Effects of creep and shrinkage on the behavior of reinforced concrete gable roof hyperbolic-paraboloids
Gallegos-Cazares, Sergio
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https://hdl.handle.net/2142/21605
Description
Title
Effects of creep and shrinkage on the behavior of reinforced concrete gable roof hyperbolic-paraboloids
Author(s)
Gallegos-Cazares, Sergio
Issue Date
1989
Doctoral Committee Chair(s)
Schnobrich, William C.
Department of Study
Civil and Environmental Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
Shell structures achieve a substantial contribution to their strength from geometry. Likewise, then as a corollary, some shells, will experience significant changes in their strength as a consequence of changes in their geometry that develope in response to loads. The special characteristics of concrete, as an aging viscoelastic material, allow the increase of deflections in time under constant load; in addition, concrete shrinks when drying, and consequently, stress redistributions due to geometric changes take place. It therefore follows that reinforced concrete shells built in certain configurations may experience problems due to time deformations.
One class of shells which apparently has experienced more than its share of such problems is the shallow hyperbolic parabola. Several roof shells built in this configuration have suffered significant structural failure from five months to as long as fifteen years after their being placed in service.
In this investigation, a general finite element program is extended to consider time dependent and time independent characteristics of concrete in shell-beam structures. Cracking, concrete compressive nonlinearity, steel nonlinearity, and concrete-steel interaction are considered in the time independent model, while aging, creep and shrinkage are included in the time dependent one.
With the model implemented, a series of studies are developed considering the structural effect of several parameters on the time dependent response of gabled roofs. Among the parameters considered, the manner of constraint in the support, and the size and position of the crown beams are important. Decrease in the load carrying capacity level considering time dependent effects has been observed with a observed final strength of only 50% to 75% of that without any time variation, displacements are increased four to eight times from the time independent ones, and large stress redistributions have been found to occur with a shift in the load carrying mechanisms from membrane to flexural. Some apparently unimportant parameters like the crown beam positioning with respect to the shell have been found to have an important role in the structural response. Design considerations emerging from the numerical results are highlighted in an effort of improve our design criteria basis for this kind of structures.
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