THE EFFECT OF SERVICE LOADING ON THE BENDING STRENGTH OF CONCRETE TIES Facility for Accelerated Service Te/tlng TRANSPORTATION TEST CENTER PUEBLO, COLORADO 81001 INTERIM REPORT OCTOBER 1981 This document is available to the public through The National Technical Information Service, Springfield, Virginia 22161 PREPARED FOR THE FAST PROGRAM AN INTERNATIONAL GOVERNMENT - INDUSTRY RESEARCH PROGRAM U.S. DEPARTMENT OF TRANSPORTATION ASSOCIATION OF AMERICAN RAILROADS FEDERAL RAILROAD ADMINISTRATION 1920 L Street. N W. Washington. DC 20590 Washington, DC 20036 RAILWAY PROGRESS INSTITUTE 801 North Fairfax Street Alexandria, Virginia 22314 © A RPJ NOTICE This document reflects events relating to testing at the Facility for Accelerated Service Testing (FAST) at the Transportation Test Center, which may have resulted from conditions, procedures, or the test environment peculiar to that facility. This document is disseminated for the FAST Program under the sponsorship of the U. S. Department of Transportation, the Association of American Railroads, and the Railway Progress Institute in the interest of information exchange. The sponsors assume no liability for its contents or use thereof. NOTICE The FAST Program does not endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of this report. Technical Report Documentation Page 1. Report No. FRA/TTC-81/11 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle The Effect of Service Loading on the Bending Strength of Concrete Ties 5. Report Date October, 1981 6. Performing Organization Cod 7. Author' s) Dr. Francis E. Dean 8. Performing Organization Report No. 9. Performing Organization Nome and Address *Battelle-Columbus Laboratories 505 King Avenue Columbus, Ohio 43201 10. Work Unit No. (TRAIS) 1 1 . Contract or Grant No. DOT-FRA-1652 12. Sponsoring Agency Name and Address **U.S. Department of Transportation Federal Railroad Administration Office of Research and Development Washington, DC 20590 13. Type of Report ond Period Covered Interim Report July 1979 14. Sponsoring Agency Code RRD-32 IS. Supplementary Notes U.S. Department of Transportation *Under Transportation Systems Center contract to: Kendall Square Cambridge, MA 02142 ** Issued by: FAST Program Transportation Test Center Pueblo, CO 81001 16. Abstract Concrete tie bending strength tests were conducted by Battelle-Columbus Laboratories at Columbus, Ohio, as part of the Tie and Fastener Verification Studies contract (DOT-FRA-1652) sponsored by the FRA Office of Rail Safety Research. The object of the testing was to determine the effects of service loading on the strength of concrete ties and to formulate assumptions about the economy of their use compared to wood ties. Of interest, also, is the comparison of concrete ties meeting the 1973 AREA structural requirements to earlier design types and to the manufacturers' test results. Used and unused ties from the same production runs were provided by the Transportation Test Center, Pueblo, Colorado, from a rebuilt section of the FAST track. Tabulations of tie strength for each group are presented, methods of testing are described, and the significance of the findings is discussed. 17. Key Words Bending Strength Crack Propagation Bending Moment Structural Crack Ultimate Load 18. Distribution Statement Document is available to the U.S. public through the National Technical Information Service Springfield, VA 22161 19. Security Classif. (of this report) Unclassified 20. Security Classif. (of this page) Unclassified 21. No. ot Pages 28 22. Price Form DOT F 1700.7 (8-72; Reproduction of completed page authorized i PREFACE The tests of concrete tie bending strength described in this report were conducted under a contract entitled "Tie and Fastener Verification Studies" (Contract No. DOT-FRA-1652 ) which was sponsored by the Office of Rail Safety Research of the Federal Railroad Administration (FRA). The Contracting Officer's Technical Representative was Mr. Howard Moody. Concrete ties in new and used condition were supplied by the Facility for Accelerated Service Testing (FAST) and were selected according to Battelle specifications by Mr. John Weber, consultant to the Association of American Railroads. Collection and shipment were performed by personnel of the FAST organization at the Transportation Test Center. The tests were carried out in the Battelle Fatigue Laboratory by Mr. Kenneth Schueller. 