Browsing by Author "Salim, Wanjala Ramadhani"

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    First order Elasto-plastic limit analysis of structural plane frames: numerical approach.
    (University of Dar es Salaam, 1994) Salim, Wanjala Ramadhani
    A numerical technique for first order elasto-plastic limit analysis of structural plane frame subjected to combined bending moment and axial force actions is presented. The technique takes into account the influence of axial forces on the ultimate load carrying capacity of the structure. It also allows for reversal of plastic hinge formation. The technique is based on direct stiffness method of elastic analysis. The algorithm of the technique has been programmed in a software named Elasto Plastic Limit Analysis of plane Frames (EPLAF). The program written in standard FORTRAN - 77 code gives the location and sequence of formation of plastic hinges plus the corresponding load factors at which the hinges are formed, collapse loads, nodal displacements, member actions, support reactions and plastic hinge rotations. The applicability of the procedure has been demonstrated through two case studies. The numerical solutions of the two case studies are compared to those obtained in the traditional simple elasto-plastic analysis which neglects the effects of axial forces on the ultimate load carrying capacity of the structure. The numerical solutions obtained in the two case studies showed that when the amount of axial force in the elements of a frame exceed 15 % of the respective element plastic axial force, the conventional first order elasto-plastic limit analysis method over estimates the load carrying capacity of structures, grossly mispredicts the bending moment distributions and moment-normal force interaction behaviour of the structure at fully plastic stage and gives results which violate the plastic condition of the fundamental conditions of simple plastic theory. Further, the new technique increased the rate of structure stiffness degradation and altered the number, location and sequence of formation of plastic hinges and the type of collapse mechanism mode when axial forces were large.