Steel Bridge Research at Ferguson Structural Engineering Lab

Transcription

1 Steel Bridge Research at erguson Structural Engineering Lab Investigators: Todd Helwig, Mike Engelhardt, Eric Williamson, Ozzie Bayrak, Tricia Clayton, John Tassoulas, and Lance Manuel Sponsor: Texas Department of Transportation Research Project Managers: Darrin Jensen and Wade Odell

2 Research Projects Improved Cross rame Details Strengthening Continuous Steel Girders with Post-Installed Shear Connectors Extending the Use of Elastomeric Bearings to Higher Demand Applications Partial Depth Prestressed Concrete Deck Panels on Curved Bridges Improved Tub Girder Details atigue Resistance and Reliability of High Mast Illumination Poles (HMIPs) with Pre-existing Cracks 2

3 Improved Cross rame Details Investigators: Todd Helwig, Michael Engelhardt, Karl rank Graduate Research Assistants: Weihua Wang, Anthony Battistini, and Sean Donahue Sponsor: Texas Department of Transportation

4 Research Objectives To improve the fundamental behavior of cross frames by investigating both existing and alternative details Investigate new cross frame layouts, use of steel castings, for connections, etc. Understand current performance of cross frames in strength, stiffness, and fatigue (at member and system level) Develop recommendations for cross frame design and detailing Evaluate fatigue performance of various details in traditional and new systems Some of the more interesting findings in this study, had nothing to do with the initial focus of the research 4

5 Cross rame Examples The cross frames require significant handling during fabrication. Better details can improve the efficiency and fabrication economy 5

6 Background Single Diagonal Cross rames Use increased compression capacity of diagonal to resist girder twist Results in same stiffness as tension-only system Previous laboratory tests showed feasibility M h b M S R A R B 6

7 Overview While new cross frame details were studied, in the process we found that we did not understand the stiffness behavior of the cross frame systems that are currently in practice. Most computer models have gross errors in the stiffness modeling of the braces. These errors can lead to unsafe conditions during construction, poor quality with respect to predictions of deformations during construction, and improper indications of fatigue problems. 7

8 Current Details Lab Tests: ull Scale Stiffness Cross rame Specimens Potential Details Considered Single Angle X-rame Square Tube Z-rame Single Unequal Leg Angle X-rame Single Angle K-rame Double Angle Z-rame (Single Angle Struts) Double Angle Z-rame (Double Angle Struts)

9 Background Brace Stiffness Analytical ormulas based upon truss formulations of the cross frame system. Tension-only System Tension-Compression System K rame System β bb = ES2 2 h b 3 2L c + S3 A c A h β bb = A ces 2 h b 2 L c 3 β bb = 2ES2 2 h b 3 8L c + S3 A c A h Z rames X rames K rames 9

10 Lab Tests: Large Scale Stiffness Cross rame Model irst tests carried out on full scale cross frames that allowed the direct measurement of the stiffness and strength of the braces. - h b - R A S R B 10

11 Lab Tests: Large Scale Stiffness Test Setup R R R 11

12 Lab Tests: Large Scale Stiffness Single Angle X rame Test 2C 12

13 Lab Tests: Large Scale Stiffness Single Angle X rame orces orces in Angle Members Member orces, kips top diag top 1 diag bot 2 bot Applied orce, kips Top and bottom struts are close to zero force member In elastic range, the compression diagonal contributes as much as the tension diagonal 13

14 Lab Tests: Large Scale Stiffness Single Angle X rame Stiffness M frame, kip-in y = x R² = β=872,000 kip-in/rad θ, rad 14

15 Lab Tests: Large Scale Stiffness Comparative Stiffness Behavior Type of Cross rames Single Angle X rame Test Results 872,000 Single Angle K rame 760,000 Unequal Leg Angle X rame Double Angle Z-frame (Single Struts) Double Angle Z-frame (Double Struts) Square Tube Z-frame 1,054, ,000 1,182, ,000 15

16 Lab Tests: Large Scale Stiffness Comparative Stiffness Behavior Type of Cross rames Test Results Analytical Solution Error % Single Angle X rame 872,000 1,579,000 82% Single Angle K rame 760,000 1,189,000 56% Unequal Leg Angle X rame Double Angle Z-frame (Single Struts) Double Angle Z-frame (Double Struts) Square Tube Z-frame 1,054,000 1,609,000 53% 597, ,000 52% 1,182,000 1,152, % 658, ,000-1% 16

