Capacity and Practical Implications of Driven Bearing H-Pile Design Using 50 ksi Steel

Capacity and Practical Implications of Driven Bearing H-Pile Design Using 50 ksi Steel Marwa Hasanzoi Kent A. Harries, PhD, FACI, FIIFC, PEng Jeen-Shang Lin, ScD, F.ASCE, PE

Introduction and Motivation Commonly used in short and medium span bridge foundations, steel H-piles (HP shapes) are cost-effective, more ductile and flexible than concrete alternatives and easily penetrate into soft bedrock, reaching firm strata to establish end-bearing capacity.

Driven H-piles provide higher end-bearing resistance with low side resistance.

Today, HP shapes are most commonly available as ASTM A572 Grade 50 material, having a nominal yield strength, Fy = 50 ksi.

However, until fairly recently, HP shapes were typically available as ASTM A36 shapes for which Fy = 36 ksi.

Introduction and Motivation Early LRFD requirements for HP bearing piles were calibrated to established ASD values, which were based on the use of ASTM A36 material.

Many state DOTs continue to take an essentially ASD approach to the design of driven piles, continuing to prescribe the use of Fy = 36 ksi for the design of HP bearing piles and/or prescribe greater reduction factors in order to arrive at ‘accepted’ allowable bearing capacities.

Fy = 36 ksi

Fy = 50 ksi

capacity calculation

0.25Fy

0.18Fy

0.25Fy

0.27Fy

0.28Fy

0.29Fy

0.33Fy

0.50Fy

0.55Fy

resulting stress, ksi

9 ksi

9 ksi

12.5 ksi

13 ksi

14 ksi

14.5 ksi

16.5 ksi

25 ksi

27.5 ksi

states reporting

12

3

3

1

1

1

1

14

1

Bearing Pile Structural Capacity ϕPn = ϕc(0.658Po/Pe)QAgFy Ag is the gross area of the pile; Q is a reduction factor for slender elements; Q = 1 for compact sections; Po is the equivalent nominal yield resistance; Po = QAgFy Pe is the Euler buckling load; Pe = π2EAg/(KL/r)2

For fully embedded members (i.e. L/r = 0), Pe is essentially infinite and therefore Po/Pe = 0, reducing equation to: ϕPn = ϕcQAgFy

This interpretation is supported by AASHTO §10.7.3.13.1 which prescribes the slenderness coefficient λ = 0 for fully embedded piles. Although the notation is different, λ = Po/Pe.

Bearing Pile Structural Capacity ϕP ϕPnn == 0.5QA ϕcQAggFFyy ϕc = 0.5 for H-piles “subject to damage due to severe driving conditions where the use of a pile tip is necessary”; ϕc = 0.6 otherwise. For combined axial and flexural loading conditions, ϕc = 0.7.

In this work, the discussion is based on the use of ϕc = 0.5 which is the de facto scenario in Pennsylvania. DM-4 requires driving tips be used for all point bearing and end bearing piles driven into bedrock. For driven piles for which only the wave equation is used to assess driveability, the piles are driven to twice their design nominal capacity (i.e., ϕdyn = 0.5 as prescribed by AASHTO §10.5.5.2.3). Furthermore, the driving stresses determined using a wave equation analysis and must not exceed 0.9Fy (AASHTO §10.7.8).

In instances where a Pile Driving Analyzer (PDA) is used to monitor the driving operation, ϕdyn = 0.65.

Introduction and Motivation The motivation of the present study was to assess the implications of increasing the permitted HP nominal yield strength from 36 to 50 ksi.

In Pennsylvania, for instance, DM-4 (2012) limits the specified yield strength of steel piles to Fy ≤ 36 ksi. Subsequent revisions (PennDOT 2013 and 2014) modify this limit to Fy ≤ 50 ksi. This increase was motivated by expected cost savings resulting from potentially using smaller pile sections and/or requiring fewer piles for a foundation.

