• Computers and Concrete
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• v.21 no.5
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• pp.495-504
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• 2018

The possibility of earthquakes in vulnerable regions indicates that efficient technique is required for seismic protection of buildings. During the recent decades, the concept is moving towards the insertion of base isolation on seismic prone buildings. So, investigation of structural behavior is a burning topic for buildings to be isolated in base level by bearing device. This study deals with the incorporation of base isolation system and focuses the changes of structural responses for different types of Lead Rubber Bearing (LRB) isolators. A number of sixteen model buildings have been simulated selecting twelve types of bearing systems as well as conventional fixed-base (FB) scheme. The superstructures of the high-rise buildings are represented by finite element assemblage adopting multi-degree of freedoms. Static and dynamic analyses are carried out for FB and base isolated (BI) buildings. The dynamic analysis in finite element package has been performed by the nonlinear time history analysis (THA) based on the site-specific seismic excitation and compared employing eminent earthquakes. The influence of the model type and the alteration in superstructure behavior of the isolated buildings have been duly assessed. The results of the 3D multistory structures show that the lateral forces, displacement, inertia and story accelerations of the superstructure of the seismic prone buildings are significantly reduced due to bearing insertion. The nonlinear dynamic analysis shows 12 to 40% lessening in base shear when LRB is incorporated leading to substantial allowance of horizontal displacement. It is revealed that the LRB isolators might be potential options to diminish the respective floor accelerations, inertia, displacements and base shear whatever the condition coincides. The isolators with lower force intercept but higher isolation period is found to be better for decreasing base shear, floor acceleration and inertia force leading to reduction of structural and non-structural damage. However, LRB with lower isolator period seems to be more effective in dropping displacement at bearing interface aimed at reducing horizontal shift of building structure.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.57-65
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• 2020

It is very important to allocate valuable resources efficiently when reconstructing buildings after earthquake damage. This paper proposes the use of a simple seismic retrofitting system to make buildings more resilient than the stiffer systems such as the shear walls implemented in Chile after the earthquake in 2010. The proposal is based on the use of steel chevron-type braces in RC buildings as a dual system to improve the seismic performance of multistory buildings. A case study was carried out to compare the proposal with the shear wall solution for the typical seismic Chilean RC building from the structural and economic perspectives. The results show that it is more resilient than other stiffer seismic solutions, such as shear walls, reduces the demand, minimizes seismic damage, gives reliable earthquake protection and facilitates future upgrades and repairs while achieving the level of immediate occupancy without the costs of the shear walls system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.3
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• pp.121-128
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• 2021

Piloti-type buildings in Korea are usually composed of lower frames and upper shear wall structures. Piloti-type buildings have been seriously damaged during earthquakes because of the construction of soft and weak stories. Piloti-type buildings with edge cores are two-way unsymmetric planes. This paper analyzed and obtained the dynamic response for structures modeled using a multistory two-way asymmetric system. The numerical results, obtained using the Newmark-β method, show the time-history responses and trends of maximum displacements and shear forces. The purpose of this study is to evaluate the effect of reinforcement on dynamic response when a shear wall or brace is reinforced in the corner opposite the piloti.

• Earthquakes and Structures
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• v.2 no.2
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• pp.109-126
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• 2011

The inelastic earthquake response of non-symmetric, braced steel buildings, designed according to the EC3 (steel structures) and EC8 (earthquake resistant design) codes, is investigated using 1, 3 and 5-story models, subjected to a set of 10, two-component, semi-artificial motions, generated to match the design spectrum. It is found that in these buildings, the so-called "flexible" edge frames exhibit higher ductility demands and interstory drifts than the "stiff" edge frames. We note that the same results were reported in an earlier study for reinforced concrete buildings and are the opposite of what was predicted in several other studies based on the over simplified, hence very popular, one-story, shear-beam type models. The substantial differences in such demands between the two sides suggest a need for reassessment of the pertinent code provisions. In a follow up paper, a design modification will be introduced that can lead to a more uniform distribution of ductility demands in the elements of all building edges. This investigation is another step towards more rational design of non-symmetric steel buildings.

• Structural Engineering and Mechanics
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• v.2 no.2
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• pp.211-225
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• 1994

Responses of asymmetrical multistorey buildings to earthquakes are obtained by quasi-static code approach and real time dynamic analysis, using two different structural models. In the first model, all vertical members are assumed to be restrained at the slab levels and hence their end rotations, about horizontal axes, are taken as zero. In the second model this restriction is removed and the rotation is assumed to be proportional to the lateral stiffness of the member. A simple microcomputer based procedure is used in the analyses, by both models. Numerical examples are presented where results obtained from both the models are given. Effects of modelling on the response of three buildings, each with a different type and degree of asymmetry, are studied. Results for deflections and shear forces are presented and the effects of the type of model on the response are discussed.

