Transcript Slide 1

Longer Combination Vehicles & Road
TxDOT Project 0-6095
Trains for Texas?
UTSA: Angela Weissmann, Jose
Weissmann
CTR: Robert Harrison, Jolanda
Prozzi, Kara Kockelman, Bridget
Bienkowski, C.M. Walton
Industry Panel: H-E-B, Frito-Lay,
PepsiCo
1
Background
 1982 Federal Increase
•
•
80K lb. interstate limit
14 “grandfathered” LCV states
 ISTEA
•

All truck size and weight limits “frozen”
Texas Trucking
•
•
•
59% of value
57% of the weight
44% of the miles
 Economy
•
Will higher trucking costs impair growth?
LCV Adoption
 LCV adoption is not new—so why has it failed in the
U.S?
1. Federal highways are shared—safety
2. Revenue equity issue
3. Railroads
4. Economies of scale—all modes except trucks?
0-6095 Study—Texas
 Two truck types
 Key state corridors
 Not rail competitive
 Cost impacts
LCV Types Identified by Panel
Double 53’
Source: Sunbury Transport
Source: Pioneer West
Tridem
Pavement and Bridge Analysis
Objective
Estimate potential LCV
impacts on pavements and
bridges in four Texas
corridors
IH20/IH10
IH20
IH45
IH35
IH37/US281
Data Treatment Pavements
Objective: prepare input files for the pavement
analysis.
1.
2.
3.
Divide each corridor into segments with
uniform truck traffic, same pavement and
same subgrade type;
Develop load spectra for existing and LCV
scenarios; and
Obtain subgrade and material properties, tire
pressures, detailed axle configuration.
7
152 Analysis Segments
example
8
Seg 3 = 2mi
Seg 4 = 7.3mi
Seg 5 = 8.2mi
Seg 6 = 23mi
9
LCV Scenario
Existing Class 9
35%
15%
Observed
spectra
20%
30%
97k tridem
90k double 53’
138k double 53’
Total cargo remains unchanged
10
Example
IH45 analysis segment 1
13,600 trucks /day
WIM station #539
11
Load Spectra Analysis
ADTT
LCV
scenario
Classification
counts
Axle load
frequencies
Load spectra with
& without LCVs
Legend
Data sources
WIM Data
Reports
ESALs
Analysis
direction
Data treatment
12
up
t
4. o 4
.4
4
8. to
8.
8
13 to 8
.2 13
to .2
17 17
.6 .6
22 to
2
26 to 2
.4 26
.
30 to 4
.8 30
.
35 to 8
.2 35
.
39 to 2
.6 39
.
44 to 6
.1 44
.
48 to 1
.5 48
.
52 to 5
.9 52
to .9
57
.3
Tandem axles
Tandem Axles / Day
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
No LCVs
LCV Scenario
Axle weight (kips)
13
Measures of LCV Impacts
Dlife
= Pvt. Life w/ LCV – Pvt. Life w/o LCV
|Dlife|≥1 or Life<50yrs
Dcost
= Annual. cost w/ LCV – Annual. cost w/o LCV
Dlife<1 
Dcost>0  LCV scenario worse
Dlife>1 
Dcost<0  LCV scenario better
14
How did we obtain Dlife?
For the 152 analysis segments
Load spectra with
and without LCV
Pavement
crosssections
Material and
SG properties
Maximum
strains
Nr  1.365 10
9
Na  0.0795 ε t
εc
4.477
3.291
E0.854
Nf
Lif e 
N
KENLAYER
KENSLABS
Maximum
stress
18
16
14
12
10
8
6
4
2
0
0.45
Nf
(1E6)
0.5
0.55
0.6
smax/S
15
How did we obtain Dcost?
No LCVs
No cost analysis
Life 1
Life 2
Thick HMAC overlay cost
16
Results
Recommendations
 Best pavement type for future LCV corridors: CRCP
 If flexible, analysis suggests 8” as minimum HMAC
thickness to prevent premature alligator cracking.
 Evaluate the Dallas-Houston corridor for possible
LCV operations serving the Port of Houston.
 Evaluate other LCV scenarios before cost
allocation.
 Develop sensitivity analysis combining load spectra
variations and different LCV scenarios for cost
allocation.
18
Bridge Analysis
Bridge Statistics (1713 Bridges)
Highway
IH20
Highway
Count
Percent
204
12
IH10
Count
Percent
445
26
Highway
IH45
Highway
Highway
IH35
Count
Percent
555
32
IH37
Highway
US281
Count
Percent
316
18
Count
Percent
84
5
Count
Percent
109
6
20
Traditional Methodology
Live Load Bending Moments Proposed/Rating Ratios
Live Load Moment
Ratios
