PSI - Issue 78

Paolo Ielpo et al. / Procedia Structural Integrity 78 (2026) 1024–1031

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2. The SPEAD technique In existing reinforced concrete buildings, the primary structural vulnerabilities frequently stem from the absence of design principles based on capacity design and the lack of adequate construction detailing. Such deficiencies lead to brittle behavior, which is particularly critical at beam-column joints. During seismic events, these joints are subjected to high shear stresses and bond-slip phenomena between the reinforcement bars and the surrounding concrete. The absence or lack of stirrups significantly compromises the shear capacity of the joint, making it vulnerable to premature failure. In this context, the SPEAD system is proposed as a device designed to enhance local seismic performance while adhering to sustainability principles. Its exclusively external application minimizes the impact on the existing structure, following a Life Cycle Thinking (LCT) approach that considers the entire device lifecycle, from manufacturing and installation to maintenance, recycling, and final disposal (Fig. 1). The device consists of a steel plate designed to shift the plastic hinge of the beam away from its intersection with the column, thereby increasing the seismic capacity of the joint. The device is composed of two distinct parts: one fixed to the column and the other applied to the beam. A key feature of the system is its ability to dissipate energy through the hysteretic behaviour of the steel. Specifically, the plate is equipped with holes that define an area called the “hourglass es zone”. During a seismic event, these areas undergo plastic deformation by exploiting the relative movement between the beam and the column, thus absorbing part of the seismic energy and improving the overall response of the beam-column node. Further details are reported in Santarsiero et al. (2020) and Ielpo et al. (2025).

Fig. 1. SPEAD system overview: LCT approach, functionality, and installation process

3. Experimental cyclic tests on beam-column joints An extensive experimental campaign was conducted at the Laboratory of Structures of the University of Basilicata on 26 reinforced concrete beam – column joints to analyze their behavior under cyclic loading, simulating the stresses induced by seismic events. The tested specimens featured various geometric configurations and seismic design levels. This study focuses on the joint identified as T4, designed in accordance with the seismic provisions of the OPCM 2003 code, but referring to seismic zone Z4, which corresponds to a low seismic hazard area according to the Italian classification. The joint is the intersection between a 300×300 mm column and a 300×500 mm beam, both reinforced with symmetrically