11 TABLE OF CONTENTS Section Page EXECUTIVE SUMMARY V INTRODUCTION 1 RESULTS OF BENDING STRENGTH TESTS 3 CONCLUSIONS 9 APPENDIX A LIST OF FIGURES Figure Page A-1 Loading Arrangements for Tests of Positive Rail Seat Bending Moment and Negative Tie Center Bending Moment A-2 A-2 Typical Load-Deflection Plot, For Rail Seat Test A-3 A-3 Laboratory Setup A-4 A-4 Rail Seat Test of Used Type A Tie A-5 A-5 Rail Seat Test of New Type B Tie A-6 A-6 Rail Seat Test of Used Type B Tie A-7 A-7 Tie Center Tests, After Ultimate Load A-8 in LIST OF TABLES Table Page 1 Summary of Test Results for Type A Ties 4 2 Summary of Test Results for Type B Ties 5 3 Summary of Differences Between Battelle and Tie Manufacturers' Test Results 6 A-1 Post-Test Load Cell Calibration A-9 ACRONYMS AREA American Railway Engineering Association FAST Facility for Accelerated Service Testing MGT million gross tons ABBREVIATIONS AND METRIC CONVERSIONS in inch = 25.4 mm M in microinch MGT million gross tons = 0.907 MGMg kip kilopounds = 453.597 kg lb pound = 0.454 kg V Volt o degree % percent IV EXECUTIVE SUMMARY Bending strength tests were conducted on prestressed concrete railway ties from the track at the Facility for Accelerated Service Testing (FAST) . Some of the ties had experienced 425 million gross tons (MGT) of service loading while others, of the same types and manufactured in the same production runs, were unused. Bending moments at which the ties experienced first cracks, structural cracks, tendon slippage and ultimate loads were recorded for tests at rail seats and tie centers. Results are compared with specifications of the American Railway Engineering Association (AREA) and with available data from manufacturer's tests. There were no indications of loss of bending strength except for tests representing a small number of one type of tie where top center flexural cracks had developed early in the service period. The center bending strength of these cracked ties averaged 20% below unused ties of the same type. However, there was no parallel loss of ultimate bending strength. The tests demonstrate that the FAST ties, which were designed to the latest (1973) AREA strength specifications, represent significant improvements in structural effectiveness in comparison to many earlier tie designs. Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/effectofservicelOOdean 2 3 INTRODUCTION One of the principal concerns in the development of prestressed concrete railroad ties is the rate at which the bending strength of the ties may deteriorate in service. Strength retention is critically important to the economic feasibility of concrete tie track, which competes in life cycle cost with wood tie track only when it is assumed that the average life of concrete ties is considerably greater than the life of wood ties. Many early designs of concrete ties for U.S. service have experienced premature structural failures. Bending strength specifications of the American Railway Engineering Association (AREA) have been increased several times in response to the early failures. An opportunity to test used FAST ties arose when operations were suspended in July 1979 to permit the rebuild of several track sections (see Appendix B for FAST background) . Nine hundred concrete ties produced by two manufacturers (identified as Type A and Type B) were removed from the 5° curve and 2% grade of Section 17. The ties had experienced 425 MGT of service loading under the FAST consist, which was predominantly composed of cars and locomotives with average axle loads of about 33 tons. These ties were designed to the latest and most demanding AREA bending strength specifications, which were published in 1973. An inspection of the ties removed from service-* revealed that all ties had experienced tamper damage (chipping along the lower edges of the tie) and that several patterns of minor hairline cracks had developed. Among these were: