Structural Education Module 2 (SEM2): Design of SHM Systems

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1 Structural Education Module 2 (SEM2): Design of SHM Systems Summary: The purpose of this education module is to expand your knowledge base on the topic of SHM. You will learn how to apply the SHM knowledge gained in FEMs 0 through 4 and SEM1 to specific projects. After summarizing the desired features for a specific SHM system, you will see how appropriate SHM test category, sensor types and outline of specific outcomes are selected for a certain project. EXPECTED LEARNING OUTCOMES At the completion of this module you will be able to summarize (C) the required features for a specific SHM system. use (Ap) the SHM knowledge on sensors and acquisition systems attained in FEMs covered in CE3415 to execute (Ap) a SHM plan for a specific project. outline (An) the expected outcomes from the envisioned SHM plan. YOUR ASSIGNMENT Listed above are the expected learning outcomes for this module. After you have read and reviewed the content herein provided, you will be required to take an online examination to determine if you have achieved a satisfactory mastery of these learning outcomes. Finally, you will submit an on-line response to several questions related to the content of this education module as well as list any questions you might have concerning anything you might not understand about the material. The on-line responses will be discussed in an interactive manner in a classroom setting on the date indicated below. Deadline for completion of assignment: see SHM Education Unit Opportunity on Moodle Date of classroom discussion of on-line responses: Tuesday April 25 th, 2017 INTRODUCTION In this module, we will briefly cover three case studies from SHM projects. For each project, you will find a description of the structure, the objective of the SHM activity, a summary of the chosen SHM system, and the results / lessons learned. The purpose of this module is to see how the knowledge gained in SEM1 is applied for different types of projects. The first project is here in Louisiana and the other two are in Europe (Wenzel 2009). The projects are: John James Audubon Bridge New Roads, Louisiana Neisse Railway Viaduct Zittau, Germany Bridge M6 Melk, Austria

2 As you will see, the projects were chosen to cover very different scopes that vary from damage detection, to noise emission investigation to structural behavior.

3 CASE STUDY #1: JOHN JAMES AUDUBON BRIDGE SHM PROJECT NEW ROADS, LOUISIANA In this section, you will see how all the concepts discussed in SEM1 are applied to a real project that took place here in Louisiana. Project Background The John James Audubon Project to cross the Mississippi River includes seven approach bridges in addition to the main river crossing cable-stayed bridge. The project was bid as a Design-Build contract, which means that teams consisting of a designer/contractor competed for the job. In a Design-Build project, the designer has more flexibility to make the design more suitable to the partnering contractor s capabilities. The approach bridges were design as prestressed concrete girder bridges with a continuity detail (connection between girder ends from adjacent spans). Since the chosen continuity detail was different than the standard detail used in Louisiana, a decision was made to install a SHM system in one of the bridges in the project. Monitored JJA Bridge (cross-sectional view) Project Objective The objective of the project was to understand the behavior and assess the performance of the continuity detail since Louisiana had no experience with this detail. SHM System Since this was a new bridge, it was possible to install embedded sensors. In addition to the embedded sensors, surface-mounted sensors were also included in the design of the SHM system. The critical sections that were of interest were: Mid-span, and Continuity joint. Of course the more information, the better, however, as we stated earlier budgetary constraints always play a role. So, it was decided to utilize symmetry and anti-symmetry to reduce the number of sensors.

4 BENT 23 BENT 24 BENT 25 BENT 26 51'-0" 102'-0" 89'-0" Utilization of symmetry/anti-symmetry to reduce number of gages. (top view of bridge) It was decided that Static Field Testing is the appropriate type of SHM test for the given objective. A Behavior Test was chosen since we were a proof load test for a newly constructed bridge. There were 66 total sensors installed in this SHM system. They included four types of sensors that can measure: Concrete surface strains Steel elongations/strains Relative girder end movement at the continuity joint Temperatures The bridge did not have any power utility lines in its vicinity, so a decision was made to power it using a solar panel. There were also no phone lines or internet connection nearby, so a cellular access module was chosen for remote data retrieval. General locations of the employed sensors in JJA Bridge. (top view of bridge) SHM System Performance and Results Even though the installation of the system was challenging because of the bridge location and height over the railway track, it was pleasing to not lose any of the sensors. All sensors survived the harsh construction site conditions and concrete pouring. Data was collected for almost five years and the results allowed Louisiana DOTD to understand the behavior of the continuity detail, which revealed that it may not be suitable for Louisiana weather, especially during summer seasons. It turned out that in hot Louisiana summers, the continuity detail becomes

5 subjected to large stresses as a result of thermal movements, which can lead to cracks that reduced the design life of the structure. More details about this project can be found in Hossain et al. (2014) Hossain and Okeil (2014), Hossain et al. (2014), and Hossain et al. (2013).

6 CASE STUDY #2: NEISSE RAILWAY VIADUCT ZITTAU, GERMANY Project Background Before the advent of newer efficient materials such as concrete and structural steel, many bridges were built using masonry in the form of arches. Many of these old bridges are still in service today. One of the nice things about masonry is that the main material does not deteriorate since it is a natural material such as stones. Nevertheless, other changes can take place and cause distress to the bridge. For the Neisse railway viaduct at Zittau, which was built in 1859, wide cracks started to appear as a result of dramatic lowering of the groundwater level. Changes of groundwater level typically leads to soil settlement, which affects the bridge supporting piers, especially if the settlement is not uniform under all piers. Differential settlement subjects the bridge to large straining actions (bending moments and shear forces) that can exceed the design loads. This bridge is 750 m (2461 ft) long, 8 m (26.2 ft) wide, with a varying heights that ranged from 3 m (9.8 ft) to 25 m (82.0 ft). Neisse railway viaduct at Zittau, Germany (Wenzel 2009) Project Objective The objective of the project was to twofold: Identify the cause for the continuing crack movement. Assess the degree to which the bearing capacity of the structure is affected. SHM System Unlike Case Study #1, this bridge existed and had been already in service for over a century. Therefore, the option to install embedded sensors was not possible, and surface mounted sensors were used instead to monitor the crack growth. Crack growth sensors, or crackmeters,