50/36 = 1.39 increase in theoretical capacity… easy… …perhaps not…

Issues Associated with Increasing H-pile Design Capacity Structural Steel Capacity - Although the higher yield strength improves stability and yield checks, the higher yield strength may adversely affect ductility checks associated with non-compact shapes. As the yield strength increases from 36 to 50 ksi, the flange and web slenderness ratios defining compact and noncompact section limits fall 18%: design action axial capacity

strong and weak axis flexure

AASHTO/ DM-4

plate element

slenderness limit calculation

36 ksi 50 ksi

flanges

b f 2t f  0.56 E F y

15.9

13.5

web

( d  2k ) t w  1.49 E Fy

42.3

35.9

compact flange

b f 2t f  0.38 E F y

10.8

9.2

noncompact flange

b f 2t f  0.83 E Fy

23.6

20.0

§6.9.4.2

§A6.3.2 (strong) §6.12.2.2.1 (weak)

Issues Associated with Increasing H-pile Design Capacity Effect of Corrosion - Corrosion resistance of steel piles is unaffected by strength. The use of higher strength piles may permit smaller pile sections to be used to resist the same load.

When considering the effects of corrosion, it is common to assume section loss of 1/16 in. from all surfaces.

Thus a pile having an initially smaller section area has less ‘reserve’ capacity; that is: the 1/16 in. reduction in plate thickness represents a proportionally greater section area for a smaller pile.

Additionally, accounting for 1/16 in. section loss, some shapes become slender for axial load and most shapest become noncompact for flexure.

Issues Associated with Increasing H-pile Design Capacity

axial

bf/2tf

flexure

36 ksi

50 ksi

36 ksi

9.25

compact

compact

compact

14x102 10.49

compact

compact

compact

14x89

11.95

compact

14x73

14.44

12x84

axial

bf/2tf

36 ksi

50 ksi

noncompact 10.85

compact

compact

noncompact 12.64

compact

compact

compact

noncompact noncompact 14.87

compact

slender

compact

slender

noncompact noncompact 19.03

slender

slender

8.97

compact

compact

compact

10.87

compact

compact

12x74

10.01

compact

compact

compact

noncompact 12.46

compact

compact

12x63

11.77

compact

compact

noncompact noncompact 15.38

compact

slender

12x53

13.84

compact

slender

noncompact noncompact 19.23

slender

slender

10x57

9.05

compact

compact

compact

compact

14x117

compact

50 ksi

flexure

compact

compact

11.48

36 ksi

50 ksi

all are noncompact

HP

reduced section properties

all are noncompact

gross section properties

Issues Associated with Increasing H-pile Design Capacity Tolerable Settlement - For a bearing pile, net settlement is the sum of tip displacement and pile shortening.

Tip displacement is independent of the pile steel grade.

Pile shortening is a function of the axial stress carried by the pile. If pile capacity is increased from 36 to 50 ksi, two implications for design may occur: 1) the pile capacity increases for the same pile section; or, 2) the pile area may be reduced to carry the same load. Both result in an increase in pile shortening as the pile stress (and therefore strain) is increased.

A schematic analysis has shown that settlement associated with increased stress in bearing piles will not likely exceed practical limits for piles up to 80 feet in length.

Issues Associated with Increasing H-pile Design Capacity Tip Bearing Capacity - While pile bearing capacity increases as Fy increases from 36 to 50 ksi, the soil into which the pile is driven and the strata on which it bears remains unchanged. Thus it is conceivable that a pile system whose limit state is governed by structural capacity at Fy = 36 ksi is governed by geotechnical bearing capacity at Fy = 50 ksi. This may be particularly the case for “weak rock� conditions.

Issues Associated with Increasing H-pile Design Capacity Driving Stresses and the Need for a Driving Tip - Related to tip bearing capacity, it is equally conceivable that in order to effectively drive a pile at Fy = 50 ksi, a driving tip is required which may not have been the case for Fy = 36 ksi. The use of the driving tip lowers the design capacity of the pile (Ď• decreases from 0.6 to 0.5 (AASHTO LRFD 2014)), reducing the increased pile capacity that may be realized using the higher strength steel.

Parametric Study A parametric study of 141 pile driving analyses was conducted using the commercially available program GRLWEAP (wave equation method).

Each combination of parameters represents a pile section, pile length, shaft friction and ‘target’ capacity.

Each analysis begins with trial hammer parameters (type, stroke and energy) and iterates upon these until the target capacity is attained at ‘refusal’ – defined as 240 blows/ft.

