CHAPTER 23 PILES TABLE OF CONTENTS TABLE OF CONTENTS. 23.TOC Table of Contents... 30Jan Introduction... 30Jan2018

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1 CHAPTER 23 TABLE OF CONTENTS FILE NO. TITLE DATE TABLE OF CONTENTS 23.TOC Table of Contents... 30Jan Introduction... 30Jan2018 DESIGN GUIDE FOR LATERALLY UNSUPPORTED Notes and Definitions... 30Jan Design Criteria... 30Jan Design Criteria... 30Jan Coarse Grain Soil Example... 30Jan Cohesive Soil Example... 30Jan Layered Soil Example... 30Jan Layered Soil Example... 30Jan Steel H-Pile Design Criteria... 30Jan Steel H-Pile Design Criteria... 30Jan Properties for Designing Steel H-Piles... 30Jan Steel H-Pile Design Example... 30Jan Steel H-Pile Design Example... 30Jan Prestressed Concrete Pile Design Criteria... 30Jan Prestressed Concrete Pile Design Example... 30Jan2018 LATERAL LOADED PILE ANALYSIS FOR POINT OF FIXITY Design Procedure... 30Jan Design Assumptions and Results... 30Jan L-Pile Results for Scour Condition... 30Jan L-Pile Results for Non-Scour Condition... 30Jan2018 TABLE OF CONTENTS SHEET 1 of 1 FILE NO. 23.TOC

2 INTRODUCTION It is the intent of this chapter to establish the guidelines and specific requirements of the Structure and Bridge Division for the design and analysis of laterally unsupported piles, specifically relating to the use of steel H-piles and prestressed concrete piles subjected to scour and biaxial bending. It provides design procedures and examples for determining the point of fixity, effective length factor, K, and the structural capacity of these piles. This chapter also provides a bridge specific example for determining the point of fixity for a laterally loaded pile for use in Elastic Frame Analysis using commercially available software for non-linear analysis of piles, L-Pile. Point of fixities for both the existing or final profile and the scoured condition may need to be determined. Shorter distances to points of fixities based on existing or final profile (non-scoured) can control design in exterior spans of large units and affect bridge behavior. Example calculations in this chapter show for scoured conditions, but non-scoured is similar. References to the AASHTO LRFD specifications in this chapter refer to the AASHTO LRFD Bridge Design Specifications, 7 th Edition, 2014, and VDOT Modifications (current IIM-S&B-80). The practices and requirements set forth herein are intended to supplement or clarify the requirements of the AASHTO LRFD specifications, and to provide additional information to assist the designer. In the event of conflicts(s) between the practices and requirements set forth herein and those contained in the AASHTO LRFD specifications, the more stringent requirements shall govern. Standards for prestressed concrete piles are located in the Manual of the Structure and Bridge Division, Part 3. Standard BPP-1 (Carbon Steel Strands) Standard BPP-2 (Stainless Steel Strands) Standard BPP-3 (Carbon Fiber Reinforced Polymer [CFRP] Strands) It is expected that the users of this chapter will adhere to the guidelines and requirements stated herein. Major changes and/or additions to the past office practice (Part 2 of this manual) are as follows: 1. Updated calculations for design of steel H-piles to reflect AASHTO LFRD Specifications from previously referenced AASHTO Standard Specifications. 2. Added example including as-built bridge data for a laterally loaded pile analysis using L- Pile for use in Elastic Frame Analysis. NOTE: Due to various restrictions on placing files in this manual onto the Internet, portions of the drawings shown do not necessarily reflect the correct line weights, line types, fonts, arrowheads, etc. Wherever discrepancies occur, the written text shall take precedence over any of the drawn views. INTRODUCTION SHEET 1 of 1 FILE NO

