UCSD Final Report Isa

8/12/2019 UCSD Final Report Isa

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STRUCTURAL SYSTEMS

RESEARCH PROJECT

Report No.

SSRP- 11/07 FATIGUE TESTS OF WELDED CONNECTIONS

IN CANTILEVERED STEEL SIGN STRUCTURES

by

HYOUNG-BO SIM

CHIA-MING UANG

Final Report Submitted to International Sign Association

October 2011Department of Structural Engineering

University of California, San Diego

La Jolla, California 92093-0085


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University of California, San Diego

Department of Structural Engineering

Structural Systems Research Project

Report No. SSRP-11/07

Fatigue Tests of Welded Connections in Cantilevered

Steel Sign Structures

by

Hyoung-Bo Sim

Postdoctoral Researcher

Chia-Ming Uang

Professor of Structural Engineering

Final Report Submitted to International Sign Association

Department of Structural EngineeringUniversity of California, San Diego

La Jolla, California 92093-0085

October 2011


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ACKNOWLEDGEMENTS

Funding for this research was provided by the International Sign Association

(ISA). We would like to thank Mr. Bill Dundas, ISA Director of Technical andRegulatory Affairs, and the ISA Mechanical and Structural Subcommittee, chaired by

Mr. Wes Wilkens, for providing guidance in this research. We would also like to thank

Mr. Jack Lester for preparing the specimen drawings and arranging the fabrication and

shipping of most of the specimens. Additionally, we would like to thank Mr. Roy Flahive

for coordinating efforts at the laboratory on test specimen preparation, repairs and

inspections. Union Metal (Canton, OH) donated the tapered-pole specimen (A7) and Fyfe

Company LLC (San Diego, CA) donated materials and services for the Fiber Reinforced

Polymer (FRP) repair.

The testing was conducted in the Charles Lee Powell Structural Components

Laboratory at the University of California, San Diego. Assistance from the laboratory

staff is much appreciated.


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ii

ABSTRACT

Freestanding (cantilevered) steel sign structures have been widely used by

commercial and retail business for many years. The actual probability of failure forcantilevered sign structures due to wind-induced vibration is relatively small. In this case,

failure is defined as fatigue cracking which causes collapse or loss of a structures

serviceability. While the majority of these structures have performed well in long-term

use, however, some structures have been damaged or destroyed.

This type of structure is flexible, has a low damping and, under certain

circumstances, can be prone to fatigue-type cracking due to wind-induced vibration.

Cracks at the sleeve connections, some resulting in sign failures, have been reported

when the wind speed was significantly below that used in design. In connection with its

ongoing efforts to support the safety and acceptability of signage products, the

International Sign Association (ISA) made a decision to investigate potential remedies by

sponsoring the tests described in this report.

Fatigue tests of seventeen full-scale connection details were conducted to evaluate

their relative fatigue resistance. Test specimens included four conventional (with or

without a guide ring), five repaired (with various combinations of welded gussets, grout,

steel cones or jackets and Fiber Reinforced Polymer composites), and eight alternative

connection details for new construction.

Testing demonstrated that conventional welded sleeve connections had a

relatively low fatigue resistance. All four specimens showed the same cracking pattern as

commonly observed in the field on damaged or failed structures. The use of a guide ring

had a minimal effect on the fatigue resistance. After testing, the damaged conventional

specimens were repaired with various schemes to evaluate their effectiveness.

A gusset-repaired specimen also showed relatively low fatigue resistance. Steel-

jacketed cement grouting, or the use of a welded steel cone above the upper ring,

significantly improved the fatigue resistance at the most commonly observed failure

location, although fatigue cracking later occurred at the next weak locations (i.e., the

lower pipe-to-upper ring fillet weld and the slot welds, which also are prone to fatigue).

Grouting the sleeve region or using welded patch plates did not improve the fatigue


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iii

resistance of the slot welds. An FRP-repair scheme for cracked slot welds effectively

prevented further crack growth.

Some promising alternative connections that can potentially be used for new

construction were experimentally evaluated. A bolted match-plate connection performed

relatively poorly. But a revised sleeve connection incorporating a one-sided, bottom-only

fillet weld detail at the upper pipe-to-upper ring joint was effective in enhancing the

fatigue performance compared to the conventional sleeve connections. To avoid cracking

at slot welds, the use of grout between the pipes in the sleeve region significantly

increased the fatigue resistance. Using a welded cone to provide a smooth transition

between the pipes also showed improved performance. A tapered slip-joint connection,

which requires no welded joints between the pipe sections, substantially outperformed all

of the other specimens tested.


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iv

TABLE OF CONTENTS

ACKNOWLEDGEMENTS....................................................................................................... i

ABSTRACT ........................................................................................................................ ii

TABLE OF CONTENTS......................................................................................................... iv

LIST OF TABLES................................................................................................................... vi

LIST OF FIGURES ................................................................................................................ vii

1. INTRODUCTION........................................................................................................... 10

1.1 Problem Statements ................................................................................................ 10

1.2 Past Research .......................................................................................................... 10

1.3 Objectives and Scope.............................................................................................. 13

2. TEST PROGRAM........................................................................................................... 14

2.1 Test Setup................................................................................................................ 14

2.2 Test Matrix.............................................................................................................. 15

2.3 Connection Details.................................................................................................. 16

2.3.1 Conventional Welded Sleeve Connection Details ....................................... 16

2.3.2 Repaired Connection Details ....................................................................... 19

2.3.3 Alternative Connection Details.................................................................... 24

2.4 Loading Scheme...................................................................................................... 27

2.5 Instrumentation and Crack Inspections................................................................... 273. TEST RESULTS OF CONVENTIONAL CONNECTIONS ......................................... 29

3.1 Introduction............................................................................................................. 29

3.2 Conventional Connection Details without Guide Ring .......................................... 29

3.2.1 Specimen C1 ................................................................................................ 29

3.2.2 Specimen C2 ................................................................................................ 31

3.3 Conventional Connection Details with Guide Ring................................................ 33

3.3.1 Specimen C3 ................................................................................................ 33

3.3.2 Specimen C4 ................................................................................................ 34

3.4 Comparison of Test Results.................................................................................... 35

4. TEST RESULTS OF REPAIRED CONNECTIONS ..................................................... 36

4.1 Introduction............................................................................................................. 36

4.2 Gusset Repair: Specimen R1 .................................................................................. 36

4.3 Steel-Jacketed and Cement-Grouted Repair ........................................................... 38


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4.3.1 Introduction.................................................................................................. 38

4.3.2 Specimen R2 ................................................................................................ 38

4.3.3 Specimen R3 ................................................................................................ 44

4.4 Steel Cone and Cement Grout Repair: Specimen R4 ............................................. 45

4.5 FRP Repair: Specimen R5 ...................................................................................... 52

4.6 Comparison of Test Results.................................................................................... 56

5. TEST RESULTS OF ALTERNATIVE CONNECTIONS FOR NEW

CONSTRUCTION .......................................................................................................... 58

5.1 Modified Sleeve Connection Details ...................................................................... 58

5.1.1 Specimen A1................................................................................................ 58

5.1.2 Specimen A2................................................................................................ 64

5.1.3 Specimen A3................................................................................................ 69

5.1.4 Specimen A4................................................................................................ 75

5.2 Cone Transition Connection Details....................................................................... 79

5.2.1 Introduction.................................................................................................. 79

5.2.2 Specimen A5................................................................................................ 79

5.2.3 Specimen A6................................................................................................ 81

5.3 Tapered Slip Joint: Specimen A7 ........................................................................... 82

5.4 Bolted Match-Plate Connection: Specimen A8 ...................................................... 83

6. ANALYSIS OF TEST RESULTS .................................................................................. 87

6.1 Introduction............................................................................................................. 87

6.2 Comparison of Fatigue Resistance.......................................................................... 88

6.2.1 Specimens C1 to C4..................................................................................... 88

6.2.2 Specimen R1 (Gusset-Repair)...................................................................... 91

6.2.3 Specimens R2 and R4 (Grout- or Cone-Repair) .......................................... 91

6.2.4 Specimens R5 (FRP-Repair)........................................................................ 92

6.2.5 Specimens A1 and A2 (Modified Sleeve Connection) ................................ 92

6.2.6 Specimens A3 and A4 (Modified Sleeve Connection) ................................ 93

6.2.7 Specimens A5 and A6 (Cone Transition) .................................................... 93

6.2.8 Specimen A7 (Tapered Slip-Joint)............................................................... 93

6.2.9 Specimen A8 (Bolted Match-Plate Connection).......................................... 93

7. SUMMARY AND CONCLUSIONS.............................................................................. 94

REFERENCES ...................................................................................................................... 97

