Splitting of beams caused by multiple connections along the beam span

: In the past splitting of beams caused by connection perpendicular to grain has drawn attention. Models have mainly being developed considering one mid span connection. Some semi-empirical models assume the splitting capacity to be proportional with the number of connections when sufficiently spaced. However, recent experiments show this is not the case. Experiments show a considerable drop in splitting capacity per connection. Until now only a fracture mechanical model is able to explain the result for beams loaded by two connections. Experiments with three connections along the span of a simply supported beam show an even greater drop in splitting capacity per connection. The test results are presented and evaluated and compared to model predictions

Splitting of beams caused by multiple connections along the beam span

: In the past splitting of beams caused by connection perpendicular to grain has drawn attention. Models have mainly being developed considering one mid span connection. Some semi-empirical models assume the splitting capacity to be proportional with the number of connections when sufficiently spaced. However, recent experiments show this is not the case. Experiments show a considerable drop in splitting capacity per connection. Until now only a fracture mechanical model is able to explain the result for beams loaded by two connections. Experiments with three connections along the span of a simply supported beam show an even greater drop in splitting capacity per connection. The test results are presented and evaluated and compared to model predictions

Compressive capacity perpendicular to grain of fully supported timber beams of Poplar - model comparison

In timber frame structures, for both residential and multi-storey purposes, timber elements are loaded perpendicular to grain. In the past, structural design code calculations were based on pre-set permissible strength values, applying empirical models with obscure background. Modern ultimate limit state structural design codes, like the Eurocode 5 (EC5) for timber structures, aim at using models that reflect "real" material behaviour. As more experimental results emerge, however, the reliability of the implemented EC5 model is questioned more and more. In the last decade a number of new models have been proposed. One is based on a fundamental principal, the so-called stress dispersion model, but the others are still empirical. This study shows the physically based stress dispersion model to be more reliable in predicting the bearing capacity of poplar for a wide range of practical design situations, than the empirical model of EC5

Beams loaded perpendicular to grain by connections

This contribution addresses the following issues regarding splitting: - Is the splitting strength dependent on the connection width along the grain when laterally loaded dowel-type fasteners are applied? - Is the Eurocode 5 model valid for axially loaded screws? - Is the Eurocode 5 model safe for multiple connections along the span

Infill Panels and the tube connection in timber frames

In recent years timber infill panels have been proposed for multi-story column-beam frame structures with the aim to substitute the stabilizing function of column-beam moment connections. The preliminary study reported in this paper considers a column-beam timber frame where stability is assured by cross-laminated timber (CLT) infill elements. The performance of the system depends on frame-panel connections as well as the dimensions of the CLT panel. The desk research focused on the behaviour of such an assembly using high performance reinforced frame-panel connections comprising steel tube fasteners. The numerical investigation is aimed at optimizing the interaction between frame and infill as a function of CLT panel stiffness in addition to the number and location of the connections. It is shown that the overall lateral stiffness of timber infill frames compares well with concrete infill steel frame

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

Behaviour of bond lines in dvw reinforced timber connections

This paper presents a study of the behaviour of bond lines of Densified Veneer Wood (DVW) reinforced timber connections. Studies by Leijten in the 90s have shown that reinforced timber connections with DVW results in a significant enhancement of connections properties. The DVW is in these connections glued onto the timber. Recently, these reinforced connections were studied in column-beam and splice type arrangements using connecting flitch plates. In these arrangements additional stresses are introduced in the bond line. A numerical study was performed to the bond line capacity, but experiments did not fully verify the predictions. For the present study the fracture mechanical properties of bond lines between DVW and Norway Spruce were determined experimentally, and were implemented in three dimensional finite element models. Delamination tests were performed to verify the numerical procedure. From these tests it is concluded that the numerical predictions correspond well to the experiments

Advantages of DVW reinforced moment transmitting timber joints with steel flitch plates for colum-beam application

This paper presents a study into the moment-rotation aspects of dvw (densified veneer wood) reinforced timber connections with an inter-connecting flitch plate used as middle member. Previous studies showed that reinforcing dowel-type timber connections with dvw and using expanded tube fasteners results in connections with superior structural properties regarding strength, stiffness and ductility. Drawback is the total thickness of a three-member connection. By exchanging a timber member by a much thinner steel flitch plate, the thickness can be strongly reduced. This arrangement has particular advantages as column-beam connection. This paper shows by a analytically and numerically study confirmed by experiments that the stiffness of two connections in series have the same stiffness as a single connection

Spliting of timber caused by multiple connections

The models developed in the past that aim at predicting the splitting failure of timber beams loaded perpendicular to grain by connections are empirical, semi-empirical or based linear elastic fracture mechanics and consider only one connection at mid span. These models have been calibrated to these single connection mid span test. Laboratory test are presented for multiple connections. Few model attempted to explain and predict the behavior for multiple connections but they were not very successful. The model presented in this paper by Schoenmakers [6], which is based on linear elastic fracture mechanics, explains the test results with more success although it is limited to apply to two connections for the time bein

Traditional timber frames

Due to new possibilities traditional timber framing has become increasingly popular since the beginning of the 21e century. Although traditional timber framing has been used for centuries, the expected mechanical behaviour is not dealt with in great detail in building codes, guidelines or text books. Especially the behaviour of connections is of great importance govern the stiffness (and stability) behaviour of traditional portal frames. A mechanical model is developed to describe and predict the behaviour of a portal frame. The stiffnesses used in this model are based on test data. The theoretical analysis is based on the work energy metho