Ivan Giongo

Field Testing of Flexible Timber Diaphragms in an Existing Vintage URM Building

AbstractIt is well known that the in-plane behavior of flexible timber diaphragms has a large influence on the global earthquake response of unreinforced masonry (URM) buildings. The type and the activation of out-of-plane URM wall failure mechanisms are strictly related to diaphragm stiffness, which is a property that also governs the effectiveness of the diaphragm to distribute earthquake-induced loads between lateral load resisting wall elements. However, there is a lack of reported experimental campaigns pertaining to these issues, and in particular, few experimental data have been published on the in situ behavior of existing vintage flexible timber floor diaphragms such as single straight sheathed diaphragms that are typically encountered in New Zealand URM buildings. To address this paucity of available in situ test data, an experimental campaign was executed to investigate the as-built cyclic and dynamic behavior of full-scale vintage flexible timber floor diaphragms with the outcomes being presen...

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

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.

Comparison of In Situ and Laboratory Testing for the Characterization of Old Timber Beams before and after Intervention

In this paper an investigation campaign, carried out in occasion of the restoration of a timber floor in the Belasi Castle (Trentino, Italy), is reported. In order to validate a testing procedure for the calibration and control of an innovative wood-wood strengthening technique, results of tests performed in situ on the structural elements, in both the original and the repaired condition, have been compared with those obtained in laboratory on some dismantled beams. For the characterization of the material decay, both local mechanical and global vibrational testing have been carried out. For the mechanical characterization of the beams, before and after repair, direct static bending tests have been performed, with distributed loads, on site, and according to standard four-points loading schemes, in laboratory.

Investigation on the Self-Tapping Screws Capability to Induce Internal Stress in Timber Elements

In refurbishment operation of existing timber floors could prove of some interest the possibility of hogging the existing timber beams, in case of the presence of excessive permanent midspan deflections. In the case of sagged timber floors which cannot be buttressed due to heritage issues, the possibility of cambering a timber beam by simply putting another wooden beam on the top of it and inserting screws inclined at 45° relative to the beam axis has been experimentally investigated, with some promising result. The cambering procedure has proved to be more effective when the fastener are inserting starting from the internal part of the beam, permitting to obtain significant values of upward deflection (it has been observed an upward deflection of about one three-hundredth of the total beam length): the values could possibly be increased by reducing the screw spacing or by using fasteners able to generate a greater pressure. The effectiveness of this method is based on the capability of self-tapping screws to induce internal stress in timber element during the drilling procedure: the horizontal component of the resultant pressure yielded by the inclined screws is directly related to the possibility to hog the composite system. The aim of the experimental campaign described in this paper was to investigate the values of the internal stress induced by different type of fasteners during the drilling procedure, studying the influence of different parameters such as screw angle with respect to the grain direction, initial pressure, head penetration length, threaded part length, connector typology, wood density, time-dependence.

Lateral Performance of As-Built and Retrofitted Timber Diaphragm Fastener Connections

AbstractThe in-plane stiffness of timber diaphragms commonly found in vintage unreinforced masonry (URM) buildings is largely determined by the rigidity of the fastener connections. Currently in th...

In-Plane Behavior of Timber Diaphragms Retrofitted with CLT Panels

Traditional un-reinforced masonry (URM) buildings often comprise flexible wooden floor diaphragms where a layer of floorboards is laid perpendicularly over the timber joists and fixed by means of nails. It is not rare that such floor structures need to be improved in order to satisfy serviceability and ultimate limit states criteria, as concerns their behavior both under out-of-plane and in-plane loading. A common retrofit technique, mainly aimed at improving out-of-plane floor performance, consists in the application of a layer of cross-laminated timber (CLT) panels laid over the existing floorboards and oriented parallel to the joists. Appropriate panel-to-joist shear connection determines a joist-slab composite behavior that results in a significant improvement of both the of out-of-plane strength and stiffness. In addition, if adequate connections between adjacent panels are provided, CLT elements can also increase the in-plane strength/stiffness, a key-aspect in defining the seismic response of URM buildings. Both force distribution among vertical resisting piers and out-of-plane deformation of masonry walls are in fact affected by the diaphragm in-plane behavior. Inadequate in-plane response from the diaphragms can lead to the out-of-plane collapse of large masonry portions (1st mode failures). Non-linear static and non-linear dynamic simulations proved that the above mentioned retrofit strategy can effectively increase diaphragm in-plane stiffness and limit the in-plane displacement demand of diaphragms subjected to seismic shaking.