APPENDIX A. APPLIED LOAD TIME HISTORY ............................................................. 98


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LIST OF TABLES

Table 2.1 Test matrix ........................................................................................................ 15

Table 6.1 Detail category constant and threshold (AASHTO 2010) ................................ 90


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LIST OF FIGURES

Figure 1.1 Typical configuration of a sign structure......................................................... 12

Figure 1.2 Assumed force transfer mechanism at sleeve connection (Jones 1998).......... 12

Figure 1.3 Typical failure locations of sign structures ..................................................... 12Figure 1.4 Proposed connection details (Sim and Uang 2008)......................................... 13

Figure 2.1 Test setup......................................................................................................... 14

Figure 2.2 Overall configuration of test specimens.......................................................... 17

Figure 2.3 Connection details of Specimens C1 to C4 ..................................................... 18

Figure 2.4 Connection details of Specimen R1 ................................................................ 20

Figure 2.5 Grout-repaired region of Specimens R2 to R4................................................ 20

Figure 2.6 Connection details of Specimens R2 and R3 .................................................. 21



Figure 2.9 Connection details of Specimens A1 and A2.................................................. 25

Figure 2.10 Connection details of Specimens A3 and A4................................................ 25

Figure 2.11 Connection details of Specimens A5 and A6................................................ 26

Figure 2.12 Connection details of Specimen A7 .............................................................. 26

Figure 2.13 Connection details of Specimen A8 .............................................................. 27

Figure 2.14 Loading scheme............................................................................................. 28

Figure 2.15 Sample instrumentation layout (Specimen A1)............................................. 28

Figure 3.1 Specimen C1: observed crack ......................................................................... 30

Figure 3.2 Specimen C1: measured strains near crack location ....................................... 31

Figure 3.3 Specimen C1: strain profiles near fillet weld toe (at 1500 cycles).................. 31







Figure 3.10 Comparison of fatigue resistance of conventional connections .................... 35

Figure 4.1 Specimen R1: gusset connection before testing .............................................. 37


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Figure 4.2 Specimen R1: crack at fillet weld of Gusset No. 4.......................................... 38

Figure 4.3 Specimen R2: repair procedure ....................................................................... 40

Figure 4.4 Specimen R2: crack locations ......................................................................... 41

Figure 4.5 Specimen R2: cracks at lower pipe-to-upper ring fillet weld.......................... 41

Figure 4.6 Specimen R2: crack on lower pipe at slot weld location................................. 42

Figure 4.7 Specimen R2: measured strains near lower pipe-to-upper ring welded joint.. 42

Figure 4.8 Specimen R2: grout condition after testing..................................................... 43

Figure 4.9 Specimen R2: fracture surface at slot weld location ....................................... 43

Figure 4.10 Specimen R2: measured flexural strain distribution in grout region............. 44

Figure 4.11 Specimen R3: observed crack on slot weld................................................... 45

Figure 4.12 Specimen R3: measured strains near crack location ..................................... 45

Figure 4.13 Specimen R4: repair procedure ..................................................................... 47

Figure 4.14 Specimen R4: connection after repair ........................................................... 48

Figure 4.15 Specimen R4: crack locations ....................................................................... 48

Figure 4.16 Specimen R4: crack at lower pipe-to-upper ring fillet weld ......................... 49

Figure 4.17 Specimen R4: crack on lower pipe at the slot weld location......................... 50

Figure 4.18 Specimen R4: view of inside after cut........................................................... 51

Figure 4.19 Specimen R4: fracture surface (Detail 1) ...................................................... 51

Figure 4.20 Specimen R4: fracture surface (Detail 2) ...................................................... 52

Figure 4.21 Specimen R5: crack at lower pipe-to-upper ring fillet weld ......................... 53

Figure 4.22 Specimen R5: measured strains on FRP........................................................ 54

Figure 4.23 Specimen R5: slot weld crack examination after FRP removal.................... 55

Figure 4.24 Comparison of fatigue resistance of repair connections................................ 57

Figure 5.1 Specimen A1: connection................................................................................ 59

Figure 5.2 Specimen A1: cracks on slot welds at lower ring (at 45,000 cycles) .............. 60

Figure 5.3 Specimen A1: repair procedure of damaged slot welds .................................. 60

Figure 5.4 Specimen A1: needle peening of patch plate weld.......................................... 61

Figure 5.5 Specimen A1: crack at patch plate location .................................................... 61

Figure 5.6 Specimen A1: crack on slot weld location at guide ring level ........................ 62

Figure 5.7 Specimen A1: measured strains....................................................................... 63

Figure 5.8 Specimen A1: examination of inside after testing........................................... 63


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Figure 5.9 Specimen A2: assembly procedure ................................................................. 65

Figure 5.10 Specimen A2: measured strains near upper pipe-to-upper ring .................... 66

Figure 5.11 Specimen A2: disassembly after testing........................................................ 67

Figure 5.12 Specimen A2: crack at upper pipe-to-upper ring welded joint...................... 68

Figure 5.13 Specimen A3: crack locations on slot welds ................................................. 70

Figure 5.14 Specimen A3: typical crack pattern at slot weld location ............................. 70

Figure 5.15 Specimen A3: measured strains near crack locations.................................... 71

Figure 5.16 Specimen A3: specimen cut after testing ...................................................... 71

Figure 5.17 Specimen A3: crack at Detail 1..................................................................... 72

Figure 5.18 Specimen A3: crack at Detail 2 (guide ring level) ........................................ 73

Figure 5.19 Specimen A3: fracture surface at Detail 2 (guide ring level)........................ 73

Figure 5.20 Specimen A3: crack at Detail 3 (lower ring level)........................................ 74

Figure 5.21 Specimen A3: crack at Detail 4 (lower ring level)........................................ 74

Figure 5.22 Specimen A4: crack locations ....................................................................... 75

Figure 5.23 Specimen A4: crack pattern at gusset-to-upper ring fillet weld.................... 76

Figure 5.24 Specimen A4: crack pattern at slot weld location ......................................... 77

Figure 5.25 Specimen A4: crack pattern at gusset-to-upper pipe welded joint................ 78

Figure 5.26 Specimen A5: observed crack ....................................................................... 79

Figure 5.27 Specimen A5: crack view from inside........................................................... 80

Figure 5.28 Specimen A6: observed cracks...................................................................... 81

Figure 5.29 Specimen A7: assembly using come-along hoists......................................... 82

Figure 5.30 Specimen A7: examination of inside after testing......................................... 83

Figure 5.31 Specimen A8: observed crack ....................................................................... 84

Figure 5.32 Specimen A8: examination of inside after testing......................................... 85

igure 5.33 Specimen A8: fracture surface......................................................................... 86

Figure 6.1 Summary of fatigue resistance ........................................................................ 88

Figure 6.2 S-N curves (AASHTO 2010) .......................................................................... 91

Figure A.1 Specimen C1: Applied load time history........................................................ 98





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1. INTRODUCTION1.1 Problem Statements

Freestanding (cantilevered) steel sign structures have been widely used for

commercial and retail signs. A common configuration for this type of structure is shown

schematically in Figure 1.1(a). The pole supporting the sign cabinet consists of

progressively smaller diameter pipes, with the smaller pipes inserted into larger pipes as

per a commonly used welded sleeve connection shown in Figure 1.1(b). Both the lower

and upper rings, as well as an optional guide ring which aids in alignment of the pipe

sections during erection, are first shop-welded to the upper pipe. In the field, the upper

ring is then fillet-welded to the top of the lower (outer) pipe. The lower and guide rings

are also slot- or plug-welded to the lower pipe in the field.

It is a common practice in design that the moment at the splice location is resisted

by a force couple as shown in Figure 1.2 (Jones 1998). This simplified static design

procedure has been used for decades and has served well for the majority of sign

structures. But this type of structure is flexible, has a low damping, and can be prone to

fatigue-type cracking due to wind-induced vortex shedding. Damage and collapses of

sign structures due to fracture at the sleeve connections, even with no apparent defects in

the construction, have been reported when the wind speed was far below that used in

design. Figure 1.3 shows the typical crack locations of sign structures. As shown in

Figure 1.3(a) and (b), the fatigue-type failure occurs most often in the upper pipes at the

toe of the fillet-weld between the upper pipe and the upper ring. Although the sleeve

connections have sometimes been strengthened or repaired by vertical gussets or C-

channel gussets, fatigue cracks at the gusset-to-upper pipe (or upper ring) welded joint

have been observed; see Figure 1.3(c) and (d) for the typical crack locations.

