Seminar - Alessandro Zona - Nonlinear analysis of externally prestressed steel-concrete composite beams

Monday 2 August 2010, 4.00 pm - 5.00 pm
Civil Engineering Lecture Theatre 1

Dr Alessandro Zona
University of Camerino, Italy

Abstract:
The analysis of externally prestressed beams involves some difficulties as external tendons interact with the beam at anchorages and deviators only and tendon-deviator relative slips are not prevented. The local strain of the tendon depends on the global deformation of the whole beam-tendon structural system. At the ultimate state the prestressed system undergoes significant deflections, the tendon traction increases and the beam-tendon relative position between two consecutive deviators might change considerably. The tendon traction at failure controls the ultimate capacity of the structure and a global nonlinear analysis of the whole beam-tendon system is required. In order to provide an effective model for geometric and material nonlinear analysis up to collapse of externally prestressed beams, a finite element model recently developed is presented. Differently from existing methods starting from the linear theory and then including the eccentricity variation of the tendon, the proposed analytical model is based on a nonlinear kinematical theory so that all geometric nonlinearities are included. A reduced formulation is then derived on the basis of the theory of small strains and moderate rotations. Numerically simulated response results are compared to available experimental tests. Numerical studies on steel-concrete composite girders focused on various behavioural aspects are also illustrated. In addition to the general finite element formulation, a simplified approach is presented. The simplified method reduces the analysis from the global structure level to the section level, allowing the calculation of the stress increment in the tendon and consequently the evaluation of the flexural strength without performing a nonlinear analysis of the entire beam-tendon structural system. The method is based on the observation that beams with the same structural configuration, tendon path, and loading, have a similar spatial distribution of strain at collapse. Applications to simply supported beams with common tendon configurations show that the results provided by the proposed simplified method are a good approximation of the results obtained by the general nonlinear finite element analysis.

Biography
Alessandro Zona, is an Assistant Professor of Structural Engineering at the University of Camerino, Italy, since 2005. Received his five-year degree in Civil Engineering in 1999 and his Ph.D. in Structural Engineering in 2003, both from the University of Ancona, Italy. In 2003 and 2004 served as post-doctoral researcher at the Department of Structural Engineering, University of California, San Diego, USA. His main research interests involve: nonlinear behaviour of structures and computational structural mechanics; steel and composite structures; design and management of bridges; design of innovative structural systems in earthquake prone areas. Recipient of the 2009 Moisseiff Award from the American Society of Civil Engineers for his research on the seismic response of steel-concrete composite frames. Teaches steel structures, reinforced concrete structures, structural problems in heritage buildings.