On the design of plates and stiffeners of rectangular industrial ducts

The internal pressure and the serviceability limit determine the plate thickness and the stiffener spacing associated with industrial duct,which are currently designed based on elastic large deflection plate theory. The first part of this paper establishes relations between internal pressure and stiffener spacing recognizing the partial yielding, which may result in an economical and efficient duct system. This investigation is based on finite element analysis of long plates made of elastic-plastic steel. Based on a parametric study, the paper presents design equations for industrial plates for three different design scenarios namely; 0%, 16.5% and 33% of through thickness yielding of the plate. The stiffeners are often wide flanged steel beam sections, where one flange is connected to the side panel and the other flange is unsupported. Under suction situation, the unconnected flange is in compression and the duct panel is in tension. Since the tension flange is connected to the remaining system, the duct panel and the web may provide a partial rotational restraint to the compression flange of the stiffeners, which is often not considered in the design. The second part of the paper establishes the bending capacity of such stiffeners. This investigation discovered that the stiffener web slenderness and the overall stiffener slenderness dominate the behavior and the capacity of stiffeners of industrial ducts. The paper establishes the ranges of parameters for different failure modes and it establishes the corresponding bending strengths of the stiffened steel panels. © 2013 Taylor & Francis Group, London, UK.