Optimization framework for cost and carbon emission of timber floor elements

Long-span timber floor elements increase the adaptability of a building and they exhibit a significant market potential. High cost of the floor elements is a challenge, and the timber sector is under substantial pressure to find more economical solutions without weakening otherwise favourable environmental performance. The range of technical timber-based materials and components, structural typologies, overlays and ceiling systems represent an immense solution space when searching for a competitive design for a specific building application. Finding the optimum solution requires a computational procedure. In this study a recent development for the accounting of manufacturing resources for timber elements is utilized to build an optimization framework for cost and ECO2 minimisation of timber floor elements finalized at the factory gate. The design of the element is formulated as a discrete optimization problem which is solved by a mixed-integer sequential linearization procedure. Various material combinations and constraint combinations are treated. The optimization framework provides a tool for rapid design exploration that can be used in timber floor design situations. The results of the calculations carried out in this study provide insight on the general trends of optimum floor elements. The optimization model is used to analyse the characteristics of the optimum designs, and a comparison between the current and the proposed method for the second generation of Eurocode 5 is chosen as a vehicle for demonstrating achievable implications.publishedVersio

Withdrawal of pairs of threaded rods with small edge distances and spacings

An experimental investigation on withdrawal of pairs of screwed-in threaded rods embedded in glued-laminated timber elements is presented in this paper. Specimens with varying angles between the rod axis and the grain direction (α = 15°, 30°, 60°, 90°) and 2 different configurations with respect to edge distances and spacings were tested. The diameter and the embedment length of the rods were 20 and 450 mm, respectively. The threaded rods were embedded in a row perpendicular to the plain of the grain. The edge distances and spacings were smaller than the minimum requirements according to Eurocode 5. The withdrawal capacity of pairs of rods was compared to the withdrawal capacity of single rods and the effective number, n ef , was found to be in the range 1.72–1.94, despite the small edge distances and spacings. Based on the experimental results obtained, a simple approximating expression was derived for n ef . An analytical model based on Volkersen theory with an idealized bi-linear constitutive relationship was used to estimate the withdrawal capacity and stiffness. The analytical estimations were in good agreement with the experimental results. Finally, the withdrawal stiffness was estimated by use of finite element simulations. The numerical estimations for the withdrawal stiffness were also in good agreement with the experimental results

Moment resisting on-site splice of large glulam elements by use of mechanically coupled long threaded rods

Large spans of modern timber bridges can be achieved by use of glulam arches with network hanger configuration. Since transportation and production limit the length of timber elements, the glulam arches must be spliced on bridge site. However, it is difficult to obtain practical moment resisting on-site splicing of massive glulam elements featuring flexural rigidity by the available timber splicing techniques. Consequently, the arches are often designed as trusses containing a large number of connections, which are costly and present a risk of decay development. In the present paper, a novel splicing technique suitable for large massive timber sections is presented. The flexural rigidity of the joint is obtained by the utilisation of long threaded rods having large withdrawal stiffness. Fast and easy on-site assembly is facilitated by mechanical coupling of the rods. The rods are oriented with a small inclination to grain, which prevents potential development of shrinkage cracks along the rods. Experimental and numerical methods were used to investigate the flexural joint characteristics. The joint prototypes featured large rotational stiffness without initial slip. As a basis for practical joint design, analytical relations are proposed for estimating the rotational stiffness, the moment capacity and the capacity under combined bending and normal force

On strength and stiffness of screwed-in threaded rods embedded in softwood

Screwed-in threaded rods with wood screw threads feature high axial capacity and stiffness and can be used as fasteners in highly resistant and stiff timber connections. The purpose of the present paper is to review the existing literature and design rules in the present version of Eurocode 5 (EN 1995-1-1) and European Technical Assessments, to identify gaps of knowledge and to provide some proposals for the strength and stiffness of threaded rods. A collection of experimental results is used to derive simple expressions for the withdrawal capacity and stiffness. Finally, theoretical expressions for the stiffness and the capacity of laterally-loaded threaded rods are provided

