Displacement based design for precast concrete frames with not-emulative connections

Precast concrete structures have been widely adopted in the industrial and commercial sectors owing to their cost competitiveness, short on-site construction time, improved quality control of materials as well as structural elements, and ability to cover longer and wider spans with prestressed elements. Although there are various topologies of lateral force resisting system solutions including jointed ductile connections, hybrid walls, and reinforced concrete emulative structures, a good number of European industrial buildings are still single and few-storey buildings with elementary structural layouts. This entail cantilever columns connected at the floor level and at the roof by simply supported pre-stressed and precast beams.

The columns are then placed on-site in isolated precast cup-footings or even connected to shallow foundations through mechanical splices. The column-to-beam connection is typically pinned and energy dissipation is normally provided by the development of plastic hinges at the column bases. This hinged-frame static formation and the high inter-storey height has been found to result to flexible structures where contribution of elastic displacements is more as compared to conventional reinforced concrete frames.

If not considered appropriately in the design stage, this high flexibility could lead to displacement incompatibility between structural members and between structural and non-structural elements therefore causing premature failure. For this reason, seismic performance of these structures is related to inter-story drift control as opposed to material strain limitations.

Andrea Belleri at The University of Bergamo in Italy considered in the design phase how to implement conventional details of pre-cast concrete structures, for instance, beam-to-column connections, and column-to-foundation connections. In view of column-to-foundation connections, the author investigated the effect on the system energy dissipation capacity of various connections. With regards beam-to-column connections, the author evaluated the effect on the effective height and effective mass of the substitute structure implemented in the design phase. His research work is published in peer-reviewed journal, Engineering Structures.

The author investigated Displacement Based Design methodology for precast concrete frames with not-emulative connections. He implemented the seismic design procedure to multi-storey and single-storey structures. In keeping with the general displacement principle, Andrea Belleri focused on how, considering the effect of beam-to-column and column-to-foundation precast connections; procedures as well as expressions were developed to establish the equivalent viscous damping, yield curvature, effective height, and the effective mass of the single degree of freedom substitute structure used in the Displacement Based Design.

Concerning beam-to-column connections, the author considered the effects of a degree of fixity for multi-storey and single storey structures. He derived new expressions for target displacement and displacement ductility in single storey frames. Andrea Belleri also derived refined yield displacement formulas for multi-storey frames. These formulas were also applicable to shear wall as well as coupled shear wall structures.

The selected procedure was validated through a non-linear time history evaluation taking into account single and multi-storey building with not-emulative and hinged connections. The author was able to realize a good agreement between the Displacement Based Design values and the values obtained. Ongoing research focuses on the effect of a number of connection arrangements in the equivalent viscous damping formulation.

Quote from the author “I’ve always been fascinated by the Direct Displacement Based Design (DDBD) methodology developed by prof. Priestley and tried to extend it to other structural systems”