Finite Element Modeling of Cyclic Behavior of a Reinforced Concrete Chimney Section Sami
In this study, a numerical model was presented to simulate the experimental behavior obtained for a reinforced concrete chimney section. The purpose of the previous experimental investigation conducted for the chimney section was to evaluate the effect of large openings on the cyclic response in order to reveal the performance of such structures under seismic loads. A detailed finite element model of the chimney section was constructed and all of the reinforcements of the chimney were directly taken into account by line element representations. The volume of the concrete chimney shell was modeled with hexahedral elements. A bi-linear material model was used for the reinforcements. A crucial step in the finite element approach was to employ a constitutive material model that took the multi-axial state of stress and confinement effects in concrete into account. The Winfrith concrete material model of the commercial LS-Dyna structural code was chosen for the shell of the chimney section. Comparisons of the results of the finite element study with the experimental measurements showed a good agreement for the base moment-displacement response and crack formations around the opening regions of the chimney section.
The Cyclic Behaviour of Reinforced Concrete Chimney Sections with and without Openings
The most vulnerable feature of most existing tall reinforced concrete chimneys when subject to severe earthquake excitation is the relative weakness of the sections around the openings near the chimney base. This paper documents an experimental study undertaken to investigate the cyclic behaviour of typical chimney sections with openings orientated to be bending critical and shear critical and the results are compared with previous tests with no openings. Significantly, no such cyclic tests have been previously been completed. The experimental results presented include; failure mode, over-strength factor, ultimate curvature, available ductility, hysteretic behaviour and strain distribution and the results are compared with some predictive analytical section models and design guidelines. The research indicated that chimney sections with openings were not brittle, but were significantly less ductile than sections without openings. The paper is relevant for both assessing existing chimney stacks and for the design of new chimneys in the vicinity of openings.
Earthquake response of tall reinforced concrete chimneys
The results from an experimental program have been used to develop a non-linear dynamic analysis procedure for evaluating the inelastic response of tall reinforced concrete chimney structures. The procedure is used to study the inelastic response of ten chimneys, ranging in height from 115 m to 301 m subject to earthquake excitation. Based on the study, a series of code design recommendations have been prepared and incorporated into the 2001 CICIND code to encourage reliance on the development of ductility in reinforced concrete chimneys and to prevent the formation of brittle failure modes. The basis for the selection of a structural response factor of R=2 which halves the seismic design forces is presented. The design recommendations result in both improved performance and cost savings of up to 20% compared with designs undertaken with the 1998 ACI307 and 1998 CICIND codes.