1.2 Past ResearchCase studies on ten failed sign structures and the associated finite element analyses

have been performed in an attempt to identify the cause of failure at the welded sleeve

connection (Sim and Uang 2008). It was concluded that the fatigue-type cracks in the


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upper pipe initiated at the toe of the fillet weld connecting the upper pipe to the upper

ring. The crack then propagated into the pipe section and caused failure.

Finite element analysis of a typical sign structure showed a very high, geometry-

induced stress concentration at this location. The following observations were also made

from the finite element analysis. Within the practical range of the ring plate thickness,

only 60% to 80% of the moment was transferred through the horizontal force couple. The

remaining portion was transferred by the bending of the ring plates, which is a

mechanism not reflected in a simplified, conventional design procedure. The stress

concentration at the top fillet weld became more severe if the upper pipe was allowed to

move due to defective or damaged slot welds. Based on case studies of damaged

structures and other available evidence, it was determined that a common practice of

strengthening or repairing the upper ring welded joint by installing welded gusset plates

is not effective in mitigating fatigue cracking. Adding these gussets simply moves the

critical stress concentration location to the top end of the gussets where fatigue-type

cracking also has been observed. The use of a guide ring had a minimal effect on the

stress distribution.

Based on the observations from case studies and finite element analysis results,

two alternative connection details were proposed (Sim and Uang 2008). Figure 1.4(a)

shows the first proposed connection detail. The detail and fabrication of this connection

are very similar to those of the conventional sleeve connection. However, no weld is

specified on the top side of the fillet-weld joint between the upper ring and upper pipe;

only the bottom side is welded. The second proposed connection detail is shown in

Figure 1.4(b). Instead of using a pair of rings to transfer the moment through a horizontal

force couple, a structural filler material (e.g., concrete or mortar) is used to fill the gap

between the two pipes. The lateral moment is transferred through the bearing action of

the filler material between the pipes.


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Sign

Cabinet

Steel Pipe

Sleeve

Connection

Sign

Cabinet

Steel Pipe

Sleeve

Connection

Upper Ring

Lower Ring

Upper Pipe

Lower Pipe

Guide Ring

(Optional)

(a) Elevation (b) Sleeve connection

Figure 1.1 Typical configuration of a sign structure

M

H = M/d

d

H+V

V

M

H = M/d

d

H+V

V

Figure 1.2 Assumed force transfer mechanism at sleeve connection (Jones 1998)

Upper Pipe

Upper

Ring

Crack Upper Pipe

Upper

Ring

Crack

Upper RingUpper Ring

(a) Conventional sleeve connection (b) View of lower pipe after failure

Lower

Pipe

Crack

Upper Pipe

Lower

Pipe

Crack

Upper Pipe

C-Channel

Crack

Upper

Ring

C-Channel

Crack

Upper

Ring

(c) Stiffened gusset plate connection (d) Stiffened C-channel gusset connection

Figure 1.3 Typical failure locations of sign structures


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UpperRing

UpperPipe

LowerPipe

Typ.

Lower

Ring

Filler (Mortar

or Concrete)

Lower Ring

Upper Pipe

Lower Pipe

Optional

Guide Fins

Typ.

(a) Connection detail 1 (b) Connection detail 2

Figure 1.4 Proposed connection details (Sim and Uang 2008)

1.3 Objectives and ScopeThe objective of this research was to evaluate the performance of various

alternative connection details for new construction and retrofit or repair of sign

structures, and to compare the results to those derived from similar tests of conventional-

type sleeve connections. Fatigue tests of seventeen different connection details were

conducted to evaluate the relative fatigue resistance of these connection details.


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2. TEST PROGRAM2.1 Test Setup

Figure 2.1 shows the test setup. The specimens were tested in the horizontal

position using a hydraulic actuator acting at the free end to simulate wind-induced

bending stresses at the connections. The lower pipe end was welded to a base plate and

was anchored to a reaction wall. Such base boundary was not intended to simulate the

actual base details of sign structures under study. To rule out any potential fatigue failure

at this location, it was decided to clamp the specimen 22 in. away from the specimen base

by a pair of concrete collars such that the bending stresses at the base plate weld was

greatly reduced.

ReactionWall Upper PipeLower Pipe

North

8'-6" 12'-6"

21'

3'

22"

Concre Blocks for

Fixed Boundary ConditionMo

untingPL.

Strong Floor

Hydraulic Actuator

Actuator Corbel

(a) Elevation

(b) Photo view

Figure 2.1 Test setup


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2.2 Test Matr ixA total of seventeen, 21-ft-long full-scale specimens were tested. Table 2.1shows

the test matrix. Specimens included four conventional (with or without a guide ring), five

repaired (by welded gussets, grout, or Fiber Reinforced Polymer (FRP) composites), and

eight alternative connection details. ASTM A53 Grade B steel for the pipes and A36 steel

for the plates were used for the specimens.

Table 2.1 Test matrix

Connection TypeSpecimen

DesignationConnection Details

C1 No guide ring usedNo Guide Ring

C2 Specimen C1 + peeningC3 Guide ring usedConventional

Guide RingC4

Specimen C3 + gussets

(gussets not connected to upper ring)

Gusset Repair R1 Gusset repair of Specimen C1

R2 Grout repair of Specimen C3

R3 Grout repair of Specimen C2Grout Repair

R4Steel cone & grout repair of

Specimen C4

Repair

FRP Repair R5 FRP repair of Specimen R3

A1

Conventional weld details, but without

top fillet weld at upper pipe-to-upper

ring

A2 Grout + no field welds and slot welds

A3No fillet weld at lower pipe-to-upper

ring + gussets + peening

ModifiedSleeve Connection

A4No fillet weld at upper pipe-to-upper

ring + gussets

A5Conical transition connection betweenupper and lower pipes

Cone A6 Specimen A5 + peening

Tapered A7 Tapered slip joint

Alternative

Bolted A8 Bolted match-plate connection


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2.3 Connection Details2.3.1 Conventional Welded Sleeve Connection Details

A total of four conventional sleeve connections were tested. The objectives of

testing were to (1) evaluate the failure mode as compared to field observations, (2)establish a baseline fatigue resistance for comparison with those of improved connection

details, (3) assess the significance of guide ring in improving structural performance, and

(4) assess the effect of post-weld peening treatment. After testing, these specimens were

also repaired and re-tested to evaluate the effectiveness of several repair schemes.

The overall configuration of the test specimens is shown in Figure 2.2. The

diameters of the upper and lower pipes were 18 in and 22 in, respectively. The specified

thickness of the pipes was 3/8 in (0.375 in); the measured thickness was approximately

0.35 in. The sleeve length between the upper and lower ring plate levels was 35 in.

Figure 2.3 shows the connection details of each specimen; the slot-weld details

are also provided in Figure 2.3(c). Specimens C1 and C2 did not incorporate guide rings

and were nominally identical, except that Specimen C2 received a post-weld peening

treatment at the upper pipe-to-upper ring fillet weld. Both Specimens C3 and C4 had a

guide ring, but the latter had a total of 12 gusset plates welded to the upper pipe and the

upper ring. Specimen C4 had no weld specified on the lower pipe-to-upper ring joint per

design, but this joint was welded in error during fabrication. Therefore, it was decided to

modify the details of Specimen C4 such that the lower ends of the gussets near the upper

ring were removed. Since the structural detail of the modified specimen was similar to

that of the conventional sleeve connection, Specimen C4 was grouped with the

conventional connections, assuming that the effect of the partially connected gussets on

the fatigue performance of the specimen was insignificant.


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12'-6"

8'-6"

21'

Upper Pipe

(O.D. 18" x 3/8" )

Lower Pipe

(O.D. 22" x 3/8" )

3'

Figure 2.2 Overall configuration of test specimens


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Peening

(Specimen C2 Only)

Slot Weld

6-1/2

1" Thk Guide Ring

(Specimen C3 Only)

1" Thk Lower Ring

3/16

3/8

3/16

1/41/4

1/2

5/8" Thk Upper Ring

36

(a) Specimens C1 to C3

Slot Weld

6-1/21" Thk Guide Ring

1" Thk Lower Ring

3/16

3/8

3/16

1/41/4

5/8" Thk Upper Ring

36

10

3/8" Thk Gusset, Typ

1/41/4

Typ

(b) Specimen C4

30

Lower Pipe

3

11/16

Lower or Guide

Ring PL.

(c) Slot weld details

Figure 2.3 Connection details of Specimens C1 to C4


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2.3.2 Repair ed Connection DetailsThe investigated repair scheme included (1) welded gusset plates, a procedure

commonly used in practice, (2) cement grout with steel jacketing, and (3) Fiber

Reinforced Polymer strengthening. The objective was to develop effective and

economical procedures for not only repairing damaged sign structures but also for retrofit

or new construction.

