Classical flutter of suspended bridge decks can be avoided if the torsional frequencies are lower than the vertical. Wind tunnel tests of single boxes and twin box section models with torsional natural frequencies above and below the vertical frequency has been conducted. Flutter was avoided in all tests where the torsional frequency was lower than the vertical. But too low torsional stiffness caused large static displacements of the girder at medium–high wind speeds and steady state oscillations driven by a combination of torsional divergence and stalling behavior at the critical wind seed. In order to design aerodynamically stable suspension bridges with low torsional natural frequencies it is suggested to increase the mass moment of inertia and provide adequate torsional stiffness by the main cables spacing.

Damping elastomers are often used in lightweight wooden constructions and are believed to have good sound insulating effects. In the present study the influence on the structural behaviour by using elastomer damping material (Sylomer®) in the joints, with particular respect to footsteps and floor vibrations, has been investigated. A full scale wooden mock-up was assembled with two different joint configurations and studied under free-free boundary conditions. In the first configuration, the joints between the floor and underlying walls were screwed together. In the second configuration the floor was resting free on top of ribs of elastomer damping material, equivalent to normal building practice when this material is used. Both configurations were analysed and evaluated using experimental modal analysis, in the frequency interval 10-115 Hz.

The relative (viscous) damping ratios of the modes were found to be on average 1.2% for the screwed configuration and 2.1% for the configuration with elastomer damping material in the joints. The damping was found to vary significantly between modes in the elastomer case. It was found that at low frequencies damping was high for modes with large motion on the edge where the elastomer material was. At higher frequencies (above approx. 40 Hz), however, the damping for this configuration decreased. This is believed to be caused by a vibration isolation effect of the elastomer, decoupling the floor from the walls at higher frequencies.

To assess the differences in vibration levels between the two configurations, mean acceleration levels of well spread points on the different building parts where computed and evaluated. It was found that above approximately 70 Hz, the mean vibration level in the elastomer configuration was significantly lower than for the screwed configuration. Below 70 Hz, however, for many frequencies the mean vibration level for the elastomer configuration was significantly higher than for the screwed configuration (as should be expected in vibration isolation). Problems with springiness and footsteps are due to loads in the frequency range of 10 to 50 Hz, this could indicate that elastomers, used as in the present study, could worsen these types of problems, although improving higher frequency acoustic performance.

A finite element (FE) analysis of a model representing a mock-up structure previously investigated experimentally is investigated in this study. The aim is to make a correlation and calibration between test and analysis of the full scale wooden structure; both eigenmodes and acceleration levels are compared. Large scatter is found in material properties used for light weight wooden structures in literature. In this study, a parameter evaluation is therefore made to show how different properties influence the dynamic behaviour of the structure. It is shown that the wood beam material properties influence the behaviour of the light weight wooden structure FE model most.

Two types of junctions are modelled and evaluated; a tied connection is used to simulate screwed junctions and spring/dashpot elements are used to represent elastomer junctions between the floor and the walls. The springs and dashpots used to model the elastomer in the junction work well in the bearing direction but need to be improved to obtain correct rotational stiffness, shear motion and friction. There are still many unknown parameters in a complex wooden structure that remain to be investigated. However, the results presented in this paper add data to be used for FE modelling of a complex wooden structure.

Dowel-type connections are commonly used in timber engineering for a large range of structural applications. The current generation of design rules is largely based on empiricism and testing and lacks in many parts a stringent mechanical foundation. This often blocks an optimized use of the connections, which is essential for the design of economically efficient structures. Moreover, it severely limits the applicability of the design rule, such as restrictions regarding splitting behavior or maximum ductility (e.g. maximum allowable deformations) are missing. Therefore, the demands due to a large and quickly evolving variety of structural designs in timber engineering are not reflected. The aim of this work is to study the load-carrying behavior of the connection in detail, including all loading stages, from the initial contact between dowel and wood up to the Ultimate load and failure. Distinct features during first loading as well as during unloading and reloading cycles are identified and discussed. The knowledge of the detailed load-carrying behavior is essential to understanding the effects of individual parameters varied in relation to the material and the connections design. The suitability of the current design rules laid down in Eurocode 5 (EC5) is assessed and deficiencies revealed. Tests on 64 steel-to-timber dowel-type connections loaded parallel to the fiber direction were performed. The connections were single-dowel connections with dowels of twelve millimeter diameter. The test specimens varied in wood density and geometric properties. Additionally, the effects of dowel roughness and lateral reinforcement were assessed. The experiments confirmed that connections of higher density show significantly higher ultimate loads and clearly evidenced that they are more prone to brittle failure than connections using light wood. The latter usually exhibit a ductile behavior with an extensive yield plateau until final failure occurs. With increased dowel roughness, both, ultimate load and ductility are increased. The test results are compared with corresponding design values given by EC5 for the strength and the stiffness of the respective single-dowel connections. For connections of intermediate slenderness, EC5 provided conservative design values for strength. Nevertheless, in some of the experiments the design values overestimated the actual strengths considerably in connections of low as well as high slenderness. As for the stiffness, a differentiation according to the connection width is missing, which gives useful results only for intermediate widths. Furthermore, the test results constitute valuable reference data for validating numerical simulation tools, which are currently a broad field of intensive interest.