3 GENERAL INFORMATION: For the 100 year storm, the factored capacity is checked using the AASHTO Strength and Service Load Combinations and Load Factors. For the 500 year storm, the factored capacity is checked using the AASHTO Extreme Event Load Combinations and Load Factors. AASHTO Load Combinations and Load Factors shall be in accordance with Table This guide does not indicate how to determine the axial loads and moments to be used in the formulas for analysis of piles. Because the piles are not laterally restrained, sideway is not prevented; therefore, it is recommended that the designer utilize appropriate structural modeling software, such as RCPier, to determine the applied axial loads and moments. DEFINITIONS: b Pile width in direction of bending ft D Pile embedment length into ground ft D Depth of assumed point of fixity ft N Standard Penetration Test STP Blow count c Cohesive strength N ksf S undrained shear strength of clays c ksf n rate of increase of soil modulus with depth for sands as specified in Table C E Modulus of elasticity of concrete AASHTO C ,029 ksf for f c 5,000 psi 641,962 ksf for f c 6,000 psi E Modulus of elasticity of pile ksf E soil modulus for clays S ksi A Gross area of pile in I Moment of Interia of pile ft S Elastic section modulus of pile in Z Plastic section modulus of pile in r radius of gyration of pile in L Unsupported length of pile ft (AASHTO C ) δ deflection of pile in coarse grain soils; if δ D 4, then pinned end; otherwise fixed end β deflection of pile in cohesive soils; if β D 2.25, then pinned ends; otherwise fixed end DESIGN GUIDE FOR LATERALLY UNSUPPORTED GENERAL INFORMATION AND DEFINITIONS SHEET 1 of 14 FILE NO

4 DESIGN CRITERIA: POINT OF FIXITY FOR FREE STANDING PILE DESIGN CRITERIA: Point of fixity for both the existing or final profile and the scoured condition may need to be determined. EFFECTIVE LENGTH FACTOR K: Top D must be 3D for fixity to be assumed Bottom Top: R_free & T_free R_fixed & T_free R_free & T_fixed Bottom: R_fixed & T_fixed R_fixed & T_fixed R_fixed & T_fixed K = 2.1 K = 1.2 K = 0.8 Pier bent on single row of piles with load applied in longitudinal direction Pier bent on piles with load applied in transverse direction Integral abutment on piles with load applied in longitudinal direction End Conditions: R = Rotation; T = Translation DESIGN GUIDE FOR LATERALLY UNSUPPORTED DESIGN CRITERIA SHEET 2 of 14 FILE NO

5 DESIGN CRITERIA (Cont d): Table 1 Rate of Increase of Soil Modulus with Depth, (ksi/ft) for Sand (AASHTO Table C ) Consistency Dry or Moist Submerged Loose Medium Dense Table 2 Relationship between unconfined compressive strength, standard penetration resistance, and unit weight for cohesive soils (Teng, 1962) SHEAR STRENGTH OF COHESIVE SOILS Consistency Very Soft Soft Medium Stiff Very Stiff Hard q u = Unconfined compressive strength, lb/ft Standard penetration resistance N = No. of blows per ft Unit weight, pcf (saturated) Cohesive (c) = ½ unconfined compression strength Table 3 Relationship between relative density, standard penetration resistance, angle of internal friction and unit weight for cohesive soils (Teng, 1962) RELATIVE DENSITY OF GRANULAR SOILS Very Compactness Loose Medium Dense Loose Very Dense Relative density Standard penetration resistance, N = No. of blows per foot Angle of internal friction (degrees) * 0 15% 35% 65% 85% 100% Unit weight, pcf Moist Submerged <100 < >130 >75 *Highly dependent on gradation DESIGN GUIDE FOR LATERALLY UNSUPPORTED DESIGN CRITERIA SHEET 3 of 14 FILE NO

6 POINT OF FIXITY FOR FREE STANDING PILE COARSE GRAIN SOIL EXAMPLE: Coarse grain soil, medium relative density (N = 27 blows/ft), above ground water. HP12x53 subject to biaxial bending. Pile Length 60 ft Scour Depth 10 ft D50 ft I 393 in I 127 in E 29,000 ksi r 5.03 in r 2.86 in Based on N = 27, a medium-dense soil is assumed. Use Tables 1 and 3 on File No to determine the value of n h by performing linear interpolation between a medium soil (N = 20, n h = 1.11), and a dense soil (N = 50, n h = 2.78); n 1.5 ksi/ft E I 29, D 1.8 E I n D 1.8 E I n 79,146 kip ft 79, ft 1.5 x 144 in ft 25, ft 1.5 x 144 in ft E I 29, ,576 kip ft (AASHTO C ) (AASHTO C ) δ n E I ft δ D fixed end δ n E I ft δ D fixed end D D fixed end D D fixed end Scour Depth D 10 ft 5.86 ft ft Scour Depth D 10 ft 4.68 ft ft Single row of piles with fixed ends in x-direction: in K 2.1 K x 12 ft r 5.03 Single row of piles with fixed ends in y-direction: in K 1.2 K x 12 ft 73.9 r 2.86 Where: Unsupported length of pile K Effective length factor R Radius of gyration DESIGN GUIDE FOR LATERALLY UNSUPPORTED COARSE GRAIN SOIL EXAMPLE SHEET 4 of 14 FILE NO

