P-Delta Effects Assessment in Precast Structures Via Inelastic Performance Based Spectra

Abstract

Abstract The seismic design of precast structures is significantly impacted by the inherent characteristics of precast technology. One primary concern is to deliver structural elements that are as lightweight as possible to streamline on-site assembly and cost reduction. Consequently, the slenderness of beams and columns is considerably greater compared to traditional cast-in-situ concrete constructions, and second-order effects assume a pivotal role. Furthermore, these very factors make dry pinned joints the preferred choice for designers when it comes to connecting beams and columns. Cast-in-situ concrete is typically reserved for connections between columns and foundations, as well as for topping off precast floor elements. Pinned joints result in the transformation of the frame into an ideal isostatic structure, with cantilevered columns securely anchored at the base. This transformation leads to a significant reduction in the energy dissipation capacity of the entire structure. It not only prevents the formation of plastic hinges in the beams but also amplifies the P-Delta effects in the column's response by decreasing the overall stiffness when subjected to lateral loads. A simplified approach for assessing dynamic instability in single and multi-storey precast hinged frames is presented. The objective is to create a tool for the initial design of such structures, enabling the prediction of dynamic collapse and the achievement of limit states during seismic events based on fundamental structural parameters. The impact of these parameters on the overall behaviour is explored through incremental dynamic nonlinear analysis, using real far-field accelerograms, on equivalent single-degree-of-freedom systems. The result is a set of inelastic spectra, giving the structural capacity in term of force reduction factor versus parameters like building height, column aspect ratios and floor masses configuration, with regard to different limit states usually considered in seismic design of these structures.