a. Cracks originating on the top surface at fastener shoulders and propa- gating toward the ends of the ties on many of the Type A ties. b. Transverse, top center flexural cracks which had appeared early in the FAST operations program on a small number of Type B ties. The ties had developed none of the rail seat flexural cracks which have led to premature failure of many earlier tie designs. White, D.W., Arnlund, R.C., and Prause, R.H., Economics of Concrete- and Wood-Tie Track Structures , Report No. FRA/ORD-78/2, prepared for U.S. Department of Transportation, Federal Railroad Administration, by Bechtel, Inc., and Battel le-Col umbus Laboratories, August 1978. Prause, R.H., Kennedy, J.C., and Arnlund, R.C., An Evaluation of Performance Requirements for Cross Ties and Fasteners , Report No. FRA/ORD-78/37, prepared for U.S. Department of Transportion, Federal Railroad Administration, by Battel le-Col umbus Laboratories, December 1978. Dean, F.E., Concrete and Wood Tie Performance, 425 MGT , Report No. FRA/TTC-81/06, prepared for U.S. Department of Transportation, Transportation Systems Center, by Battel le-Col umbus Laboratories, October, 1981. To test minimum samples of rail seats and tie centers of each tie type in new and used condition, and to test used ties with and without the cracking patterns identified above, a total of 15 ties of each type, 6 new and 9 used, were requested. RESULTS OF BENDING STRENGTH TESTS Twenty-eight FAST ties of two manufacturers' types were subjected to tests of higher positive rail seat bending strength or negative tie center bending strength, using the standard AREA test arrangements defined in chapter 10 of the AREA manual.'* The test procedure is described in appendix A. Most of the ties had been removed from the track after 425 MGT of service, but small samples of previously unused ties from the production runs used to construct the track were also tested to measure the extent of any change in bending strength. The service ties of each type included samples with and without a minor cracking pattern. Tables 1 and 2 summarize the tie conditions and the bending moments at which each of the following events occurred: a. First appearance of a crack, b. Crack propagation to the nearest level of prestress tendons, c. Prestress tendon slippage (on rail seat tests only), and d. Ultimate load. The tables also list the AREA bending strength specifications for qualifica- tion tests of ties spaced in the track at 24" or 30". While the FAST ties were spaced at 24", the design goal for most ties produced after 1973, when the current requirements were specified, is to satisfy the spacing requirement of 30". The test results, when compared to the AREA requirements and to available manufacturer's test data, are significant in several respects: a. For all tests, the bending moments at structural cracking (first propaga- tion of a crack to the level of a prestress tendon) exceeded AREA specifi- cations for ties installed on 30" centers. b. There was only one consistent trend in loss of bending strength at struc- tural cracking, when new ties were compared against used ties both with and without cracks. This occurred in tie center tests of the Type B ties, where a 20% reduction can be seen between the new ties and those with the top center cracks. With. the very small samples used to make this com- parison, the test results indicate a difference in mean bending strengths at the significance level of 0.05, which is usually termed "probably significant." However, all bending moments remained well above the AREA requirements, and there was no parallel reduction in ultimate loads. c. The Battelle tests produced bending strength data consistently above com- parable results from manufacturer's tests of unused ties of various ages, as shown in table 3. In some cases the manufacturer's tests were not carried to ultimate load because of inadequate loading capacity. In such 4 Manual for Railway Engineering , American Railway Engineering Association, 1978. TABLE 1. SUMMARY OF TEST RESULTS FOR TYPE A TIES. Tie Condition Before Tests Tie No. Rail Seat AREA Requirement For Structural Crack (In-kips) Initial