 Tabe 5.33 Tabe 5.34 Pushover Capacities of a HP12x53 5-Pie Two-Story X-braced Bent with H=21 and H= Pushover Capacities of a HP12x53 6-Pie Bent without X-bracing with H=1 and H=13'...82 Pushover Capacities of an HP12x53 6-Pie One-Story Singe X-braced Bent H=13 and H= Pushover Capacities of an HP12x53 6-Pie One-Story Doube X-braced Bent H=13 and H= Pushover Capacities of the 6-Pie Two-Story HP12x53 Singe X-braced Bent with H=21 and H= Pushover Capacities of an HP12x53 6-Pie Two-Story Doube X-braced Pie Bent H=21 and H= Pushover Capacities of HP1x42 3, 4, 5, 6-Pie Bents without X-Bracing...89 Pushover Capacities of HP1x42 3, 4, 5-Pie Bents with X-Bracing 9 Pushover Capacities of HP1x42 6-Pie Bents with X-Bracing...91 Pushover Capacities of HP12x53 3, 4, 5, 6-Pie Bents without X-Bracing..92 Pushover Capacities of HP12x53 3, 4, 5-Pie Bents with X-Bracing 93 Pushover Capacities of HP12x53 6-Pie Bents with X-Bracing 94 Tabe 5.35 Pushover Capacities of HP1x42 3, 4, 5, 6-Pie Bents without X-Bracing - Modified Tabe Showing, Adequacy to Resist maxdesign = kips..95 Tabe 5.36 Pushover Capacities of HP1x42 3, 4, 5-Pie Bents with X-Bracing - Modified Tabe Showing, Adequacy to Resist maxdesign = kips..96 Tabe 5.37 Pushover Capacities of HP1x42 6-Pie Bents with X-Bracing - Modified Tabe Showing Adequacy to Resist maxdesign = kips..97 Tabe 5.38 Pushover Capacities of HP12x53 3, 4, 5, 6-Pie Bents without X-Bracing - Modified Tabe Showing, Adequacy to Resist maxdesign = kips.98 xii

13 Tabe 5.39 Pushover Capacities of HP12x53 3, 4, 5-Pie Bents with X-Bracing - Modified Tabe Showing, Adequacy to Resist maxdesign = kips..99 Tabe 5.4 Pushover Capacities of HP12x53 6-Pie Bents with X-Bracing Modified Tabe Showing Adequacy to Resist maxdesign = kips 1 xiii

14 FIGURES Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure2.5 Figure 2.6 Figure 2.7 Figure 2.8 Figure 2.9 Figure 2.1 Figure 2.11 Figure 2.12 Figure 2.13 Figure 2.14 Figure 2.15 Figure 2.16 Typica ALDOT X-Braced Pie Bents.5 One-Story Bridge with Stee H-Pie Encased and Sway-Bracing Omitted. 6 Reationship Between Water Pressure, and Design Water Veocity for C D = Debris Raft for Bent Design..11 Debris Raft Force, F T, for Various Debris Raft Dimensions (B) and (A) with V design = 6mph 12 Typica Pie Bent Supported Bridge over a Stream...13 Sections Showing Longitudina And Transverse Food Water Loading on Bent Pan View of Pier Showing Stream Fow Pressure A=3, Veocity vs A=6, Veocity vs A=9, Veocity vs Direct Iteration Soution Procedure...21 Exampes of Noninear Response Requiring Load Incrementation...22 Pie Bent Anayzed to Determine P- top Curve in Transverse Direction..24 P- top Curves in Transverse Direction for HP1x42 Pie Bent in Figure P- top Curves in Transverse Direction for Pie Bent in Figure 2.14 for Batter = xiv

15 Figure 2.17 Figure 2.18 Figure 3.1 Figure 3.2 Figure 3.3 Figure 3.4 Figure 3.5 Figure 3.6 Figure 4.1 Figure 4.2 Figure 4.3 Figure 4.4 Figure 4.5 Figure 4.6 Figure 4.7 Figure 4.8 Figure 4.9 Figure 6.1 P- top Curves in Transverse Direction for Pie Bent in Figure 2.14 for Batter = P- top Curves in Transverse Direction for Pie Bent in Figure 2.14 for Batter = Debris Raft for Pier Design 29 Bent Force for Various Debris Raft Dimensions for V Design = 6mph 32 HP1x42 Unbraced 5-Pie Bent with H=13, S=, and P=1kips Pushover Anaysis Resuts.33 HP1x42 Unbraced 5-Pie Bent with H=13, S=15, and P=1kips Pushover Anaysis Resuts.33 Typica Unbraced Bent and Typica Loading Conditions.35 Typica X-Braced Bent and Typica Loading Conditions.36 Typica Noninear Pie Bent Pushover Curve 38 X-Braced Pie Bent Sidesway Bucking or Pushover Faiure Load..39 Evauation of Bent Pie Kick-Out Load from Extreme Food/Scour Event..39 Typica Pie Bent Support Bridge Over Stream.41 Debris Raft and Food Water Load for Checking Adequacy of Pie Bent During Major Food Event.42 Force for Various Debris Raft Dimensions for V Design = 6mph.43 GTSTRUDL Pushover Anaysis Resuts for HP1x42 4 Pie Bents, Bents Pinned at Ground, H=13ft, S=ft.44 Pan View of Pier Showing Stream Fow and Latera Pressure.46 Evauation of Bent Pie Kick-Out Load from Extreme Food/Scour Event..46 Screening Too (ST) Macro Fowchart 14 xv