The details of the repair procedure investigated in this study are presented below.

Gusset-Repaired Connection (Specimen R1)

Specimen R1 is the repaired Specimen C1. After testing of Specimen C1, the

damaged fillet weld between the upper pipe and upper ring was repaired, and gusset

plates (A36 steel) were then added to strength the connection. Specimen R1 represents a

common practice of attempting to strengthen or repair sleeve connections by installing

gussets. Figure 2.4 shows the gusset connection details. Six 3/8-in.-thick gussets were

fillet-welded to the upper pipe and the upper ring. A slight modification on the gusset

weld was made such that the fillet weld at the tip of the gusset was not wrapped around

for three of the gussets (located on the top side in the test setup), while welds on the other

three gussets were wrapped around (located on the bottom side in the test setup).

Cement Grout-Repaired Connection (Specimens R2 to R4)

Figure 2.5shows the region where the connection was strengthened by grouting.

Specimens R2 and R3 had a steel collar installed above the upper ring, and Specimen R4

used a steel cone. Specimens R2 and R3 were grouted between the steel collar and the

upper pipe. Compared to Specimen R2, Specimen R3 was also grouted between the two

pipes in the sleeve region. Specimen R4 was grouted only in the sleeve region. The

connection details of the repair specimens are shown in Figure 2.6and Figure 2.7. The

repair procedures are described in Section 4.3.

FRP-Repaired Connection (Specimen R5)

Specimen R5 was the repaired Specimen R3. After testing of Specimen R3, Fiber

Reinforced Polymer (FRP) composites were used to strengthen the cracked lower pipe at

the slot weld. Figure 2.8 shows the connection details. The repair was performed by

FYFE CO. LLC. The FRP was applied symmetrically with respect to the crack location


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in the longitudinal direction. Five layers of FRP (oriented longitudinally) and three layers

of FRP (oriented transversely) were applied, as shown in Figure 2.8. For surface

preparation, a 4-in grinder with a rough wire wheel was first used to remove the mill

scale of the steel, and then an 80-grit flapper disk was used for a clean finish. Two

separate epoxy resins were used. Epoxy resin (Tyfo MB-3) was used for improved

adhesion to the metal and between layers of the fabric, and epoxy resin (Tyfo S) was used

to saturate the fabric.

1/41/4

Typ

3/8" Thk Gusset PL (6 Total)

10

1/2

Figure 2.4 Connection details of Specimen R1

6'

3'

3'

(a) Specimen R2 (b) Specimen R3 (c) Specimen R4

Figure 2.5 Grout-repaired region of Specimens R2 to R4


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3"

6"

6"

6"

6"

6"

3"

3'-0"

3 8"

2'-11"

No Weld

No Weld

1 / 4

Non-Shrink Grout

See Detail

R = 0 to 1/4

f = 0 to 1/8

= 45

R = 0 to 1/4

f = 0 to 1/8

= 45

(a) Elevation (b) CJP weld details

5/16PJP

Same size Pipe

Tack Weld

Nuts in Place

1/2" x 1.5" Bolts

1/4" x 3" Flat Bar

(Yellow Zinc Grade 8, Snug-Tight)

Tack Weld

Nuts in Place

1/2" x 1.5" Bolts

1/4" x 3" Flat Bar

(Yellow Zinc Grade 8, Snug-Tight)

(c) Exploded view (d) Plan view of splice sleeve

Figure 2.6 Connection details of Specimens R2 and R3


24/105

22

3 ft3 ft

(a) Elevation (b) Exploded view

(c) Detail A

(d) Detail B (e) Detail C



25/105

23

32"

40"

24"

24"

Apply 5 Layers of FRP,

Oriented Longitudinally

Taper 2 LayersEvery 4 inches

Apply 2 Layers of FRP,Oriented Transversely Overtop

the Longitudinal Fiber

Section A-A

32"

40"

24"

24"

Apply 5 Layers of FRP,

Oriented Longitudinally

Taper 2 LayersEvery 4 inches

Apply 2 Layers of FRP,Oriented Transversely Overtop

the Longitudinal Fiber

Section A-A

(a) Elevation

APPLY 5 LAYERS OF THE

SCH-41-2X SYSTEM (SECOND),

ORIENTED LONGITUDINALLY

APPLY 2 LAYERS OF THE

SCH-41-2X SYSTEM (LAST),

ORIENTED TRANSVERSELY

0-1/2" GAP, TYP.

22"

21.25"

APPLY 1 LAYER OF THE TYFO

WEB SYSTEM (FIRST) TO ACT AS A

DIELECTRIC BARRIER TO THE STEEL

6" OVERLAP, TYP.

(b) Cross section (Section A-A)



26/105

24

2.3.3 Alternat ive Connection DetailsModified Sleeve Connection Details (Specimens A1 to A4)

Specimen A1, shown in Figure 2.9(a), used the same connection details as

Specimen C3, except that no weld was specified on the top of the fillet-welded jointbetween the upper pipe and the upper ring; only the bottom side was welded. Specimen

A2, shown in Figure 2.9(b), also eliminated the top-side fillet weld like Specimen A1.

But slot welds were not used to avoid potential cracking at these locations. Instead, the

gap between the two pipes in the sleeve region was filled by grout after the upper pipe

was inserted into the lower pipe. Furthermore, the lower pipe-to-upper ring field fillet

weld was eliminated.

The connection details of Specimens A3 and A4 are shown in Figure 2.10. Each

specimen used a total of twelve gusset plates; see Figure 2.10(b) for the gusset details.

Both specimens had similar connection details, but the weld detail in the sleeve region of

each specimen was slightly different. While Specimen A3 used no weld at the lower

pipe-to-upper ring joint, Specimen A4 used no weld at the upper pipe-to-upper ring joint.

Cone Transition Connection Details (Specimens A5 to A6)

Specimens A5 and A6 incorporated a steel conical section between the upper and

lower pipes. Both specimens were identical, except that Specimen A6 received a post-

weld peening treatment. The connection details are provided in Figure 2.11. Complete-

joint-penetration (CJP) welds were used to connect the cone to the pipes.

Tapered Slip-Joint (Specimen A7)

Specimen A7, shown in Figure 2.12, incorporated a tapered slip-joint between the

two pipes. The upper pipe was slipped into the lower pipe until a target slip engagement

length (= 38 in) was achieved. No welds were needed to connect the two pipes.

Bolted Match-Plate Connection Details (Specimen A8)

Specimen A8 incorporated a bolted match-plate connection between the upper

and lower pipes. The connection details are shown in Figure 2.13. Each pipe was CJP-

welded to a circular match plate in the shop. Two pipe sections were then connected by


27/105

25

pretension bolting of two match plates in the field. No field welding is required for this

type of connection.

Slot Weld

6-1/2

1" Thk Guide Ring

1" Thk Lower Ring

3/16

3/8

1/41/4

1/2

5/8" Thk Upper Ring

36

No Weld at Top

No Weld

No Weld at Top

3/8

1/4

1/4

Grout

No Slot Weld

(a) Specimen A1 (b) Specimen A2

Figure 2.9 Connection details of Specimens A1 and A2

1" Thk Lower Ring

1/41/4

5/8" Thk Upper Ring

Gusset, Typ

3/83/8

3/163/16Peening

Specimen A4

Only

Specimen A3 Only

Slot Weld

1" Thk Guide Ring

(12 Total)

1" Thk Lower Ring

1/41/4

5/8" Thk Upper Ring

Gusset, Typ

3/83/8

3/163/16Peening

Specimen A4

Only

Specimen A3 Only

Slot Weld

1" Thk Guide Ring

(12 Total)

(a) Specimens A3 and A4 (b) Gusset details



28/105

26


15'-8"

1'-758

"

1'-212

"

12'-6"

8'-6"

SECTION

BASE SECTION

3/8" FORMED PLATE

TOP SECTION

3/8" FORMED PLATE

O.D. UPPER OUTER PIPE 18"

O.D. LOWER INNER PIPE 17.25"

O.D. UPPER OUTER PIPE 18.89"

O.D. LOWER INNER PIPE 18.14"

SECTION

(a) Elevation (b) Slip-joint

Figure 2.12 Connection details of Specimen A7


29/105

27

R1'-1" 1" BOLT ASTM A325

1" PLATE

118"

R1'-3"

(Pretensioned)

R1'-1" 1" BOLT ASTM A325

1" PLATE

118"

R1'-3"

(Pretensioned)

(a) Plan view (b) Weld details

Figure 2.13 Connection details of Specimen A8

2.4 Loading SchemeThe cyclic testing was conducted in a displacement-controlled mode. Since it was

not possible to measure the nominal strain on the upper pipe section at the upper ring

level of the sleeve connection due to stress concentration, a free-end displacement target

for each specimen was determined based on the recorded strains on an upper pipe section

away from the connection such that a nominal stress range of 30 ksi ( 15 ksi) was

applied to the critical upper pipe section (see Figure 2.14). (The instrumented section was

selected to be sufficiently away from the critical section such that it would remain in the

elastic range.) The measured actuator forces applied to the specimens are provided in

Appendix A. Testing was conducted with a loading frequency ranging from 1.0 to 1.3 Hz.

