For structural engineers, the two most important design criteria are utility andsafety. It is about making sure that a structural component is reliable enough not toendanger any of a building's users, while at the same time being as sustainable andefficiently designed as possible. In other words, an element must be safe enough towithstand the improbability and sufficiently cheap to be relevant for the design.Considering this, using a material such as wood instead of metal may prove to be asustainable alternative for certain building components.Timber can be designed to sustain high temperatures and fire; it has a high strengthrelative to its weight and is naturally produced. Furthermore, an engineered woodproduct such as birch plywood has proven very strong in structural applications,especially when glued. Therefore, birch plywood has great potential as a reliablematerial in structural components. In this work, a total of 24 specimens with birchplywood connections were tested experimentally.The specimens were designed to enforce stress states that would occur in actualtrusses. Additionally, Specimens were assembled with two different connectionmethods, one being a dowel-type connection and the other being a glued-type. Eachtype of connection was tested in both tension and compression, with a total of threerepetitions each. For the glued-type specimens, birch plywood plates wereinvestigated in three different angles to the face grain; 0°, 5° and 15°. Theload-displacement relationships and the failure modes are of specific interest in thisthesis.Test results showed that failure modes were semi-brittle and distinct, and the testsshowed that glued-type connections withstood 37% higher loads than dowelledtypes. Specimens might withstand even higher loads if gluing were performed in amore controlled environment. The load-to-face-grain angle of plywood also had asignificant impact on the capacity of connections. For the 0°-specimens with gluedconnections tested in compression, no failures occurred in the plywood, and testsreached loads as high as 82 kN. Calculations were made estimating the load capacityas high as 95 kN, but possibly a more realistic approximation would be 85 kN. Thiswould imply that the 0°-specimens are around 20% stronger than the 15°-specimensand approximately 17,7% stronger than the 5°-specimens tested in compression.Birch plywood is promising to be used in connections of timber structures whereplates transfer forces between structural elements.

En 1879 nace Eugène Freyssinet, padre reconocido del hormigón pretensado. Cuarenta años antes de su nacimiento, ingenieros americanos ya habían empezado a pretensar perfiles de hierro fundido, para evitar que cuando éstos entrasen en tracción, se quebraran. Ciento setenta años después el hormigón armado pretensado se estudia en centenares de artículos, revistas especializadas y tesis doctorales diversas, mientras que el acero pretensado no ha tenido el mismo desarrollo desde unos cincuenta años atrás. Raras son las ocasiones dónde se llega a justificar que pretensar una estructura metálica es necesario y razonable económicamente. Si nos centramos en estructuras de edificación, aún serán menos estas ocasiones. La presente tesis estudia la historia de las estructuras metálicas pretensadas, la mayoría de edificación, algunas de ellas a fondo, como las recientemente construidas en Catalunya. También se repasan las posibilidades que el pretensado metálico ofrece al consultor de estructuras, completándolo con algunos ejemplos. Se ofrece un análisis pormenorizado de la viga Fink, con especial cuidado en su predimensionado y en el cálculo tanto manual, como matricial. Se incluye un análisis de refuerzo de techos formados por viguetas reforzadas trasnversalmente por una viga que cambia su rigidez según criterio del proyectista. Al final se desarrolla una solución de unión de viga y pilar metálico unidos mediante tendones pretensados, para facilitar el montaje en obra, resolviendo las holguras gracias a la unión mediante nudos semirrígidos. / Eugène Freyssinet, born in 1879, is the acknowledged father of prestressed concrete. Forty years before his birth, American Engineers had begun to prestress cast iron profiles to prevent them from breaking after entering in tension. One hundred and seventy years after prestressed concrete is studied in hundreds of articles, journals and diverse dissertations, while prestressing of steel has not had the same development since about fifty years ago. Rare are the occasions where the technician is able to justify that prestressing steel structures is necessary and economically reasonable. If we are considering building structures, these occasions to presstress the structure will be even less. This thesis studies the history of prestressed steel structures, some of them in depth, as some of thoses recently built in Catalonia. It also reviews the possibilities that metallic prestressed structures offer to the consultant, including some examples. It provides a detailed analysis of the Fink truss beam, with special care in their pre-dimensioning and calculation both manually as matrix. It includes an analysis of strengthening reinforced slabs, with a beam that changes its stiffness at the discretion of the designer. Eventually it develops a joint solution of a beam and a steel column, connected by prestressed tendons, to make assembly easier, meeting the gaps with the connection by means of semi-rigid joints.