• Earthquakes and Structures
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• v.20 no.3
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• pp.239-260
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• 2021

Torsional response of buildings is attributed to poor structural configurations in plan, which arises due to two factors - torsional eccentricity and torsional flexibility. Usually, building codes address effects due to the former. This study examines both of these effects. Buildings with torsional eccentricity (e.g., those with large eccentricity) and with torsional flexibility (those with torsional mode as a fundamental mode) demand large deformations of vertical elements resisting lateral loads, especially those along the building perimeter in plan. Lateral-torsional responses are studied of unsymmetrical buildings through elastic and inelastic analyses using idealised single-storey building models (with two degrees of freedom). Displacement demands on vertical elements distributed in plan are non-uniform and sensitive to characteristics of both structure and earthquake ground motion. Limits are proposed to mitigate lateral-torsional effects, which guides in proportioning vertical elements and restricts amplification of lateral displacement in them and to avoid torsional mode as the first mode. Nonlinear static and dynamic analyses of multi-storey buildings are used to validate the limits proposed.

• International Journal of High-Rise Buildings
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• v.10 no.4
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• pp.265-283
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• 2021

To ensure that fire induced collapse of a building is prevented it is important to understand the sequence of events that can lead to this event. In this paper, the initiation of collapse mechanisms of generic a multi-storey steel frame subjected to vertical and horizontal travelling fires are analysed computationally by tracking the formation of plastic hinges in the frame and generation of fire induced loads. Both uniform and travelling fires are considered. In total 58 different cases are analysed using finite element software LS-DYNA. For the frame examined with a simple and generic structural arrangement and higher applied fire protection to the columns, the results indicate that collapse mechanisms for singe floor and multiple floor fires can be each split into two main groups. For single floor fires (taking place in the upper floors of the frame (Group S1)), collapse is initiated by the pull-in of external columns when heated beams in end bays go into catenary action. For single floor fires occurring on the lower floors(Group S2), failure is initiated (i.e. ultimate strain of the material is exceeded) after the local beam collapse. Failure in both groups for single floor fires is governed by the generation of high loads due to restrained thermal expansion and the loss of material strength. For multiple floor fires with a low number of fire floors (1 to 3) - Group M1, failure is dominated by the loss of material strength and collapse is mainly initiated by the pull-in of external columns. For the cases with a larger number of fire floors (5 to 10) - Group M2, failure is dominated by thermal expansion and collapse is mainly initiated by swaying of the frame to the side of fire origin. The results show that for the investigated frame initiation of collapse mechanisms are affected by the fire type, the number of fire floors, and the location of the fire floor. The findings of this study could be of use to designers of buildings when developing fire protection strategies for steel framed buildings where the potential for a multifloor fire exists.

• Earthquakes and Structures
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• v.12 no.3
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• pp.263-270
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• 2017

In this study, two geometrically identical multi-storey steel buildings with different lateral load resisting systems are structurally analyzed under same earthquake conditions and they are compared with respect to their construction costs of their structural systems. One of the systems is a steel structure with eccentrically steel braced frames. The other one is a RC wall-steel frame system, that is a steel framed structure in combination with a reinforced concrete core and shear walls of minimum thickness that the national code allows. As earthquake resisting systems, steel braced frames and reinforced concrete shear walls, for both cases are located on identical places in either building. Floors of both buildings will be of reinforced concrete slabs of same thickness resting on composite beams. The façades are assumed to be covered identically with light-weight aluminum cladding with insulation. Purpose of use for both buildings is an office building of eight stories. When two systems are structurally analyzed by FEM (finite element method) and dimensionally compared, the dual one comes up with almost 34% less cost of construction with respect to their structural systems. This in turn means that, by using a dual system in earthquake zones such as Turkey, for multi-storey steel buildings with RC floors, more economical solutions can be achieved. In addition, slender steel columns and beams will add to that and consequently more space in rooms is achieved.

• International Journal of High-Rise Buildings
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• v.7 no.4
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• pp.389-396
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• 2018

This paper presents a numerical investigation on the structural response of a multi-story building subjected to spreading multi-compartment fires. A recently proposed simple fire model has been used to simulate two spreading multi-compartment fire scenarios in a 10-story steel-framed office building. By assuming simple temperature rising and distribution profiles in the fire exposed structural components (steel beams, steel column and concrete slabs), finite element simulations using a three-dimensional structural model has been carried out to study the failure behavior of the whole structure in two multi-compartment fire conditions and also in a standard fire condition. The structure survived the standard fire but failed in the multi-compartment fire. Whilst more accurate fire models and heat transfer models are needed to better predict the behaviors of structures in realistic fires, the current study based on very simple models has demonstrated the importance and necessity of considering spreadingmulti-compartment fires in fire resistance design of multi-story buildings.

• Geomechanics and Engineering
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• v.9 no.1
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• pp.39-55
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• 2015

Usually the analyses of structures are carried out by assuming the base of structures to be fixed. However, the soil beneath foundation alters the earthquake loading and varies the response of structure. Hence, it is not realistic to analyze structures by considering it to be fixed. The importance of soil-structure interaction was realized from the past failures of massive structures by neglecting the effect of soil in seismic analysis. The analysis of massive structures requires soil flexibility to be considered to avoid failure and ensure safety. Present study, considers the seismic behavior of multi-storey reinforced concrete narrow and wide buildings of various heights with and without shear wall supported on raft foundation incorporating the effect of soil flexibility. Analysis of the three dimensional models of six different shear wall positions founded on four different soils has been carried out using finite element software LS DYNA. The study investigates the differences in spectral acceleration coefficient (Sa/g), base shear and storey shear obtained following the seismic provisions of Indian standard code IS: 1893 (2002) (IS) and International building code IBC: 2012 (IBC). The base shear values obtained as per IBC provisions are higher than IS values.