Crack Bending Moment ( 1 n— kip) at: Structural Tendon Ultimate Crack Slip Load (a) Positive Ral I Seat Bending Moment Tests New Ties RT-2 RT-3 A B A B 300 (30- inch spaci ng) 250 (24-inch spaci ng) 326 390 359 388 384 453 391 417 646 610 608 650 646 610 609 650 MEAN 366 411 629 629 Used Ties Without Top Surface End Cracks 0389 0653 0795 A B A B A B 342 359 384 384 371 396 371 405 417 425 400 417 592 696 650 655 597 650 609 696 650 655 601 651 MEAN 373 406 640 644 Used Ties With Top Surface End Cracks 0774 0805 0844 A^ B A B A B 442 417 376 409 300 Precrack* 442 438 421 425 318 342 667 717 630 684 500 512 667 717 630 684 530 601 MEAN 389 398 618 638 (b) Negative Tie Center Bending Moment Tests New Ties RT-1 RT-4 RT-5 200 (al 1 tie spacings) 331 304 308 331 326 336 - - 541 526 548 MEAN 314 331 - - 538 Used Ties - Random Condition (No Center Cracks) 0333 0698 0905 298 311 326 336 336 345 - - 517 541 541 MEAN 312 339 - - 533 Indicates growth of an existing crack, TABLE 2. SUMMARY OF TEST RESULTS FOR TYPE B TIES. Tie Condition Before Tests Tie No. Rail Seat AREA Requirement For Structural Crack (in-kips) Bending Moment (In-kl Initial Structural Tendon Crack Crack Slip p) at: U 1 1 1 mate Load (a) Positive Rai 1 Seat Bend I ng Moment Tests New Ties CC1 CC2 A B A B 300 (30- inch spacing) 250 (24- inch spacing) 363 400 380 400 414 425 409 434 784 780 700 755 784 780 747 784 MEAN 386 421 755 774 Used Ties, Random Selection (no rai 1 seat cracks) 0092 0248 0501 A B A B A B 318 384 434 376 363 384 385 429 475 413 384 400 650 696 743 713 700 708 692 696 747 717 700 708 MEAN 377 414 701 710 (b) Negative Tie Center Bending Moment Tests New Ties CC3 CC4 CC5 200 (al 1 tie spaci ngs) 313 304 345 385 - - 504 547 MEAN 309 365 - - 526 Used Ties Without Top Center Flexural Cracks 0088 0244 0581 318 304 251 336 325 280 550 550 512 MEAN 291 314 - - 537 Used Ties With Top Center Flexural Cracks 0232 0252 0292 Precracked Precracked Precracked 287 284 298 - - 532 534 519 MEAN 291 - - 528 TABLE 3 . SUMMARY OF DIFFERENCES BETWEEN BATTELLE AND TIE MANUFACTURERS' TEST RESULTS. Bending Moment (in-kips) for: Battel le Percent Tests** Manufacturers' Tests Difference RAIL SEAT TESTS (Mean values) (Age of Test Ties) Type A Ties (Mean values unless indicated by # for single test) Initial Crack 366 338 (3-7 days) 8 277 (4.5 months) 28 314 (3.3 years) 15 Structural Crack 411 323 (3.3 years) 24 Ultimate Load 629 >536* (3-7 days) <16 >526* (4.5 months) <18 >559* (3.3 years, no <12 test failures) Type B Ties Initial Crack 386 344# (<6 months) 12 Structural Crack 421 373# (<6 months) 12 Ultimate Load 774 646# (<6 months) 18 TIE CENTER TESTS Type A Ties Initial Crack 314 277# (1-3 weeks) 13 312# (18 months) 0.6 Ultimate Load 538 500# (1-3 weeks) 7 569# (18 months) -6 Type B Ties Initial Crack 309 270# (<6 months) 13 Structural Crack 365 297# (<6 months) 21 * >Indicates that some test ties did not fail at maximum applied load. ** Age of all Battelle test ties was approximately 3.6 years. cases only an upper bound to the percent difference between test results could be obtained. While all tests were conducted in accordance with the nominal procedures specified in reference 4, the possibility of systematic differences in test procedure exists. CONCLUSIONS a. The tests of FAST ties were designed to determine the possible effects on tie strength of the service history, particularly of the minor cracking patterns. Very little effect of service loading was found. Transverse, top center flexural cracks on one type of tie were found to have reduced average tie center bending strength by 20%, but strength levels remained well above the maximum requirements of the latest AREA specifications. b. The preceding results are significant because the FAST ties had experienced 425 MGT of service under severe loading conditions (5 curve, 2% grade, average axle loads of about 33 tons). Also, tamper bars had defaced the bases of all the ties early in the program due to use of improper length tamping bars and cylinder opening for concrete ties. Although several minor cracking patterns developed, there were no flexural rail seat cracks of the type that have led