Stability analysis of continuum skeletal fibre matrix systems.

New technologies for the manufacturing of glass reinforced plastics (G.R.P.) with possible outlets into the construction industry have broadened the capabilities of this material as well as the structural efficiency in design and construction. The pultrusion technique, although not a new production process, has not been used greatly in the structural field in spite of its enhanced strength and stiffness values, over the hand-lay production method, due to the unidirectional arrangement of the fibres. However, if a folded plate continuum G.R.P. structure of low modulus material requires to be stiffened by a compatible material, pultruded sections could be used to form a skeletal/continuum system with a much improved performance, the present work has investigated G.R.P. skeletal/continuum systems which are connected only at nodal points. In the present work the pultruded sections have a glass/polyester ratio of 65-35% by weight whilst the continuum component is manufactured by the hand lay-up method using chopped strand mat glass laminates with polyester resin with a glass/polyester ratio of 30-70% by weight. The theoretical analysis was undertaken by the finite element technique which provided a linear and a stability analyses of the skeletal/continuum G.R.P. space structures. The analytical procedure involved the combination of the stiffnesses of two types of elements in one overall stiffness matrix, these elements are the line element representing a two ended skeletal member in space of six degrees of freedom per node; three translational and three rotational (deltax, deltay, deltaz, thetax, thetay, thetaz) given by Livesley (9) and a rectangular plate element of four nodes and compatible degrees of freedom per node with the line element developed by Scordelis (15). The stability analysis was based on small displacements and the distinct bifurcation point related non-linearly only with the level of axial stresses in the skeletal members and the continuum. Small scale models were manufactured from perspex materials and tested; these were undertaken mainly to verify the theoretical analysis. The analytical solutions were then used to undertake parameter studies. Applications to G. R. P. composites included flat plates stiffened by pultruded members and a prototype vee sectioned composite roof system. All G. R. P. models were tested to failure to investigate experimentally the buckling characteristics of the composite systems; the results were compared with the buckling loads predicted theoretically. It was concluded that the theoretical method satisfactorily predicted the linear behaviour of skeletal/continuum systems as well as the stability behaviour of such systems in predicting the buckling loads of these composites