On the Use of Sound Spectral Analysis for the In Situ Assessment of Structural Timber

This paper focuses on the possibility of using sound spectral analysis as a diagnostic technique for the assessment of existing timber structures. The basic idea is to perform a spectral analysis, through the Fast Fourier Transform (FFT) algorithm, of the sound (recorded by a smartphone microphone) that is produced by hitting the wood surface of the element with a hammer or an equivalent tool. The sound spectrum is compared to a reference spectrum obtained for sound wood in standard environmental conditions in order to detect the presence of damage or decay. Differently from “classic” stress wave propagation methods that are based on the determination of the time-of-flight of the stress wave, the proposed technique relies on the local acoustic properties of wood. A first insight on the method applicability was obtained by testing the technique on several timber specimens in different conditions, from sound to completely decayed. Registration of the signals was performed by using two different mid-market smartphone models. Moment analysis, by calculating the spectral and frequency energy centroid of the sound spectra, was used to evaluate and compare numerous experimental recordings. The parameters that have the most significant impact on the sound signal (e.g. impact tool, microphone distance, boundary conditions, etc.) and that can negatively influence the assessment were then identified and investigated. Finally, pros and cons of the presented method and future developments are examined and discussed.

Special issue on “existing timber structures”

Timber structures are an important part of the Architectural and Cultural Heritage. Therefore, any action concerning the conservation, repair, retrofit, and monitoring of the built heritage cannot prescind from understanding how timber structures behave from the material level to the whole structure. The selection of manuscripts included in this special issue aims at supplementing the existing knowledge on the topic. The articles cover a wide variety of aspects, from the material assessment and structural analysis to the design and evaluation of retrofit strategies. In order to promote the preservation of the cultural heritage by favoring minimal-impact restoration strategies, it is very important to know how the structures were originally supposed to behave. To this regard Tardini (2018) presents an interesting review on the evolution process undergone by design principles for timber elements, from heuristic rules and geometric proportions to scientific-based criteria. A particularly important role in this process to which contributed people of the caliber of Andrea Palladio, Galileo Galilei, and Claude-Louis Navier, just to name a few, was played by Pierre Bullet’s table as clearly evidenced in the article. A large portion of the timber-built heritage is composed of the roofs and diaphragms present in unreinforced masonry buildings that include an extremely wide range of typologies, differing from each other in many aspects such as the layout and arrangement of the components, the type of decking, framing system and carpentry joints. Faggiano et al. (2018) present an inventory of roof and floor structural typologies used in monumental heritage buildings by referring to the iconic case-study of the Royal Palace of Naples built in the 17 century. Ten hall rooms have been analyzed by the authors, focusing on six roof types and three floor types. Blaha et al. (2018) report a peculiar example of cultural contamination regarding timber roof structures in Czech Republic. The authors studied the unique case of a building in Prague where the original Gothic roof was replaced with an Italian Baroque roof (by architect Martino Allio in 1685). The comparison of the Gothic roof and the Italian Baroque roof to a typical Czech Baroque roof resulted in some very interesting findings. It appears evident that the possible scenarios when intervening on timber-built heritage are potentially countless. Therefore, in addition to being effective and reliable, assessment procedures and analysis models need to be characterized by simplicity and versatility. In the article by Bertolini Cestari and Marzi (2018), a multi-disciplinary analysis of the issues related to the conservation of heritage timber roof structures is presented. The authors’ considerations and remarks stem from the experience acquired during thirty years of working on research projects. Ten case-studies located in northern Italy (five of which are included on the UNESCO World Heritage List) are analyzed to support the authors’ point of view. Mosoarka and Keller (2018) present instead a new procedure for the assessment of historic timber roof structures. The methodology relies on a multi-disciplinary and transdisciplinary approach that, in addition to providing a cost-effective condition assessment, aims at regulating future interventions based on a priority list. Macchioni and Mannucci (2018) focused their attention on the “triangular truss” which is the most representative structural assemblage of historical roofs in Italy. The article, after a thorough description of the most common features of the Italian trusses, analyses in detail all the aspects of the assessment procedure, from the viewpoint of the wood technologist. The discussion is further developed by addressing some case studies. Sousa and Neves (2018) investigated the application of structural reliability concepts to existing timber structures. Traditional semiprobabilistic methods usually adopted for the design of new structures are compared with probabilistic methods. For a better understanding, the target reliability indexes, defined by the authors by balancing costs and hazards, are illustrated by using a case study. Reliable and effective assessment/intervention procedures can only stem from accurate knowledge of the mechanical behavior of the various components. To this extent, invaluable insight is certainly provided by experimental testing performed both onsite and in laboratory. Branco et al. (2018) performed onsite INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE 2018, VOL. 12, NO. 4, 505–506 https://doi.org/10.1080/15583058.2018.1453327

Seismic Assessment Procedures for Flexible Timber Diaphragms

A review of the available procedures and guidelines for the in-plane assessment of existing timber diaphragms in unreinforced masonry (URM) buildings is provided. Most of the provisions that concern flexible wood floors and that are valid for URM, can as a matter of fact be adopted for historic masonry buildings reinforced with timber frames. Recommendations from the most recent international standards like ASCE 41-13 and NZSEE 2015 were thoroughly analysed. Particular attention was given to producing a step-by-step practice-oriented guideline that provides background information which helps understand better the procedure frame work and also gives suggestions for alternative interpretations when multiple choices are possible.