A computer method for moment-curvature analysis of composite steel-concrete cross-sections of arbitrary shape

This paper presents a new computer method for moment-curvature analysis of arbitrary-shaped composite steel-concrete cross-sections that are subjected to biaxial bending and axial force. The complete moment-curvature diagrams are determined such that axial force and bending moment ratio is kept constant. A strain-driven algorithm has been developed, the solution of the nonlinear equilibrium equations is controlled by the assumed strain values in the most compressed point and by solving just two coupled nonlinear equations. Such an approach may be used to assess accurately the main features of the elasto-plastic behaviour of composite cross-sections: multiple yielding points associated to different materials, flexural and axial rigidity, moment-curvature relationship in pre and post-critical domain and curvature ductility detecting also unloaded regions of the cross-sections that may occur even under monotonically increasing of the total bending moment. Since the Jacobian’s of the resulted nonlinear system of equations is always positive definite the convergence stability is not sensitive to the initial/starting values of the iterative process and to the strain softening exhibited by the concrete in compression. By using a path integral technique on boundary of cross-section area, gradual spread of plasticity and residual stress distribution assumed for encased steel elements are accurately considered reducing also the computational time significantly. In order to illustrate the proposed method and its accuracy and efficiency, a computer program has been developed and used to study several representative examples. The numerical studies presented and comparisons made prove the effectiveness and time saving of the proposed method of analysis

Refined NSA approach for seismic assessment of regular RC frames

Nelinearni dinamički proračun s primjenom vremenskog zapisa, često vrlo dugo traje i nije praktičan. U radu se predlaže nova računalna metoda razvijena u okviru Eurokoda 8. Metoda se temelji na određivanju kapaciteta konstrukcije pomoću metode postupnog guranja, i seizmičkog zahtjeva primjenom nelinearnog dinamičkog proračuna s vremenskim zapisom za sustav s jednim stupnjem slobode. Posebno se razmatra utjecaj raspodjele horizontalnog opterećenja na određivanje kapaciteta, te utjecaj histereznih modela na odgovor sustava pri određivanju seizmičkog zahtjeva.The nonlinear time-history analysis is often a time-consuming and impractical procedure. A new computer method, developed in the framework of the Eurocode 8 is proposed in this paper. It is based on the determination of both structural capacity - using pushover analysis - and seismic demand - using nonlinear time-history analysis of a single-degree-of-freedom system. An emphasis is placed on the effect of different lateral load distribution on capacity determination, and on the effect of hysteretic models on the determination of seismic demand