In-Plane Assessment of Existing Timber Diaphragms in URM Buildings via Quasi-Static and Dynamic <i>In Situ</i> Tests

Abstract

Mechanical and dynamic in-plane properties of timber diaphragms are known to be key parameters when determining both the local and global seismic response of unreinforced masonry (URM) buildings. However, few data pertaining to experimental campaigns on this issue are available in the literature, especially regarding existing floors. In this work, the outcomes of a field testing campaign on full-scale old timber diaphragms are presented. Two specimens, whose size was 5.6 x 9.6 m2 and 4.7 x 9.6 m2 were obtained from a 17 x 9.6 m2 floor and were subjected to a series of both cyclic and snap back tests in the direction orthogonal to the joists. Since the original anchoring system was deficient, new epoxy-grouted anchors were installed before starting the testing procedure. So as to reproduce the inertial load distribution, an ad hoc loading system was developed by means of wire ropes and steel pulleys. After testing the diaphragms in the as-built condition, the effect of different refurbishment techniques was also investigated. From the results, it seems that even simple and cost-effective solutions such as the re-nailing of the flooring are sufficient to achieve a significant increase in the equivalent shear stiffness.

Seismic vulnerability of roof systems combining URM gable walls and timber diaphragms

“…Two full cycles at ±10, ±50, ±100, and ±150 mm were applied as relative displacement between the roof base and the ridge beam followed by a monotonic imposed displacement up to 400 mm (see box in Figure 7A). 23 Similarly to Peralta et al 24 this behaviour can be approximated by a bilinear idealisation defined by a yield load, F y , an initial stiffness K 1 and a secondary stiffness K 2 . This pronounced non-linearity is mainly due to nail yielding and nail slip.…”

“…The observed cyclic behaviour is consistent with the results of as-built laboratory 22 and in situ tests. 23 Similarly to Peralta et al 24 this behaviour can be approximated by a bilinear idealisation defined by a yield load, F y , an initial stiffness K 1 and a secondary stiffness K 2 . A third stiffness K 3 , beyond displacement value of 80 mm (drift equal to 2.2%), is here proposed to model the stiffening phenomenon as well.…”

Fragility Functions for Tall URM Buildings around Early 20th Century in Lisbon. Part 1: Methodology and Application at Building Level

“…Group 17 characterizes the flexible behaviour of timber floors, represented by the shear modulus (G) of an equivalent finite membrane element with 0.022 m of thickness, corresponding to the thickness of the timber boards. The range of variation is defined in (NZSEE, 2017), which proposes reference values as a function of the floor system and state of conservation, based on (Giongo et al, 2013). The Monte Carlo simulations are defined for each variable starting from the continuous probability density function attributed and considering additional correlations between variables, as described in the following.…”

Comparing In-Plane Equivalent Shear Stiffness of Timber Diaphragms Retrofitted with Light and Reversible Wood-Based Techniques

“…Depending on the specific contexts, the variety of construction methods and configurations of diaphragms led to a number of research studies focusing on the assessment of the seismic response of the floors and the development of retrofitting methods. Several authors (Peralta et al 2004;Corradi et al 2006;Parisi and Piazza 2007;Piazza et al 2008;Valluzzi et al 2008;Baldessari 2010;Valluzzi et al 2010;Brignola et al 2012;Giongo et al 2013;Wilson et al 2014;Branco et al 2015;Gubana and Melotto 2018;Mirra et al 2020) have emphasized the often poor characteristics in terms of in-plane strength and stiffness of as-built diaphragms, and have proposed different refurbishment techniques. Among innovative options such as use of fiber-reinforced polymers (FRPs) (Corradi et al 2006;Piazza et al 2008) or cross-laminated timber (CLT) (Branco et al 2015;Gubana and Melotto 2018), all research studies also focused on light and reversible strengthening systems, due to their wide versatility and applicability in existing buildings, from houses to monumental constructions.…”