• Earthquakes and Structures
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• 제6권4호
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• pp.409-436
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• 2014

Although it is widely accepted that the interaction -between masonry infill and structural members significantly affects the seismic response of reinforced concrete (RC) frames, this interaction is generally neglected in current design-oriented seismic analyses of structures. Moreover, the role of masonry infill is expected to be even more relevant in the case of existing frames designed only for gravitational loads, as infill walls can significantly modify both lateral strength and stiffness. However, the additional contribution to both strength and stiffness is often coupled to a modification of the global collapse mechanisms possibly resulting in brittle failure modes, generally related to irregular distributions of masonry walls throughout the frame. As a matter of principle, accurate modelling of masonry infill should be at least carried out by adopting nonlinear 2D elements. However, several practice-oriented proposals are currently available for modelling masonry infill through equivalent (nonlinear) strut elements. The present paper firstly outlines some of the well-established models currently available in the scientific literature for modelling infill panels in seismic analyses of RC frames. Then, a parametric analysis is carried out in order to demonstrate the consequences of considering such models in nonlinear static and dynamic analyses of existing RC structures. Two bay-frames with two-, three- and four-storeys are considered for performing nonlinear analyses aimed at investigating some critical aspects of modelling masonry infill and their effects on the structural response. Particularly, sensitivity analyses about specific parameters involved in the definition of the equivalent strut models, such as the constitutive force-displacement law of the panel, are proposed.

• Structural Engineering and Mechanics
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• 제77권1호
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• pp.115-135
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• 2021

This paper focuses on examining the effects of span arrangements on displacement responses of plan-symmetric RC frame buildings designed using the direct displacement-based design (DDBD) method by employing non-linear analyses and the skew seismic attack. In order to show the desired performance of DDBD design approach, the force-based design approach is also used to examine the seismic performance of the selected structures. To realize this objective, 8-story buildings with different plans are selected. In addition, the dynamic behavior of the structures is evaluated by selecting 3, 7, and 12-story buildings. In order to perform non-linear analyses, OpenSees software is used for modeling buildings. Results of an experimental model are used to validate the analytical model implemented in OpenSees. The results of non-linear static and non-linear dynamic analyses indicate that changing span arrangements does not affect estimating the responses of structures designed using the DDBD approach, and the results are more or less the same. Next, in order to apply the earthquake in non-principle directions, DDBD structures, designed for one-way performance, are designed again for two-way performance. Time history analyses are performed under a set of artificial acceleration pairs, applied to structures at different angles. It is found that the mean maximum responses of earthquakes at all angles have very good agreement with the design-acceptable limits, while the response of buildings along the height direction has a relatively acceptable and uniform distribution. Meanwhile, changes in the span arrangements did not have a significant effect on displacement responses.

• Computers and Concrete
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• 제12권5호
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• pp.681-695
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• 2013

In 1999 Marmara and 2011 Van earthquakes in Turkey, majority of the existing buildings either sustained severe damage or collapsed. These buildings include masonry infill walls in both the interior and exterior R/C frames. The material of the masonry infill is the main variant, ranging from natural stones to bricks and blocks. It is demanding to design these buildings for satisfactory structural behavior. In general, masonry infill walls are considered by its weights not by interaction between walls and frames. In this study, R/C buildings with infill walls are considered in terms of structural behavior. Therefore, 5 and 8-story R/C buildings are regarded as the representative models in the analyses. The R/C representative buildings, both with and without infill walls were analyzed to determine the effects of structural behavior change. The differences in earthquake behavior of these representative buildings were investigated to determine the effects of infill walls leading structural capacity. First, pushover curves of the representative buildings were sketched. Aftermath, time history analyses were carried out to define the displacement demands. Finally, fragility analyses were performed. Throughout the fragility analyses, probabilistic seismic assessment for R/C building structures both with and without infill walls were provided. In this study, besides the deterministic assessment methodology, a probabilistic approach was followed to define structural effect of infill walls under seismic loads.

• Earthquakes and Structures
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• 제10권2호
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• pp.409-428
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• 2016

To realise the full benefits of a self-centering seismic resilient system, the designer must ensure that the entire structure does indeed re-center following an earthquake. The idealised flag-shaped hysteresis response that is often used to define the cyclic behaviour of self-centering concrete systems seldom exists and the residual drift of a building subjected to an earthquake is dependent on the realistic cyclic hysteresis response as well as the dynamic loading history. Current methods that are used to ensure that re-centering is achieved during the design of self-centering concrete systems are presented, and a series of cyclic analyses are used to demonstrate the flaws in these current procedures, even when idealised hysteresis models were used. Furthermore, results are presented for 350 time-history analyses that were performed to investigate the expected residual drift of an example self-centering concrete wall system during an earthquake. Based upon the results of these time-history analyses it was concluded that due to dynamic shake-down the residual drifts at the conclusion of the ground motion were significantly less than the maximum possible residual drifts that were observed from the cyclic hysteresis response, and were below acceptable residual drift performance limits established for seismic resilient structures. To estimate the effect of the dynamic shakedown, a residual drift ratio was defined that can be implemented during the design process to ensure that residual drift performance targets are achieved for self-centering concrete wall systems.

