Field load experiments and computer modeling of a steel truss bridge for assessment

長岡技術科学大学 The Nagaoka University of Technology The Graduate School of Engineering Faculty of Civil and Environmental Engineering Field Load Experiments and Computer Modeling of a Steel Truss Bridge for Assessment A Thesis in Civil Engineering by TRAN DUY KHANH Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science Nagaoka, Niigata July 2015 i The thesis of TRAN DUY KHANH was reviewed and approved by the following: Takeshi MIYASHITA Associate Professor of Civil Engineering Eiji IWASAKI Professor of Civil Engineering Takumi SHIMOMURA Professor of Civil Engineering ii An abstract of Field load experiments and computer modeling of a steel truss bridge for assessment In Japan, it can be surely predicted that in 2030s, more than 50 percent of existing bridges, which were primarily constructed during the post World War II, a rapid economic growth between 1955 and 1975, is assumed more than 50 years of age The research investigated an in-service, multi-span old steel through truss highway bridge constructed and opened to the traffic in 1937 The bridge, also known as a city symbol, which is on the National Highway No.351, spans the Shinano River, in Nagaoka City, Japan The bridge was constructed with materials of steel for frames and concrete for the deck, consists of 13 spans composing of cantilever anchored spans, and 11 suspension spans and cantilever central anchored spans alternatively connected via hinges at upper level and pins at lower level with a total length of 850 meters To ensure the normal service of the aging bridge and meet the transportation demand of citizens, a set of full-scale field load tests including static, dynamic load and short-term monitoring experiments was performed on the bridge to identify the current health status, and characterize the response to practical load conditions The responses of the excited bridge was recorded continuously and simultaneously at 200 Hzsampling frequency through an array of 100 strain gages installed on 25 identical and key members, and each of 26 displacement sensors and accelerometers instrumented at each span center point The exciters used in these tests were three-axle 20-ton dump trucks for controlled tests and normal daily traffic for the short-term monitoring measurement A three-dimensional finite element model of the bridge superstructure was constructed with geometry and structural arrangement extracted from recovered drawings The model, simulated the in-situ tests, was validated manually through a comprehensive comparison of analytical results and measurement data in terms of internal forces, vertical displacements The axial force extracted from the upper chords and diagonal chords instrumented in the static loading tests was compared the computational axial iii forces from the static load analysis Similarly, the maximum vertical deflections at each span middle point were also an objective for model validation when making a comparison between test and analytical results The comprehension of the transverse direction behavior of the structure through the load distribution to the truss characterized by the dynamic load test utilizing a single known-weight truck controlled to travel on the different traffic lanes Bending natural frequencies based on power spectral density extracted from the measured acceleration data via Fast Fourier Transform and the peak picking method was compared to computational analysis generated frequencies for the model validation process The boundary condition of the current bridge was qualified with changes in bearing support types and various stiffness level of Gerber hinges in three directions of vertical, horizontal and rotational Based on the controlled dynamic loading tests and short-term monitoring with daily traffics, dynamic loading allowance were observed by using a digital signal filter tool called low-pass Butterworth with a cut-off frequency and filtering order The maximum static response were filtered and compared to the corresponding practical dynamic response to obtain a dynamic loading allowance The correlation between the impact factor and measuring types of strain and vertical displacement were examined The dynamic loading factor magnitude is strongly correlated with instrumented member maximum static strain with a general decrease trend in the static strain increase In contrast, the dynamic loading allowance shows a quite stable trend in the maximum deflection increase The calibrated model of the bridge is used to perform a load rating analysis based on Manual for Bridge Evaluation published 2013 and described by AASHTO The load rating factors of those instrumented truss members with the values greater than one implies the bridge is safe for the applied loading iv Table of Contents List of Figures ix List of Tables xiii Acknowledgments xiv Chapter Introduction 1.1 Background 1.2 Objectives of the research 1.3 Scopes of research Chapter Bridge description, field loading tests and monitoring 2.1 Introduction 2.2 Bridge description 