The catastrophic earthquake which struck the city of L'Aquila at the beginning of April 2009, caused several damages at University of L’Aquila buildings [1]. Serious level of damage occurred at masonry structures, including partial collapses; instead the reinforced concrete structures performed generally with sufficient resistance also in the presence of large deformations. Among these edifices the ones of the Engineering Faculty have suffered particularly for seismic induced large structural displacements and accelerations which have brought them out of order due to the failure of non-structural elements (infills, false ceilings, door and window frames), the breakage of wiring and piping systems and the destruction of furniture and machineries. In particular, among the three recently-built buildings of the campus, erected in the early 90’s, the so-called “Edifice A” presents the most critical damage scenario, which needs a significant rehabilitating intervention. The structural behaviour of the building, composed by seven independent substructures, is object of an intensive investigation to achieve an adequate level of knowledge. Therefore, a series of coherent steps have been followed such as: exhaustive structural and geotechnical survey able to clearly define site and damage conditions, material characterization through destructive and non-destructive test campaigns, dynamic testing and identification to qualify the overall structural dynamic behaviour [2], finite element model updating and seismic structural analysis.

The present paper aims to synthesize the lessons learned comparing the immediate damage scenario and its evolution during the aftershocks, to the reproduction of the seismic nonlinear structural response with both nonlinear pushover analysis and direct time-integration of motion equation under a significant example of seismic accelerations. A considerable number of simulated response spectrum compatible time-histories has been used to perform non linear dynamic analysis. Different pushover procedures has been considered, as the conventional (first mode load distribution, uniform distribution) and modal pushover method (MPA). The constitutive nonlinearities have been considered defining lumped and fiber models, conveniently placed in the beam, column and shear wall elements.

The irregularity of each substructures, in terms of geometry, stiffness and weight distribution, allows to carry out a fruitful evaluation in terms of predicted ultimate displacement capacity obtained by the different analyses. Afterwards, the capacity curves obtained by the nonlinear pushover analysis were compared with the spectrum demand to evaluate the adequacy of structural performance following the newest design recommendations. The time histories displacement of some significant nodes further than the sequence of the plastic hinges activation will be analyzed to confirm the substructures vulnerabilities shown during the seismic event. The variety of substructure characteristics represents an attractive case of study to interpret different damage scenarios through nonlinear numerical analyses.

The entire knowledge acquired along the process have permitted the design of an innovative retrofitting intervention to enhance the seismic structural performance of the Edifice “A” of the Engineering Faculty of the University of L’Aquila.

Bibliografia

[1]  Ceci AM, Contento A, Fanale L, Galeota D, Gattulli V, Lepidi M, Potenza F (2010). Structural performance of the historic and modern buildings of the University of L’Aquila during the seismic events of April 2009. Engineering Structures vol 32(7), pp.1899-1924.

[2]  Ceci AM, Fanale L, Galeota D, Gattulli V, Lepidi M, Potenza F (2010). Seismic retrofitting o the recently-built edifices of the Engineering Faculty of L’Aquila. Proc. of Sustainable development strategies for constructions in Europe and China, Rome, Italy, 6 April.