7 POINT OF FIXITY FOR FREE STANDING PILE COHESIVE SOIL EXAMPLE: Cohesive soil, blow count N 12 blows/ft Pile Length: 60 ft Scour Depth 10 ft D50 ft HP12x53 subject to biaxial bending. I 393 in I 127 in b in E 29,000 ksi r 5.03 in r 2.86 in b in c 0.125N ksf 1.5 ksf S c1.5 ksf E S ksi Note: Soil modulus is reduced for pile spacing < 8 times the pile width, see Article C (For this example, since a specific pile spacing is not provided, no reduction is assumed.) D 1.4 E I E D 1.4 E I E β E x 12 in E I ft ft 1 x 12 in 7.42ft ft 1 x 12 in 5.59ft ft β D fixed end (AASHTO C ) (AASHTO C ) β E x 12 in E I ft ft β D fixed end D D fixed end D D fixed end Scour Depth D 10 ft 7.42 ft ft Scour Depth D 10 ft 5.59 ft ft Single row of piles with fixed ends in x-direction: in K 2.1 K x 12 ft r 5.03 Single row of piles with fixed ends in y-direction: in K 1.2 K x 12 ft r 2.86 Where: Unsupported length of pile K Effective length factor R Radius of gyration DESIGN GUIDE FOR LATERALLY UNSUPPORTED COHESIVE SOIL EXAMPLE SHEET 5 of 14 FILE NO

8 POINT OF FIXITY FOR FREE STANDING PILE LAYERED SOIL EXAMPLE: Soil Layer 1: Sand, N = 5 blows/ft n h1 = ksi/ft Depth, d 1 = 4 ft Soil Layer 2: Sand, N = 10 blows/ft n h2 = 0.60 ksi/ft Depth, d 2 = 4 ft Soil Layer 3: Sand, N = 20 blows/ft n h3 = 1.11 ksi/ft Depth, d 3 = 20 ft Determination of the point of fixity for a layered soil condition is based on a trial and error approach, using an initial assumption of n h, selected based on the soil conditions observed. In this case, the values for n h were determined using linear interpolation based on the compactness description of the soil from the provided N values, and the n h values provided in Table 1 on File No Assume an initial average n h : n 0.50 ksi/ft Pile EI 79,146 kip ft D 1.8 EI n 79, x 144 in ft ft d ft Due to rigidity of pile and soil profile, point of fixity does not extend into third soil layer; therefore, recalculate fixity based on two-layer soil profile. Calculate second moment of area for two-layer soil diagram taken about D: n 3 D n d 3 n d y ksi ft Use new n h to calculate new D: 79,146 D ft x 144 in ft d ft DESIGN GUIDE FOR LATERALLY UNSUPPORTED LAYERED SOIL EXAMPLE SHEET 6 of 14 FILE NO

9 POINT OF FIXITY FOR FREE STANDING PILE LAYERED SOIL EXAMPLE (Cont d): n ksi ft 79,146 D ft x 144 in ft Use this value as convergence. Where: d i = depth of layer y i = distance from assumed D to center of layer DESIGN GUIDE FOR LATERALLY UNSUPPORTED LAYERED SOIL EXAMPLE SHEET 7 of 14 FILE NO

