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Experimental Behavior of Concrete Joint Interfaces under Reversed Cyclic Loading
No full textA large scale test on concrete joints subjected to constant compressive confinement and reverse cyclic shear load is performed. Shear strength, dilatancy degradation, and overall response are reported. A description of roughness as composed by two orders of asperities with different sizes is used to analyze the results and prompts the extension of an existing generalized joint model. The validity of the interpretation and the role of the proposed extension are pointed out by means of comparisons between numerical simulations and experimental results
Experimental Behaviour of Concrete Joints Under Reversed Cyclic Loading
No full textInterface joints play an important role in the seismic response of masonry and concrete
structures especially for large and unreinforced ones.. Despite their different origin, all these
discontinuities can be generically characterized as “joint” to be modelled through a single
generalized formulation, Puntel et al. (2006). Joint models abound in the literature and have
reached levels of significant sophistication and maturity specially when examined through the
prisms of fracture, plasticity or damage mechanics. However, most of them are inherently
developed under the assumption of monotonic loading conditions thus disregarding specific
features of reversed cyclic loading; in some cases this can lead to gross mistakes such as
unsafe overestimation of joint opening. This deficiency is partly explained by the
comparatively small number of test data and by the concurrent lack of experimentally derived
relationships.
As such, this paper addresses the scarcity in relevant tests. First, a complex experimental set-
up is described and results reported of large scale tests on concrete joints subjected to constant
compressive confinement and reverse cyclic shear load. After the analysis and discussion of
the results, many evidences have prompted an interpretation based on a description of joint
roughness as composed by two orders of asperities each with its own size and degradation
properties. In view of these findings, an enhancement of the aforementioned generalized
model previously developed by the authors has been motivated. Finally the numerical
response of both the existing and the updated joint models has been compared with the
experimental one. Thus the role of the proposed extension is clarified showing in particular
the effectiveness of the asperity description in explaining at the same time both the shear
strength and the dilatancy behaviour
An experimental and numerical investigation of concrete dam joints
No full textThis communication summarises the results of a comprehensive investigation aimed at improving the
understanding of the cyclic behaviour of concrete dam joints, covering both experimental and numerical
aspects.
In the laboratory work, a jointed concrete block is subjected to reversed cyclic slip at imposed normal stress.
The specimen is intended to represent a portion of either a lift joint or the dam-foundation interface. Aspects
of novelty can be found in the test setup and in the specimen size (90×70×30 cm). The tests performed so far,
though limited in number, have allowed to assess and approximately quantify for concrete the characteristic
influence of joint roughness on the observed shear strength and dilatancy.
A generalised interface model is proposed in order to describe the joint behaviour, including all the
phenomena commonly accounted for in mixed mode fracture of cohesive quasi-brittle materials and the
effects of surface roughness. This result has been obtained by combining a fracture-mechanics based interface
model for concrete [1] with a cyclic one [2] for rock joints. Simulations carried out so far evidence a good
qualitative agreement with results available in literature
Unexpected hardening effects in bilayered gel beams
Full text linkA classical problem in structural mechanics is the evaluation of beam stretching and curvature in slender bilayered beams, due to mechanical actions, thermal distortions, differential growth, and more recently, to swelling. We investigate the non–monotonic changes in the curvature of swollen bilayer beams due to mismatches in physical properties of the two layers starting from a simple structural approach, and discuss the apparent contrast with the well–known Timoshenko’s formula through a scaling analysis. Due to the large strains involved in the problem, we also discuss the problem through a thermodynamics based on Gent model for the elastic contribution to the free–energy of the gels
An asymptotic approach to the torsion problem in thin rectangular domains
No full textA rather straightforward derivation of the Γ-limit of the torsion problem on a thin rectangle as the thickness goes to zero is obtained. The limit stresses are evaluated and the distributional nature of one of the stress components is clarified
An Asymptotic Approach to the Torsion Problem in Thin Walled Beams
No full textA rather straightforward derivation of the Γ-limit of the torsion problem as the thickness goes to zero is obtained for generic thin walled beams. The limit stresses are evaluated and the distributional nature of one of the stress components is clarified
Finite bending solutions for layered gel beams
No full textWe investigate the swelling-induced bending of a gel bilayer beam with homogeneous beam-like components, when the beam is embedded in a solvent bath of assigned chemical potential. We set the problem within the limits of finite elasticity with large distortions, with these latter determined via chemical equilibrium, by the elastic modulus of the gel, the chemical potential of the bath and the solvent-gel interaction parameter. We borrow our method of solution from finite bending of soft and incompressible beams, and get a non dimensional nonlinear equation governing the solution of the problem, whose solution is validated through a campaign of numerical experiments based on a complete stress-diffusion model. © 2016 Elsevier Ltd
A displacement rate dependent softening model applied to the unstable propagation of shear crack in soft rock
No full textPrediction of critical state and load carrying capacity of structures is the fundamental
issue in engineering practice. Critical states are often govemed by formation and
growth of tension and/or shear cracks. The safety assessment of a concrete arch dam
against large earthquake excitation, for example, requires consideration of shear crack
growth at the rock foundation.