The objective of each analysis is to achieve the target pile capacity with the smallest (i.e. least energy) hammer (of those considered) while still providing at least a 0.5 foot working stroke range (PennDOT DM-4)

Parametric Study - Cases Case 1: The pile is driven using a constant hammer stroke analysis such that the following capacities are attained at 240 blows/ft refusal: a) AgFy, representing twice the AASHTO LRFD design capacity for severe driving conditions; that is: 2 x 0.5AgFy;

b) 0.66AgFy, representing twice the current DM-4 design capacity for severe driving conditions; that is: 2 x 0.33AgFy; c) 0.50AgFy, representing twice the DM-4 design capacity prior to 2013 when Fy was specified to be 36 ksi; that is: 2 x 0.35Ag(36 ksi) = 25.2 ksi ≈ 0.5Ag(50 ksi).

Parametric Study - Cases Case 2: In order to assess maximum potential pile capacity, a fourth case is considered, using the same hammer as used in Case 1a (or Case 1b, or both) in which the pile is driven using a constant hammer stroke analysis such that the driving stress is 0.9Fy = 45 ksi at 240 blows/ft refusal.

Parametric Study - Cases Case 3: Using the same hammer as used in Case 1a, the pile is driven using a constant hammer stroke analysis such that the capacity is 0.66AgFy or the driving stress reaches the prescribed lower limit of 25 ksi at 240 blows/ft refusal (PennDOT DM-4).

This represents the minimum PennDOT-acceptable capacity to which the pile/hammer case may be driven.

If the difference in required stroke between cases 2 and 3 does not exceed 0.5 ft, a different hammer is selected and cases 2 and 3 repeated.

Case 4: Using the same hammer as used in Case 1a, the pile is driven using a constant hammer stroke analysis such that the driving stress is 25 ksi at 240 blows/ft refusal.

Parametric Study - Parameters Piles Shapes: HP 14x117 is a representative heavy section which is compact for axial load at Fy = 50 ksi.

HP 12x74 is a representative medium section and is the most common shape used in Pennsylvania.

HP 10x57 is a compact section having capacity at Fy = 50 ksi suitable to ‘replace’ 36 ksi HP12x74 piles; theoretically affecting a weight savings of 17 lbs/ft or 23%.

Embedded lengths of 20, 50 and 80 feet were considered

Parametric Study - Parameters Parameter pile section embedded length pile length hammer

Values considered in analyses HP 10x57, HP 12x74 and HP 14x117 20, 50 and 80 ft (6.1, 15.2 and 24.4 m) 24, 54 and 84 ft (7.3, 16.5 and 25.6 m) smallest hammer of those listed that achieves target capacity at 240 blows/ft (787 blows/m)

toe damping

0.10 sec/ft (0.33 sec/m) (rock) 0.15 sec/ft (0.49 sec/m) (soil; 50 ft long HP 12 x 74 only)

toe quake

0.05 in. (1.3 mm) (hard rock) 0.10 in. (2.6 mm) (soft rock; 50 ft long HP 12 x 74 only)

skin damping

0.05 sec/ft (0.16 sec/m) (non-cohesive soil) 0.20 sec/ft (0.66 sec/m) (cohesive soil; 50 ft long HP 12 x 74 only)

skin quake shaft friction

0.10 in. (2.6 mm) 20% and 30%

Parametric Study - Parameters Hammers: GRPWEAP parameter GRLWEAP ID

units

ICE I-12v2

Pileco D19-42

ICE I-30v2

ICE I-36v2

ICE I-46v2

-

1501

852

1504

1505

1506

ram weight

kips

2.82

4.01

6.61

7.94

10.14

maximum stroke

ft

11.45

12.6

12.6

13.1

13.1

rated stroke

ft

10.5

10.6

11.5

11.8

11.8

ram diameter

in.

11.8

12.6

16.5

19.7

19.7

-

0.80

0.80

0.80

0.80

0.80

kip-ft

29.6

42.5

76.0

93.7

119.8

fuel setting

psi

1450

1520

1570

1510

1560

cushion area

in2

398

398

398

491

491

cushion modulus

ksi

175

285

175

175

175

cushion thickness

in.

