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Anchorages in normal and high performance concretes subjected to medium and high strain rates

Objective


* New mixes of High Performance Concrete with steel fibbers have been experimented and mechanically tested under static and dynamic conditions. A rich database of mechanical properties of NC and HPC has been produced. It comprises full stress-strain curves ideally suited for calibrating material models for concrete. Some of the dynamic tests with the concrete cubes were performed for the first time; the strain-rate hardening behaviour of the material has been verified and quantified.
* Workable models for concrete have been developed or further advanced by adding new features into them, such as the strain rate, steel fibbers content etc. They are based on the micro-plane model, the lattice model, and the damage based model (with strain gradients). Reliable code implementation of the above models in well-known Finite Element programs (PLEXIS-3C, ABAQUS, FEAP) has been made.
* Quite unique experimental results of static and dynamic pull-out tests of rebars and anchors have been produced using Hopkinson bar techniques. Dynamic tests with anchor diameters of 16mm were performed for the first time. Full force-displacement curves have been obtained, ideal as reference measurements. It has been 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 loads under similar embedment depth conditions. It has been demonstrated that force-displacement diagrams for dynamic loading tend to always 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.)
* Validation of the material models and their code implementation against the above experimental results on actual structural components has been successfully attempted.
* Finally, design rules concerning anchorages have been better verified, and some adjustments according to the results of this study have been proposed.
Objectives and content
The anchorages considered consist of a metallic element,
rebar or anchor, and the concrete base material, where
the metallic element is embedded with or without a
bonding agent. Improving the base material mechanical
characteristics and enhancing our understanding of the
anchorage response, principally to dynamic loads, are the
two key issues of the proposed work. New materials
design of high performance concrete, materials modelling
(including the strain rate dependence of the stressstrain curve of concrete and its softening branch) and
numerical simulation tools will be pursued. An extensive
experimental programme will support all theoretical
developments. Central in this high strain-rate testing
activity, will be the employment of various Hopkinson bar
techniques, particularly suited for precision pull-out
tests.
Anchorage systems, as load bearing elements, keep
receiving particular attention in the construction
industry due in part to the following global trends:
use of pre-fabricated structural elements,
use of sophisticated construction methods in regions
with low-skilled construction labour, requiring on-site
adjustments to anchors and attachments,
increased interest in earthquake retrofitting worldwide,
increased interest in preservation of the historical
built environment and in the re-use and rehabilitation of
existing structures, particularly in Europe, and
elevated anchorage demands in some structures subjected
inherently to cyclic dynamic loads (seismic regions,
offshore construction), and potentially to explosive type
loads (nuclear power plants, military installations,
conduits, tanks, silos, etc.).
Thus, the principal objective of the proposed project is
to produce the scientific knowledge necessary for the
development of reliable design techniques for competitive
anchorage systems in normal and high performance concrete
structures (NC and HPC) when subjected to dynamic
loading.
This body of knowledge will comprise:
Basic static and dynamic material data for NC and HPC.
Material models development and implementation into a
Finite Element Method (FEM) code.
Results of anchorage (cast-in-place and post-installed)
dynamic pull-out tests on full-scale structural specimens
of NC and HPC, and their numerical FEM validation.
Design rules for standardisation purposes and for the
end-user.
The envisaged anchorage system should:
be easily castable and placeable,
have a service life at least as long as that of the
concrete structure,
retain its load carrying capacity after being subjected
to a dynamic loading with a strain rate in the range
static < ' < 20/ sec, if so designed.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Densit A/S
Address
44,Rordalsvej
9100 Alborg
Denmark

Participants (6)

Bekaert SA/NV
Belgium
Address
2,Bekaertstraat
8550 Zwevegem
CESI CENTRO ELETTROTECNICO SPERIMENTALE ITALIANO GIACINTO MOTTA SPA
Italy
Address
Via Rubattino 54
Milano
Commission of the European Communities
Italy
Address
Via Enrico Fermi
21020 Ispra
Hilti AG
Liechtenstein
Address

9494 FL Schaan
POLYTECHNIC OF MILAN
Italy
Address
Piazza Leonardo Da Vinci 32
20133 Milano
University of Patras
Greece
Address

26110 Patras