• Earthquakes and Structures
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• 제11권2호
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• pp.265-280
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• 2016

Environmental and operational benefits of green roofs are manifolds; however, their main disadvantages are cost and weight. New technology enabled the use of plastics to reduce the weight of green roof systems to promote their installation. To maximize their potential benefits, green roofs can be installed on existing structures. This study evaluates the influence of green roofs on the seismic response of 3, 6, and 8 storey reinforced concrete ductile moment resisting frames, which were designed according to current seismic standards, however, not designed for green roofs. For each frame, three different types of roofs are considered: gravel flat roof, extensive green roof, and intensive green roof. Nonlinear dynamic time history analysis using an ensemble of twenty real earthquake records was performed to determine the inter-storey drift demand and roof drift demand for each frame. Eigenvalue analysis was also performed to determine the impact of green roofs weight on the elastic and cracked periods of the structure. Results from the analysis demonstrated that intensive and extensive green roofs do not affect the seismic performance of reinforced concrete frame structures.

• Earthquakes and Structures
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• 제10권6호
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• pp.1369-1389
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• 2016

The soil-structure interaction effect significantly influences the design of multi-storey buildings subjected to lateral seismic loads. The shear walls are often provided in such buildings to increase the lateral stability to resist seismic loads. In the present work, the nonlinear soil-structure analysis of a G+5 storey RC shear wall building frame having isolated column footings and founded on deformable soil is presented. The nonlinear seismic FE analysis is carried out using ANSYS software for the building with and without shear walls to investigate the effect of inclusion of shear wall on the moments in the footings due to differential settlement of soil mass. The frame is considered to behave in linear elastic manner, whereas, soil mass to behave in nonlinear manner. It is found that the interaction effect causes significant variation in the moments in the footings. The comparison of non-interaction and interaction analyses suggests that the presence of shear wall causes significant decrease in bending moments in most of the footings but the interaction effect causes restoration of the bending moments to a great extent. A comparison is made between linear and nonlinear analyses to draw some important conclusions.

• Smart Structures and Systems
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• 제5권6호
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• pp.613-632
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• 2009

The present paper is concerned with the design of a proper patch actuator network in order to track a desired displacement of the sidewalls of a one-storey frame structure; both, for the static and the dynamic case. Weights for each patch of the actuator network found in our previous work were based on beam theory; in the present paper a refinement of these weights by modeling the sidewalls of the frame structure as thin plates is presented. For the sake of calculating the refined weights approximate solutions of the plate equations are calculated by an extended Galerkin method. The solutions based on the analytical plate model are compared with three-dimensional Finite Element results computed in the commercially available code ANSYS. The patch actuator network is put into practice by means of four piezoelectric patches attached to each of the two sidewalls of the frame structures, to which electric voltages proportional to the analytically refined patch weights are applied. Analytical and numerical results coincide very well over a broad frequency range.

• Structural Engineering and Mechanics
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• 제11권3호
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• pp.287-299
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• 2001

Columns in multi-storey frames are presently categorised as either braced or unbraced, usually by means of the stability index criterion, for estimating their effective length ratios by design aids such as 'alignment charts'. This procedure, however, ignores the transition in buckling behaviour between the braced condition and the unbraced one. Hence, this results in either an overestimation or an underestimation of effective length estimates of columns in frames that are in fact 'partially braced'. It is shown in this paper that the transitional behaviour is gradual, and can be approximately modelled by means of a 'fuzzy logic' based technique. The proposed technique is simple and intuitively agreeable. It fills the existing gap between the braced and unbraced conditions in present codal provisions.

• Coupled systems mechanics
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• 제7권4호
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• pp.455-483
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• 2018

The study deals with physical modeling of a typical three storeyed building frame supported by a pile group of four piles ($2{\times}2$) embedded in cohesive soil mass using three dimensional finite element analysis. For the purpose of modeling, the elements such as beams, slabs and columns, of the superstructure frame; and that of the pile foundation such as pile and pile cap are descretized using twenty noded isoparametric continuum elements. The interface between the pile and the soil is idealized using sixteen node isoparametric surface element. The soil elements are modeled using eight nodes, nine nodes and twelve node continuum elements. The present study considers the linear elastic behaviour of the elements of superstructure and substructure (i.e., foundation). The soil is assumed to behave non-linear. The parametric study is carried out for studying the effect of soil- structure interaction on response of the frame on the premise of sub-structure approach. The frame is analyzed initially without considering the effect of the foundation (non-interaction analysis) and then, the pile foundation is evaluated independently to obtain the equivalent stiffness; and these values are used in the interaction analysis. The spacing between the piles in a group is varied to evaluate its effect on the interactive behaviour of frame in the context of two embedment depth ratios. The response of the frame included the horizontal displacement at the level of each storey, shear force in beams, axial force in columns along with the bending moments in beams and columns. The effect of the soil- structure interaction is observed to be significant for the configuration of the pile groups and in the context of non-linear behaviour of soil.

• Steel and Composite Structures
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• 제8권1호
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• pp.53-83
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• 2008

A rational and efficient seismic design methodology for irregular space steel frames using advanced methods of analysis in the framework of Eurocodes 8 and 3 is presented. This design methodology employs an advanced static or dynamic finite element method of analysis that takes into account geometrical and material non-linearities and member and frame imperfections. The inelastic static analysis (pushover) is employed with multimodal load along the height of the building combining the first few modes. The inelastic dynamic method in the time domain is employed with accelerograms taken from real earthquakes scaled so as to be compatible with the elastic design spectrum of Eurocode 8. The design procedure starts with assumed member sections, continues with the checking of the damage and ultimate limit states requirements, the serviceability requirements and ends with the adjustment of member sizes. Thus it can sufficiently capture the limit states of displacements, rotations, strength, stability and damage of the structure and its individual members so that separate member capacity checks through the interaction equations of Eurocode 3 or the usage of the conservative and crude q-factor suggested in Eurocode 8 are not required. Two numerical examples dealing with the seismic design of irregular space steel moment resisting frames are presented to illustrate the proposed method and demonstrate its advantages. The first considers a seven storey geometrically regular frame with in-plan eccentricities, while the second a six storey frame with a setback.