2.0

2.0

2.0

4.0

4.0

-

0.91

0.80

0.91

0.91

0.91

efficiency energy/power

coefficient of restitution

Parametric Study - Example HP12x74 [L = 50 ft; SF = 0.20; TD = 0.10 s/ft; TQ = 0.05 in.; SD = 0.015 s/ft; SQ = 0.10 in.]

Case

1a 1b 1c 2a 2b 3 4

Hammer

ICE 1-36v2 Pileco D19-42 ICE 1-12v2 ICE 1-36v2 Pileco D19-42 ICE 1-36v2 ICE 1-36v2

Pile capacity at 240 blows/ft (787 blows/m) refusal 1/AsFy 1.00 0.66 0.50 0.73 0.70 0.66 0.43

ksi 50.0 33.0 25.0 36.5 35.0 33.0 21.6

kips 1090 719 545 800 763 719 466

Driving stress at refusal ksi 62.0 39.0 30.8 44.8 41.5 39.5 25.2

Stroke at refusal

Energy at refusal

ft 11.81 9.75 8.66 8.20 10.60 7.11 4.90

kip-ft 52.0 23.6 12.9 29.9 26.5 23.4 11.3

Parametric Study - Example HP12x74 [L = 50 ft; SF = 0.20; TD = 0.10 s/ft; TQ = 0.05 in.; SD = 0.015 s/ft; SQ = 0.10 in.]

Case

1a 1b 1c 2a 2b 3 4

Hammer

ICE 1-36v2 Pileco D19-42 ICE 1-12v2 ICE 1-36v2 Pileco D19-42 ICE 1-36v2 ICE 1-36v2

Pile capacity at 240 blows/ft (787 blows/m) refusal 1/AsFy 1.00 0.66 0.50 0.73 0.70 0.66 0.43

ksi 50.0 33.0 25.0 36.5 35.0 33.0 21.6

kips 1090 719 545 800 763 719 466

Driving stress at refusal ksi 62.0 39.0 30.8 44.8 41.5 39.5 25.2

Stroke at refusal

Energy at refusal

ft 11.81 9.75 8.66 8.20 10.60 7.11 4.90

kip-ft 52.0 23.6 12.9 29.9 26.5 23.4 11.3

The AASHTO-permitted capacity of the HP12x74, corresponding to a capacity at refusal of AgFy, cannot be reached without significantly exceeding the driving stress limit of 0.9Fy = 45 ksi

Parametric Study - Example HP12x74 [L = 50 ft; SF = 0.20; TD = 0.10 s/ft; TQ = 0.05 in.; SD = 0.015 s/ft; SQ = 0.10 in.]

Case

1a 1b 1c 2a 2b 3 4

Hammer

ICE 1-36v2 Pileco D19-42 ICE 1-12v2 ICE 1-36v2 Pileco D19-42 ICE 1-36v2 ICE 1-36v2

Pile capacity at 240 blows/ft (787 blows/m) refusal 1/AsFy 1.00 0.66 0.50 0.73 0.70 0.66 0.43

ksi 50.0 33.0 25.0 36.5 35.0 33.0 21.6

kips 1090 719 545 800 763 719 466

Driving stress at refusal ksi 62.0 39.0 30.8 44.8 41.5 39.5 25.2

Stroke at refusal

Energy at refusal

ft 11.81 9.75 8.66 8.20 10.60 7.11 4.90

kip-ft 52.0 23.6 12.9 29.9 26.5 23.4 11.3

The PennDOT-permitted capacity of the HP12x74, corresponding to a capacity at refusal of 0.66AgFy, can be reached without exceeding the driving stress limit of 0.9Fy = 45 ksi

Parametric Study - Example HP12x74 [L = 50 ft; SF = 0.20; TD = 0.10 s/ft; TQ = 0.05 in.; SD = 0.015 s/ft; SQ = 0.10 in.]

