Seismic Behavior of Precast Buildings With Dissipative Connections

Lorenzo De Stefani,Roberto Scotta

doi:10.3389/fbuil.2021.639777

Abstract

Recent earthquakes in southern Europe highlighted that the connections of cladding panels to R.C. frames in precast buildings had a major role in the structural collapse. For this reason, there is an urgent need for a review of the design methods for these connections as well as for an improvement in the manufacturing technology. This article aimed to assess the efficiency of dissipative panel-to-structure and roof connections in R.C. precast buildings. A parametric study consisting of linear and non-linear analyses on one case-study building is performed. Different sensitivity analyses are performed varying their mechanical properties (i.e., stiffness, strength, and ductility) to analyze the behavior of the CP/frame connections. The study focuses on dissipative connections with an elastic–plastic behavior, placed between cladding panels (CPs) and frames in precast buildings with stacked horizontal cladding panels. The introduction of dissipative CP/frame connections implies the inclusion of panels in the global seismic resisting system. The “panels + frame” system highlights a high stiffness until the yield strength of the CP/frame connections is reached. The results, obtained from non-linear dynamic analyses (NLDAs), clearly show how the proposed connection improves the structural seismic performance. By contrast, this is no longer true for R.C. precast structures with flexible diaphragms, especially for intermediate columns, far from panels aligned to seismic action. In this case, significant and unexpected axial forces arise on out-of-plane connections between panels and columns. The integration of an efficient diaphragm is essential to prevent these critical issues both on intermediate columns and CP/column connections; it enables the dissipative capacity of the “panels + frame” system, and it significantly limits the forces and displacements of intermediate alignments. Unfortunately, the achievement of a rigid diaphragm is not always feasible in precast buildings. A possible alternative to activate dissipative capacities of the roof diaphragm with limited in-plane stiffness is the use of dissipative connections linking roof beams and main beams. The solutions described in this article can be applied both in the design of new buildings and for the seismic upgrading of existing ones with easy-to-install and low-impact applications.

Highlights

The current design of R.C. precast buildings is typically based on bare frame models where perimetral cladding panels are considered only as seismic mass which does not contribute to the global lateral stiffness and resistance (i.e., non-structural elements (NSEs))
Base forces and top displacement reduce for yielding ratios ry lower than 10% due to both the energy dissipation introduced by weak cladding panels (CPs)/ frame connections and the “skew effect” which allows the migrations of the actions from out-of-plane loaded facades to the perpendicular ones, whereas base forces and top displacement increase for ry>20%, especially for constant stiffness values of the connections
5.2.2 Results for Seismic Action Along the Y Direction Supplementary Figure S4 shows the forces and the drift of the CP/frame dissipative connections, and Figure 8 presents the axial forces on the column/CP connections obtained from non-linear dynamic analyses (NLDAs) with seismic action along the Y direction

Summary

Introduction

The current design of R.C. precast buildings is typically based on bare frame models where perimetral cladding panels are considered only as seismic mass which does not contribute to the global lateral stiffness and resistance (i.e., non-structural elements (NSEs)). The panels are typically linked to the structure with fragile connections designed with local calculations for wind and/or seismic actions, evaluating only anchoring forces orthogonal to the plane of the panels. Independent of the theoretical design approach of their connections, cladding panels behave as shear walls modifying the seismic response of precast buildings. Forces on panel connections are related to the global mass of the building, and they mainly lay in the plane of the panels. Forces on the connections are completely different from those evaluated with a local design approach

Objectives

Results

Conclusion