Currently there is little guidance available on an experimentally-validated detailed seismic assessment procedure for vintage flexible timber diaphragms such as are routinely encountered in New Zealand unreinforced masonry buildings. The results from recent testing of full-scale diaphragms are presented and interpreted with particular attention given to the definition of shear stiffness and shear strength values, whilst acknowledging that the recommendations derive from a small data set. References are provided to information previously published elsewhere to justify the theoretical framework adopted, and the procedure is linked to ASCE 41-13 for guidance regarding diaphragm scenarios that have not been studied by the authors. A procedure is provided to account for the effects on diaphragm response of supplementary stiffness due to masonry end walls. The performance of several diaphragms that were improved with either overlays or underlays is reported as potential proof-tested standard solutions. The assessment procedure is demonstrated by providing a mock worked example of a detailed diaphragm assessment.
The paper focuses on a retrofit strategy applicable to existing reinforced concrete (RC) frame structures to reduce their seismic vulnerability.The intervention strategy, for the sake of brevity named RC-TP (Reinforced Concrete-Timber Panels), consists in the removal of the existing masonry infills and in their replacements with Cross Laminated Timber (CLT) panels fixed to the concrete elements by means of a timber subframe and a dissipative connection comprised of metal dowel-type fasteners.The analyses were performed via finite element modelling by adopting numerical strategies with different levels of refinement.In particular, refined 3-dimensional models (created using the software Abaqus) and simpler 2-dimensional models (created using the software SAP2000) were used.At first, the refined modelling approach was validated on experimental evidence on timber and concrete connectors available from the literature.Then, such 3-dimensional models were used to investigate the connection system of the proposed retrofit strategy paying particular attention to possible out-of-plane effects that cannot be directly observed with 2-dimensional models.The obtained results were used to calibrate the 2-dimensional models so that these "secondary" effects could be accounted for even in the simplified modelling.Subsequently, both modelling approaches were used to analyse an isolated one-storey one-bay frame via nonlinear static analyses that addressed the a) bare, b) original masonry infilled, and c) retrofitted configurations.The two alternative numerical strategies showed consistent results, both suggesting that the proposed intervention can significantly improve the seismic behaviour of existing RC frames.
The durability of timber structures subjected to biotic attacks is becoming of increasing concern due to several recent examples of failures caused by early degradation. Therefore, the design process of a timber building cannot prescind from accounting for the possible degradation due to biotic attack, especially in light of the recent spread of high-rise timber buildings. Furthermore, it is of extreme importance that reliable models to foresee possible sources of degradation in existing buildings are made available so that retrofit interventions can be programmed before it is too late. In the work presented herein, the decay due to fungal attack was predicted through a risk-based approach where decision trees were created to address all the possible scenarios where water or moisture can intrude within the construction details that most affect the durability. These decision trees allow to assign a risk class, defined based on a thorough review of the major European standards addressing timber "use-classes". The trees also lead to the selection of a proper prediction function for estimating the decay depth, chosen among suitable functions available in the literature. The proposed methodology was applied to selected case studies where a good correlation was found between the decay level detected onsite and the results from the prediction model. To facilitate the application of the methodology to both the design of new durable timber buildings and the assessment of existing timber structures, an ad hoc software tool named TSafe was developed. In the present paper, due to the length limit, the focus is on the decision trees and the risk classes, while just a brief description of the case study used for the procedure validation is given.
Construction of vertical expansions on top of existing structures can be considered as an economical and practical solution to contain urban sprawl.The use of timber, due to its lightness, suitability for modularity and prefabrication, and due to environmental benefits, emerges as an interesting option for the realisation of vertical additions in existing buildings.Unfortunately, in seismic-prone areas, the construction of vertical expansions clashes with seismic safety.Current standards require that the safety level of the existing structure after the expansion be that prescribed for new buildings.This requirement represents a major obstacle to vertical expansion because vintage buildings rarely comply with the provisions of the seismic standards even without any addition, making costly retrofit intervention necessary.In this paper, a case study is selected and analysed to try and understand how the vertical timber addition of existing buildings can impact their seismic behaviour.The selected case study is a 1980s four-story RC frame building with masonry infill walls.Following current design practices, a one-storey timber vertical expansion was designed by adopting a cross-laminated timber shear-wall system.The seismic response of the building with and without the timber expansion was then simulated via finite element modelling.The outcomes of the numerical simulations were then used to perform a seismic fragility analysis and assess the effect of vertical expansion on the seismic performance of the case study building.The results of the analysis showed how, in some cases, the vertical timber addition not only does not worsen the safety level of the building but can actually improve it.This outcome opens new paths for future research to further investigate the effect of vertical expansions and maximize their beneficial effect on the seismic response of existing buildings.
Accurate determination of thermal parameters in building envelope components is crucial for evaluating energy performance. While response factor theory has been applied to accelerate the experimental characterization of steady-state thermal properties such as the U-value, periodic thermal properties remain underexplored despite their growing relevance due to global warming. This study presents a novel model based on response factor theory to characterize the unitary heat flux on the opposite side of a pulse solicitation as a function of time and four key parameters. A unified testing methodology is proposed, enabling simultaneous characterization of stationary and periodic thermal properties through a single hot box experiment. Key aspects of the setup, testing protocol, and data processing are detailed. The method was first validated via numerical simulations. Simulations, performed using a Finite Element Method, demonstrate the high accuracy of the proposed method in estimating both stationary and periodic thermal parameters with deviations under 5 %. The method also showed resilience to boundary condition noise (mainly below ± 10 %). Following on from this point, experimental validation on an insulated wall confirmed the approach’s effectiveness, with deviations under 10 % compared to traditional decoupled methods. This approach offers a streamlined pathway for standardized thermal characterization assessment.
1 Ivan Giongo, Department of mechanical and structural Engineering, University of Trento, via Mesiano 77, I-38123 Trento, Italy, ivan.giongo@ing.unitn.it 2 Maurizio Piazza, Department of mechanical and structural Engineering, University of Trento, via Mesiano 77, I-38123 Trento, Italy, maurizio.piazza@ing.unitn.it 3 Roberto Tomasi, Department of mechanical and structural Engineering, University of Trento, via Mesiano 77, I-38123 Trento, Italy, roberto.tomasi@ing.unitn.it Cambering of timber composite beams by means of screw fasteners
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.
It 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 presented herein. Two sections of a diaphragm located in a vintage two-story URM building, measuring 6.4×9.6 m and 4.6×9.6 m, were subjected to a series of cyclic and snap back tests in the direction orthogonal to the floor joists. In order to reproduce a realistic inertial load distribution to the test specimens, an ad hoc loading system using wire ropes and steel pulleys was developed. The loading system was designed to be lightweight, versatile, and relocatable between test specimens. From the obtained test results, it was identified that the equivalent stiffness of existing timber diaphragms (in the direction orthogonal to the joists) is predicted with a certain degree of conservativeness using the most recent procedures currently available in literature, while reliance on the ASCE standard can lead to an overestimation of the floor diaphragm stiffness, even at small displacements. Due to the nonlinear behavior of the tested flexible timber diaphragms, the measured natural period proved to be highly dependent on the target displacement.