• Earthquakes and Structures
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• v.9 no.1
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• pp.145-171
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• 2015

Due to earthquakes, many structures suffered extensive damages that were attributed to the torsional effect caused by mass, stiffness or strength eccentricity. Due to this type of asymmetry torsional moments are generated that are imposed by means of additional shear forces developed at the vertical resisting structural elements of the buildings. Although the torsional effect on the response of reinforced concrete buildings was the subject of extensive research over the last decades, a quantitative index measuring the amplification of the shear forces developed at the vertical resisting elements due to lateral-torsional coupling valid for both elastic and elastoplastic response states is still missing. In this study a reliable index capable of assessing the torsional effect is proposed. The performance of the proposed index is evaluated and its correlation with structural response quantities like displacements, interstorey drift, base torque, shear forces and upper diaphragm's rotation is presented. Torsionally stiff, mass eccentric single-story and multistory structures, subjected to bidirectional excitation, are considered and nonlinear dynamic analyses are performed using natural records selected for three hazard levels. It was found that the proposed index provides reliable prediction of the magnitude of torsional effect for all test examples considered.

• Structural Engineering and Mechanics
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• v.76 no.3
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• pp.279-291
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• 2020

The seismic design of conventional frame structures is meant to enhance plastic deformations at beam ends and prevent yielding in columns. To this end, columns are made stronger than beams. Yet yielding in columns cannot be avoided with the column-to-beam strength ratios (about 1.3) prescribed by seismic codes. Preventing plastic deformations in columns calls for ratios close to 4, which is not feasible for economic reasons. Furthermore, material properties and the rearrangement of geometric shapes inevitably make the distribution of damage among stories uneven. Damage in the i-th story can be characterized as the accumulated plastic strain energy (W_pi) normalized by the product of the story shear force (Q_yi) and drift (δ_yi) at yielding. Past studies showed that the distribution of the plastic strain energy dissipation demand, W_pi/ΣW_pj, can be evaluated from the deviation of Q_yi with respect to an "optimum value" that would make the ratio W_pi/(Q_yiδ_yi) -i.e. the damage- equal in all stories. This paper investigates how the soil type and ductility demand affect the optimum lateral strength distribution. New optimum lateral strength distributions are put forth and compared with others proposed in the literature.

• Earthquakes and Structures
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• v.22 no.4
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• pp.345-353
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• 2022

The configuration of an open ground floor (pilotis) is a common and very critical irregularity observed in multistory reinforced concrete frame structures. The characteristics and the geometrical formation of the beams of the first story proved to be a critical parameter for the overall seismic behavior of this type of Reinforced Concrete (RC) structures. In this work the combination of open ground floor (pilotis) morphology with very strong perimetrical beams at the level of the first story is studied. The observation of the seismic damages and the in situ measurements of the fundamental period of four buildings with this morphology and Π-shaped plan view are presented herein. Further analytical results of a pilotis type Π-shaped RC structure are also included in the study. From the measurements and the analytical results yield that the open ground floor configuration greatly influences the fundamental period whereas this morphology in combination with strong beams can lead to severe local shear damages in the columns of the ground floor. The structural damage was limited in the columns of the ground floor and yet based on the changes of the in situ measured fundamental period the damaged level is assessed as DI=88%. Furthermore, due to the Π-shape of the plan view the tendency of the parts of the building to move independently strongly influences the distribution of the damages over the ground floor vertical elements.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1273-1290
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• 2015

JK wall is a shear wall made of lightweight EPS mortar and reinforced with a 3-D galvanized steel mesh, called JK panel, and truss-like stiffeners, called JK stiffeners. Earlier studies have shown that low strength lightweight concrete has the potential to be used in structural elements. In this study, seismic contribution of the JK infill walls surrounded by steel frames is numerically investigated. Adopting a hybrid numerical model, behavior envelop of the wall is derived from the general purpose finite element software, Abaqus. Obtained backbone would be implemented in the professional analytical software, SAP2000, in which through calibrated hysteretic parameters, cyclic behavior of the JK infill can be simulated. Through comparison with earlier experimental results, it turned out that the proposed hybrid modeling can simulate monotonic and cyclic behavior of JK walls with good accuracy. JK infills have a panel-type configuration which their dominant failure mode would be ductile in flexure. Finally technical and economical advantages of the proposed JK infills are assessed for two representative multistory buildings. It is revealed that JK infills can reduce maximum inter-story drifts as well as residual drifts at the expense of minor increase in the developed base shear.

• Earthquakes and Structures
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• v.8 no.2
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• pp.305-377
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• 2015

The problem of earthquake induced torsion in buildings is quite old and although it has received a lot of attention in the past several decades, it is still open. This is evident not only from the variability of the pertinent provisions in various modern codes but also from conflicting results debated in the literature. Most of the conducted research on this problem has been based on very simplified, highly idealized models of eccentric one-story systems, with single or double eccentricity and with load bearing elements of the shear beam type, sized only for earthquake action. Initially, elastic models were used but were gradually replaced by inelastic models, since building response under design level earthquakes is expected to be inelastic. Code provisions till today have been based mostly on results from one-story inelastic models or on results from elastic multistory idealizations. In the past decade, however, more accurate multi story inelastic building response has been studied using the well-known and far more accurate plastic hinge model for flexural members. On the basis of such research some interesting conclusions have been drawn, revising older views about the inelastic response of buildings based on one-story simplified model results. The present paper traces these developments and presents new findings that can explain long lasting controversies in this area and at the same time may raise questions about the adequacy of code provisions based on results from questionable models. To organize this review better it was necessary to group the various publications into a number of subtopics and within each subtopic to separate them into smaller groups according to the basic assumptions and/or limitations used. Capacity assessment of irregular buildings and new technologies to control torsional motion have also been included.