Apresenta-se um trabalho numérico e experimental, com o objetivo de estudar o comportamento dos pavimentos de concreto estruturalmente armados, quando submetidos a forças verticais estáticas e repetidas. Avalia-se a contribuição da armadura de flexão, na resistência de placas de concreto apoiadas sobre meio elástico. Verifica-se experimentalmente o modo de ruína de placas submetidas a carregamento monotônico e a carregamento repetido, com e sem armadura, e acompanha-se o desenvolvimento das fissuras no concreto e das deformações no aço. Comparam-se os resultados obtidos, com as recomendações da NBR 6118:2003, para o dimensionamento de estruturas submetidas à fadiga. É desenvolvido modelo numérico capaz de representar a interface do solo com a placa do pavimento, a fissuração do concreto, a contribuição da armadura e o comportamento pós-fissuração. Com auxílio do modelo numérico, validado a partir dos resultados experimentais, estuda-se a influência de alguns parâmetros importantes para o dimensionamento dos pavimentos, tais como: capacidade de suporte da fundação, espessura das placas, área de aço, dimensões das placas em planta, posição de aplicação da força e presença de juntas de transferência de deslocamento. Os resultados experimentais mostram uma significativa contribuição da armadura positiva na resistência de placas isoladas sob forças verticais centradas. Verificou-se que as forças repetidas provocam fadiga do aço e que o número de ciclos depende da deformação provocada na armadura. A partir dos resultados são traçadas diretrizes para o dimensionamento...
Os ensaios de arrancamento cíclicos são utilizados para avaliar o comportamento de sistemas de solo reforçado quando submetidos a carregamentos cíclicos, podendo ser aplicados na área de pavimentos reforçados com geossintéticos ou em comportamento sísmico de solos reforçados com geossintéticos. O comportamento de sistemas de solo reforçado submetidos a carregamentos cíclicos ainda não é bem compreendido. Em vista disso, equipamentos de arrancamento cíclicos de geossintéticos são desejáveis para o estudo deste comportamento. O equipamento de arrancamento de geossintéticos existente no laboratório de geossintéticos da Escola de Engenharia de São Carlos da Universidade de São Paulo foi modificado para a realização de ensaios de arrancamento cíclico de geossintéticos. Dois tipos de ensaios foram implementados para avaliar o comportamento cíclico de sistemas de solo reforçado com geogrelhas: o ensaio de módulo de cisalhamento de resiliência de interface solo-geogrelha, Gi, e o ensaio de resistência pós-ciclagem. Foram realizados 20 ensaios, entre ensaios de arrancamento monotônico, cíclicos e de testes, de geogrelhas. Foram avaliados dois sistemas, um deles de inclusão longa, de 510 mm de comprimento e 310 mm de largura; e o outro de inclusão curta...
The misunderstanding of the overall behaviour of traditional timber trusses can result in incorrect
strengthening interventions or, frequently, on their replacement. Timber roof structures need a more
concise knowledge of the real behaviour to determine internal loads and control the load transfer. For
that, laboratory tests on scaled or full-scale specimens of members, connections and trusses are needed.
In this paper, an accurate geometric and mechanical evaluation of the timber elements of two Kingpost
timber trusses, based on grading results with data gathered from non-destructive tests (NDT),
including mechanical evaluation of the modulus of elasticity in bending (MoE), followed by full-scale carrying
tests were performed. The trusses were reassembled in laboratory and submitted to a series of symmetric
and non-symmetric cyclic tests, according to the Limit States. Strengthening techniques evaluated
in precedent research steps were used in a second phase of the load-carrying tests.
The present works intends to represent a further step in the knowledge of timber log-houses through an
experimental approach, from which only few information is available. The main part of the experimental work is based
on in-plane static tests conducted on timber log walls with distinct transversal stiffness, two vertical compression levels
and two values of slenderness. Monotonic and cyclic tests were performed according to EN 12512:2001. The formers
were performed to define the elastic slip values and assessment of the failure mechanisms while the lasts allowed
evaluating impairment of strength, to measure the ductility and to quantify the energy dissipation. In a first step
research, an extensive characterization of the timber logs was made. The connection between the first timber log and the
basement was also evaluated.
In-situ cyclic tests on an existing traditional timber truss were performed. The main goal of
the tests was to evaluate the overall behavior of the timber truss under symmetric and non-symmetric loading.
Moreover, the influence of the location of point loads application, without and with eccentricity relatively to
joints, was assessed. The carrying tests were preceded by a visual and non-destructive inspection aiming to
collect geometric data and to assess the decay level. The field tests results of a queen-post truss are presented
and analyzed. A numerical model was developed to reproduce the test results.