Abstract A new type of semi-rigid timber beam-to-beam connection and its behavior under bending is presented. This connection consists of four identical steel parts, which are inserted into the timber beams in the tension and compression zone of the connection. These steel parts are easily connected by mounting bolts on the construction site. In order to avoid initial slip, gaps between the timber and the steel parts are filled using two different types of filler materials, namely cement based (CEM) or polyurethane based (PUR) filler. In this study, the connection is modeled by means of the Finite Element (FE) Method and the modeling results are compared to the results of an experimental assessment of the proposed connection under bending. The material model for timber encompasses a Hill criterion in combination with cohesive surface contact in order to depict both, yielding in compression and brittle failure in shear and tension perpendicular to the grain. The experimentally observed decisive failure mode, i.e. shear block failure, could be reproduced by the model. Subsequently, the FE model was used to investigate the effect of using different filler materials, or not considering the filler in the analysis at all. In addition, a particular influence of clamping bolts in the timber on the strength of the connection was revealed. The FE analysis excluding these bolts showed good agreement with the experiments in terms of the strength of the connection, while considering these bolts led to an overestimation of the strength. This is a consequence of the considerable influence of the clamping bolts on stresses perpendicular to the grain in the timber in the block-shear area, and therefore, on shear failure initiation. Using the CEM filler hardly changed the overall behavior of the connection as compared to the analyses without filler material, while the PUR filler leads to a less ductile overall behavior. This is well in line with experimental observations. The application of modeling approaches for timber has proven suitable for the analysis of such a type of timber beam-to-beam connection and, consequently, might be used for further optimization of this connection.

A stiffness model for inclined screws in timber joints, or as shear connectors in composite timber-to timber members, is presented. Elastic conditions applicable to the initial or linearized part of the load deformation response in the serviceability limit state are assumed. The model for the stiffness or slip modulus is general in nature; it includes both the dowel (or shearing) action and withdrawal action of the screw, the friction between the members and it takes into account possible dissimilar properties and geometries of the different parts of the joint configuration. The model is simplified in the sense that the screw is assumed rigid and the withdrawal stresses along the length of the screw are assumed evenly distributed. However, the effects of flexibility and extensibility of the screw are taken into account by applying a theoretically derived correction factor for the embedment and withdrawal stiffness modulus, respectively. The proposed model is illustrated showing the total stiffness versus the inclination, as well as the relative contributing effect from the shearing and withdrawal stiffness, respectively, the influence of the friction coefficient. Also, the effect of dissimilar properties and geometries between the two parts of the joint is illustrated. Experimental verification of the proposed model is also given. Comparisons with other stiffness models are also made. (C) 2017 Elsevier Ltd. All rights reserved.

