The final development of V3 for the UBC Brock Commons tall wood project pushes the boundaries of timber construction into new and experimental realms. This third exploration ( see V1, and V2) uses a hex grid system combined with reciprocal framing. A system of this nature presents unique challenges in terms of assembly and connection optimization. Reciprocal framing makes use of distributed load paths which can allow for smaller dimensions of the material used. Depending on the final configuration this can result in overall material savings, but more commonly the usage of smaller sizes of materials (yet overall higher volume) which can also result in cost savings.
A basic dimension of 6 m for the hexagon arm length, or hex radius was used to allow for appropriate room sizes and for the building to fit within the lot sizing allocations. These hex grid panels are broken up into six sections of 6 m equilateral triangles. A reciprocal framed floor breaks this grid down smaller to 3 m equilateral floor panels. This size of floor panel makes the units easy to move and allows for enhanced mass production. This also gives us the option for a variety of manufacturing techniques. The first technique allows massive adaptability, but takes more install time by installing each 3 m equilateral CLT panel individually onto the reciprocal frame. The second involves using the larger 6 m equilateral grid section (comprised of four, 3 m panels). The smaller 3 m CLT panels are prefabricated along with the reciprocal beam grid and services into a larger 6 m equilateral base panel. These large base panels placed on the reciprocal beam grid system are landed in a special six way steel connector which is attached to a glulam (or LVL/ parallam) column. As a third, and likely most cost-effective option floor panels can be produced in regular manufacturing widths and installed in 12 m lengths, reducing overall crane time and manufacturing re-work.
Due to the nature of the grid, bracing is spread out between a 3 component plane. Depending on the direction of exterior forces they are dispersed as X/Y components into the hex-grid structure. Bracing is placed in key walls arranged within the hex grid. This supplies a unique architectural challenge, yet can still produce a beautiful quality of space. There are specific challenges around the elevator core and how to fit a square unit into a distinct geometric pattern. This would be an area of ongoing analysis. A concrete service core runs up through both towers, also providing stiffness to the structure. Specially attention needs to be paid to differential height changes with moisture content in the vertical members. Although this is minimized by only using end grain there are still tolerances to be implemented.
One of the key advantages of the reciprocal framing used in this instance is its vibration mitigation effects. The triangular based grid changes the manner in which vibration propagates throughout the structure. This has profound effects on the sound and impact insulation of the floor system. This allows us to use thinner CLT or solid wood panels and reduce the amount of topping materials.
The structure can be wrapped in a cable stay system for enhanced seismic performance. Along this line of thought we also explored the use of a reciprocal framed shell structure or grid-shell for the facade system. New commercial applications should come out soon in light of enhanced modelling capabilities, see Reciprocal Framing Made Easy (4mb pdf).
This third exploration into the UBC Brock Commons student housing project is highly experimental in nature, and provides new concepts for tall timber projects. These types of approaches further illustrate the adaptability of timber to create limitless possibilities in structural and architectural design.