2.5 Instrumentation and Cr ack InspectionsThe specimens were instrumented with uni-axial and rosette strain gages to

measure local strains. Figure 2.15 shows a sample instrumentation layout. Strain gage

locations varied for each test specimen. During testing, strains were recorded at interval

(e.g., every 5,000 loading cycles) and strain variations at critical welded joints were

monitored to identify any cracking. Dye penetrant, magnetic particle, and ultrasonic

testing inspections were also conducted by a local inspection company.


30/105

28

L2 L1

L1L2

Nominal Flexural Strain Profile

Strain Gages

top

bot

)10(103429000ksi)(E

30ksi)(

6

target

target

21

1bottop

0 LL

L

2

0

L1L2

L1L2L2 L1

L1L2

Nominal Flexural Strain Profile

Strain Gages

top

bot

)10(103429000ksi)(E

30ksi)(

6

target

target

21

1bottop

0 LL

L

2

0

L1L2

L1L2

Figure 2.14 Loading scheme

ReactionWall

18"x0.375" Pipe22"x0.375"

Pipe

3'-112

"6"

Section1

Section4

Section 4Section 1

North

8'-6" 12'-6"

21'

1'-3"

Section3

Section 3Section 2S10

Section2

1'-3"

0.375" (Typ.)

Figure 2.15 Sample instrumentation layout (Specimen A1)


31/105

29

3. TEST RESULTS OF CONVENTIONAL CONNECTIONS3.1 Introduction

Figure 2.3 shows the details of the four conventional welded sleeve connection

specimens. The testing had the following objectives:

to evaluate the fatigue resistance and the associated failure mode for comparison

with field observations,

to provide a baseline for comparison with alternative connection details,

to evaluate the effectiveness of using a guide ring,

to evaluate the effectiveness of peening as a post-weld treatment.

3.2 Conventional Connection Details without Guide Ring3.2.1 Specimen C1

Testing of Specimen C1 was completed at 22,000 cycles when the crack length

was about 14 in long (or 25% of the circumference). The specimen cracked at the upper

pipe-to-upper ring fillet welded joint. The observed crack on the top side of the specimen

is shown in Figure 3.1. No cracks were observed on the bottom side. The crack initiated

at the toe of the fillet weld between the upper pipe and the upper ring, and then

propagated into the upper pipe wall thickness along the weld toe circumference.

Strain range variations measured near the crack location are shown in Figure 3.2;

the strain gage locations are provided in Figure 3.1. The strain range began to decrease at

early stage, which indicates that the crack may have initiated very early. The strain range

gradually decreased as the crack propagated. To monitor the strain concentration at the

weld toe, Specimen C1 was instrumented with a strip gage, which was a series of five

closely spaced gages. As shown in Figure 3.1(a), one strip gage (S1 to S5) was placed on

the upper pipe right above the upper ring, and another strip gage (S6 to S10) was placed

on the lower pipe right below the upper ring. The centerline of each strip gage was

located 3/8 in away from the weld toe. The strain profiles measured by the strip gages are

shown in Figure 3.3. For comparison purposes, the nominal strain range (= 1034 )

based on beam theory was also shown. High strain readings (with large strain gradient)


32/105

30

on the upper pipe near the weld toe are clearly shown, while the lower pipe had low

strains. This experimental evidence on stress concentration is consistent with that

reported in a finite element analysis (Sim and Uang 2008).

Lower Pipe

Upper Pipe

Upper

Ring

Crack Location

(Fillet Weld Toe)

S1 to S5

S6 to S10

Lower Pipe

Upper Pipe

Upper

Ring

Crack Location

(Fillet Weld Toe)

S1 to S5

S6 to S10

(a) Crack location

0.375

S1 to S5

Upper Ring

Upper Pipe

0.375

S1 to S5

Upper Ring

Upper Pipe

(b) Close-up view of crack

Figure 3.1 Specimen C1: observed crack


33/105

31

0 10 20 300

500

1000

1500

2000

2500

3000

Number of Cycles (x 1000)

S1

S2

S4

S5

Strain

Range(x10-6)

S3 Malfunctioned

Nominal Strain Range

at Sleeve Connection

0 10 20 300

500

1000

1500

2000

2500

3000


S1

S2

S4

S5

Strain

Range(x10-6)

S3 Malfunctioned

Nominal Strain Range

at Sleeve Connection

Figure 3.2 Specimen C1: measured strains near crack location

0.0 0.2 0.4 0.60

500

1000

1500

2000

2500

3000

Distance from Fillet Weld Toe (in.)

StrainRange(x

10-6) S1

S2

S4 S5

0.0 0.2 0.4 0.60

500

1000

1500

2000

2500

3000


StrainRange(x

10-6) S1

S2

S4 S5

0.0 0.2 0.4 0.60

500

1000

1500

2000

2500

3000


StrainRange(x

10-6)

S6 S7 S8 S9 S10

0.0 0.2 0.4 0.60

500

1000

1500

2000

2500

3000


StrainRange(x

10-6)

S6 S7 S8 S9 S10

(a) on upper pipe (b) on lower pipe

Figure 3.3 Specimen C1: strain profiles near fillet weld toe (at 1500 cycles)

3.2.2 Specimen C2Specimen C2 was nominally identical to Specimen C1, except that Specimen C2

received a post-weld peening treatment at the upper pipe-to-upper ring fillet-welded joint.

If properly applied, peening the toe of a weld termination can effectively increases the

fatigue resistance by producing beneficial compressive residual stresses (Fisher et. al

1998). However, it was realized after testing that peening had not been performed

according to specifications in AWS D.1.1, Section 5.27 (AWS 2006). Therefore, the

effect of peening on this specimen might be minimal.

Testing of Specimen C2 was completed at 17,000 cycles when the maximum

crack length was about 15 in. Specimen C2 showed the same crack pattern as that

observed in Specimen C1. Figure 3.4 shows the crack at the upper pipe-to-upper ring

fillet welded joint. While Specimen C1 cracked on the top side only, Specimen C2


34/105

32

cracked on both the top and bottom sides of the pipe. Strain range variations measured

near the crack locations on both the top and bottom sides are shown in Figure 3.5. The

strain ranges began to decrease between 10,000 and 15,000 cycles, which indicates that

the cracks initiated during this period.

Crack

Lower Pipe

Upper Pipe

Upper Ring

S5 (on Top Side)

S6 (on Bottom Side)

0.375

Crack

Lower Pipe

Upper Pipe

Upper Ring

S5 (on Top Side)

S6 (on Bottom Side)

0.375


0 10 20 300

500

1000

1500

2000

2500

3000


StrainRange(x10-6)

S6

S5

0 10 20 300

500

1000

1500

2000

2500

3000


StrainRange(x10-6)

S6

S5



35/105

33

3.3 Conventional Connection Details with Guide Ring3.3.1 Specimen C3

Specimen C3 was nominally identical to Specimen C1, except that Specimen C3

had a guide ring. Testing of Specimen C3 was completed at 17,000 cycles when the cracklength was about 10 in. Specimen C3 had the same crack pattern as that observed in both

Specimens C1 and C2. Figure 3.6shows the crack observed at the upper pipe-to-upper

ring fillet welded joint on the top side of the specimen. Strain range variations measured

near the crack location, shown in Figure 3.7, showed the similar trend as that observed in

Specimen C2.

Crack Location(Fillet Weld Toe)

Lower Pipe

Upper Pipe

Upper Ring

S2

0.375

Crack Location(Fillet Weld Toe)

Lower Pipe

Upper Pipe

Upper Ring

S2

0.375

(a) Crack location

Upper PipeCrack at Weld Toe

Upper Ring

Fillet Weld

Upper PipeCrack at Weld Toe

Upper Ring

Fillet Weld

(b) Close-up view of crack



36/105

34

0 10 20 300

500

1000

1500

2000

2500

3000


S2

Strain

Range(x10-6)

0 10 20 300

500

1000

1500

2000

2500

3000


S2

Strain

Range(x10-6)


3.3.2 Specimen C4As described in Section 2.3.1, inspections of this specimen detected a misplaced

weld due to a fabrication error, so it was decided to detach the gusset plates from the

upper ring. This modified connection is similar to, but not exactly the same as that of

Specimen C3.

