Massimiliano Lazzari

Non-linear dynamic analysis of cable-suspended structures subjected to wind actions

Abstract The numerical analysis of the response of wind-loaded flexible structures is presented. Initially the modeling and simulation of wind velocity are studied, by considering stationary, multivariate stochastic process, according to its prescribed cross-spectral density matrix. In the second part of the paper, geometrically non-linear structures subjected to wind loads are investigated, by means of a finite element approach. One test example is presented to show the reliability of the numerical procedure to solve geometrically non-linear problem in dynamic field. Finally, the study of a real structure characterized by an initial pre-tension layer subject to wind action is carried out.

Dynamic behavior of a tensegrity system subjected to follower wind loading

Abstract The aim of this paper is to present a possible develop-line for the study of large lightweight roof structures by non-linear geometric analysis, under the dynamic effects of the turbulent action of the wind, that can be applied into the classical engineering applications. In particular the paper deals with the study of tensegrity systems, that can be defined as pattern that results when push (struts) and pull (tendons) have a win–win relationship with each other. The pull is continuous and the push is discontinuous. The continuous pull is balanced by the discontinuous push producing an integrity of tension–compression. Static and dynamic analyses of the wind action effects on one example of such tensegrity system, i.e. the roof over the La Plata stadium, Argentina, have been performed by using the geometrically non-linear FE procedure named “Loki”. The wind loads are simulated as deformation-dependent forces. Both experimental data and numerical results available from the roof designers, have permitted to control the reliability of the proposed mathematical model.

Optimal design of seismic retrofitting of RC frames with eccentric steel bracing

This paper focuses on optimal design for dissipative steel bracing in seismic retrofitting of gravity load designed RC frame buildings. An optimized iterative force/strength-based design procedure is presented, for simultaneous yielding of bracing of all storeys, in order to induce an global damage mechanism in the building which maximizes the hysteretic damping effect. The procedure complies with the capacity design rule, whereby the bracing system enters the plastic range before the existing RC frame. The iterative design procedure of the system is applied here to a regular RC shear frame, with various design behavior factors.

Seismic improvement of slender masonry tower by using hysteretic devices and partial prestressing technique

An innovative system for seismic improvement of slender masonry towers by using hysteretic devices and partial prestressing technique was developed and applied to a case study. The proposed technique consists in a low level of prestressing of the upper part of the tower in order to localize in the un-prestressed lower part of the tower, i.e. a limited zone near the basement, the vertical displacements due to the cracking of masonry under seismic action. The positioning of dissipative devices, such as the Buckling-Restrained Axial Dampers, across the localization zone allows a significant contribution in terms of damping for hysteretic dissipation. The main effect of such an intervention is the reduction of the seismic demand to the tower and consequently the reduction of the top displacement as well as of the level of damage of the masonry. Both numerical analyses and experimental tests on a scale model of a Venetian bell tower were carried out showing the efficiency and reliability of the proposed technique.

F.E. Analysis of Montreal Stadium Roof Under Variable Loading Conditions

The drastic reduction in the ratio of permanent weight to variable load makes lightweight structures particularly sensitive to the effects of wind and snow. The dynamic nature of wind action can cause oscillations and deformations of such amplitude that they jeopardize the function of the roof and, in the worst cases, its structural stability. On the other hand, the static effect of snow represents an extremely heavy load for this type of structure, even reaching as high as 70-80% of the total load. Melchers [1] demonstrated that one of the primary causes of collapse (corresponding to approximately 45% of the cases analyzed) lies in an erroneous evaluation of the loading conditions and of the structural response. With improvements in the methods for in-depth analysis in the design of lightweight wide-span roofing, theoretical studies can and must be used in combination with experimental tests performed in wind tunnels and in situ. From the observation of structures that have completely or partially collapsed: