• Earthquakes and Structures
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• v.26 no.5
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• pp.349-361
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• 2024

Excessive torsional behaviour is one of the major reasons for failure of buildings, as inferred from past earthquakes. Numerous seismic codes across the world specify a displacement-based or drift-based criterion for classifying buildings as torsionally irregular. In recent years, quite a few researchers have pointed out some of the inherent deficiencies associated with the current codal guidelines on torsional irregularity. This short communication paper aims to envisage the need for a revision of the displacement-based guidelines on torsional irregularity, and further highlight the appropriateness of a rotation-based criterion. A set of 6 reinforced concrete building models with asymmetric shear walls are analysed using ETABS v18.0.2, by varying the number of stories from 1 to 9, and the torsional irregularity coefficient of various stories is calculated using the displacement-based formula. Since rotation about the vertical axis is a direct indication of the twist experienced by a building, the calculated torsional irregularity coefficients of all stories are compared with the corresponding floor rotations. The conflicting results obtained for the torsional irregularity coefficients are projected through five categories, namely mismatch with floor rotations, inconsistency in trend, lack of clarity in incorporation of negative values, sensitivity to low values of displacement and error conceived in the mathematical formulation. The findings indicate that the irregularity coefficient does not accurately represent the torsional behaviour of buildings in a realistic sense. The Indian seismic code-based values of 1.2 and 1.4, which are used to characterize buildings as torsionally irregular are observed to be highly sensitive to the numerical values of displacements, rather than the actual degree of rotation. The study thus emphasizes the revision of current guidelines based on a more relevant rotation-based or eccentricity-based approach.

• Computers and Concrete
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• v.14 no.4
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• pp.405-417
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• 2014

The poor seismic performance of reinforced concrete buildings during the latest earthquakes has become a serious issue in the building industry in Turkey. This case, designing new buildings without structural irregularities against earthquake loads reveals to be quite significant. This study mainly is focused on the effects of different torsional irregularities on construction costs and earthquakes performance of reinforced concrete buildings. In that respect, structural torsional irregularities are investigated based on the Turkish Earthquake Code. The study consists of major eight main parametric models. In this models consist of totally 49 models together with the variations in the number of storey. With this purpose, the earthquake performances and construction costs (especially steel quantities) of reinforced concrete buildings which having different structural torsional irregularities were obtained with the help of Sta4-CAD program. Each model has been analyzed by both the methods of equivalent earthquake loading and dynamic analysis. The obtained results reveal that the model-1 which has lower torsional irregularity coefficient shows the best earthquake performance owing to its regular plan geometry. Also, economical comparisons on costs of the torsional irregularity are performed, and results-recommendations are given.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.10
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• pp.191-198
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• 2019

In this paper the evaluation scheme for determining torsional irregularity of Hanok has been proposed. The proposed method can evaluate torsional irregularity of Hanok easily only with characteristics of Hanok shapes, arrangement of lateral load resisting frames and their lateral stiffness without time consuming and complicate 3-dimensional structural analysis. The proposed formula is expressed as allowable maximum eccentricity, and torsional irregularity is evaluated by comparing this value with actual eccentricity. The applicability of the proposed scheme was evaluated by applying it to the line shape plan Hanok with two symmetrically arranged walls and the result was expressed by formula and graph. The results showed that the allowable maximum eccentricity is 10% of plan dimension perpendicular to the seismic load when the walls are placed at the extreme end. The proposed formula was expressed as a generalized formula so it can be applied generally to the various plan shape and wall arrangement of Hanok.

• Earthquakes and Structures
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• v.11 no.6
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• pp.1027-1041
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• 2016

Different incident angles of ground motions have been considered to evaluate the relationship between floor rotation and torsional irregularity coefficient. The issues specifically addressed are (1) variability in torsional irregularity coefficient and floor rotations with varying incident angles of ground motion (2) contradictory relationship between floor rotation and torsional irregularity coefficient. To explore the stated issues, an evaluation based on relative variation in seismic response quantities of linear asymmetric structure under the influence of horizontal bi-directional excitation with varying seismic orientations has been carried out using response history analysis. Several typical earthquake records are applied to the structure to demonstrate the relative variations of floor rotation and torsional irregularity coefficient for different seismic orientations. It is demonstrated that (1) Torsional irregularity coefficient (TIC) increases as the story number decreases when the ground motion is considered along reference axes of the structure. For incident angles other than structure's reference axes, TIC either decreases as the story number decreases or there is no specific trend for TIC. Floor rotation increases in proportion to the story number when the ground motion is considered along reference axes of structure. For incident angles other than structure's reference axes, floor rotation either decreases as the story number increases or there is no specific trend for floor rotation and (2) TIC and floor rotation seems to be approximately inversely proportional to each other when the ground motion is considered along reference axes of the structure. For incident angles other than structure's reference axes, the relationship can even become directly proportional instead of inversely proportional.