Testing of Specimen C4 was completed at 25,000 cycles when the maximum

crack length was about 14 in. Specimen C4 also showed the similar crack pattern as that

observed in the previous specimens. Figure 3.8 shows the crack location. Both the top

and bottom sides cracked, but the crack length on the bottom side (3 in at 25,000 cycles)

was shorter when compared with the top side crack (14 in long at 25,000 cycles). Strain

range variations measured near the crack location on the top side are shown in Figure 3.9.

1

S11

S13

Crack Location

(Fillet Weld Toe)

LowerPipe

UpperRing

Top Edge Line

1

S11

S13

Crack Location

(Fillet Weld Toe)

LowerPipe

UpperRing

Top Edge Line



37/105

35

0 10 20 300

5001000

1500

000

500

3000


Strain

Range(x10-6)

S11

S13

0 10 20 300

5001000

1500

000

500

3000


Strain

Range(x10-6)

S11

S13


3.4 Compar ison of Test ResultsAll four conventional welded sleeve connection specimens showed the same crack

pattern in which the crack initiated at the toe of the fillet weld between the upper pipe andthe upper ring due to high strain concentration. The cracks then propagated into the upper

pipe section and along the weld toe circumference. The crack pattern from testing was

similar to that observed in the failed sign structures like that shown in Figure 1.3(a). The

use of a guide ring had an insignificant effect on the fatigue resistance of the critical joint.

This experimental evidence is consistent with the finding from a finite element analysis

(Sim and Uang 2008).

0

50

100

150

200

FailureCycles(x103)

C1

Specimen No.

C2 C3 C40

50

100

150

200

FailureCycles(x103)

C1

Specimen No.

C2 C3 C4

Figure 3.10 Comparison of fatigue resistance of conventional connections


38/105

36

4. TEST RESULTS OF REPAIRED CONNECTIONS4.1 Introduction

Each of the four tested conventional sleeve connection specimens was repaired by

various methods to evaluate their effectiveness. One specimen was repaired twice,

resulting in a total of five repaired specimens (R1 to R5, see Table 2.1). Figures 2.4 to 2.8

depict the design of these repaired specimens.

4.2 Gusset Repair : Specimen R1After repair, the tested specimen C1 is designated as R1 (see Figure 2.4). The

damaged fillet weld between the upper pipe and upper ring was repaired first, and then

gusset plates were added to strength the connection. Specimen R1 represents a common

means of attempting to strengthen or repair sleeve connections by installing gussets in the

field. Figure 4.1shows the connection with the designation of six gussets. Along the long

side of the gusset plate, the fillet weld at the tip was not wrapped around for three gussets

(Gussets 1, 2, and 6), while the other three gussets (Gussets 3, 4, and 5) were wrapped

around. On the short side, fillet weld was wrapped around for all specimens.

Specimen R1 cracked early during testing at the short side (i.e., horizontal side

when the specimen is in an upright position) of the gusset weld. Figure 4.2 shows thecrack observed at the bottom gusset (Gusset 4) fillet weld at 4,200 cycles. The top gusset

(Gusset 1) fillet weld also showed a similar crack pattern. The crack first initiated at the

wrap-around location, and propagated along the gusset weld length. After the welds along

the short side of the gusset failed, the connection behaved like a conventional sleeve

connection, and additional cracks similar to those observed in Specimens C1 to C4

occurred at the toe of the fillet weld between the upper pipe and the upper ring. Testing of

Specimen R1 was completed at 13,000 cycles when the crack length of the upper pipe-to-

upper ring fillet weld reached about 20% of the upper pipe circumference.

Note that the location of the weld fracture is different from that commonly

observed in the field, as shown in Figure 1.3(c). This is mainly due to the very short

horizontal weld length for connecting the gussets to the upper ring.


39/105

37

West

2

1

6

Upper Pipe

Lower Pipe

Upper Ring

Gusset

Designation

Fillet WeldNot Wrapped Aroundfor Gussets 1, 2, and 6

West

2

1

6

Upper Pipe

Lower Pipe

Upper Ring

Gusset

Designation

Fillet WeldNot Wrapped Aroundfor Gussets 1, 2, and 6

(a) Top side

Lower Pipe

Upper Ring

Upper Pipe

3

West

4

5

Fillet Weld

Wrapped Around

for Gussets 3, 4, and 5

Lower Pipe

Upper Ring

Upper Pipe

3

West

4

5

Fillet Weld

Wrapped Around

for Gussets 3, 4, and 5

(b) Bottom side

Figure 4.1 Specimen R1: gusset connection before testing


40/105

38

Upper Ring

Gusset

Upper Ring

Gusset

Upper RingUpper Ring

(a) View from East (b) View from West

Figure 4.2 Specimen R1: crack at fillet weld of Gusset No. 4

4.3 Steel-Jacketed and Cement-Grouted Repair4.3.1 Introduction

Two tested conventional sleeve connections (Specimens C2 and C3) were repaired

by a steel jacketed grouting scheme. It has been shown in an analytical study (Sim and

Uang 2008) that the bending moment from the upper pipe is not completely transferred as

a force couple (see Figure 1.2) to the lower pipe. As well as aiming to reduce the stressconcentration at the upper ring welded joint, the intent of this strengthening scheme was

to transfer the moment through bearing action of the filler material between the pipes.

After the testing of Specimens R2 and R3, another weakness in the existing slot-

welded location surfaced. Therefore, Specimen R3 was again repaired using Fiber

Reinforced Polymer (FRP) material, and the twice-repaired specimen is designated as R5.

4.3.2 Specimen R2Specimen R2 was the repaired Specimen C3 [see Figure 2.5(a) and Figure 2.6].

After testing of Specimen C3, the damaged fillet weld between the upper pipe and the

upper ring was first repaired, and the specimen was strengthened by steel jacketing and

grouting using cement (Rapid Set Cement All Grout), a non-shrinking, multipurpose

grout which can attain a 2,000 psi compressive strength in one hour.


41/105

39

Figure 4.3 shows the repair procedure. After the weld repair, a steel collar was

first installed and welded to the upper ring. The steel collar consisted of two separate

halves, and these were connected by snug-tight bolts. The gap between the steel collar

and the upper pipe was then filled with grout. After grouting, a cap ring consisting of two

separate half pieces was welded to the collars to seal the grout. The cap ring pieces were

first fillet-welded to the steel collars but not to the upper pipe, and then they were

connected together by partial-joint-penetration groove welds.

Although cracks did not occur at the upper pipe-to-upper ring welded joint with

the grout-repair scheme, fatigue cracks occurred at the next weak locations as the number

of cycles imposed on the specimen increased. Figure 4.4 shows the crack locations

observed during testing. As shown in Figure 4.5(a), the crack first occurred at the existing

fillet weld between the lower pipe and the upper ring on the bottom side. As the testing

continued, another crack on the lower pipe at the slot weld location of the lower ring was

observed as shown in Figure 4.6. Near the end of the testing, a small crack at the lower

pipe-to-upper ring fillet weld on the top side was observed, as shown in Figure 4.5(b).

Strain range variations measured near the cracked fillet welds are shown in Figure 4.7;

see Figure 4.5for the strain gage locations.

Testing of Specimen R2 was completed at 155,000 cycles when the length of the

crack in Figure 4.6propagated to 16 in. After testing, the steel jackets were removed to

examine the condition of the grout (see Figure 4.8). A visual inspection showed that the

quality of grout remained sound with no crushing observed. A steel piece at the slot weld

location was also cut out for examination (see Figure 4.9). The fractured surface showed

that the crack may have initiated at the ends of the slot weld and propagated outward

through the lower pipe wall thickness.

Figure 4.10shows the measured flexural strain profiles on the upper pipe and the

steel collar, respectively. As shown in the plots, the strains on the upper pipe gradually

decreased from the grout cap level to the upper ring level, while the strain on the steel

collar gradually increased. Figure 4.10(a) shows that the jacketed grout was effective in

reducing the stresses transferred to the existing upper ring weld. Therefore, the crack

potential at this welded joint was significantly reduced.


