EVALUATION OF THE CORROSION STATE OF GUSSET-PLATE CONNECTIONS ON STEEL TRUSS BRIDGE AND CORROSION INSPECTION RECOMMENDATIONS

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EVALUATION OF THE CORROSION STATE OF GUSSET-PLATE CONNECTIONS ON STEEL TRUSS

BRIDGE AND CORROSION INSPECTION RECOMMENDATIONS

By

Nguyen Xuan Tung

Graduate School of Urban Environmental Sciences Department of Civil and Environmental Engineering

Tokyo Metropolitan University, Tokyo, Japan

Tokyo, Japan

2015

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ADVISORY COMMITTEE

Supervisor:

Professor Kuniei NOGAMI

Graduate School of Urban Environmental Sciences Department of Civil and Environmental Engineering Tokyo Metropolitan University, Tokyo, Japan

Co-supervisors:

Professor Kimitaka UJI

Graduate School of Urban Environmental Sciences Department of Civil and Environmental Engineering Tokyo Metropolitan University, Tokyo, Japan

Associate Professor Hitoshi NAKAMURA

Graduate School of Urban Environmental Sciences

Department of Civil and Environmental Engineering

Tokyo Metropolitan University, Tokyo, Japan

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Acknowledgement

For over the past three years at Tokyo Metropolitan University, I have received substantial supports and encouragement from many individuals, which have helped to fulfill my challenging journey with confidence and success.

First of all I would like to extend my heartfelt gratitude to Professor Kuniei NOGAMI, my supervisor and mentor, for his valuable guidance, excellent and constructive advice as well as significant supports. Without him my research and this dissertation may have not been accomplished.

I would also like to convey my gratitude to Professor Kimitaka UJI and Associate Professor Hitoshi NAKAMURA, my co-supervisors, for all of the insights and suggestions, which have helped to improve the contents of this dissertation.

My gratitude also goes to Professor Teruhiko YODA (Waseda University), Associate Professor Hideyuki KASANO (Nihon University), Dr. Jun MURAKOSHI, Hiroaki HONDA, Daiki TASHIRO (Center for Advanced Engineering Structural Assessment, Public Works Research Institute) for giving me comments, suggestions and support during the experiments in Public Works Research Institute. My special appreciation also goes to many professors and individuals at TMU, particularly at the Department of Civil and Environmental Engineering for their supports and encouragement.

I would like to extend my thank you and love to my parents and parents-in-law, for all of their love and endless supports. My special thanks also go to my wife, Tran My Hanh, for her always supports, patient, and care; my two little angels, Minh Chau and Minh Long, for all their laughter and joy.

I would like to also thank Tokyo Metropolitan Government for giving me the financial

supports, all the staffs at the International Student Support Section at TMU for their assistance

and provision of cultural experiences through many interesting seminars. Last but not least,

thank you to all friends and colleagues from Japan, Vietnam and others, within TMU and

outside of TMU for the friendship and encouragement.

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Abstract

In the world today, numbers of steel structures are increasing rapidly. In parallel with the new construction of steel structures, numbers of aging structures are also increasing recently. Japan is not an exception to this situation. In Japan, many steel bridges were built during the period of high economic growth from the 1950s to the 1970s, so the number of aging bridges in the country is now growing rapidly. With this rising number of bridges over 50 years old, there have been reports of serious corrosion damage, including the cases of the Kiso river bridge on National Highway Route 23 and the Honjo bridge on National Highway Route 7 in 2007. Around the same time, the Minneapolis I-35W truss bridge suddenly collapsed. Normally, in steel truss bridge, there is the damage tendency on its members and the connections between them. These damages detected when inspecting steel truss bridges and steel arch bridges is mostly corrosion of steel members or their connections. Sectional loss of the main structural members of a steel bridge may lead to the loss of structural integrity. It is clear that an evaluation method is needed for the health of steel bridges based on corrosion loss. Besides, in order to verify the safety of an entire bridge system, there is a need for an inspection and maintenance regime that evaluates the impact of such corrosion efficiently and properly.

Up to now, numbers of research on investigation of corrosion state of gusset plate connection on the actual steel truss bridge, the effects of corrosion damage of connections to the ultimate strength of the whole structure are still a few. The purpose of this research is corrosion damage assessment by detailed corrosion measurement and corrosion state evaluation of gusset plates connections on actual steel truss bridge. The targeted bridge in this study is the Choshi bridge, a five-span cantilever steel truss bridge, crossed the estuary of Tone river. This bridge was removed in accordance with the opening of new bridge in 2009 after approximately 50 years of service. Due to the influence of salt attack, the corrosion damage occurred severely on every members of this bridge even the repainting was carried out several times in its service life. Moreover, during its service life, the diagonal members, the gusset plate connections, floor beams were reinforced and the lateral bracing was replaced.

Besides, the corrosion also occurred severely at the transition areas and the bolt area because

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of stagnant water and the lack of coating thickness, respectively. The load carrying capacity and the earthquake resistance of the bridge also were decreased due to the corrosion damage on superstructure and concrete spall on the RC piers because of severe corrosion of inner reinforcement caused by water leaking. Because of the severe damage, the Choshi bridge was dismantled in 2009, with several parts (connections and diagonal members) were cut off for corrosion research.

Furthermore, as part of the research effort to determine the influence of corroded connections on the ultimate strength of the whole bridge system, this study investigated crevice corrosion at contact surfaces on gusset plate connections, which has not been clarified until now. The 5 connections used in this study were cut from a dismantled Choshi steel truss bridge, the upper connections on the second span (P25d), the upper connections on the forth span (P51u), one upper (P73d) and two lower (P72d and P72u) connections on the fifth span.

Among these 5 connections, the crevice corrosion specimens were cut from two selected connections, P51u and P72u, for further evaluation of corrosion state at the contact surfaces.

The contact surfaces of these specimens were measured in detail in order to clarify their corrosion states.

This study focuses on the following main objectives: 1) to investigate the corrosion state of the five connections on the steel truss bridge; 2) to investigate the crevice corrosion state of the two specific connections; 3) to propose the corrosion inspection and maintenance guidelines for new and existing steel truss bridge.

This dissertation is composed of six chapters.

Chapter 1 is the introduction that contains the background, motivation, and objectives of this study. A comprehensive review of literature and a description of the scopes and method were presented in this chapter.

