Abstract Timber, with strength-to-weight and modulus-to-strength ratios comparable to steel, is increasingly utilized in seismic retrofitting due to its versatility, sustainability, and rapid installation potential. However, concerns exist regarding its capacity to respond effectively to seismic events, particularly the risk of delayed activation compared to existing structural damage. Timber retrofits high deformability, largely attributed to the ductility of metal connections, enables significant displacements without compromising stability. Nonetheless, challenges arise when timber systems interact with brittle materials, such as in retrofits of reinforced concrete (RC) and masonry buildings, questioning the conventional ultimate limit state. This study examines the application of cross-laminated timber (CLT) panels for retrofitting RC buildings, as part of the Sustainable Timber Retrofit Of reinforced coNcrete buildinGs (STRONG) project conducted at STRULAB, University of Patras, within the ERIES framework. A two-storey RC frame with masonry infill, representative of 1950–1970 Mediterranean construction practice, was retrofitted using a CLT-based technique (RC-TP) and tested under lateral cyclic loading up to ultimate conditions. The intervention prioritized life safety and global stability over damage containment during high-intensity events. This paper outlines the design criteria and experimental results, highlighting the potential of CLT panels to enhance seismic performance while ensuring structural stability.
Unreinforced masonry (URM) buildings are characterized by high vulnerability to lateral loading, which is often manifested when an earthquake occurs.The present study investigates the effectiveness of a timber-based retrofit solution aimed at reducing the seismic vulnerability of existing URM structures.The retrofit technique consists of connecting timber-based panels, to the interior surface of the walls of a building using mechanical or adhesive pointto-point connections.The application of those panels allows to considerably increase both the in-plane and the out-of-plane capacity of the URM walls, while preserving the original external facades of the retrofitted building.This solution resulted to be relatively fast and easy to install and the reversible nature of the system allows to reduce the impact of the retrofit intervention.In this work the in-plane behaviour of the retrofitted walls was investigated numerically, building on previous preliminary analyses and in the lights of the results of experimental evidence collected by the authors' research team.The effectiveness of this retrofit solution was analysed on several masonry types, considering different masonry properties and geometries.The influence of various parameters (such as masonry-to panel connection typology, connectors number and position) on the increase of lateral capacity of the retrofitted walls was studied by means of a series of non-linear quasi-static simulations.
The paper presents a new connection system for cross-laminated timber (CLT) structures, named X-RAD. This innovative connection system is characterised by the use of a single connector type that is positioned at the corners of the CLT panels. X-RAD is formed by a metal part surrounding a hardwood insert that is fixed to the panels by means of all-threaded screws introduced with double inclination. The peculiar geometry of the connector and the combination of different materials allow the full exploitation of the capacity of the CLT panels while ensuring a ductile response of the connection. Construction modularity, fast assembly/disassembly speed and prefabrication are some of the aspects that can be associated with X-RAD development. The outcomes of an extensive testing campaign on the new connector are also presented in the paper.
An in-situ experimental campaign investigating the in-plane behavior of retrofitted timber floor diaphragms was undertaken on full-scale specimens located in a two-story clay brick unreinforced masonry building constructed circa 1913. The diaphragm retrofit strategies included renailing of board-to-joist connections, use of a fire-rated ceiling, use of steel chords, and the application of a plywood sheet overlay. When compared with as-built single straight-sheathed diaphragms, all tested solutions provided significant stiffening of the in-plane diaphragm response, with the sole exception being the configuration incorporating steel chords, where the chord influence was observed to be negligible. The fire-rated ceiling showed noticeable strength degradation due to cyclic loading while the plywood sheet overlay exhibited no strength loss between cycles to the same deformation levels, demonstrating the ability of the plywood-overlaid diaphragm to resist multicyclic loading. The subsequent phase of the study included comprehensive numerical modeling of the adopted retrofit strategies and their validation against the attained experimental results. A detailed parametric study on retrofitted timber floor diaphragms was also undertaken and is reported herein. These numerical investigations allowed evaluation of the most efficient overlay pattern, and also allowed the influence of aspects such as the plywood thickness and connection properties to be considered.
Long-span structures such as school gyms and sports centres are often used by the Italian Department of Civil Protection as post-catastrophe shelters or headquarters. The Emilia 2012 earthquake drew the attention of the department to this type of structure due to the damage that many of these buildings suffered. In this work, a dataset of 101 timber structures was analysed based on a simplified methodology that detects the major vulnerabilities in long-span timber roofs in order to help plan further investigations and retrofit interventions. Using fast and straightforward approaches, the elements most vulnerable to seismic action were analysed quantitatively and qualitatively. Quantitative evaluation of the vulnerabilities was achieved by applying the Italian Building Code. The aspects not considered in the quantitative evaluation were assessed through qualitative parameters inspired by damage identification forms (e.g. the AeDES form). The analysed structures are located near the epicentres of the last strong earthquakes that struck Italian territory: Abruzzo in 2009, Emilia in 2012 and central Italy in 2016. Damage and retrofits, identified by interviewing owners, designers and builders, showed a good correlation between the real behaviour shown by the surveyed structures and the vulnerabilities detected using the simplified methodology.
