Creep Deformation of a Composite Beam Subjected to Combined Axial and Bending Loads

The theoretical analysis presented here considers the general case of the creep deformation of a composite beam subjected to combined axial and bending loads. The beam may be considered to consist of two components bonded together or of numerous continuous fibres discretely dispersed in a matrix. The equations may also be reduced to the particular case of a beam composed of just one material so that present day problems involving combined loads may be analysed.

Though elastic analyses have shown the advantages of a composite beam, it was noted that improvements in strength are further accentuated under creep loading conditions since the deformation is then generally more stress sensitive. For a composite member, it was found that even small percentages of reinforcing material substantially reduced the axial strain, curvature and stresses. Under the action of a bending moment, the composite was even more efficient when the reinforcement was incorporated in the outermost fibres of the beam. The effects of thermal strains were noted especially in the primary creep stages and their importance under possible load and/or temperature cycling conditions discussed.

Although an iterative procedure, involving the use of a computer, is required to solve the analytical equations, it is shown that values for the strain and curvature may be approximately determined by use of the rule of mixtures approach.