In chapter 2, the corrosion measurement devices and measurement method were

presented. In this chapter, the measurement methods were introduced, normally there are two

methods, direct and indirect, and also their devices. For examples, direct method (contact with

the specimen’s surface) uses resonance, ultrasonic, mechanical and electromagnetic devices,

while camera and laser meter are used in the indirect method (in a distance from the

specimen’s surface). In this chapter, the mechanical and electromagnetic devices were

introduced in detail. Besides, as the indirect measurement, the newly-developed device, laser

measurement equipment that was used for measurement on the whole research time was

presented.

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In chapter 3, the corrosion states of the five connections were revealed. These five typical connections were selected on the five-span cantilever steel truss bridge (two connections on the second span and three remaining ones on the fifth span). In this chapter, the corrosion of five connections were measured in detail and then the corrosion depth profiles of outer and inner surfaces and several narrow surfaces of each connection were created. Besides, the corrosion state of the transition area between gusset plates and flange of diagonal member was also investigated in this chapter.

Chapter 4 presents the crevice corrosion state of the two connections among the five ones that mentioned above. Since the corrosion state between the contact surfaces of connection has not been investigated previously, in this study, the two connections were prepared as specimens for study: the gusset plate was cut off from an upper connection, P51u,; and attached plates on a lower connection, P72u, that used for reinforcement by high strength bolts to satisfy loading capacity requirements during the service life of the bridge in 2002 were removed. These specimens were then measured using laser measurement equipment and evaluated in detail to clarify the actual state of crevice corrosion on these gusset plate connections and the reinforced area. Further, deformation of the rivets on to the tensile diagonal member of connection P51u was also evaluated.

Chapter 5 summarizes the corrosion types in detail of the five connections in chapter 3, 4 Furthermore, the corrosion inspection and maintenance guidelines for new steel bridge and existing steel bridge were proposed.

Chapter 6 summarizes the research results and presents the overall conclusions of the

thesis.

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Publications

Some parts and selected results of this dissertation have been published, presented, and submitted for publications and/or presentations in peer reviewed international and domestic journals as well as conferences. Details of the publication can be viewed in the following list:

Peer Reviewed Journals:

1*. X.T. Nguyen, K. Nogami T. Yoda, H. Kasano, J. Murakoshi, M. Sawada: Evaluation of corrosion state of gusset plate connections on steel truss bridge, Journal of Steel Structures of JSSC, Vol 21 No83, 2014.09, pp. 71- 83.

2*. X.T. Nguyen, K. Nogami T. Yoda, H. Kasano, J. Murakoshi, H. Honda, D. Tashiro:

Evaluation of corrosion state on contact Surface of gusset plate connections in steel truss bridge. Journal of Steel Structures of JSSC, Vol 22 No85, 2015.03, pp. 161-171.

Full Paper Peer Reviewed Proceedings

1*. X.T. Nguyen, K. Nogami T. Yoda, H. Kasano, J. Murakoshi, T. Enomoto, D. Tashiro:

Evaluation for crevice corrosion state of the two gusset plate connections in steel truss bridge, Proceedings of Eurosteel 2014, Napoli, Italia 2014.09. (CD-R 52-036)

2*. X.T. Nguyen, K. Nogami T. Yoda, H. Kasano, J. Murakoshi, H. Honda, D. Tashiro:

Corrosion evaluation of gusset plate connection removed from steel truss bridge, Proceedings of Elegance in Structures in Nara, Japan 2015.03 (CD-R IA-2).

International Conferences

1*. X.T Nguyen, K. Nogami, T.Yamamoto, T.Yamasawa, T. Yoda, H. Kasano, Proceedings of J. Murakoshi, N.Toyama, M.Sawada, “A new method of corrosion measurement and evaluation for corrosion state of gusset plate connection on steel truss bridge”, Proceedings of Sustainable Built Environment for Now and The Future, Hanoi - Vietnam, pp 481-488. 2013.3.

2*. X.T Nguyen, K. Nogami, T.Yamamoto, T.Yamasawa, T. Yoda, H. Kasano, J.

Murakoshi, N.Toyama, M.Sawada, “A measurement of corroded gusset plate connection of

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steel truss bridge and evaluation for its corrosion state”, Proceedings of Design, Fabrication and Economy of Metal Structure, Miskloc – Hungary, pp 657-662,2013.4.

3*. X.T Nguyen, K. Nogami, S.Takahashi, M.Kurihara, T. Yoda, H. Kasano, J. Murakoshi, N.Toyama, T.Enomoto, “Evaluation for crevice corrosion state of gusset plate on steel truss bridge”, Proceedings of 12nd Japan – Korea Joint Symposium on Steel Bridges, Okinawa – Japan, 2013.8 (CD-R 1-3)

4*. M.Kurihara, K. Nogami, S.Takahashi, X.T Nguyen, T. Yoda, H. Kasano, J. Murakoshi,

“Corrosion state of lower gusset plate connections on steel truss bridge anhd the loading test result”, Proceedings of 12nd Japan – Korea Joint Symposium on Steel Bridges, Okinawa – Japan, 2013.8 (CD-R 1-1)

5*. X.T Nguyen, K. Nogami, S.Takahashi, M.Kurihara, T. Yoda, H. Kasano, J. Murakoshi, N.Toyama, M.Sawada, “Evaluation for corrosion state of lower gusset plate connections on steel truss bridge”, Proceedings of The Thirteenth East Asia-Pacific Conference on Structural Engineering and Construction, Sapporo – Japan, 2013.9 (CD-R I-4-6).

6*. X.T Nguyen, K. Nogami, T.Yamamoto, S.Takahashi, M.Kurihara, T. Yoda, H. Kasano, J.

Murakoshi, N.Toyama, M.Sawada, “Evaluation the corrosion state of the gusset plate connections on steel truss bridge” Proceedings of Pacific Structural Steel Conference, Singapore, 2013.10. (CD-R 024).

7*. X.T Nguyen, K. Nogami, M.Kurihara, T. Yoda, H. Kasano, J. Murakoshi, T.Enomoto:

Evaluation for corrosion state of reinforced gusset plate connection on Steel truss bridge, Proceedings of Life-Cycle of Structural System: Design, Assessment, Maintenance and Management, Tokyo, Japan 2014.11 (CD-R CH097).

