D-BAUG - Departement Bau, Umwelt und Geomatik - ETH Zürich

Highlights ▪ Structures
Numerical simulation of rock fall
impact on reinforced concrete slabs
In order to improve the design of rock fall
protection galleries, impact load capacity
of reinforced concrete slabs is studied
using finite element simulations.
Applicability of numerical analysis is validated calibrating the
results with falling-weight impact tests carried out in 2007.By
using finite element results obtained simulating the impact
loads which initiated the failure during the experiment, a criterion
is proposed to investigate failure in the slabs. This provided
a reasonable base for extrapolation of the numerical results
beyond the range of performed experiments (Fig.1,Fig.2).
In addition,a numerical approach is proposed for modelling reinforced
concrete slabs subjected to consecutive impact loading,
to improve understanding the behaviour of rock fall protection
galleries subjected to impact of more than one rock in
their history.The gained knowledge is used to model an existing
rock fall protection gallery and to study a possible failure.
Finite element methods will also be used to investigate the influence
of parameters and assumptions made for a proposed
analytical model.The model,which is based on a system of multiple
degrees of freedom,enables an efficient way to carry out
a performance based design and to predict shear and bending
failure.
The combination of analytical and finite element models facilitates
a better understanding of the behaviour of slabs subjected
to impact loads and allows the knowledge to be applied
in improving design of rock fall protection galleries and calculating
the capacity of the existing ones.
54 ▪ D-BAUG Annual Report 2009
Elastic wave propagation in a segmented
X-ray computed tomography concrete
model.
by S. Ghadimi-Khasraghy, T. Vogel / IBK by G. K. Kocur, T. Vogel / IBK
3D Structure of Concrete Specimens
Cuboid-shaped, undestroyed concrete specimens (12x12x16
cm) were scanned with X-ray computed tomography (CT)
at the Institute of Diagnostic Radiology of the University
Hospital Zurich. Based on the recorded two-dimensional
X-ray slice data, the 3D structure was reconstructed in the
post processing. By means of segmenting, the concrete
constituents such as aggregate grains (Fig. 3, left) and air
inclusions (Fig. 3, right) could be identified as different
phases and separated digitally. In segmentation, related areas
of contiguous pixels (2D) or voxels (3D) are allocated to
a certain material (phase), i.e. based on threshold values.
The digital format of the segmented phases (Fig. 4, left) can
be used for further numerical procedures such as the simulation
of wave propagation in concrete. The numerical
simulations are performed with the finite difference
method.
The application of the segmented CT models allows for a
differentiated study on the influence of single phases on
the wave propagation behavior. The emphasis is on the
scattering effect of air inclusions on the propagating wave
fronts (Fig. 4, right) and the associated decreasing wave velocities.
The study aims at quantifying these influences
and at comparing with experimental results.
The segmented CT model which represents the inner structure
of the concrete specimen can as well be used to verify
purely numerically generated concrete models.