Delamination and decay are common structural defects in old glued laminated timber (glulam) buildings, which, if left undetected, could cause severe structural damage. This paper presents a new damage detection method for glulam inspection based on moment analysis and wavelet transform (WT) of impact acoustic signals. Acoustic signals were collected from a glulam arch section removed from service through impact testing at various locations. The presence and positions of internal defects were preliminarily determined by applying time centroid and frequency centroid of the first moment. Acoustic signals were then decomposed by wavelet packet transform (WPT) and the energy of the sub-bands was calculated as characteristics of the response signals. The sub-bands of 0–375 Hz and 375–750 Hz were identified as the most discriminative features that are associated with decay and delamination and therefore are indicative of the presence of delamination or decay defects. A defect diagnosis algorithm was tested for its ability to identify internal decay and delamination in glulam. The results show that depth of delamination in a glulam member can be determined with reasonable accuracy.
In this paper a novel and efficient structural system, that comprises steel beams and prefabricated timber slabs is developed and tested under short-term service and ultimate limit state loading conditions. In the proposed steeltimber composite (STC) system, bolt and coach screws are employed to transfer shear between steel beam and prefabricated timber slab and provide a composite connection. A series of experimental push-out tests were carried out on cross-banded LVL-Steel and CLT-Steel hybrid specimens to investigate the behaviour of different connection types. Furthermore, the load-deflection response of full-scale STC beams was captured by conducting 4-point bending tests on STC beams. The failure modes of connections and composite beams have been monitored and reported. The results illustrate advantages of using timber panels in conjunction with steel girders in terms of increasing strength and stiffness of composite beams
For enhancing productivity of glulam, high frequency (HF) curing technique was researched in this study. Heat energy is generated by electromagnetic energy dissipation when HF wave is applied to a dielectric material. Because both lamina and adhesives have dielectric property, internal heat generation would be occurred when HF wave is applied to glulam. Most room temperature setting adhesives such as phenol-resorcinol-formaldehyde (PRF) resin, which is popularly used for manufacturing glulam, can be cured more quickly as temperature of adhesives increases. In this study, dielectric properties of larch wood and PRF adhesives were experimentally evaluated, and the mechanism of HF heating, which induced the fast curing of glue layer in glulam, was theoretically analyzed. Result of our experiments showed relative loss factor of PRF resin, which leads temperature increase, was higher than that of larch wood. Also, it showed density and specific heat of PRF, which are resistance factors of temperature increase, were higher than those of wood. It was expected that the heat generation in PRF resin by HF heating would occur greater than in larch wood, because the ratio of relative loss factor to density and specific heat of PRF resin was greater than that of larch wood. Through theoretical approach with the experimental results, the relative strengths of ISM band HF electric fields to achieve a target heating rate were estimated.
Within the context of efficient and sustainable design of buildings a trend towards lightweight structures, e.g. timber structures, is recognizable. This trend implies the necessity of being able to predict serviceability and comfort as well as sound transmission in order to fulfill vibroacoustic requirements. To generate reliable prediction methods, the transfer of energy between building components has to be investigated. Therefore, a detailed understanding of the modeling of the building components, e.g. walls or ceilings, is compulsory. In the low frequency range the Finite Element Method (FEM) is a convenient tool to predict the vibroacoustic behavior. However, without appropriate post-processing it is limited due to the sensitivity of the results at higher frequencies. In the mid-frequency range a sufficient number of modes per band enables the use of statistical methods like the Statistical Energy Analysis (SEA). It delivers averaged results and thus copes with the sensitivity. As both techniques have a restricted validity regarding the frequency range, averaging techniques of the SEA are applied in the post-processing of the FEM to obtain an adapted hybrid approach, the Energy Flow Analysis. This contribution will focus on the Finite Element Model of the building components out of cross laminated timber modeled as orthotropic plates. The Young’s modulus of wood is perpendicular to the fiber comparatively low, which leads to low velocities of longitudinal and shear waves. Hence, at high frequencies thickness-stretch and thickness-shear modes play an important role. These can be activated already at low frequencies within the stiffness controlled region of their amplification function. Hence, their non-resonant contribution can be identified evaluating the potential energy compared to the kinetic one. This phenomenon is verified with the help of solid elements - in comparison with shell elements - by varying the points of excitation across the thickness. Moreover, the dimensions will be modified as well as the junction by inserting an elastic layer. Whereas the SEA is typically not able to represent through-thickness effects of plate-like structures, the energy flow between a wall and a ceiling will be investigated using the hybrid approach.
This paper examines the performance and apparent temperature in cross-laminated timber (CLT) school buildings. The research presents empirical data on the performance and provides the first set of data on apparent temperature in CLT school buildings. The development is in the New England area of the Northeast of the US. The investigation was conducted in the summertime. The principal aim of the investigation is to evaluate the performance, occupants’ comfort, apparent temperature, and other thermal indices concurrently in CLT school buildings. The research intends to understand if occupants of CLT school buildings are susceptible to thermal stress in summer and assess whether apparent temperatures are consistent with sensation. The study also discusses other indices, practical implications, and applications of the outcomes. To achieve the research aim, the study considered the field measurements of variables. Occupants’ comfort is accessed using the PMV and adaptive methods of various comfort standards. During the survey, the development was occupied from 8am-6pm and partly operated from 7pm-7am. The mean temperatures during the occupied and non-occupied periods varied from 22.1°C-22.4°C. The overall RH was 59.2%. The PMV range and sensation showed the occupants were comfortable. Approximately 80% of the users were satisfied with the thermal environment. The temperatures were within the acceptable bands of ASHRAE-55, CIBSE TM52, and EN16798-1 thermal comfort models. The results showed that the apparent temperatures are consistent with the outcomes of the sensation at different periods. The mean indices ranged from 18.8°C-23.5°C. The study recommends that further research should be conducted on occupants’ comfort and heat indices in school buildings during the first few hours of occupation to understand changes that occupants can make to remove unwanted heat from the thermal environment. The study also recommends that various designers should consider heat stress analyses along with thermal comfort assessment at the design phase to determine possible interventions to improve the thermal environment of schools and other buildings.