The reconstruction of Lisbon Downtown after the 1755 earthquake was based on a novel constructive system based on masonry buildings with an internal three-dimensional timber-framed structure named “gaiola pombalina”. This internal structure aimed at improving the global stability of masonry buildings, enhancing their capacity to dissipate energy under seismic loadings. This paper aims at getting experimental insight on the mechanical behaviour of such timber–framed walls subjected to in-plane loading, as only scarce information is available in literature, in order to assess their effective performance to seismic actions. To do this, the experimental results of cyclic tests carried out on traditional timber-framed walls with distinct typologies will be analyzed, in order to evaluate the failure modes, lateral resistance and energy dissipation; moreover, a hysteretic model will be derived for traditional timber-framed walls. Additionally, the possibility of strengthening the traditional connections of the walls by means of GFRP is also addressed.
Half-timbered buildings represent an important historical heritage in many countries. They are diffused in
various regions for different reasons, among which for being able to resist seismic actions.
Despite the great popularity of this kind of structures, few studies are available on their global behaviour or on
that of their single structural elements. The aim of this paper is to study the behaviour under cyclic loading of
traditional half-timbered walls, with connections, materials and elements dimensions encountered in existing
Cyclic tests have been performed in order to evaluate the performance of distinct traditional retrofitting
techniques of the connections, namely: (1) increasing the number of nails at the connection; (2) use of steel bolts;
(3) use of steel plates. The idea is to compare the performance in terms of hysteresis loops and the assessment of
the improvements of the cyclic response in terms of ductility and energy dissipation.
Timber connections are an important part of a timber structure and a great variability exists in terms of types of connections and mechanisms. Taking as case study the traditional timber frame structures, the half-lap joint was selected. Connections play a major role in the overall behaviour of a structure, particularly when assessing their seismic response, since damage is concentrated at the connections. Therefore, an experimental campaign was carried out on traditional half-lap joints to assess their in-plane response, carrying out pull-out and in-plane cyclic tests. Subsequently, the connections were retrofitted using self-tapping screws, steel plates and GFRP sheets. In this paper, the experimental results are presented taking into account factors such as dissipated energy, damping and influence on the wall behaviour.; As ligações em madeira constituem uma parte importante das estruturas em madeira e existe uma grande variabilidade em termos de tipologia de ligações e mecânismos. Considerando como caso de estudo os edifícios com paredes de madeira tradicionais (paredes de frontal), foi adotada a ligação madeira-madeira. As ligações tem uma função fundamental no comportamento global da estrutura, em particular na analise sismica...
Damage reports after recent earthquakes proves that slippage between steel reinforcing bars and the surrounding concrete is one the common causes of damage and collapse of existing RC building structures. The bond-slip mechanism assumes particular importance in RC building structures built until the 70’s, with plain reinforcing bars, previously to the enforcement of modern seismic codes. This type of structures is usually characterized by poor reinforcement detailing, poor bond properties and inadequate concrete confinement. In RC buildings subjected to cyclic loads, as the induced by earthquakes, high stress concentration occurs at the beam-column joints, making this regions prone to the occurrence of severe damage. Beam-column joints are particularly sensitive to the bond-slip mechanism due to the stress concentration, but also due to the fact that anchorage of beam and column longitudinal reinforcing bars is typically made in the joint vicinity.
In this paper are presented the main results of the cyclic tests performed on two full-scale beam-column joints with the same geometry and reinforcement detailing, representative of interior joints in RC building structures built until the mid-70’s, without adequate seismic detailing. One specimen was built with plain reinforcing bars (poor bond properties) and the other with deformed bars (good bond properties). For a better comprehension of the bond properties influence on the cyclic behavior of the beam-column joints...
The seismic performance of RC elements with plain reinforcing bars is particularly sensitive to the bond-slip
mechanism. In this paper are described the cyclic tests performed on a two-spans beam with plain reinforcing
bars and two beam-column joints with the same geometry and reinforcement detailing, one with plain
reinforcing bars and the other with deformed bars. The main experimental results are presented and the
comparison between the global behaviour of the two joints is established. A numerical model of the beam was
developed within the OpenSees platform and calibrated with the experimental results. Particular attention was
given to the bond-slip mechanism. Additional numerical analyses were developed without considering bond-slip.
The comparison between the main numerical and experimental results shows the great importance of considering
the bond-slip mechanism in the numerical models in order to have a precise simulation of the cyclic response of
RC elements with plain reinforcing bars.
