CUMULATIVE FATIGUE DAMAGE CHARACTERISTICS OF PLAIN CONCRETE

Abstract

THE PRIMARY GOAL WAS TO EVALUATE THE EFFECT OF VARIABLE LOADS ON THE FATIGUE LIFE-TO DETERMINE WHETHER THE MINER HYPOTHESIS ADEQUATELY REPRESENTS CUMULATIVE DAMAGE. IN THE LABORATORY WORK, 6 X 6 X 64-IN. BEAMS WERE TESTED STATICALLY AND ALSO UNDER MONOTONIC OR VARIABLE LOADINGS. MOST SPECIMENS WERE MOIST-CURED FOR 7 DAYS AND THEN STORED IN NORMAL LABORATORY AIR FOR AN AVERAGE OF 425 DAYS BEFORE TESTING. THE SINUSOIDAL FATIGUE TESTS WERE CONDUCTED AT A LOADING RATE OF 450 CPM, WITH THE RATIO OF MINIMUM TO MAXIMUM STRESS EQUAL TO 0.15. THE SPECIMENS IN THE VARIABLE LOAD SERIES WERE SUBJECTED TO 2 LEVELS OF LOADING. A RANGE OF CONDITIONS WAS PROVIDED BY RAISING OR LOWERING THE STRESS LEVEL, BY VARYING THE NUMBER OF CYCLES AT THE FIRST LEVEL AND BY VARYING THE STRESS RANGE. THE TEST DATA INDICATED A WIDE SCATTER IN STRENGTH FOR CONCRETE SUBJECTED TO EXTENDED DRYING CONDITIONS. THE APPLIED FATIGUE STRESSES WERE NORMALIZED BY USING A MULTIPLE LINEAR REGRESSION PROCEDURE TO PREDICT THE STATIC STRENGTH. THE VARIABLE LOAD FATIGUE TESTS WERE EVALUATED AGAINST THE BASIC S/N DATA. IT IS CONCLUDED THAT THE MINER HYPOTHESIS REPRESENTS THE CUMULATIVE DAMAGE CHARACTERISTICS OF PLAIN CONCRETE IN A REASONABLE MANNER. BECAUSE OF THE VARIABILITY OF CONCRETE STRENGTH, A MORE ELABORATE RATIONALE IS NOT WARRANTED. THE ACCURACY OF THE S/N DIAGRAM IS VERY DEPENDENT ON THE ACCURACY OF THE PREDICTION OF THE NORMALIZING STRENGTH VALUES. /AUTHOR/