8*. X.T. Nguyen, K. Nogami T. Yoda, H. Kasano, J. Murakoshi, H. Honda, D. Tashiro Evaluation for corrosion state of the transition area between gusset plates and flange of diagonal members on the connections of steel truss bridge. Proceedings of The 4th International GIGAKU Conference in Nagaoka (IGCN 2015). 2015.06

1*. M.Kurihara, K. Nogami, S.Takahashi, X.T Nguyen, T.Yamasawa, “Characteristics of

corrosion on the lower chord members and gusset plate connections on Steel truss bridge”,

Proceedings of the 68th Annual Conference of the Japan Society of Civil Engineers, 2013.09

(In Japanese) (CD-R 1-196).

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2*. X.T Nguyen, K. Nogami, Y. Kishi, T. Yoda, H. Kasano, J. Murakoshi, T.Enomoto, D.

Tashiro: Evaluation crevice corrosion of the upper connection on steel truss bridge, Proceedings of JSCE Kanto Brach Meeting, Nagaoka, Japan, 2014.02. (CD-R E0148).

3*. X.T Nguyen, K. Nogami, Y. Kishi, T. Yoda, H. Kasano, J. Murakoshi, T.Enomoto, D.

Tashiro :Crevice corrosion state of gusset plate connections on Steel truss bridge, Proceedings

of JSCE conference, Osaka, Japan 2014.09. (CD-R 1-610)

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List of Tables

Table 2-1 Camera properties ... 16

Table 2-2 Laser measurement equipment properties ... 19

Table 2-3 Clamp stand properties ... 20

Table 3-1 Choshi bridge properties ... 29

Table 3-2 Dimensions and materials of connection P25d ... 29

Table 3-3 Dimensions and materials of connection P51u ... 30

Table 3-4 Dimensions and materials of connection P72d ... 31

Table 3-5 Dimensions and materials of connection P72u ... 31

Table 3-6 Dimensions and materials of connection P73d ... 31

Table 3-7 Severely corroded regions on the outer surface upper chord members of connection P51u (mm) ... 44

Table 3-8 Severely corroded regions on the inner surface of connection P51u (mm) .... 44

Table 3-9 Severely corroded regions on the outer surface of connection P72d ... 49

Table 3-10 Severely corroded regions on the outer surfaces ... 51

Table 3-11 Severely corroded regions on inner surface of connection P73d ... 56

Table 3-12 Remaining thickness of upper connections ... 68

Table 3-13 Remaining thickness of lower connections ... 69

Table 4-1 Diameter of the rivets (mm) ... 78

Table 4-2 Characteristics of contact and outer surfaces of gusset-plate specimen (mm)82 Table 4-3 Characteristics of contact and outer surfaces of tensile diagonal specimen (mm) ... 83

Table 4-4 Severely corroded regions on the upstream side of the connection P72u ... 86

Table 4-5 Severely corroded regions on the downstream side of the connection P72u . 86 Table 5-1 Characteristics of corrosion at edges of inner surface of connection P51u .... 92

Table 5-2 Characteristics of corrosion around the rivet heads of P51u connection ... 96

Table 5-3 Characteristics of corrosion around the rivet heads of P73d connection ... 98

Table 5-4 Lost areas on the upstream side of P25d connection ... 99

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List of Figures

Figure 1-1 Bridge types ratio in Japan from 1960 to 1980 ... 2

Figure 1-2 Bridge construction comparison between United States and Japan in the 20th century ... 3

Figure 1-3 Over 50 years of age bridge in near future ... 4

Figure 1-4 Bridge replacement reason ... 4

Figure 1-5 Bridge damage types ... 5

Figure 2-1 Electro-Magnetic Acoustic Resonance (EMAR) ... 9

Figure 2-2 Ultrasonic device principal ... 11

Figure 2-3 Ultrasonic thickness gauge ... 11

Figure 2-4 Local water depth induced ultrasonic ... 11

Figure 2-5 Types of calipers ... 12

Figure 2-6 Types of micrometer ... 13

Figure 2-7 Eddy current induction procedure ... 15

Figure 2-8 Pulsed-Eddy current device ... 16

Figure 2-9 Camera measurement result ... 16

Figure 2-10 Controlling program screen ... 22

Figure 2-11 Calthick program controlling screen ... 23

Figure 2-12 Typical measurement setup ... 24

Figure 2-13 Range measurement division... 24

Figure 2-14 Corrosion depth calculation ... 25

Figure 2-15 Electricity measurement based caliper device... 26

Figure 3-1 Choshi bridge’s location and its overview ... 27

Figure 3-2 Detailed dimensions of Choshi bridge ... 28

Figure 3-3 The overview of connecting bridge on the Chiba prefecture side ... 28

Figure 3-4 Overview of connecting bridge on the Ibaraki prefecture side ... 28

Figure 3-5 The locations of connections in the 5 spans cantilever truss bridge ... 30

Figure 3-6 Corrosion measurement and corrosion depth calculation method ... 33

Figure 3-7 Measurement range of outer surface ... 36

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Figure 3-8 Corrosion depth distribution of outer surface of upper ... 36

Figure 3-9 Corrosion depth distribution of gusset-plate of outer surfaces ... 37

Figure 3-10 Dimensions of holes in gusset-plate on the upstream side ... 37

Figure 3-11 Corrosion depth distribution of gusset-plate of inner surfaces... 39

Figure 3-12 Corrosion depth distribution profile of lower surface of chord member .... 39

Figure 3-13 Corrosion depth distribution profile of outer surface of tensile diagonal member ... 40

Figure 3-14 Corrosion depth distribution profile of inner surface of tensile diagonal member ... 41

Figure 3-15 Corrosion depth distribution profile of inner surface of compression diagonal member ... 41

Figure 3-16 Corrosion depth distribution profile of inner surface of compression diagonal member ... 42

Figure 3-17 Measurement ranges of connection P51u ... 43

Figure 3-18 Corrosion depth distribution of outer surface of upper chords members of connection P51u ... 43

Figure 3-19 Corrosion depth distribution on the outer surface of connection P51u ... 44

Figure 3-20 Corrosion depth distribution on the inner surface of connection P51u ... 45

Figure 3-21 Measurement ranges on outer surfaces of connection P72d ... 46

Figure 3-22 Corrosion depth distribution on the outer surface of connection P72d ... 47

Figure 3-23 Corrosion depth distribution of the outer surface of lower chord member of connection P72d ... 47

Figure 3-24 Corrosion depth distribution on the inner surface of connection P72d ... 49

Figure 3-25 The measurement ranges of outer surfaces of connection P72u ... 51

Figure 3-26 Corrosion depth distribution on the outer surface of the gusset-plates of connection P72u ... 51