Case

1a 1b 1c 2a 2b 3 4

Hammer

ICE 1-36v2 Pileco D19-42 ICE 1-12v2 ICE 1-36v2 Pileco D19-42 ICE 1-36v2 ICE 1-36v2

Pile capacity at 240 blows/ft (787 blows/m) refusal 1/AsFy 1.00 0.66 0.50 0.73 0.70 0.66 0.43

ksi 50.0 33.0 25.0 36.5 35.0 33.0 21.6

kips 1090 719 545 800 763 719 466

Driving stress at refusal ksi 62.0 39.0 30.8 44.8 41.5 39.5 25.2

Stroke at refusal

Energy at refusal

ft 11.81 9.75 8.66 8.20 10.60 7.11 4.90

kip-ft 52.0 23.6 12.9 29.9 26.5 23.4 11.3

The maximum capacity at refusal that can be achieved, respecting the driving stress limit of 0.9Fy = 45 ksi is 0.73AgFy Requiring a minimum driving stress of 25 ksi (172 MPa) at refusal results in a ‘minimum’ capacity at refusal of 0.43AgFy

Parametric Study - Example HP12x74 [L = 50 ft; SF = 0.20; TD = 0.10 s/ft; TQ = 0.05 in.; SD = 0.015 s/ft; SQ = 0.10 in.]

Case

1a 1b 1c 2a 2b 3 4

Hammer

Pile capacity at 240 blows/ft (787 blows/m) refusal

1/AsFy ICE 1-36v2 1.00 Pileco D19-42 0.66 ICE 1-12v2 0.50 ICE 1-36v2 0.73 Pileco D19-42 0.70 ICE 1-36v2 0.66 ICE 1-36v2 0.43

ksi 50.0 33.0 25.0 36.5 35.0 33.0 21.6

kips 1090 719 545 800 763 719 466

Driving stress at refusal ksi 62.0 39.0 30.8 44.8 41.5 39.5 25.2

Stroke at refusal

Energy at refusal

ft 11.81 9.75 8.66 8.20 10.60 7.11 4.90

kip-ft 52.0 23.6 12.9 29.9 26.5 23.4 11.3

The effect of increasing the pile design capacity from Fy = 36 to 50 ksi resulted in a) a pile capacity increase of 32% (545 to 719 kips at refusal); b) a larger hammer (ICE I-12v2 to Pileco D19-42) being required to drive the pile (energy increase of 77%); and, c) a resulting 20.5% increase in pile driving stress (31 to 39 ksi)

Parametric Study Results – Driving Stress

However, this does not imply that a design capacity of 0.5AgFy cannot be achieved, it only requires a larger value of ϕdyn to be engaged such as when PDA is used – in which case the target capacity at refusal is only 0.5AgFy/0.65 = 0.77AgFy

70 ← AsFy  pile capacities at refusal 

60 50

driving stress (ksi)

Driving stress will always exceed nominal stress.

Therefore piles cannot achieve an nominal stress of AgFy when driving stress is limited to 0.9Fy.

← >0.80AsFy 0.90Fy = 45 ksi

40

← 0.66AsFy

30

← 0.50AsFy

20

25 ksi HP10x57

10 0

HP12x74

HP14x117

six data points per HP section; left to right: L = 20 ft L = 20 ft L = 50 ft L = 50 ft L = 80 ft L = 80 ft sf = 0.20 sf = 0.30 sf = 0.20 sf = 0.30 sf = 0.20 sf = 0.30

Parametric Study Results – Pile Capacity

Using the minimum permitted driving stress of 25 ksi, all pile capacities ultimately fell between 0.40AgFy and 0.50AgFy

0.8

0.7

pile stress ratio, Pn/AsFy

Driving piles to the maximum permitted driving stress of 0.90Fy = 45 ksi, resulted in pile capacities at refusal ranging from 0.64AgFy to 0.76AgFy

0.6

maximum driving stress 0.90AsFy = 45 ksi using hammer required for driving to capacity = 0.66AsFy

0.5

0.4 minimum driving stress = 25 ksi using smallest available hammer 0.3

0.2

HP10x57

HP12x74

HP14x117

six data points per HP section; left to right: L = 20 ft L = 20 ft L = 50 ft L = 50 ft L = 80 ft L = 80 ft sf = 0.20 sf = 0.30 sf = 0.20 sf = 0.30 sf = 0.20 sf = 0.30

Ratio of Driving Stress to Ultimate Stress Pile shape all all all all HP 10x57 HP 12x74 HP14x117

Pile length all 20 ft (6.1 m) 50 ft (15.3 m) 80 ft (24.4 m) all all all

Average 1.23 1.27 1.22 1.19 1.19 1.21 1.29

COV 0.06 0.05 0.05 0.06 0.05 0.05 0.04

Low High 1.07 1.40 1.12 1.40 1.15 1.37 1.07 1.36 1.07 1.32 1.10 1.30 1.20 1.40

Given the relatively consistent COV values, it is proposed that these ratios may be used as a rule of thumb for estimating driving stress based on required pile nominal capacity.

