The objective of the research programme has been to investigate the effects of pre-buckling low frequency inelastic cyclic hysteresis upon a range of imperfection sensitive circular hollow section struts. The programme has involved experimental and theoretical studies and computer graphics are widely employed throughout. The subject matter is introduced from a variety of perspectives, phenomenological, historical, theoretical and experimental in Chapter 1, together with an appreciation of therole of the digital computer within the research programme. Experimental factors are initially presented in Chapter 2 whilst the formal testing programme is described in Chapter 3. Original findings are definitively set out in Sections 3.3 and 3.7 wherein the concept of the 'cyclic step' is first introduced, theremaining sections in the chapter providing the necessary supporting data. Theoretical studies are reported in Chapter 4 with the novel moment-thrust-curvature modelling described in Sections 4.2 and 4.3 being of central importance. This modelling enables the formulation of a predictive cyclic strut system effectivelyrequiring of the end user the solution of only a pair of simultaneous equations and yet capable of providing data trends consistent with the experimental findings. Design interpretation together with an overview of the experimental and theoretical studies and their interrelationshipare set out in Chapter 5. A practical design procedure oriented about the effect of a pre-buckling cyclic action phase upon otherwise static strut performance is delineated and anappropriate design chart is provided. Conclusions are drawn with respect to the primary researchfindings in Chapter 6 wherein suggestions are also made regarding possible further studies. An Appendix is included providing the bibliography, nomenclature and respective published work; selected supporting documentation is also presented.