Civil MDC

Concrete Shell Structures—Practice and Commentary ACI 334.1R-92 2

Concrete Shell Structures—Practice and Commentary ACI 334.1R-92


1.1.1 Concrete Shell Structures Thin shells—Curved or folded slabs whose thick-nesses are small compared to their other dimensions. They are characterized by their three-dimensional load-carryingbehavior, which is determined by their geometrical shape, their boundary conditions, and the nature of the applied load.Thin shells are usually bounded by supporting members and edge members.

1.1.2Auxiliary members—Ina broad sense, any memberlocated along the boundary of a shell or shell segment, witha capacity to stiffen the shell and distribute or carry load incomposite action with the shell. They are classified as follow sin accordance with established usage, although for certainshells a member may serve in a combination of capacities:

a)Supporting members—Beams, arches, trusses, diaphragms, etc., along the edges of thin shells thatserve both to support and to stiffen the thin shell.

b)Edge members—Beams, trusses, etc., along the edges ofthin shells that do not form part of the main supportingstructure, but serve to stiffen and act integrally, that is,in composite action with the thin shell to carry loads tothe supporting members.

c)Stiffening members—Ribsthat serve only to stiffen thethin shell or to control local deformations.

1.1.3Elastic analysis—Anystructural analysis based onelastic behavior and involving assumptions that are suitableto approximations of three-dimensional elastic behavior.Analyses based on the results of elastic model tests, whenconducted properly, are considered as valid elastic analyses.

With the increased use of thin shells has come an increasedunderstanding of their behavior through field observations,laboratory tests, and mathematical refinement of analyticprocedures. However, because of the wide range of geometrypossible with thin shells, the accumulated understanding isstill limited. For some thin shell systems, such as cylindricalbarrel shells, the design can be made with the same degree ofaccuracy as for conventional reinforced concrete construction.For other thin shell systems, such as those of doublecurvature, the design must be at times based on less-refinedanalyses in the same sense as the empirical design of flatplate floors. Therefore, it was felt desirable to divide thisreport into two parts.

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