HIGH STRENGTH REINFORCEMENT IN REINFORCED CONCRETE BEAMS PART II' CRACK WIDTHS, DEFLECTIONS, FATIGUE STRENGTH

TEST RESULTS PRESENTED SHOW CRACK WIDTHS AND DEFLECTIONS OF SIMPLE RECTANGULAR BEAMS REINFORCED WITH HIGH-STRENGTH STEEL AND STRESSED UP TO 50 KSI. THE RESULTS ARE COMPARED WITH THEORY AND WITH THE RESULTS OF OTHER INVESTIGATIONS. IT IS CONCLUDED THAT ACCEPTABLE DESIGN METHODS EXIST FOR THE LIMITATION OF CRACK WIDTHS AND THAT HIGH STRENGTH REINFORCEMENT MAY BE STRESSED TO 30 KSI OR MORE WITHOUT OBJECTIONABLE CRACKING OCCURRING PROVIDED PROPER ATTENTION IS GIVEN TO THE SIZE AND ARRANGEMENT OF BARS. THE OBSERVED DEFLECTIONS WERE IN FAIR AGREEMENT WITH CALCULATED VALUES BASED ON THE CRACKED TRANSFORMED SECTION. AN INCREASE IN WORKING STRESS WILL LEAD TO A MORE THAN PROPORTIONATE INCREASE IN DEFLECTION IF HIGHER WORKING STRESSES ARE USED. ON THE BASIS OF A LIMITED NUMBER OF REPEATED LOAD TESTS IT IS CONCLUDED HIGH STRENGTH REINFORCING BARS HAVE SUBSTANTIALLY GREATER FATIGUE STRENGTH THAN INTERMEDIATE GRADE BARS. A FORMULA FOR ALLOWABLE WORKING STRESSES IS PROPOSED BASED ON YIELD STRESS AND THE RATIO OF DEAD LOAD MOMENT TO LIVE LOAD MOMENT. /CGRA/