• Earthquakes and Structures
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• v.9 no.2
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• pp.353-373
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• 2015

In this paper, the effects of different types of irregularity along the height on the seismic responses of moment resisting frames are investigated using nonlinear dynamic analysis. Furthermore, the applicability of consecutive modal pushover (CMP) procedure for computing the seismic demands of vertically irregular frames is studied and the advantages and limitations of the procedure are elaborated. For this purpose, a special moment resisting steel frame of 10-storey height was selected as reference regular frame for which the effect of higher modes is important. Forty vertically irregular frames with stiffness, strength, combined-stiffness-and-strength and mass irregularities are created by applying two modification factors (MF=2 and 4) in four different locations along the height of the reference frame. Seismic demands of irregular frames are computed by using the nonlinear response history analysis (NL-RHA) and CMP procedure. Modal pushover analysis (MPA) method is also carried out for the sake of comparison. The effect of different types of irregularity along the height on the seismic demands of vertically irregular frames is investigated by studying the results obtained from the NL-RHA. To demonstrate the accuracy of the enhanced pushover analysis methods, the results derived from the CMP and MPA are compared with those obtained by benchmark solution, i.e., NL-RHA. The results show that the CMP and MPA methods can accurately compute the seismic demands of vertically irregular buildings. The methods may be, however, less accurate especially in estimating plastic hinge rotations for weak or weak-and-soft top and middle storeys of vertically irregular frames.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.629-636
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• 2011

It has been suggested that buildings designed for strong ground motions will also have improved resistance to air blast loads. As an initial attempt to quantify this behavior, the responses of a ten story steel building, designed for the 1994 building code, with lateral resistance provided by perimeter moment frames, is considered. An analytical model of the building is developed and the magnitude and distribution of blast loads on the structure are estimated using available computer software that is based on empirical methods. To obtain the relationship between pressure, time duration, and standoff distance, these programs are used to obtain an accurate model of the air blast loading. A hemispherical surface burst for various explosive weights and standoff distances is considered for generating the air blast loading and determining the structural response. Linear and nonlinear analyses are conducted for these loadings. Air blast demands on the structure are compared to current seismic guidelines. These studies present the displacement responses, story drifts, demand/capacity ratio and inelastic demands for this structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.108-116
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• 2017

In this study, the prototype structure of seismically designed steel moment frame was analyzed statically and dynamically in order to demonstrate the applicability of energy-based approximate analysis with the dynamic effect of sudden column loss in the evaluation of the collapse resistance and a method for assessing the sensitivity to progressive collapse was proposed. For the purpose of comparing the structural behavior of buildings with different structural systems, the sensitivity of the structure to the sudden removal of vertical members can be used as a significant measure. The energy-based approximate analysis prediction for the prototype structure considered in the study showed good agreement with the dynamic analysis result. In the sensitivity evaluation, the structural robustness index that indicates the ability of a structure to resist collapse induced by abnormal loads was used. It was confirmed that the proposed methods can be used conveniently and rationally in progressive collapse analysis and design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.2
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• pp.9-20
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• 2014

Steel intermediate moment frames (IMFs) have been generally used as seismic load resisting systems (SLRSs) of a building to provide resistances against strong ground shaking. However, most of low and mid-rise steel buildings in Korea were constructed during pre-seismic code era or before the introduction of well-organized current seismic codes. It has been recognized that the seismic performance of these steel IMFs is still questionable. In order to respond to such a question, this study quantitatively investigates the seismic capacities of steel IMFs. Prototype models are built according to the number of stories, the levels of elastic seismic design base shear and the ductilities of structural components. Also, the other prototype models employing hysteretic energy dissipating devices (HEDDs) are considered. The collapse mechanism and the seismic performance of the prototype models are then described based on the results obtained from nonlinear-static and incremental-dynamic analyses. The seismic performance of the prototype models is assessed from collapse margin ratio (CMR) and collapse probability. From the assessment, the prototype model representing new steel IMFs has enough seismic capacities while, the prototype models representing existing steel IMFs provide higher collapse probabilities. From the analytic results of the prototype models retrofitted with HEDDs, the HEDDs enhance the seismic performance and collapse capacity of the existing steel IMFs. This is due to the energy dissipating capacity of the HEDDs and the redistribution of plastic hinges.

• Steel and Composite Structures
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• v.16 no.5
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• pp.533-557
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• 2014

In this study, the performances of the SMRF building equipped with energy dissipating devices are studied. Three types of these structures with different heights are considered. The Added Damping and Stiffness (ADAS) devices are used as energy dissipating devices in these structures. The behavior of these structures with ADAS devices subjected to near source ground motions are investigated. Three SMRF buildings with five, ten and fifteen-story, with ADAS devices were chosen. The nonlinear time history analysis was used by applying the near source ground motions with PERFORM 3D.V4 and conclusions are drawn upon an energy criterion. The effect of PGA variation and height of the frames are also considered based on the energy criterion.