• Structural Engineering and Mechanics
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• 제61권4호
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• pp.511-518
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• 2017

This paper presents an experimental investigation on the contribution of RCC strip in the in-filled RC frames. In this research, two frames were tested to study the behavior of retrofitted RC frame under cyclic loading. In the two frame, one was three bay four storey R.C frame with central bay brick infill with RCC strip in-between brick layers and the other was retrofitted frame with same stiffened brick work. Effective rehabilitation is required some times to strengthened the RC frames. Ferrocement concrete strengthening was used to retrofit the frame after the frame was partially collapsed. The main effects of the frames were investigated in terms of displacement, stiffness, ductility and energy dissipation capacity. Diagonal cracks in the infill bays were entirely eliminated by introducing two monolithic RCC strips. Thus more stability of the frame was obtained by providing RCC strips in the infill bays. Load carrying capacity of the frame was increased by enlarging the section in the retrofitted area.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.641-652
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• 2017

In general, conventional analysis and design of reinforced concrete (RC) frame structures overlook the role of beam-column (RCBC) joints. Nowadays, the rigid joint model is one of the most common for RCBC joints: the joint is assumed to be rigid (unable to deform) and stronger than the adjacent beams and columns (does not fail before them). This model is popular because (i) the application of the capacity design principles excludes the possibility of the joint failing before the adjacent beams and (ii) many believe that the actual behaviour of RCBC joints designed according to the seismic codes produced mainly after the 1980s can be assumed to be nominally rigid. This study investigates the relevance of the deformation of RCBC joints in a standard pushover analysis at several levels: frame, storey, element and cross-section. Accordingly, a RC frame designed according to preliminary versions of EN 1992-1-1 and EN 1998-1 was analysed, considering the nonlinear behaviour of beams and columns by means of a standard sectional fibre model. Two alternative models were used for the RCBC joints: the rigid model and an explicit component based nonlinear model. The effect of RCBC joints modelling was found to be twofold: (i) the flexibility of the joints substantially increases the frame lateral deformation for a given load (30 to 50%), and (ii) in terms of seismic performance, it was found that joint flexibility (ii-1) appears to have a minor effect on the force and displacement corresponding to the performance point (seismic demand assessed at frame level), but (ii-2) has a major influence on the seismic demand when assessed at storey, element and cross-section levels.

• Earthquakes and Structures
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• 제8권5호
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• pp.1255-1276
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• 2015

The importance of considering soil-structure interaction effect in the analysis and design of RC frame buildings is increasingly recognized but still not penetrated to the grass root level owing to various complexities involved. It is well established fact that the soil-structure interaction effect considerably influence the design of multi-storey buildings subjected to lateral seismic loads. The shear walls are often provided in such buildings to increase the lateral stability to resist seismic lateral loads. In the present work, the linear soil-structure analysis of a G+5 storey RC shear wall building frame resting on isolated column footings and supported by deformable soil is presented. The finite element modelling and analysis is carried out using ANSYS software under normal loads as well as under seismic loads. Various load combinations are considered as per IS-1893 (Part-1):2002. The interaction analysis is carried out with and without shear wall to investigate the effect of inclusion of shear wall on the total and differential settlements in the footings due to deformations in the soil mass. The frame and soil mass both are considered to behave in linear elastic manner. It is observed that the soil-structure interaction effect causes significant total and differential settlements in the footings. Maximum total settlement in footings occurs under vertical loads and inner footings settle more than outer footings creating a saucer shaped settlement profile of the footings. Each combination of seismic loads causes maximum differential settlement in one or more footings. Presence of shear wall decreases pulling/pushing effect of seismic forces on footings resulting in more stability to the structures.

• Earthquakes and Structures
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• 제6권1호
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• pp.89-110
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• 2014

Nonlinear dynamic analyses are carried out to investigate the influence of the pinching hysteretic response of the exterior RC beam-column joints on the seismic behavior of multistory RC frame structures. The effect of the pinching on the local and global mechanisms of an 8-storey bare frame and an 8-storey pilotis type frame structure is evaluated. Further, an experimental data bank extracted from literature is used to acquire experimental experience of the range of the real levels that have to be considered for the pinching effect on the hysteretic response of the joints. Thus, three different cases for the hysteretic response of the joints are considered: (a) joints with strength and stiffness degradation characteristics but without pinching effect, (b) joints with strength degradation, stiffness degradation and low pinching effect and (c) joints with strength degradation, stiffness degradation and high pinching effect. For the simulation of the beam-column joints a special-purpose rotational spring element that incorporates the examined hysteretic options developed by the authors and implemented in a well-known nonlinear dynamic analysis program is employed for the analysis of the structural systems. The results of this study indicate that the effect of pinching on the local and global responses of the examined cases is not really significant at early stages of the seismic loading and especially in the cases when strength degradation in the core of exterior joint has occurred. Nevertheless in the cases when strength degradation does not occur in the joints the pinching may increase the demands for ductility and become critical for the columns at the base floor of the frame structures. Finally, as it was expected the ability for energy absorption was reduced due to pinching effect.