Abstract: In the paper the results of calculations of the dynamic
response of a multi-storey reinforced concrete building to a strong
mining shock originated from the main region of mining activity in
Poland (i.e. the Legnica-Glogow Copper District) are presented. The
representative time histories of accelerations registered in three
directions were used as ground motion data in calculations of the
dynamic response of the structure. Two variants of a numerical model
were applied: the model including only structural elements of the
building and the model including both structural and non-structural
elements (i.e. partition walls and ventilation ducts made of brick). It
turned out that non-structural elements of multi-storey RC buildings
have a small impact of about 10 % on natural frequencies of these
structures. It was also proved that the dynamic response of building
to mining shock obtained in case of inclusion of all non-structural
elements in the numerical model is about 20 % smaller than in case
of consideration of structural elements only. The principal stresses
obtained in calculations of dynamic response of multi-storey building
to strong mining shock are situated on the level of about 30% of
values obtained from static analysis (dead load).
Abstract: Interior brick-infill partitions are usually considered as
non-structural components and only their weight is accounted for in
practical structural design. In this study, their effect on the progressive
collapse resistance of an RC building subjected to sudden column loss
is investigated. Three notional column loss conditions with four
different brick-infill locations are considered. Column-loss response
analyses of the RC building with and without brick infills are carried
out. Analysis results indicate that the collapse resistance is only
slightly influenced by the brick infills due to their brittle failure
characteristic. Even so, they may help to reduce the inelastic
displacement response under column loss. For practical engineering, it
is reasonably conservative to only consider the weight of brick-infill
partitions in the structural analysis.
Abstract: Recordings from recent earthquakes have provided evidence that ground motions in the near field of a rupturing fault differ from ordinary ground motions, as they can contain a large energy, or “directivity" pulse. This pulse can cause considerable damage during an earthquake, especially to structures with natural periods close to those of the pulse. Failures of modern engineered structures observed within the near-fault region in recent earthquakes have revealed the vulnerability of existing RC buildings against pulse-type ground motions. This may be due to the fact that these modern structures had been designed primarily using the design spectra of available standards, which have been developed using stochastic processes with relatively long duration that characterizes more distant ground motions. Many recently designed and constructed buildings may therefore require strengthening in order to perform well when subjected to near-fault ground motions. Fiber Reinforced Polymers are considered to be a viable alternative, due to their relatively easy and quick installation, low life cycle costs and zero maintenance requirements. The objective of this paper is to investigate the adequacy of Artificial Neural Networks (ANN) to determine the three dimensional dynamic response of FRP strengthened RC buildings under the near-fault ground motions. For this purpose, one ANN model is proposed to estimate the base shear force, base bending moments and roof displacement of buildings in two directions. A training set of 168 and a validation set of 21 buildings are produced from FEA analysis results of the dynamic response of RC buildings under the near-fault earthquakes. It is demonstrated that the neural network based approach is highly successful in determining the response.
Abstract: Concrete strength evaluated from compression tests
on cores is affected by several factors causing differences from the
in-situ strength at the location from which the core specimen was
extracted. Among the factors, there is the damage possibly occurring
during the drilling phase that generally leads to underestimate the
actual in-situ strength. In order to quantify this effect, in this study
two wide datasets have been examined, including: (i) about 500 core
specimens extracted from Reinforced Concrete existing structures,
and (ii) about 600 cube specimens taken during the construction of
new structures in the framework of routine acceptance control. The
two experimental datasets have been compared in terms of
compression strength and specific weight values, accounting for the
main factors affecting a concrete property, that is type and amount of
cement, aggregates' grading, type and maximum size of aggregates,
water/cement ratio, placing and curing modality, concrete age. The
results show that the magnitude of the strength reduction due to
drilling damage is strongly affected by the actual properties of
concrete, being inversely proportional to its strength. Therefore, the
application of a single value of the correction coefficient, as generally
suggested in the technical literature and in structural codes, appears
inappropriate. A set of values of the drilling damage coefficient is
suggested as a function of the strength obtained from compressive
tests on cores.