NCHRP Project 10-70sp.bridges.transportation.org/Documents/2011 SCOBS...Advanced Technology for...

Advanced Technology for Large Structural Systems CenterLehigh University

Sougata Roy, Richard Sause, John W. Fisher, Yeun Chul Park, Eric J. Kaufmann

NCHRP Project 10-70:Cost-Effective Connection Details for Highway Sign, Luminaire and Traffic Signal Structures

Recommended Specification —Application Examples


Project Summary (2006-11) 80 full scale specimens

– Rational experiment design to establish infinite life

– Multiple details and geometric combinations

– 158 tests including re-runs ( approx. 2000 million cycles)• Approximately 330 details tested (cumulative 5000 million cycles)

Parametric FEA using 30,000+ models

– Extended experimental results over a broad range of structure sizes and geometric combinations

Specification for cost-effective fatigue design

Final Report (in the process of publication)


NCHRP Project 10-70 @ LehighFritz Lab ATLSS Lab

Analytical and experimental evaluation 80 full size specimens, 158 tests Revisions to the AASHTO Specification 2006-11


Critical Details Tube-to-transverse plate connections

– Mast arm-to-transverse plate

– Pole-to-base plate

Handhole– Reinforced

– Unreinforced

Mast arm-to-pole connection– Gusseted box

– Ring stiffened

Mast arm-to-pole pass-through connection


Tube-to- Transverse Plate Connections

Fillet-weldedor

SocketFull-penetration

Groove-welded

Stiffened Socket


Tube-to-Transverse Plate Connection Displacement Induced Fatigue

– Relative stiffness of components important Fatigue resistance of connections depends on

– Member cross section• Round vs. Multisided

– Connection Geometry• Tube diameter and thickness (relative to plate)• Plate thickness (use minimum 2 in)• Number of fasteners and bolt circle ratio• Opening in end plate (groove welded connections only)• Stiffened vs. Unstiffened

– Detail Configuration• Fillet (socket), Groove welded etc.

– Weld Geometry• Weld shape and size (Weld termination angle)


Geometric Parameters

DT

tT

tTP

DOP

DBC

NB


Specification - What’s New 2 level specification

– Nominal stress-based design for most cases– Local stress-based and experiment-based design for special

cases (Appendix D)

Proposed for both finite and infinite life– Infinite life : new design– Finite life : assessment

Format similar to AASHTO LRFD Bridge Design Specification (2009 Interim)

Fatigue resistance defined as function of geometric parameters


Stress Concentration Factors – KF , KI

Base equations for round section geometries

– Geometric SCF (finite life - KF)– Socket and groove welded connections have different

equations

Modification multiplier for infinite life (KI)

For multisided cross sections modify SCF equations for round section

For stiffened connections modify SCF equations for unstiffened connections


Nominal Stress Calculation (1) Fillet-welded (socket) connection

– Section at fillet weld toe on tube wall

Stiffened connections– Section at stiffener top weld toe on tube wall– Section at fillet weld toe on tube wall

• Ignore stiffener section (Implicitly considered in SCF equations in Table 11-1 and in Table C11-1)


Nominal Stress Calculation (2) Groove-welded connections with

backing ring not welded at top– Section at groove weld toe on tube wall– Ignore backing ring section

Groove-welded connection with backing ring welded at top

– Section at groove weld toe on tube wall

– Section at toe of backing ring top weld on tube wall


Mandatory Requirements Thickness of transverse plate ≥ 2 in Unstiffened tube-to-transverse plate connections

– Fillet welds and weld reinforcements shall be unequal leg welds (approximately 30o on tube side)

– Backing ring • height ≤ 2 in• thickness ≤ ¼ in• Backing ring can be welded to tube only when quality of weld can be

ensured (recommended DT ≤ 16 in)


Fatigue critical details– Mast-arm-to-transverse plate connection– Column-to-transverse plate connection– Mast-arm-to-pole connection– Handholes– Anchor rods

Design Example 1 : Sign/Signal Structure


Mast-arm/Pole-to-Transverse Plate Connection

Design criteria– (f )n ≤ (F )n

Nominal stress range at mast-arm base– (f )n : depends on tube section property (DT, tT )

Nominal fatigue resistance – (F )n : depends on connection geometry (DT, tT , tTP, DOP,

etc…)

Fatigue design load (due to galloping)– PG = 21IF

MG


Fatigue Resistance in Proposed Spec.

Three choices

– Use Table C11-1 • Tested details in NCHRP 10-70 for infinite life

– Use Table 11-2 and equations for tubular structures

– Appendix D • Only for innovative details


Choice 1: Table C11-1

(F )n = (F )TH = 10.0 ksi (Category C)

(f )n < (F )n → infinite life (OK !)

