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An attempt has been made to develop efficient and versatile displacement type finite element computer programs which contain general constitutive relations, a family of isoparametric elements, a variety of nonlinear solution algorithms and systematic convergence tests in order to break some of the 'non-linear and cost barriers'. A unified finite element formulation for geometrically and physically nonlinear problems in matrix form has been developed and the isoparametric elements are shown to be highly versatile in both Lagrangian and Eulerian forms. Several alternative nonlinear solution algorithms have been studied and amongst them the newly developed 'alpha constant stiffness method' of accelerated iteration has been shown to possess computer economy. This new method has enabled the first solutions of 'strain softening and non-associated flow laws' to be obtained. Indeed the method has been extended for cracking and large deformation problems. The 'residual force' calculated from direct numerical integration has been used to check the equilibrium at every stage. This routine has now become an essential ingredient of all the nonlinear solution algorithms. The explicit forms of several elastic and elasticplastic stress-strain relationships for small and large strain cases have been presented. A useful form of an angular invariant has enabled several plasticity forms such as Tresca, Von Mises, Mohr-Coulomb, Drucker-Prager and several other yield and potential functions to be included into one program. The elastic-plastic relationships are also generalised to include non-associated flow rule and kinematic hardening rule. S-2 Comparative studies of various solution algorithms, element types, plasticity forms and reduced integration order have been made. For many cases parabolic elements with reduced 2-point integration rule give optimum results. In addition the preliminary investigations of complex material behaviour and a floating airport study based on the analysis of axisymmetric plate on elastic foundation are given. As an off-shoot an attempt has been made to find the order of magnitude of limiting value of deflection for von Karman plate theory. The finite deformation theory expressions which are usually available in tensor notation are redexived in matrix form. Finally the thesis reflects the power of numerical integration techniques and isoparametric elements for nonlinear analysis.

The main goal of this dissertation is to develop simple and accurate models for thetransient monotonic and cyclic deformation behaviour of bitumen and asphalt mixes. The first part of this dissertation is concerned with an experimental and theoreticalinvestigation of the deformation behaviour of bitumen. The second part is concernedwith the deformation of bituminous mixes. A brief description of the main literature on composition, structure and mechanicalbehaviour of pure and polymer-modified bitumens is presented in chapter 2.An extensive experimental study comprising of monotonic, continuous cyclic andpulse loading tensile experiments for two pure and two polymer-modified bitumensis detailed in chapter 3. Based on these experimental findings a simple constitutivephenomenological model including the effects of rate dependent recovery is proposedfor bitumen. Comparisons between experiments and model predictions are presentedwith good agreement. The spherical indentation behaviour of bitumen under monotonic and cyclic loadingconditions is studied in chapter 4. A simple extension to the power-law indentationmodel of Bower et al. (1993) is proposed for bitumen with good agreement withexperimental results. Chapter 5 presents a review of the main research on continuum and micro-mechanicalmodels for the deformation behaviour of bituminous mixes. An extensive experimental investigation of the monotonic and cyclic compressivedeformation behaviour of bituminous mixes with varying volume fractions of aggregate,for uniaxial and triaxial conditions, is described in chapters 6 and 7, respectively. An extension to the phenomenological model proposed for bitumen is proposed forthese mixes. The predictions of the model are compared with the experimental resultswith good agreement. In chapter 8, a micro-mechanical constitutive model for the deformation behaviourof asphalt is assembled using micro-mechanical theories and experimental observations. The model predictions are compared with uniaxial and triaxial experimentalresults, showing reasonably good agreement. Finally, conclusions and recommendations for future work are presented in chapter 9.

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