Experimental Study on Steel Fiber Reinforced UHPC Rectangular Beams Without Conventional Steel Reinforcement

The torsional performance of the steel fiber reinforced UHPC rectangular beams without conventional reinforcement is studied, and the influence of steel fiber patterns on the pure torsional behavior of the beam of such type is analyzed. Four UHPC rectangular beam specimens were prepared for tests, including one with short straight steel fibers, one with long, circular and straight steel fibers, and one with end-hooked steel fibers, the corresponding fiber lengths are 13，20 and 13 mm, respectively, with a diameter of 0. 2 mm and mixing content of 2%. A set of loading equipment was designed for the pure torsional performance tests of the specimens. With the test results，multiple items were analyzed，including the torsional moment-torsional rate curve, cracking strength, ultimate torsional moment, torsional moment-strain curve and crack patterns. The expression of the torsional resistance of the UHPC rectangular beam was derived. The calculated results were compared with the test results for verification. It is shown that after adding steel fibers, the damage of UHPC specimen transforms from brittle failure to ductile failure, and the cracking strength and torsional moment are significantly improved, even with a maximum improvement of 45. 6% and 100.6%，respectively. When the mixing content keeps constant, the influence of steel fiber types on the cracking torsional moment and torsional rate of the UHPC beam without reinforcement is negligible, but still significant on the ultimate torsional moment and torsional rate. The torsional resistance and ductility of specimens mixed with either the end-hooked steel fibers or the long, circular and straight steel fibers are superior to those of the specimen mixed with short, circular and straight fibers. Compared with the specimen without steel fibers, the UHPC beam with steel fibers has got higher principal tensile and compressive strains under pure torsional forces, indicating that steel fibers can effectively bridge the UHPC matrix. The average ratio of test and calculated torsional resistance of the specimens is 0.93，with a standard deviation of 0. 09. The proposed torsional resistance expression demonstrates satisfactory calculation accuracy. For the UHPC components without reinforcement or with a small amount of reinforcement, the end-hooked steel fibers and long circular steel fibers are suggested，which are favorable to improve the torsional ductility and post-cracking load bearing capacity of the structure. © 2023 Wuhan Bridge Research Institute. All rights reserved.