Maurizio Piazza

Seismic behavior and retrofitting of joints in traditional timber roof structures

The seismic quality of traditional timber structures, as those supporting roofs in old buildings, mostly depends on the condition of their connections. A research program has investigated the behavior of old timber joints and examined retrofitting criteria. The main parameters affecting the mechanical behavior of the connection have been singled out and their effects quantified by means of experimentation and numerical analysis. A synthetic model of the cyclic behavior has been formulated, implemented in a finite element format, and used in the analysis of timber structures in seismic conditions. The model has been verified with full-scale experimentation on a roof truss. Different reinforcing methods have been compared on the basis of experimental observation and calculated structural response. The study has shown that a satisfactory post-elastic response, comparable to that of new structures, may be reached for suitably retrofitted structures.

Refurbishment of a Traditional Timber Floor with a Reversible Technique: Importance of the Investigation Campaign for Design and Control of the Intervention

The strengthening and stiffening of traditional timber floors with the addition of timber planks and the use of dry connections falls into the category of “traditional” repair methods. Nevertheless, a high degree of innovation and scientific/industrial research is implicit in some modern applications of this type of intervention. If newly developed systems are to be satisfactorily adopted to repair ancient structures, their effectiveness and reliability need to be adequately evaluated. The study highlights the importance of investigation actions for the design, calibration, and control of intervention in the restoration of heritage structures. On the occasion of the adoption of an innovative timber-to-timber strengthening technique for the rehabilitation of a traditional timber floor in a mediaeval castle in Italy, a thorough investigation was carried out. Tests were performed in situ on the structural elements, in both the original and the repaired condition, and the results were compared with those obtained in the laboratory on a dismantled member. Despite some differences between the experimental conditions on site and in the laboratory, the two testing campaigns showed a good agreement of results. In particular, an increase of more than four times the effective bending stiffness was achieved, in both cases, after repair.

Typological and Structural Authenticity in Reconstruction: The Timber Roofs of Church of the Pieve in Cavalese, Italy

In case of exceptional or accidental destructive events (e.g., earthquakes, floods, fire), the advisability of completely reconstructing a vanished artifact may be questionable. Among the possible approaches for reconstruction, the so-called philological method allows the complete reading of the whole building. Analogous to the study of literary texts, this method is based on the analysis of the “architectural language” of a building that is its form and its technical characteristics as well as its structural behavior. This case study concerns reconstruction of the timber roof of the Church of the Pieve in Cavalese (Italy), destroyed during a fire on March 29, 2003, for which the philological approach has been chosen. The design process consisted of two important phases: first the determination of the precise form of the original roof, by considering different kinds of evidence, then the introduction of necessary modifications, to meet the present-day structural standards. Such design choice, far from being a simplistic solution, involved the participation of different experts and a thorough multidisciplinary investigation.

Morphology-based macro-scale finite-element timber models

This paper presents a non-invasive technique that can extract an accurate geometrical description of growth layer surfaces in wood. The method has been validated for sawn spruce elements (Picea Abies Karst.). The aim is to implement a procedure to model domain geometry in the numerical analysis of wooden elements, taking into account the intrinsic variability of the material. The approach presented by the authors avoids internal imaging and achieves a digital 3D model of growth layers, using, as input data, images of the ring pattern, which represents the growth surface boundary curves, visible on all the cut faces of the wooden element.

Direct Displacement-Based Design of Glulam Timber Frame Buildings

We introduce a direct Displacement-Based Design methodology for glued laminated timber portal frames with moment-resisting doweled joints. We propose practical expressions to estimate ultimate target displacement and equivalent viscous damping, and we demonstrate that these expressions provide prior values that are close to those obtained a posteriori using a more refined model. Applied to case studies, the method yields base-shear forces lower than those obtained using the force-based approach of Eurocode 8. This is due to the high dissipation capacity of the specific connection technology, which apparently is conservatively accounted for in the q-factor of Eurocode 8.

Shaking Table Testing of a Full-Scale Prefabricated Three-Story Timber-Frame Building

Shake table tests were carried out on a 7 m × 5 m three-story, timber light-frame building (7.5 m height) at the TreesLab laboratory (Eucentre) in Pavia. The aim of the research was to evaluate the seismic behavior of a typical Italian prefabricated timber building and to study the interaction between the individual structural components tested in quasi-static manner in a previous experimental study. The 1979 Montenegro Earthquake ground motion, recorded at the Ulcinj-Hotel Albatros station, was selected as the ground motion for seismic tests. The maximum peak ground acceleration was scaled to 0.07 g, 0.27 g, 0.5 g. 0.7 g, and 1 g in order to evaluate the building’s performance at different levels of seismic input. More than 100 instruments were used to monitor the behavior of the building during seismic tests measuring acceleration, displacement, and forces. The visual inspection shows that the building did not show any damage during all seismic tests. However the data analysis (dynamic identification, capacity spectrum, inter-story drift) confirm that during the 1.00 g test the structure went beyond its linear elastic limit. The results obtained from this experimental study suggest that the design hypotheses commonly adopted in practice for seismic analysis (e.g., in terms of force distributions between the walls, and also the behavior factor q) are not always consistent with the real behavior of timber frame multi-story buildings, and should be backed by more accurate knowledge of the contributions of the individual structural components.

On Estimating the Seismic Displacement Capacity of Timber Portal-Frames

An analytical model is proposed to estimate the seismic displacement capacity, at serviceability and ultimate limit states, of timber portal frame structures with dowelled joints. The predictions from the simplified formula are compared with the results of numerical analyses carried out on a sample of representative cases. These cases result from a simulated design procedure, consistent with Eurocode 8, and are generated via Monte Carlo sampling, with varying sizes, materials and load conditions and also uncertainties in these parameters. Based on the outcome of the analysis we propose a set of practical formulas which allow prediction of the displacement with a given percentile of overestimates. In addition, it is shown that these equations for displacement capacity can be used to generate fragility curves for performance-based earthquake engineering applications. Prescription of an overstrength factor in code provisions is recommended to avoid brittle failure.

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.

Innovative construction system for sustainable buildings

This paper deals with a contemporary integrated and sustainable construction technology for new residential buildings. Specifically, this research aims at developing innovative steel-timber hybrid structures which allow a rapid assembly of the individual prefabricated components, minimizing the construction times and limiting the costs of the work. The numerical analyses performed on a multi-storey building for social housing will be presented and discussed. The in-plane behaviour of the floors and shear walls will be analysed, considering in particular the types and arrangement of the different timberand steel-timber joints. The connections to be used among the construction elements will be selected in order to develop a sufficient stiffness, ductility and bearing capacity according to the design criteria for seismic-resistant structures. These connections allow to enhance the on-site assembly operations, therefore working effectively also under harsh climatic conditions.