1,319 research outputs found

    Seismology and seismic hazard

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    Low cycle fatigue tests of reinforced concrete columns and joints built with ribbed reinforcement and plain stirrups

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    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 effect of the number of response cycles on the behaviour of reinforced concrete elements subject to cyclic loading

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    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

    Experimental response of RC columns built with plain bars under unidirectional cyclic loading

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    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

    Construction design, building standards and site selection. Guidance note 12

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    Cyclic response of RC beam-column joints reinforced with plain bars: an experimental testing campaign

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    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

    Resilient Based Design Interventions on Critical Buildings in Sri Lanka

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    Healthcare and education (H&E) services are two of the pillars of development and are central to SDG 3 “Ensure healthy lives and promote wellbeing for all at all ages” and SDG4 “Ensure inclusive and equitable quality education and promote lifelong learning opportunities for all”. Functioning H&E services are also critical to community post-disaster recovery and support return to normalcy. In recognition of this, the Sendai Framework for DRR 2015–2030 has as one of its global targets to “substantially reduce disaster damage to critical infrastructure and disruption of basic services, among them health and educational facilities, including through developing their resilience”. This shift from risk to resilience effectively sets a challenge to engineers, who should not only consider life-safety in the design and retrofit of buildings for natural hazard effects, but also what can be done to ensure a rapid restoration of buildings’ functionality. In fact, in the case of H&E services, implementation of resilient design requires a paradigm shift where hospitals and school buildings are not considered as individual assets, but rather as a part of a network of assets that together provide healthcare and education to communities across geographical scales. This paper looks to provide examples of where resilience concepts have been/are being used to understand the impact that a future tsunami might have on the healthcare and education system in coastal areas of Sri Lanka. The work presented is part of the research being conducted under the auspices of two research projects funded by Research England called ReSCOOL (2019-ongoing) and HEARTS-SL (2018-2020). These projects comprise international teams of researchers from University College London, Imperial College and Southampton University (UK), University of Moratuwa, University of Peradeniya, South Eastern University (Sri Lanka) and University of Naples Federico II (Italy)

    Nonlinear modeling of the cyclic response of RC columns

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    Cyclic load reversals (like those induced by earthquakes) result in accelerated bond degradation, leading to significant bar slippage. The bond-slip mechanism is reported to be one of the most common causes of damage and even collapse of existing RC structures subjected to earthquake loading. RC structures with plain reinforcing bars, designed and built prior to the enforcement of the modern seismic-oriented design philosophies, are particularly sensitive to bond degradation. However, perfect bond conditions are typically assumed in the numerical analysis of RC structures. This paper describes the numerical modeling of the cyclic response of two RC columns, one built with deformed bars and the other with plain bars and structural detailing similar to that typically adopted in pre-1970s structures. For each column, different modeling strategies to simulate the column response were tested. Models were built using the OpenSees and the SeismoStruct platforms, and calibrated with the available tests results. Within each platform, different types of nonlinear elements were used to represent the columns. Bond-slip effects were included in the OpenSees models resorting to a simple modeling strategy. The models and the parameters adopted are presented and discussed. Comparison is established between the most relevant experimental results and the corresponding results provided by the numerical models. Conclusions are drawn about the capacity of the tested models to simulate the columns response and about the influence of considering or not considering the effects of bars slippage

    Tsunami Scour and Forces at Onshore Structures

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    Tsunami induced scour at onshore coastal structures can cause exposure of the foundations and lead to failure. This paper presents experimental observations of a 147 s crest-led wave inundation, causing scouring and loading on 0.2 m wide square and 0.4 m wide rectangular onshore structures. At 1:50 Froude scale these equate to a 17.3 min inundation at 10 and 20 m wide structures. Scour development is measured using GoPro cameras situated inside the Perspex structures. The hydrostatic load is calculated from the integration of pressure readings along the front face of the structures, and the hydrodynamic loading is estimated from the approach flow velocity, as measured by a Vectrino II profiler. The results show that the maximum scour depth occurs during the inundation before significant slumping decreases the end scour depth. Both the in-test and final scour depths for the 0.4 m structure are greater, due to the larger blockage causing greater acceleration of the flow around the structure. For both structures, the hydrostatic loading is dominant over hydrodynamic load

    Seismic performance of buried electrical cables: evidence-based repair rates and fragility functions

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    The fragility of buried electrical cables is often neglected in earthquakes but significant damage to cables was observed during the 2010–2011 Canterbury earthquake sequence in New Zealand. This study estimates Poisson repair rates, similar to those in existence for pipelines, using damage data retrieved from part of the electric power distribution network in the city of Christchurch. The functions have been developed separately for four seismic hazard zones: no liquefaction, all liquefaction effects, liquefaction-induced settlement only, and liquefaction-induced lateral spread. In each zone six different intensity measures (IMs) are tested, including peak ground velocity as a measure of ground shaking and five metrics of permanent ground deformation: vertical differential, horizontal, maximum, vector mean and geometric mean. The analysis confirms that the vulnerability of buried cables is influenced more by liquefaction than by ground shaking, and that lateral spread causes more damage than settlement alone. In areas where lateral spreading is observed, the geometric mean permanent ground deformation is identified as the best performing IM across all zones when considering both variance explained and uncertainty. In areas where only settlement is observed, there is only a moderate correlation between repair rate and vertical differential permanent ground deformation but the estimated model error is relatively small and so the model may be acceptable. In general, repair rates in the zone where no liquefaction occurred are very low and it is possible that repairs present in this area result from misclassification of hazard observations, either in the raw data or due to the approximations of the geospatial analysis. Along with hazard intensity, insulation material is identified as a critical factor influencing cable fragility, with paper-insulated lead covered armoured cables experiencing considerably higher repair rates than cross-linked polyethylene cables. The analysis shows no trend between cable age and repair rates and the differences in repair rates between conducting materials is shown not to be significant. In addition to repair rate functions, an example of a fragility curve suite for cables is presented, which may be more useful for analysis of network connectivity where cable functionality is of more interest than the number of repairs. These functions are one of the first to be produced for the prediction of damage to buried cables
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