10 STEEL H-PILE DESIGN CRITERIA: Compression members shall satisfy the following slenderness ratios: K r 120; For primary members Determine axis for elastic critical buckling resistance: If >, Use about the x-axis, otherwise use about the y-axis If K < K, flexural buckling shall be applicable: P π E K r A (AASHTO ) If K > K, torsional buckling and flexural torsional buckling shall be applicable: P π EC GJ A (AASHTO ) K z I I Check compressive slenderness limits of member elements: If 0.56, then: Q 1.0 (AASHTO ) If 0.56 < 1.03, then: Q (AASHTO ) If 1.03, then: Q. (AASHTO ) Determine compressive resistance: P Q F A If 0.44, then: P = P (AASHTO ) If 0.44, then: P = 0.877P (AASHTO ) P P (AASHTO ) DESIGN GUIDE FOR LATERALLY UNSUPPORTED STEEL H-PILE DESIGN CRITERIA SHEET 8 of 14 FILE NO

11 STEEL H-PILE DESIGN CRITERIA (Cont d): Where: 0.7 for combined axial & flexural resistance of H-piles as specified in Article C w = warping torsional constant (See HP Shapes Properties Table on Sheet 9) G = shear modulus for elasticity for steel determined as specified in Article J = St. Venant torsional constant (See HP Shapes Properties Table on Sheet 9) Q s = slender element reduction factor determined as specified in Article P o = equivalent nominal yield resistance determined as specified in Article b = half-flange width of rolled I- and tee sections as specified in Table Check flexural slenderness limits of flanges: λ = = slenderness ratio for flange (AASHTO ) λ = 0.38 = limiting slenderness ratio for compact flange (AASHTO ) λ = 0.83 = limiting slenderness ratio for non-compact flange (AASHTO ) If λ λ, then: M M 1.5F S M M 1.5F S (AASHTO ) If λ λ λ, then: M 11 S λ λ Z 0.45 E F Z Fyf M 11 S λ λ Z 0.45 E F Z Fyf (AASHTO ) If λ λ, then: M F S M F S M M M M (AASHTO C ) (AASHTO ) Where: 1.0 for combined axial & flexural resistance of H-piles as specified in Article Check combined axial and flexure: If 0.2, then: If 0.2, then: P 2.0P M M M M 1.0 (AASHTO ) P P 8 9 M M M M 1.0 (AASHTO ) DESIGN GUIDE FOR LATERALLY UNSUPPORTED STEEL H-PILE DESIGN CRITERIA SHEET 9 of 14 FILE NO

12 PROPERTIES FOR DESIGNING STEEL H-: HP Shapes Dimensions Shape HP14x117 x102 x89 x73 HP12x84 x74 x63 x53 Area, A Depth, d Web Thickness, t w Width, b f Flange Thickness, t f in. 2 in. in. in. in HP10x57 x Properties Shape Nominal Weight Axis X-X Axis Y-Y l S r Z l S r Z HP14x117 x102 x89 x73 lb/ft in. 4 in. 3 in. in. 3 in. 4 in. 3 in. in HP12x84 x74 x63 x HP10x57 x DESIGN GUIDE FOR LATERALLY UNSUPPORTED PROPERTIES FOR DESIGNING STEEL H- SHEET 10 of 14 FILE NO

13 STEEL H-PILE DESIGN EXAMPLE: Coarse grain soil, medium relative density, above ground water. HP 12x53 Fy = 50 ksi E = 29,000 ksi Strength I Loading 100 Year Storm Pile Length = 60 ft Scour Depth = 10 ft D = 50 ft P 124 kip M 250 kip in M 50 kip in K K 2.1 K ft Determine axis for critical buckling resistance: K r K r 73.9 (See coarse grain soil example.) Kl 120, element satisfies limiting slenderness ratio requirement. Since K r K r critically bucking, K, will be determined about the x-axis. K x 12 in in ft K x12 in in ft Since K K, torsional buckling and flexural torsional buckling shall be applicable: P π EC GJ A K ; I I where G E 1.12x10 ksi π kip 1.12x Check compressive slenderness limits of member elements: b t E F By inspection, 0.56 E F b t 1.03 E F Q b t F E DESIGN GUIDE FOR LATERALLY UNSUPPORTED STEEL H-PILE DESIGN EXAMPLE SHEET 11 of 14 FILE NO

