Designing Floors for Reuse

Many buildings are demolished long before their structures wear out. Yet when traditional composite slabs are removed, steel beams are cut and recycled while concrete is crushed and downcycled, losing most of its embodied value. This wasteful end-of-life scenario is largely caused by welded shear studs that realize a monolithic structure made of steel and concrete.

Design for Disassembly (DfD) offers a more rational approach: maintaining structural performance while enabling future disassembly and reuse. Recently researchers at Northeastern University have proposed deconstructable composite floor systems that achieve this goal through the use of reversible mechanical connections and prefabricated components (https://www.sciencedirect.com/science/article/pii/S0143974X18301639 https://ascelibrary.org/doi/10.1061/9780784480410.004), which is also one of the challenges of TIMELESS. The objective is achieving nearly 100% reusability of the composite floor’s structural elements, significantly reducing waste and environmental impact. This is achieved through the use of specialized components developed in the railway industry, clamping connectors, which enable composite floor elements to be joined without any drilling operations. In railway applications, these connectors are primarily used to clamp and secure the rails to the supporting concrete structure, providing a high-strength, vibration-resistant fastening system. By avoiding drilling and welding, they ensure faster installation, minimize structural weakening of the steel members, and simplify maintenance. The same technology is now applied to construction, offering robust and reversible connections for composite floor systems.

How Clamping Connectors Work

The core of the system are mechanical clamping connectors that replace welded shear studs. Each connector uses a high-strength T-bolt inserted into a cast-in channel within the precast concrete plank. When tightened, the clamp teeth grip the underside of the steel beam flange, and the bolt pretension generates normal force at the steel–concrete interface. This produces friction-based shear transfer, allowing steel and concrete to work compositely. If friction is exceeded, the clamp’s mechanical bearing action continues to provide shear resistance, ensuring strength and large ductility.

When the structure must be adapted or dismantled, loosening the bolts is enough to detach beams and slabs intact for reuse. This reversible solution — protoryped through push-out and beam tests — was first developed in the research led by Hajjar and collaborators, demonstrating strength and ductility comparable to conventional stud-connected systems.

Why It can Perform Like a Conventional Composite System

Laboratory tests showed that clamping connectors have the potential to achieve:

• Excellent slip capacity and ductility

• High shear resistance under monotonic and cyclic loading

• Energy dissipation suitable for seismic conditions

Unlike other demountable solutions, no holes are drilled in the steel beams, preserving their structural properties — critical for reuse. Cast-in channels also give flexibility in beam positioning, making the system adaptable to future layouts without modifying the slabs.

Environmental Benefits

Composite floor systems dominate commercial construction because they are efficient and economical. However, in their current design they typically permit zero reuse of concrete and only partial reuse of steel. In contrast, a demountable composite system enables:

• recovery and reuse of entire precast slabs,

• full reuse of steel beams without reprocessing,

• major reduction in demolition waste,

• improved adaptability during renovation.

LCA show that, when reclaimed components are reused at least once, the global warming potential (carbon emissions) can be reduced by over 60 % compared to conventional construction.