to premature failures of several earlier concrete tie designs. It is assumed that the ties could have sustained at least several hundred MGT of additional service, and possibly would have sustained the equivalent of an average 50-year life (1,000 MGT at 20 MGT/year) under the FAST loading environment. c. It. should be recognized that the development of flexural cracks and an associated loss of bending strength do not necessarily indicate that the tie will prematurely fail in service. A service failure is defined as loss of the ability to sustain bending loads, or deterioration to the extent that too-frequent maintenance is required to keep the track alined, the ties spaced, or the fasteners maintained. The most extensive test of cracked ties is in progress at FAST, where 100 previously cracked ties from the Kansas Test Track (RT-7 ties) were installed on tangent track and have provided satisfactory service for over 450 MGT. It is possible that colder and wetter climates or less stable subgrades would cause more rapid deterioration from repeated freeze-thaw cycles, rusting of the prestress tendons or less uniform support conditions. However, this example shows that in environments comparable to that at FAST, concrete ties can function satisfactorily long after structural cracks have developed. APPENDIX A TEST PROCEDURE The ties were positioned in a servo-controlled, 500-kip load machine as shown in figure A-1 . The loading arrangements conform to those prescribed in figures I and II of the AREA Manual for Railway Engineering, chapter 10. Load was applied by lifting a strongback beam which supported the tie. For rail seat tests, the opposite end of the tie was supported by a sling which became slack as the beam was lifted. The upper reaction load P was monitored through a load cell whose output was continuously recorded on the Y-axis of the X-Y plot. The X-axis of the plot consisted of the "bending deflection" of the tie between its support points, as illustrated on the typical plot of figure A-2. Dial indicators were attached to the end of the tie (figure A-3) during the rail seat tests to detect tendon slippage. When slippage occurred separately from ultimate load, it was normally accompanied by a dip in the load-deflection curve, and it occurred with an easily detectable magnitude of at least several thousandths of an inch. Cracking events were detected with the aid of lines drawn on each tie face to indicate the levels of prestress tendons. Mirrors were placed under the tie at the load centerline as an additional aid to detection. Alcohol was applied to the tie face as soon as a crack was detected, to aid in following crack propagation. Applied loads at various cracking events were recorded by releasing a hand-held control switch that caused a small perturbation in the X-Y plot. The relationships between applied load P and bending moment M, consistent with the dimensions shown in figure A-1, are: a. Rail Seat Tests M = 6.04 P, and b. Tie Center Tests M = 13.5 P. Photos of typical tie failure modes are shown in figures A-4 through A-7. After completion of the tests, an error was discovered in the load calibration conducted before the start of testing. The machine was recal- ibrated using a proving ring calibrated at the National Bureau of Standards. The load-voltage relationships for the load cell range of 200 kips (used exclusively during the tests) is shown in table A-1. From the calibration, the load-voltage relationship which existed during the tests was established by the ratio of the shunt resistance offset voltages which were measured during testing and during the proving ring calibration. A-1 Balancing sling (Slack when load applied) Measured reaction load P f-14.33"*Wi4.33"-*| mil — Shim to top level of rail seat — > | I "ror (a) Rail Seat Test Measured Reaction Load P Machine lifts Strongback to apply load (b) Tie Center Test FIGURE A-1. LOADING ARRANGEMENTS FOR TESTS OF POSITIVE RAIL SEAT BENDING MOMENT AND NEGATIVE TIE CENTER BENDING MOMENT. A- 2 T3 cu p - — — 1 U I I - c c I 0.1 1 o K I C T3 " •H O i V- CiH OS 1 ' I ft 1 1 I T3 m 1 | J 1 C " •H P u fO CD " OS in ■hi | cr> P 1 G u 1 -iH CD 00 1 Q-ICSI ' Bend Defl T3 CD G - 1 CO f 1 CD S / J 1 O-icj / T3 H J CD +J fO e ■H \ P ' < D u / ^H U / rO (0 / H ^ / , 3 U / P 1/ . CJ -H ¥ 3 ro ^ M CD 4J 3 M CO -P 9 u —i . 