TESTS TO DETERMINE THE NECESSARY ANCHORAGE LENGTHS OF REINFORCING STEELS IN LIGHTWEIGHT REINFORCED CONCRETE

VERSUCHE ZUR BESTIMMUNG DER NOTWENDIGEN VERANKERUNGSLAENGEN VON BETONSTAEHLEN IN STAHLLEICHTBETON

THE MOST IMPORTANT RESULTS OF THE CURRENT TESTS WITH LB 300 ON STRAIGHT BARS OF ST II RK 0 12 ARE: 1 - THE ACCEPTABLE BOND STRESSES OF A HORIZONTAL RIBBED STEEL CONCRETED INTO LIGHTWEIGHT CONCRETE, GIVEN A WORKING LOAD OF 0.1 MM AND SUFFICIENT CONCRETE COVER, ARE GREATER THAN THE STRENGTH ASSOCIATED WITH NORMAL CONCRETE; 2 - THE INFLUENCE OF THE POSITION OF THE REINFORCEMENT AS REGARDS THE DIRECTION OF CONCRETING IS LESS WITH LIGHTWEIGHT CONCRETE THAN WITH NORMAL CONCRETE, EVEN IN THE CASE OF EXTREMELY SOFT LIGHTWEIGHT CONCRETES. WITH SMALLER CONCRETE COVERS (HERE 2 0 = 2.4 CM) HOWEVER, ONE HAS TO RECKON ON NOTICEABLE SEGREGATION AT THE TOP EDGE OF THE CONCRETE IN THE CASE OF VERY SOFT FRESH CONCRETE (DEGREE OF COMPACTION V 1.10). THE GENERALLY LOWER SPLITTING TENSILE STRENGTH OF LIGHTWEIGHT CONCRETE COMPARED WITH NORMAL CONCRETE IS FURTHER REDUCED BY SHRINKAGE STRESSES AT THE EDGE, SO THAT THE CONVENTIONAL CONCRETE COVER FOR NORMAL CONCRETE IS NOT SUFFICIENT FOR LIGHTWEIGHT CONCRETE CONTAINING SPHERICAL EXPANDED CLAY AGGREGATE WITH A HIGH WATER ABSORPTION CAPACITY. 3 - CREEP OF LIGHTWEIGHT CONCRETE UNDER BONDING STRESS IS NO GREATER THAN WITH NORMAL CONCRETE. IF NORMAL CONCRETE IS HIGHLY STRESSED INITIALLY, THE CREEP RELATED TO THE INITIAL SLIP IS IN FACT SIGNIFICANTLY GREATER THAN WITH LIGHTWEIGHT CONCRETE. 4 - WITH LIGHTWEIGHT CONCRETE HAVING A COVER OF UE(B) = 5.4 CM, CONTINUOUS LOADING, EVEN WITH SLIP VALUES = TO 0.1 MM, CAN LEAD TO SPLITTING FAILURE WITHIN AN HOUR. WITH THE DANGER OF SPLITTING OF THE CONCRETE COVER UNDER CONTINUOUS LOADING, ONE HAS TO RECKON ON SLIP VALUES WHICH ARE SIGNIFICANTLY LESS THAN 0.1 MM IN CONVENTIONAL PRACTICAL CONSTRUCTION (UE(B) = 2.0).