In-situ cyclic tests on a Portuguese Queen-post timber truss were performed. The main goal of the tests was to evaluate the overall behaviour of the timber truss under symmetric and nonsymmetric
loading. Moreover, the influence of the number and location of point loads, without and
with eccentricity relatively to joints, was assessed. The carrying tests were preceded by a visual
inspection and non-destructive evaluation aiming to collect geometric data and to assess the decay
level presented by the timber elements. The tests results have been reproduce through a finite element model assuming the moment-rotation laws proposed in previous research steps for the joints behaviour.
Existing reinforced concrete (RC) buildings constructed until the mid-70’s, with plain reinforcing bars, are expected to behave poorly when subjected to earthquake actions. This paper describes an experimental program designed to investigate the influence of poor detailing on the cyclic behaviour of RC beam-column joint elements.
Cyclic tests were performed on five interior and five exterior full-scale beam-column joints with different detailing characteristics and reinforced with plain bars. An additional joint of each type was built with deformed bars for an evaluation of the influence of bond properties on the cyclic response of the structural element. The force-displacement global response, energy dissipation, equivalent damping and damage behaviour of the joints was investigated and the main results are presented and discussed. The experimental results indicate that the bond-slip mechanism has significantly influenced the cyclic response of the beam-column joints. The specimens built with plain bars showed lower energy dissipation, stiffness and equivalent damping.
A large number of existing reinforced concrete (RC) buildings structures were designed and built before mid-70’s, when the reinforcing bars had plain surface and prior to the enforcement of the modern seismic-oriented design philosophies.
This paper describes a series of unidirectional cyclic tests performed on seven full-scale columns built with plain reinforcing bars, without adequate reinforcement detailing for seismic demands. The specimens have different reinforcing steel details and different cross sections. A further monotonic test was also carried out for one of the specimens and an additional column, built with deformed bars, was cyclically tested for comparison with the results for the specimens with plain bars. The main experimental results are presented and discussed. The influence of bond properties on the column behaviour is evidenced by differences observed between the cyclic response of similar specimens with plain and deformed bars. The influence of reinforcement amount and displacement history on the column response is also investigated.
The information available in the literature about the cyclic behaviour of reinforced concrete elements with plain reinforcing bars is scarce. As a consequence, the influence of bar slippage in elements with plain bars is not yet comprehensively understood. In this paper are presented and discussed the main results of the cyclic tests carried out on five full-scale reinforced concrete beam-column joints with plain bars and without specific detailing for seismic demands. An additional joint specimen with deformed bars was also tested for comparison. Furthermore, numerical models were built to simulate the response of two of the specimens. Particular attention was given to the influence of bar slippage. The results of the conducted analyses underline the importance of accounting for bond-slip in the numerical modelling of elements with plain bars and also highlight the need for specific models to simulate the effects of this mechanism in the presence of plain bars.
The majority of existing reinforced concrete (RC) buildings were built prior to the introduction of seismic codes.
As observed in various recent earthquakes, due to their lack of structural capacity and ductility such structures
are very vulnerable and have suffered considerable damage. The number of cyclic tests that have been carried
out to investigate the behaviour of RC components with detailing typical of these buildings is very limited. Such
tests are very relevant for seismic vulnerability assessment purposes. In this paper, a low-cycle fatigue testing
campaign on RC columns and connections specifically devised to investigate various physical parameters that
affect damage development, is presented. The campaign consists of 19 columns and 7 beam-column connections.
Some of the preliminary results and observations are presented and discussed.
The development of damage in reinforced concrete (RC) structures is a cumulative process. Some damage
indices used to quantify damage make use of the number of response cycles as an Engineering Demand
Parameter (EDP) relating with damage development. Other indices make use of deformation in terms of
displacement or chord rotation. These functions are generally a function of whether the response is monotonic or
cyclic, and are insensitive to the number of major deflection cycles leading to that state of damage. Many such
relations are derived from experimental data from low-cycle fatigue tests performed on RC elements. The
loading in such tests generally consists of either a monotonic increase in load or a gradually increasing cyclic
load. Since damage development is a cumulative process, and hence depends on the load history, the loading
pattern in low-cycle fatigue tests for assessment purposes should reflect the response of an earthquake. This
paper will discuss a procedure to determine a loading history for cyclic tests, based on earthquake demands. The
preliminary results of a campaign of low-cycle fatigue tests on RC elements to investigate the effect of using
different load histories are also discussed.
