This paper presents and assesses a new numerical framework for the nonlinear, inelastic analysis of two-dimensional (2D) vertical wood building systems that incorporate sheathed light-frame wood shear walls as seismic force-resisting system. The 2D building model is based on a sub-structuring approach that considers each floor diaphragm as a rigid body with three kinematic degrees-of-freedom (DOF). Each inter-storey shear wall assembly, including the floor diaphragms above and below, can then be simulated by a six-DOF sub-structure element with internal nonlinear DOF. The shear wall element takes into account deformations in the framing members, contact/ separation phenomena between framing members and diaphragms, anchoring equipment such as anchor bolts and hold-downs and all sheathing-to-framing connections. Corotational descriptions are used to solve for displacement fields that satisfy the equilibrium equations in the deformed configuration, accounting for geometric nonlinearity and P-Δ effects. To appraise the proposed numerical framework, the predictions of the numerical model are compared to experimental results from single and two-storey full-scale shear wall specimens. These examples demonstrate the capability of the numerical framework to simulate accurate load paths in the shear wall assemblies and successfully predict variations in strength, stiffness and energy dissipation characteristics of the seismic force-resisting system.
ANALYSIS OF THE DYNAMIC BEHAVIOR OF BASE ISOLATED STRUCTURES BY STATE-SPACE FORMULATION
The seismic behaviour of base isolated buildings is herein analysed by using an innovative mathematical formulation in the state space, that allows us to describe the dynamic response of structures in the case of non-classical damping. Particularly, the seismic response of base isolation with linear–viscous behaviour is herein investigated by studying the mode shapes, the frequencies and the modal participation factors, that are obtained by the proposed formulation varying the main design parameters. In such a manner, the effect of these parameters on the isolated structure behaviour as a whole is evident.
Seismic design methods of concentrically braced steel frames
SUMMARY – The work described here is addressed to the evaluation and the comparison of different seismic design methods of multistory steel frame structures with concentric braces. In particular, a multistory frame is designed through both the simplified method currently proposed by the recent code provisions (OPCM 3431, DM 24/01/2008, Eurocode 8 ) and an alternative simplified one, based on the partial contribution due to the brace under compression. The assessment of the seismic response of the two structures is then performed by means of static analyses, where the non-linearities of the geometry and of the materials are included, in order to compare the related seismic performances. In addition, the seismic response of the frame designed with the new method is assessed through non-linear dynamic analyses and incremental dynamic analyses, to particularly highlight the properties of the alternative adopted method, which permit to achieve less conservative solutions, more economical in terms of amount of material and characterized by more effective collapse mechanisms.
For this paper is available an extended abstract after the text in Italian
Optimal scaling of earthquake records for reproduction by shaking table with limited stroke
The paper presents an overview of a new originally developed quasi-optimal control algorithms for reproduction of earthquakes by shaking tables. As known, shaking tables are widely used for testing of structures, models or structural details subjected to earthquakes or other types of dynamic loadings. In order to obtain dynamic response of a tested model close to that of a real structure, the shaking table should reproduce real dynamic excitations with high accuracy. Moreover, the shaking table control algorithm should consider real restrains in the platform displacements. Changing the ground acceleration record by time scaling, like it is common in existing algorithms, yields undesired effect on the tested models dynamic behaviour. The originally developed approach, described in this paper, is based on optimal signals perturbation and filtering technique. It includes quasi-optimal spline approximation and further optimal smoothening of the dynamic loading signal, decreasing negative effects. Selecting the smoothening parameters is an adaptive procedure, performed by comparing the spectrum characteristics of the original and reproduced signals. The effectiveness of the proposed method is demonstrated by obtaining responses of multi-story structural models subjected to various seismic excitations. It is shown that the proposed algorithm is a very effective method for reproduction of real earthquakes by using shaking tables with limited stroke.
Il cambiamento di scala delle strutture per la verifica sismica su tavola vibrante: un telaio in c.a. progettato per carichi verticali
The work presented here is one of the fundamental phases of a research programme on seismic evaluation of existing buildings, funded by the Department of Civil Protection and developed at the European Centre for Training and Research in Earthquake Engineering (Eucentre). The present article contains a brief summary of the general theory on scaling: this concepts are then specialised for RC structures to be tested on shaking tables. These ideas are finally applied to the numerical model of the studied building and actually under testing on the Eucentre shaking table.
This paper is available in Italian only.
Strutture prefabbricate in c.a. in zona sismica: stato della pratica costruttiva italiana e principali problematiche di progettazione
The work presented here is the starting point of a two-year numerical and experimental research programme, funded by the Department of Civil Protection and developed at the European Centre for Training and Research in Earthquake Engineering (Eucentre), the main goal of which will be the evaluation of the seismic local and global response of RC precast structures. The present article concerns a preliminary overview of the main design issues following the recent development of the code requirements.
This paper is available in Italian only.