high performance steel cost comparison study · high performance steel cost comparison study joint...

Edward Power, P.E.

High PerformanceSteel CostComparison StudyACEC / NCDOTBridge CommitteeHPS Bridge WorkshopOctober 22, 2007

Acknowledgements:

High Performance Steel Cost Comparison Study

Joint Study between HDR Engineeringand University of Nebraska at Lincoln

Sponsored by FHWA

Richard Horton, P.E.Gary Krupicka, P.E.Atorod Azizinamini, Ph.D., P.E.

Coauthors:

HPS has been used successfully now on many projects in several states.

Tennessee – One of the first applicationsState Route 53 Bridge over Martin Creek,Jackson CountyWeight Savings 24%

HPS Cost Comparison Study

HPS 70W provides significant advantages over conventional Grade 50W Steel.

Material

Strength

Weldability

Toughness

Weathering

HPS 70W

HPS 70W material cost is greater thanconventional Grade 50W Steel.

Material

ost HPS 70W

When does greater strength and performance outweigh material unit cost to achieve overall economy?

MaterialOve

Study showed the economy of hybrid girders.

HPS 70W

COST COMPARISON STUDY GOALSCompare girder weight and fabricationcost associated with designs usingGrade 50W and HPS 70W steel

Develop relative trendsConsidering Variable:

Span lengthGirder spacingMaterial combinations + HybridsGirder depth

COST COMPARISON STUDY GOALSDevelop fabrication cost comparisonswith Fabricator input

Determine deflection effects (L/800)

Determine fatigue effects

Determine trends for box girders

Two-Span bridge arrangement considered for study

• Positive and negative moment regions

• Simple design approach

• Popular grade separation structure

4 SPA. @ 9'- 0"

5 Girders @ 9’ Spacing

Design forInterior Girder

3 SPA. @ 12'- 0"

4 Girders @ 12’ Spacing

Design forInterior Girder

Design Flowchart

HPS COSTCOMPARISON

SPAN LENGTHS

150’-150’ 200’-200’ 250’-250’100’-100’

Design Flowchart

HPS COSTCOMPARISON

SPAN LENGTHS

150’-150’ 200’-200’

9’ SPA 12’ SPA

250’-250’

GIRDERSPACING

100’-100’

12’ SPA

Design Flowchart

HPS COSTCOMPARISON

SPAN LENGTHS

150’-150’ 200’-200’

9’ SPA 12’ SPA

250’-250’

50 W HPS 70 W HYBRIDS1-5

GIRDERSPACING

YIELD STRESS

100’-100’

12’ SPA

Design Flowchart

HPS COSTCOMPARISON

SPAN LENGTHS

150’-150’ 200’-200’

9’ SPA 12’ SPA

250’-250’

50 W HPS 70 W HYBRIDS1-5

L/35L/30L/25

GIRDERSPACING

YIELD STRESS

WEB DEPTHOPTIMIZATION

100’-100’

12’ SPA

50 ksi70 ksi50 ksi

HYBRID 1

50 ksi

70 ksi

50 ksi

Consider Hybrid 1 for shorter spans where Fatiguecan control at positive moment bottom flanges.

70 ksi70 ksi70 ksi

HYBRID 2

50 ksi

70 ksi

50 ksi

70 ksi

50 ksi

70 ksi

70 ksi70 ksi70 ksi

HYBRID 3

50 ksi

70 ksi

50 ksi

70 ksi

70 ksi70 ksi70 ksi

HYBRID 4

50 ksi

70 ksi

50 ksi

Hybrid 4 was typically the most cost effective

70 ksi70 ksi70 ksi

HYBRID 5

50 ksi

70 ksi

50 ksi

AASHTO LRFD 2nd Edition with 2000 Interim

Design parameters:

•Interior girder

•25 ft. max cross frame spacing

•12” x 3/4” minimum flange

Design Criteria

Girder Optimization

Plate width transitionat field splices

One thicknesstransition - 800# minweight savings

No thickness transitions

Partially stiffened web designStiffener cost 4x web plate cost

HPS 70W mill lengths

50’Quenching and Tempering(Q&T)

> 2”

120’Thermo Mechanical ControlledProcessing (TMCP)

<= 2”

Process LengthThickness

GirderWeight

Web Depth

Grade 50W

Grade HPS 70W

Performance Characteristics

Optimal Depth

GirderWeight

Web Depth

Grade 50W

Grade HPS 70W

Deflection L/800

GirderWeight

Web Depth

Grade 50W

Grade HPS 70W

Phases 1 & 2

49 design combinations

170 girder designs

Fatigue

Deflection L/800

Optimal Depth and Deflection

2030405060708090

100 150 200 250

Span Length (ft.)