17 Lab Tests: Large Scale Stiffness Comparative Stiffness Behavior Type of Cross rames Test Results Analytical Solution Error % Line Element Solution Error % Single Angle X rame 872,000 1,579,000 82% 1,572,000 81% Single Angle K rame 760,000 1,189,000 56% 1,180,000 55% Unequal Leg Angle X rame Double Angle Z-frame (Single Struts) Double Angle Z-frame (Double Struts) Square Tube Z-frame 1,054,000 1,609,000 53% 1,614,000 53% 597, ,000 52% 905,000 52% 1,182,000 1,152, % 1,152, % 658, ,000-1% 647,000-2% 17

18 Lab Tests: Large Scale Stiffness Comparative Stiffness Behavior Type of Cross rames Test Results Analytical Solution Error % Line Element Solution Error % Shell Element Solution Error % Single Angle X rame 872,000 1,579,000 82% 1,572,000 81% 867,000-1% Single Angle K rame 760,000 1,189,000 56% 1,180,000 55% 781,000 3% Unequal Leg Angle X rame Double Angle Z-frame (Single Struts) Double Angle Z-frame (Double Struts) Square Tube Z-frame 1,054,000 1,609,000 53% 1,614,000 53% 1,065,000 1% 597, ,000 52% 905,000 52% 616,000 3% 1,182,000 1,152, % 1,152, % 1,164, % 658, ,000-1% 647,000-2% 657,000 0% 18

19 The reduction in the stiffness is due to the bending caused by the eccentric connection 19

20 Lab Tests: Large Scale Stiffness Observations Truss formulations and line element models overestimate the stiffness of cross frames with single angle members Error largely due to eccentric connection of single angle Results from EA shell element model have good agreement with all test results Use validated model to perform parametric studies 20

21 Computational Modeling Cross rame Stiffness Reduction Parametric studies were performed to find a correction value for single angle X and K frames: R=β EA / β analytical R was found to be dependent upon S/h b, y, and t R can be applied to the truss formulation R can be applied to modify the member area in a computer software model when cross frames are modeled using line elements 21

22 Computational Modeling X Cross rame Reduction actor R β analytical [1000 kip-in/rad] β reg-sx β β EA [1000 EA-SX kip-in/rad] 1 1

23 Computational Modeling K Cross rame Reduction actor R β analytical [1000 kip-in/rad] R β analytical β ana-sk β β EA [1000 β EA-SK EA kip-in/rad]

24 Design Recommendations Reduction actor Verification Type of Cross rames Test Results Analytical Solution Error % Single Angle X rame 872,000 1,579,000 82% Single Angle K rame 760,000 1,189,000 56% Unequal Leg Angle X rame 1,054,000 1,609,000 53%

25 Design Recommendations Reduction actor Verification Type of Cross rames Test Results Analytical Solution Error % R*Analytical Solution Error % Single Angle X rame 872,000 1,579,000 82% 860, % Single Angle K rame 760,000 1,189,000 56% 762, % Unequal Leg Angle X rame 1,054,000 1,609,000 53% 1,018, %

26 Impact of Overestimating X-rame Stiffness rom a stability perspective, overestimating the stiffness of the cross frames will lead to larger forces induced in the cross frames compared to the computer prediction (unconservative). In the finished bridge, over estimating the stiffness of the cross frame will lead to over prediction of the cross frame forces from truck traffic, which can therefore lead to predictions of potential fatigue issues that are not actually a problem. (conservative but potentially very costly). 26

27 Lab Tests: Large Scale Stiffness Conclusions Eccentric connection of single angle reduces stiffness due to bending Using truss models or line element solutions can significantly over predict stiffness of single angle cross frames Applying reduction factor to analytical models can produce relatively accurate estimate of cross frame stiffness Concentric members show good agreement with analytical models and do not require reduction factor Extensive fatigue testing also showed angles are Category E and not E as in AASHTO. Backside welds on K-frames can be omitted, greatly simplifying handling during fabrication. 27

28 ERGUSON STRUCTURAL ENGINEERING LABORATORY TxDOT Research Project Strengthening Continuous Steel Bridges with Post-Installed Shear Connectors Graduate Research Assistants: Kerry Kreitman and Amir Reza Ghiami Azad

29 Post-Installed Shear Connectors Double-nut bolt High-tension friction-grip bolt Adhesive anchor Conventional connectors such as wedge anchors experienced too much slop in shear behavior.