Figure 3-27 Corrosion depth distribution of the outer surface of lower chord member of connection P72u ... 51

Figure 3-28 Measurement range of connection P73d ... 53

Figure 3-29 Corrosion depth distribution on the outer surface of connection P73d ... 54

Figure 3-30 Corrosion depth distribution on the outer surface of the upper chord of connection P73d ... 54

Figure 3-31 Corrosion depth distribution on the inner surface of connection P73d ... 55

Figure 3-32 The considered transition area on the outer surfaces of connection P51u .. 57

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Figure 3-33 The considered transition area on the outer surfaces of connection P25d .. 57

Figure 3-34 Corrosion depth frequency of the transition area on outer surface ... 57

Figure 3-35 Corrosion depth frequency of the transition area on outer surface ... 58

Figure 3-36 Corrosion depth frequency of the transition area on outer surface ... 58

Figure 3-37 Corrosion depth frequency of the transition area on outer surface ... 58

Figure 3-38 The considered transition area on the inner surfaces of connection P25d .. 59

Figure 3-39 The considered transition area on the inner surfaces of connection P51u .. 60

Figure 3-40 Corrosion depth frequency of the transition area on inner surface ... 60

Figure 3-41 Corrosion depth frequency of the transition area on inner surface ... 60

Figure 3-42 Corrosion depth frequency of the transition area on inner surface ... 61

Figure 3-43 Corrosion depth frequency of the transition area on inner surface ... 61

Figure 3-44 The considered transition area on the outer surfaces of connection P72d .. 62

Figure 3-45 The considered transition area on the outer surfaces of connection P73d .. 62

Figure 3-46 Corrosion depth frequency of the transition area on outer surface ... 63

Figure 3-47 Corrosion depth frequency of the transition area on outer surface ... 63

Figure 3-48 Corrosion depth frequency of the transition area on outer surface ... 63

Figure 3-49 Corrosion depth frequency of the transition area on outer surface ... 64

Figure 3-50 The considered transition area on the inner surfaces of connection P72d .. 65

Figure 3-51 The considered transition area on the inner surfaces of connection P73d .. 65

Figure 3-52 Corrosion depth frequency of the transition area on inner surface ... 65

Figure 3-53 Corrosion depth frequency of the transition area on inner surface ... 66

Figure 3-54 Corrosion depth frequency of the transition area on inner surface ... 66

Figure 3-55 Corrosion depth frequency of the transition area on inner surface ... 66

Figure 3-56 Divided parts of connections ... 71

Figure 4-1 Four views of the specimen (mm) ... 74

Figure 4-2 Rivet location ... 78

Figure 4-4 Dimensions of the contact surfaces ... 79

Figure 4-5 P51u specimen corrosion ... 80

Figure 4-6 Corrosion depth distribution of contact surface of gusset-plate specimen .... 81

Figure 4-7 Frequency distribution of contact surface corrosion depth for gusset-plate . 81 Figure 4-8 Corrosion depth distribution of outer surface of the gusset-plate specimen . 81 Figure 4-9 Remaining thickness distribution of gusset-plate specimen... 81

Figure 4-10 Corrosion depth distribution of contact ... 82

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Figure 4-11 Frequency distribution of corrosion depth of contact surface of diagonal

member specimen ... 82

Figure 4-12 Corrosion depth distribution of outer surface of the diagonal member specimen ... 82

Figure 4-13 Remaining thickness distribution of flange of diagonal member specimen 82 Figure 4-14 P72u specimen corrosion depth calculation ... 85

Figure 4-15 Corrosion depth distribution of P72u outer surfaces of gusset-plate ... 86

Figure 4-16 Frequency distribution of corrosion depth of transition area on downstream side of connection P72u ... 87

Figure 4-17 Corrosion depth distribution of P72u attached plates ... 88

Figure 5-1 Corrosion types on steel truss bridge ... 90

Figure 5-2 Corrosion depth distribution on the inner surface of connection P72d ... 91

Figure 5-3 Corrosion depth distribution on the inner surface of connection P73d ... 91

Figure 5-4 Severe corrosion at the edges of inner surfaces of connection P51u ... 92

Figure 5-5 Damage occurrence at the severe corroded edges of connection P51u ... 93

Figure 5-6 Corrosion around the rivet head on the compression side of gusset-plate of the P51u downstream side ... 94

Figure 5-7 Corrosion around the rivet head on the tensile side of gusset-plate of the P51u downstream side ... 94

Figure 5-8 Corrosion around the rivet head on the tensile side of gusset-plate of the P51u upstream side ... 95

Figure 5-9 Corrosion around the rivet head on the compression side of gusset-plate of the P51u upstream side ... 95

Figure 5-10 Corrosion around the rivet head on the tensile side of gusset-plate of the P73d upstream side ... 97

Figure 5-11 Corrosion around the rivet head on the compression side of gusset-plate of the P73d upstream side ... 97

Figure 5-12 Corrosion around the rivet head on the compression side of gusset-plate of the P73d downstream side ... 98

Figure 5-13 Corrosion around the rivet head on the tensile side of gusset-plate of the P73d downstream side ... 98

Figure 5-14 Holes due to pitting corrosion on the upstream side of P25d connection ... 99

Figure 5-15 Crevice corrosion area on the flange of tensile diagonal member specimen

... 100

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Figure 5-16 New steel bridge guidelines ... 102

Figure 5-17 Corrosion prevention methods ... 103

Figure 5-18 Maintenance and ultimate strength evaluation guideline flowchart ... 105

Figure 5-19 Priority checked locations on steel bridge ... 106

Figure 5-20 Steel truss bridge healthy evaluation steps ... 110

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List of Photos

Photo 2-1 Camera method ... 16

Photo 2-2 Laser meter ... 17

Photo 2-3 Dimension of the laser measurement equipment ... 19

Photo 2-4 Laser measurement equipment composing ... 20

Photo 2-5 Several parts of the laser measurement equipment ... 20

Photo 2-6 Clamp stand ... 21

Photo 2-7 Measurement with clamp stand support ... 21

Photo 3-1 New cable-stayed Choshi bridge ... 29

Photo 3-2 Outer measurement status ... 32

Photo 3-3 Procedure for making plaster specimens ... 34

Photo 3-4 Plaster measurement status ... 34

Photo 3-5 Outer surface measurement ... 36

Photo 3-6 Inner surfaces conditions of connection P25d ... 38

Photo 3-7 Inner surface conditions from tensile diagonal member side ... 38

Photo 3-8 Inner surface conditions from compression diagonal member side ... 38

Photo 3-9 Inner surface conditions from view ○

³

... 39

Photo 3-10 Outer surface measurement ... 43

Photo 3-11 The conditions of the inner surfaces of connection P51u ... 45

Photo 3-12 Connection P72d outer surface measurement status ... 47

Photo 3-13 The floor beam on upstream side of the connection P72d ... 48

Photo 3-14 Corrosion condition of the inner surface of connection P72d ... 48

Photo 3-15 Plaster making, (a), and plaster measurement, (b), for inner surface of connection P72d ... 49

