Railroad Concrete Tie Failure Analysis Hailing Yu, David Jeong, Brian Marquis, and Michael Coltman 2014 International Crosstie & Fastening System Symposium June 3-5, 2014 The National Transportation Systems Center Advancing transportation innovation for the public good U.S. Department of Transportation Office of the Assistant Secretary for Research and Technology John A. Volpe National Transportation Systems Center 1
Outline Three main concrete tie failure modes studied at Volpe Center Prestress cracks Flexural cracks Rail seat deterioration Approach Results Future work/research needs Acknowledgements 2
Cracking Related to Prestresses (Source: Mayville, R.A., Jiang, L., and Sherman M., Performance Evaluation of Concrete Railroad Ties on the Northeast Corridor, DOT/FRA/RPD-14/03, 2014.) (Source: NDT Corporation.) 3
Flexural Cracks Rail seat cracking Center bound cracking (Source: Zeman, J. C., Hydraulic Mechanisms of Concrete-Tie Rail Seat Deterioration, M.S. Thesis, University of Illinois at Urbana-Champaign, 2010.) 4
Finite Element Model of Concrete Tie Components Steel reinforcement Concrete Steel-concrete interface 5
Concrete Damaged Plasticity Uniaxial tension: linear elasticity followed by tension stiffening Uniaxial compression: linear elasticity followed by strain hardening and strain softening Multi-axial yield function d t tensile damage variable d c compressive damage variable 6
Interface Micromechanics 7
Homogenized Interface Model τ = + 2 2 τ s τ t 8
Elastoplastic Bond Model Interface stresses = σ n + τ 1 s + τ t σ 2 Interface displacements el = u n + u s + u t u = u + u u n t1 t2 Elasticity e el σ = D u = D Yield surface F σ, τ = ( ) 0 Plastic flow Q du pl = dλ σ e ( pl u u ) τ = + 2 2 τ 1 τ 2 pl 9
Adhesive-Frictional Bond Model for Smooth Wire 10
Bond Model Calibration Untensioned pullout tests Pretensioned prism tests 11
Bond Model Validation with Concrete Ties Made in Plant 12
Transfer Length in Concrete Ties with Smooth Wire: Test vs. FEA Transfer length (in.) 22 20 18 16 14 12 10 Average test data Simulation, f c =6000 psi Simulation, f c =4500 psi 95% AMS ZL 13
Stresses upon Pretension Release and under Rail Seat Loading (Well Supported) Deformation scale factor = 100 14
AREMA Center Negative Moment Test 15
Center Binding Condition with Assumed Deteriorated Ballast Support 16
Static Analysis Two-step simulation Pretension release Center binding Simulated center binding scenarios AREMA test Deteriorated ballast support with h=0.5 in. Eight-strand concrete tie Concrete compressive strength: 7,000 psi Homogenized, frictional steel-concrete interface Calculation of equivalent wheel load assumes that a rail seat carries 50% of wheel load Average rail seat displacement calculated relative to tie center displacement 17
Center Bound Cracks: AREMA Test vs. Deteriorated Ballast Support 18
Force-Relative Displacement: AREMA Test vs. Deteriorated Ballast Support 45 40 35 30 25 20 15 10 AREMA specified pass/fail load 5 0-0.05 0 0.05 0.1 0.15 0.2 Relative rail seat displacement (in.) Equivalent wheel load (kip) AREMA test Deteriorated ballast ( h=0.5 Series2 in.) 19
Dynamic Analysis Import damaged initial state 100 of tie from the static 90 analysis 80 70 Increase max tie-ballast gap 60 ( h) to 2.5 in.; the gap 50 under the rail seat is around 40 1 in. 30 Apply dynamic rail seat load 20 according to graph on the 10 right 0 Equivalent wheel load (kip) 0 0.1 0.2 Time (sec) 20
Concrete Damage Under Dynamic Load h=2.5 in. 21
Force-Relative Displacement Relation Equivalent wheel load (kip) 100 80 60 40 20 0 Dynamic analysis h=2.5 in. Frame #67, 68 kips 0 0.5 1 1.5 Relative rail seat displacement (in.) Static analysis ( h=0.5 Series1 in.) 22
Dynamic Analysis Import damaged initial state of tie from the static analysis Apply dynamic rail seat load according to graph on the right Vary the max tie-ballast gap ( h): 1.25, 2, and 2.5 in. Equivalent wheel load (kip) 70 60 50 40 30 20 10 0 0 0.05 0.1 Time (sec) 23
Concrete Damage Under Dynamic Load h=2 in. 24
Force-Relative Displacement Relation Equivalent wheel load (kip) 100 80 60 40 20 0 Dynamic analysis h=2.5 in. h=1.25 in. h=2 in. h=2.5 in. 0 0.5 1 1.5 Relative rail seat displacement (in.) Static analysis ( h=0.5 Series1 in.) 25
Future Work/Research Needs Develop elastoplastic bond models for indented wires/strands Apply in analysis of prestress cracks Design tests to characterize the interface normal stressdilation relations Detailed (smaller-scale) interface modeling 26
Future Work/Research Needs Simulate asymmetric, center binding ballast support conditions Correlate simulated cracking pattern with field observation and wheel load level Verify analysis results with experiments Characterize mechanical properties and geometric profile of fouled ballast 27
Acknowledgements Office of Research and Development at the Federal Railroad Administration, U.S. Department of Transportation sponsored the presented research. Pullout and transfer length test data were provided by Professors Robert J. Peterman and B. Terry Beck and their research team at Kansas State University. 28
Questions? 29