30 Post-Installed Shear Connectors While the original research study focused on non-composite simple span bridges, there are a number of continuous steel girder systems that are non-composite. Many of these bridges are load rated and therefore a simple method of strengthening that does not require closing the bridge are highly desireable

31 Composite Behavior Shear connectors Non-composite beam Negligible slip at interface ully composite beam Slip at interface Steel and concrete act separately Partially composite beam Steel and concrete act together Increased strength and stiffness Composite ratio: Some slip at interface

32 Project 6719 Overview Strengthen continuous bridges ocus on negative moment region over piers Positive moment Compression Tension Negative moment Tension Compression Positive moment Compression Tension Composite action is less efficient

33 Project 6719 Overview Strengthen continuous bridges ocus on negative moment region over piers Considered two strengthening methods: 1. Install connectors along entire bridge 2. Install connectors in positive moment regions only and allow for moment redistribution Concern of repeated yielding Additional fatigue testing of connectors

34 Moment Redistribution Controlled by shakedown limit state ormation of residual moments that counteract applied loads uture cycles resisted elastically (no significant increase in deflection with cycles) Experimentally proven for steel, but not composite beams Steel is ductile, concrete is not

35 Test Setup (Design based on bridges from survey of non-composite bridges in Texas) 30% composite W30x90

36 Installing Connectors

37 Testing Procedure irst Specimen 1. Elastic testing of non-composite beam 2. Install connectors 3. Elastic testing of composite beam 4. Cycles of load up to first yield 5. Cycles of load up shakedown limit 6. atigue testing 7. Static ultimate strength testing (?) Completed Current

38 Inelastic Cyclic Loading P 1 16 P 2 P

39 Preliminary Test Results Elastic behavior similar to predictions Shakedown observed at up to 5% beyond the predicted shakedown limit Deflections stabilized with cycles Promising technique for strengthening

40 Elastic Testing -0.4 Distance Along Beam (ft) P 1 = 40 kips -0.2 Deflection (in) ANSYS, non-composite ANSYS, composite, 440 k/in ANSYS, composite, 800 k/in ANSYS, composite, 1600 k/in ANSYS, fully composite Test, non-composite Test, composite

41 Inelastic Testing irst yield predicted Predicted shakedown limit P 1 (kips) (P 1 = 0.87*P 2 ) P 2 (kips) Cycles to Shakedown Residual Deflection (in) Incremental Peak Deflection (in) Colors in table coincide with bars in chart Cycle Number P1=140k P1=161k P1=187k Criteria: Shaken down when change in deflection < 0.01 in.

42 Inelastic Behavior

43 Inelastic Behavior

44 inite Element Modeling 4 P Not shaken down after 10 cycles Deflection under P 1 Load (in) Test EM prediction P 2 P Applied P 1 or P 2 Load (kips)

45 atigue: Overall Approach Small-Scale atigue Tests Showed Conventional stress-based approach Too conservative for partially composite beams VQ/I is inaccurate (assumes no slip) ocus on developing a slip-based approach Compute slip demand Compare to allowable slip limit

46 atigue Test 1 (South Span) Setup P Strain Gages and Slip Transducers irst test was carried out on span that had not been subjected to shakedown. P=50 kips (cycle from 2 to 52 kips) Slip transducers and strain gages used along the length of the beam. Test Results - >2 Million cycles of load and no failure A gap around the fasteners tends to form that greatly reduce the fatigue-induced stress.

47 atigue Test 2 (North Span) Setup P1 Strain Gages and Slip Transducers Slip Transducers P1 = 2 to 77 kips both during fatigue testing and intermittent static testing Strain Gages and Slip transducers positioned around postinstalled connectors. Test stopped at approximately 340,000 because the specimen was tending towards a non-composite girder (for service levels of load). At ultimate we think the fasteners will engage to give composite section.

48 Current Work Test current continuous beam to ultimate load. Construct another specimen increasing total length by approximately 25%. Shakedown test atigue tests Ultimate load test Parametric EA work Project will complete in August

49 Questions?