THE STRUCTURAL DESIGN OF CONCRETE PAVEMENTS - PART 4 - A STUDY OF THE STRUCTURAL ACTION OF SEVERAL TYPES OF TRANSVERSE AND LONGITUDINAL JOINT DESIGNS

THE DEVELOPMENT OF THEORY AND PRACTICE IN REGARD TO JOINT CONSTRUCTION IN CONCRETE PAVEMENTS IS TRACED. IT APPEARS THAT JOINTS IN CONCRETE PAVEMENTS MAY BE CLASSIFIED ACCORDING TO THEIR INTENDED FUNCTION: (1) THOSE DESIGNED TO PROVIDE SPACE IN WHICH UNRESTRAINED EXPANSION CAN OCCUR, (2) THOSE DESIGNED FOR THE RELIEF OR CONTROL OF THE DIRECT TENSILE STRESSES CAUSED BY RESTRAINED CONTRACTION, AND (3) THOSE DESIGNED TO PERMIT WARPING TO OCCUR, THUS REDUCING RESTRAINT AND CONTROLLING THE MAGNITUDE OF THE BENDING STRESSES DEVELOPED BY RESTRAINED WARPING. IN STUDYING THE STRUCTURAL ACTION OF JOINTS IN THIS INVESTIGATION, EACH JOINT WAS SUBJECTED TO TESTS TO DETERMINE ITS RELATIVE EFFECTIVENESS OR: (1) PERMITTING UNRESTRAINED EXPANSION AND CONTRACTION, (2) PERMITTING UNRESTRAINED WARPING AT THE JOINT, AND (3) REDUCING THE STRUCTURAL WEAKNESS CREATED BY THE BREAK IN THE SLAB CONTINUITY AT THE JOINT. INSTALLATION AND DETAILS OF TRANSVERSE AND LONGITUDINAL JOINTS ARE DESCRIBED. EXPANSION JOINTS SHOULD BE PROVIDED IN NO GREATER INTERVALS THAN ABOUT 100 FEET IN ORDER TO KEEP THE JOINT OPENINGS FROM BECOMING EXCESSIVE. THE SPACING OF CONTRACTION JOINTS WILL BE DETERMINED BY THE PERMISSIBLE UNIT STRESS IN THE CONCRETE. IF THIS IS RESTRICTED TO A LOW VALUE, WHICH IS DESIRABLE, CONTRACTION JOINTS SHOULD BE PROVIDED AT INTERVALS OF ABOUT 30 FEET. JOINTS TO CONTROL WARPING SHOULD BE SPACED AT INTERVALS OF ABOUT 10 FEET. THE DOWELED TRANSVERSE JOINTS INVESTIGATED WERE QUITE EFFECTIVE IN RELIEVING STRESSES CAUSED BY EXPANSION, CONTRACTION, AND WARPING, BUT THEY WERE NOT PARTICULARLY EFFECTIVE IN CONTROLLING LOAD STRESSES NEAR THE JOINT EDGE. THE DOWEL- PLATE JOINT TESTED HAS MERIT AS A MEANS FOR LOAD TRANSFER, THOUGH IT OFFERED MORE RESISTANCE TO EXPANSION AND CONTRACTION THAN IS DESIRABLE. AGGREGATE INTERLOCK AS IT OCCURS IN WEAKENED-PLANED JOINTS CANNOT BE DEPENDED UPON TO CONTROL LOAD STRESSES. EVEN WHEN JOINTS OF THIS TYPE ARE HELD CLOSELY BY BONDED STEEL BARS THERE IS WIDE VARIATION IN THE CRITICAL STRESS VALUE CAUSED BY A GIVEN LOAD. IT APPEARS NECESSARY, THEREFORE, TO PROVIDE INDEPENDANT MEANS FOR LOAD TRANSFER IN PLANE-OF-WEAKNESS JOINTS. TONGUE-AND-GROOVE JOINTS HELD TOGETHER BY BONDED STEEL BARS WERE FOUND TO BE THE MOST STRUCTURALLY EFFICIENT OF ANY OF THE JOINTS STUDIED.