16 Figure 6.2 Figure 6.3 Screening Too Fowchart for Assessing Pie Bent Adequacy During an Extreme Food/Scour Event in pocket on back cover Debris Raft and Food Water Load For Checking Adequacy of Pie Bent During Major Food Event Figures A.1-A.4 Figures A.5-A.8 Figures A.9-A.12 Figures A.13-A.16 Figures A.17-A.2 Figures A.21-A.24 Figures A.25-A.28 Figures A.29-A.32 Figures A.33-A.36 Figures A.37-A.4 Figures A.41-A.44 Figures A.45-A.48 Figures A.49-A.52 HP1x42 Unbraced 3-Pie Bents with H=1, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Unbraced 3-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 X-Braced 3-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 X-Braced 3-Pie Bents with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Two-Story X-Braced 3-Pie Bents with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Two-Story X-Braced 3-Pie Bents with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Unbraced 4-Pie Bents with H=1, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Unbraced 4-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 X-Braced 4-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 X-Braced 4-Pie Bents with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Two-Story X-Braced 4-Pie Bents with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Two-Story X-Braced 4-Pie Bents with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Unbraced 5-Pie Bents with H=1, A=6, and Varying P-oads Pushover Anaysis Resuts xvi

17 Figures A.53-A.56 Figures A.57-A.6 Figures A.61-A.64 Figures A.65-A.68 Figures A.69-A.72 Figures A.73-A.76 Figures A.77-A.8 Figures A.81-A.84 Figures A.85-A.88 Figures A.89-A.92 Figures A.93-A.96 HP1x42 Unbraced 5-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 X-Braced 5-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 X-Braced 5-Pie Bents with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Two-Story X-Braced 5-Pie Bents with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Two-Story X-Braced 5-Pie Bents with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Unbraced 6-Pie Bents with H=1, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Unbraced 6-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Singe X-Braced 6-Pie Bent with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Singe X-Braced 6-Pie Bent with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts 2-23 HP1x42 Doube X-Braced 6-Pie Bent with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Doube X-Braced 6-Pie Bent with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts Figures A.97-A.1 HP1x42 Two-Story Singe X-Braced 6-Pie Bent with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts Figures A.11-A.14 HP1x42 Two-Story Singe X-Braced 6-Pie Bent with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts Figures A.15-A.18 HP1x42 Two-Story Doube X-Braced 6-Pie Bent with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts Figures A.19-A.112 HP1x42 Two-Story Doube X-Braced 6-Pie Bent with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts xvii

18 Figures B.1-B.4 Figures B.5-B.8 Figures B.9-B.12 Figures B.13-B.16 Figures B.17-B.2 Figures B.21-B.24 Figures B.25-B.28 Figures B.29-B.32 Figures B.33-B.36 Figures B.37-B.4 Figures B.41-B.44 Figures B.45-B.48 Figures B.49-B.52 Figures B.53-B.56 Figures B.57-B.6 HP12x53 Unbraced 3-Pie Bents with H=1, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Unbraced 3-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 X-Braced 3-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 X-Braced 3-Pie Bents with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Two-Story X-Braced 3-Pie Bents with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Two-Story X-Braced 3-Pie Bents with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Unbraced 4-Pie Bents with H=1, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Unbraced 4-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 X-Braced 4-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 X-Braced 4-Pie Bents with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Two-Story X-Braced 4-Pie Bents with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Two-Story X-Braced 4-Pie Bents with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Unbraced 5-Pie Bents with H=1, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Unbraced 5-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 X-Braced 5-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts xviii

19 Figures B.61-B.64 Figures B.65-B.68 Figures B.69-B.72 Figures B.73-B.76 Figures B.77-B.8 Figures B.81-B.84 Figures B.85-B.88 Figures B.89-B.92 Figures B.93-B.96 Figures B.97-B.1 HP12x53 X-Braced 5-Pie Bents with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Two-Story X-Braced 5-Pie Bents with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Two-Story X-Braced 5-Pie Bents with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Unbraced 6-Pie Bents with H=1, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Unbraced 6-Pie Bents with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Singe X-Braced 6-Pie Bent with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Singe X-Braced 6-Pie Bent with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts HP1x42 Doube X-Braced 6-Pie Bent with H=13, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Doube X-Braced 6-Pie Bent with H=17, A=6, and Varying P-oads Pushover Anaysis Resuts HP12x53 Two-Story Singe X-Braced 6-Pie Bent with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts Figures B.11-B.14 HP12x53 Two-Story Singe X-Braced 6-Pie Bent with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts Figures B.15-B.18 HP12x53 Two-Story Doube X-Braced 6-Pie Bent with H=21, A=6, and Varying P-oads Pushover Anaysis Resuts Figures B.19-B.112 HP12x53 Two-Story Doube X-Braced 6-Pie Bent with H=25, A=6, and Varying P-oads Pushover Anaysis Resuts xix

