Inverse Calculation Of The Stress-Crack Width Relation Of UHPC And Its Application

Ultra High Performance Concrete(UHPC)is a new type of cement-based composite material with ultra-high strength and toughness.Due to its superior mechanical properties,it's used in marine engineering,bridge construction,and defense facilities.With its wide application of UHPC in engineering structure,the stress-crack width relation plays a crucial role in the design,bearing prediction and fracture analysis of structures.In this paper,the tensile mechanical properties of UHPC with different fine fiber content were studied.The cracking process of UHPC notched beam was studied by three-point bending test and digital image correlation method.The fictitious crack model(FCM)and fracture toughness criterionwas used to analyze the process of crack propagation,and the expressions of the stress intensity factor and crack width of the UHPC notched beam were derived.Based on this,a calculation program was compiled to inversely calculate the the multi-linear stress-crack width relation of UHPC.Finally,the load-crack width relation of UHPC beam was obtained by applying the multi-linear stress-crack width relation,then it was compared with that of experiment.The main work of this paper is as follows:(1)The initial cracking strength and tensile strength of UHPC increase with the increase of the volume of steel fiber.When the fiber volume content is higher than1%,the UHPC exhibits the characteristics of strain hardening and multiple cracking after cracking.The higher the volume content of steel fiber,the higher the fracture toughness,the stronger the crack resistance,the slower the crack propagation rate,and the better the ability to hinder crack propagation.However,the fiber volume content has little effect on the relationship of UHPC notched beam.(2)The fracture toughness,crack propagation rate,the crack length-crack open displacement relation,and the load-crack length relation of UHPC is obtained from three-point bending test of UHPC notched beam;The load will increase firstly and then decrease with the increases of crack open displacement and crack extension length;The crack will always maintain the triangular shape in the cracking process of UHPC notch beam.(3)According to the expression of the stress intensity factor and crack width ofthe UHPC notch beam,the load and the crack propagation length relation,the initial cracking strength and the fracture toughness of the UHPC,the multi-linear stress-crack width relation was obtained the self-programming procedure with determination of the value of the crack gap.(4)The load-crack width relation of UHPC beam at three-point bending was analyzed by the multi-linear stress-crack width relation.The Curve characteristics and initial crack load and crack width at ultimate load are consistent with the experimental results while the ultimate load is slightly higher than the experimental result.