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 STRESS-STRAIN CURVE OF CONCRETE AND NONLINEAR DESIGN
Difficulties of experimentally obtaining the descending part of the stress-strain curve of concrete in uniaxial compression and methods of overcoming these difficulties are described. The influence of testing parameters on the stress-strain curves are presented. Based on the experimentally observed stress-strain relationship, an analytical model was developed to predict the moment-curvature relationships of reinforced concrete sections. These moment-curvature relationships are compared with some available experimental data obtained and with those obtained by two other analytical models.
Pasteurella haemolytica serotype 1 colonization of the nasal passages of virus-infected calves.
Nasal passages of calves with a virus-induced respiratory tract disease became colonized by Pasteurella haemolytica serotype 1 after they were inoculated intranasally with P haemolytica. Inoculation with infectious bovine rhinotracheitis virus caused a more severe clinical illness and resulted in a greater degree of colonization with P haemolytica than developed after inoculation with parainfluenza-3 virus. Nasal passages of parainfluenza-3 virus-inoculated calves were colonized to a greater degree with P haemolytica than were those of healthy, nonstressed calves. Calves were susceptible to P haemolytica colonization during or shortly after virus-induced illness, even though they had been previously exposed to P haemolytica and had serum antibody and nasal secretion antibody to P haemolytica.