Hot-rolled Ribbed Steel Bar Mechanical Connection And Anchorage Performance Of Basic Research

At present, how to exert adequately the materials potential properties and realize reduce quantity's purpose is the hotspot for Materials Science and Engineering. Therefore, on the one hand, it is important to improve materials' essence properties, e.g. mechanical properties, on the other hand it is can't be ignored that the usage properties of materials are to the greatest extent exerted on using condition when the materials potential properties are utilized.In this paper, based on need of rebars' mechanical connection, the distribution of microstructure and mechanical properties along radius of Φ25 V-N micro-alloyed hot rolled rebar and Φ32 Φ25 tempcore rebar were investigated by means of mechanical properties test and microstructure examination. The difference of anchorage properties between the symmetrical and unsymmetrical transverse ribbed rebar was studied considering improving materials' usage and anchorage properties by pull-out test.The experimental results show that: (l)The microstructure of cross section in V-N micro-alloyed rebar was ferrite and pearlite, grain size of ferrite and volume fraction of pearlite along radius of rebar are almost unchangeable. The microstructure of longitudinal section in rebar was banded ferrite and pearlite and the ferrite band density reduced gradually along radius of rebar. The microstructure along radius of tempcore rebar was tempered martensite, bainite, ferrite and pearlite. (2) Mechanical properties along radius of Φ25V-N micro-alloyed hot rolled rebar were almost unchangeable, the difference of strength was less than 20 MPa, but the distribution of strength along radius of tempcore rebar reduced gradually, the maximal difference was 115MPa and 60MPa for the yield strength and the tensile strength respectively. (3) The nominal carrying capacity reduced about 0.58% after peeling off the rib of Φ25V-N micro-alloyed hot rolled rebar. But for the tempcore rebar, the nominal carrying capacity reduction values were 9.2% and 5.76% for the Φ25 and Φ32 rebar respectively. (4) The bond-anchoring strength of rebar (whether transverse ribs distributed symmetrically or not) increased with increase in concrete strength when they had the same of anchorage length. (5) Whether ribs distributed symmetrically or not, the pull-out strength increased with increase in the anchorage lengthwhen concrete had the same strength. (6) The anchorage properties between the symmetrical and unsymmetrical ribbed rebar had no obvious difference.Applying on the mechanical connection of rebars, the cold-rolled straight screw connection technology and none cold-rolled straight screw connection technology should be used on O25V-N micro-alloyed hot rolled rebar and tempcore rebar respectively. Cold-rolled portion straight screw connection technology should be adopted for 3)25 rebar produced by other technology because the nominal carrying capacity should reduce about 0.58% —9.2% after peeling off the ribs.Anchorage properties of rebar had less relations with distribute of ribs (whether ribs distributed symmetrically or not). So the anchorage properties wouldn't be affected when the rebars with symmetrical ribs were utilized to improve the anti-seismic performance and it will promote the using of the rebar with symmetrical ribs.