L/D=25

Web Depth Correspondingto L/D=25

2030405060708090

100 150 200 250

Span Length (ft.)

L/D=25 50W

Optimal Depth 50W

2030405060708090

100 150 200 250

Span Length (ft.)

L/D=25 50W HPS70W

Optimal Depth HPS 70W

2030405060708090

100 150 200 250

Span Length (ft.)

L/D=25 50W HPS70W HY4

Optimal Depth HY 4

2030405060708090

100 150 200 250

Span Length (ft.)

L/D=25 50W HPS70W HY4 L/800

∆=L/800

Optimal Girder Depths

94 (93)87 (91)12’

76 (70)72 (69)12’

616012’

86 (86)77 (84)9’250’-250’

7270 (68)9’200’-200’

53569’150’-150’

414012’100’-100’

Hybrid - 4GirderSpacing

HPS 70WBridgeSpans

( ) – Depth where deflection equals L/800

Fatigue

When does Fatigue affect the costeffectiveness of HPS 70W steel?

Fatigue

When does Fatigue affect the costeffectiveness of HPS 70W steel?Fatigue resistance is a variable basedon:

detail category

average daily truck traffic

Fatigue

Welded Cross FrameStiffenerCategory C’

Stud Shear ConnectorCategory C

Two Fatigue Detail CategoriesConsidered

Fatigue

Limiting value of Average Daily TruckTraffic (ADTT) used for study

Results in conservative lower boundfatigue resistance.

Corresponds to Interstate roadway orurban arterial.

Ramps, overpasses, rural roads, etc. withlower ADTT will have higher fatigue resistancelimits.

Span Lengths (ft.)

50 ksi70 ksiHybrid-4

Load Induced FatigueBottom Category C’ - 12 ft. Girder Spacing

100 150 200 250

GirderWeight

Web Depth

Grade 50W

Grade HPS 70W

Girder Weight Comparisons

Deflection L/800

Web Depth (in)

70 ksi

Optimal Depth

50 ksi

50 ksi70 ksi

Girder Weight Comparisons100 ft. Spans & 12 ft. Girder Spacing

Optimal Depth

35 37 39 41 43 45 47 49

Web Depth (in)

35 37 39 41 43 45 47 49

70 ksi

50 ksi Fatigue

70 ksi Fatigue

Optimal Depth

50 ksi

50 ksi70 ksi

6% (FAT

Optimal Depth

50 55 60 65 70 75 80L/25L/30L/35

Optimal Depth

50 ksi70 ksi

Girder Weight Comparisons150 ft. Spans & 12 ft. Girder SpacingG

Web Depth (in)

50 55 60 65 70 75 80L/25L/30L/35

17%∆=L/800

70 ksi Fatigue

Optimal Depth

50 ksi70 ksi

Web Depth (in)

55 60 65 70 75 80 85 90 95 100L/40 L/25L/30

OptimalDepth

Optimal Depth

Web Depth (in)

50 ksi

70 ksi

55 60 65 70 75 80 85 90 95 100L/40 L/25L/30

OptimalDepth

Optimal Depth

∆=L/800

Web Depth (in)

50 ksi

70 ksi

“L/D” 25

70 75 80 85 90 95L/30L/35L/40100 105

Optimal Depth

50 ksi70 ksi

Web Depth (in)

70 75 80 85 90 95L/30L/35L/40100 105

∆=L/800

Optimal Depth

“L/D” 25

50 ksi70 ksi

Web Depth (in)

10121416182022

100 150 200 250

Span Length (ft.)

Girder Weight ComparisonsWeight Savings from 50W

10121416182022

100 150 200 250

Span Length (ft.)