Photo 3-16 The measurement status connection P72u ... 50

Photo 3-17 The inner surfaces conditions of connection P72u ... 52

Photo 3-18 The inner surfaces conditions of connection P72u from view ○

¹

... 52

Photo 3-19 Outer surface measurement of connection P73d ... 53

Photo 3-20 Corrosion condition of the inner surface of connection P73d ... 55

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Photo 4-1 Specimen location ... 73

Photo 4-2 View ○

²

no sediment ... 74

Photo 4-3 View ○

¹

sediment thickness of about 5mm ... 74

Photo 4-4 View ○

³

no sediment on the inner surface ... 75

Photo 4-5 View ○

⁴

sediment thickness of about 5mm ... 75

Photo 4-6 Cutting specimen from connection P51u ... 76

Photo 4-7 Rivet removal process ... 76

Photo 4-8 Finished specimen ... 76

Photo 4-9 Rivet condition ... 77

Photo 4-10 P51u specimen measurement setup ... 80

Photo 4-11 Condition of P72u connection before removal ... 84

Photo 4-12 Condition of connection P72u after removal... 84

Photo 4-13 P72u specimen measurement set up ... 85

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Chapter 1 Introduction

1.1 Background and purpose

In the world today, numbers of steel structures are increasing rapidly. In parallel with the new construction of steel structures, numbers of aging structures are also increasing recently. Japan is not an exception to this situation. In Japan, many steel bridges were built during the period of high economic growth from the 1950s to the 1970s, so the number of aging bridges in the country is now growing rapidly. With this rising number of bridges over 50 years old, there have been reports of serious corrosion damage, including the cases of the Kiso river bridge on National Highway Route 23 and the Honjo bridge on National Highway Route 7 in 2007. Around the same time, the Minneapolis I-35W truss bridge suddenly collapsed. Normally, in steel truss bridge, there is the damage tendency on its members and the connections between them. These damages detected when inspecting steel truss bridges and steel arch bridges is mostly corrosion of steel members or their connections. Sectional loss of the main structural members of a steel bridge may lead to the loss of structural integrity. It is clear that an evaluation method is needed for the health of steel bridges based on corrosion loss. Besides, in order to verify the safety of an entire bridge system, there is a need for an inspection and maintenance regime that evaluates the impact of such corrosion efficiently and properly.

Up to now, numbers of research on investigation of corrosion state of gusset-plate

connection on the actual steel truss bridge, the effects of corrosion damage of connections to

the ultimate strength of the whole structure are still a few. The purpose of this research is

corrosion damage assessment by detailed corrosion measurement and corrosion state

evaluation of gusset-plates connections on actual steel truss bridge. The targeted bridge in this

study is the Choshi bridge, a five-span cantilever steel truss bridge, crossed the estuary of

Tone river. This bridge was removed in accordance with the opening of new bridge in 2009

after approximately 50 years of service. Due to the influence of salt attack, the corrosion

damage occurred severely on every members of this bridge even the repainting was carried

out several times in its service life. Moreover, during its service life, the diagonal members,

the gusset-plate connections, floor beams were reinforced and the lateral bracing was replaced.

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2 Besides, the corrosion also occurred severely at the transition areas and the bolt area because of stagnant water and the lack of coating thickness, respectively. The load carrying capacity and the earthquake resistance of the bridge also were decreased due to the corrosion damage on superstructure and concrete spall on the RC piers because of severe corrosion of inner reinforcement caused by water leaking. Because of the severe damage, the Choshi bridge was dismantled in 2009, with several parts (connections and diagonal members) were cut off for corrosion research.

Furthermore, as part of the research effort to determine the influence of corroded connections on the ultimate strength of the whole bridge system, this study investigated crevice corrosion at contact surfaces on gusset-plate connections, which has not been clarified until now. The 5 connections used in this study were cut from a dismantled Choshi steel truss bridge, the upper connections on the second span (P25d), the upper connections on the forth span (P51u), one upper (P73d) and two lower (P72d and P72u) connections on the fifth span.

Among these 5 connections, the crevice corrosion specimens were cut from two selected connections, P51u and P72u, for further evaluation of corrosion state at the contact surfaces.

The contact surfaces of these specimens were measured in detail in order to clarify their corrosion states.

1.1.1 Japan steel bridge in general

(1) The current conditions of bridges in Japan

Figure 1-1 Bridge types ratio in Japan from 1960 to 1980

In Japan, numbers of bridge with the length larger than 2m has reached 670000 and still increasing. However, 80% of bridges with the length shorter than 15m, small and medium- sized bridges, are on municipal roads. On the other hand, the numbers of bridge larger than 15m exceeded 150,000, most of them were constructed from 1960 to 1980. The bridge types ratio during the period 1960 – 1980 in quantitive and length are shown in Figure 1-1a and

4.5%

41.0%

19.8%

34.8% 49.8%

15.6%

29.1% 鋼

鉄橋

筋 5.5%

Others Steel

Reinforced concrete Pre-stressed concrete

(a) Numbers of bridge (b) Length of bridge

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3 Figure 1-1b, respectively. As can be seen clearly in this period, about 60% of bridges are reinforced concrete and prestressed concrete bridges which are very popular at that time. In comparison with the bridge construction in United States, as shown in Figure 1-2, the bridge construction development of Japan is 30 years behind (MLIT 2013). As shown in this Figure, the old bridge in Japan, more than 50 years of age, increased rapidly start from 2010. With this increasing, numbers of old bridges will reach 65% of existing bridges in 2032 as shown in Figure 1-3. Most of these bridges were built in the high economic development period without the inappropriate checking and insufficient quality. The recent serious deteriorations have been reported as a result. Therefore, reasonably and efficiently, it is important to propose an adequate inspection, monitoring and maintenance for those old bridges.

