School of Civil, Environmental and Mining Engineering

Postgraduate research

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Current and completed research by our postgraduate students.

Contact

Hossein Bineshian

Phone: (+61 8) 7122 2217


Start date

Jul 2011

Submission date

Oct 2014

Hossein Bineshian

Hossein Bineshian profile photo

Thesis

Effects of stress non-uniformity on failure mechanisms of concrete/rocks

Summary

Mechanical response of concrete to tension and compression including pre and post- peak portions are studied and therefore evaluation of the effect of bending moment on failure mechanisms of concrete and rocks using strain measurements has been presented. An extensive series of uniaxial/triaxial compression/tension tests are conducted on concrete using: spherical upper and lower platens (Case 1, most reliable case), spherical upper and fixed lower platens (Case 2), and fixed upper and lower platens (Case 3). The external factors producing the bending moment during compression are assessed via FEA in ABAQUS. Its accuracy is confirmed using energy plots and sensitivity analyses by 99.84%. Two methods for strain measurements including DIC technique using VIC-3D and conventional method using polyester foil strain gauges are used and the results are compared. Longitudinal strain, strain rate, displacement, velocity, principal strain angle, and in-plane rotation for full FOV are calculated. Measured strain is 1.02 times the observed values. Standard deviation and relative error for measured strain equals 0.00001 and 2.38% respectively. In uniaxial compression, no dominant fracture pattern is recognised for the Case 1. For the Cases 2 and 3 the shear fracture is recognised in 60 and 90% of incidents, which means that an external factor affected the failure process. Investigations conducted on principal strain angle and longitudinal strain and strain rate demonstrated a deviation from vertical axis for principal strain, which is an evidence for appearing the heterogeneous strains that can be a result of existence of an eccentric load that creates the bending moment. It is concluded that the presence of the bending moment in compression, is unavoidable, while all external and known factors are eliminated from the test condition. The analytical approach based on the mathematical function of Bineshian criterion (2000) led to development of a new failure criterion, which considers bending moment generated during compression. It can provide linear and nonlinear envelopes capable of describing most compression and tension test data that provides credible estimations of these values similar to those determined in laboratory. Its relative scatter is decreasing inversely proportional to the strength. New CDP constitutive model’s parameters for CQD-G class concrete is developed, which is applicable in numerical modelling of failure and post-failure responses of concrete and especially in design of high strength concrete/rock structures. CQD (Concrete Quality Designation) is an applicable empirical classification that is introduced in this research.

Why my research is important

This research is important in terms of prediction of the bending moment effect on failure mechanisms of concrete and rocks in related researches, laboratorial works, and practical projects in the field of geotechnical/geomechanical engineering. Knowing this effect on the failure mechanisms of the aforesaid materials can provide an essential findings in design of underground and surface structures in rocks including large openings, caverns, tunnels, penstocks, slopes, dams abutments, dam foundations, and mines, concrete structures, and infrastructures like concrete dams, foundations, and towers. It also provides an improved practical strain measurements technique, which optimises the time-cost of the practical projects.

Proposed failure criterion for concrete/rocks/coals together with the engineering classification developed for concrete (CQD) can be used in design of civil and mining geotechnical and concrete structures.

Funding

  • DET CRC

Observed value against predicted value by proposed strength criterion for concrete specimens with CQD-E and UCS > 130 MPa.
 

School of Civil, Environmental and Mining Engineering

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Last updated:
Thursday, 19 September, 2013 11:39 AM

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