MG = 215 k-in

tT = 0.239 inDT = 13 in

(f )n = 7.2 ksi

Option 1

Option 2

tTP = 2.0 in

DOP = 4 in

tTP = 2.5 in

DOP = 7 in


Choice 2 : Table 11-2 / EquationsRound Full-penetration Groove-welded Tube-to-Transverse Plate Connection

Applied Moment M 215 k-in

Transverse Plate Thickness t TP 2.0 inTube Thickness t T 0.239 inTube Diameter D T 13.0 inNumber of Fasteners N B 4Bolt Circle Diameter D BC 23.3 inTransverse Plate Opening D OP 4 in

Applied Nominal Stress ( f )n 7.2 ksi

Stress Concentration Factor K F 1.6K I 2.9

Constant Amplitude Fatigue Threshold ( F )TH 10 ksi OK

LINK


Note : Groove-welded Connections Existing specification : Category E

Proposed specification :

– depending on connection geometry (tT, DT, tTP, DBC, DOP, and NB )

• Category E, D or C


Table 11-2Description Finite Life Constant,

A×108 (MPa3 (ksi3))

Thresholdf, (F)TH

(MPa (ksi))

Potential Crack Location Example

SECTION 1 — GROOVE-WELDED CONNECTIONS 4.5 Full-penetration groove-welded tube-to-transverse plate connections with backing ring attached to the plate with a full penetration weld, or with a continuous fillet-weld around interior face of backing ring, and the backing ring not welded to the tube.

KF ≤ 1.6 : 3750 (11.0) 1.6 < KF ≤ 2.3 : 1330 (3.9)

KI ≤ 3.2 : 69 (10.0) 3.2 < KI ≤ 5.1 : 48 (7.0) 5.1 < KI ≤ 7.2 : 31 (4.5)

In tube wall along groove-weld toe.

Column-to-base-plate connections. Mast-arm-to-flange-plate connections.

SECTION 2 - FILLET-WELDED CONNECTIONS 5.4 Fillet-welded tube-to-transverse plate connections

KF ≤ 3.0 : 1330 (3.9)

KI ≤ 3.0 : 48 (7.0) 3.0 < KI ≤ 5.7 : 31 (4.5) 5.7 < KI ≤ 7.2 : 18 (2.6)

In tube wall along fillet-weld toe. Column-to-base-plate or mast-arm-to-flange-plate socket connections.

SECTION 3 - ATTACHMENTS 6.2 Tube-to-transverse plate connections stiffened by longitudinal attachments with partial- or full penetration groove-welds, or fillet-welds in which the tube is subjected to longitudinal loading and the welds are wrapped around the attachment termination.

KF ≤ 2.5 : 3750 (11.0)

(See detail 5.4)

KI ≤ 5.5 : 48 (7.0)

(See detail 5.4)

In tube wall at the toe of the attachment to tube weld at the termination of attachment. In tube wall at the toe of tube-to-transverse plate weld.


