Parametric study of multi-webbed composite timber joists (original) (raw)
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Structural evaluation of castellated timber -joists
Engineering Structures, 2011
A novel timber I-joist with a castellated web is presented. While castellated webs are common in steel joists, this concept is new to timber joists. The openings provided by the castellation process provide for the easy passage of services during construction or subsequent remodelling of a building. The manufacturing process is described together with details of tests on twelve 241 mm and eleven 305 mm deep joists. The load-deflection response, failure loads and modes of failure are given. The mean failure moment and shear force for the 241 mm deep joists were found to be 8.2 kN m and 6.0 kN, respectively. The corresponding values for the 305 mm deep joists were 12.5 kN m and 6.9 kN. The predominant failure modes were tension failure in the web at the corner of the openings and shear failure in the web at middepth between the openings. The effect of the web openings on the joist stiffness is not significant but the shear capacity is reduced. The reduction in shear capacity compares favourably with the shear capacity of commercial joists of equivalent sizes with circular or rectangular openings.
Analytical, numerical and experimental assessment of vibration performance in timber floors
Engineering Structures, 2018
The assessment of the dynamic properties and vibration performance of two full-scale timber floor specimens is presented. The specimen set comprised a Timber-Concrete Composite floor and a Cross Laminated Timber floor. The floors, which are characterized by the same length and mass, are located in two separate five-storey timber buildings constructed in the urban area of Trento (Italy). The assessment was conducted by adopting analytical and numerical methods as well as by performing onsite experimental tests. Mock up samples of the floor specimens were also made and tested in laboratory. Multiple analytical methods that are available in literature were evaluated and compared. The Vibration Dose Value (VDV) method, as proposed by ISO 10137 and BS 6472, was used as reference method for the numerical modelling and the laboratory testing. To determine the VDV, loading associated to human walking was simulated. Dynamic identification tests, where the floors were excited by a modal hammer, were also performed in order to investigate the dynamic properties (i.e. natural frequencies, damping and mode shapes) of the floors. Discussion on the vibration performance of the timber floor typologies studied herein and on the effectiveness of the different assessment approaches (i.e. analytical, numerical and experimental) is provided.
Serviceability Criteria for Design of Timber Floors
2019
This paper summarizes current regulations for comfort assessment of structural vibrations of timber floors in Europe and main design practices of timber floors on this aspect among the European countries. For building design, human activities are the most important internal sources of vibration in timber floors. The daily human activities such as walking, jumping or running on the floor may lead to an uncomfortable feeling to the users when magnitudes of the vibration are uncontrolled. Comparisons of vibration serviceability criteria for design of timber floors among the European countries were conducted and the recommendations on vibration serviceability design of timber floors are proposed.
Engineering Structures, 2013
As part of the research work carried out by the Working Group 3 of COST Action FP0702, the need for vibrational comfort design for buildings and current regulations for comfort assessment of structural vibrations of timber floors in Europe have been summarised. Also the design practices of timber floors with respect to vibrational serviceability criteria, including those for fundamental frequency, unit point load deflection and unit impulse velocity, in up to thirteen European countries have been gathered and their differences been further assessed by analysing flooring systems constructed with three types of joists, i.e. solid timber joists, engineered I-joists and metal web joists. The unit point load deflection criterion is the most crucial one for structural design of timber floors with various types of joists and usually dominates the whole design. Finland tends to be the strictest, followed by Italy, the Netherlands, Austria and Norway, while Denmark, the UK and Ireland are the most generous. Even though EN 1995-1-1 has given general criteria for vibrational serviceability design of timber floors, the variations in the design equations and design limits are still large in the European countries, and hence further harmonisation is still needed.
Transverse Distribution of Concentrated Loads on Timber Composite Floors
Proceedings, 2018
Timber-concrete composite floors can be seen as bi-dimensional elements constituted by repeatable longitudinal elements (timber beams) connected through an element capable to spread the load on the transverse direction (concrete slab). This is usually a fact to “take advantage of” in terms of design, in the light of current regulations, with the analysis of a “T-shape” beam. Nevertheless, when concerning the action of concentrated loads, considering them supported entirely by the beam to which they are applied can result in a disadvantage rather than an advantage. This study focus on the distribution of load in the transverse direction when composite floors are subjected to concentrated loads. There were analyzed not only timber-concrete composite floors, that already have proven their value, but also relatively new solutions as those using cross laminated timber (CLT) combined with steel beams. The results show that the load received by “the loaded beam” can be far from 100%.
Engineering Structures, 2018
Timber exposed to compression perpendicular to grain stresses is of concern in all timber constructions. The challenge is the high diversity of possible load configurations, which mandates for a generic approach with basic properties and case individual adaptations of resistance and stiffness. As the consequences of exceeding the allowed stresses are relatively small, there has been a lively debate on whether compression perpendicular to grain should be treated as an ultimate or better as a serviceability limit state. This debate takes also its place in the currently ongoing revision of Eurocode 5 (EC 5), the European design code for timber structures. In the course of this revision regulations for structural timber products not currently anchored in EC 5, in particular for cross laminated timber (CLT), are now being sought. The product CLT is so far lacking in specifications for the testing, basic properties and design. In awareness of the necessity for generally applicable and reliable design approaches, I aim to present the state-of-the-art on compression perpendicular to grain/plane by focusing on the design, i.e. stress dispersion models, and cross laminated timber. In addition, I present the main data and findings from a comprehensive test campaign and adapt van der Put's stress dispersion model for stress dispersion in directions parallel and perpendicular to grain. This new approach allows an explanation of the influences caused by (i) contact area, (ii) load configurations, (iii) support conditions, (iv) layup and thickness of the CLT element, and (v) clear edge distances and clear spacing. The same approach is applicable for both strength and modulus of elasticity. The necessity to consider the orthogonal layup emerged in the case of CLT. I conclude with recommendations for testing and evaluation, propose basic properties and regulations for the main influencing parameters as also a generic design approach generally applicable for all linear and planar, unidirectional and orthogonal laminated structural timber products.
Experimental and Numerical Analysis of Timber I-Joists with Cut-Outs
2018
This contribution presents the results of an experimental and numerical campaign evaluating the influence of cut-outs on the strength and stiffness of composite timber I-joists. These cut-outs are often introduced in the webs during the instalment of utility lines. The presence of these cut-outs will have an impact on the structural behaviour of the element. However, these influences are not taken into account in the current design standards. In order to evaluate the impact of the cut-outs, an experimental campaign was set up in which the structural behaviour of seven composite I-joist beam was analysed. The geometry and spacing of the cut-outs were varied along these seven beam elements. The experimental results clearly show the reduction in stiffness and the influence on the failure mechanism of the beam elements caused by the cut-outs. Additional to the experimental study, a numerical campaign in which the structural response of these I-joists is modelled is also performed. Nonli...