Dowel-type fasteners in combination with steel plates are widely used in engineered timber structures. Since dowel groups are designed as semi-rigid connections subjected to an arbitrary set of internal forces, the corresponding structural behaviour of the surrounding timber matrix must be considered in the design process accordingly, including the effect of reinforcements. Corresponding stress states and failure mechanisms in the timber matrix of dowel groups are discussed herein. Surface strain fields from tests of dowel groups under complex loading situations were used to identify the sequence of cracking, as well as to assign the related failure modes. First cracking events were caused by stress peaks at the most loaded dowels and by a combination of shear stresses and stresses perpendicular to the grain, while later crack- ing events were associated with a predominant action of individual stress components. Thus, the non- linear global moment-relative rotation behaviour of dowel groups could be related to failure mechanisms in the surrounding timber matrix. The corresponding strain state was qualitatively as well as quantita- tively reproduced by means of a numerical model, which gave access to stresses in the timber matrix and has potential to be implemented as a sub-model in engineering design software. The numerical model supported the feasibility of a decomposition of the stress state due to the global bending moment into stresses caused by a couple of equal forces parallel and perpendicular to the grain, which could be used in the design process. Based on experimental and numerical findings, essential aspects for a design procedure for the timber matrix in dowel groups loaded by a combination of internal forces are proposed. 

Natural frequencies, damping ratios and mode shapes of a prefabricated timber floor element have been assessed experimentally in laboratory with different boundary conditions and in situ (in field) at different stages of construction. In laboratory the change in modal parameters was studied with free-free boundary conditions and simply supported on two sides. Three different simply supported tests with changes in boundary conditions were carried out; the floor placed on the support without any fastening or interlayer between support and floor, the floor screwed to the supports and the floor placed on an elastic interlayer between support and floor. The in situ tests were carried out first on the single floor element and then on the entire floor of the room into which the floor element was built in. The damping ratio of the floor increased from 1% to 3% when simply supported in laboratory to approximately 5% when placed upon a polyurethane interlayer (Sylodyn) in situ, and to approximately 6% when fully integrated in the building. Thus the in situ conditions have considerable influence on the damping and the values assessed are very high in comparison with damping values suggested in design codes. Regarding natural frequencies it was concluded that the major change in these occur as the floor element is coupled to the adjacent elements and when partitions are built in the studied room, the largest effect is on those modes of vibration that are largely constrained in their movement.

In this paper, the influence of torsional warping of thin-walled cross-sections of twisted Functionally Graded Material (FGM) beams with a longitudinal polynomial variation of the material properties on their eigenvibrations is investigated, considering the secondary deformations due to the angle of twist. The transfer relations needed for the transfer matrix method are derived. Based on them, the local finite element equations of the twisted FGM beam are established. The warping part of the first derivative of the twist angle, caused by the bimoment, is considered as an additional degree of freedom at the beam nodes. The focus of the numerical investigation, with and without consideration of the Deformation due to the Secondary Torsional Moment (STMDE), is on modal analysis of straight cantilever FGM beams with doubly symmetric open and closed cross sections. The influence of the longitudinal variation of the material properties and the secondary torsion moment on the eigenfrequencies is investigated. The obtained results are compared with the ones calculated by a very fine mesh of standard solid and warping beam finite elements.

In recent years, research has shown that the lower frequency portion of impact sound, down to 20 Hz, is of significant importance to residents' perception in buildings that have lightweight timber floors. At low frequencies, the finite element method is a useful tool for predictive analysis. Impact sound frequency response functions, which are easily calculated using finite element software, are useful as they offer a common ground for studies of correlations between measurements and analyzes. On the measurement side, the tapping machine is well defined and has become the standard excitation device for building acoustics. When using a tapping machine, the excitation force spectrum generated - necessary to achieving experimental frequency force to sound response functions - is unknown. Different equipment may be used for excitation and force measurements and if a structure behaves linearly, the use of any excitation devices should result in the same frequency response functions. Here, an ISO tapping machine hammer is fitted with an accelerometer, enabling estimates of input force spectra. In combination with measurements of the sound in the receiver room, frequency response functions are then achieved using an ISO tapping machine. Various excitation devices have been used on a floor partition in a timber building and on a cross-laminated timber (CLT) lab. floor in order to compare the resulting frequency response functions. Structural nonlinearities are evident, implying that for accurate frequency response measurements in acoustically low frequencies, excitation magnitudes and characteristics that are similar to these which stem from human excitations, should preferably be used.

