A general bearing deformation model for timber : compression perpendicular to grain

This study focuses on a new and unique model to determine the elastic bearing deformation of structural timber. Available models that aim to predict the deformation are usually limited in their application. The performance of a simple model is compared to three other models, all being evaluated using experimental test data for the wood species Norway Spruce, Poplar, Beech, Cumaru and Akki and covering eight different load cases. The results show a simple model to have the best performance in deformation prediction and so is a potential candidate for introduction in updated structural timber design codes

Perpendicular to grain bearing strength of timber

Compressive strength perpendicular to the grain of timber beams is a difficult problem as that not only many different load cases occur in practice but also there is the lack of a reliable model. Furthermore, in the US, Europe and Australia/ New Zealand the standardised test methods to determine the compressive strength lead to very different strength values. A physical model with a reference compressive strength as starting point is presented, which claims to account for the differences mentioned. The evaluation accounts for a total of 590 radiate pine test results that cover four load cases and two specimen sizes. It is shown that the model presented is able to explain test results previously regarded incompatible. The model offers a consistent and simple way to bridge the differences between ASTM, ISO, CEN, Australian and New Zealand test standards. Introduced in structural design codes the model enables a more accurate estimate of bearing capacity

The bearing strength capacity perpendicular to grain of Norway spruce:Evaluation of three structural timber design models

The perpendicular to grain compressive strength of timber is known to be much lower than the strength parallel to grain. Many timber structures, however, rely on this property especially in bearings that occur frequently in building practice. The linear elastic–plastic behaviour of structural timber loaded perpendicular to grain has been a problematic issue for decades which is reflected in the differences between the prediction models in structural design codes over the world. This article concentrates on the evaluation of the strength predictive ability of three of the latest bearing models having an empirical, semi-empirical or physical background. On the bases of a large database of over 1000 test results covering eight practical load cases, it is shown that the accuracy and consistency of the physical model is the best, which makes it a potential candidate for the new generation timber design codes

The local bearing capacity perpendicular to grain of structural timber elements

The accuracy and reliability of empirical models for the local bearing capacity perpendicular to grain of timber beams is questionable as it is not based on any fundamental principal. This study shows that a physically based stress dispersion model can successfully be applied for a wide range of practical design situations. The credibility of this model is based on experiments, FEM and optical techniques used to assess and quantify the strength affecting parameters. This model is a potential candidate to be incorporated in future structural timber design standards

Structural performance and advantages of DVW reinforced moment transmitting timber joints with steel plate connectors and tube fasteners

This paper presents a study to the moment-rotation aspects of two 3-member DVW reinforced timber connections with an inter-connecting steel plate used as middle member. Previous studies showed that reinforcing dowel-type timber connections with ‘densified veneer wood’ (DVW) and using expanded tube fasteners results in connections with superior structural properties compared to all conventional connections. In this connection type, the DVW prevents premature timber splitting. The tube fasteners aid a high initial stiffness, a high ductility and a high reliability. A drawback of the connection, already in a 3-member connection, is the total thickness. By using only two side members and a much thinner, steel middle member, the thickness is strongly reduced. The steel middle member is used as a connecting interface in a flitch plate connection. This generally results in a 50% reduction of the rotational stiffness. However, it is shown by an analytical and numerical study, that the rotational stiffness of two closely spaced, flitch plate DVW connections acting in series remains unchanged if certain conditions are fulfilled. Two full connection tests are performed to confirm the analytical and numerical results. Additionally, the paper presents a comparison to a conventional connection, which confirms the structural quality of the reinforced connection

The bearing strength perpendicular to the grain of locally loaded timber blocks

The compressive strength perpendicular to the grain is one of those wood properties that are important for structural design but are difficult to tackle due to its semi-plastic behaviour. It depends on deformation, the specimen type and loading condition. For long no common definition for the standard compressive strength was agreed. A comprehensive survey of research work is given by Augustin and Schickhofer [1], Kollmann [4], Gehri [3], Madsen [6] and Blass and Görlacher [2]. Some empirical models were proposed by Madsen [6] and Riberholt [7]. Van der Put [10] presented a physical model as early as 1988, based on plasticity theory. He showed the ability and accuracy of his model with test data from literature. Despite of his effort the absence of any reference to his model in later publications indicate the model is not well understood. To convince those who are still in doubt a comparison follows between the Van der Put model and the empirical model of Eurocode 5. It is concluded that Eurocode 5 is unsafe while Van der Put's model is by far superior

Duration of load effects on the splitting behaviour of timber loaded perpendicular to the grain by dowel-type connections

The duration of load (DOL) effects of timber, and mainly the time-to-failure (TTF), are investigated numerous times in the past, and are now fairly well understood. The time-to-failure of connections is investigated mainly for joints parallel to the grain. Comparison of these connections and timber shows a rather similar TTF behaviour. Only a limited number of investigations are known that address the TTF effects of timber loaded perpendicular to the grain by connections with dowel-type fasteners, where splitting cracks are the primary cause of failure. From this it follows that the timeto-failure behaviour is more severe for these types of connections. The same applies for variations in temperature and relative humidity of the test environment. This paper describes duration of load tests on the splitting strength of timber loaded perpendicular to the grain by dowel-type connections, where the connections have introduced high stress levels since late 2006