Baffles stiffener design

Conventional concrete structures, and prefabricated steel structures assembled on site and filled with concrete after placement are used in various structures. Precast concrete modules would also be used. Wide use of removable formwork is employed to limit steel exposure to potential corrosion. Prefabrication of reinforced rebar modules is extensively used. In some places mechanical rebar splices are used to reduce the weight of prefabricated modules. All of these techniques have been employed in previous nuclear power plant construction. Steel structures such as the air baffle, and the containment vessel are constructed of steel panels. Panels are made of stiffened steel or corrugated plate depending on availability and cost panels for the baffle are designed with thermal expansion of the containment vessel in mind. Future inspection and maintenance are taken into consideration. 

Baffles are frequently used in pressure vessels, either vertical or horizontal, to divide the interior volume into different compartments. These compartments may be used to segregate liquids or provide overflow weirs for the separation of liquids. Baffles may be stiffened or unstiffened. When welded across the entire cross section of the vessel, they must be checked that they are not unduly restricting the diametral expansion of the vessel. If the unrestrained radial expansion of the ve.ssel exceeds that of the baffle by more than Vie in. % in. on the diameter), then a flexible t) pe of connection between the vessel shell and the baffle should be utilized. Various flexible attachment designs are shov m within the procedure. 

The majority of baffles are flat and as a result are very inefficient from a strength standpoint. Deflection is the governing case for flat plates loaded on one side. Tire preference is to have unstiffened baffles, and they should always be the first choice. This will be acceptable for small baffles. However, lor larger baffles, as the baffle thickness becomes excessive, stiffeners offer a more economical design. Therefore stiffeners are frequently used to stiffen the baffle to prevent the thickness of the baffle from becoming e.xces-sive. The number, size, and spacing of stiffeners are dependent on the baffle thickness. selected. There is a continual trade-off between baffle thickness and stiffener parameters. 

The stiffeners themselves are designed next. A section of the baffle is assumed as acting with the stiffener and as contributing to the overall stiffness. This combined section is known as the composite stiffener. The composite section is checked for stress and deflection. Both vertical and horizontal stiffeners can be added as required. 

AT — differential temperature (design temperature minus 70°F), °F (Th = bending stress in baffle, psi bending stress in stiffener, psi A = radial expansion, in. 

If stiffeners are added, the first step is to find the maximum "a and b dimensions that vill meet the allowable deflection for a given panel size. This will establish the stiffener spacing for both horizontal and vertical stiffeners. The ultimate design is a balance between baffle thickness, stiffener spacing, and stiffener size. 

Side-to-side flow is provided by the segmental baffle arrangement of Fig. 10.5a. In the design shown, the baffles are made with a collar to provide a friction fit in the shell, are kept in place by spacer posts, and are fitted with an edge lip which not only stiffens the baffle but also provides a means of collecting a pool of dispersed liquid on... 

The design of a baffle with stiffeners is an iterative process. The procedure for the design of the stiffeners is first to divide the baffle into panel sections that are rigid enough to withstand the pressure applied on one side. Each individual panel is checked as a flat plate of the dimensions of the panel. The stiffeners are assumed to be strong enough to provide the necessary edge support for the panel. 

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