2.3 Field loading tests and monitoring 13 2.3.1 Background and purpose 13 2.3.2 Test instrumentation 16 2.3.3 Static loading test 24 2.3.4 Dynamic loading test 24 2.3.5 Short-term monitoring 26 2.4 Measurement processing for developing a finite element model 27 2.4.1 Internal forces 27 2.4.2 Vertical displacement 29 2.4.3 Thermal axial stress 29 v 2.4.4 Acceleration 33 Chapter Finite element model validation 36 3.1 Introduction 36 3.2 Literature review 36 3.3 Finite element (FE) model construction 40 3.3.1 Input data 40 3.3.2 Boundary conditions 43 3.3.3 Other assumptions 46 3.3.4 Loading 47 3.3.5 Mesh refinement 48 3.4 Model updating 50 3.4.1 Parameter study: Boundary condition study 53 3.4.2 Model validation 55 3.4.2.1 Axial force 55 3.4.2.2 Vertical displacement 58 3.4.2.3 Thermal induced axial stress 59 3.4.2.4 Lateral distribution stiffness 59 3.4.2.5 Natural frequencies 62 Chapter Dynamic loading allowance 64 4.1 Introduction 64 4.2 Literature review 64 vi 4.2.1 Definition of dynamic loading allowance 64 4.2.2 Specification prescribed dynamic load allowance 64 4.2.2.1 Constant dynamic load allowance 65 4.2.2.2 Span length varying dynamic load allowance 65 4.2.2.3 Frequency varying dynamic load allowance 66 4.2.3 Dynamic field testing of bridges 67 4.2.4 Other dynamic load allowance studies 68 4.3 Utilized method 69 4.3.1 Determine the low-pass cut-off frequency 70 4.3.2 Determine the filtering order 72 4.3.3 Filtering by Matlab 73 4.3.4 Controlled dynamic load test data 75 4.3.5 Short-term monitoring data 78 4.3.5.1 Impact factor versus strain measurement 78 4.3.5.2 Impact factor versus displacement measurement 81 Chapter Bridge Assessment by AASHTO Code 85 5.1 Introduction 85 5.2 Load rating procedure 85 5.3 FE model analysis 88 5.4 Load rating results 90 Chapter Conclusions and recommendations 93 vii 6.1 Conclusions 93 6.2 Recommendations 94 References 95 Appendix A 99 Appendix B 106 Appendix C 114 Appendix D 138 Appendix E 139 viii List of Figures Figure 1-1 Composition of bridge’s age to the total number of bridge in Japan Figure 1-2 Total number of highway bridges and construction year in Japan Figure 2-1 Location of the target study bridge Figure 2-2 A view of Chyosei Bridge-Niigata, Japan Figure 2-3 Cross-section of the bridge at mid-span and support Figure 2-4 Elevation of the Chyosei Bridge with condition of hinges and bearings as designed Figure 2-5 Typical cross-sections 11 Figure 2-6 Upper (a) and lower (b) bracing systems 12 Figure 2-7 Location of sensors in the field test 17 Figure 2-8 Instrumentation in the field tests: a) Strain gages in Upper chord; b) Strain gages in Diagonal member; c) Displacement transducer in Lower chord; d) Accelerometer in Vertical member; e) Accelerometer over wheel guard of the pedestrian bridge 19 Figure 2-9 Strain gage location in instrumented members: a) Foil strain gages in Upper chord Layout; b) Foil strain gages in Diagonal member Layout; c) Detail of Upper chord Layout; d) Detail of Diagonal member Layout 20 Figure 2-10 Test truck configuration 21 Figure 2-11 Cross-section of trucks utilized for loading tests 21 Figure 2-12 Load configurations used for the first load test 22 Figure 2-13 Load configuration used for the second load test 22 Figure 2-14 Dimensions of the trucks used for the load tests 23 ix Figure 2-15 Patterns for static load tests 24 Figure 2-16 Location of test trucks in dynamic loading test 26 Figure 2-17 Typical strain gauges’ location and internal force notation 28 Figure 2-18 Deflections by spans in the static load tests 29 Figure 2-19 Temperature time history 30 Figure 2-20 Temperature and normal stress relation of an upper chord in the 6th span 31 Figure 2-21 Normal stress time history of an upper chord in 6th 32 Figure 2-22 Dynamic component stress history 32 Figure 2-23 Axial stress and thermal changes correlation 33 Figure 2-24 Typical frequency spectra for the truck passing (a) and the truck left (b) 35 Figure 3-1 Arbitrary cross-sections 42 Figure 3-2 Element types used in 3D-FE model 42 Figure 3-3 The studied bridge structure and its restraints 44 Figure 3-4 Gerber hinge modeled by 2-node links, SP2TR, SP2RO 45 Figure 3-5 Deck system (Left) and computer simulation (Right) 46 Figure 3-6 Bearing support computer simulation 46 Figure 3-7 Typical loading simulation of static load test in the first span 47 Figure 3-8 Division size and output values correlations 49 Figure 3-9 Meshed finite element model 50 Figure 3-10 Model validation procedure 53 x ... comparisons between analytical results from the computer analysis and practical results extracted from the on-site static and dynamic loading tests, evaluating dynamic load factors, and finally... extracted from the Manual for Bridge Evaluation (MBE) 2013, AASHTO will be listed and applied to rate the load- carrying capacity of the target aging steel bridge Finally, Chapter presents a summary... Professor of Civil Engineering ii An abstract of Field load experiments and computer modeling of a steel truss bridge for assessment In Japan, it can be surely predicted that in 2030s, more than 50