• Earthquakes and Structures
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• 제4권2호
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• pp.157-179
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• 2013

Vulnerability studies on the existing building stock require that a large number of buildings is analyzed to obtain statistically significant evaluations of the seismic performance. Therefore, analytical evaluation methods need to be based on simplified methodologies of analysis which can afford the treatment of a large building population with a reasonable computational effort. Simplified Pushover-Based Earthquake Loss Assessment approach (SP-BELA), where a simplified methodology to identify the structural capacity of the building through the definition of a pushover curve is adopted, was developed on these bases. Main objective of the research work presented in this paper is to validate the simplified methodology implemented in SP-BELA against the results of more sophisticated nonlinear dynamic analyses (NLDAs). The comparison is performed for RC buildings designed only to vertical loads, representative of the "as built" in Italy and in Mediterranean countries with a building stock very similar to the Italian one. In NLDAs the non linear and degrading behaviour, typical of the structures under consideration when subjected to high seismic loads, is evaluated using models able to capture, with adequate accuracy, the non linear behaviour of RC structural elements taking into account stiffness degradation, strength deterioration, and pinching effect. Results show when simplified analyses are in good agreement with NLDAs. As a consequence, unsatisfactory results from simplified analysis are pointed out to address their current applicability limits.

• 한국지진공학회논문집
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• 제20권7_spc호
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• pp.473-483
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• 2016

In this paper, seismic performance assessment has been examined for a mid-rise RC building subjected to 2016 Gyeongju earthquake occurred in Korea. For the purpose of the paper, 2D external and internal frames in each direction of the building have been employed in the present comparative analyses. Nonlinear static pushover analyses have been conducted to estimate frame capacities. Nonlinear dynamic time-history analyses have also been carried out to examine demands for the frames subjected to ground motions recorded at stations in near of Gyeongju and a previous earthquake ground motion. Analytical predictions demonstrate that maximum demands are significantly affected by characteristics of both spectral acceleration response and spectrum intensity over a wide range of periods. Further damage potential of the frames has been evaluated in terms of fragility analyses using the same ground motions. Fragility results reveal that the ground motion characteristics of the Gyeongju earthquake have little influence on the seismic demand and fragility of frames.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.194-201
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• 2000

In this study the modified seismic coefficient method for seismic analysis of buried box structures is developed for practical purpose. The loading coefficient in the modified seismic coefficient method is determined from the results of the response displacement analysis. In the developed method adequate velocity response spectrum in accordance with soil condition is also needed to seismic design of buried box structures, In order to investigate applicability of the modified seismic coefficient method various analyses are performed with different parameters such as depth of base rock height and width of box buried depth and value of standard penetration test. Results from the modified seismic coefficient method are compared with those of the response displacement method in terms of the maximum bending moment and the location of it. From the comparison it is shown that the feasibility of the modified seismic coefficient method for seismic analysis of buried box structures.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.380-387
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• 2005

Little has been understood about the seismic behavior of curved bridges due to the different structural characteristics compared to straight bridges. In this study, a simple numerical model, widely used for seismic analysis, is modified for a more realistic estimation of the seismic behavior. The seismic response of curved bridges obtained with the modified simple numerical model was compared with the result using a more sophisticated model to verify the feasibility. Seismic analyses were performed on three-span continuous curved bridges, which is a structural system widely used in highway structures. Numerical model of the three-span continuous curved bridges were subjected to seismic loads in diverse directions. From the result of the analysis. it was found that the direction of the seismic load have significant effect of the seismic behavior of curved bridges when the central angle exceeds 90 degrees.

• 한국지진공학회논문집
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• 제19권3호
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• pp.133-143
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• 2015

It is very important to assure the seismic performance of equipment as well as building structures in seismic design of nuclear power plant(NPP). Seismically isolated structures may be reviewed mainly on the horizontal seismic responses. Considering the equipment installed in the NPP, the vertical earthquake responses of the structure also should be reviewed. This study has investigated the vertical seismic demand of seismically isolated structure by lead rubber bearings(LRBs). For the numerical evaluation of seismic demand of the base isolated NPP, the Korean standard nuclear power plant (APR1400) is modeled as 4 different models, which are supported by LRBs to have 4 different horizontal target periods. Two real earthquake records and artificially generated input motions have been used as inputs for earthquake analyses. For the study, the vertical floor response spectra(FRS) were generated at the major points of the structure. As a results, the vertical seismic responses of horizontally isolated structure have largely increased due to flexibility of elastomeric isolator. The vertical stiffness of the bearings are more carefully considered in the seismic design of the base-isolated NPPs which have the various equipment inside.

• Structural Engineering and Mechanics
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• 제11권6호
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• pp.651-662
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• 2001

In order to investigate the seismic behavior and seismic design methods in the transverse direction of a shield tunnel, a series of model shaking table tests and a two-dimensional finite element dynamic analysis on the tests are carried out. Two kinds of static analytical methods based on ground-tunnel composite finite element model and beam-spring element model are proposed, and the validity of the static analyses is verified by model shaking table tests. The investigation concerns the dynamic response behavior of a tunnel and the ground, the interaction between the tunnel and ground, and an evaluation of different seismic design methods. Results of the investigation indicate that the shield tunnel follows the surrounding ground in displacement and dynamic characteristics in the transverse direction; also, the static analytical methods proposed by the authors can be used directly as the seismic design methods in the transverse direction of a shield tunnel.