20 CHAPTER 1: INTRODUCTION 1.1 INTRODUCTION Aabama has hundreds of highway bridges that were designed and constructed prior to 199 and therefore not designed for scour. In addition, there are hundreds of county bridges constructed using standardized designs for which scour anaysis was not part of the foundation design. ALDOT is currenty performing an assessment of scour susceptibiity of its bridges, and a part of this assessment requires an evauation of the structura stabiity of these bridges for an estimated scour event. A common design/construction procedure of highway bridges in Aabama is the use of stee HP pies driven to a firm stratum with a ength above ground/water up to the eve of a concrete bent cap which supports the bridge superstructure. The use of 3, 4, 5, or 6 such pies in a row with the two end pies battered are very common bridge pie bents. The bents are sometimes X-braced in the pane of the pies for atera support and sometimes the pies are encased in concrete from the bent cap down to 3 feet beow ground eve (and the X-bracing eiminated). In an extreme fooding and scour event, the possibiity of considerabe debris buid-up at the bridge bents is very reaistic. This in turn coud resut in sizeabe atera oadings on the bent piing which aso have their unbraced ength enarged consideraby due to scour. This coud create a possibe ack of strength or stabiity probem for the bent and in turn a bridge faiure condition. Investigating this possibiity is the impetus and purpose of this research. 1

21 1.2 OBJECTIVES The objectives of this investigation are as foows: 1. To determine appropriate food debris buid-up mode, resuting bridge bent oadings, mode of bent faiure, and a faiure oad anaysis procedure appropriate for anayzing pie bents in extreme food/scour events. 2. Appy the debris buid-up mode and anaysis procedure identified in (1) and determine the adequacy of some typica ALDOT pie bents over a range of scour eves. 1.3 WORK PLAN A brief work pan to accompish the research objectives cited above is given beow: 1. Review the iterature and AASHTO Design Specifications pertaining to river food debris buid-up and oadings on bridge piers and bents. 2. Deveop bridge bent food oading modes in the transverse direction in extreme scour cases. 3. Identify the potentia modes of faiure of bridge bents for the bent modes in two above. 4. Identify the appropriate anaysis assumptions and procedures for assessing the adequacy or faiure of bridge bents in (2) and (3) above. 5. Appy the debris buid-up mode and anaysis procedure identified above, and anayticay/numericay test the adequacy of some typica ALDOT pie bents over a range of scour eves. 2

22 6. Make recommendations on the easiest and the most appropriate way of incuding this oading and potentia faiure mode in the Bridge Bent Screening Too being deveoped. 7. Prepare a fina report on the research work. 1.4 SCOPE This investigation was imited to a review of the iterature and design specifications on food debris buid-up and bridge pie bent oadings during extreme food events. Anaytica/numerica anayses of some typica ALDOT pie bents subject to a range of food buid-up and scour eves were conducted to assess the adequacy of the pie bents. No aboratory or fied testing was conducted to verify or refute the resuts of the anaytica anayses. 3

23 CHAPTER 2: BACKGROUND AND LITERATURE REVIEW 2.1 BACKGROUND Scour is the movement of the stream bed from around the foundation, and this can significanty change the structura system, creating a situation that must be considered in the design (Barker and Puckett 1997). As noted in the introduction, scour has not been taken into account in the design of a great number of Aabama s bridges. This is cause for concern considering a majority of bridges that have faied in the United States and esewhere have faied due to scour (AASHTO 1997). The specific type of bridge substructure to be examined in this report is the pie bent pier. The pie bent pier has individua supporting pies in a row with the end pies typicay being battered in the transverse directions (Tonias 1995). In Auburn University s Phase I Report to ALDOT it was found that bridges having HP1x42 and HP12x53 pies are of particuar interest because these are the pies sizes commony used by ALDOT (23). Pie bent configurations having 3, 4, 5, and 6-pies are widey used by ALDOT. In the Phase I Report it was found the average bridge width was 32 feet, and the average span ength was 36 feet (23). Pie bents are typicay X-braced in the pane of the pies for atera support, via one-story or two-story X-bracing as shown in Figure 2.1. For short bents, i.e. height < 13 feet, ALDOT aows contractors to encase the pies from 3 feet beow ground ine up to the bent cap and omit the X-bracing as shown in Figure