Inventory Rating
Axle
Steering
Tractor
Trailer
TOTAL
Axle Loads
6,846
34,089
56,065
97,000
Case Study Configurations- 97K Tridem
97k tridem
 Axle Spacing: 14ft 35ft
 Axle Loads: 7K 34K 56K
Case Study Configurations- Double 53’
90k double 53’
138k double 53’
 Axle Spacing: 18ft 41ft 19ft 41ft
 Axle Loads: 12K 31.5K 31.5K 31.5K 31.5K
 Axle Loads: 12K 19.5K 19.5K 19.5K 19.5K
Overstress Ratios from Literature
 Recent designs
(80s) can support
20% weight
increase.
 Older designs
susceptible to 10%
weight increases.
Essentially all prestressed girders, modern steel girders, and most bridge decks
could tolerate a 20% increase in truck weight with no reduction in life. Unfortunately,
most Minnesota steel girder bridges were designed before fatigue-design
specifications were improved in the 1970’s and 1980’s. Typically, an increase in truck
weight of 20% would lead to a reduction in the remaining life in these older steel
bridges of up to 42% (a 10% increase would lead to a 25% reduction in fatigue life).
Moment Ratio Statistics All Routes
97K Tridem
97k tridem 120
Cumulative %
100
80
60
40
20
0
0.8
1
1.2
1.4
1.6
1.8
Moment Ratio
2
2.2
2.4
2.6
Moment Ratio Statistics All Routes
Double 53’ Cubed out
90k double
53’
120
Cumulative %
100
80
60
40
20
0
0
0.2
0.4
0.6
0.8
1
Moment Ratio
1.2
1.4
1.6
1.8
Analysis Methodology
 Check if bridge deficient
for existing traffic.
 Check if bridge is
deficient for proposed
LCV configuration.
 Record deck area and
traffic volume.
Supported by
Level 1Analysis
Results 97K Tridem
97k tridem
1.1 Moment Ratio Criteria
Highway Count
IH10
145
IH20
255
IH35
289
IH45
89
IH37
42
US281
60
Total
880
Area (sqft)
1,092,520
2,694,798
7,097,868
1,954,679
793,428
999,060
14,632,353
ADT
3,822,520
3,657,001
10,091,459
4,962,040
1,258,670
617,330
24,409,020
PV Cost $
207,578,743
512,011,639
1,348,594,958
371,388,953
150,751,358
189,821,457
2,780,147,108
1.2 Moment Ratio Criteria
Highway
IH10
IH20
IH35
IH45
IH37
US281
Total
Count
126
189
183
47
14
23
582
Area (sqft)
836,570
1,274,125
2,938,770
643,122
137,679
164,369
5,994,635
ADT
3,300,400
1,886,420
6,130,009
1,324,970
433,460
113,730
13,188,989
PV Cost $
158,948,357
242,083,712
558,366,357
122,193,237
26,158,972
31,230,015
1,138,980,650
Results Mixing All Configurations
1.1 Moment Ratio Criteria
Highway
IH10
IH20
IH35
IH45
IH37
US281
Total
Count
145
257
293
89
42
60
886
Area (sqft)
1,092,520
2,709,810
7,169,479
1,954,679
793,428
999,060
14,718,976
ADT
3,822,520
3,678,501
10,346,609
4,962,040
1,258,670
617,330
24,685,670
PV Cost $
207,578,743
514,863,919
1,362,201,010
371,388,953
150,751,358
189,821,457
2,796,605,440
1.2 Moment Ratio Criteria
Highway
IH10
IH20
IH35
IH37
IH45
US281
Total
Count
130
202
246
36
53
23
690
Area (sqft)
914,899
1,449,063
6,023,241
694,103
837,670
164,369
10,083,345
ADT
3,403,570
2,090,690
8,770,989
1,225,590
1,879,790
113,730
17,484,359
PV Cost $
173,830,753
275,322,008
1,144,415,828
131,879,608
159,157,262
31,230,015
1,915,835,474
Summary for all Configurations
 97K Tridem: 2.8 to 1.1 billion
 138K Double 53’ 1.2 to 1 billion
 90K Double 53’ NO IMPACTS
Bridge Statistics – Structure Type
(Preliminary Fatigue Research)
3%
8%
3%
8%
14%
47%
17%
Concrete Slab 101
Concrete Girders 102
Concrete Continuous Slab 201
Steel Continuous girders 402
Prestress conrete girder 502
Prestress concrete box 505
Other
Using Fatigue Concepts
(Preliminary Research)
NSm=C
Log N = C – m Log S
 N – number of cycles
 S – Stress Range
 m – Constant Material
dependent
 C – Constant
 AASHTO specifies 75
year design life
 This achievable with
inventory rating stress
levels.
Using Fatigue Concepts
(Preliminary Research)