42/105

40

(a) Weld Repair (b) Install steel collars and

bolt together

(c) Groove weld of steel

collar to upper ring

(d) Grouting (e) Install cap cover ring

Figure 4.3 Specimen R2: repair procedure


43/105

41

(3) Last location where crack was observed

(crack at lower pipe-to-upper ring fillet weld)

(1) Location where crack was first observed


(2) Location where crack was next observed

(crack at slot weld at lower ring level)

Top Edge Line

Slot Weld Orientation

(at Lower Ring Level)

45, Typ.

South

Lower Pipe

Steel

Collar

axis of bending(3) Last location where crack was observed


(1) Location where crack was first observed


(2) Location where crack was next observed

(crack at slot weld at lower ring level)

Top Edge Line



45, Typ.

South

Lower Pipe

Steel

Collar

axis of bending

Figure 4.4 Specimen R2: crack locations

Lower Pipe

Crack Length = 17

at 150,000 Cycles

Steel Collar

UpperR

ing0.375

S24

Lower Pipe

Crack Length = 17

at 150,000 Cycles

Steel Collar

UpperR

ing0.375

S24

(a) Bottom side

Lower PipeCrack Length = 3at 155,000 Cycles

Steel Collar

UpperRing

0.375

S16

Lower PipeCrack Length = 3at 155,000 Cycles

Steel Collar

UpperRing

0.375

S16

(b) Top side

Figure 4.5 Specimen R2: cracks at lower pipe-to-upper ring fillet weld


44/105

42

CrackLength

16in.

at155,000Cycles

Crack

CrackLength

9in.

at132,000Cycles

Slot Weld Location

CrackLength

16in.

at155,000Cycles

Crack

CrackLength

9in.

at132,000Cycles

Slot Weld Location

Figure 4.6 Specimen R2: crack on lower pipe at slot weld location

0 50 100 150 2000

500

1000

1500

2000

2500

3000


S24StrainRa

nge(x10-6)

S16

0 50 100 150 2000

500

1000

1500

2000

2500

3000


S24StrainRa

nge(x10-6)

S16

Figure 4.7 Specimen R2: measured strains near lower pipe-to-upper ring welded joint


45/105

43

Cut-Out Location

Grout

Cut-Out Location

Grout

Figure 4.8 Specimen R2: grout condition after testing

LowerRing

Upper Pipe

Lower Pipe

Slot Weld

LowerRing

Upper Pipe

Lower Pipe

Slot Weld

(a) Cut-out piece

Slot WeldSlot Weld

(b) Fracture surface

Figure 4.9 Specimen R2: fracture surface at slot weld location


46/105

44

0 10 20 300

200

400

600

800

1000

5

10

15

20

25Top SurfaceBottom Surface

StrainRange(x10-6)

x, Distance from Upper Ring (in.)

x

UpperRing

Level

GroutCap

Level

Location for Plots

Top Surface

Bottom Surface

StressRange(ksi)

Lower

Pipe

Upper

Pipe

0 10 20 300

200

400

600

800

1000

5

10

15

20


StrainRange(x10-6)


x

UpperRing

Level

GroutCap

Level

Location for Plots

Top Surface

Bottom Surface

StressRange(ksi)

Lower

Pipe

Upper

Pipe

0 10 20 300

200

400

600

800

1000

5

10

15

20


StrainRange(x10-6)


Location for Plots

Top Surface

Bottom Surface

x

UpperRing

Level

GroutCap

Level

StressRange(ksi)

LowerPipe

Upper

Pipe

0 10 20 300

200

400

600

800

1000

5

10

15

20


StrainRange(x10-6)


Location for Plots

Top Surface

Bottom Surface

x

UpperRing

Level

GroutCap

Level

StressRange(ksi)

LowerPipe

Upper

Pipe

(a) Strain profiles on upper pipe (b) Stain profiles on steel collar

Figure 4.10 Specimen R2: measured flexural strain distribution in grout region

4.3.3 Specimen R3Specimen R3 was the repaired Specimen C2 [see Figure 2.5(b) and Figure 2.6].

After testing of Specimen C2, the damaged fillet weld between the upper pipe and the

upper ring was first repaired. The slot weld was ground flush for an UT inspection; the

inspection revealed no rejectable weld cracks. Then the specimen was strengthened by

steel jacketing and grouting. The same repair procedure as used in Specimen R2 was

applied, except that Specimen R2 was grouted above the upper ring only while Specimen

R3 was grouted in the sleeve region as well. Two holes (2 in diameter) on the upper

ring were drilled to accommodate the grouting in the sleeve region.

Figure 4.11shows the crack location. The crack occurred on the lower pipe at the

slot weld location of the lower ring. Strain range variations near the cracked slot weld are

shown in Figure 4.12. Specimen R2 was subjected to a large number of cycles (155,000

cycles), however the slot-weld crack had extended to a length of 5 in. at only 40,000

cycles. To better utilize this specimen, it was decided to stop the testing of R3 at that

point such that the potential of using fiber reinforced polymer composites to repair the

cracked slot welds could be evaluated in Specimen R5.


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Steel Collar

Lower

Pipe

Crack at SlotWeld Location

Top

Edge

Lin

e

4 in



axis of

bending

Steel Collar

Lower

Pipe

Crack at SlotWeld Location

Top

Edge

Lin

e

4 in



axis of

bending

Crack

S15

S13

1 (Typ)

Crack

S15

S13

1 (Typ)

(a) Crack location (b) Close-up view of crack

Figure 4.11 Specimen R3: observed crack on slot weld

0 50 100 150 2000

500

1000

1500

2000

2500

3000


S15S13S

trainRange(x10-6)

0 50 100 150 2000

500

1000

1500

2000

2500

3000


S15S13S

trainRange(x10-6)

Figure 4.12 Specimen R3: measured strains near crack location

4.4 Steel Cone and Cement Gr out Repair : Specimen R4Specimen R4 was the repaired Specimen C4 [see Figure 2.5(c) and Figure 2.6].

After testing of Specimen C4, the damaged fillet weld between the upper pipe and upper

ring was first repaired, and the specimen was strengthened by a steel cone and cement

grouting above and below the upper ring, respectively. Figure 4.13 shows the repair

procedure. The gap between the pipes above the guide ring in the sleeve region was first

filled by grout; small holes on the upper ring were drilled to accommodate the grouting.

The gap between the pipes below the guide ring was also filled by grout; small holes on

the lower pipe right below the guide ring were also drilled to accommodate the grouting.


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A steel cone (A36 steel) was then installed and welded to the upper ring and the upper

pipe. The steel cone consisted of two separate half pieces, and they were connected by

welding (see Figure 2.5). Figure 4.14shows the connection after repair.

Figure 4.15 shows the crack locations observed during testing. As shown in

Figure 4.16(a), the crack (on the bottom side) first occurred at the existing fillet weld

between the upper ring and the lower pipe. As the testing continued, another crack on the

lower pipe at the slot weld location was observed, as shown in Figure 4.17(a). Testing of

Specimen R4 was completed at 105,000 cycles. At the end of testing, the length of the

crack in Figure 4.16(a) propagated to 30 in and the length of the crack in Figure 4.17(b)

was 11 in.

After testing, the specimen was cut to examine the inside, as shown in Figure

4.18. The grout remained intact and its condition was good. The fracture surfaces on the

slot weld are shown in Figures 4.19 and 4.20. A visual inspection on the fracture surface

indicated that the crack initiated at both ends of the slot weld and propagated outward

through the lower pipe wall thickness. This slot-weld failure appeared to be caused by

high bending stresses on the lower pipe together with a geometric imperfection resulting

from the slot weld itself.