Moment resisting splice of timber beams using long threaded rods and grout-filled couplers – Experimental results and predictive models

In order to achieve larger spans of timber arch bridges, glulam massive timber sections must be spliced on-site by moment resisting and rotationally stiff joints. In this paper, a novel timber splice connection utilizing long threaded rods and grout-filled couplers is presented. Flexural characteristics of the splice joint were investigated by full-scale experimental tests and 3D finite element models. An analytical model is proposed for determining the moment capacity and the rotational stiffness of the splice connection. The experimentally measured efficiency of the splice connection with regard to moment capacity and rotational stiffness was 69% and 66%, respectively

Withdrawal of pairs of threaded rods with small edge distances and spacings

An experimental investigation on withdrawal of pairs of screwed-in threaded rods embedded in glued-laminated timber elements is presented in this paper. Specimens with varying angles between the rod axis and the grain direction (α = 15°, 30°, 60°, 90°) and 2 different configurations with respect to edge distances and spacings were tested. The diameter and the embedment length of the rods were 20 and 450 mm, respectively. The threaded rods were embedded in a row perpendicular to the plain of the grain. The edge distances and spacings were smaller than the minimum requirements according to Eurocode 5. The withdrawal capacity of pairs of rods was compared to the withdrawal capacity of single rods and the effective number, n ef , was found to be in the range 1.72–1.94, despite the small edge distances and spacings. Based on the experimental results obtained, a simple approximating expression was derived for n ef . An analytical model based on Volkersen theory with an idealized bi-linear constitutive relationship was used to estimate the withdrawal capacity and stiffness. The analytical estimations were in good agreement with the experimental results. Finally, the withdrawal stiffness was estimated by use of finite element simulations. The numerical estimations for the withdrawal stiffness were also in good agreement with the experimental results.submittedVersionThis is a pre-print of an article published in [European Journal of Wood and Wood Products]. The final authenticated version is available online at: https://doi.org/10.1007/s00107-016-1146-

Wedge splitting test of wood for fracture parameters estimation of Norway Spruce

Crack evolution in wood from Norway Spruce during mode I wedge splitting tests was measured using a Digital Image Correlation (DIC) system. The resulting series of deformation fields were post-processed in order to obtain kinematically based crack tip location histories throughout the loading procedure, by a purposely made algorithm. The developed algorithm is based on generic mode patterns which are fitted to the observed deformation fields and optimized. The developed procedure and its application are explained and the resulting crack paths are presented. Subsequently, fracture energies, critical stress intensity factors and experimental resistance curves were derived based on the crack path data. Comparisons of the obtained material parameters for fracture mechanics with literature values show that the proposed method is a powerful alternative to the more traditional methods. Moreover, experimentally derived crack tip location histories give more detailed insight into the behaviour of wood (Norway Spruce) during mode I fracture and may replace indirect methods and crack length assumptions

Long‑term behaviour of Norway spruce glulam loaded perpendicular to grain

The mechanical behaviour of timber loaded in compression perpendicular to grain is essential for a rational design of many timber structures. Structural components frequently exposed to such loading include studs on bottom rails, stress-laminated timber decks, timber elements lying in between vertical load-bearing columns as well as traditional timber joints mating surfaces in compression. Compression perpendicular to grain has been a repeated topic for discussion both in the current European regulations for timber structures, as well as in the ongoing work with the next generation of Eurocode 5-timber structures. However, the long-term behaviour is quite complex, taking both time and moisture variation into consideration, and to improve the understanding and the ability to consider the long-term effects in practical design, a simplified one-dimensional model is given herein. The paper presents novel results from long-term compression orthogonal to grain tests performed with load and moisture control. The purpose of the testing was to evaluate the effect of transversal creep on the long-term behaviour of timber elements including the effect of the mechanosorptive deformation. The test results were in turn used to calibrate a one-dimensional model for the prediction of the long-term response of timber. The model takes into account the combined effects of loading and moisture variations. The effective material properties are defined by use of effective pith locations together with the orthotropic material parameters. Finally, a comparison between the model results and experimental observations is given, showing an overall good prediction of the response