Browsing by Author "Veludo, J."
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- Bond strength of textured micropiles grouted to concrete footingsPublication . Veludo, J.; Dias-da-Costa, D.; Júlio, E.N.B.S.; Pinto, P.L.In a previous research study the authors performed push-out tests with smooth micropile inserts grouted under varying confinement conditions. It was shown that: (i) failure always occurs at the steel-to-grout interface; and (ii) the connection capacity increases with the passive confinement. To increase the connection capacity, it is a common practice to weld steel rings on the surface of the micropile and execute grooves in the predrilled hole. Therefore, a new study is herein presented aiming to widen the conclusions already drawn by analysing the influence of most important parameters in the bond strength of textured micropiles grouted to concrete footings. Laboratory tests were specifically designed for assessing the effect on the connection capacity of the: (i) diameter of the predrilled hole; (ii) insert’s embedment length; (iii) active confinement of the footing; and (iv) treatment of the hole surface. Eighteen textured micropile inserts grouted in RC footings were submitted to monotonic push-out tests until failure. In brief, it can be stated that the capacity of the micropile-to-footing connection increases by increasing the insert’s embedment length and by decreasing the hole diameter. Moreover, an adequate active confinement must be provided to achieve the required capacity.
- Compressive strength of micropile-to-grout connectionsPublication . Veludo, J.; Júlio, E.N.B.S.; Dias-da-Costa, D.Strengthening foundations with micropiles is progressively being used, due to the major advantages that this technique presents. Nevertheless, the influence of some relevant parameters in the overall behavior of the retrofitted foundations has not yet been studied. Generally, micropiles are installed in holes drilled through the existing RC footing, which are then filled with grout. The efficiency of the load transfer mechanism depends on the bond strength of both the micropile-grout and the concrete-grout interfaces. This paper describes an experimental study performed to specifically study the influence of the following parameters on the bond strength between micropile-grout interface: hole diameter; embedment length of the micropile; and level of confinement of the grout mass. Thirty micropile-grout specimens were submitted to monotonic push-off tests, until failure. Bond strength was found to increase with a decrease of the hole diameter and with an increase of the confinement level. © 2011 Elsevier Ltd. All rights reserved.
- An element enriched formulation for simulation of splitting failurePublication . Dias-da-Costa, D.; Veludo, J.; Alfaiate, J.; Júlio, E.Radial cracking propagation is often related to the bond transfer mechanism induced by slippage of a deformed bar. However, this failure pattern can also develop in other situations, namely: (i) concrete pipes submitted to an excessive inner pressure or (ii) concrete structures exposed to adverse environmental conditions under which corrosion or frost develops. In this paper a new contribution for the simulation of radial splitting failure is given. A discrete strong discontinuity formulation is presented which is fully capable of embedding radial discontinuities into axisymmetric finite elements. Numerical examples are used to show: (i) the capability of fully softening the applied inner pressure and (ii) mesh independence. Comparison with two published analytical approaches is performed for varying brittleness numbers. Finally, the model is applied to the simulation of both plain and reinforced concrete cylinders subjected to increasing inner pressure. A good agreement with experimental data is obtained.