• Journal of the Earthquake Engineering Society of Korea
• /
• v.24 no.1
• /
• pp.29-37
• /
• 2020

This study is to investigate the effect of a retrofitted reinforced concrete frame with non-seismic details strengthened by embedded steel moment frames with an indirect joint, which mitigates the problems of the direct joint method. First, full-scale experiments were conducted to confirm the structural behavior of a 2-story reinforced concrete frame with non-seismic details and strengthened by a steel moment frame with an indirect joint. The reinforced concrete frame with non-seismic details showed a maximum strength of 185 kN at an overall drift ratio of 1.75%. The flexural-shear failure of columns was governed, and shear cracks were concentrated at the beam-column joints. The reinforced concrete frame strengthened by the embedded steel moment frames achieved a maximum strength of 701 kN at an overall drift ratio of 1.5% so that the maximum strength was about 3.8 times that of the specimen with non-seismic details. The failure pattern of the retrofitted specimen was the loss of bond strength between the concrete and the rebars of the columns caused by a prying action of the bottom indirect joint because of lateral force. Furthermore, methods are proposed for calculation of the specified strength of the reinforced concrete frame with non-seismic details and strengthened by the steel moment frame with the indirect joint.

• Structural Engineering and Mechanics
• /
• v.54 no.1
• /
• pp.19-33
• /
• 2015

Open ground storey (OGS) buildings are characterized by the sudden reduction of stiffness in the ground storey with respect to the upper infilled storeys. During earthquakes, this vertical irregularity may result in accumulated damage in the ground storey members of OGS buildings without much damage in the upper storeys. Hence, the structural design of OGS buildings needs special attention. The present study suggests a modification of existing displacement-based design (DBD) procedure by proposing a new lateral load distribution. The increased demands of ground storey members of OGS buildings are estimated based on non-linear time history analysis results of four sets of bare and OGS frames having four to ten storey heights. The relationship between the increased demand and the relative stiffness of ground storey (with respect to upper storeys) is taken as the criterion for developing the expression for the design lateral load. It is also observed that under far-field earthquakes, there is a decrease in the ground storey drift of OGS frames as the height of the frame increases, whereas there is no such reduction when these frames are subjected to near-field earthquakes.

• Structural Engineering and Mechanics
• /
• v.77 no.6
• /
• pp.721-734
• /
• 2021

The seismic analysis of structures without applying the effects of soil can undermine functional objectives of structure so that it can affect all the desired purposes at the design and control stages of the structure. In this research, employing OpenSees and MATLAB software simultaneously and developing a definite three-dimensional finite element model of a high-rise concrete structure, designed using performance-based plastic design approach, the performance of Tuned Mass Damper (TMD) and Active Mass Damper (AMD) is both examined and compared. Moreover some less noted aspects such as nonlinear interaction of soil and structure, uplift, nonlinear behavior of structure and structural torsion have received more attention. For this purpose, the analysis of time history on the structural model has been performed under 22 far-field accelerogram records. Examining a full range of all structural seismic responses, including lateral displacement, acceleration, inter-story drift, lost plastic energy, number of plastic hinges, story shear force and uplift. The results indicate that TMD performs better than AMD except for lateral displacement and inter-story drift to control other structural responses. Because on the one hand, nonlinear structural parameters and soil-structure interaction have been added and on the other hand, the restriction on the control force applied that leads up to saturation phenomenon in the active control system affect the performance of AMD. Moreover, the control force applied by structural control system has created undesirable acceleration and shear force in the structure.

• Structural Engineering and Mechanics
• /
• v.53 no.4
• /
• pp.791-818
• /
• 2015

RC buildings constitute the prevailing type of construction in earthquake-prone region like Kathmandu Valley. Most of these building constructions were based on conventional methods. In this context, the present paper studied the seismic behaviour of existing RC buildings in Kathmandu Valley. For this, four representative building structures with different design and construction, namely a building: (a) representing the non-engineered construction (RC1 and RC2) and (b) engineered construction (RC3 and RC4) has been selected for analysis. The dynamic properties of the case study building models are analyzed and the corresponding interaction with seismic action is studied by means of non-linear analyses. The structural response measures such as capacity curve, inter-storey drift and the effect of geometric non-linearities are evaluated for the two orthogonal directions. The effect of plan and vertical irregularity on the performance of the structures was studied by comparing the results of two engineered buildings. This was achieved through non-linear dynamic analysis with a synthetic earthquake subjected to X, Y and $45^{\circ}$ loading directions. The nature of the capacity curve represents the strong impact of the P-delta effect, leading to a reduction of the global lateral stiffness and reducing the strength of the structure. The non-engineered structures experience inter-storey drift demands higher than the engineered building models. Moreover, these buildings have very low lateral resistant, lesser the stiffness and limited ductility. Finally, a seismic safety assessment is performed based on the proposed drift limits. Result indicates that most of the existing buildings in Nepal exhibit inadequate seismic performance.

