Adaptive Floor Systems

Concrete flat slabs are commonly used as floor systems in buildings primarily due to the ease of construction. However, since the material is not optimally distributed to take the bending caused by external loads, they are significantly oversized. Considering that floor slabs account for more than 50% of the material mass embodied in common low-rise reinforced concrete buildings, lightweight floor systems could have a significant impact on reducing the carbon footprint of new constructions

A new integrated structure-control optimization process that can be applied to one-way and two-way slabs is formulated. Actuation is performed via tendons (i.e., cables) that are embedded in concrete ribs supporting the slab. The tendons are unbounded through a duct, which enables variable post-tensioning to counteract the effect of different loading conditions. The tension force is applied eccentrically to the neutral axis of the slab-ribs assembly. This creates a system of forces that generates a bending moment, which counteracts the moment caused by the external load. The design process involves the placement of passive as well as active ribs. A greedy algorithm using a heuristic informed by the direction of principal stresses is implemented. The deflection of the slab is reduced by adjusting the tendon tensile forces computed by a quasi-static controller that employs bounded least-square optimization to obtain the actuator commands. Different tendon profiles are compared. Since floor systems must have a relatively low depth to avoid losing valuable residential or commercial space, a simple straight profile in most cases suffices to obtain a significant response reduction compared to more complex profiles such as a parabolic one. A numerical study on an 8 × 8-m configuration shows that the adaptive slab solution produced with this method achieves up to 67% material savings compared with an equivalent passive flat slab. A 10 × 6-m adaptive ribbed slab prototype has been designed using this method and is being constructed at the ILEK experimental facility to validate the numerical predictions.

The adaptive slab solution has been compared to several other established floor system technologies. The selected construction technologies are evaluated based on their maturity level, ease of construction, and widespread use in practice. A multi-span model with two layout variations is considered, featuring spans of 7 x 7m and 7 x 14m. Loading scenarios range from 4 to 7 kN/m², representing lower and upper bounds in accordance with the design requirements of Eurocode 1 – Part 1-1, applicable to most residential and commercial buildings. Material properties are specified for each slab configuration, with a minimum story height of 2.6 meters and a structural fire resistance class of R60 required for all combinations of materials, support layouts, and construction technologies.

The benchmark results show that the adaptive slab solution could potentially outperform all existing technologies displaying the relationship between self-weight, selected construction technology, and main span length. Additional information is available in the guidelines “A practical guide to the New European Bauhaus self-assessment method and tool”, Joint Research Center – European Commission, 2024.