Seismic response of structures with coupled vertical stiffness–strength irregularities

Sadashiva, Vinod K.; MacRae, Gregory A.; Deam, Bruce

doi:10.1002/eqe.1121

Cited by 19 publications

(11 citation statements)

References 10 publications

(18 reference statements)

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“…The irregularity on the first story generally has a larger effect compared with the irregularity on the median story. This result is similar to the variation rule in the existing relevant studies [Valmundsson and Nau, 1997a;Sadashiva et al, 2012]. …”

Section: Stiffness Irregularitysupporting

confidence: 93%

“…The first aspect is the assessment of the seismic control effect of the vertical irregularity limit parameters in the seismic design codes [Das and Nau, 2003;Jeong et al, 2012;Pirizadeh and Shakib, 2013;Habibi and Asadi, 2013;Shakib and Pirizadeh, 2014]. The second aspect is the analysis of the seismic response demand of the vertically irregular structures [Choi, 2004;Chintanapakdee and Chopra, 2004;Athanassiadou, 2008;Basu, 2009;Lee 2011;Sehgal et al, 2011;Kirac et al, 2012;Sadashiva et al 2012;Zhou et al, 2011b;Mondal and Tesfamariam, 2014;Varadharajan et al, 2014]. The third aspect is to propose simplified methods to assess seismic performance and control measures for seismic design [Fragiadakis et al, 2006;Men et al, 2008;Sarkara et al, 2010;Zhou et al, 2013c].…”

Section: Introductionmentioning

confidence: 98%

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Least Favorable Probability of Failure for 5- and 10-story RC Frame Structures with Vertical Irregularities

Zhou

Zhao

Mao

2015

Journal of Earthquake Engineering

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This article evaluates the seismic control effect of vertical irregularity factors for RC frame structures using the Monte Carlo simulation method. Typical 5-and 10-story frame structures with different irregularities of strength or stiffness are assessed. The upper-and lower-bound probabilities of failure exceeding the limit state are studied. The results indicate that the exceeding probability increases as the vertical irregularity factor decreases. The upper-bound probability of failure, which is sensitive to the vertical irregularities and is an effective indicator for evaluating the performance control parameter, is significantly larger compared with the lower-bound probability of failure. A minimum strength and stiffness irregularity factor of 0.7 can serve as the seismic control limit.

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Section: Stiffness Irregularitysupporting

confidence: 93%

Section: Introductionmentioning

confidence: 98%

Least Favorable Probability of Failure for 5- and 10-story RC Frame Structures with Vertical Irregularities

Zhou

Zhao

Mao

2015

Journal of Earthquake Engineering

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“…Sadashiva et al . analysed the structures with 3, 5, 9 and 15 storeys with the floor mass at all levels kept the same. The maximum interstorey ratio demands of the regular and irregular structures were compared.…”

Section: Introductionmentioning

confidence: 99%

Torsional response of nonductile structures with soft‐first‐storey

Goh

Pan

2014

Earthq Engng Struct Dyn

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SUMMARY In this paper, torsional response of nonductile structures with soft‐first‐storey subjected to bidirectional ground motions is studied using a simplified two‐storey model with two‐way eccentricities. The stiffness ratio of second storey to first storey is varied to create different levels of soft‐first‐storey effect, while the stiffness eccentricity is varied to create torsional effects. Different overstrength ratios are used in the simplified models to study the response of structure with different structural capacity. Hysteretic model with strength deterioration and stiffness degradation properties is used to capture the deterioration of element stiffness and strength. Ductility capacity of 2.0 is used as the models are for nonductile structures. In general, displacement amplification of irregular model with respect to regular model increases as stiffness ratio increases, while no consistent trend of changes in displacement amplification is found with increase in stiffness eccentricity. It is found that the displacement amplification due to only soft‐first‐storey effect can be conservatively taken as 1.5. Coupling of torsional and soft‐first‐storey effects is more significant in affecting the displacement amplification of elements at flexible side. The trend of changes in displacement amplification of elastic system is similar to that of inelastic system. The displacement amplification of elements at the flexible side is larger than that at the stiff side. The elements at the flexible side in the direction of shorter uncoupled lateral period have larger displacement response than those in the orthogonal direction. Ductility demand–capacity curves subsequently constructed can be used to approximately assess the seismic performance of existing structures and as guidelines for designing structures in Singapore to withstand the maximum credible earthquake considering the coupling of torsional and soft‐first‐storey effects. Copyright © 2014 John Wiley & Sons, Ltd.