Equation : Groove-weld Connection

0.0674 1.121.95

0.0029 0.689

1.01.35 0.982 1.0 17.3 2.602.24 0.764

BC TF T TP

B OP

C DK t tN C

DT

DOP

tT

tTP

DBC

2940 Geometric Combinations (FEA Models)

GSCF: Geometric Stress Concentration Factor


Significance of Geometric Parameters

NB neglected CBC neglected

COP neglected

tT neglected DT neglected


Simplified Equations (Unstiffened)…

Round Fillet-welded connections

Round Groove-welded connections

0.0474

0.0105

1.15 2.36

2.16 0.908 0.924 4.54 52.1

14.6 1.17

BCF T

B

T TP

CK tN

D t

0.03 1.2 2.52.2 4.6 1 2 15 10F BC T T TPK C t D t

0.0674

0.0029

1.121.95

0.689

1.35 0.982 1.0 17.3

1.02.602.24 0.764

BCF T

B

TTP

OP

CK tN

D tC

0.02

20.7

11.35 16 1 15 54 3

BCF T T TP

OP

CK t D tC


Simplified Equations (Stiffened) ……

Stiffened connections at stiffener termination

Stiffened connections at fillet-weld toe on tube wall

0.334

0.707

1.60 1.42 0.797 2.91

4.36 1.00.160 0.864

1.0 1.122.26

0.870 0.02930.519 0.257

ST

STTF

ST ST

T

T

ST T T ST

thtK t h

t

DN t t t

0.4 0.8

0.7 1.20.3 0.9 0.4ST TF

T ST

t DKt N

1.03

0.914

0.631

F

0.1299.84 4.891.82 6.56

2.790.859 0.80212.9

K of unstiffened

T T

ST ST

TPF

ST

D DN h

tKt

0.15

1.5 0.5

F

0.13 6.51.0 130 17

K of unstiffened

T

F ST ST ST

DK N h t


…… But Comes with a Cost

Simplified Proposed Equation

0.02

20.7

11.35 16 1 15 54 3

BCF T T TP

OP

CK t D tC

Proposed Equation

0.0674

0.0029

1.121.95

0.689

1.35 0.982 1.0 17.3

1.02.602.24 0.764

BCF T

B

TTP

OP

CK tN

D tC

groove-welded connections


Infinite Life Stress Concentration Factor Includes local notch effect

(1.76 1.83 ) 4.76 0.22 FKIT

F

Kt

K


Alternative Design Chart (Groove)COPNB

DT

tT tTP CBC

2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4

1.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.5

0.5

0.625

42

0.125

0.1875

0.25

0.3125

0.375

10 13 18 24 30 36

90% 60% 30%4 6 8 12 16 : Category C

: Catogory D

: Catogory E

: Combination cannot be used

Equation as-is


Effect of Simplification (Groove)COPNB

DT

tT tTP CBC

2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4

1.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.5

90% 60% 30%

10 13 18 24 30 36 4216

0.125

0.1875

0.25

0.3125

0.625

4 6 8 12

0.375

0.5

: Category C: Category C → D: Catogory D: Category D → E: Catogory E: Category E → None: Combination cannot be used


Solution Using Simplified Design ChartCOPDT

tT tTP CBC

2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4 2 2.5 3 3.5 4

1.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.51.251.51.7522.252.5

30

0.375

0.5

0.625

60% 30%36 42

0.125

0.1875

0.25

0.3125

90%10 13 18 24

E

E E

E

E

E

E

D

D D

D D DD

CC C C C C C22.7 ksi 13.3 ksi

15.4 ksi

11.8 ksi 6.9 ksi

9.0 ksi

MG = 215 k-in

(f )n = 9.0 ksi

(F )n = (F )TH = 10.0 ksi (C)

or

(f )n = 6.9 ksi

(F )n = (F )TH = 7.0 ksi (D)

(f )n < (F )n : Category C

: Catogory D

: Catogory E

: Combination cannot be used


Summary of DesignFillet

Option 1 Option 2

t TP (in) 2.0 2.5 2.5 3.5 2.5

t T (in) 0.239 0.239 0.25 0.1875 0.239

D T (in) 13 13 13 13 18

D BC (in) 23.3 23.3 19.5 19.5 24

D OP (in) 4 7 11 11 —

( f )n (ksi) 7.2 7.2 6.9 9.0 3.7

( F )n (ksi) 10.0 10.0 7.0 10.0 4.5

Table C11‐1 Table 11‐2 / Equation

Table 11‐2 / Equation

Option3

Groove


Mast-arm-to-column Connection


Design Example 2 : Highmast Luminaires

Fatigue critical detail

– Pole-to-transverse plate connection


Option 1 : Stiffened ConnectionStiffened Tube-to-transverse Plate Connection


Transverse Plate Thickness t TP 2.0 inTube Thickness t T 0.5 inTube Diameter D T 42.0 inNumber of Fasteners N B 12Bolt Circle Diameter D BC 50.0 inNumber of Stiffeners NST 12Height of Stiffeners hST 12.0 inThickness of Stiffeners tST 0.625 in


Stiffener Termination K F 2.1K I 5.1


Fillet-weld on Tube Wall K F 1.7K I 4.0

Constant Amplitude Fatigue Threshold ( F )TH 4.5 ksi NOT SAFE

LINK


Option 2 : Groove-weld ConnectionRound Full-penetration Groove-welded Tube-to-Transverse Plate Connection


Transverse Plate Thickness t TP 3.5 inTube Thickness t T 0.5 inTube Diameter D T 42.0 inNumber of Fasteners N B 12Bolt Circle Diameter D BC 50.0 inTransverse Plate Opening D OP 30 in


Stress Concentration Factor K F 2.0K I 5.0


LINK


Note : Stiffened Connections Existing specification : E´

Proposed specification :

– depending on connection geometry (NST, hST, tST, DT, tT)• Category D


Choice 3 : Appendix D

Methodology for assessing fatigue performance of innovative connection details

– Analytical Protocols

– Experimental Protocols


AcknowledgementsSponsorsAASHTO / FHWA

TRB – NRC, National Academies

NCHRP Project Panel

DisclaimerThe opinions and conclusions expressed or implied in the presentation arethose of the research agency. They are not necessarily those of the AmericanAssociation of State Highway and Transportation Officials, or the individualstates participating in the National Cooperative Highway Research Program.

Research SupportState Departments of TransportationsMr. Reilly Thompson, Mr. Nirab Manandhar, Dr. Eric J. Kaufmann, Dr. Ben T. YenDr. Karl Frank, Dr. Justin Ocel, Mr. Carl MacchiettoValmont Inc.; Millerbernd Manufacturing; Union Metal

Research support at Lehigh University

Thank You

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