Bruno Calderoni

Static vs. Modal Analysis of Asymmetric Buildings: Effectiveness of Dynamic Eccentricity Formulations

The use of modal analysis appears necessary in order to reduce both displacement demand under weak seismic events and ductility demand under strong earthquakes. Static analysis can be effective only if used with proper values of additional eccentricities. To overcome the inaccuracy of the code formulations, the authors propose a simple procedure that gives the exact values of these eccentricities and discuss the influence of the main parameters that govern the structural behavior. They also point out the difficulty in evaluating some parameters (stiffness radius of gyration, structural eccentricity) in the case of multistory buildings and discuss the validity of simplified formulations proposed to overcome this problem. The effectiveness of static analysis, applied to three-dimensional multistory structures with properly evaluated corrective eccentricities, is analyzed with reference both to regularly asymmetric multistory schemes and to an actual irregularly asymmetric structure (the main building of the Faculty of Engineering at the University of Catania, Italy).

Statistical analysis of seismic behaviour of steel frames: Influence of overstrength

Abstract The influence of structural overstrength on the seismic behaviour of steel structures and on the assessment of the q factor has been studied by means of a suitable procedure, based on the selection of a significant set of homogeneous historical earthquakes and on the statistical analysis of the dynamic inelastic response of the structure to these accelerograms. Six schemes of steel frames, proportioned according to different design criteria and therefore with different amounts and distribution of overstrength, have been analysed. Three values of the behaviour factor have been considered for each one. The large number of results, obtained by more than 4800 dynamic analyses, has been elaborated in a statistical way, providing damage level indexes which express the probability of yielding and collapse and the plastic level reached, both for the single section and the whole frame. Interesting conclusions have been obtained. In particular, the effectiveness of the capacity design criteria in reducing the probability of collapse of frames has been highlighted. Similar good results have been obtained even when the same overstrength is given to all columns, without any particular attention to its distribution, while the increment of the beam resistance was not favourable in any case. Moreover, a very large improvement in safety has been obtained with just a little increase in the column strength over that supplied by the application of the capacity design criterion. The global behaviour appears thus connected to a new parameter, herein defined and named “effective behaviour factor”, which takes into account the mean overstrength both of beams and columns

Non-Destructive Tests and Bending Tests on Chestnut Structural Timber

In the context of a more wide research study for in situ mechanical identification of ancient timber structures by non-destructive techniques, the paper illustrates the experimental activity developed on structural elements made of old chestnut timber, 4x4x76 cm size: 24 squared specimens were extracted by six elements in actual dimensions, already used in a previous tests campaign. Non-destructive (ND: hygrometric, sclerometric and resistographic) and destructive (D: bending) tests were performed, the latter according to UNI EN 408 (2004) standard, in order to assess the mechanical properties and the collapse mechanisms of chestnut timber. Data gathered are presented in detail and, NDT-DT correlations, obtained through a linear regression approach, are provided to predict wood density, strength and modulus of elasticity of the tested members.

Ultimate Behaviour Of R.c. Frames Under Seismic Loads: Influence Of Design Parameters

A procedure for the analysis of the ultimate behaviour of reinforced concrete (R.C.) frames under seismic loads is defined in detail and it is applied to four schemes, each one designed many times with different behaviour factors and design criteria. The results obtained confirm the effectiveness of the adopted procedure, pointing out the influence of the intensity of the seismic event on the structure. The possibility of relating the entity of damage and the probability of failure to the design parameters allows a proper evaluation of the influence of these parameters, giving the national authorities a powerful tool particularly useful in order to define the optimal value of the boxed coefficients to be inserted in Eurocode 8.