Laboratory study on mechanical properties of mine pre-stressed steel bars

With the advantages of high pretension， high elongation and good bearing capability， the pre-stressed steel bars have been more and more widely used in roadway support engineering of coal mines.In order to further explore the mechanical properties of pre-stressed steel bars used in coal mine， tensile tests， metallographic analysis， impact toughness test， pre-stress loss test， eccentric load test， installation resistance test and performance of matching locks of pre-stressed steel bar were carried out in the laboratory.The results show that the ultimate load-bearing capacity of 20 mm diameter pre-stressed steel bar is 422 kN，which is an increase of 176% compared to the 20 mm diameter HRB335 anchor bar， and the average elongation after breaking is 13.3%，which is 2.4 times of the anchor cable， and the cup-cone fracture formed after steel bar breaks.The impact absorption energy before and after breaking of the steel bar is 46.0 J and 23.3 J respectively；the structure of the material is tempered sorbite， and the grain size is 9.5 and 8.5， which belongs to ultra-fine grain size.When the bearing force length is 1 230 mm and 1 500 mm，the pre-stress loss is 38.37%，and 36.74%.As the load increases，the preload loss rate decreases；As the steel bar increases，the preload loss rate of the steel rod decreases； When the eccentric load angles are 5°， 10°， 15°， 20°， and 25°， the ultimate bearing capacity decreases are 18.3%，22.5%，26.4%，26.9%，and 27.5%；When drilling in 28 mm，the average maximum propulsion resistances of steel rods with diameters of 18 mm and 20 mm are 179 N and 453 N， respectively.The difference is 274 N，but both are easier to advance.The average carrying capacity of the pre-stressed steel bar anchorage is 398.2 kN， and the Rockwell hardness of the anchor ring and clamp are 27.78 and 58.39 respectively，which meets the requirements of national standard and mechanical properties of steel bar materials.