International Concrete Abstracts Portal

Shell structures mobilize geometry to activate both the membrane and the flexural internal force systems to efficiently support any distributed loads applied to those structures. Based primarily on their efficiency, these geometric structural forms are employed in a number of industrial applications such as pressure vessels, containment structures, etc., where the principal function of the structure is to contain or sustain a particular loading environment. This selection is especially true when substantial loads such as high internal pressures are involved. The shell structures selected for these applications are simple forms, most frequently combinations of various shells of revolution such as cylinders, cones, spheres, and (for the pressure vessels) the torospherical or ellipsoidal shapes, because of their ability to respond to most loads by a membrane state over the major area of the shell. Edge effects are confined to a narrow zone near the edge or around a zone of discontinuity that may be present as a result of geometry changes. In addition, shell forms contain a number of functional, economic and aesthetic virtues that make them logical choices for applications to building structures. For repetitive structures and for those needing long, column-free spans, reinforced concrete shell roofs have often been chosen. Furthermore, these structures provide a clean inner surface, often in a pleasant geometric shape. They have good fire-resistance qualities. By proper orientation or shape selection, glass areas can be placed so that natural lighting can be directed onto all or nearly all the covered ground plan.

Umbrella and gable configurations are two of the most popular hyperbolic parabolic geometries. Early design of those shells was accomplished through the use of membrane theory. This determinant theory predicted overall behavior of these shells as a double cantilever beam for the inverted umbrella and as a simple beam for the gable shell. As long as the dimensions of these shells were small enough, this theory was adequate. However, with increased spans and with flatter applications, the theory proves to be inadequate. Bending solutions achieved by a finite element analysis prove to be necessary. Results from such analysis demonstrate the influence of several design parameters. The major role played by the dead weight of the edge and ridge beams is demonstrated.

A review of the state of the art for the membrane analysis of hyperbolic parabolic (HP) shells is presented. Membrane solutions using simple statics are given for HP shells having square, rectangular, or parallelogram shapes in plan and subjected only to uniform vertical loading over the horizontal projection of the shell. Statics of shell-edge beam systems are discussed for saddle shells, inverted umbrellas, gable shells, and shells on two supports. Membrane stresses for general loadings on parallelogram-shaped HP shells obtained using a differential equation approach are described. Stress transformation formulas are given that can be used to find principal membrane stresses in the shell and boundary stresses to be transmitted to the edge members. Membrane stresses in HP shells having an arbitrary quadrilateral shape are discussed and procedures for determining them are discussed.

The equations for a bending theory of shallow shells are specialized to the case of the hyperbolic paraboloid shell. The nature of the analytic solutions to these equations that have been achieved for this class of shells is described. Such analytical solutions involve boundary conditions that depart significantly from those present in real shell applications. Types of numerical approximate solutions present as alternatives are noted and the details of one of these, the finite element method, are described. The importance of the dead weight of perimeter or support beams is noted, demanding a bending solution with real support conditions. Some representative solutions are included as examples.

A review of the state of the art for the analysis and design of HP saddle shells is presented. Design considerations and basic load carrying mechanisms are discussed. Results of a detailed parameter study are presented for loadings on a saddle shell with tips free. These were carried out with a linear finite element analysis computer program that includes membrane and bending action in the shell and edge beams. Results are given and compared for shell membrane stresses and bending moments, edge beam stress resultants, and vertical displacements for the following parameters: 1) loading-shell DL + LL, edge beam DL, and shell and edge beam loads; 2) deep shell and shallow shell; and 3) uniform edge beam cross-section and tapered edge beam cross section. Additional brief discussions are given on the following effects: 1) rise-span ratio; 2) type of vertical supporting system; 3) edge beam eccentricity; 4) horizontal thrust supporting system; 5) prestressing; and 6) inelastic behavior and ultimate strength.