7 measure the relative displacement between both sides of the crack. Therefore, they have to be installed across an existing crack; i.e. one end of the gauge is fixed to one side of the crack and the other end of the gauge to the other side of the crack. This is typically done perpendicular to the crack, although it may be of interest in some projects to get more information and a multdimensional gauge may be used. Distribution of sensors within the Neisse Viaduct superstructure Zittau, Germany (Wenzel 2009) Not many sensors were needed for this study. The focus was on a few cracks that required a limited number of crackmeters. Because massive structures are usually susceptible to thermal loads, it was also decided to monitor temperatures and see if there is any correlation between crack movement and ambient temperatures. Thermal load effects on the structure are relatively slow. So, it was decided that a Static Field Testing (Behavior Test) is the appropriate type of SHM test for the given objective. The crack movement monitoring was carried out for a long period of time (about 90 days). There were 10 total sensors installed in this SHM system. They included four types of sensors that can measure: Velocities Crack Widths Strain Gauges Temperatures Sensor details for Neisse railway viaduct at Zittau, Germany (Wenzel 2009) The power source for the monitoring system was not provided in the reference (Wenzel 2009). But it can be assumed that a local power source capable of keeping the SHM system existed. A local power source can be a solar panel or a series of rechargeable heavy duty batteries if the power outlet was not available.

8 SHM System Performance and Results The long-term monitoring of the crack width together with other monitored parameters showed that the whole cross section of the superstructure was cracked. The correlation between changes in crack width change and changes in the temperature of the structure was very solid. Based on these results, it was determined that the progressive foundation settling as well as the traffic had no obvious irreversible influence on crack evolution. Crack width versus structural temperature at Neisse viaduct. (Wenzel 2009)

9 CASE STUDY #3: BRIDGE M6 SHM PROJECT MELK, AUSTRIA Project Background Thin-walled steel structures (like I-shaped beams) are susceptible to vibrations. Thin-walled beams are very optimized to have a high strength for the cross section as a whole, however, each plate is relatively slender and can vibrate easily, especially for structures that have sources of excitation such as vehicular traffic on highway bridges. In addition to the problems vibrations may cause structurally, a vibrating plate can also emit noise. In residential areas, this can be a huge concerns to people living in the vicinity of a noisy structure, especially during night hours. So, this research project focused on noise emission and vibration transmission related to the global and local vibration behavior of railway bridges to study the sound emission radiated by steel structures. Melk Bridge M6, Austria (Wenzel 2009) Project Objective The objective of the project was to twofold: Measure noise emission during a train passage and compare it to the frequency response of the girder webs. Conduct an initial dynamic investigation to assess the global response of the structure that could serve as base for future implemented monitoring concepts and for upgrading the noise emission from the structure.

10 SHM System Unlike Case Study #1, this bridge existed and was already in service. Therefore, the sensors were installed on the surface of the various plates at the critical sections that were of interest for the scope of the study. These were the webs and bottom flanges of the steel girders. This was a very focused study looking into the relationship between bridge component vibrations and noise emissions. Therefore, a few sensors were needed because of the limited scope. It was decided that Dynamic Field Testing is the appropriate type of SHM test for the given objective. This kind of test produces results in a short period of time, therefore, a long-term system was not needed. A mobile measurement system based upon ambient and forced vibration technology was chosen for the project. There were 11 total sensors installed in this SHM system. They included four types of sensors that can measure: Accelerations Reactions Load Cells Temperatures Sensor details for Melk Bridge M6 (Wenzel 2009) It is not clear from the reference (Wenzel 2009) what kind of power source was used, but mobile systems typically come with their own power source such as batteries or light generators that only need to last for the duration of a short test (typically less than one day). SHM System Performance and Results The dynamic load tests, both ambient and forced vibration, resulted in the same natural frequency for the global vertical mode; f = 1.86 Hz. The beam s webs had much higher natural frequencies in the range of Hz, Hz and Hz as can be seen in the figure below. Based on these results, it was determined that the sound emission of steel structures were mainly comes from the local vibration behavior of the girder webs.

11 Response of a web element, Melk Bridge M6. (Wenzel 2009)

12 REFERENCES Wenzel, H. (2009) Health Monitoring of Bridges, John Wiley & Sons Ltd, Chichester, Hossain, T., Okeil, A. M., and Cai, C.S. (2014) Calibrated Finite Element Modeling of Creep Behavior of Prestressed Concrete Bridge Girders, Structural Journal, ACI, Vol. 111, No. 6, pp Hossain, T., and Okeil, A. M. (2014) Force Transfer Mechanism in Positive Moment Continuity Details for Prestressed Concrete Girder Bridges, Computers and Concrete, Techno Press, Vol. 14, No. 2, pp DOI: / Hossain, T., Okeil, A. M., and Cai, C.S. (2014) Field Test and Finite Element Modeling of a Three Span Continuous Girder Bridge, Journal of Performance of Constructed Facilities, ASCE, Vol. 28, No. 1, pp DOI: /(ASCE)CF Okeil, A. M., Hossain, T., and Cai, C.S. (2013) Field Monitoring of Positive Moment Continuity Detail In A Skewed Prestressed Concrete Bulb-T Girder Bridge, PCI Journal, SPR 13, pp