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The use of timber pins in connecting timber elements is a valid alternative to the employment of metallic devices, and apart from being quite spread in prefabricated timber frames, it could be an efficient solution in the field of restoring timber structures. The design rules for pinned joints are universally based on Johansen’s theory, (European Yield Model), but their application to timber pegged connections still shows some unsolved problems, linked to: 1) dowel-bearing strength; 2) bending strength of the pin; 3) shear strength of the pin; 4) the feasibility of the fourth failure Mode of EYM. Many studies analysing one or more of those aspects can be found in literature, but there isn’t yet an analytical formulation alternative to this on which the EYM is based. Authors are carrying on an extended experimental research, trying to better understand the complex mode of failure of timber joints connected by timber pegs, and consequently improving design rules. A first phase has involved double shear plane joints of glulam fir connected by ash pins, varying thickness of jointed board, pointing out the role of bending strength. In a second step the role of dowel-bearing strength has been investigated, choosing as base material three wood essences with quite different densities. Now the final step of the whole research is presented: first of all, the role of pin shear strength has been studied; then all obtained results are employed in analyzing the behaviour of double shear plane joints with varying timber essences and its transposition in using design rules.

This study is part of a larger research devoted to the analysis of the behavior of timber joints connected with timber pins, which of course is quite different from that in presence of steel bolts. As in the last case design formulas are based on the Yield European Model, which involves mechanical characteristics of the dowel as well as of the timber elements constituting the joint, the whole research aims to the identification of similar properties in the case in hand. Specifically the present study analyzes, with an experimental approach, the dowel-bearing behavior when employing a timber pin instead of a steel connecting device. The final task is the definition of a procedure to identify the value of the dowel-bearing strength of the jointed elements' timber to be inserted in design formulas, going through the understanding of the role of the timber pin behavior when confined inside the joint and its influence on the dowel-bearing behavior.

This bridge has a single 55 m span, whose cross-section is V shaped, and of variable size, in order to approach as far as possible to a uniformly stressed structure. The variation in cross-section depends on a reduction of height, from the span centre towards the abutments, whilst the thickness of the box section remains constant. The post-tensioning reinforcement consits of 22 cables, of 42 mm diam., BBRV system. They run along the bottom part of the V section, but rise towards the top of the section as they approach the abutments. The arrangement enables the curvature of the cables to be kept very low, and consequently the friction losses are also minimal. Owing to the length of the cables, such losses would have been substantial in a normal design. Measurements during the tensioning operations have shown that friction losses were in fact small, varying between 9 and 12%., El puente consta de un solo tramo de 55 m de luz, con sección en V y perfil variable, para acercarse de esta forma a la resistencia uniforme. La variación de la sección se ha realizado disminuyendo la altura desde el punto medio hacia los apoyos y dejando que las paredes conserven la misma inclinación. La armadura de precompresión, formada por 22 cables de 42 Ø 6, sistema BBRV, está alojada en el vértice inferior de la V; avanzando hacia los apoyos, los cables se elevan a lo largo de las paredes, anclándose todos en los extremos. Tal disposición ha permitido mantener los ángulos de elevación dentro de valores muy bajos (máximo valor, 5° 10') y limitar, por tanto, las pérdidas por rozamiento, ya que, dada la longitud de los cables, esto constituía una notable limitación en el aprovechamiento de los aceros. En efecto, de las medidas efectuadas durante las operaciones de tensión se han encontrado pérdidas por rozamiento modestas, variables del 9 al 12 por 100.