FRP-confined concrete in circular sections: Review and assessment of stress-strain models

Abstract The effect of material microstructure on crack growth and force–deformation behaviour under uniaxial tension has been investigated in an extensive numerical study. A simple beam lattice model has been used to estimate the effect of strength and stiffness contrast, and particle density in a three-phase particle composite as found in concrete. The results from these explicit three-phase analyses have been compared to the outcome of simulations where the effects of microstructure were mimicked by assigning random strength values drawn from a Weibull or Gauss distribution to a regular triangular lattice. The results indicate that strength contrast is more important than stiffness contrast, and that global behaviour is largely governed by percolation of the weakest material phase. This behaviour was obvious from the three-phase analyses. The results from the different Weibull simulations resemble the mode of failure observed in the more realistic three-phase particle overlay. Bridging is a salient phenomenon observed in these analyses. In contrast the (symmetric) Gauss distribution is not appropriate. Although a large variety in force–deformation diagrams can be simulated, depending on the two parameters in the Gauss distribution and the lattice geometry, the failure mode along a single straight crack does not resemble the real fracture behaviour of three-phase composites like concrete. It is not recommended to use statistical strength distributions for simulating the behaviour of three-phase particle composites. Furthermore, the results clearly indicate that the force–deformation diagram cannot be used as a single indicator for judging the accuracy of a model for the fracture behaviour of materials. The crack mechanisms and the ensuing crack patterns are considered a salient element in such judgements. The model simulations can be applied as a guideline to design real three-phase composites. In particular optimization of tensile strength of the composite by selecting the correct amount of particles seems possible.

Fractures mechanisms in particle composites: Statistical aspects in lattice type analysis

Influence of glass fibers on mechanical and durability performance of concrete with recycled aggregates

Combined effects of supplementary cementitious materials (silica fume, GGBS, fly ash and rice husk ash) and steel fiber on the hardened properties of recycled aggregate concrete

In this paper, the partial replacement of volcanic pumice powder (VPP) was investigated for use as a supplementary cementitious material. High-strength concrete (HSC) was prepared using two sets of VPP (10% and 20%) incorporated with three sets of polypropylene fiber (PF) (0.20%, 0.35%, and 0.50%) to produce different concrete mixtures. Several tests, including slump, compressive strength, indirect tensile strength, flexural strength, water absorption, initial surface absorption, and sorptivity, were conducted to evaluate HSC performance. Results showed the prepared specimens with 10% cement replacement with VPP and 0.20% PF content indicated a slight increase in compressive strength compared with the control concrete at later ages. Indirect tensile and flexural strengths were optimized at 10% VPP replacement with 0.50% PF content. Furthermore, adding PFs to mixes increased indirect tensile and flexural strength but decreased slump. The sorptivity test indicated low water soaking due to VPP content in the mixes compared with the control mix (HSC); it declined as the replacement of VPP increased. The different standard tests on mixes depicted favorable results and good prospects for the inclusion of VPP in HSC structures.

Durability and strength characteristics of high-strength concrete incorporated with volcanic pumice powder and polypropylene fibers

Performance evaluation of polypropylene fibre reinforced recycled aggregate concrete

A probability based model for the erosive wear of concrete by sediment bearing water

A three-dimensional discrete element modelling capability for concrete based on rigid particles of arbitrary shape and size has been developed. The novel particle generation algorithm allows control of particle size, angularity and flakiness. General rigid body kinematics including finite rotations is accounted for, and an explicit time integration algorithm that conserves energy and momentum is implemented. An efficient contact algorithm with several features to increase the efficiency of the contact computations has been developed. This enables the gravity packing problem for arbitrary shaped particles to be solved in reasonable run time. The proposed procedure is used to generate assemblies of concrete specimens of various sizes that are homogeneous and isotropic in the bulk, and can capture the wall effect due to the formwork. The calibrated specimens are seen to be capable of accurately capturing experimentally observed macro stress strain response and failure patterns. The influence of aggregate shape on texture formation in the packed specimen, and on macro strength and failure patterns in hardened concrete, is demonstrated and is seen to be consistent with experimental results.

A discrete element implementation for concrete: particle generation, contact calculations, packing under gravity and modeling material response

This study investigates the localization of deformation and factors that influence the spread of damage zones in cylindrical concrete columns confined with fiber-reinforced polymer (FRP) wraps. The findings indicate that the effect of confining pressure on failure loads is strongly nonlinear with the confinement pressure required to exceed a threshold value to arrest shear band growth and lead to a significant gain in failure loads. The gain in column strength was influenced by the nature of the interfacial bond between concrete and FRP. Assuming a tied interface may significantly overestimate the confining pressure acting on the concrete. For a more realistic cohesively bonded interface, the confining pressure depends on the bond stiffness in addition to the properties of the FRP. Results of numerical analyses indicate that the confinement pressure must exceed a certain threshold value to arrest the growth of localization. Similarly small values of bond stiffness led to little or no increase in the failure loads.

Localized failure in fiber-reinforced polymer-wrapped cylindrical concrete columns

The effect of damage at the cohesive concrete—laminate interface on failure of FRP-reinforced concrete columns is considered. Analytical expressions, obtained for the shear stress at the interfacia...

Ramkrishna Dandapat

Papers

Performance evaluation of polypropylene fibre reinforced recycled aggregate concrete

A probability based model for the erosive wear of concrete by sediment bearing water

A discrete element implementation for concrete: particle generation, contact calculations, packing under gravity and modeling material response

Localized failure in fiber-reinforced polymer-wrapped cylindrical concrete columns

Failure modes for FRP wrapped cylindrical concrete columns