• Structural Engineering and Mechanics
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• v.46 no.1
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• pp.1-17
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• 2013

In this study, the modified finite element- transfer matrix methods are proposed for free vibration analysis of asymmetric structures, the bearing system of which consists of shear wall-frames. In the study, a multi-storey structure is divided into as many elements as the number of storeys and storey masses are influenced as separated at alignments of storeys. The shear walls and frames are assumed to be flexural and shear cantilever beam structures. The storey stiffness matrix is obtained by formulating the governing equation at the center of mass for the shear walls and the frames in the i.th floor. The system transfer matrix is constructed in the dimension of $6{\times}6$ by transforming the obtained stiffness matrix. Thus, the dimension, which is $12n{\times}12n$ in classical finite elements, is reduced to the dimension of $6{\times}6$. To study the suitability of the method, the results are assessed by solving two examples taken from the literature.

• Earthquakes and Structures
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• v.1 no.1
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• pp.43-67
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• 2010

A gradient-based evolutionary optimization methodology is presented for finding the optimal design of both the added dampers and their supporting members to minimize an objective function of a linear multi-storey structure subjected to the critical ground acceleration. The objective function is taken as the sum of the stochastic interstorey drifts. A frequency-dependent viscoelastic damper and the supporting member are treated as a vibration control device. Due to the added stiffness by the supplemental viscoelastic damper, the variable critical excitation needs to be updated simultaneously within the evolutionary phase of the optimal damper placement. Two different models of the entire damper unit are investigated. The first model is a detailed model referred to as "the 3N model" where the relative displacement in each component (i.e., the spring and the dashpot) of the damper unit is defined. The second model is a simpler model referred to as "the N model" where the entire damper unit is converted into an equivalent frequency-dependent Kelvin-Voigt model. Numerical analyses for 3 and 10-storey building models are conducted to investigate the characters of the optimal design using these models and to examine the validity of the proposed technique.

• Earthquakes and Structures
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• v.27 no.3
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• pp.227-237
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• 2024

The incidence angle of seismic excitation relative to the two orthogonal major axes of structures has been a subject of considerable research interest. Previous studies have primarily focused on single-storey symmetric and asymmetric structures, suggesting a minimal effect of incidence angle on structural behavior. This research extends the investigation to multi-storey structures, including vertically irregular configurations, using a comprehensive set of 20 near fault and 20 far field seismic excitation. The study employs nonlinear time-history analysis with a bidirectional hysteresis model to capture inelastic deformations accurately. Various structural models, including one-storey and two- storey regular structures (R1, R2) and vertically irregular structures with setbacks in one direction (IR1) and both directions (IR2), are analysed. The analysis reveals that the incidence angle has no discernible impact over the response of regular multi-storey structures. However, vertically irregular structures exhibit notable responses at corner columns, which decrease towards central columns, irrespective of the incidence angle. This response is attributed to the inherent mass distribution and stiffness irregularities rather than the angle of seismic excitation. The findings indicate that for both near fault and far field seismic excitation, the incidence angle's impact remains marginal even for complex structural configurations. Consequently, the study suggests that the angle of incidence of seismic excitation need not be a primary consideration in the seismic design of both regular and vertically irregular structures. These conclusions are robust across various structural models and seismic excitation characteristics, providing a comprehensive understanding the impact of incidence angle on seismic response.

• Earthquakes and Structures
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• v.24 no.5
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• pp.353-364
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• 2023

In this study, a method has been proposed for the static and dynamic nonlinear analysis of multi-storey buildings, which takes into account the contribution of axial deformations in vertical load-bearing elements, which are especially important in tall and narrow structures. Shear deformations on the shear walls were also taken into account in the study. The presented method takes into account the effects that are not considered in the fishbone and flexural-shear beam models developed in the literature. In the Fishbone model, only frame systems are modeled. In the flexural shear beam model developed for shear wall systems, shear deformations and axial deformations in the walls are neglected. Unlike the literature, with the model proposed in this study, both shear deformations in the walls and axial deformations in the columns and walls are taken into account. In the proposed model, multi-storey building is represented as a sandwich beam consisting of Timoshenko beams pieced together with a double-hinged beam. At each storey, the total moment capacities of the frame beams and the coupled beams in the coupled shear walls are represented as the equivalent shear capacity. On the other hand, The sums of individual columns and walls moment at the relevant floor level are represented as equivalent moment capacity at that floor level. At the end of the study, examples were solved to show the suitability of the proposed method in this study. The SAP2000 program is employed in analyses. In a conclusion, it is observed that among the solved examples, the proposed sandwich beam model gives good results. As can be seen from these results, it is seen that the presented method, especially in terms of base shear force, gives very close results to the detailed finite element method.

• Structural Engineering and Mechanics
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• v.60 no.3
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• pp.433-453
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• 2016

During earthquake, the motion of ground is affected significantly by source characteristics, source-to-site path properties and local site conditions. Due to the influence of local soil conditions different places experience distinctive amplitude of surface ground motion. Ground response analysis of a specific site utilizing the borehole information at different locations is done in present study. The ground motion with the highest peak ground acceleration for this site obtained from the ground response analysis is used in finite element soil-structure interaction analysis of multi-storey shear wall buildings with various positions of shear walls. The variation in seismic response of buildings and advantageous position of shear wall are determined. The study reveals that providing shear wall at the core of buildings at the specific site is advantageous among all shear wall configurations considered.