Towards a European code for seismic assessment and strengthening of existing buildings

Abstract

In Europe, actions towards preparing a code document regarding assessment and strengthening of existing reinforced concrete structures are already present in the draft document Part 3 of EC8. However, for the case of strengthening by the addition of new reinforced concrete, specific provisions, to check the capacity of the connections between contact surfaces, are missing. Structural design of strengthened concrete elements can be placed into the framework of the currently known processes of design, which are used for new constructions, supplemented by a crucial investigation at the interface between the contact surfaces, to ensure that failure in each strengthened element precedes failure at the interface, between the old and the new material. For that reason, shear forces and shear resistances at the interfaces, between the old and the new element, must be examined. An evaluation of the shear force that develops between the contact surfaces can be obtained in a similar way as for steel and concrete composite structural elements. The main mechanisms that contribute to the shear resistance at the interface are: (a) concrete-to-concrete adhesion, (b) concrete-to-concrete friction, (c) connecting action from steel bars placed across the interface between the old and the new concrete and (d) bent steel bars welded between the bars of the old and the new concrete. The total shear resistance between contact surfaces can be found by summing the individual shear resistances that are mobilised by each individual mechanism for a common interface slip. To prevent a brittle failure at the interface, a minimum amount of steel shear connectors in the form of dowels or bent steel bars must be provided.