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Proving Ring Load (NBS-Calibrated) Reference Cell Strain Working Cell Output Voltage Nominal Corrected Load Load (Uin/in) (V) (kips) (kips) 20 19.99 97 1.01 40 39.90 192 2.015 60 60.10 289 3.03 80 79.94 385 4.04 100 100.06 483 5.05 120 120.14 - - _ _* 140 139.87 677 7.065 160 159.88 774 8.08 180 179.84 871 9.09 200 200.08 970 10.11 160 159.88 772 8.05 120 120.14 578 6.04 80 79.94 383 4.01 40 60.10 190 1.99 20 19.99 95 .98 .003 Reading missed because of hesitation in hydraulic system. A-9 APPENDIX B FAST BACKGROUND FAST has been installed and operating at the DOT Transportation Test Center since September 1976. The physical facilities include a 4.8 mi loop of track, a fleet of cars and locomotives, and a maintenance facility. The orga- nization includes a staff of people to operate the trains, perform maintenance and inspections, carry out regular performance measurements on vehicles and track and manage the storage and retrieval of data. This facility was created as a joint effort of the Federal Railroad Administration (FRA), the Association of American Railroads (AAR), the Transportation Test Center (TTC), the Transportation Development Agency of Canada, the railroads and the Railway Progress Institute. The purpose of FAST is to simulate the service environment of both track and vehicles at rates of tonnage accumulation much higher than those of average revenue service. The train runs five nights a week, and maintenance and performance measurements are carried out during the day. From the beginning of operations in September 1976 up to the shutdown for rebuild in July 1979, the test train accumulated approximately 425 MGT, for an annual rate of 150 MGT, over seven times that of an average mainline track (about 20 MGT per year). Future rates can be expected to increase, since several shut- downs have been required for repair of vehicles and track. The test train fleet, which is loaned by the railroads, normally consists of 80 cars and five locomotives. Regular maintenance and measurements are performed on four cars each day, so that about 76 cars and 4 locomotives are in the consist. A wide range of performance measurements are regularly made on both the vehicles and track. Track performance data are collected at tonnage intervals ranging from 1 to 50 MGT. Additional track performance measurements are required before and after many maintenance procedures. The data are digitized and stored on permanent files at TTC. The FAST track is divided into 22 sections providing many combinations of track construction components, as shown in Figure A-1. Twenty of the 22 sec- tions were initially built with wood ties. Section 06 was initially built with steel ties which were removed at 28 MGT. Section 17 is 6,100' long and contains 2,886 concrete ties installed on 24" centers, with short transitions of wood tie track at either end of the section. Much of this evaluation con- cerns the performance of this concrete tie section. B-1 LEGEND : Test Section 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Description/Test Variable Existing No. 20 Turnout Rubber Pads (0-358 MGT) Wood and Reconstituted Ties (358 MGT - Present) Rail Metallurgy (Changed at 425 MGT) Spiral, Standard Track (0-358 MGT) Wood and Reconstituted Ties (358 MGT - Present) Bonded Joints (Removed) Steel Ties (Removed at 28 MGT) Fasteners/Wood Ties (Changed at 135 MGT and 358 MGT) Spiral, Standard Track Dowel Laminated, Reconstituted Ties Elastic Spikes, Spring Frogs (Removed) Joints (Originally included Frogs and Guardrails which were removed before 200 MGT) Spiral, Standard Track Spike Hole Filler Test (Deleted) Existing No. 20 Turnout Ballast Shoulder Width Glued No. 20 Turnout Concrete Tie Track Ballast Depth Oak and Fir Ties Ballast Type and Depth, Rail Anchors Welded No. 20 Turnout (Straight Railed, Deleted) Spiking Patterns and Rail Anchors (Test Deleted) FIGURE B-1. SUBSECTIONS OF THE FAST TRACK LOOP. B-2 GPO 833 - 778