14 STEEL H-PILE DESIGN EXAMPLE (Cont d): Determine compressive resistance: P Q F A kip P P P P kip P P kip Check flexural slenderness limits of flanges: λ b 12 2t λ 0.38 E F λ 0.83 E F Section is non-compact. λ λ λ, M 11 S λ λ Z 0.45 E F Z Fyf M 3.54x10 kip in M 11 S λ λ Z 0.45 E F Z Fyf M 1.37x10 kip in M M x x10 kip in M M x x10 kip in Check combined axial and flexure: P P P 8 P 9 M M M M Pile is adequate. DESIGN GUIDE FOR LATERALLY UNSUPPORTED STEEL H-PILE DESIGN EXAMPLE SHEET 12 of 14 FILE NO

15 PRESTRES SSED CONCRETE PILE DESIGN CRITERIA: Per AASHTO , the effects of slenderness may be neglected if: Kl r 22 : For compression members not braced against sidesway Per AASHTO , the allowable stresses at the serviceability limit state after prestress losses shall be such that: Tension stresses: f P M c A I 0 ksi, for components with unbonded prestressing tendons 0.19 f ksi, for components with bonded prestressing tendons subjected to not worse than moderate corrosion conditions f ksi, for components with bonded prestressing tendons subjected to severe corrosion conditions Compression stresses: f P M c A I f P M c A I 0.45 f ksi, compression due to prestress plus permanent loads f ksi, compression due to prestress plus total load Where: P = applied axial load M = applied moment = M x + M y Properties Size in. Area A A g in. 2 Moment of Inertia I g 4 in. Section Modulus S in Radius of Gyration r in Compressive stress in concrete due to effective prestress forces only (after allowances for all prestess losses), f cpe psi Std. PS ** Strandss Stainless ** Steel Strands CFRP Strands * Values for f cpe taken from VDOT Standard BPP Plan sheets ** With square strand pattern DESIGN GUIDE FOR LATERAL LLY UNSUPPORTED PRESTRESSED CONCRETE PILE DESIGN CRITERIA SHEET 13 of 14 FILE NO

16 PRESTRESSED CONCRETE PILE DESIGN EXAMPLE: 12 prestressed concrete pile using standard prestress strands (4), moderate corrosion conditions. f c = 5 ksi Strength I Loading 100 Year Storm Pile Length = 60 ft Scour Depth = 10 ft D = 50 ft K = 1.2 P 72 kip M 120 kip in M 12 kip in Kl r in x 12 ft Slenderness effects shall be considered. Check serviceability stresses: f P A M c I 0.19 f f P M c ksi ksi A I Tension OK f P A M c I 0.45 f f P M c ksi 2.25 ksi A I Compression OK f P A M c I 0.60 f f P M c ksi 3.0 ksi A I Compression OK For 12 prestressed concrete pile using standard prestess strands, f cpe is the same value for both square and circular strand patterns. For pile sizes with different values, check serviceability stresses for both patterns. Reference: Teng, W. C Foundation Design. Prentice-HalI, Inc., Englewood Cliffs, New Jersey. DESIGN GUIDE FOR LATERALLY UNSUPPORTED PRESTRESSED CONCRETE PILE DESIGN EXAMPLE SHEET 14 of 14 FILE NO