70W FAT

HY4 FAT

Girder Weight ComparisonsWeight Savings from 50W

Weight Savings at Optimal Depth from 50W

20%21% (19%)12’

15%17%12’

16% (14%)17% (15%)12’

13%17%9’250’-250’

16%17%9’200’-200’

11% (9%)17% (13%)9’150’-150’

13% (8%)13% (8%)12’100’-100’

Hybrid - 4Girder Spacing HPS 70WBridge Spans

( ) - Weight savings considering fatigue

( ) - Weight savings considering deflection

Goal: Determine relative cost effectiveness of HPS70W steel over Grade 50W

Fabricator participation requested for cost comparison• Costs requested for 16 designs• 10 Fabricators selected to represent entire country

Costs included material and labor

Fabricator Cost Estimates

Fabricator Average Unit Costs ($/lb.)

$0.14/lb

$0.92/lb

$0.78/lbBoxI-Girder

$0.17/lb

$0.87/lb

$0.70/lb

Phase III 2004

$0.14/lb$0.14/lbDifference

$0.52/lb$0.61/lb50W

$0.66/lb$0.75/lbHPS 70W

Phase II2002

Phase I2000

Steel Grade

Fabricator Average Cost Estimates ($/lb.)

Bridge Spans Girder 50W HPSSpacing 70W

150’ - 150’ 9’ N.R. N.R. 12’ 0.56 0.71

200’ - 200’ 9’ 0.53 0.67 12’ 0.51 0.63

250’ - 250’ 9’ N.R. N.R. 12’ 0.48 0.61

Average 0.52 0.66

55 60 65 70 75 80 85 90 95 100

Girder Cost ComparisonsTypical Cost Comparison for All Hybrid Alternatives

Web Depth (in)

50 ksi70 ksiHybrid-1Hybrid-2Hybrid-3Hybrid-4Hybrid-5

Girder Cost Comparisons100 ft. Spans & 12 ft. Girder Spacing

34 36 38 40 42 44 46 48 50

Web Depth (in)

Optimal Depth

Optimal Depths

34 36 38 40 42 44 46 48 50

70 ksi Fatigue

50 ksi Fatigue

HY-4 Fatigue

Web Depth (in)

50 55 60 65 70 75 80 85$155

Optimal Depth

Web Depth (in)

L/35 L/25L/30

50 55 60 65 70 75 80 85$155

70 ksi Fatigue

HY-4 Fatigue

Optimal Depth

5% (FAT

Web Depth (in)

L/35 L/25L/30

55 60 65 70 75 80 85 90 95 100

70 ksi Deflection (L/800)

HY-4 Deflection (L/800)Optimal Depth

Optimal Depth

Web Depth (in)

L/40 L/25L/35 L/30“L/D” 25

70 75 80 85 90 95 100 105

70 ksi Deflection (L/800)

Optimal Depth

HY-4 Deflection (L/800)

Web Depth (in)

Optimal Depth

L/40 L/30L/35“L/D” 25

-16-14-12-10

-8-6-4-202468

100 150 200 250

Span Length (ft.)

Cost Savings from 50WGirder Cost Comparisons

-16-14-12-10

-8-6-4-202468

100 150 200 250

Span Length (ft.)

70W FAT

HY4 FAT

Cost Savings from 50WGirder Cost Comparisons

9% 1%12’

6%-3%12’

8% (5%)-2% (-6%)12’

6%-3%9’250’-250’

7%-4%9’200’-200’

4% (2%)-4% (-8%)9’150’-150’

2% (-4%)

Hybrid - 4HPS 70W

-8% (-14%)12’100’-100’

GirderSpacing

( ) – Cost savings considering fatigue

Relative Girder Fabrication Cost Savings w.r.t. Grade 50W

Summary and Conclusions

The study compared weight, depth and cost of 49girder configurations for a range of span lengths,girder spacing, and steel types.

Performance Issues:• Use of homogenous HPS 70W steel resulted in weight savingsof 13% to 20% relative to 50W. Hybrid 4 had 11% to 20%savings.

• Greater weight savings occur at shallower depths.

• Optimal girder depths were shallower by an average of 8% to9% in all spans except 100’.

• Fatigue affected 100’ and 150’ spans. Truck volume is afactor.