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(a) Weld repair (b) Grouting between upper and guide rings

(c) Grouting between guide and lower rings (d) Installation of steel cone

Figure 4.13 Specimen R4: repair procedure


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PJP Weld

Upper Pipe

Cone

Cone

Lower Pipe

Upper Pipe

Cone

Lower Pipe

PJP Weld

Upper Pipe

Cone

Cone

Lower Pipe

Upper Pipe

Cone

Lower Pipe

Figure 4.14 Specimen R4: connection after repair

(2) Crack at Slot

Weld Location

Cone

Lower

Pipe

(1) Crack at Lower Pipe-

to-Upper Ring Fillet Weld

(Bottom Side Only)

5 in



axis ofbending

(2) Crack at Slot

Weld Location

Cone

Lower

Pipe

(1) Crack at Lower Pipe-

to-Upper Ring Fillet Weld

(Bottom Side Only)

5 in



axis ofbending

5 in



axis ofbending

Figure 4.15 Specimen R4: crack locations


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CrackS18

Ring

LowerPipe

Cone

0.375

CrackS18

Ring

LowerPipe

Cone

0.375

(a) Crack location

0 50 100 150 2000

500

1000

1500

2000

2500

3000


Strain

Range(x10-6)

S18

0 50 100 150 2000

500

1000

1500

2000

2500

3000


Strain

Range(x10-6)

S18

(b) Measured strains

Figure 4.16 Specimen R4: crack at lower pipe-to-upper ring fillet weld


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Crack

S29

1 in

1 in

South

S25

Crack

S29

1 in

1 in

South

S25

(a) Crack location

0 50 100 150 2000

500

1000

1500

2000

2500

3000


StrainRange(x10-6)

S29

S25

0 50 100 150 2000

500

1000

1500

2000

2500

3000


StrainRange(x10-6)

S29

S25


Figure 4.17 Specimen R4: crack on lower pipe at the slot weld location


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Cone

Top Side

during Testing

Lower

Pipe

Guide Ring LevelLower Ring Level

Detail 1 Grout

Detail 2

Cut-out

Piece

Cone

Top Side

during Testing

Lower

Pipe

Guide Ring LevelLower Ring Level

Detail 1 Grout

Detail 2

Cut-out

Piece

Figure 4.18 Specimen R4: view of inside after cut

Ring

Slot Weld

Upper Pipe

Grout

Ring

Slot Weld

Upper Pipe

Grout

Figure 4.19 Specimen R4: fracture surface (Detail 1)


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Outer Surface of Lower Pipe Slot WeldOuter Surface of Lower Pipe Slot Weld

Figure 4.20 Specimen R4: fracture surface (Detail 2)

4.5 FRP Repair: Specimen R5Observations made from testing of Specimens R2 and R3 revealed two additional

weaknesses in existing welds: the slot welds connecting the lower ring to the lower pipe

and the fillet weld connecting the upper ring to the lower pipe, both made in the field. For

Specimen R2, cracking first occurred in the fillet weld, followed by cracking in the slot

weld. Specimen R3 first experienced cracking in one slot weld in the early stage of

testing. It was then decided to stop the testing at 40,000 cycles and repair the specimen

with Fiber Reinforced Polymer (FRP) composites to prevent further cracking in the slot

weld. The repaired specimen is designated as R5. See Figure 2.8 for the strengthening

scheme and location.

Figure 4.21shows the crack location and measured strain. The crack (on the top

side) occurred at the lower pipe-to-upper ring fillet weld. Strains on the FRP material

were also monitored during testing to identify any failure. Figure 4.22(a) shows the

rosette strain gage locations; the gages in parentheses were located on the bottom side.

The measured strains are provided in Figure 4.22(b). As shown, the strain ranges on the

FRP remained constant during testing, which indicates no failure of the FRP.


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Testing of Specimen R5 was completed at 120,000 cycles when the length of the

crack shown in Figure 4.21(a) was about 20 in. After testing, the FRP was removed [see

Figure 4.23(a)] to examine the pre-existing crack. As shown in Figure 4.23(b), the

Magnetic Particle (MT) test showed that the pre-existing crack length remained at 5 in.,

indicating no further crack growth after the FRP composites were applied to the

specimen. The bottom slot weld was also examined and no cracks were observed.

Crack

Upper Pipe

Lower Pipe

Upper Ring

S11

0.375

Crack

Upper Pipe

Lower Pipe

Upper Ring

S11

0.375

(a) Crack location

0 50 100 150 2000

500

1000

1500

2000

2500

3000


StrainRange(x10-6

)

S11

0 50 100 150 2000

500

1000

1500

2000

2500

3000


StrainRange(x10-6

)

S11


Figure 4.21 Specimen R5: crack at lower pipe-to-upper ring fillet weld


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3 ft

R1b

(R2b) R1y(R2y)

R1r(R2r)

3 ft

R1b

(R2b) R1y(R2y)

R1r(R2r)

(a) Strain gage locations

0 50 100 150 2000

500

1000

1500

2000

2500

3000


Strain

Range(x10-6)

R1bR2bR2r, R1rR2y, R1y

0 50 100 150 2000

500

1000

1500

2000

2500

3000


Strain

Range(x10-6)

R1bR2bR2r, R1rR2y, R1y


Figure 4.22 Specimen R5: measured strains on FRP


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FRP

Upper

Pipe Upper Ring

Cut-out Location

FRP

Upper

Pipe Upper Ring

Cut-out Location

(a) Specimen cut

FRP

Crack Indication by

Magnetic Particle Test

FRP

Crack Indication by

Magnetic Particle Test

(b) Crack inspection

Figure 4.23 Specimen R5: slot weld crack examination after FRP removal


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4.6 Compar ison of Test ResultsFigure 4.24 compares the fatigue resistance of the repaired specimens. For

comparison purposes, the mean failure cycle from the conventional sleeve connection

specimens is also shown. The failure cycles were 13,000 (Specimen R1: gusset repair),

155,000 (Specimen R2: grout repair), 40,000 (Specimen R3: grout repair), 105,000

(Specimen R4: cone and grout repair), and 160,000 (Specimen R5: FRP repair). Since the

testing of Specimen R3 was completed early for the FRP repair, this specimen is

excluded in the comparison of fatigue resistance.

Specimen R1 showed early cracking at the gusset-to-upper ring welded joint. After

the gusset welds failed, the specimen experienced the same crack pattern as that observed

in the conventional connection specimens. The fatigue resistance of this specimen is

similar to that of the conventional connection (see Figure 3.10).

Specimens R2 and R4 performed better, showing significant improvements in

fatigue resistance. Cement grouting (above the upper ring) with steel jackets in Specimen

R2, and the use of a steel cone (above the upper ring) in Specimen R4 effectively

prevented cracks at the upper pipe-to-upper ring fillet welded joint. However, cracks

occurred at the next weak locations (i.e., the lower pipe-to-upper ring fillet weld and the

slot welds). As demonstrated in the testing of Specimens R3 and R4, grouting below the

upper ring was not effective in preventing cracks at the next weak locations, although thefatigue life of the entire connection was significantly improved.

Based on visual inspections of the fractured surface of the lower pipe at the slot-

weld locations, the cracks appeared to be caused by high bending stresses on the lower

pipe with cracking initiated from the inner surface of the pipe (likely at the slot-weld

terminations of stress concentration). This observation indicates that the slot welds, when

used, should be oriented such that the bending stresses at the slot-weld locations are

minimized. As shown in Figure 4.4, the slot welds of Specimen R2 were located away

from the top and bottom sides, where the highest bending stresses on the pipe section

were developed in testing. The slot-weld crack length at 132,000 cycles was 9 in (see

Figure 4.6). On the other hand, Specimen R3 experienced cracking at the slot weld in the

early stage of testing (the crack length was 5 in at 40,000 cycles), possibly due to a

different slot-weld orientation. As shown in Figure 4.11(a), the slot weld of Specimen R3


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was located near the top side, where the bending stress was higher. In actual applications,

the optimal slot weld locations are 45 degrees from the design longitudinal and transverse

axis of the cross section.

The cracks on the lower pipe-to-upper ring joint occurred at the fillet weld, not in

the base metal. The failure of this fillet weld also did not significantly contribute to the

reduction of the specimen global stiffness during testing. Since the failure was in the fillet

weld, the fatigue resistance of this detail can be increased with a larger size of fillet weld

in repair.

Specimen R5, which used FRP as a repair scheme for the slot welds, was effective

in enhancing the fatigue resistance. An inspection after the FRP removal indicated no

further growth of the pre-existing crack.

0

50

100

150

200

FailureCycles(x103)

R1

Specimen No.

R2 R3 R4R5

GussetRepair

GroutRepair

(TestingStoppedEarly

forFRP

Repair)

Grout

Repair

Cone&

Grout

Repair

FRP

Repair

mean failure cycleof conventional

sleeve connections0

50

100

150

200

FailureCycles(x103)

R1

Specimen No.

R2 R3 R4R5

GussetRepair

GroutRepair

(TestingStoppedEarly

forFRP

Repair)

Grout

Repair

Cone&

Grout

Repair

FRP

Repair

mean failure cycleof conventional

sleeve connections

Figure 4.24 Comparison of fatigue resistance of repair connections


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5. TEST RESULTS OF ALTERNATIVE CONNECTIONS FOR NEWCONSTRUCTION

5.1 Modified Sleeve Connection Details5.1.1 Specimen A1

The connection details of Specimen A1 were the same as those of Specimen C3,

except that no weld was specified on the top of the fillet-welded joint between the upper

pipe and the upper ring; only the bottom side is welded. See Figure 2.9(a) for the

connection details. The intent of this detail was to eliminate the high stress conce

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UCSD Final Report Isa