Effect of geometrical properties on strength of externally prestressed steel–concrete composite beams

A parametric study was carried out to investigate the structural behaviour of composite steel-concrete T-beams under different prestressing conditions. The studied parameters include different cases of loading, tendon profiles, beam spans, initial prestressing levels and different dimensions of steel sections and concrete deck. The studied beams were modelled by the finite-element software Ansys. The effect of three geometrical parameters was investigated for three different tendon profiles. It was found that straight tendon profiles are more appropriate for beams under distributed loads, whereas a draped tendon profile is more convenient for beams under concentrated loads. In addition, the ratio of the tension flange area to the compression flange area is the most effective geometrical parameter on the ultimate resistance of the studied prestressed beams. For instance, increasing this ratio from 1 to 3 resulted in increasing the additional resistance of the beam due to prestressing from 15·4 to 46·1%. For composite beams, the presence of the concrete slab prevented the lateral-torsional buckling and accordingly minimised the effect of the span. Moreover, increasing the slab thickness-to-width ratio resulted in enhancing the average increase in beam strength from 13·5 to 19·9%

An imported enteric fever caused by a quinolone-resistant Salmonella typhi

Recent reports indicate that nalidixic acid susceptibility correlates well with the clinical outcome of patients with Salmonella Typhi infection treated with quinolones. We report a case of enteric fever caused by S Typhi in which the isolate was resistant to nalidixic acid, but showed in vitro susceptibility to ciprofloxacin. Following treatment with ciprofloxacin, the clinical outcome was not satisfactory and the patient had a relapse. However, after using a higher dose of ciprofloxacin, the patient was cured. We recommend that all Salmonella systemic infections resistant to nalidixic acid with in vitro but decreased susceptibility to fluoroquinolones be treated with other antibiotics like third-generation cephalosporins or azithromycin. These patients should be closely followed up and observed for further relapse