The “Bolt of Lightning” is a wood-wood joint used in the traditional way.
For the construction of the porticos of the new chapel of St. John Paul II in the Almudena Cathedral, we implemented a reinterpretation of this joint, achieving elements of greater height. We make a brief analysis of it.
“Bolt of Lightning” or “Trait-de-Jupiter”. A curious traditional wooden scarf joint
This wood joint or splice is a carpentry method that has been used for a long time. Its purpose is to connect two pieces of lumber end-to-end, creating a longer continuous piece. It is especially useful when longer pieces of wood are required, as it allows shorter sections to be combined to achieve the desired length without sacrificing strength.
To create such a joint, the ends of the wood pieces are precision cut with angled surfaces that provide a greater friction surface. These angles can vary depending on factors such as wood species, loading requirements and specific project needs. Typical angles range from 8-12 degrees, although other configurations may be available with right-angle machining.
This bonding is usually done dry, although sometimes the surfaces are prepared to evenly apply an adhesive to ensure an optimal connection. Wooden keys, dowels, or even metal fasteners, such as screws or bolts, can also be added to increase strength and stability.
A challenge in the Chapel of St. John Paul II at the Almudena
Our technical team has deepened in the analysis of this union as a constructive solution to one of the most recent projects. This is the new Chapel of St. John Paul II, in the Almudena Cathedral in Madrid, a work conceived by the Cano y Escario studio, constructively resolved and executed by Grupo GUBIA.
The architectural firm’s initial concept was a parametric envelope of wooden squares inserted into one of the building’s side chapels. To achieve this intention, the structure had to have a considerable height. This condition required the use of wooden elements up to 9 meters in length.
Our R&D department undertook the challenge of overcoming the length limitations of the available wood, while maintaining the formal requirements of the project and structural integrity. To this end, we designed an end-joint with a wood-wood loop, reinterpreting the Jupiter Beam. This design was materialized in full-scale mock-ups and programmed in our numerical control machining center (CNC) to be carried out in series, an essential factor in this type of operation. In these operations, automated work allows for precise joining and greater geometric complexity.
Geometric reinterpretation of the Bolt of Lightning joint
This joint between squares is repeated at different heights according to the height of the portico in question, along the entire perimeter. The final joint consisted of an inclined broken line, with rounded angles that generated a subtle joint between the pieces of wood. The longest friction line includes two machined sections, which concealedly house pieces of wood. These are responsible for facilitating the flush between the faces of the brackets. Two stainless steel screws reinforce the joint, increasing its rigidity. The species of wood used, cedro cedrela odorata, is a light but highly resistant wood, which facilitated the machining work and the subsequent performance of the joint.
In addition to this interesting connection method, the brackets were machined one by one in the areas where the porticoes break. In this case, with different angles in up to three directions, and some of them, lowered at their edges to accommodate continuous LED lighting.
More than a solution, a work philosophy
In general, the analysis of the joints carried out to achieve the slender pieces made it possible to bring the physical quality of the Bolt of Lightning joint closer and to reinvent it in a more contemporary form, which meant a success in the shaping of the porticoes.
The use of applied knowledge, with the help of machinery for the automation of machining, is one of the working tools in our daily work. It is important to understand the use of these review strategies, comparative, samples, mock-ups, testing and samples within the conception of wood projects from the beginning as an integrated process of technical consulting to ensure the effectiveness of the works. In this case, an intervention of great significance was achieved for this historic building in the city.