Characteristics of Grade 60 and Grade 72.5 Re-bars in Pakistan
In Pakistan, quality assurance of re-bars is practically non-existent and there is no generally accepted testing method for testing of re-bars. Steel re-bars of Grade 60 are exclusively used in Pakistan; however production of high strength re-bars has recently started. In this study, thirty samples of steel re-bars of Grade 60 and thirty samples of Grade 72.5 were tested using ASTM standard testing protocol to obtain the stress-strain curves and comparisons were made between the experimental results of Grade 60 and Grade 72.5 re-bars. It can be concluded that Grade 72.5 steel shows less deformation capacity as compared to Grade 60 steel. For Grade 60 re-bars, the yield strengths of all individual re-bars were much higher than the prescribed minimum yield strength, i.e. 60 ksi. For the Grade 72.5 rebars, about 50 % of the re-bars did not reach the prescribed minimum yield strength of 72.5 ksi. The experimental curves were then compared with an idealized stress-strain curve developed by using a fractional equation. It is recommended that instead of producing Grade 72.5 ksi reinforcing bars, the traditional ASTM Grade 75 reinforcing bars be produced.
Complete Triaxial Stress-Strain Curves for Concrete
A method to predict the ascending and the descending parts of stress-strain curve of concrete subjected to triaxial compressive stresses is presented. The proposed analytical stress-strain relationship depends on the values of the three principal stresses and strains at the ultimate compressive strength. A criterion to predict the triaxial compressive strength is proposed, which is sensitive to all three stress invariants. To enable predictions of the post-peak stress-strain relation, experiments were conducted on concrete confined by steel tube. Concretes with different compressve strengths were confined by steel tubes of varying thicknesses. The predicted stress-strain curves compared favorably with the available experimental data on uniaxial, biaxial, and triaxial compression.
Arc flash hazard assessment in the mining industry
When it comes to electrical safety in the workplace, arc flash has become the most prominent topic over the past decade. The Occupational Safety and Health Administration (OSHA, including state chapters) is the only government body that recognizes NFPA-70E, Standard for Electrical Safety in the Workplace. However, OSHA does not have jurisdiction in mining operations. Electrical safety for the metal and nonmetal surface mining industry is covered by the Code of Federal Regulations (CFR) Title 30, Part 56, Subpart K (Electricity). The Mine Safety and Health Administration (MSHA) is responsible for enforcing electrical safety in mining operations. CFR Title 30 does not reference personal protective equipment (PPE) to protect electrical workers against arc flash hazards. This paper provides maintenance and safety personnel in surface Metal/Nonmetal mining operations with a step by step guide to implementing an electrical safety program that meets the requirements of MSHA, CFR Title 30 and NFPA-70E.