CULVERT LOAD RATING & LOAD TESTING Ping Lu*, Scott Neubauer*, Brent Phares**, Ahmad Abu- Hawash* * The Office of Structures and Bridges Iowa Department of Transportation ** Bridge Engineering Center Iowa State University Ping.lu@dot.iowa.gov 515-239-1290 1
Acknowledgement Appreciate all the coauthors for their contribu2ons to this work Iowa DOT for funding the load tes2ng program through Federal SPR funding 2
What is Load Rating Determina2on of the live load carrying capacity based on current condi2on Using as- built plans Using latest field inspec2on data Results are expressed as Ra2ng Factor (RF) or tonnage for a par2cular vehicle General equa2on for load ra2ng RF= C DL/LL In which, C = Capacity of bridge element DL = Dead load effect LL = Live load effect 3
Why Do We Need Load Rating Ensure public safety and serviceability of structures over 2me Evaluate pos2ng needs Processing overload permits Maintenance priori2za2on Comply with federal regula2ons : required by NBIS (Na2onal Bridge Inspec2on Standards) need to be reported every year 4
Guidelines for Culvert Load Rating AASHTO Manual for Bridge Evalua2on (MBE) Sec2on 6A.5.12, AASHTO MBE, 2nd Edi2on, with 2013 Interim Revisions AASHTO LRFD/Standard Bridge Design Specifica2ons Iowa DOT Bridge Ra2ng Manual Iowa DOT Bridge Design Manual 5
Problems in Rating Older Culverts Rated with LRFR, many exis2ng culverts that were designed to LFD or ASD specifica2ons are seen as deficient; they cannot even support the dead load Most of these in- service culverts have performed sa2sfactorily for decades This is a common problem for older culverts A na2onwide survey was conducted by Iowa DOT in 2013 through AASHTO SCOBS (Sub- Commi_ee of Bridges & Structures) Replies from more than 21 agencies were received; and 10 indicated they have the same problem 6
Reasons Changes in Design Guidelines AASHTO Standard Specifica2ons evolved Ver2cal earth pressure (EV) Horizontal earth pressure (EH) Compare to Standard Specifica2ons, LRFD recommends, in general, higher Live load distribu2on through the earth fill Live load surcharge Dynamic load impact factor Factors contribute the most to the ra2ng problems in Iowa Live load distribu2on and impact EH 7
Dynamic Impact 0.35 0.3 0.25 LRFD Standard Impact 0.2 0.15 0.1 0.05 0 0 1 2 3 4 5 6 7 8 9 Fill Depth - H (ft) 8
Live Load Distribution Fill depth < 2c Standard LRFD Perpendicular to the span E E Parallel to the span concentrate load L T +LLDF(H) E=96+1.44S E in inch and S in ft 9
Live Load Distribution (Con t) Fill depth >= 2c Standard LRFD Spread w (Perpendicular) 1.75(H) W+LLDF(H) Spread l (Parallel) 1.75(H) L+LLDF(H) 10
Live Load Distribution (Con t) Fill depth >= 2c (P=16k) Wheel Pressure (psf) 1800 1600 1400 1200 1000 800 600 400 200 0 LRFD Design Truck Standard Design Truck 305.4psi 145.1psi 0 5 6ft 10 15 20 25 Fill Depth - H (ft) 11
Lateral Earth Pressure (EH) Standard Specifications Before 1983 After 1983 LRFD & MBE EH= k a γ s z (30pcf)z EH k a = 1 sin /1+sin 60/30pcf 60/30pcf 12
Earth Pressure used in Iowa Culvert Standards Office loading: EV = 140pcf EH = 36pcf AASHTO loading: EV = 120pcf EH = 60pcf 1987 standards (single and twin boxes): office earth pressure 1994/1995 standards (metric units) Triple boxes were added AASHTO loading was adopted Early 2000 s (US units) Single/twin boxes Office loading (87 standards were used) Triple boxes AASHTO loading (Metric standards were converted to US unit) 2012 LRFD 13
Culvert Load Testing Live load distribu2on through earth fill Lateral Earth Pressure (EH) 14
Live Load Testing Six culverts tested FHWA No. County Earth Fill Sizes Year Built 1 605880 Boone <1ft 2X12X6X70 1989 2 15351 Boone 11 2X12X10X124 1979 3 15190 Boone 2 2X10X8X160 1962 4 15371 Boone 15 2X12X12X142 1979 5 26600 Hamilton 5 2X12X14X135 1968 6 27111 Hardin 3 2X10X10X86 1976 15
Live Load Testing (Con t) Sensor deployment 1-9 are 9 Strain Rosettes 16
Live Load Testing - Results FHWA #15190 (fill depth = 2c) 10 by 8 Twin box built in 1962 carries US 30 over Noah Creek in Boone County ADT = 7900, 9% truck 17
Live Load Testing - Results Strain (με) FHWA #15190 (fill depth = 2c) 16.0 14.0 12.0 10.0 8.0 6.0 4.0 2.0 R4: Max R4: X- axis R4: Y- axis 0.0 0.0-2.0 20.0 40.0 60.0 80.0 20.0 100.0 120.0 Loca/on (0) Stress (psi) 50.0 40.0 30.0 10.0 Max Strain = 13.9µƐ Max Stress = 43.53psi Max Moment = 6.1k-in R4: Max R4: X- axis R4: Y- axis 0.0 0.0 20.0 40.0 60.0 80.0 100.0 120.0-10.0 Loca/on (0) 18
Results Discussion Load Testing (k-in) Standard (k-in) LRFD (k-in) Max M+ of Slab 6.1 47.5 49.9 Standard LRFD 19
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Conclusions LRFD/LRFR for concrete box culvert might be overly conserva2ve in es2ma2ng LL and EH effects Current AASTO guideline for concrete box culvert ra2ng is not adequate More research is required 26
Questions? 27
Thank You! 28