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Multiple earthquakes occur at many regions around the world where complex fault
systems exist. These fault systems usually do not relieve all accumulated strains at once
when the first rupture takes place. Therefore high stresses form at different locations
causing sequential ruptures until the fault system is completely stabilized. The sequential
ruptures along the fault segment(s) lead to multiple earthquakes which are often hard to
distinguish them as fore-, main- and after-shocks, or a sequence of earthquakes from
proximate fault segments.
Field investigations reported failure of structural systems under repeated earthquakes,
especially where structural retrofitting was not provided due to the short time frames
between the successive shaking. In most failure cases the reported damage is mainly due
to dramatic loss of stiffness and strength of structural elements as a result of material
deterioration under repeated earthquake loadings. Deterioration effects are obvious in
structures that experienced main-shock aftershock earthquake sequence and were able to
withstand the main-shock however they collapsed in the smaller aftershock.
Limited research has addressed the seismic behavior of structures subjected to multiple
earthquakes. Repeated shaking induces accumulated damage to structures that affects
their level of stiffness and strength and hence their response. Given the complexity of
depicting the degrading behavior of structures using the current numerical tools, previous
researchers used simplified approaches to compensate for the absence of important
numerical model features of stiffness and strength degradation, alongside pinching of
load-displacement loops. Moreover ground motion sequences used in previous studies
were randomized and hence the characteristics of ground motions effects on the response
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A seismic design procedure considering performance criteria for two distinct limit states is presented, involving analysis of a
feasible partial inelastic model of the structure using currently available powerful tools. The procedure is developed in a format
appropriate for incorporation into modern design codes, such as the Eurocode 8, and two alternatives are explored, one involving time–history analysis for appropriately scaled input motions, and a simpler one involving inelastic static (pushover) analysis. The proposed method is found to lead to better seismic performance than the standard code procedure, at least in the case of regular multistorey reinforced concrete frame structures studied herein, and in addition leads to a more economic design of transverse reinforcement in the members that develop very little inelastic behaviour even for very strong earthquakes.
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Micro Structure Effect of Concrete Degradation for Compressive Strength of Concrete Burned in High Temperature
Author: Setyowati E W , Soehardjono A , Zacoeb A , Fuad A , Mufti N | Size: 767 KB | Format:PDF | Quality:Unspecified | Publisher: International Journal of Emerging Technology and Advanced Engineering | Year: 2012 | pages: 06
Abstract- It is generally recognized that the
environmental degradation of the concrete infrastructure is
a serious, large scale and costly problem in many parts of
the world. This study discussed about the power of concrete
structure especially the comparison of the compressive
strength of concrete due to higher temperature of fire with
the micro structure of concrete degradation . The
methodology consisted of experiment using the concrete
samples that was carried out by trial kinds temperature of
400°C, 600°C, and 800°C with factor of cement water was
steady in 28 days and then carried out process at the
burner wich burned . The study highlights thecapabilities
of the methods for the analysis of concrete towards the
determination of hardenedcement paste degradation. The
methods ascertain that the samples XRD results showed
small quantity of ettringite, calcium, carboaluminate
hydrate , and a complete leach of portlandite fase and to be
smaller than in high temperature and to be loos at 800
oC.The result for the SEM it will be degradation at micro
structure of concrete, like the micro crack on material
concrete at high temperature (800oC). The result
compressive test for 80 samples of concrete is the
compressive strength for the material concrete is become
lower than in high temperature, up to70 % .
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SEISMIC ASSESSMENT OF AN IRREGULAR THREE-STOREY FULL SCA LE RC TEST STRUCTURE WITH SUBSTANDARD DETAILS
Author: S. J. PARDALOPOULOS Civil Engineer, (AUTh), MSc (DUTh), Greece [email protected] GEORGIA E. THERMOU PhD Candidate, Department of Civil Engineering Demokritus University of Thrace, Greece, STAVROULA J. PANTAZOPOULOU | Size: 737 KB | Format:PDF | Quality:Unspecified | pages: 17
ABSTRACT
Seismic assessment of a full scale 3-storey, irregular reinforced concrete structure that was tested in the European Laboratory for Structural Assessment (ELSA) is presented in the paper. The structure is representative of older design and construction practices in Southern Europe, prior to the introduction of capacity design principles or modern detailing. Parametric analyses where carried out to quantify the effect of plan
eccentricity with the various mechanisms of resistance throughout the frame system, using the same ground motion records and PGA that were used in the actual tests. Mechanisms considered are member effective stiffness, member flexure, member shear, development capacity of anchorages and lap splices, and joint shear. Response parameters considered are the time-histories of the trajectories of the Center of Mass in the three floors, interstorey drift and floor twist. Also calculated are the time histories of demand/supply ratios, λi, for the various mechanisms of resistance.
