Prefabrication experiments - 527 - Modular volumetric structural organizations

 

Buildings generated from modular volumetric construction in timber, steel, reinforced concrete, or from hybrid compositions of these materials follow two principal structural strategies: As the modules are self-supporting, the first simply stacks volumes; loads are distributed through their faces from one box frame to another. The second, architecturally iconic, employs a mega support structure onto which the self-supporting boxes are inserted as if carefully placed in a scaffold or on a shelf. The first strategy remains the path of least redundancy as having a mega structure has proven to increase costs, although it becomes necessary in tall modular buildings.

 

Without a secondary supporting rack, gravitational loads are distributed through bearing walls or vertical columns creating paths or grids analogous to those found in post and beam or wall and slab construction. In lightweight timber construction, module corners are sometimes reinforced with columns composed of 2-by stock or by using steel elements. As vertical loads are distributed through modules, lower modules bear the weight of the entire structure. In a six-story building, the lower volumes must be structurally more robust, which also implies a production management strategy to sequence and nuance production according to each module’s placement within the overall structure. 

 

Efficient structures are also contingent to alignment. All elements that are cantilevered or out of alignment, angled, or rotated complexify structural design and particularize the manufacturing of those design elements, which in turn increases costs. To account for horizontal loads and bracing, module walls and floors can be designed as rigid diaphragms active over multiple modules. In skeletal modular structures, in steel for example, bracing strategies vary from rigid connections to conventional X-bracing of each unit and external surface materials that brace adjacent units.  For tall buildings, reinforced concrete cores and complex structural connections between units and cores are designed to respond to seismic criteria.

 

A combination of the two structural archetypes can also be designed. A stack, 3 or 4 modules high (the feasible economic limit without structural reinforcement), is carried by a mega-structure. A tall building can be organized in this manner by providing a specially designed structural floor at every 4 stories as shown in the project shown below. 

TREET project's structural strategy