Davide Bellotti

The seismic retrofit of existing reinforced concrete (RC) buildings equipped with dissipative bracing systems requires not only a global performance-based assessment, but also a rigorous verification of the local behavior of critical structural connections. In this context, the present study focuses on the numerical seismic performance of a beam–column connection extracted from a retrofitted RC hospital building located in Italy. The investigated joint represents a central node where two orthogonal steel bracing systems converge and transfer seismic forces to an RC column strengthened with heavy steel jacketing and anchorage devices. A detailed three-dimensional finite element model of the connection is developed using solid elements for concrete and steel components, explicit modeling of reinforcement bars, bolts, and anchor rods, and advanced nonlinear constitutive laws for both materials. Two modeling strategies are considered, including the explicit simulation of contact interfaces between steel components, in order to capture local stress redistribution and potential interaction effects. The connection is subject to seismic demand derived from the global structural analysis, corresponding to different values of the behavior factor, thus ensuring consistency between global design assumptions and local verification. The results highlight the progressive activation of nonlinear mechanisms within the steel components, the development of cracking and compression damage in the concrete core, and the preservation of a clear hierarchy of resistances under design-level seismic actions. The numerical outcomes allow a critical discussion on the role of local connection behavior in supporting the global dissipative strategy and provide quantitative insights into the evaluation of the behavior factor from a local-response perspective. The study emphasizes the importance of detailed connection-level analyses in the seismic retrofit of strategic facilities and supports a more consistent integration between global performance objectives and local structural design.

The beam‐to‐column connection is a critical structural component of precast concrete structures. Failures of these connections, which can be categorized as semi‐rigid or hinged, frequently lead to loss of beam support and roof collapse. Despite this relevance, the seismic response of these connections remains surrounded by uncertainties. Although design codes offer guidelines for the estimation of the ultimate shear strength of common beam‐to‐column connections, accurately predicting their performance is still challenging. The paper focuses on dowel‐based connections, which encompass mechanical devices and thus represent an enhancement of the traditional frictional version. The goal herein is to model and analyze the seismic behavior of three different types of such dowel‐based connections, featuring a flat or a fork‐like column top, without and with the presence of transverse reinforcement in the fork. The role played by the investigated connection types on the pushover curve of a single‐storey case study building, modeled in OpenSees, is discussed.

This paper presents a global performance-based seismic assessment of an existing reinforced concrete hospital building retrofitted with dissipative bracing systems. The study aims to evaluate the overall effectiveness of different dissipative configurations, two traditional systems and one innovative low-activation solution in enhancing the seismic performance of the structure in compliance with the Italian Building Code (NTC 2018). The analyses were carried out using nonlinear static (pushover) procedures to determine the global capacity, equivalent damping, and displacement demand at the Life Safety (SLV) and Near Collapse (SLC) limit states. The retrofitting interventions were modeled assuming elastic connections between the existing RC frames and the added steel members, consistent with standard design practice in which connections are dimensioned with overstrength to avoid premature failure. The results demonstrate that the integration of dissipative systems significantly increases stiffness and damping, effectively reducing lateral displacements and improving the seismic safety index above the 60% threshold required for strategic facilities. The study highlights the importance of global assessment methodologies in guiding the seismic upgrading of hospitals and other critical infrastructures, while local detailing and device-level optimization are identified as topics for future research.

This study presents a novel structural framing solution designed to improve seismic energy dissipation and limit displacements, aiming to serve as an effective alternative to traditional precast systems employing pendulum-based isolation. While pendulum mechanisms mitigate seismic forces by decoupling the superstructure from ground motion, they are typically characterized by high implementation costs, mechanical complexity, and post-event maintenance challenges. In contrast, the proposed approach integrates seismic performance enhancements within the structural frame itself, removing the dependency on external isolation components. The system leverages a combination of pinned and semi-rigid beam-to-column joints that are tailored for use within dry precast construction technologies. These connection types not only support rapid and labor-efficient assembly but also, when properly detailed, offer robust hysteretic behavior and deformation control under dynamic loading. The research includes both experimental testing and numerical simulations focused on the cyclic response of these connections, enabling a comprehensive understanding of their role in dissipating energy and delaying damage progression. Recognizing the industry’s frequent emphasis on construction speed and upfront cost-efficiency, often at the cost of long-term reparability, this work introduces an alternative framework that emphasizes resilience without compromising construction practicality. The resulting system demonstrates improved post-earthquake functionality and reduced downtime, making it a promising and economically viable option for seismic applications in precast construction. This advancement supports current trends toward performance-based design and enhances the structural reliability of dry-assembled systems in seismic regions.