• Earthquakes and Structures
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• v.7 no.1
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• pp.39-55
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• 2014

A modified procedure is presented for assessing the seismic response of elastic non-proportionate multistory buildings. This procedure retains the simplicity of the methodology presented by the author in earlier papers, but it presents higher accuracy in buildings composed by very dissimilar types of bents. As a result, not only frequencies and peak values of base resultant forces are determined with higher accuracy, but also the location of the first mode center of rigidity (m1-CR). The closeness of m1-CR with the axis passing through the centers of floor masses (mass axis) implies a reduced rotational response and it is demonstrated that in elastic systemsa practically translational response is obtained when this point lies on the mass axis.Besides, when common types of buildings are detailed as planar structures under a code load, this response is maintained in the inelastic phase of their response as a result of the almost concurrent yielding of all the resisting bents. This property of m1-CR can be used by the practicing engineer as a guideline to form a structural configuration which will sustain minimum rotational response, simply by allocating the resisting elements in such a way that this point lies close to the mass axis. Inelastic multistory building structures, detailed as above, may be regarded as torsionally balanced multistory systems and this is demonstrated in eight story buildings, composed by dissimilar bents, under the ground motions of Kobe 1995 (component KJM000) and Friuli 1976 (component Tolmezzo E-W).

• Earthquakes and Structures
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• v.8 no.3
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• pp.591-617
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• 2015

Standards for seismic assessment and retrofitting of buildings provide deformation limit states for structural members and connections. However, in order to perform fully consistent performance-based seismic analyses of soil-structure systems; deformation limit states must also be available for foundations that are vulnerable to nonlinear actions. Because such limit states have never been established in the past, a laboratory testing program was conducted to study the rotational capacity of small-scale foundation models under combined axial load and moment. Fourteen displacement-controlled monotonic and cyclic tests were performed using a cohesionless soil contained in a $2.0{\times}2.0{\times}1.2m$ container box. It was found that the foundation models exhibited a stable hysteretic behavior for imposed rotations exceeding 0.06 rad and that the measured foundation moment capacity complied well with Meyerhof's equivalent width concept. Simplified code-based soil-structure analyses of an 8-story building under an array of strong ground motions were also conducted to preliminary evaluate the implication of finite rotational capacity of vulnerable foundations. It was found that for the same soil as that of the experimental program foundations would have a deformation capacity that far exceeds the imposed rotational demands under the lateral load resisting members so yielding of the soil may constitute a reliable source of energy dissipation for the system.

• Structural Engineering and Mechanics
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• v.83 no.2
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• pp.229-244
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• 2022

This paper investigates the seismic performance of buildings designed using DDBD (Direct Displacement based Design) and FBD (Force based Design) approaches from the probabilistic viewpoint. It aims to estimate the collapse capacity of structures and assess the adequacy of seismic design codes. In this regard, (i) IDA (Incremental Dynamic Analysis) curves, (ii) interstory drift demand distribution curves, (iii) fragility curves, and (iv) the methodology provided by FEMA P-695 are applied to examine two groups of RC moment resistant frame buildings: 8-story structures with different plans, to study the effect of different span arrangements; and 3-, 7- and 12-story structures with a fixed plan, to study the dynamic behavior of the buildings. Structural modeling is performed in OpenSees software and validated using the results of an experimental model. It is concluded that increasing the building height would not significantly affect the response estimation of IDA and fragility curves of DDBD-designed structures, while the change in span arrangements is effective in estimating responses. In the investigation of the code adequacy, unlike the FBD approach, the DDBD can satisfy the performance criteria presented in FEMA P-695 and hence provide excellent performance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.103-110
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• 2020

In the recent seismic design code KDS 41 17 00, selection and modification procedures of ground motions which are used for nonlinear dynamic analyses were adopted. However, its practical applications are still limited due to the lack of literatures. This paper introduces case studies which used site-response analyses to select and modify ground motions for nonlinear dynamic analyses. Based on the case studies, design criterion for site-response analyses were reviewed thoroughly in the viewpoint of practical applications. It was found that design requirements related with bedrock motions are too conservative that ground motions are selected and modified in the excessive manner. It is especially true for low-rise building structures with period ranges including acceleration-sensitive regions. Even though surface motions have shown appropriate responses, such building structures have to re-select and re-modify ground motions based on pre-analysis procedures rather than post-ones according to the current seismic design code. Also, it was observed that building structures with soft soils under strong ground motions need more comprehensive investigations on soil properties and efficient analysis methods in order to perform site-response analyses. This is due to the fact that lack of reliabilities on soil properties and analysis methods could result in unstable site-responses.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1363-1386
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• 2015

