ASCE/AISC Student Steel Bridge Competition Mid-Continent Division Stillwater, Oklahoma. Displacement Measurement Results

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1 ASCE/AISC Student Steel Bridge Competition Mid-Continent Division Stillwater, Oklahoma Displacement Measurement Results April 24, 2014 Complements of: BRIDGE DIAGNOSTICS, INC th Court North, Suite 100 Boulder, CO

2 Table of Contents Introduction... 3 Displacement Measurement Procedures... 3 Test Results for Each Bridge... 4 University of Missouri of Science and Technology (MST)... 6 University of Kansas (KU)... 7 University of Missouri Columbia (MIZZ)... 8 University of Missouri Kansas City (UMKC)... 9 Kansas State University (KSU) University of Arkansas (ARK) Southern Illinois University Edwardsville (SIUE) University of Nebraska Lincoln (UNL) University of Oklahoma (OU) Oklahoma State University Institute of Technology (OSUIT) St. Louis University (SLU) University of Nebraska Omaha (UNO) Suggestions for Future Competitions

3 Introduction BDI was asked by the ASCE student chapter at Oklahoma State University (OSU) to record displacement measurements during the load testing phase of the ASCE/AISC Mid-Continent Steel Bridge Competition held in Stillwater on April 24 th, The competition rules specify that vertical displacements must be measured at three locations on each bridge throughout the loading procedures. Therefore, BDI provided two personnel along with a data acquisition system and a set of non-contact displacement sensors on the testing day. In addition to the digital data acquisition system, tape measures were used by the judges, and as seen in the following graphs, both sets of measurements correlated well. Displacement Measurement Procedures Two of the original 14 bridges were disqualified for technical reasons prior to load testing, therefore, measurements were only required to be recorded on 12 bridges. As each bridge was placed in the loading area, 5 x7 lightweight aluminum plates were clamped at each gage location to act as targets for the ultrasonic non-contact displacement sensors. ASCE had supplied adjustable sensor stands, so the displacement sensors were mounted to these using standard C-clamps and then adjusted to be approximately 10 below each target. This system was very fast to move around and adjust for each test and an example of this setup is shown in both Figure 1 and Figure 2. Figure 1 Test setup with reference stands and data acquisition system Figure 2 Non-contact displacement sensor & target During each loading sequence, data was recorded at 10 Hz on all channels and displayed as a function of time on a screen using a PC projector as shown in Figure 3. In addition, as each bridge was loaded, one of the judges called out 200 lb load increments so that marks could be put into the data at those points using a software feature. Since any predicted analytical results would only involve the amount of load applied, not the time it took to apply the load, the data from each test was subsequently converted from a function of time to a function of load magnitude. Students should be able to calculate anticipated deflections at the various load levels and compare them to the measured values. 3

4 Figure 3 Real time test data displayed during loading sequence Test Results for Each Bridge As described above, the displacement data for each bridge is displayed in the following graphs as a function of applied load. The graphs show that having continuous data can provide insights into the actual structural responses during the load application. Figure 4 illustrates a zoomed in view of a typical load response history where the steps due to each piece of angle iron can be seen. Figure 4 Typical load response illustrating each loading step 4

5 In our testing experience, it is often the shape of the strain, displacement, and/or rotation response histories and not just the peak magnitude that describes the issue with a structure. For example: At a glance, it can immediately be determined if one side is deflecting more than the other. For some bridges, it was clear that one side was stiffer, even though they had been symmetrically built. It could be quickly determined whether or not deflections were still occuring without an increase in load (moving into non-linear range). Possible slipping in connections become apparent. It is easy to calculate linear stiffness values for each bridge by calculating the slope of the linear portion of each load-displacement curve. Due to a missed step in the sensor setup for the first test (MST), the sensing range was exceeded and only approximately 90% of the test was recorded. However, this was rectified for all remaining tests and the ultrasonic measurements can be considered to be more accurate than the tape measures since they have been calibrated to within approximately accuracy. The data and photos of each bridge are provided in the order in which they were load tested, and the acronyms that match the scoring spreadsheet for each school are also provided. 5

6 University of Missouri of Science and Technology (MST) 6

7 University of Kansas (KU) Rapid failure observed in both the continuous data and photographs 7

8 University of Missouri Columbia (MIZZ) 8

9 University of Missouri Kansas City (UMKC) 9

10 Kansas State University (KSU) 10

11 University of Arkansas (ARK) It should be noted that Arkansas had the best spirit squad to cheer the team on. Side sway observed in both the continuous data and photographs 11

12 Southern Illinois University Edwardsville (SIUE) 12

13 University of Nebraska Lincoln (UNL) 13

14 University of Oklahoma (OU) Non-symmetric stiffness observed in both the continuous data and photographs 14

15 Oklahoma State University Institute of Technology (OSUIT) 15

16 St. Louis University (SLU) Rapid failure observed in both the continuous data and photographs 16

17 University of Nebraska Omaha (UNO) 17

18 Suggestions for Future Competitions BDI was happy to participate in this event primarily as it provided an opportunity to illustrate to future civil engineers how digital data acquisition can verify how a structure is performing since many will encounter this concept in their careers. Based on this experience, we thought that if digitized data is to be recorded during future competitions, some of the following ideas might be useful: In addition to the vertical deflections, record horizontal movements in both the lateral and longitudinal directions to quickly indicate any lateral buckling. Record load magnitude at 100 lb intervals or even less if possible. Add a photo of each bridge to the ranking spreadsheet as part of the documentation if not currently being done. Require a sign on each bridge for the school s name so that photos can be easily sorted. Take photos of every bridge at end of the test to illustrate its final state. If applicable, record the failure mode (broken weld, lateral buckling, deformed connection, etc.). Record the actual final load that was applied since this should be known within the weight of one piece of angle iron. Have a printer available to immediately print out the data histories for each team. Use a laser pointer on a string to replace the plumb bob. This will provide a readily-visible dot on the floor target rather than requiring the judge to lean over the loaded bridge to estimate where center of plumb bob is pointing. Bring four 5 x7 aluminum plates to support bridge corners in case plywood is being used under the support posts (don t want plywood to crush and affect the vertical displacement measurements). If possible, require 4 x4 targets be built into the bottom of each bridge at each measurement point as they can be used for any type of displacement measurement device, whether electronic or not. The data files for each test can also be useful for participating teams and their faculty advisors as a important competition wrap-up where students perform a quantitative analysis of their bridge s behavior. Since the data is measured continuously, different behavior mechanisms can be extracted from the data, quantified, and discussed. These mechanisms include the linear elastic range of the structural responses, points at which the deformations turn plastic, and even non-linear responses. Effects of the initial loading and subsequent changes to the structure can also be observed and analysed in order to help teams improve on bridge designs for the following year s competition. 18