24 a. Two-Story X-Braced Bent b. One-Story X-Braced Bent Figure 2.1 Typica ALDOT X-Braced Pie Bents 5

25 Figure 2.2 One-Story Bridge with Stee H-Pie Encased and Sway-Bracing Omitted 6

26 2.2 LITERATURE REVIEW Pie bent piers are extremey popuar in marine environments where mutipe, simpe span structures cross reativey shaow water channes (Tonias 1995). However, deterioration of exposed pies, impact from marine traffic, and accumuation of stream debris are a maintenance probems associated with pie bent piers (Tonias 1995). Section of AASHTO LRFD Bridge Design Specifications (1997) requires scour at bridge foundations to be investigated for two conditions. These two conditions are outined in Section tited Bridge Scour and are as foows: Condition 1: The design food for scour: the streambed materia in the scour prism above the tota scour ine sha be assumed to have been removed for design conditions. The design food storm surge tide, or mixed popuation food sha be the more severe of the 1-year event or an overtopping food of esser recurrence interva. Condition 2: The check food for scour: the stabiity of bridge foundation sha be investigated for scour conditions resuting from a designated food storm surge, tide or mixed popuation food not to exceed the 5-year event or an overtopping food of esser recurrence interva. Excess reserve beyond that required for stabiity under this condition is not necessary. The Extreme Event imit state sha appy. Aso in Section of AASHTO it states that if the site conditions, due to ice or debris jams, and ow taiwater condition near stream confuences dictate the use of a more severe food event for either the design or check food for scour, the Engineer may use such food event (1997). Spread footings on soi or erodibe rock sha be 7

27 ocated so that the bottom of footing is beow scour depths determined for the check food for scour. Spread footings on scour-resistant rock sha be designed and constructed to maintain the integrity of the supporting rock. Many Aabama bridges were not designed for this condition of having a debris jam and a severe food event. Maximum scour on some of Aabama s bridges is estimated to be up to 15 feet. The combination of scour and debris buid-up coud resut in substantia atera oading on the bent piing which aso have their height and unbraced engths enarged consideraby due to scour. Food debris buid-up oading are considered to be channe forces. Channe forces are those oads imposed on a structure due to water course-reated features. These forces incude, but are not imited to stream fow, foating ice, and buoyancy (Tonias 1995). In Aabama, foating ice is very infrequent, thus it wi not be taken into consideration. Buoyancy conditions woud ony take pace in severe fooding conditions. Bridges with components (e.g., piers) which are submerged underwater can sometimes suffer from the effects of buoyancy; however, this generay is a probem ony for very arge structures (Tonias 1995). Buoyance can aso impact pier footings and pies (Tonias 1995). Foating ogs, roots and other debris may accumuate at piers, and by bocking parts of the waterway, increase stream veocity and pressure oad on the pier (AASHTO 1997). Such accumuation is a function of the avaiabiity of such debris and eve of maintenance efforts by which it is removed (AASHTO 1997). Water fowing against and around the substructure as we as the possibiity of debris buid-up creates a atera force directy on the substructure (Barker and Puckett 1997). Channe forces, simiar to 8

28 seismic forces, primariy affect substructure eements (Tonias 1995). Such water forces are most critica in food conditions (Barker and Puckett 1997). According to Tonias (1995), excessive stream fow veocity, (V) in addition to increasing water pressure on the substructure proportiona to V 2, can ead to adverse scour conditions which can undermine footings and threaten the integrity of the structure. AASHTO specifications state that the pressure of fowing water acting in the ongitudina direction of substructures (this is usuay transverse to the ongitudina direction of the bridge as shown in Figure 2.6) sha be taken as foows: where, p = pressure of fowing water (KSF) p = C D V 2 /1, (2.1) C D = drag coefficient for piers as specified in Tabe 2.1 beow V = design veocity of water for the design food in strength and service imit states and for the check food in the extreme event imit state (FT/SEC) Tabe 2.1 Drag Coefficients (AASHTO 1997) AASHTO Specification Type C D semi-circuar nosed pier.7 square ended pier 1.4 debris odged against the pier 1.4 wedged nosed pier with nose ange 9 or ess.8 The reationship between water pressure and design veocity for C D = 1.4 can be seen in the Figure

29 .25.2 Water Pressure, (ksf) Design Water Veocity, (mph) Figure 2.3 Reationship Between Water Pressure and Design Water Veocity for C D = 1.4 As noted above, the ongitudina direction refers to the major axis of the substructure unit, which is usuay perpendicuar to the ongitudina axis of the bridge. The drag coefficient, C D presented in AASHTO was adopted from the 1983 Ontario Highway Bridge Design Code. The transverse (to the bridge) drag force sha be taken as the product of stream water pressure as given by Equation 2.1, and the area of the debris raft projected on a vertica surface, as indicated in Equation 2.2 and Figure

