Effects of Properties and Simulations for Dry Granular Soils on Buckling Loads of Portal Frames

Salah R. Al Zaidee; Teghreed H. Ibrahim; Ehab G. Al Hasany

Salah R. Al Zaidee Lecturer, Civil Eng. Dept. College of Engineering, University of Baghdad
Teghreed H. Ibrahim Assistance lecturer, Civil Eng. Dept. College of Engineering, University of Baghdad
Ehab G. Al Hasany M. Sc. Student, Civil Eng. Dept., College of Engineering, University of Baghdad

Keywords: Buckling loads, portal steel frame, finite element analysis, Winkler's model, simulation of soil mass

Abstract

This paper aims to use different finite element models to show how different soil conditions and different soil simulations can affect buckling loads for portal frames. All soils are assumed granular and dry while spread footing is assumed for foundation system.
Two soil simulations have been adopted. In the first simulation, Winkler's foundations is used where continuous soil media has been replaced with uncoupled springs. Shear forces between adjacent soil prisms and the corresponding stiffness are both lost in this simulation. In the second model, soil mass under footing have been isolated and simulated with brick elements.
Soil elastic modulus and Poisson ratio have been estimated based on correlations with the SPT value.
Results indicate that, the critical loads determined with hinge simulation of spread footing are underestimated compared with the more accurate value of soil mass simulation, while critical loads estimated from fixed supports simulation are close to that of soil mass simulation even for compressible soils with SPT value in the range of 10.
Critical loads determined from Winkler soil simulation are close to those loads of soil mass simulation with a difference not greater than 7% and with correlation coefficient of 0.99. Two logarithmic functions, have been developed based on nonlinear regression analyses.