International Concrete Abstracts Portal

This paper reviews representative tests used to study the buckling of thin shell concrete structures of two basic types: roof shells and shell walls. Roof shells include spherical domes, cylindrical barrels, hyperbolic paraboloids, and elliptic para-boloids; and shell walls include cylindrical tanks, hyperbolic cooling towers, and torroidal cylinders. The major factors described for each test series are model materials and geometry, boundary conditions, loadings, measuring devices and interpretationsof results. The goal of all such tests is to insure that shell safety is not controlled by buckling.

The analytical and numerical techniques applicable to the determination of an estimate of the buckling strength of rein-forced concrete shell structures are discussed. A brief resume of the most appropriate methods is presented. Both bifurcation and nonlinear techniques are included in the review. Attention is not restricted to only mechanics approaches such as developed within the aerospace industry. Particular attention is focused on the numerical techniques that allow consideration of shell structure configurations that include supporting members such as are employed for roof or other architectural structures. For reinforced concrete shells an influence of material characteristics must play a dominant role in the establishment of the buckling load. Imperfection sensitivity and other aspects that have a significant impact on the buckling load for some shells of aerospace configurations and loadings do not contribute to a corre-sponding level.

The objectives of this review of the buckling of cooling tower shells are to survey available experimental results, to discuss various analytical and numerical approaches, and to evaluate current practice for buckling predictions in design. The paper focuses on the problem of stability of large, concrete hyperboloids subject to wind loadings. There exists only a small body of experimental results relevant to this problem. Three categories of analysis approach are identified and reviewed: (a) scaled-up wind tunnel tests, (b) methods based on axisymmetry, and (c) methods not based on axisymmetry. No single approach is universally accepted or used, and various views of structural modeling are discussed. For example, some designers and research-ers advocate a local buckling criterion as opposed to a global stability treatment. Some other differences include: bifurcation predictions as opposed to limit-point analyses, reduced shell theories to obtain lower bounds rather than full shell theories, and axisymmetric simplifications instead of full nonaxisymmetric methods. It appears that bifurcation calculations with well-verified methods can provide an acceptable estimate of wind-loaded hyperboloid buckling for routine design purposes. The prediction of buckling for the design of cooling tower shells could be improved by more experimental evidence for the verification and comparison of prediction methods.

A review of research activities directed to evaluating the onset of buckling of reinforced concrete folded plate stru-tures is presented. Guidelines and recommendations to the designer as to when buckling might be a problem and how to consider this in the design are also presented. The review includes a description of the development of methods of analysis and, for a limited application, specific formulas suitable for use with mini-computers. The validity of the analytical methods is discussed in view of a number of studies made on small, elastic models and tests on buckling of reinforced concrete plates. The results of the various studies, which were almost solely limited to prismatic structures, indicate local plate buckling, as opposed to lateral stability, is indeed a problem which should be considered for long-span structures. The present methods of analysis for buckling which consider the inelastic material response of concrete, are approximate but felt to be conservative.

The purpose of this paper is to present a state-of-the-art review of the stability of reinforced concrete domes and hyperbolic paraboloids aimed principally at presenting useful information to the designers of such shells. Analytical results, experimental results, and applications to design, together with appropriate references, will be reviewed and summarized for each of the following shell types: (1) spherical domes, (2) translational and other double curvature domes, (3) hyperbolic parab-loids, and (4) groin vaults. The effects of the following important parameters on the buckling of reinforced concrete shells are discussed: (1) geometric imperfections, (2) creep, (3) cracking of concrete and amounts of reinforcement, and (4) material non-linearity. A design approach is suggested to account for these effects. A number of examples of existing large span reinforced concrete shells are cited to illustrate the range of dimensions which have been used successfully in the past.