30 B High Water Leve (HWL) F T A/3 A Debris Raft Stream Bed Leve Bent Figure 2.4 Debris Raft for Bent Design (AASHTO 1997) = p [shaded area in Fig. 2.4] (2.2) A = ½ x water depth, but not greater than 1 B= ½ x sum of adjacent span engths, but not greater than 45 sha be assumed to act at the centroid of the shaded area. Thus acts at a distance A/3 down for the water surface. In this study the water depth was taken to be at the top of the bent cap, and B was assumed to be 3 feet. These are considered to be conservative approximations. The inear reationships between F T, for a range of vaues 11

31 for A, and B for a stream with V design = 6 mph are dispayed in Figure A=9 15 F d, kips A=6 1 A= B Figure 2.5 Debris Raft Force, F T, for Various Debris Raft Dimensions (B) and (A) with V design = 6mph A pan view of a typica pie bent supported bridge over water with a bent debris raft is shown in Figure 2.6, and section views of a typica bent showing ongitudina and transverse food water oadings are shown in Figure

32 Stream Edge Note: >> F L Debris Raft 1 F L 2 Direction of Stream Fow Pie Bents Bridge Superstructure PLAN VIEW Figure 2.6 Typica Pie Bent Supported Bridge over a Stream 13

33 Superstructure not shown F L F L << FT F L is transmitted aong the superstructure to the abutments, therefore negect F L. SECTION 1 Superstructure not shown P P P P P Assumed HWL A/3 V MAX DEPTH = "H" Origina Ground Leve SCOUR SECTION 2 Figure 2.7 Sections Showing Longitudina And Transverse Food Water Loading on Bent (see Fig. 2.6) 14

34 As seen in Figure 2.6, bridge ongitudina forces may be considered. Longitudina forces resut from vehices braking or acceerating whie on a bridge (Tonias 1995). AASHTO specifies that 5 percent of the appropriate ane oad aong with the concentrated force for moment (for a trave anes going in the same direction) be used as the resuting ongitudina force (AASHTO 1997). This force is appied 6 above the top of the deck surface (Tonias 1995). The effect of ongitudina forces on the superstructure is inconsequentia, however, substructure eements are affected more significanty (Tonias 1995). In genera, the more stiff or rigid the structure, the more severe the effects of ongitudina forces wi be (Tonias 1995). Aso, as seen in Section 2 of Figure 2.6, superstructure gravity oads, i.e. the P- oads in Figure 2.6, are aways acting on the bridge bents. In this study, P-oads of 1, 12, 14, and 16 kips were considered with one such oad paced above each bent pie. These oads in conjunction with the debris raft oad,, probaby constitute the governing design oad on a bridge bent. In anayzing the performance of a bent for this oad combination, the P- effect shoud be considered. In this study, GTSTRUDL pushover anaysis was utiized to consider both the geometric and materia noninearity of this oad combination to determine the adequacy of the bridge bents. Typicay bridge piers/bents are oriented with their ongitudina axis parae to the direction of stream fow. However, sometimes the substructure may be oriented at an ange to the stream fow, as shown in Figure 2.8. AASHTO provides Equation 2.3 and Tabe 2.2 to determine the atera pressure on the pier. 15

35 Figure 2.8 Pan View of Pier Showing Stream Fow Pressure (AASHTO ) The atera drag force sha be taken as the product of the atera stream pressure and the surface exposed thereto (AASHTO 1997). The greater the ange of the fow to the pier/bent the greater risk of possibe bent faiure. Potentia modes of bent faiure are discussed more in depth in Chapter 4. p = C L *V 2 /1 EQN 2.3 Where, p = atera pressure (KSF) C L = atera drag coefficient specified in Tabe 2.2. V = stream design fow veocity in (fps). 16

36 Tabe 2.2 Latera Drag Coefficient (AASHTO 1997) Ange, θ, between direction of fow and ongitudina axis of the pier C L The veocity, V, of the water in Equations 2.1 and 2.3 is typicay estimated based on the conditions at the site. A range of different configurations of pie bent span engths and water heights can resut in a considerabe number of vaues for A, B and thus thousands of different vaues for. The vaue of is found using Equation 2.2. Figures simpify the process of evauating by using a range of vaues for A, B and V. Once the force for a particuar bent is found, one must determine if the bridge is safe for this oading. But what is the argest force that a particuar bent can hande and sti be considered safe? In this report the answer to this question was anayzed using a noninear pushover anaysis performed in GTSTRUDL. Using GTSTRUDL s pushover anaysis, the (force due to debris oads) that woud pushover various pie bents were determined. In the pushover anaysis different eves of scour and different oadings were paced on the pie bents to determine the effects of scour on the bridges. 17

37 4. B=2 B=3 B= Ft, kips Veocity, mph Figure 2.9 A=3, Veocity vs. 4. B=2 B=3 B= Ft, kips Veocity, mph Figure 2.1 A=6, Veocity vs. 18