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“…Research on the effects of plan irregularity (e.g., Rutenberg (2002), Chopra and Goel (2004), De Stefano and Pintucchi (2006)) has received more attention than the vertical irregularity effects. Earlier studies on the influence of vertical stiffness and strength irregularity on the performance of structures have been summarised by Sadashiva et al (2011). It includes studies by Valmundsson and Nau (1997), Al-Ali and Krawinkler (1998) and Michalis et al (2006).…”

mentioning

confidence: 99%

“…An effective methodology to determine vertical regularity limits was developed and then applied on shear-type structures to evaluate the effects of vertical mass irregularity (Sadashiva et al 2009). A study on the effects of coupled vertical stiffnessstrength irregularity due to a change in member properties on realistic code-complying structures was conducted (Sadashiva et al 2011) using the same method. The method involved using the NZS 1170.5 Equivalent Static (ES) method to design both the regular and irregular structures to the same target drift, and comparing the actual drift demands from inelastic dynamic time-history analyses.…”

mentioning

confidence: 99%

Effects of coupled vertical stiffness-strength irregularity due to modified interstorey height

Sadashiva

MacRae

Deam

2011

BNZSEE

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Structures may have vertical stiffness or strength irregularity for many reasons. In many practical cases, a change in storey stiffness, results a change in strength at the same storey. In this paper, the effect of a change in interstorey height is quantified. In order to do this, relationships between storey stiffness and strength resulting due to a modified interstorey height for a few common lateral force resisting systems was considered. It was applied to simple shear-type structures of 3, 5, 9 and 15 storeys, assumed to be located in Wellington. All structures were considered to have a constant mass at every floor level. Both regular and irregular structures were designed in accordance with the Equivalent Static method of the current New Zealand seismic design Standard, NZS 1170.5. Regular structures were designed to either (i) produce a constant target interstorey drift ratio at all the storeys simultaneously or (ii) to have uniform stiffness distribution over the height of the structure, with the target interstorey drift ratio at the first storey. An “interstorey height ratio” was defined as the ratio of modified to initial interstorey height, and applied separately at the first storey, mid-height storey and at the topmost storey by amounts between 0.5 and 3. The modified structures were then redesigned until the target interstorey drift ratio was achieved at the critical storey/storeys. Design structural ductility factors of 1, 2, 3, 4 and 6, and target (design) interstorey drift ratios ranging between 0.5% and 3%, were used in this study. Inelastic dynamic time-history analysis was carried out by subjecting these structures to code design level earthquake records, and the maximum interstorey drift ratio demands due to each record were used to compare the responses of regular and irregular structures. It was found that structural types in which only the storey stiffness was modified due to a change in the interstorey height produced the maximum increase in drift demands rather than structural forms with other stiffness-strength coupling cases. Shorter structures having an increased first storey height, and taller structures with an increased middle storey height generally produced greater interstorey drift demands than regular structures. For cases of increased storey stiffness due to decreased storey heights, the shorter structures with a decreased middle storey height resulted in higher median peak ISDR due to irregularity. A simple equation describing the maximum increase in response due to modifications to a storey height was developed. The equation was used along with the realistic correlations between storey stiffness and strength to obtain the governing code regularity limit.

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Seismic response of structures with coupled vertical stiffness–strength irregularities

Cited by 19 publications

References 10 publications

Least Favorable Probability of Failure for 5- and 10-story RC Frame Structures with Vertical Irregularities

Least Favorable Probability of Failure for 5- and 10-story RC Frame Structures with Vertical Irregularities

Torsional response of nonductile structures with soft‐first‐storey

Effects of coupled vertical stiffness-strength irregularity due to modified interstorey height

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