Prepared by E. Farm and M. Ferry

3 FEB 99

• STEP 1: Gather Information
  • design and overload vehicle axle loading
  • bridge options (i.e. glulam, portable, concrete)
  • bridge design references (i.e. USFS, FERIC, AASHTO)
  • computer models (i.e. BRIDGE, TBSR)
  • abutment design
  • field notes of site survey
  • distributor information (web)
  • hydrologic data (i.e. 100 yr. flood level)

• STEP 2: Determine Bridge Specifications
  • determine span length from site survey
  • determine road width from design/overload vehicle
  • determine if simple or continuous span is required
  • specify type of decking (will give bending/shear properties)
  • specify type of beam (will give bending/shear properties)
  • determine the dead load (decking, running surface, curb/railing)

• STEP 3: Hand Calculations based on USFS Timber Bridge Manual
  • Reference Bridge Design Procedure prepared by Mark Ferry
  • define basic bridge configuration and design criteria (see STEP 2)
  • select beam combination symbol
  • determine deck dead load and dead load moment
  • determine live load moment
  • determine beam size based on bending
  • check live load deflection
  • check horizontal shear
  • check lateral and longitudinal loads
  • determine bearing strength and stress
  • determine camber

• STEP 4: Computer Model Calculations based on USFS TBSR program
  • Reference Process Diagram for Using Timber Bridge Superstructure Rating Program prepared by Eric Farm
  • input design specifications
  • ensure distribution factor (df) is nearly equal for interior and exterior stringers
  • input design vehicle/axle load
  • ensure inventory(design) and operating(overload) ratios are greater than 1
  • if ratio is greater than 1 design is acceptable, if ratio is less than 1 design will fail under specified loading

• STEP 5: Verification of Computer Model
  • compare output of model to hand calculations based an same design inputs