38 4. B=2 B=3 B= Ft, kips Veocity, mph Figure 2.11 A=9, Veocity vs. Pushover anaysis is a noninear anaysis procedure that was born in the seismic anaysis community. The technique is based on the conventiona dispacement method of anaysis. Standard eastic and geometric stiffness matrices for the structure eements are progressivey modified to account for geometric (P effect) and/or materia noninearity under constant gravity oads and incrementay increasing atera oads or vice versa. In GTSTRUDL, a Newton-Raphson soution technique based on the tangent stiffness method is used to sove the noninear equations resuting from the geometric and materia noninearities. This soution technique is iustrated in Figure 2.12 (GTSTRUDL 22). Load incrementation is particuary vauabe for the noninear anaysis of structures which exhibit dramatic changes in stiffness during the course of oad appication. 19

39 Typica exampes incude cabe structures, which demonstrate stress-stiffening behavior, and frame structures, which exhibit instabiity behavior (e.g. bucking). Stress stiffening behavior is characterized by rapidy increasing stiffness for sma changes in strain, typicay during the eary stages of oading (see Figure 2.13a) (GTSTRUDL 22). Frame structure instabiity is characterized by rapidy decreasing stiffness for sma changes in deformation during the ate stages of oading when the coapse oad is approached (see Figure 2.13b) (GTSTRUDL 22). In situations such as these, the noninear anaysis may not converge if the tota oading is appied as a singe increment of sufficient magnitude to encompass the regions where the oad-dispacement response exhibits rapid stiffness change. Breaking the tota oading into a smaer number of increments, particuary in the regions of rapid stiffness change, can significanty improve the success of the convergence and subsequent anaysis. 2

40 Figure 2.12 Direct Iteration Soution Procedure (GTSTRUDL 22) 21

41 Figure 2.13 Exampes of Noninear Response Requiring Load Incrementation (GTSTRUDL 22) Pushover anaysis is described in GTSTRUDL Reference Manua, Vo. 3 as an automated incrementa oad anaysis which aso contains a procedure that automaticay searches for the oad eve at which structura instabiity or coapse occurs (22). In 22

42 GTSTRUDL, the Pushover Anaysis Data and Perform Pushover Anaysis commands are used together to perform a pushover anaysis. The Pushover Anaysis Data command is used to specify the vaues for a series of parameters that contro the pushover anaysis procedure and must be given first. The Perform Pushover Anaysis command foows and is used to execute the pushover anaysis procedure. A Print Pushover Anaysis Data command is used to verify the parameter vaues specified by the Pushover Anaysis Data command. FB-Pier recenty added a pushover tab/anaysis capabiity to their software. Thus, their software can now perform a noninear pushover anaysis of a pie or pie bent in a soi setting. In the anaysis procedure, two oad cases are required one for permanenty appied oads and one for oads to be incremented. The 5-pie bent shown in Figure 2.14 was anayzed via FB-Pier pushover anaysis for scour vaues of S=, S=5, S=1, S=15, and S=2. In the anayses, the 1 kip horizonta force at the bent cap was hed constant and the P oads were incrementay increased unti FB-Pier woud not converge (this was viewed as the faiure oad). Note in this case, the pies were bending about their weak axis (Y Y axis). Soi and other parameter vaues used in the FB-Pier modeing are given in Tabe 2.3. The resuting P top curves generated in the anayses are shown in Figure

43 Figure 2.14 Pie Bent Anayzed to Determine P- top Curve in Transverse Direction 24

44 Tabe 2.3 Soi and Other Parameter Vaues Used in FB-Pier Modeing of Probems Shown in Figure 2.14 Pie: HP1x42 Pie ength: 8 ft Initia pie ength above ground: 2 ft. Sand (Reese): Unit weight = 12 pcf Interna friction ange = 35 Subgrade moduus = 15b./in.^3 Poisson's ratio =.3 Shear moduus = 3.5 ksi Vertica faiure shear = 1152 psf Torsiona shear stress = 1152 psf Tip: Shear moduus = 3.5 ksi Poisson's ratio =.35 Axia bearing faiure = 64 kips Scour depth (ft.):, 5, 1, 15, 2 25

45 Figure 2.15 P- top Curves in Transverse Direction for HP1x42 Pie Bent in Figure 2.14 (Brown and Ramey 23) To determine the sensitivity of pie bent P top curve in the transverse direction to the end pie batter, the pie bent shown in Figure 2.14 was re-anayzed using FB-Pier, for end pie batters of 1 in 12 or.83, 1½ in 12 or.125, and 2 in 12 or.167. The same soi setting and conditions as identified in Tabe 2.3 were used in the anayses, and the resuts are shown in Figures These figures iustrate some of the capabiities and vaues of pushover anayses. 26

46 Figure 2.16 P- top Curves in Transverse Direction for Pie Bent in Figure 2.14 for Batter =.83 (Brown and Ramey 23) Figure 2.17 P- top Curves in Transverse Direction for Pie Bent in Figure 2.14 for Batter =.125 (Brown and Ramey 23) 27