• Steel and Composite Structures
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• v.42 no.4
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• pp.501-511
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• 2022

Earthquake Resistant Design Philosophy seeks (a) no damage, (b) no significant structural damage, and (c) significant structural damage but no collapse of normal buildings, under minor, moderate and severe levels of earthquake shaking, respectively. A procedure is proposed for seismic design of low-rise reinforced concrete special moment frame buildings, which is consistent with this philosophy; buildings are designed to be ductile through appropriate sizing and reinforcement detailing, such that they resist severe level of earthquake shaking without collapse. Nonlinear analyses of study buildings are used to determine quantitatively (a) ranges of design parameters required to assure the required deformability in normal buildings to resist the severe level of earthquake shaking, (b) four specific limit states that represent the start of different structural damage states, and (c) levels of minor and moderate earthquake shakings stated in the philosophy along with an extreme level of earthquake shaking associated with the structural damage state of no collapse. The four limits of structural damage states and the three levels of earthquake shaking identified are shown to be consistent with the performance-based design guidelines available in literature. Finally, nonlinear analyses results are used to confirm the efficacy of the proposed procedure.

• Journal of the Korean Society for Advanced Composite Structures
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• v.4 no.3
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• pp.22-29
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• 2013

In recent years, the construction of high-rise buildings are promoted. According to these, there are many needs about new technologies to strengthen the building performance and high-strength steel is regarded as one of these for promoting building performance. In Korea, high-strength steels which stress are over 600MPa are on market and in aborad, super high-strength steels over 1000MPa are developing and they expected to promote the building performance. But there are still doubts about applying high-strength steel members because of size effect and worry of brittle fracture. In this reports, we propose results of performance and analysis tests for use with general steel. We propose the characteristic of high-strength steels first and next the results of performance test to show they satisfy the performance that designers expect. And last, we compare the results of test and analysis for acquire the alanysis reliability in non-linear analysis with high-strength steels.

• Earthquakes and Structures
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• v.14 no.1
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• pp.1-10
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• 2018

Seismic retrofitting of existing buildings and design of earth-quake resistant buildings are important issues associated with earthquake-prone zones. Use of metallic-yielding dampers as an energy dissipation system is an acceptable method for controlling damages in structures and improving their seismic performance. In this study, the optimal distribution of dampers for reducing the seismic response of steel frames with multi-degrees freedom is presented utilizing the uniform distribution of deformations. This has been done in a way that, the final configuration of dampers in the frames lead to minimum weight while satisfying the performance criteria. It is shown that such a structure has an optimum seismic performance, in which the maximum structure capacity is used. Then the genetic algorithm which is an evolutionary optimization method is used for optimal arrangement of the steel dampers in the structure. In continuation for specifying the optimal accurate response, the local search algorithm based on the gradient concept has been selected. In this research the introduced optimization methods are used for optimal retrofitting in the moment-resisting frame with inelastic behavior and initial weakness in design. Ultimately the optimal configuration of dampers over the height of building specified and by comparing the results of the uniform deformation method with those of the genetic algorithm, the validity of the uniform deformation method in terms of accuracy, Time Speed Optimization and the simplicity of the theory have been proven.

• Structural Engineering and Mechanics
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• v.51 no.3
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• pp.487-502
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• 2014

In buildings structures, the flexural stiffness reduction of beams and columns due to concrete cracking plays an important role in the nonlinear load-deformation response of reinforced concrete structures under service loads. Most Seismic Design Codes do not precise effective stiffness to be used in seismic analysis for structures of reinforced concrete elements, therefore uncracked section properties are usually considered in computing structural stiffness. But, uncracked stiffness will never be fully recovered during or after seismic response. In the present study, the effect of concrete cracking on the lateral response of structure has been taken into account. Totally 120 cases of 3 Dimensional Dynamic Analysis which considers the real and accidental torsional effects are performed using ETABS to determine the effective structural system across the height, which ensures the performance and the economic dimensions that achieve the saving in concrete and steel amounts thus achieve lower cost. The result findings exhibits that the dual system was the most efficient lateral load resisting system based on deflection criterion, as they yielded the least values of lateral displacements and inter-storey drifts. The shear wall system was the most economical lateral load resisting compared to moment resisting frame and dual system but they yielded the large values of lateral displacements in top storeys. Wall systems executes tremendous stiffness at the lower levels of the building, while moment frames typically restrain considerable deformations and provide significant energy dissipation under inelastic deformations at the upper levels. Cracking found to be more impact over moment resisting frames compared to the Shear wall systems. The behavior of various lateral load resisting systems with respect to time period, mode shapes, storey drift etc. are discussed in detail.

• Earthquakes and Structures
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• v.9 no.1
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• pp.73-91
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• 2015

The effectiveness of tuned mass dampers (TMDs) in reducing the seismic response of civil structures is still a debated issue. The few studies regarding TMDs on inelastic structures indicate that they would perform well under moderate earthquake loading, when the structure remains linear or weakly nonlinear, while tending to fail under severe ground shaking, when the structure experiences strong nonlinearities. TMD seismic efficiency should be therefore rationally assessed by considering to which extent moderate and severe earthquakes respectively contribute to the expected cost of damages and losses over the lifespan of the structure. In this paper, a method for evaluating, in a life-cycle cost (LCC) perspective, the seismic effectiveness of TMDs on inelastic building structures is presented and exemplified on the SAC LA 9-storey steel moment-resisting frame benchmark building. Results show that the LCC concept may provide an appropriate alternative to traditional performance criteria for the evaluation of the effectiveness of TMDs and that TMD installation on typical existing middle-rise buildings in high seismic hazard regions may significantly reduce building lifetime cost despite the poor control performance observed under the most severe seismic events.