The October 23 2011 Van Earthquake is studied from an earthquake engineering point of view. Strong ground motion processing was performed to investigate features of the earthquake source, forward directivity effects during the rupture process as well as local site effects. Strong motion characteristics were investigated in terms of peak ground motion and spectral acceleration values. Directiviy effects were discussed in detail via elastic response spectra and wide band spectograms to see the high frequency energy distributions. Source parameters and slip distribution results of the earthquake which had been proposed by different researchers were summarized. Influence of the source parameters on structural response were shown by comparing elastic response spectra of Muradiye synthetic records which were performed by broadband strong motion simulations of the earthquake. It has been emphasized that characteristics of the earthquake rupture dynamics and their effects on structural design might be investigated from a multidisciplinary point of view. Seismotectonic calculations (e.g., slip pattern, rupture velocity) may be extended relating different engineering parameters (e.g., interstorey drifts, spectral accelerations) across different disciplines while using code based seismic design approaches. Current state of the art building codes still far from fully reflecting earthquake source related parameters into design rules. Some of those deficiencies and recent efforts to overcome these problems were also mentioned. Next generation ground motion prediction equations (GMPEs) may be incorporated with certain site categories for site effects. Likewise in the 2011 Van Earthquake, Reverse/Oblique earthquakes indicate that GMPEs need to be feasible to a wider range of magnitudes and distances in engineering practice. Due to the reverse faulting with large slip and dip angles, vertical displacements along with directivity and fault normal effects might significantly affect the engineering structures. Main reason of excessive damage in the town of Erciş can be attributed to these factors. Such effects should be considered in advance through the establishment of vertical design spectra and effects might be incorporated in the available GMPEs.

• Earthquakes and Structures
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• v.26 no.5
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• pp.349-361
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• 2024

Excessive torsional behaviour is one of the major reasons for failure of buildings, as inferred from past earthquakes. Numerous seismic codes across the world specify a displacement-based or drift-based criterion for classifying buildings as torsionally irregular. In recent years, quite a few researchers have pointed out some of the inherent deficiencies associated with the current codal guidelines on torsional irregularity. This short communication paper aims to envisage the need for a revision of the displacement-based guidelines on torsional irregularity, and further highlight the appropriateness of a rotation-based criterion. A set of 6 reinforced concrete building models with asymmetric shear walls are analysed using ETABS v18.0.2, by varying the number of stories from 1 to 9, and the torsional irregularity coefficient of various stories is calculated using the displacement-based formula. Since rotation about the vertical axis is a direct indication of the twist experienced by a building, the calculated torsional irregularity coefficients of all stories are compared with the corresponding floor rotations. The conflicting results obtained for the torsional irregularity coefficients are projected through five categories, namely mismatch with floor rotations, inconsistency in trend, lack of clarity in incorporation of negative values, sensitivity to low values of displacement and error conceived in the mathematical formulation. The findings indicate that the irregularity coefficient does not accurately represent the torsional behaviour of buildings in a realistic sense. The Indian seismic code-based values of 1.2 and 1.4, which are used to characterize buildings as torsionally irregular are observed to be highly sensitive to the numerical values of displacements, rather than the actual degree of rotation. The study thus emphasizes the revision of current guidelines based on a more relevant rotation-based or eccentricity-based approach.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.525-530
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• 1998

The objective of this experiment is to observe the elastic and inelastic behaviors of high-rise reinforced concrete frames with nonseimic details. To do this, a building frame designed according to Korean seismic code and detailed in the Korean conventional manner was selected. An 1:12 scale plane frame model was manufactured according law. Reversed lateral load tests and monotonic push-over test were performed under the displacement control. To simulate the earthquake effect, the lateral force distribution was maintained to be an inversed triangular by using whiffle tree. From the tests, story displacements, lateral story forces, local plastic rotations and the relations between inter-story drift versus story shear are obtained. Based on the test results, conclusions on the characteristics of the elastic and behaviors of a high-rise reinforced concrete frame with nonseismic details are drawn.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.437-442
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• 2002

The purpose of this study is to investigate nonlinear behavior and estimate ultimate resistance of the wall structure against seismic loading. Experimental data for RC coupling elements are used for specifying the strength deterioration and stiffness degradation factor of hysteretic model. Modified coupling element models are used in the push over analysis and time history analysis. In the time history analysis, three earthquake waves are used in the analysis and their peak ground accelerations are changed to be 0.2g. The conclusions of this study are as follows : (1) In the push over analysis, yielding of coupling elements occurred at lower story with small story drift ratio as 0.3%. (2) In the time history analysis, the story drift ratio is sufficient for the requirement of Korean Code, But coupling elements at most stories of the buildings occurred yielding. i. e. the earthquake resistant capacity of shear wall structures is not sufficient at 0.2g.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.52-55
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• 2004

Before incorporating the earthquake-resistance design in design code(998), most of existing residential buildings were built without having lateral resistance capacity in addition to their structural peculiarity such as exterior stair ways, exterior elevator room. For these reasons, the retrofitting research demands for existing buildings arise recently and many retrofitting methods are proposed. These tasks are important to reduce the enormous economic loss and environmental issues. In this study, Scaled residential buildings with/without lateral resistance were tested and monitored with external lateral load especially toward the longer side of the building. From these experiments, enhanced retrofitting methods of old shear wall system are proposed and also compared with structural analysis.

• The Journal of Engineering Research
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• v.8 no.1
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• pp.5-11
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• 2006

In order to evaluate the seismic performance of a reinforced concrete building structure, four different analyses are carried out. Firstly, conventional pushover analysis with code-specified inverted triangular load pattern is conducted. Secondly, the pushover analysis with uniform load pattern is performed. Thirdly, adaptive pushover analyses with spectral amplification for both EC 8 artificial and Northridge earthquake are carried out. Lastly, Incremental dynamic analyses under a number of scaled PGA for both EC 8 artificial and Northridge earthquake record are performed. Comparative studies demonstrate that the adaptive pushover analysis may be able to explain the response characteristics that conventional pushover analysis with fixed load distribution fails to capture.