Wood is a hygro-mechanical, non-isotropic and inhomogeneous material concerning both modulus ofelasticity (MOE) and shrinkage properties. In stress calculations associated with ordinary timber design,these matters are often not dealt with properly. The main reason for this is that stress distributions ininhomogeneous glued laminated members (glulam) and in composite beams exposed to combinedmechanical action and variable climate conditions are extremely difficult to predict by hand. Severalexperimental studies of Norway spruce have shown that the longitudinal modulus of elasticity and thelongitudinal shrinkage coefficient vary considerably from pith to bark. The question is how much thesevariations affect the stress distribution in wooden structures exposed to variable moisture climate. Thepaper presents a finite element implementation of a beam element with the aim of studying how woodencomposites behave during both mechanical and environmental load action. The beam element is exposedto both axial and lateral deformation. The material model employed concerns the elastic, shrinkage, mechano-sorption and visco-elastic behaviour of the wood material. It is used here to simulate the behaviourof several simply-supported and continuous composite beams subjected to both mechanical and environmentalloading to illustrate the advantages this can provide. The results indicate clearly both the inhomogeneityof the material and the variable moisture action occurring to have had a significant effecton the stress distribution within the cross-section of the products that were studied.

Plastic analysis in engineered structures requires ductility of structural components, which in timber structures is primarily provided by joints made of dowel-type fasteners. A prerequisite for nonlinear analysis is realistic modeling of joint stiffness and load distribution in dowel-type joints. A joint model suitable for structural analysis is presented and validated in this contribution. The semi-analytical joint model is based on kinematic compatibility and equilibrium considerations. It accounts for local fastener slip by means of nonlinear elastic springs. Influences of nonlinearity and orientation dependence of fastener slip are assessed. Elastic deformations of the timber in between dowels are however neglected. The model allows for predicting global joint stiffness, as well as load distribution within the joint, taking explicitly the effect of simultaneously acting internal forces into account. Model validation builds upon an experimental database that spans from embedment testing on the material scale up to joint testing on the structural scale. Application examples demonstrate the broad applic- ability of the model for structural analysis. Moreover, they illustrate effects of assumptions of fastener slip on the joint and structural behavior. Limitations, as well as pros and cons of these assumptions are discussed. Special attention is drawn to load distribution within the joint, since it is important for fastener-based design, currently prescribed by the European design standard. Load distribution in joints is also important for verification against brittle failure modes. As an alternative to fastener-based design, joint-based design, by means of a framework for applying the presented model to plastic design of timber structures with ductile joints, is proposed.

The present investigation focuses on evaluating the entire load displacement relationship, especially the softening part, of light-frame wall segments subjected to in-plane monotonic forces when the load-slip curves of the individual sheathing-to-framing fasteners are considered. Different sheathing-to-framing joint characteristics, including unloading behaviour, and stud-to-rail joint characteristics are incorporated in the analyses. Two loading cases are investigated: Horizontal loading resulting in uplift of the leading stud and diagonal loading representing a fully anchored wall. Two common types of finite element (FE) models for the sheathing-to-framing joints are used for the analyses: A single spring model and a spring pair model, where the joint characteristics valid for the timber properties perpendicular and parallel to the grain are used. The maximum capacity of the wall segments is somewhat overestimated when using the spring pair model compared to that of the single spring model. The softening parts of the load displacement curves are significantly affected, regardless of whether the perpendicular or parallel characteristics of the joints are used. The results from FE simulations using models with perpendicular and parallel characteristics are compared with full scale test results for walls with a single segment loaded horizontally and diagonally. The behaviour of the wall segments subjected to horizontal loading is dominated by fastener displacements perpendicular to the bottom rail. Hence, FE models including perpendicular characteristics should be used. For diagonal loading the behaviour of the wall segments is dominated by displacements parallel to the framing members, and FE models including parallel characteristics should therefore be used. The analyses were extended to multiple segment walls resulting in the same type of behaviour as single segment walls. (C) 2014 Elsevier Ltd. All rights reserved.

Four different elastic models for sheathing-to-framing connections are presented and evaluated on asingle connection level and on a shear wall level. Since the models are elastic in their nature they aresuitable mainly for cases where the sheathing-to-framing connections are subjected to monotonicallyincreasing displacements. Of the four models one is uncoupled and the others are coupled with respect tothe two perpendicular displacement directions in a two-dimensional model. Two of the coupled modelsare non-conservative, while the third is conservative, indicating a path independency with respect to thework done to reach a defined state of deformation. When the different models are compared it is obviousthat the uncoupled model gives strength and stiffness values higher than the others; however it is notobvious which of the models to use in a shear wall analysis, each of the models having its advantages anddisadvantages. For the experimental data used as input in the analyses of this study however, a couplednon-conservative model seems the most appropriate.