Using average values and a driving stress limit of 0.9Fy: HP10x57 sections may be driven to a capacity at refusal of 0.75AgFy (0.9/1.19 = 0.75) HP14x117 sections would be limited to 0.70AgFy (0.9/1.29).

Estimation of Cost In order to assess potential cost savings realized by utilizing Fy = 50 ksi for the design of steel H-piles, a rudimentary cost comparison was made.

Costs were normalized on the basis of driven pile capacity. To do this, the cost of driving 100,000 kips of pile capacity (at refusal) was established using the capacities determined from the wave equation analyses presented.

The following assumptions were made: • Cost of steel HP sections was taken as $0.50 per pound (ENR 2014 Q4 Cost Report).

• Pile hammer rental, mobilization/demobilization and driving costs are given below.

• Support crane rental and mobilization/demobilization costs are those given below.

• Production rates are 4500 linear feet of driven pile per month per hammer.

• Costs do not include on site moves.

Hammer Pilco D19-42 ICE I-12v2 ICE I-30v2 ICE I-36v2 ICE I-46v2

hammer monthly rental $8,098 $7,049 $9,116 $11,200 $15,368

hammer mob/demob. $1,500 $1,500 $1,500 $1,500 $1,500

required crane capacity 90 ton 70 ton 140 ton 140 ton 140 ton

crane monthly rental $12,000 $10,000 $16,000 $16,000 $16,000

crane mob/demob.

driving cost

$10,000 $6,000 $20,000 $20,000 $20,000

$7.02/lf $5.46/lf $10.35/lf $10.82/lf $11.76/lf

Estimation of Cost - Example 100,000 kips capacity of HP12x74 using a Pilco D19-42 hammer to drive to 50 ft embedded depth to a capacity at refusal of 719 kips is shown: unit or cost item piles required total pile length hammer months required cost of steel cost of hammer and crane rental cost of hammer and crane mobilization/demobilization driving cost Total cost to drive 100,000 kips capacity cost per driven kip cost per driven kip per foot embedment cost per pile

calculation 100,000/719 kips 140 x 50 ft 7000/4500 lf/mo 74 lb/ft x 7000 ft x $0.50 ($8098 + 12,000) x 1.56 mo. $1500 + $10,000 7000 lf x $7.02/lf $350.993/100,000 kip $3.51/50 ft $350,993/140 piles

amount or cost 140 piles 7000 lf (2135 m) 1.56 months $259,000 $31,353 $11,500 $49,140 $350,993 $3.51 $0.07 $2507

Estimation of Cost - Summary Cost per driven kip capacity

$10

Illustrates dominance of steel material cost to overall cost

$8

HP10x57

$9

cost per driven kip capacity

HP12x74 HP14x117

L = 80 feet

$7

$6 $5

L = 50 feet

$4 $3 $2 L = 20 feet

$1 $0 10

12

14

16

18

20

pile LRFD design capacity (ksi)

22

24

Estimation of Cost - Summary

Illustrates general trend of falling cost with increased pile design capacity Increasing the design pile capacity 31% from 12.6 ksi to 16.5 ksi (as was effectively done in Pennsylvania by increasing Fy from 36 to 50 ksi) results in a cost savings of approximately 20% which is independent of pile size and length.

