Ductile Chord Connectors for Reinforced Precast Concrete Structures

Background

Precast concrete diaphragm systems, particularly double-tee and hollow-core flooring structures, are widely utilized in the construction of parking garages, offices, and warehouses. Because these structures are assembled from discrete prefabricated panels, they require robust connections to ensure structural integrity and a long service life. A critical requirement in this field is the ability to safely transfer large in-plane tension forces across the diaphragm during seismic events. Consequently, the construction industry continuously seeks reliable connection methods that can withstand severe cyclic loading and meet stringent building codes without compromising the speed and efficiency that make precast concrete an attractive building method.

Traditionally, transferring these seismic tension forces relies on field-cast concrete pour strips, while alternative mechanical connections often suffer from performance limitations under complex stresses. Field-cast pour strips negate many of the inherent advantages of precast construction by complicating the building process, slowing down construction schedules, and significantly increasing on-site labor costs. Furthermore, existing connection methods can struggle under combined tension and shear loading, creating a risk of brittle failure, premature weld tearing, or reinforcing bar fracture. These vulnerabilities ultimately compromise the deformation capacity, overall quality, and seismic resilience of the completed building system.

Technology

The Ductile Chord Connector for Precast Concrete Construction is an engineered dry chord connection designed for precast concrete diaphragm systems, including double-tee and hollow-core flooring structures. Built to embed within 6000 psi concrete panels, the modular assembly features a cast steel main body, reinforcing rebar, field connection slug plates, a front flange, a faceplate, a tube, weld slots, a transition region, and an unbonded length. Its core feature is a specialized yield shaft that acts as a mechanical fuse, ensuring a ductile failure mechanism in tension and achieving a deformation capacity of approximately 0.6 inches under cyclic loading. Additionally, the system incorporates a debonded or padded anchorage system using foam sleeves, alongside accessible weld slots that allow the connectors to be deployed individually or in modular groups.

This technology is differentiated by its ability to reliably transfer in-plane seismic tension forces while completely eliminating the need for traditional, field-cast concrete pour strips. Removing the pour strip significantly accelerates construction, reduces labor costs, and improves overall building quality and service life. Furthermore, the padded anchorage system uniquely minimizes shear stiffness, preventing brittle failure under combined loading by allowing shear compliance while maintaining robust tension force transfer. Validated through finite element analysis, the design achieves target force and displacement capacities without premature weld tearing or bar fracture, offering a scalable, easy-to-install solution for seismic resilience.

Benefits

• Eliminates the need for field-cast concrete pour strips in precast concrete construction
• Accelerates construction timelines and reduces labor costs
• Enhances seismic performance through high deformation capacity and ductile tension failure
• Prevents brittle failure under combined loading by allowing compliance and movement in shear
• Simplifies field installation with accessible weld slots and slug plates
• Offers scalable strength through modular deployment as individual units or groups
• Improves the overall quality and service life of precast concrete building systems

Applications

• Precast concrete parking garage construction
• Seismic-resistant office building construction
• Precast warehouse flooring installation
• Double-tee concrete floor connections
• Hollow-core slab diaphragm systems

Additional info

Clay Naito is a professor of civil and environmental engineering at Lehigh. His research interests include experimental and analytical evaluation of reinforced and prestressed concrete structures subjected to extreme events including earthquakes, tsunamis, and intentional blast demands, and forensic evaluation of buildings and bridges for assessment of remaining service life.