The studies of shear crack growth in geological materials consist of three aspects; 1)
formation of shear cracks (or strain localization), 2) localization of shear cracks, and
3) instability of crack growth. The present study focuses on the condition for the
initiation of unstable growth of a localized shear crack.
Experimental studies have shown that the growth of localized shear crack in soft rock
is captured with the initiation condition and the softening law for shear cracks
obtained from element tests. The instability of shear crack growth in structural tests is
found to occur before the released energy reaches the fracture energy. Hence, it is
necessary to find the initiation condition of unstable crack growth.
In the present study, a rate dependent softening law is introduced in the softening law
of the shear crack. Effect of the rate dependence in softening law is at first
investigated for a one-dimensional model. Then, mode I crack propagation is
investigated with interface elements that satisfy the rate dependent softening
relationship along the crack. The ability to predict unstable crack growth by means of
a rate dependent softening law is demonstrated.
Finally, analysis of shear crack propagation in soft rock is conducted. It is shown that
the unstable crack growth and associated sudden load drop observed in structural tests
are captured by the present analysis. It is concluded that the rate dependence of the
softening behavior along the shear crack is a promising candidate for the goveming
mechanism of unstable crack growth in geological materials
On the Stability of Surface Growth: The Effect of a Compliant Surrounding Medium
Full text linkAbstract
In a recent paper Abeyaratne et al. (J. Mech. Phys. Solids 167:104958, 2022) concerning the stability of surface growth of a pre-stressed elastic half-space with surface tension, it was shown that steady growth is never stable, at least not for all wave numbers of the perturbations, when the growing surface is traction-free. On the other hand, steady growth was found to be always stable when growth occurred on a flat frictionless rigid support and the stretch parallel to the growing surface was compressive. The present study is motivated by these somewhat unexpected and contrasting results.
In this paper the stability of a pre-compressed neo-Hookean elastic half-space undergoing surface growth under plane strain conditions is studied. The medium outside the growing body resists growth by applying a pressure on the growing surface. At each increment of growth, the incremental change in pressure is assumed to be proportional to the incremental change in normal displacement of the growing surface. It is shown that surface tension stabilizes a homogeneous growth process against small wavelength perturbations while the compliance of the surrounding medium stabilizes it against large wavelength perturbations. Specifically, there is a critical value of stretch,
λ
cr
∈
(
0
,
1
)
, such that growth is linearly stable against infinitesimal perturbations of arbitrary wavelength provided the stretch parallel to the growing surface exceeds
λ
cr
. This stability threshold,
λ
cr
, is a function of the non-dimensional parameter
σ
κ
/
G
2
, which is the ratio between two length-scales
σ
/
G
and
G
/
κ
, where
G
is the shear modulus of the elastic body,
σ
is the surface tension, and
κ
is the stiffness of the surrounding compliant medium.
It is shown that
(
a
)
λ
cr
→
1
as
κ
→
0
and
(
b
)
λ
cr
→
0
+
as
κ
→
∞
, thus recovering the results in Abeyaratne et al. (J. Mech. Phys. Solids 167:104958, 2022) pertaining to the respective limiting cases where growth occurs
(
a
)
on a traction-free surface and
(
b
)
on a frictionless rigid support. The results are also generalized to include extensional stretches
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