$0.15 HP10x57

cost per driven kip capacity per foot embedment

Cost per driven kip capacity per foot

HP12x74 HP14x117 $0.10

$0.05

12.6 to 16.5 ksi

$0.00 10

12

14

16

18

20

pile LRFD design capacity (ksi)

22

24

Estimation of Cost - Example

The driving requirements to achieve the increased pile capacity increase the hammer costs and unit driving costs resulting in a net savings of 19% for the case shown

$3,500 cost per pile (right axis)

$6

$3,000

$5

$2,500

impact of hammer selection

driving costs $4

$2,000

$3

$1,500 cost of steel ($0.50/lb)

$2

$1,000

12.6 to 16.5 ksi

$1

$500

HP12x74 driven to L = 50 ft (SF = 0.20) $0

$0 10

12

14

16

18

pile LRFD design capacity (ksi)

20

cost per pile

The cost of steel is essentially linear and falls in proportion to the increase in steel yield strength used for design; i.e., the cost of steel falls 31%.

$7

cost per driven kip capacity

100,000 kips capacity of HP12x74 using a Pilco D19-42 hammer to drive to 50 ft embedded depth to a capacity at refusal of 719 kips is shown.

Estimation of Cost - Example $3,500 cost per pile (right axis)

$6

$3,000

$5

$2,500

impact of hammer selection

driving costs $4

$2,000

$3

$1,500 cost of steel ($0.50/lb)

$2

$1,000

12.6 to 16.5 ksi

$1

$500

HP12x74 driven to L = 50 ft (SF = 0.20) $0

$0 10

12

14

16

18

pile LRFD design capacity (ksi)

20

cost per pile

Cost per pile increases from $2353 to $2507 (6.5%), the number of piles required falls from 184 to 140 (31%) as the design stress increases from 12.6 ksi to 16.5 ksi resulting in the 19% net savings.

$7

cost per driven kip capacity

100,000 kips capacity of HP12x74 using a Pilco D19-42 hammer to drive to 50 ft embedded depth to a capacity at refusal of 719 kips is shown.

Conclusions A parametric study investigating the impact of increasing the yield capacity from Fy = 36 ksi to Fy = 50 ksi on design capacity and driving analysis of steel H-piles was presented.

Results indicate that the AASHTO-permitted pile capacity of 0.5AgFy is not technically achievable without the reduction in required over strength (increase in Ď•dyn) permitted using a PDA. Even using a PDA, this capacity may only be achievable for smaller pile sections.

The PennDOT-permitted pile capacity of 0.33AgFy in which Fy = 50 ksi is achievable in cases considered although driving stress in large HP14x117 piles approaches the limit of 0.9Fy.

Conclusions The theoretical increase in pile capacity realized by accounting for the increase of Fy from 36 to 50 ksi results in a theoretical increase in pile capacity of 139%; this increase is achievable for all cases considered.

Driving piles to the maximum permitted driving stress of 0.90Fy = 45 ksi, resulted in pile capacities at refusal ranging from 0.64AgFy to 0.76AgFy with smaller pile sections having marginally higher achievable capacities.

All HP10x57 piles considered, for instance, could be driven to values exceeding 0.70AgFy without exceeding driving stress limits.

Conclusions A representative cost analysis – normalized on the basis of 100,000 kips driven pile capacity and a number of fundamental assumptions concluded that increasing the design capacity of a pile results in a decrease in cost per driven pile capacity although due to the need for larger hammers and cranes, permitting design capacities greater than 16.5 ksi results in only marginal additional savings.

Deliverables Revisions were proposed to the following DM-4 sections 5.5.4.2.1 5.13.4.1 6.5.4.2

6.15.2 6.15.3 6.15.3.1 6.15.3.2 Tables 6.15.3.2P-1 and -2 ďƒ Eq 6.12.2.2.1-2 (corrects error)

References Hasanzoi, M., Harries, K.A., and Lin, J-S. (2016) Capacity and Practical Implications of Driven Bearing H-Pile Design Using 50 ksi Steel, ASCE Journal of Bridge Engineering http://dx.doi.org/10.1061/(ASCE)BE.1943-5592.0000900 Harries, K.A., Lin, J-S and Hasanzoi, M. (2015) 50 ksi Steel Hpile Capacity, Report FHWA-PA-2015-005-PIT WO 1, 78 pp.

This study was funded by the Pennsylvania Department of Transportation. The contents of this presentation do not necessarily reflect the official views or policies of the US Department of Transportation, Federal Highway Administration, or the Commonwealth of Pennsylvania