NONLINEAER FINITE ELEMENE ANALYSIS OF REINFORCED CONCRETE DOMES WITH PRECAST RIBS

Abstract

The investigation described here deals with the non linear analysis of reinforced concrete or composite hemispherical domes of monolithically or partially interconnected ribs , running in the meridional directions of the dome . A simplified three dimensional finite element model is developed in ANSYS package, it's analysis, which may be applied to three cases of hemispherical domes: unribbed, monolithic ribs, and composite ones. The eight –node SOLID65 brick element is used to model the concrete cover and the precast ribs, while the beam element BEAM188 is used to model the monolithic radial ribs. The steel reinforcing bars within the cover in the radial and hoop directions are modeled by the two nodded axial LINK8 element which is capable to undergo plastic deformation. The interfaces between the precast radial ribs and the abutting cover (in composite domes) are modeled by a system of LINK8 and COMBIN14 to account for shear transfer at those portions . Material non-linearity due to cracking and crushing of the concrete and yielding of the reinforcing steel bars are taken into consideration during the analysis. The current application included, initially, the analysis of unribbed hemispherical reinforce concrete domes (case 1) by the recent finite element model and by the membrane theory of shells. The two approaches have shown very high agreement in the membrane meridional and hoop normal stress values which were all within the 3.3% margin of difference. Application of the present numerical model to hemispherical ribbed domes of the two specified types(monolithic concrete and composite ones) has produced variations of the three orthogonal normal stresses in the Cartesian coordinate system and the vertical displacement along meridional path (from apex to base of dome) which are in prefect agreement with the logical structure behavior of such domes that is drawn from high structural inspection. IV A wide parametric study was performed to compare domes in the three cases to evaluate the quantitive effects of the main parameters in the aspects of geometry, constitutions and material properties. Numerical percentages of variation in values of the ultimate load and the vertical deflection at dome apex with variation of each of those parameters were computed from which fundamental guidelines for the structural design of such domes were established. The concluding remarks drawn from the present study has led to recommendations for supplementary investigations in this field including the numerical model, loads and structural system enhancement aspects.