Papers by Keyword: Stress-Strain Relationship

Abstract: This paper presents an experimental investigation on the influence of specimen slenderness on axial compressive behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs). A total of 18 aramid FRP- (AFRP) confined high-strength concrete (HSC) specimens with circular cross-sections were tested. Specimens with height-to-diameter ratios of 1, 2, 3 and 5 were manufactured and tested, with all specimens maintaining a nominal diameter of 150 mm. The results indicate that specimens with an H/D of 1 exhibit significantly higher strength and strain enhancements compared to specimens with H/D ratios of 2 to 5. The influence of slenderness on specimens with H/D ratios between 2 and 5 was found to be significant in regards to axial strain enhancement, with a decrease observed as specimen slenderness increased. On the other hand, the influence of slenderness on axial strength enhancement of specimens with H/D ratios between 2 and 5 was found to be negligible.

Abstract: The axial compressive stress-strain relationship of concrete reflects its basic mechanical performance, which is important in analyzing the performance of materials, especially in the analyzing of the elastic modulus, ductility and carrying capacity. In order to study the mechanical properties of polymer-modified concrete and steel fiber reinforced polymer concrete, a comparative study of the compressive stress-strain relationship of polymer-modified concrete and steel fiber reinforced polymer concrete was carried out, the complete compressive stress-strain curves were obtained, and the influence of polymer and steel fiber on concrete elastic modulus and compressive ductility was also studied. It is demonstrated that the compressive ductility index of steel fiber reinforced polymer concrete can reach 7.39 which is greater than that of polymer-modified concrete with the same ingredients. The results also show that steel fiber reinforced polymer concrete is better than both polymer-modified concrete and steel fiber reinforced concrete.

Abstract: A mechanical behavior of solid waste during foundation pit excavation is discussed on the base of the in-situ monitoring results of earth pressure and field measured data in solid waste. During excavation, the soil strength increases, which is mostly because of the variances of characteristics of soil in unloading state. Measurement of earth pressure is less than computation, and the value gradually decreases during excavation. In the end, it tends to be stable or slightly higher than the minimum. Compared with soft soil, the change is not only related to the deformation but also the change of soil property, especially, the influence of fiber to the shear strength of solid waste. By analyzing changing characteristics of earth pressure in solid waste, from the surface of earth within 0m~5m, experience value of lateral earth pressure coefficient is 0.35 during excavation and 0.25 after excavation, and within 5m~10m, the value is 0.55 during excavation and 0.45 after excavation.The conclusions will provide the reference for future similar projects.

Abstract: The Stress-Strain Relationship of Materials can only be Obtained by Experimental Testing, and it is an Important Relationship Needed to Calculate the Plastic Deformation of the Materials. in this Paper, the Stress-Strain Relationships of Sintered Tungsten Powders and Swaged Tungsten Bars were Measured by Upsetting Tests on Gleeble1500, and the Relationships were Described in Four Dimensions by MatlabÔ which Displays the Relationships more Comprehensively and Clearly and Makes them Easy to be Understood and Compared with each other.

Abstract: Confinement by fiber reinforced polymer (FRP) wraps can significantly enhance strength and ductility of concrete. Although various models exist for envelope curves of concrete confined by transverse reinforcement and FRP, only a few simple models represent the hysteretic behavior of the confined concrete; therefore, development of stress–strain model of unloading and reloading paths for confined concrete is needed. In this paper, an experimental and numerical investigation for describing the cyclic stress–strain behavior of lateral ties and FRP confined polyolefin fibre reinforced concrete (FRPCFRC) prisms under repeated axial compressive loading is presented. The study focuses on the effect of repeated unloading and reloading cycles on confined concrete prisms. The combined effect of spacing of lateral ties, FRP wraps and volume fraction of polyolefin fibres was studied both experimentally and numerically from the point of deformability characteristics of concrete under repeated loading as loading, unloading and reloading.The envelope curve is derived from the results of uniaxial, monotonic, compression loading tests on specimens. It explicitly accounts for the effects of lateral tie spacing of 145mm spacing and 75mm spacing, single layer of woven roving(GFRP) and polyolefin fibres of volume fractions 0.7% and 1.2% on concrete prisms of size 150 ×150 ×300 mm were investigated. The behaviour was also simulated in finite element numerical model in ANSYS software, with a view to analyzing FRPCFRC prisms under repeated loading. This analysis accounts for energy dissipation through hysteretic behavior, stiffness degradation as damage progresses, and degree of confinement. It was observed from hysteretic behavior that for increased confinement by FRP wraps and addition of polyolefin fibres the degradation of strength and stiffness reduces significantly.