• Earthquakes and Structures
• /
• v.11 no.2
• /
• pp.195-215
• /
• 2016

Rehabilitation of historical unreinforced masonry (URM) buildings is a priority in many parts of the world, since those buildings are a living part of history and a testament of human achievement of the era of their construction. Many of these buildings are still operational; comprising brittle materials with no reinforcements, with spatially distributed mass and stiffness, they are not encompassed by current seismic assessment procedures that have been developed for other structural types. To facilitate the difficult task of selecting a proper rehabilitation strategy - often restricted by international treaties for non-invasiveness and reversibility of the intervention - and given the practical requirements for the buildings' intended reuse, this paper presents a practical procedure for assessment of seismic demands of URM buildings - mainly historical constructions that lack a well-defined diaphragm action. A key ingredient of the method is approximation of the spatial shape of lateral translation, ${\Phi}$, that the building assumes when subjected to a uniform field of lateral acceleration. Using ${\Phi}$ as a 3-D shape function, the dynamic response of the system is evaluated, using the concepts of SDOF approximation of continuous systems. This enables determination of the envelope of the developed deformations and the tendency for deformation and damage localization throughout the examined building for a given design earthquake scenario. Deformation demands are specified in terms of relative drift ratios referring to the in-plane and the out-of-plane seismic response of the building's structural elements. Drift ratio demands are compared with drift capacities associated with predefined performance limits. The accuracy of the introduced procedure is evaluated through (a) comparison of the response profiles with those obtained from detailed time-history dynamic analysis using a suite of ten strong ground motion records, five of which with near-field characteristics, and (b) evaluation of the performance assessment results with observations reported in reconnaissance reports of the field performance of two neoclassical torsionally-sensitive historical buildings, located in Thessaloniki, Greece, which survived a major earthquake in the past.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.14 no.4
• /
• pp.29-36
• /
• 2010

To investigate the cyclic characteristics of exterior joints in RC frame buildings which are typically used after 1988, 70% scaled T-shaped beam-column subassemblies were designed and tested with a displacement control that is composed of 9 steps, until 3.5% story drift was reached. Axial forces are applied to columns during the experiment to simulate a real situation. The results show that the non-seismic detailed specimens failed before reaching 0.85% story drift, and their strengths are less than 0.85 times the nominal flexural strength which beam or columns should reach. The relationship of principal stress and story drift of exterior joints is similar to the one that Priestly proposed.

• Magazine of the Korea Concrete Institute
• /
• v.11 no.2
• /
• pp.187-196
• /
• 1999

An experimental investigation was conducted to study the structural behavior of concrete columns confined with welded grids. The full-scale columns with different volumetric ratio, spacing and arrangement of welded reinforcement grids were tested under simulated seismic loading. The columns were subjected to constant axial compression of approximately 20% or 40% of their capacities accompanied by incrementally increasing lateral deformation reversals. The results indicate that the welded reinforcement grid can be used effectively as confinement reinforcement provided that the steel used, have sufficient ductility and the welding process employed does not alter the strength and elongation characteristics of steel. The grids improved the structural performance of columns, which developed lateral drift ratios in excess of 3% with the spacing and volumetric ratio of transverse reinforcement similar to those required by the ACI 318-95 Building Code. Drift capacity further increased when grids with larger number of cells were used. Furthermore, the use of grids reduced congesting of reinforcement while the dimensional accuracy provided perfect support to longitudinal reinforcement.

• Earthquakes and Structures
• /
• v.6 no.4
• /
• pp.437-455
• /
• 2014

Some conventional lateral load patterns for pushover analysis, and proposing a new accurate pattern was investigated in present research. The new proposed load pattern has load distribution according weight and stiffness variation in height and mode shape of structure. The assessment of pushover application with mentioned pattern in X type braced steel frames and steel moment resisting frames, with stiffness and mass variation in height, was studied completely and the obtained results were compared with nonlinear dynamic analysis method (including time history analysis). The methods were compared from standpoints of some basic parameters such as displacement, drift and shape of lateral load pattern. It is concluded that proposed load pattern results are closer to nonlinear dynamic analysis (NDA) compared to other pushover load patterns especially in tall and medium-rise buildings having different stiffness and mass during the height.

• Architectural research
• /
• v.3 no.1
• /
• pp.53-60
• /
• 2001

The proposed building upgrading technique employs prestressing cables to function as bracing to improve the seismic performance during future events. A four-story reinforced concrete moment resisting frame damaged from an ultimate limit state earthquake is assessed and upgraded using the proposed technique. Both existing and upgraded buildings are evaluated in regard of seismic performance parameters performing static lateral load to collapse analysis and dynamic nonlinear time history analysis as well. To obtain realistic comparison of seismic performance between existing and upgraded frames, each frame is subjected to its critical ground motion that has strength demand exceeding the building strength supply. Furthermore, reliability of static lateral load to collapse analysis as a substitute to time history analysis is evaluated. The results reveal that the proposed upgrading technique improves the stiffness distribution compared to the ideal distribution that gives equal inter-story drift. As a result, the upgraded building retains more stories that contribute to energy dissipation. The overall behavior of upgraded building beyond yield is also enhanced due to the gradual change of building stiffness as the lateral load increases.

• Transactions on Electrical and Electronic Materials
• /
• v.12 no.1
• /
• pp.7-10
• /
• 2011

High voltage (HV) integrated circuits are viable alternatives to discrete circuits in a wide variety of applications. A HV device generally used in these circuits is a lateral double diffused metal oxide semiconductor (LDMOS) transistor. Attempts to model LDMOS devices are complicated by the existence of the lightly doped drain and by the extension of the poly-silicon and the gate oxide. Several physically based investigations of the bias-dependent drift resistance of HV devices have been conducted, but a complete physical model has not been reported. We propose a new technique to model HV devices using both the BSIM3 SPICE model and a bias dependent resistor model (sub-circuit macro model).