47 Figure 2.18 P- top Curves in Transverse Direction for Pie Bent in Figure 2.14 for Batter =.167 (Brown and Ramey 23) In a preceding separate study for ALDOT, it was found that the most appropriate and sound way to anayze bridge pie bents was using GTSTRUDL s pushover anaysis capabiities. Thus, in this study ony GTSTRUDL was used to anayze bridge pie bents. 28

48 CHAPTER 3: DESCRIPTION OF BRIDGE PILE BENT DEBRIS BUILD-UP AND LOADING MODEL FOR EXTREME FLOOD/SCOUR EVENTS 3.1 GENERAL Each bridge over water that is supported by pie bents and may be susceptibe to an extreme food/scour event shoud be checked to make sure that the bent is abe to withstand a combined transverse debris raft force,, gravity oads appied by the bridge superstructure, and an extreme eve of scour. This transverse oad,, can be used to check the bent for a pushover faiure from combined gravity and food water atera oads in conjunction with the extreme scour of the bent site. The oading mode used to assess the adequacy of bridge pie bents when debris buid-up is in pace was taken from AASHTO C (1997). The debris raft mode is shown in Figure 3.1. B High Water Leve (HWL) Debris Raft F T A/3 A Water Depth (after scour) Stream Bed Leve Bent Figure 3.1 Debris Raft for Pier Design (AASHTO 1997) 29

49 3.2 DESCRIPTION OF DEBRIS BUILD-UP MODEL In Figure 3.1, is the food water force appied to the bridge pie bent due to debris buid-up. As discussed in Chapter 2, this force is based on the pressure of the fowing water in kips per square foot, the size of the debris raft in square feet, and C D, the drag coefficient, which is equa to 1.4 for debris odged against a pier. is appied at a distance of A/3 down from the water surface as shown in Figure 3.1. The equations to find are given in the AASHTO Specifications and are as foows (1997): p = C D x (V 2 /1) where V is in fps and p is in ksf (3.1) = p x (1/2 x A x B) (3.2) A = ½ x water depth, but not greater than 1 B= ½ x sum of adjacent span engths, but not greater than 45 As covered earier, a GTSTRUDL pushover anaysis was the method empoyed to find the pushover vaues of for different bent sizes and conditions. The GTSTRUDL pushover anaysis determines the argest force that a bent can hande before pushingover, and aso cacuates the corresponding defection. Pushover curves with defection versus the pushover force,, for pie bridge bents commony used by ALDOT can be found in the Appendices of this report. These curves may be used to find the pushover force,, for a particuar bent and oading condition. Once the appropriate for a particuar bent is found it may be used in conjunction with the screening too presented in Chapter 6 of this report to check and see if a faiure by pushover is possibe or imminent. The debris raft mode presented in Sections C of the AASHTO was used to decide where the transverse oad,, was to be paced on the GTSTRUDL mode of the pie bents. The mode gives guideines for where a debris oad is ikey to impact a bent. 3

50 According to the mode the debris raft force,, is ikey to be appied a distance A/3 from the high water eve (HWL). In this study the high water eve was aways taken at the top of the bent cap. This eve was seected because bridge eevations are typicay seected so that the HWL does not impinge on the bridge superstructure. In the debris raft mode shown in Figure 3.1, the ony vaue needed to perform a pushover anaysis in GTSTRUDL was the vaue of A. The vaue of B was not needed to perform the GTSTRUDL anaysis because the span ength has no effect upon the ocation of on the bent. The B vaue does affect the magnitude of, but most spans are short, and a vaue of B equa to 3 feet was taken for a bridges in determining the force. The ocation of the force is dependent ony on the vaue of A. As seen in Figure 3.1 the ocation of is ocated at a distance of A/3 down from the HWL. Figure 3.2 shows the appied bent force,, for various vaues of A and B for an assumed V design = 6 mph. To examine a range of vaues, A was taken as either equa to 3, 6, or 9. A may not be taken arger than 1 as per AASHTO C , thus, this range of vaues was chosen to exhibit the compete combination of possibe conditions. It was found that the pushover oad when modeing the debris raft with a vaue of A between A=3, 6, or 9 is somewhat dependent on the amount of scour. If a bent has zero scour the differences between pushover oads for vaues of A between A=3, 6 or 9 vary sighty. For exampe, in Figure 3.3 beow, pushover oad varies by about 7 kips between the two extreme cases of A=3 and A=9. However, if the bridge has a arge scour such as scour equa to 15, the differences between pushover oads for various vaues of A barey differ at a as can be seen in Figure

