Papers by Author: Sang Mook Han

Abstract: Using experimental study, major emphasis of the present study is to determine the influence of reinforcement ratio on structural behavior of the prestressed beams made of UHPCC in terms of first crack load, peak load, ductility, and load-deflection characteristics. A UHPCC mixing proportion was presented firstly. 8 rectangular beams of size 100x300x3000mm made of UHPCC were designed, fabricated and tested in this investigation. Influence of reinforcement ratio of load bearing capacity, deflection and crack pattern of beams were performed and analyzed. Based on experimental results, some conclusions were drawn.

Abstract: The purpose of this study was to reduce production costs for UHPFRC members by using a bundle of longitudinal reinforcement bars as a substitute for steel fiber. Experiments on the ductile behavior of Ultra High Performance Concrete (UHPC) rectangular beams with a combination of steel fiber and longitudinal reinforcement bars were performed.The volume fractions of steel fiber were 0%, 0.7%, 1%, 1.5%, 2%, and the reinforcement ratios of longitudinal reinforcement bars that promoted ductile behavior were 0.0036, 0.016, 0.029 and 0.036.Fifteen UHPC beams were made with the combination of these test factors. Both the steel fiber and the longitudinal reinforcement bars had the effect of induciing ductile behavior for UHPC structural members. The load-deflection relationship, the concrete stress variation and the crack pattern indicated the usefulness of the bundle of longitudinal bars that have a small diameter with close arrangement.

Abstract: To simplify the analysis, an elastic perfectly plastic stress-strain law was presented for UHPFRC. The post-cracking behavior was described by the average constant post-crack tensile strength. A strain parameter μ is proposed to evaluate the performance and efficiency of steel fibre reinforcement. 8 rectangular beams were tested in this investigation. Based on the proposed constitutive model, the full history of their flexural moment-curvature relationship for UHPFRC beams was calculated and compared with experimental data on prestressed UHPFRC beams. Good agreement between calculated strengths and experimental data was obtained.

Abstract: This paper presents a numerical simulation of quasi-brittle fracture in UHPFRC I-beam as a linear complementarity problem. Based on the investigation of Tin-Loi and Attard, the simulation of quasi-brittle fracture in concrete has been extended to model UHPFRC I-beam by including a tensile hardening. Fracture is simulated through a hardening-softening fracture constitutive law in tension and a softening fracture constitutive law in shear at the boundary nodes, with the material within the triangular unit remaining linear elastic. LCP is used to formulate the path-dependent hardening-softening behavior in non-holonomic rate form. The good matching of test results and numerical results indicates the effectivity of this method.

Abstract: Direct uniaxial tension test of ultra high performance cementitious composites I shape specimens have been investigated in this paper. A nonlinear analytical model based on continuum damage mechanics is developed to characterize tensile stress-strain constitutive response of UHPCC. Basic governing equations of damage evolution and material constitutive relation are established considering random damage which conforms to a modified Weibull type distribution proposed in this paper. Calculation suggests that Weibull distribution can describe damage evolution of UHPCC and predict the constitutive relation and damage evolution equation.

Abstract: An R-curve formula for ultra high performance cementitious composites is derived in this paper. The fracture mechanics based on R-curve is used to predict the load-deflection relation of ultra high performance cementitious composites. The reductions of stress intensity factor and CTOD by steel fiber reinforcement are assumed as conforming linear distribution along crack propagation. The effective numbers of steel fiber on unit area based uniform distribution is used here. Results of the theoretical predictions show a good agreement with test results of three point bending beam of UHPCC. The modified R-curve formula for UHPCC can be a reference for future study of fracture performances of UHPCC.

Abstract: This paper concerns the theoretical research of shear failure load of steel fiber reinforced ultra high performance cement composites (SFR-UHPCC) beam. Based on test investigation, an analytical model of prestressed SFR-UHPCC beam is constituted. Two formulae of ultimate failure load, i.e. the upper bound and the lower bound of shear loading capacity, all have been obtained according to the limit analysis of concrete plasticity. In the process of upper bound analysis, uniform distribution of steel fiber has been assumed, and virtual work induced by steel fiber has been divided into two parts, i.e. pulling-out virtual work and debonding virtual work. Five coefficients are introduced considering some defects. Twelve SFR-UHPCC beams with three kinds of shear span ratio i.e. 2.7, 5.6 and 8.5 are tested and compared with the results from the proposed equations.