Figure 1-2 Bridge construction comparison between United States and Japan in the 20th century

(2) Damage types

The result of the investigation for replacement reason of bridges that was conducted by the Ministry of Land, Infrastructure and Transport in 2006 is shown in Figure 1-4. According to this result, about less than 15% bridges were replaced because of the structural damages.

The malfunction problems are also the cause for the replacement with 23.8% of bridges. The replacement reason of steel bridge is also summarized in Figure 1-4. As can be seen in this Figure, the tendency is almost the same as for the whole bridges. The damage types of whole bridges and steel bridges are introduced in Figure 1-5a and Figure 1-5b, respectively. As

Bridge construction in United States Numbers of bridge (thousand)

Bridge construction in Japan Numbers of bridge (thousand)

 All bridges

 Bridges on National Highway and provincial roads Source: Ministry of Land, Infrastructure and Transport Source: Int’l Construction Company

Year

Year Old in 1980

30 years behind

Old in 2010

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4 described in this Figure, the corrosion damages accumulated 50.6% of the inspected steel bridges. The floor slab damages are also the popular one in the inspected bridges. In the total inspected bridges, the concrete fracture is 34.1% of the damages.

Figure 1-3 Over 50 years of age bridge in near future

Figure 1-4 Bridge replacement reason

1.1.2 Corrosion research worldwide

Corrosion is the gradual destruction of materials (usually metals) by chemical reaction with their environment. It means that, where metals are available, there may have corrosion occurrence. There are a lot of researches related to corrosion worldwide with different approaching such as causes, forms, inspections, monitoring….However, each corrosion form on specific metal structure (mainly steel) has their own properties, causes that depend much

(a) 2012 16%

80%

60%

40% 35%

65%

Over 50 years of age Below 50 years of age

13.3%

1.6%

23.8%

51.3%

3.8 %

4.5%

1.7% 12.3%

5.4%

1.5%

53.0% 23.8%

2.7 % 1.3%

Superstructure Substructure

Ultimate strength Mal-function problem

Improve requirement

Seismic Others

(a) Reason for bridge replacement (b) Reason for steel bridge replacement

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5 on the structure location and surrounding environment conditions. Since this research focus on corrosion measurement, the author only mention corrosion research related to corrosion inspection, monitoring and measurement in this part.

Figure 1-5 Bridge damage types

Among corrosion inspection, monitoring and measurement the two formers having variety field of study with the high possibility in pratical application while the latter focused in specific cases such as parts of structure, members of bridges…

‘Corrosion Inspection’ – is the means by which corrosion (and other) damage may be located in a structure, as well as gaining insight to the amount and severity of that damage.

Usually inspection tools are used less frequently than corrosion monitoring devices, often on an annual or even longer basis.

‘Corrosion monitoring’ – is a way of determining how corrosive the fluids are within a specific environment. The various techniques available are typically used to give frequent, short time interval measurements, thereby allowing the day-to-day control of corrosion mitigation / prevention approaches such as corrosion inhibition.

Based on the above definitions, corrosion measurement results can be obtained from the inspection and monitoring process. Normally there are two expecting measurement results, weight loss and thickness loss. Depending on the expecting result, the measurement and monitoring methods will be chosen.

(1) Corrosion inspection

There are several methods of corrosion inspection. They are visual inspection, radiography inspection, ultrasonic inspection, eddy currents, magnetic particle inspection...

Corrosion Concrete fracture Floor slab

Malfunction of bearings Steel members Others

2.2%

12.8%

21.8%

34.1%

25.7%

3.4%

3.5%

2.3%

5.2%

50.6%

29.6%

8.7%

(a) Damage types of bridge (b) Damage types of steel bridge

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6 Among these methods, visual and eddy current inspection are the most popular ones. While visual method, appropriate for corrosion detection on the outer surfaces or the areas that expose to the environment, the eddy current is suitable for corrosion detection under the insulation (painting, coating layers…) which has not seen clearly and narrow surfaces.

Visual method is a common method of quality control, data acquisition, and data analysis. Visual Inspection, used in maintenance of facilities, mean inspection of equipment and structures using either or all of raw human senses such as vision, hearing, touch and smell and/or any non-specialized inspection equipment. In order to evaluate corrosion exactly, the inspector should be the experienced ones.

(2) Corrosion monitoring and measurement

Depend on the purposes of corrosion research, the monitoring and measurement device will be chosen. The monitoring and measurement device are varied in types, principals and method (direct and indirect):

- Mechanical devices such as caliper, micrometer…

- Electro-Magnetic Acoustic Resonance device - Ultrasonic device

- Electromagnetic device or eddy current based device - Digital Camera (image method)

- Laser meter.

Depend on the using purposes of measurement results, thickness loss or weight loss, the monitoring and measurement device will be selected. Recently, almost corrosion research in steel structure in general and steel bridge in particular prefer using thickness loss than weight loss because in FEM software the input data is normally thickness data. However the weight loss also can be calculated from the thickness loss data. These devices will be introduced clearly in Chapter 2 of this thesis.

1.2 Objectives

This study focuses on the following main objectives:

1) Investigate the corrosion state of the five connections on the steel truss bridge;

2) Investigate the crevice corrosion state of the two specific connection;

3) Propose the corrosion inspection and maintenance guidelines for new and existing steel truss bridge.

1.3 Outline of the dissertation

This dissertation is composed of six chapters.

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7 Chapter 1 is the introduction that contains the background, motivation, and objectives of this study. A comprehensive review of literature and a description of the scopes and method were presented in this chapter.

In chapter 2, the corrosion measurement devices and measurement method were presented. In this chapter, the measurement methods were introduced, normally there are two methods, direct and indirect, and also their devices. For examples, direct method (contact with the specimen’s surface) uses resonance, ultrasonic, mechanical and electromagnetic devices, while camera and laser meter are used in the indirect method (in a distance from the specimen’s surface). In this chapter, the mechanical and electromagnetic devices were introduced in detail. Besides, as the indirect measurement, the newly-developed device, laser measurement equipment that was used for measurement on the whole research time was presented.

In chapter 3, the corrosion states of the five connections were revealed. These five typical connections were selected on the five-span cantilever steel truss bridge (two connections on the second span and three remaining ones on the fifth span). In this chapter, the corrosion of five connections were measured in detail and then the corrosion depth profiles of outer and inner surfaces and several narrow surfaces of each connection were created. Besides, the corrosion state of the transition area between gusset-plates and flange of diagonal member was also investigated in this chapter.