17 POINT OF FIXITY ANALYSIS FOR LATERALLY LOADED SINGLE PILE: Design Procedure for single pile analysis: The design of a pile foundation requires the designer to consider factors involving performance, costs and methods of construction. Two aspects of design are the computation of loading that will cause the pile to fail as a structural member and the level of loading that will cause an unacceptable lateral deflection. This step-by-step procedure describes the use of an acceptable software program that has the capacity to develop p-y curves to determine the pile length to establish fixity. The final pile length (structural length) can then be used to determine the structural capacity of the selected pile. 1. Collect all relevant data, including the soil profile, soil properties, magnitude and type of loading, and performance requirements for the structure being analyzed. Since limiting deflection criteria is a service condition, the loads used will be service limit state (unfactored). 2. Select a pile type and size for analysis. If a prestressed concrete pile is chosen, reinforcing will also be needed to determine pile properties. The analysis program selected may then compute remaining pile information used for analysis. 3. Develop site specific p-y curves based on in-situ data. The designer can obtain the soil data required from the selected analysis software using boring logs in conjunction with Tables 1 through 3 on File No Alternatively, soil parameters can be obtained directly from a geotechnical engineer. Most analysis programs have the ability to select p-y curves for each soil layer based on the provided soil input information. Alternatively, the user may input developed p-y curves. 4. Run software analysis using an initial pile depth based on the limiting project specific deflection criteria. Plot deflection verse depth curves for each load case under study. Several trial sizes and depths may be required to achieve the established design criteria. After the deflection criteria has been satisfied, the determination of fixity can be determined from the plots of Pile Depth verse Deflection. 5. Select the point of fixity from the plotted curves. Point of fixity is where the deflection curve crosses the zero line when subjected to service lateral loads. There is no universal opinion as to whether fixity should occur at one or two crossings of the zero line. Choosing fixity at the second crossing would be a conservative assumption and will be used for this example. The software used in this sample analysis is L-Pile 2016, Version 9. L-Pile is a multi-purpose program that can analyze a pile subjected to lateral loading. It computes deflection, shear, bending moment and soil response with respect to depth in nonlinear soils. The soil and rock is modeled using lateral load transfer curves (p-y) based on either published recommendations, or alternatively, user input p-y curves developed for each soil layer. Several types of pile head loading conditions may be selected along with the structural properties of the pile. The determination of point of fixity for a laterally loaded pile requires a pile deflection verse pile depth curve for all of the chosen load cases, as well as the soil profile along the length of pile. For this analysis, loads at the service limit state were chosen. Soils information from the boring logs was used in conjunction with the corresponding values for the soil properties provided in Tables 1 through 3 on File No The Coefficient of Horizontal Subgrade Reaction (k) was chosen by L-Pile using the user provided information. LATERAL LOADED PILE ANALYSIS FOR POINT OF FIXITY DESIGN PROCEDURE SHEET 1 of 4 FILE NO

18 DESIGN ASSUMPTIONS AND RESULTS: Loading: 1. The loads used for this example are per pile and unfactored. The loads used are 134 kips vertical, 4.15 kips lateral longitudinal, 6.68 kips lateral transverse. 2. Moment at the top of pile was not used for this analysis. Both a fixed and free head (i.e., top of pile) condition is achievable without moment input, and therefore was not calculated for this example. 3. Since this analyses is for point of fixity, service limit state loads were used. Pile head deflection may have a limiting value depending on performance criteria that has been established. For this example, ½ inch at the top of pile is used. 4. Pile group effects were not considered. 5. In the longitudinal direction, the pile is assumed to be in a free head condition (i.e., rotation free and translation free). In the transverse direction, the pile is assumed to be in a fixed head condition (i.e., rotation fixed and translation free; slope equals zero). Soils: 1. Soil properties used were determined using boring logs in conjunction with Tables 1 through 3 on File No A 3.5 foot scour depth was assumed for this example. Results: 1. Plots of pile head deflection verse pile depth for scour and non-scour conditions are shown on File Nos and -4, respectively. 2. The analysis considers the nonlinear properties of the soils. For this example, the effects of scour can be seen as negligible as shown by the top of pile deflections of the plots. 3. From both plots, the first inflection point is at a depth of approximately -18 ft. for the free head condition and approximately -23 ft. for the fixed head condition. The second inflection point occurs at approximately -36 ft. for both cases. The second inflection point is chosen for fixity and an unbraced length of 36 ft. below the pile head is assumed for determining the structural capacity of the pile. LATERAL LOADED PILE ANALYSIS FOR POINT OF FIXITY DESIGN ASSUMPTIONS AND RESULTS SHEET 2 of 4 FILE NO

19 LATERAL LOADED PILE ANALYSIS FOR POINT OF FIXITY L-PILE RESULTS FOR SCOUR CONDITION SHEET 3 of 4 FILE NO

20 LATERAL LOADED PILE ANALYSIS FOR POINT OF FIXITY L-PILE RESULTS FOR NON-SCOUR CONDITION SHEET 4 of 4 FILE NO