• Structural Engineering and Mechanics
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• v.74 no.5
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• pp.699-709
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• 2020

Torsional irregularity is one of the most probable types of horizontal irregularity and existence of this irregularity in most of the structural loading codes is determined by calculating the ratio of the maximum to the average story drift. No specific method has been previously recommended by the codes to calculate the mentioned ratio in the response spectrum analyses. In the current investigation, nine steel building structures with different plan layouts and number of stories have been analyzed and designed in order to evaluate the efficiency of three methods for calculating the ratio of the maximum to the average story drift in the response spectrum analyses. It should be noted that one of these methods is the approach used by current version of ETABS software andother ones are proposed in this paper. The obtained results using the proposed methods are compared with the time history analysis results. The comparisons show that one of these methods underestimates the mentioned ratio in all studied models, however, the other two methods have shown similar results. It is also found that the plan layouts and irregularities can affect how these methods estimate the ratios compared to those obtained by the time history analysis. Generally, it can be concluded that all of these methods can properly predict the ratio with acceptable errors.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.219-222
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• 2005

Many RC building structures of multiple uses constructed in Korea have the irregularities of torsion and soft story at bottom stories. A typical irregular building was selected as prototype and shaking table tests were performed to investigate the seismic performance of this building. The objective of this study is to evaluate the correlation between the experimental and analytical responses of this irregular building structure subjected to the earthquake excitation by using OpenSees(Open System for Earthquake Engineering Simulation). The results of analyses simulate well the behavior of the building having torsional irregularity and weak stories.

• Fibers and Polymers
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• v.3 no.1
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• pp.31-37
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• 2002

Most fibers are irregular, and they are often subjected to combined loading conditions during processing and enduse. In this paper polyester and wool fibers under the combined tensile and torsional loads have been studied for the first time using the finite element method (FEM). The dimensional irregularities of these fibers are simulated with sine waves of different magnitude and frequency. The breaking load and breaking extension of the fibers at different twist or torsion levels are then calculated from the finite element model. The results indicate that twist and level of fiber irregularity have a major impact on the mechanical properties of the fiber and the effect of the frequency of irregularity is relatively small.

• Structural Engineering and Mechanics
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• v.14 no.2
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• pp.237-243
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• 2002

It is well known that torsionally unbalanced buildings are more vulnerable to earthquake hazards than are the regular structural systems. In this paper, a parametric investigation is presented, in order to observe the amplification in the internal forces, when increased eccentricities are used instead of the ones corresponding to the 5% accidental eccentricity. A series of five, ten-story framed and walled structures, with rather high torsional irregularity coefficients, are selected and a numerical test procedure is applied. Numerical results show that the maximum amplification in the internal forces at the most critical beams and columns at the flexible sides of the structures is about 10%. It is concluded that, more serious measures in the codes are needed in the case of this rather dangerous type of irregularity.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.5
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• pp.237-243
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• 2013

In the Korean Building Code (KBC), the Design Eccentricity involves the torsional amplification factor (TAF), and the inherent and accidental eccentricities. When a structure of less than 6-stories and assigned to seismic design category C or D is designed using equivalent static analysis method, both KBC-2006 and KBC-2009 use the TAF but apply different calculation methods for the of design eccentricity. The design eccentricity in KBC-2006 is calculated by multiplying the sum of inherent eccentricity and accidental eccentricity at each level by a TAF but that in KBC-2009 is calculated by multiplying only the accidental eccentricity by a TAF. In this paper, the damage indices of a building with planar structural irregularity designed by different design eccentricities are compared and the relationship between the earthquake damage and design eccentricity of the building is evaluated. On the basis of this study, the increment of design eccentricity results in the decrement of final eccentricity and global damage index of structure. It is observed that design eccentricity in KBC-2006 reduces the vulnerability of torsional irregular building compared to design eccentricity in KBC-2009.

• Journal of Korean Society of Steel Construction
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• v.29 no.5
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• pp.361-368
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• 2017

ASCE 7-10 defines the torsional irregular structure as the one that has large torsional responses caused by the eccentricity. The code requires that these structures should be designed abide by the torsional provisions. This study evaluates the influence of torsional provisions on the performance of the designed multiple steel moment frames with different eccentricity. In this study, 3D response history analyses are performed. The results show that the moment frame design according to the standard with torsional irregularity provisions showed larger performance as the eccentricity increased and the distribution of plastic hinges similarly to orthopedic structures.