• Deflection (L/800) affected 70W design at 250’ spans atoptimal depth. In 200’ spans, depths below optimal wereaffected.

• At optimal depths, homogenous Grade 50 designs were typicallymore economical than HPS 70W designs. Advantage reduces withspan length.

• At shallower depths, HPS 70W designs were typically moreeconomical.

Cost Issues:

• Hybrid designs were the most economical with cost savings of2% to 9% at optimal depths. Savings increase with span length.

• Hybrid 4 was the most economical with:HPS 70W top and bottom flanges in negative moment regionHPS 70W bottom flanges in positive moment regionGrade 50 top flanges in positive moment region and all webs

Additional cost savings can be realized with HPS 70W inshipping and erection, foundations, and reduced approach fillheights.

Cost Issues Continued:

High Performance SteelBox Girder Study

2 Box Girder Section

12'- 0" 12'- 0" 12'- 0"

14Longitudinal

Stiffener (LS)when used

HPS Box Girder Study

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.00.0

50 ksi70 ksi

E.Q. 6.11.8.2-2(70)

E.Q. 6.11.8.2-3(70)

E.Q. 6.11.8.2-3 (50)

E.Q. 6.11.8.2-2(50)

Flange b/t Ratio

)HPS Box Girder Study

300 250 200 150Spans50W

50 ksi50 ksi

50 ksi

50 ksi 50 ksi

50 ksi

70 ksi

Top Flange

Hybrid B1

150 ft Spans – HY, HY LS

200 ft Spans – HY

250 ft Spans – HY

50 ksi50 ksi

50 ksi

50 ksi 50 ksi

50 ksi

70 ksi

Top Flange

50 ksi50 ksi

70 ksi

Hybrid B2

200 ft Spans – HY LS

Bottom Flange

70 ksi70 ksi

50 ksi

50 ksi 50 ksi

50 ksi

70 ksi

Top Flange

50 ksi50 ksi

Bottom Flange Bottom FlangeBottom Flange70 ksi

Hybrid B3

300 ft Spans – HY

70 ksi70 ksi

50 ksi

50 ksi 50 ksi

50 ksi

70 ksi

Top Flange

Bottom Flange Bottom FlangeBottom Flange70 ksi

Hybrid B4

Weight Savings from 50W

101214161820

150 200 250 300Span Length (Feet)

Box Girder Weight Comparisons

Weight Savings with Longitudinal Stiffener

1012141618

150 200 250 300Span Length (Feet)

ings HY to HY LS

50 to 50 LS

Box Girder Weight Comparisons

Fabricator participation requested for cost comparison• Costs obtained for 16 designs• 4 Fabricators participated

Costs included material and labor

0.920.290.630.780.290.49Average0.740.740.790.84TotalMaterial

0.490.480.490.48

50W HPS 70W

0.890.260.630.26250 - 250

0.921.00TotalLabor

0.300.37

0.630.25300 - 300

0.630.36150 - 150

0.620.30200 - 200

MaterialLaborSpan

$0.14/lb

$0.92/lb

$0.78/lbBoxI-Girder

$0.17/lb

$0.87/lb

$0.70/lb

Phase III 2004

$0.14/lb$0.14/lbDifference

$0.52/lb$0.61/lb50W

$0.66/lb$0.75/lbHPS 70W

Phase II2002

Phase I2000

Steel Grade

150 200 250 300

Span Length (Feet)

Cost Savings from 50WBox Girder Cost Comparisons

Cost Savings with Longitudinal Stiffener

150 200 250 300

Span Length (Feet)

HY to HY LS50 to 50 LS

Box Girder Cost Comparisons

• Hybrid design with bottom flange longitudinal stiffening isthe most economical use of HPS 70W in box girders.• Effectiveness of HY increases with increasing span length• Effectiveness of bottom flange negative momentlongitudinal stiffening decreases with increasing span length.• The optimal HY combination varies. All optimal hybrids hadHPS 70W in negative moment top flanges, and 50W for allwebs. Bottom flanges had varying use of HPS 70Waccording to span length and use of bottom flangelongitudinal stiffening.

Edward Power, P.E.

High PerformanceSteel CostComparison Study

Questions?

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