51 Figure 3.2 Bent Force for Various Debris Raft Dimensions for V Design = 6mph 32

52 45 4 A=3' A=6' A=9' 35 3 Ft (kips) 25 2 Ft P P P P P Estimated High Water Leve Center Line of Pie origina ground ine S = Scour Defection, (in) Figure 3.3 HP1x42 Unbraced 5-Pie Bent with H=13', S=', and P=1kips Pushover Anaysis Resuts 25 A=3' A=6' A=9' 2 15 Ft (kips) 1 Ft P P P P P Estimated High Water Leve 5 Center Line of Pie origina ground ine S = Scour Defection, (in) Figure 3.4 HP1x42 Unbraced 5-Pie Bent with H=13',, and P=1kips Pushover Anaysis Resuts 33

53 In Chapter 5, A was aways taken equa to 6 feet, to simpify the resuts and to reduce the quantity of pushover curves. If studying a bent with ow scours, and the depth of the debris raft is characterized as something other than A=6, then the differences discussed above shoud be taken into account. 3.3 DESCRIPTION OF LOADING MODEL Based on the Phase I report submitted to ALDOT by Ramey and Brown (23), a samping of the most common pie bents and oading configurations were seected to be studied in greater depth. Bents having 3, 4, 5 and 6-pies were examined. Concentrated gravity P oads of 1 kips, 12 kips, 14 kips and 16 kips were appied to the bents and centered above each of the pies. This range of P oads between 1 kips and 16 kips represents a conservative range of vaues. These vaues were determined by using information provided in the Phase I report (Brown and Ramey 23). Bents having HP1x42 and HP12x53 pies were examined. If the height of the bent is sma, i.e., H < 13ft., the bent may be unbraced, but have the piing encased in concrete. Aternatey, if H < 13ft. the bent piing may be unencased, but be X-braced. If 13ft < H < 19ft. the bent wi aways be X-braced, and if 2ft < H < 25ft the bent wi have verticay stacked X- bracing (two-stories). The 3, 4, and 5-pie X-braced bents are singe X-braced (either one-story or two-story bracing); however, the 6-pie bents may have side-by-side X- bracing or doube X-bracing. In this study, in the GTSTRUDL Pushover Anaysis, the horizonta,, force is the force being incremented and simuating the presence of a food water oading condition and a debris raft buidup. An exampe of a typica bent oading condition may be seen in Figure

54 P P P P P Estimated High Water Leve Center Line of Pie origina ground ine S = Scour Figure 3.5 Typica Unbraced Bent and Typica Loading Conditions The back dots at the bottom of the pies in Figure 3.5 represent pinned connections. Pinned connections at the ground ine were used after determining that this woud be the best method for modeing the end conditions. Two other bent pie end conditions were considered, those being fixed and fixed with an added 5 of exposed pie ength. This added 5 of ength to the end of the pie was determined by a preceding separate study. It is reaized that in actua site conditions the actua fixity condition may be something in between pinned and fixed conditions. This presents some amount of inaccuracy into this study, and shoud be taken into account if it is known that the fixity conditions are something other than pinned. In concusion of this study, it was determined that pinned connections woud be the most conservative approach to take; thus, a pushover anayses were performed using pinned end conditions. 35

55 On X-braced bents there are dots where the X-bracing connects to the bent pies. A picture of a typica X-braced bent may be found beow in Figure 3.6. The back dots connecting the X-bracing to the bent pies simpy represent ocations where the X-bracing is connected to the pies in the bent, and do not represent hinges or pins. P P P P P Estimated High Water Leve Center Line Origina of Pie Ground Line "S" = Scour Figure 3.6 Typica X-braced Bent and Typica Loading Conditions On the versus defection pushover curves presented in the Appendices A and B, drawings of the bent and the particuar oading condition are given on each graph for carity on the bent geometry, bracing condition, and oading condition represented by the P- curves of that figure. 36

56 CHAPTER 4: POTENTIAL MODES OF PILE BENT FAILURE DURING FLOOD DEBRIS BUILD-UP AND SCOUR EVENTS 4.1 GENERAL Extreme food/scour event oadings, in conjunction with ever present gravity P- oads on a bridge pie bent can be a controing oad condition if the bent transverse oad,, and scour, S, are arge (see Figure 4.1). Even for bents which are X-braced in the transverse direction, a significant P- effect and a bent pushover faiure may be possibe in the region from the new ground ine (NGL) to approximatey 4 feet above the origina ground ine (OGL) as indicated in Figure 4.2. Additionay, for extreme food/scour events, bent pie kick-out faiures may occur if the eve of scour approaches that of the origina eve of pie embedment as indicated in Figure 4.3. Each of these potentia faiure modes is discussed in the sections beow. 4.2 PILE BENT PUSHOVER FAILURE It is possibe for a pie bent to fai due to pushover, and the presence of scour and a debris oad in a food condition make a faiure due to pushover more probabe. To determine the maximum appied bent food water oad,, the current ALDOT bridge/bent information database may need to be expanded to incude the additiona parameter vaues isted beow. This expansion is needed in order to check the bent for a possibe pushover faiure from combined gravity and food water atera oads. It shoud 37