Abstract: This paper mainly concerns the non-linear strength characteristics of the loess. A series of consolidated undrained triaxial tests(CU test) and consolidated drained triaxial tests (CD test) of normal consolidation and over consolidation loess specimens are carried out by using the normal triaxial apparatus of strain control. The stress-strain relationship curves and strength characteristics of loess are investigated and analyzed. The results show that the stress-strain relationship obtained by CU tests appears strain softening, while the stress-strain relationship for CD tests appears strain hardening. Different failure modes have different stress-strain relationships. Furthermore, the results also show that the peak strength, residual strength and residual strength ratio change with the different confining pressure. Based on the triaxial shear tests of normal consolidated loess, the influences of over-consolidated loess on the stress-strain relationships and strength characteristic are discussed. Several conclusions obtained in this paper can be referenced for the loess experimental study.

Abstract: Although various models exist for envelope curves of concrete confined by transverse reinforcement, only a few simple models represent the hysteretic behavior of the confined concrete; therefore, development of stress–strain model of unloading and reloading paths for confined concrete is needed. In this paper, an experimental and numerical investigation for describing the cyclic stress–strain behavior of lateral ties confined and polyolefin fibre reinforced concrete (CPFRC) prisms under repeated axial compressive loading is presented. The study focuses on the effect of repeated unloading and reloading cycles on confined concrete prisms. The combined effect of spacing of lateral ties and volume fraction of polyolefin fibres was studied both experimentally and numerically from the point of deformability characteristics of concrete under repeated loading as loading, unloading and reloading.The envelope curve is derived from the results of uniaxial, monotonic, compression loading tests specimens. It explicitly accounts for the effects of lateral tie spacing of 145mm spacing and 75mm spacing and polyolefin fibres of volume fractions 0.7% and 1.2% on concrete prisms of size 150 ×150 ×300 mm were investigated. The behaviour is implemented in the finite element program in ANSYS software, with a view to analyzing CPFRC prisms under repeated loading. This analysis accounts for energy dissipation through hysteretic behavior, stiffness degradation as damage progresses, and degree of confinement. It was observed from hysteretic behavior that for increased polyolefin fibres volume fractions the degradation of strength and stiffness reduces significantly.

Abstract: In this investigation, the combined confinement effect of spacing of lateral ties, volume fraction of polyolefin fibres and fibre reinforced polymer(FRP) wraps was studied both experimentally and analytically from the point of deformability characteristics of concrete for seismic resistance. Low modulus synthetic fibers such as polyolefin based fibers, it is shown that polyolefin fibers with sufficient tensile strength can successfully enhance the mechanical properties of concrete. The mechanism of delaying and arresting the progressive internal cracking by the fibres can be made use in passive confinement of concrete. In this study the confinement effectiveness of GFRP wraps of single and double layer and polyolefin fibres of volume fractions 0.7% and 0.9% in addition to lateral ties of spacing 145mm and 75mm on concrete prisms of size 150 ×150 ×300 mm were investigated. Such concrete is termed as FRP confined fiber reinforced concrete(FRPCFRC).This paper presents an analytical model(profile) for predicting the constitutive behaviour of FRPCFRC based on the experimental and analytical results. A total of thirty nine prisms of size 150 ×150 ×300 mm were cast and tested under strain control rate of loading. The results of the testing demonstrate the behavioral differences between FRP confined concrete and FRP confined FRC and the ability of the synthetic macro fiber to be used as secondary reinforcement in performance based seismic resistance applications.

Abstract: In this investigation, the combined effect of spacing of lateral ties and volume fraction of polyolefin fibres was studied both experimentally and analytically from the point of deformability characteristics of concrete. Low modulus synthetic fibers such as polyolefin based fibers, it is shown that polyolefin fibers with sufficient tensile strength can successfully enhance the mechanical properties of concrete. The mechanism of delaying and arresting the progressive internal cracking from transition zone to the matrix by the fibres can be made use in passive confinement of concrete. Such concrete was termed as polyolefin fiber reinforced concrete (PFRC). In this study the confinement effectiveness of polyolefin fibres of volume fractions 0.3%,0.5%,0.7%,0.9% and 1.2% in addition to lateral ties of spacing 290mm, 145mm and 75mm on concrete prisms of size 150 ×150 ×300 mm were investigated. Such concrete is termed as confined polyolefin fiber reinforced concrete (CPFRC).This paper presents an analytical model(profile) for predicting the constitutive behaviour of CPFRC based on the experimental and analytical results. A total of seventy two prisms of size 150 ×150 ×300 mm were cast and tested under strain control rate of loading. The increase in strength and strain of CPFRC were used in formulating the constitutive relation. The results of the testing demonstrate the behavioral differences between plain and CPFRC and the ability of the synthetic macro fiber to be used as secondary reinforcement in seismic resistance applications.

Abstract: Based on the consolidated undrained triaxial test of soft clay, a formula for computing pore water pressure is developed, by using of the critical state theory of volume strain and the characteristic normalization of soft clay. It is shown that the new proposed formula is reasonable to reveal the nonlinear stress-strain relationship and the dilatancy characteristics of soft clay. With the comparison between the pore water pressure simulation results by the new formula and the experimental data, it is shown that the simulation values agree well with the experimental data. Meanwhile, based on the failure criterion, a formula for the critical pore water pressure is proposed. It is shown that the new formula is reasonable to simulate the critical pore water pressure. It is very useful to predict the foundation stability.