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Prove sugli ancoraggi nel calcestruzzo sottoposti ad azioni dinamiche

pubblicazioni - Articolo

Prove sugli ancoraggi nel calcestruzzo sottoposti ad azioni dinamiche

Steel rebars and anchors embedded in a concrete base with or without a bonding agent are the anchorage systems considered in this study. The special attention given to anchorages in concrete is due to some global trends in the construction industry, such as, increasing use of pre-fabricated structural elements, increased interest in earthquake retrofitting world-wide, increased interest in preservation of the historical built environment, re-use and rehabilitation of existing structures (particularly in Europe), other special anchorage demands (offshore construction, road safety barriers, nuclear power plants etc.). Improving the base material mechanical characteristics and enhancing our understanding of the anchorage response, principally to dynamic loads, have been the two key issues of this activity. Considerable work has been expended towards designing the numerous specimens of normal (NC) and high performance concrete (HPC, steel fiber reinforced), which include: plain concrete specimens, cast-in-place and post-installed rebars and cast-in-place and post- installed anchors. Rebars of 20mm diameter and anchors of 12mm and 16mm diameter have been used, respectively. Some of the main results can be summarised as follows: A rich data-base of mechanical properties of NC and HPC has been produced. It comprises full stress-strain curves ideally suited for calibrating material models for concrete for strain rates from 10 -6 /sec up to 20/sec. Dynamic tests with realistic concrete volume specimens and with aggregate size of 16mm were successfully performed. The strain-rate hardening behaviour of the material has been verified and quantified; at higher strain rates doubling of compressive strengths with respect to static conditions has been encountered. Quite unique experimental results of static and dynamic pull-out tests of rebars and anchors have been produced. Employing Hopkinson bar techniques at the Large Dynamic Test Facility of the JRC, dynamic pull-out tests with large anchor diameters have been performed. Concrete cone breakout failure has been predominantly induced. Full force-displacement curves have been obtained, ideal as reference measurements. The test results have shown that properly post-installed rebars or anchors can achieve the same load bearing capacity as the cast-in-place ones. It has also been verified that the three different types of anchors (HVZ with chemical adhesive, HDA undercut, and Headed Studs) can develop comparable concrete failure tensile loads under similar embedment depth conditions. Test results have demonstrated that force-displacement diagrams for dynamic loading tend in general to lie above the corresponding static ones. This proves that anchorages in concrete can indeed provide additional safety margins in cases of transient monotonic loading (blast, impact, seismic load etc.) Finally, construction design rules concerning anchorages have been better verified, and the results of this study allow for some adjustments to be proposed.

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