SORACE Stefano; TERENZI Gloria; MAGONETTE GEORGES; MOLINA RUIZ FRANCISCO JAVIER
Fonte: American Concrete InstitutePublicador: American Concrete Institute
Tipo: Contributions to ConferencesFormato: CD-ROM
Relevância na Pesquisa
An experimental investigation was carried out on a base isolation system incorporating stainless steel-Teflon bearings, operating as sliders, and silicone fluid viscous spring-dampers. In this system, the dampers are connected to the base-floor of the isolated building to provide the desired passive control of superstructure response, as well as to guarantee its complete re-centring after termination of a seismic action. Two types of experiments were conducted: sinusoidal and random cyclic tests, and a pseudodynamic test in “substructured” configuration. The cyclic tests were aimed at characterising the hysteretic response of the spring-dampers, the frictional behaviour of the steel-Teflon bearings, and the combined response of their assembly. The pseudodynamic test simulated the installation of the protection system at the base of a three-story steel frame structure. The results of the performed tests, as well as of relevant mechanical interpretation and numerical simulation analyses, are presented in this paper.
Keywords: pseudodynamic tests; substructuring; cyclic tests; seismic protection; sliding bearings; fluid viscous devices; base isolation; supplemental damping.; JRC.G.5-European laboratory for structural assessment
The development of novel strengthening techniques to address the seismic vulnerability of masonry elements is gradually leading to simpler, faster and more effective strengthening strategies. In particular, the use of fabric reinforced cementitious matrix systems is considered of great potential, given the increase of ductility achieved with simple and economic strengthening procedures. To assess the effectiveness of these strengthening systems, and considering that the seismic action is involved, one important component of the structural behaviour is the in-plane cyclic response. In this work is discussed the applicability of the diagonal tensile test for the assessment of the cyclic response of strengthened masonry. The results obtained allowed to assess the contribution of the strengthening system to the increase of the load carrying capacity of masonry elements, as well as to evaluate the damage evolution and the stiffness degradation mechanisms developing under cyclic loading.; This research was carried in the framework of InoTec, Innovative material of ultra-high 16
ductility for the rehabilitation of the built patrimony, funded by COMPETE/QREN/FEDER 17
(NORTE-07-0202-FEDER-023024). InoTec project is promoted by CiviTest company 18
and University of Minho. S&P Clever Reinforcement Ibérica is gratefully acknowledged 19
for providing the materials used in the strengthening of the masonry specimens.
The reconstruction of Lisbon Downtown after the 1755 earthquake was based on a novel constructive system based on masonry buildings with an internal three-dimensional timber-framed structure named "gaiola pombalina". This internal structure aimed at improving the global stability of masonry buildings, enhancing their capacity to dissipate energy under seismic loadings. This paper aims at getting experimental insight on the mechanical behaviour of such timber-framed walls subjected to in-plane loading, as only scarce information is available in literature, in order to assess their effective performance to seismic actions. To do this, the experimental results of cyclic tests carried out on traditional timber-framed walls with distinct typologies will be analyzed, in order to evaluate the failure modes, lateral resistance and energy dissipation; moreover, ahysteretic model will be derived for traditional timber-framed walls. Additionally, the possibility of strengthening the traditional connections of the walls by means of GFRP is also addressed.; A reconstrução da Baixa de Lisboa após o terramoto de 1755 foi feita com base num novo sistema construtivo de edifícios de alvenaria com uma estrutura tridimensional interna de madeira designada de "gaiola pombalina"...
Investment into offshore wind farms has been growing to address the growing threat of climate change. The majority of offshore wind turbines (both current and planned) are founded on monopiles, large circular steel pipe piles ranging from 4.0 m ? 7.5 m in diameter. Based on available borehole records, most planned wind turbines in the UK will be founded in overconsolidated clay deposits. Monopile design is done via usage of the well established p-y curves. However, there are issues with the usage of the p-y curves. Firstly, the curves may be unsuitable to model the monopile?s behaviour as it is expected to behave similarly to a rigid pile rather than flexibly. Secondly, the curves may not accurately estimate the initial pile-soil stiffness. Thirdly, the curves are not comprehensive enough to account for the accumulated strain and stiffness changes resulting from cyclic loading. Considering these issues, research was carried out to improve the current design of monopiles in clay by carrying out displacement controlled monotonic and load controlled cyclic load tests in a centrifuge.
Results from monotonic tests suggest that the DNV (2014) design methodology to construct p-y curves in clay based on Matlock?s (1970) soft clay criterion significantly underestimate stiffness. Findings suggested that the experimental p-y curves could be characterised through modification of the criterion. Modification of the criterion produced estimates that matched the 3.83 m monopile experimental curves. Pile toe shear force was observed to contribute little to ultimate lateral resistance and stiffness. Despite the marginal contribution...