Chapter 4 presents the crevice corrosion state of the two connections among the five ones that mentioned above. Since the corrosion state between the contact surfaces of connection has not been investigated previously, in this study, the two connections were prepared as specimens for study: the gusset-plate was cut off from an upper connection, P51u,; and attached plates on a lower connection, P72u, that used for reinforcement by high strength bolts to satisfy loading capacity requirements during the service life of the bridge in 2002 were removed. These specimens were then measured using laser measurement equipment and evaluated in detail to clarify the actual state of crevice corrosion on these gusset-plate connections and the reinforced area. Further, deformation of the rivets on to the tensile diagonal member of connection P51u was also evaluated.

Chapter 5 summarizes the corrosion types in detail of the five connections in chapter 3, 4 Furthermore, the corrosion inspection and maintenance guidelines for new steel bridge and existing steel bridge were proposed.

Chapter 6 summarizes the research results and presents the overall conclusions of the

thesis.

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8

Chapter 2 Corrosion measurement method

2.1 Introduction

Corrosion measurement employs a variety of techniques to determine how corrosive the environment is and at what rate metal loss is being experienced. Corrosion measurement is the quantitative method by which the effectiveness of corrosion control and prevention techniques can be evaluated and provides the feedback to enable corrosion control and prevention methods to be optimized.

A wide variety of corrosion measurement techniques exists, including:

Non Destructive Testing Analytical Chemistry

• Ultrasonic testing

• Radiography

• Thermography

• Eddy current/magnetic flux

• Intelligent pigs Operational Data

• pH

• Flow rate (velocity)

• Pressure

• Temperature

Corrosion Monitoring

•

Weight loss coupons

• Electrical resistance

• Linear polarization

• Hydrogen penetration

• Galvanic current Analytical Chemistry

• pH measurement

• Dissolved gas (O

2

, CO

2

, H

2

S)

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9 • Metal ion count (Fe

²⁺

, Fe

³⁺

)

• Microbiological analysis Fluid Electrochemistry

• Potential measurement

• Potentiostatic measurements

• Potentiodynamic measurements

• A.C. impedance

Some corrosion measurement techniques can be used on-line, constantly exposed to the process stream, while others provide off-line measurement, such as that determined in a laboratory analysis. Some techniques give a direct measure of metal loss or corrosion rate, while others are used to infer that a corrosive environment may exist.

Typically, a corrosion measurement, inspection and maintenance program used in any industrial facility will incorporate the measurement elements provided by the four combinations of on-line/offline, direct/indirect measurements.

In this chapter the author will mainly focus on the direct/indirect measurements.

2.2 Direct method 2.2.1 Resonance method

In Resonance method, the Electro-magnetic Acoustic Resonance, as shown in Figure 2-1, device is used for measurement.

Figure 2-1 Electro-Magnetic Acoustic Resonance (EMAR)

An electromagnetic acoustic transducer is provided which includes magnets and a sheet type coil unit. The magnets are permanent magnets or electromagnets to provide a static magnetic field to an object to be inspected. The coil unit includes a pair of spiral or meander coils of an electrically conductive material, sandwiched between upper and middle insulation sheet and middle and lower insulation sheet. The coils are used for transmission and reception, respectively. All the ends of the respective coils extend through holes formed through the

N

S

Specimen

Received the dominant frequency due to resonance between the plate thickness Transverse wave

Permanent magnet

Planar coil

S

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10 upper and middle insulation sheets to the surface of the ultrasonic transducer, and are connected to external leads. The ends for earth are commonly connected to form a common ground terminal. The inspection system with the electromagnetic acoustic resonance which is a combination of resonant technique and a non-contact electromagnetic acoustic transducer can accomplish evaluating the absolute value of ultrasonic attenuation.

2.2.2 Ultrasonic method

Ultrasonic method uses high frequency sound energy to conduct examinations and make measurements. In most common UT applications, very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz, and occasionally up to 50 MHz, are used.

Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, material characterization, and more. A common example is ultrasonic thickness measurement, which tests the thickness of the test object, for example, to monitor pipework corrosion. To illustrate the general inspection principle, a typical pulse/echo inspection configuration as illustrated below will be used.

A typical ultrasonic device inspection system consists of several functional units, such as the pulser/receiver, transducer, and display devices as shown in Figure 2-2. A pulser/receiver is an electronic device that can produce high voltage electrical pulses. Driven by the pulser, the transducer generates high frequency ultrasonic energy. The sound energy is introduced and propagates through the materials in the form of waves. When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected back from the flaw surface. The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen. In the Figure 2-2, the reflected signal strength is displayed versus the time from signal generation to when a echo was received. Signal travel time can be directly related to the distance that the signal traveled. From the signal, information about the reflector location, size, orientation and other features can sometimes be gained.

In order to measure the thickness using ultrasonic method, two types of ultrasonic devices are used, they are ultrasonic thickness gauge and local water depth induced ultrasonic for thickness measurement as shown in Figure 2-3 and Figure 2-4, respectively.

2.2.3 Mechanical device

Mechanical method is the process of using mechanical devices. There are two typical types of mechanical device, caliper and micrometer as shown in Figure 2-6.

(1) Caliper

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11

Figure 2-2 Ultrasonic device principal

Figure 2-3 Ultrasonic thickness gauge

Figure 2-4 Local water depth induced ultrasonic

A caliper is a device used to measure the distance between two opposite sides of an object. A caliper can be as simple as a compass with inward or outward-facing points. The tips of the caliper are adjusted to fit across the points to be measured, the caliper is then removed and the distance read by measuring between the tips with a measuring tool, such as a ruler. There are several types of micrometer as follow:

- Inside calipers are used to measure the internal size of an object.

Transmitting transducer

Acoustic divided surface Receiving transducer

Couplant surface

Measured object Insulating

Material (wood)

Longitudinal wave

Water The vertical immersed probe Water container for

immersed probe Couplant surface

触させる

Thickness is determined by the arrival time and the speed of sound of the reflected waves from

the back surface

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12

Figure 2-5 Types of calipers

- Outside caliper is used to measure the external size of an object. The same observations and technique apply to this type of caliper, as for the above inside caliper. With some understanding of their limitations and usage these instruments can provide a high degree of accuracy and repeatability. They are especially useful when measuring over very large distances, consider if the calipers are used to measure a large diameter pipe. A vernier caliper does not have the depth capacity to straddle this large diameter while at the same time reach the outermost points of the pipe's diameter. They are made from high carbon steel.

