Chapter 16. Trail Bridges ...................................................................................... 16-1 16.1. Bridge Site Evaluation ................................................................................ 16-1 16.2. Selecting a Bridge Design .......................................................................... 16-7 16.2.1. Log Stringer Bridge ................................................................................. 16-9 16.2.1.1. Applications .................................................................................... 16-9 16.2.1.2. Attributes ........................................................................................ 16-9 16.2.1.3. Limitations ...................................................................................... 16-9 16.2.1. Milled Stringer Bridge ........................................................................... 16-11 16.2.1.1. Applications .................................................................................. 16-11 16.2.1.2. Limitations .................................................................................... 16-11 16.2.2. Glue-Laminated (Glulam) Stringer Bridge ............................................. 16-13 16.2.2.1. Applications .................................................................................. 16-13 16.2.2.2. Attributes ...................................................................................... 16-14 16.2.2.3. Limitations .................................................................................... 16-14 16.2.2.4. Drop Down Deck Design .............................................................. 16-15 16.2.2.5. Arched Bridge Design .................................................................. 16-17 16.2.3. Overhead Wooden Truss Bridge .......................................................... 16-17 16.2.3.1. Applications .................................................................................. 16-17 16.2.3.2. Attributes ...................................................................................... 16-17 16.2.3.3. Limitations .................................................................................... 16-18 16.2.4. Hip Truss Wooden Bridge ..................................................................... 16-19 16.2.4.1. Applications .................................................................................. 16-19 16.2.4.2. Attributes ...................................................................................... 16-19 16.2.4.3. Limitations .................................................................................... 16-20 16.2.5. All Weather Steel I Beam Bridge .......................................................... 16-20 16.2.5.1. Applications .................................................................................. 16-20 16.2.5.2. Attributes ...................................................................................... 16-20 16.2.5.3. Limitations .................................................................................... 16-21 16.2.6. Galvanized Steel I Beam Bridge ........................................................... 16-23 16.2.6.1. Applications .................................................................................. 16-23 16.2.6.2. Attributes ...................................................................................... 16-23 16.2.6.3. Limitations .................................................................................... 16-24 16.2.7. Steel Truss Bridge ................................................................................ 16-25 16.2.7.1. Applications .................................................................................. 16-25 16.2.7.2. Attributes ...................................................................................... 16-25 16.2.7.3. Limitations .................................................................................... 16-25 16.2.8. Aluminum Truss Bridge ........................................................................ 16-26 16.2.8.1. Applications .................................................................................. 16-26 16.2.8.2. Attributes ...................................................................................... 16-26 16.2.8.3. Limitations .................................................................................... 16-26 16.2.9. Fiber Reinforced Plastic (Fiberglass) I Beam Bridge ............................ 16-27 16-i 16.2.9.1. Applications .................................................................................. 16-27 16.2.9.2. Attributes ...................................................................................... 16-27 16.2.9.3. Limitations .................................................................................... 16-28 16.2.10. Fiber Reinforced Plastic (Fiberglass) Pony Truss Bridge .................. 16-28 16.2.10.1. Applications .................................................................................. 16-28 16.2.10.2. Attributes ...................................................................................... 16-28 16.2.10.3. Limitations .................................................................................... 16-29 16.2.11. Suspension Bridge ............................................................................ 16-29 16.2.11.1. Applications .................................................................................. 16-29 16.2.11.2. Attributes ...................................................................................... 16-30 16.2.11.3. Limitations .................................................................................... 16-30 16.2.12. Pipe Bridge ........................................................................................ 16-31 16.2.12.1. Applications .................................................................................. 16-31 16.2.12.2. Attributes ...................................................................................... 16-31 16.2.12.3. Limitations .................................................................................... 16-31 16.2.13. Architectural and Historical Considerations ....................................... 16-32 16.3. Selecting an Abutment Design ................................................................ 16-32 16.3.1. Earthen/Rock Abutment ........................................................................ 16-33 16.3.1.1. Applications .................................................................................. 16-33 16.3.1.2. Attributes ...................................................................................... 16-34 16.3.1.3. Limitations .................................................................................... 16-34 16.3.2. Soil/Rock Retention Abutments ............................................................ 16-34 16.3.3. Interlocking Wooden/Plastic Cribbed Abutment .................................... 16-35 16.3.3.1. Applications .................................................................................. 16-35 16.3.3.2. Attributes ...................................................................................... 16-35 16.3.4. Multi-Tier Rock Abutment ..................................................................... 16-36 16.3.4.1. Applications .................................................................................. 16-36 16.3.4.2. Attributes ...................................................................................... 16-37 16.3.4.3. Limitations .................................................................................... 16-37 16.3.5. Concrete Abutments ............................................................................. 16-38 16.3.5.1. Applications .................................................................................. 16-38 16.3.5.2. Attributes ...................................................................................... 16-38 16.3.5.3. Limitations .................................................................................... 16-38 16.3.6. Trestle Abutments ................................................................................ 16-39 16.3.6.1. Applications .................................................................................. 16-39 16.3.6.2. Attributes ...................................................................................... 16-40 16.3.6.3. Limitations .................................................................................... 16-42 16.3.7. Abutment Sills ....................................................................................... 16-42 16.3.7.1. Types of Abutment Sills ................................................................ 16-43 16.3.7.2. Sizing an Abutment Sill ................................................................ 16-44 16.3.7.3. Length of a Mudsill ....................................................................... 16-47 16-ii 16.4. Initial Best Management Practices .......................................................... 16-48 16.5. Abutment Layout ....................................................................................... 16-49 16.5.1. Establishing a Center Line and Clearing............................................... 16-49 16.5.2. Determining the Abutment Elevations .................................................. 16-51 16.5.3. Excavating Earthen Abutments and Abutment Foundations ................