Abstract

The use of shells in foundation structures over traditional forms has grown steadily since their inception in the early nineteen-fifties. Shell foundations outperform conventional flat footings and are reputable performers especially when heavy super–structural loads are to be transmitted to weak bearing soil. The geotechnical performance of shells in an elastic continuum concerns their bearing capacities and settlement behaviour, whose study has been trailing behind that of their structural performance. Bringing contact pressures closer to uniformity at the soil–shell structure interface is essential in developing a viable behavioural response under vertically concentric and monotonic loading conditions. This study encapsulates the development of new shell foundation geometries employing shell inversion under such loading conditions. Experimental investigation involves validation of the numerical phase in a comparative study following a two–dimensional analysis of shell models using commercially available geotechnical software with finite element analysis. New inverted triangular footings embedded in sand composed of ultra–high performance iShell Mix concrete using fiber–reinforced polymeric (FRP) microfibers are analyzed. A parametric analysis examines key sensitivity elements including shell angle and shell thickness in granular soil for both upright shells and their inverted counterpart. Linearly–elastic behaviour of concrete material is assumed while soil media is modeled under nonlinear elastic perfectly–plastic conditions following the Mohr–Coulomb yield criterion for loose, medium and dense sand states. Theoretical modeling was developed to generate inverted shell bearing capacity factors to predict ultimate bearing capacities of the shell footings. Simulation efforts scrutinized reveal comparable performance with bearing capacity increase of 3 – 5% for the inverted shells over upright shell models and notable improvements of 42 – 45% over conventional flat footings. The developed models investigated represent forefront configurations of superior performance signifying that shells in foundations be highly regarded and fully exploited whenever feasible.

KEYWORDS: shell, contact pressure, bearing capacity, settlement, finite element analysis