Assuming no influence of load spectra
(equal number of passages of the
proposed load):
BRINSAP Bridge Type m
Prestress conrete girder 502
3.5[2]
Prestress concrete box 505
3.5[2]
2. Altry, A.K., Arabbo, D.S.,
Crowin, E.B., Dexter, R.J. and
French, C.E., (2003). “Effects of
increasing truck weight on steel
and
prestressed
bridges”,
Mn/DOT final report (2003-16),
Minnesota
Department
of
Transportation
M AS m
F   F /(
)
M BC




F’ Calculated bridge life due to proposed load
F Current bridge life= 75-Bridge Age
m material constant
MAS/MBC Moment ratio from MOANSTR
analysis
Results Using Fatigue Concepts
(Preliminary Research)
97k tridem
Hghway
IH10
IH20
IH35
IH45
IH37
US281
Totals
Total # Bridges
145
255
289
89
42
60
880
# Bridges
ratio > 1.4
93
29
39
8
0
18
187
# Bridges
ratio <= 1.4
52
225
250
81
42
40
690
Discount rate 5%
PV Cost Bridges
PV Cost Bridges ratio
ratio>1.4
<=1.4
95,652,327
49,340,578
29,743,816
188,538,999
73,419,591
369,055,608
7,345,514
109,020,049
51,468,909
23,967,778
29,241,925
230,129,026
796,666,067
Total PV
144,992,905
218,282,815
442,475,199
116,365,563
51,468,909
53,209,703
1,026,795,093
Total PV W/O Fatigue
207,578,743
512,011,639
1,348,594,958
371,388,953
150,751,358
189,821,457
2,780,147,108
Combined recommendations
BRIDGES
AND
PAVEMENTS
Cubed-out double 53’
 FINDING: “cubed-out” double 53’ has no
impacts on bridges or pavements.

Related recommendations


90k
Strictly enforce the 19.5K tandem weight limit
(to prevent bridge impacts).
Estimate and allocate the (external) cost of this
enforcement in the candidate corridors.
138k
and
97k
 FINDING: “weighed-out” double 53’ and 97K
tridem have impacts on bridges but not on
pavements. 97K tridem bridge impacts are
more significant.

Related recommendations


Develop cost-allocation / cost-recovery procedure
for bridge costs.
Pavement cost reductions estimated in this study
too sensitive to input data variations and are not
accurate enough for cost allocation. Sensitivity
analysis and additional traffic mix scenarios
needed.
Report URL
Potential Use of Longer Combination Vehicles in Texas:
Second-Year Report
http://www.utexas.edu/research/ctr/pdf_reports/0_6095_2.pdf