- Divider caliper is used in the process of marking out locations In the metalworking field

- Oddleg caliper is generally used to scribe a line a set distance from the edge of a workpiece. The bent leg is used to run along the workpiece edge while the scriber makes its mark at a predetermined distance, this ensures a line parallel to the edge.

- Vernier caliper is to measure the internal and the external diameters of an object. To measure using a vernier scale, the user first reads the finely marked "fixed" scale (in the diagram). This measure is typically between two of the scale's smallest graduations. The user then reads the finer vernier scale (see diagram), which measures between the smallest graduations on the fixed scale—providing much greater accuracy. Depends on the purposes of using, the dial caliper and digital

Caliper gauge Vernier caliper

Divider caliper

Inside calipers Outside calipers Oddleg calipers

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13 caliper are also used. The mechanism is the same as Vernier caliper but the measured results output are different with high accuaracy.

(2) Micrometer:

Figure 2-6 Types of micrometer

Micrometer sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for precise measurement of components in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier , and digital calipers. Micrometers are usually, but not always, in the form of calipers (opposing ends joined by a frame), which is why micrometer caliper is another common name. The spindle is a very accurately machined screw and the object to be measured is placed between the spindle and the anvil. The spindle is moved by turning the ratchet knob or thimble until the object to be measured is lightly touched by both the spindle and the anvil. There are several types of micrometer, as shown in Figure 2-6, they are:

+ Outside micrometer (micrometer caliper): typically used to measure wires, spheres, shafts and blocks.

+ Inside micrometer: used to measure the diameter of holes.

+ Depth micrometer: measures depths of slots and step

Modern micrometer Digital micrometer

Digital depth micrometer Outside, inside, and depth

micrometers

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14 2.2.4 Electromagnetic method

Electromagnetic method, or Electromagnetic Testing, is the process of inducing electric currents or magnetic fields or both inside a test object and observing the electromagnetic response. If the test is set up properly, a defect inside the test object creates a measurable response. The term "Electromagnetic Testing" is often intended to mean simply Eddy-Current Testing. However with an expanding number of electromagnetic and magnetic test methods, "Electromagnetic Testing" is more often used to mean the whole class of electromagnetic test methods, of which Eddy-Current Testing is just one.

Eddy-Current Testing (ECT) is used to detect near-surface cracks and corrosion in metallic objects such as tubes and aircraft fuselage and structures. ECT is more commonly applied to nonferromagnetic materials, since in ferromagnetic materials the depth of penetration is relatively small.

Pulsed eddy current enables the detection of large-volume metal loss in steel objects from a considerable stand-off, allowing steel pipes to be tested without removing insulation.

Eddy currents are created through a process called electromagnetic induction. When alternating current is applied to the conductor, such as copper wire, a magnetic field develops in and around the conductor. This magnetic field expands as the alternating current rises to maximum and collapses as the current is reduced to zero. If another electrical conductor is brought into the close proximity to this changing magnetic field, current will be induced in this second conductor. Eddy currents are induced electrical currents that flow in a circular path. They get their name from “eddies” that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right. The eddy current procedure is described by six steps as follow:

Step 1: In order to generate eddy currents for an inspection, a “probe” is used. Inside the probe is a length of electrical conductor which is formed into a coil.

Step 2: Alternating current is allowed to flow in the coil at a frequency chosen by the technician for the type of test involved.

Step 3: A dynamic expanding and collapsing magnetic field forms in and around the coil as the alternating current flows through the coil.

Step 4: When an electrically conductive material is placed in the coil’s dynamic

magnetic field electromagnetic, induction will occur and eddy currents will be induced in the

material.

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15

Figure 2-7 Eddy current induction procedure

Step 5: Eddy currents flowing in the material will generate their own “secondary”

magnetic field which will oppose the coil’s “primary” magnetic field. This electromagnetic induction process to produce eddy currents may occur from several hundred to several million times each second depending upon inspection frequency.

Step 6: When flaw is introduced to the conductive material, the eddy current are disrupted.

These 6 steps are illustrated in the Figure 2-7 and the typical Pulsed-Eddy current device is shown in Figure 2-8.

One of the major advantages of eddy current as an NDT tool is the variety of inspections and measurements that can be performed. In the proper circumstances, eddy currents can be used for:

- Crack detection

- Material thickness measurements - Coating thickness measurements

Step 1 Step 2 Step 3

Step 4 Step 5 Step 6

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16

Figure 2-8 Pulsed-Eddy current device

- Conductivity measurements for:

+ Material identification + Heat damage detection + Case depth determination + Heat treatment monitoring 2.3 Indirect method

2.3.1 Camera (image method)

Photo 2-1 Camera method

Table 2-1 Camera properties Model Canon E0S Kiss digital Image size 3072 × 2048

Resolution 6.3 megapixel

Lens SIGMA 50mm F2.8 EX DG MARCO

Figure 2-9 Camera measurement result

In camera method, the high quality with high resolution camera will be used for capturing parts of the specimen as shown in Photo 2-1 and its properties are described in Table 2-1. In this method, the distance between camera and specimen is selected at about 50cm and the base line is about 15cm. Several based points are selected manually. In order to achieve the corrosion image, the reference window with square of 15×15 pixel is selected in advance then projective transformation will assume the data color base on the based points

Exciting coil Magnetic field

Eddy current Detection coil

The change of eddy current corresponding to the plate

thickness Lift-off

(Separation)

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17 (JSCE 2009). After that, the full specimen image will be made by attaching the parts’ image using computer. The result of the camera method is shown in Figure 2-9.

2.3.2 Laser meter

Laser meter, as shown in Photo 2-2 is the popular device using in measurement equipment because its compatible, convenience and accuracy (JSCE 2009, X.T. Nguyen et al., 2013).

Photo 2-2 Laser meter

The measurement methods that were mentioned above have the same limitation which is the measurement scale. Regarding to the indirect methods, they are applicable with the specific size specimens and some of them still under the development.

Since the purpose of this study if measuring the big size of specimens, the laser meter was choose because of its compatible and easy-attaching to the designed-movable frame.

EVALUATION OF THE CORROSION STATE OF GUSSET-PLATE CONNECTIONS ON STEEL TRUSS BRIDGE AND CORROSION INSPECTION RECOMMENDATIONS