Assessment of the equivalent viscous damping ratio for hybrid wall-to-foundation connections of precast wall panels

Abstract eng:
In the last decade, efficient solutions based on the concept of “controlled rocking” (hybrid) behaviour have been proposed for both beam-column and wall-to-foundation connections of precast members. These systems show the benefits of minimizing the residual displacements (using unbonded post-tensioning tendons), limiting the damage to the connection interfaces (thanks to the rocking mechanism) and controlling the maximum displacements (through the introduction of dissipative devices). The direct displacement based design (DDBD) procedure appears as a suitable method to control the peculiar rocking behaviour of these systems. This procedure requires the determination of the structural properties at the design displacement. In particular, the correct assessment of the equivalent viscous damping ratio ξeq is fundamental to get reliable results. Nevertheless, few studies dealt with the definition of ξeq of “hybrid” systems, furnishing formulas valid only for limited cases. The shape of the hysteretic loops has been recognized to be function of the value of the parameter λ, defined as the ratio of the re-centring to the dissipative bending moments. This paper addresses the precast panel walls characterized by “hybrid” wall-to-foundation connections, with the following aims: i) realizing a reliable numerical model; ii) developing formulae and charts which allow a proper evaluation of the required amount of post-tensioned and mild steel as function of the design point and the chosen value of λ; iii) suggesting expressions and charts to assess correctly the value of ξeq as function of the ductility, through an extensive campaign of nonlinear quasi-static and dynamic analyses, for different values of λ.

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