DESCRIPTION OF THE LABORATORY RESEARCH FACILITY:

Transcription

1 DESCRIPTION OF THE LAORATORY RESEARCH FACILITY: Introduction Drexel researchers have designed and built a laboratory (Figure 1) in order to support several ongoing field research projects and to facilitate advances in numerous research areas. A physical laboratory model was created along with controlled load input systems, extensive instrumentation, data acquisition and online monitoring capabilities to serve as a tool to develop, evaluate, demonstrate and validate structural health monitoring, damage assessment techniques, integration of experimental systems and intelligent-automated control systems in structural engineering. Figure 1: Drexel University Intelligent Infrastructure Institute (DI3) Laboratory Description of the Physical Laboratory Model The model is designed to represent many behavioral attributes of typical deck-on-beam highway bridges. The model is a single span, simply supported structure with a 20 ft. clear span and an overall width of 9 ft. The primary structural system consists of rectangular steel tube sections, bolted together a grid arrangement and a composite laminate deck. The framing plan for the laboratory model, illustrated in Figure 2 has 3 longitudinal tube sections and 14 transverse tube sections that frame into the longitudinal members at right angles. Each longitudinal member end is supported by an individual stand as shown in Figure 3. A shallow roller bearing is located between each member and its support stand. These bearings permit unrestrained rotation at the member ends providing simply supported boundary conditions. In addition, bolts can be inserted into holes located in the bearings to lock-off the rotational degree of freedom. This enables the model to simulate behavior associated with H-1

2 boundary conditions that are more complex. A photograph of a typical bearing used for the model is shown in the inset of Figure ft = 20 ft A 4.50 ft A 4.50 ft A A 3" x 2" x 3/16" - 20' long 3" x 2" x 3/16" - 4.5' long Figure 2: Laboratory Model Framing Plan The model incorporates a composite laminate deck on top of the steel tube section grid. The composite laminate deck was manufactured using the same materials and techniques that have been used to fabricate several in-service composite material highway bridges. Figure 3: Laboratory Model Steel Grid and Typical oundary Condition The composite laminate deck is attached to the steel tube section grid using a series of steel plates and bolts located along the three longitudinal tube sections. This connection, which is depicted in Figure 4, effectively clamps the deck to the steel grid and permits shear transfer between the steel and composite material elements of the model. Loads applied to the model are resisted by the laminate deck and the steel tube grid. This simulates the composite behavior of most reinforced concrete on steel beam highway bridges. The bolted-clamp connection used for the model also permits the level of shear transfer between the deck and the steed grid to be modified by loosening selected bolts. In this manner, some effects of deterioration and damage H-2

3 can be realistically simulated with the laboratory model. Figure 4: olted-clamp Connection Detail A steel load frame has been designed and constructed in order to test the laboratory model (Figure 1) Load Input System, Servo-Controlled Hydraulic Actuators To apply static and dynamic loading on the test structure from several locations, two actuators are attached to the load frame over the physical laboratory model. The system consists of two fatigue rated Atlas hydraulic actuators each have a stroke of 8-10 inches and a load capacity of ±5000 lbs, which are maintained by a 10gpm servo valve each, and a high-capacity hydraulic pump, capable of driving the system to an amplitude of 0.3 inches at 16Hz frequency. The actuators are equipped with internal displacement transducers (LVDTs) and external load cells for feedback and closed loop control of servo valves. A LabVIEW PID control algorithm is developed to control the motion of the actuators. Instrumentation and Data Acquisition Systems In order to scientifically characterize the behavior of the model, an extensive array of sensors has been installed on both the composite laminate deck and the steel grid members. A flow chart depicting the instrumentation and data acquisition process in the laboratory is shown in Figure 5. H-3

4 LOAD CONTROLLER MUX CONTROLLED INPUT AVW SPECIMENS CR10X CONTINUOUS DAQ CONTINUOUS DYNAMIC TEST SPECIMEN CAMERA SERVER ST AD CARD MEGADAC IMAGE ACQUISITION WORLD WORLD WIDE WIDE WE WE DYNAMIC DAQ LAN LAN INTERNET USERS DATASERVER DAQ a) Real Time Data Acquisition and Monitoring System Process Flow-Chart Servo-Valve Actuator Video CAM1 Video Server Router Video CAM2 Switch Switch WORLD WORLD WIDE WIDE WE WE LVDT Load Cell OPTIM Electronics MEGADAC Adapter Single Mode Fiber Structure & Sensors Campbell Scientific CR10 Adapter Internet Users PID Control Hewlett Packard VXI Adapter Serial, GPI port drivers Actuator Control DAQ Control Data Server b) Integration of the Components Figure 5: Real Time Data Acquisition and Monitoring System H-4

