Load Transfer Mechanisms in Existing RC Footings Strengthened with Textured Micropiles

D. DIAS-DA-COSTA Assistant Professor INESCC, Dep. of Civil Engineering, Univ. of Coimbra, Portugal dcosta@dec.uc.pt

D. Dias-da-Costa received his Ph.D. degree in Civil Engineering in 2010 from the University of Coimbra where he is an assistant professor since then. His main research interests include the numerical modelling of quasi-brittle materials.

E. JÚLIO

Full Professor

ICIST, DECivil IST-UTL,

Lisbon, Portugal

ejulio@civil.ist.utl.pt

E. Júlio is a full professor at the Instituto Superior Técnico of the Technical University of Lisbon. His research interests are in the field of Structural Concrete. He is member of IABSE WC 3, fib Commission 5 and ACI 364 Committee.

RC footing strengthened with steel micro-piles is a wide-spreading method. Although the most important parameters influencing the connection capacity are already identified, these were empirically evaluated. For these reasons, an experimental study has been undertaken aiming to quantify the influence of: (1) the diameter of the predrilled hole; (2) the embedment length of the micropile; (3) the roughness of the predrilled hole; (4) the roughness of the micropile; and (5) the active confinement applied to the existing RC footing. Eighteen micropile-to-grout specimens were submitted to monotonic push-off tests until failure. Results are discussed in detail and conclusions are drawn. For short, it can be stated that, in order to maximize the load capacity of the micropile- to-RC footing connection, spiral bars or shear rings have to be welded along the micropile, grooves have to made on the pre-drilled hole and an active confinement of the footing has to be provided.