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EXPERIMENTAL MULTI-LEVEL SEISMIC PERFORMANCE ASSESSMENT OF 3D RC FRAME DESIGNED FOR DAMAGE AVOIDANCE
Author: Brendon A Bradley1* , Rajesh P Dhakal1 , John B Mander1 , Louman Li1 . 1 Department of Civil Engineering, University of Canterbury, , New Zealand | Size: 591 KB | Format:PDF | Quality:Unspecified | pages: 33
This paper experimentally investigates the application of damage avoidance design (DAD) philosophy to moment resisting frames with particular emphasis on detailing of rocking interfaces. An 80% scale 3-dimensional rocking beam-column joint sub-assembly designed and detailed based on damage avoidance principles is constructed and tested.
Incremental dynamic analysis (IDA) is used to select ground motion records to be applied to the sub-assembly to conduct a multi-level seismic performance assessment (MSPA).
Analyses are conducted to obtain displacement demands due to the selected near and medium
field ground motions that represent different levels of seismic hazard. Thus predicted
displacement time histories are applied to the sub-assembly to conduct quasi-earthquake displacement (QED) tests. The sub-assembly performed well reaching drifts up to 4.7% with only minor spalling occurring at rocking beam interfaces and minor flexural cracks in beams.
Yielding of post-tensioning tendons occurred, but the sub-assembly did not collapse. The externally attached energy dissipaters provided large hysteretic dissipation during large drift
cycles. The sub-assembly satisfied all three seismic performance requirements, thereby verifying the superior performance of the DAD philosophy.
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Effect of floor slabs on the seismic performance of RC frames
Author: S.M Ahmed & U. Gunasekaran Anna University, Chennai, India. | Size: 1.3 MB | Format:PDF | Quality:Unspecified | Year: 2014 | pages: 13
ABSTRACT: In monolithic reinforced concrete structures, portions of the floor slabs act as flanges to the girders, thereby increasing the strength and stiffness of the girders. The question of how much the slab contributes to the lateral strength is very important for the design of structures; therefore this paper describes the effect of slabs at the joints in moment-frame structures subjected to large seismic deformations. A simple method to model a beam-column joint subassembly including the effects of both beam growth/elongation and the floor slab is introduced. The model is developed by establishing the slab crack pattern at the joint and the state of strain in the slab bars. The results of the models excluding and including slab effects are verified with the experiential test results. The joint model is incorporated in the nonlinear dynamic analyses for a five-storey and four-bay moment frame structure. Two different ground motions (El-Centro 1940 and Northridge 1994) are considered for the analyses. The results show that the cyclic inelastic bending causes the beams to increase in length and the floor slabs significantly restrain this phenomenon and cause the columns to displace by different amounts, changing the distribution of shear among the columns, and increasing the base shear of the columns. These additional forces may lead to a failure mechanism different from the anticipated one. The effect of floor slab including beam elongation effect is thus illustrated for a two dimensional moment frame building and this model works well for the lateral load analysis of frames.
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SEISMIC PERFORMANCE OF HIGH-ST RENGTH-CONCRETE HOLLOW BRIDGE PIERS UNDER MULTI-DIRECTIONAL LOADING
Author: R. Burgueño , X. Liu and E. M. Hines | Size: 1.2 MB | Format:PDF | Quality:Unspecified | pages: 11
High-strength-concrete (HSC) offers the potential of transforming the design of structural elements under seismic loads by harnessing the enhanced capacities associated with axial load, flexural compression zone confinement and web shear crushing of wall webs. However, the limits to which such performance features can be reliably taken into account require careful exploration, in particular, when considering multi-directional seismic loads. Of the noted aspects enhanced by HSC, that associated with the inelastic web crushing capacity of hollow rectangular bridge piers is still unresolved in view of the guidance of capacity design philosophy which suppresses possible shear failures. Nonetheless, recent research has demonstrated that structural walls can exhibit dependable ductile behavior before being ultimately limited by web crushing shear failures. And that this inelastic capacity can be further improved with HSC. However, the threedensional demands and damage accumulation of HSC structural walls under multi-directional loading needs to be properly evaluated to establish reliable nlimits that satisfy the noted inelastic performance requirements.
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Seismic Performance of Strength Degraded Structures
Author: Rupali S Bhamare , Bidur Kafle , Nelson Lam , John Wilson , Emad Gad | Size: 423 KB | Format:PDF | Quality:Unspecified | pages: 11
ABSTRACT:
Traditionally, performance assessment of a structure is based on trading off strength demand with
ductility demand. In high seismicity region, the design provisions are based on the concept of conservation
of energy; such guidelines (FEMA 273) recommend a very low drift capacity for strength
degraded structures. Furthermore, the application of these guidelines, results in most of the strength
degraded structures deemed unsafe when subjected to earthquake excitations in low and moderate
seismic regions. This paper presents results of nonlinear time history analyses (THA) for such
strength degraded structures for a range of near-field and far-field earthquake scenarios of different
M-R combinations. Fragility curves defining probability of failure of structures have been developed.
The insensitivity of the probability of failure of the URM wall on its height (i.e. vertical span
length) is an interesting finding in this study. Also, the extent of strength degradation in an unreinforced
masonry wall is not shown to have increased its probability of failure.
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