5 The sensors are used to measure many parameters including strains, linear and rotational displacements, accelerations, member and ambient temperatures, and images. Table 1 summarizes the types, quantities, measured parameters, and measurement speed of sensors currently installed on the model. The model is also equipped with a variety of off-the-shelf data acquisition systems. The primary data acquisition systems include OPTIM Electronics MEGADAC System, Campbell Scientific CR-10 System, Hewlett-Packard E8041A VXI Mainframe and data acquisition systems for fiber optic gauges. Integration and synchronization of different data acquisition systems on a single platform has also been developed in Drexel University Laboratory using one comprehensive program, written in LabVIEW. A local area network (LAN) is constructed with network enabled data acquisition components and two servers to control data acquisition and to serve and publish real-time online data. This will permit remote and real-time control of the data acquisition systems through an Internet browser and link them to a graphical database (Figure 6) Sensor Table 1: Sensors Installed On The Laboratory Model H-5 Quantity Measured Parameter Measurement Speed Geokon VSM-4000 Strain Gage (6 in) 8 Strain Low Hitec 350 Ohm Weldable Strain Gage 42 Strain High Geokon VK-4100 Weldable Strain Gage (2 in) 2 Strain Low Fiber ragg Grating Strain Gages 6 Strain High Jewell Inertial Sensor (Servo Type) 28 Tilt High Geokon 6350 Vibrating Wire Tiltmeter 2 Tilt Low Applied Geomechanics Model 801 Tiltmeter 1 Tilt Low Celesco PT101 Slide Wire Potentiometer 15 Displacement High Tokyo Sokki 50 mm Clip Gage 33 Displacement High TML LVDT 6 Displacement High Handar Model 425 Ultrasonic Wind Sensor 1 Wind Speed & Direction LM60 Temperature Sensor 2 Temperature High PC Model 393C ICP Accelerometer 18 Acceleration High PC Model 370A03 Capacitive Accelerometer 11 Acceleration High Sony EVI DC30 Camera 1 Image High High

6 Figure 6: Internet ased Real-Time Laboratory Monitor Uncertainties Governing The ehavior Of The Physical Model The behavior of the physical model, and behavior of the loading, sensing and information management systems are governed by various types of uncertainty that are expected to mimic those in real-life. Some mechanisms leading to uncertainty that are relatively easy to identify and characterize are listed in Table 2 Table 2: Uncertainties Governing The ehavior Of The Physical Model Systems Uncertainty Type Uncertainty Source oundary Conditions Lack of ideal boundaries (pin-roller, non-linear viscoelastic pads) Physical Deck Material Fiber-reinforced polymer composite (in plane multi-directional properties) Deck to Grid Connectivity Lack of full composite action (loose and discontinuous connectivity) Design Errors Lack of rigor or heuristic knowledge Experimental Sensory and DAQ Errors Mechanical and signal errors (noise, cross-talk, other) Processing Errors Calibration and Data reduction incompatibilities Loading Control Control system inadequacy (mechanical system and control software response delays) Loading Loading Inaccuracy Sensory feedback and control loop variance Operator Errors Human decision and action factors Environmental Effects Interaction with other loading mechanisms Model development and misrepresentation of system Conceptualization Numerical behavior Modeling Levels Micro-macro-mixed levels parameters Property changes, connection loosening, lack of support Aging Effects and stiffness Other Critical Regions Variation due to system construction Failure Modes Unpredictability H-6

7 Conclusion The laboratory model is an essential facility complementing the actual instrumented bridge test specimens for many reasons. The model enables concept and technology development and validation for health-monitoring and especially the calibration of measurement systems. The model also permits a controlled study of system-identification and damage assessment of structures with complex structural and boundary conditions while controlling the levels of uncertainty in these characteristics. Finally the composite materials used in the deck permit a study of the issues in system-identification of structures incorporating such a new material with high level of variability and nonlinearity. The development of intelligent agent components for the system will allow the integration of the system identification, damage assessment and realtime components. The system will then change from a forensic type study of damage assessment to a real-time damage prediction, tracking and controlled zoomed-targeted damage propagation monitoring and response development leading to intelligent active control capabilities. H-7