Load Rating of Precast Box Culverts Brian Barngrover
Load Rating of Precast Box Culverts Brian Barngrover, P. E. January 18, 2018
What is a Load Rating? 2 Rigid Rugged Resilient
What is a Load Rating? • “Units of live load that can be supported by a bridge before the structure reaches a defined limit state” 3 Rigid Rugged Resilient
What is a Limit State? 4 Rigid Rugged Resilient
What is a Limit State? • (from LRFD) – “A condition beyond which the bridge or component ceases to satisfy the provisions for which is was designed. ” 5 Rigid Rugged Resilient
Simple example: 6 Rigid Rugged Resilient
Simple example: 7 Rigid Rugged Resilient
Simple example: 8 Rigid Rugged Resilient
Simple example: RF = 2. 0 9 Rigid Rugged Resilient
Where are Load Ratings defined? 10 Rigid Rugged Resilient
Rating Equation (from MBE): 11 Rigid Rugged Resilient
Rating Equation: RF = (C – DL) / LL 12 Rigid Rugged Resilient
Rating Equation: RF = (C – DL) / LL • C = Capacity of the bridge element (limit state) 13 Rigid Rugged Resilient
Rating Equation: RF = (C – DL) / LL • C = Capacity of the bridge element (limit state) • DL = Dead load effects (essentially all non-live loads) 14 Rigid Rugged Resilient
Rating Equation: RF = (C – DL) / LL • C = Capacity of the bridge element (limit state) • DL = Dead load effects (essentially all non-live loads) • LL = Live load effects (based on one ‘unit’ of live load) 15 Rigid Rugged Resilient
Which culverts need to be rated? • Only bridges are load rated • Bridges were defined as having clear spans > 20’ • The definition of a bridge has been changing 16 Rigid Rugged Resilient
Required Load Ratings 17 Rigid Rugged Resilient
Required Load Ratings • Inventory Rating 18 Rigid Rugged Resilient
Required Load Ratings • Inventory Rating • Operating Rating 19 Rigid Rugged Resilient
Trucks used in Rating Factors 20 Rigid Rugged Resilient
Vehicles used in Rating Factors • Design Vehicle 21 Rigid Rugged Resilient
Vehicles used in Rating Factors • Design Vehicle • Permit Vehicle 22 Rigid Rugged Resilient
Vehicles used in Rating Factors • Design Vehicle • Permit Vehicle • Legal Vehicle 23 Rigid Rugged Resilient
Load Rating Culverts • Which limit states are checked? 24 Rigid Rugged Resilient
Load Rating Culverts • Which limit states are checked? • Flexure 25 Rigid Rugged Resilient
Load Rating Culverts • Which limit states are checked? • Flexure • Shear 26 Rigid Rugged Resilient
Load Rating Culverts • Which limit states are checked? • Flexure • Shear • Where are these limit states checked? 27 Rigid Rugged Resilient
Load Rating Culverts • Which limit states are checked? • Flexure • Shear • Where are these limit states checked? • At the critical sections 28 Rigid Rugged Resilient
Where are the critical sections? 29 Rigid Rugged Resilient
Where are the critical sections? • For flexure, there are three possible locations (+ mid-span) 30 Rigid Rugged Resilient
Where are the critical sections? • For flexure, there are three possible locations 31 Rigid Rugged Resilient
Where are the critical sections? • For flexure, there are three possible locations 32 Rigid Rugged Resilient
Where are the critical sections? • For flexure, there are three possible locations 33 Rigid Rugged Resilient
Where are the critical sections? • For shear, there are two possible locations (+ midspan) 34 Rigid Rugged Resilient
Where are the critical sections? • For shear, there are two possible locations 35 Rigid Rugged Resilient
Where are the critical sections? • For shear, there are two possible locations 36 Rigid Rugged Resilient
Getting to 1. 0 • Maximum moment/maximum shear • Axial loads • Steel yields • Critical section locations – can you move them? • Haunches in the structural model • Always distribute wheel loads • Always check iterative beta • Critical section depths 37 Rigid Rugged Resilient
Problems with Rating Culverts 38 Rigid Rugged Resilient
Problems with Rating Culverts • Older culverts design using LFD or ASD 39 Rigid Rugged Resilient
Problems with Rating Culverts • Older culverts design using LFD or ASD • Culverts at depths where LL can be neglected 40 Rigid Rugged Resilient
Live ETCulvert Demo 41 Rigid Rugged Resilient
Questions?
- Slides: 42