Period-dependent seismic force reduction factors for short-period structures

Tso, W. K.; Naumoski, N.

doi:10.1139/l91-069

Cited by 13 publications

(9 citation statements)

References 5 publications

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“…To achieve a more uniform distribution of ductility demands for buildings having different fundamental periods, the seismic design forces for shortperiod buildings should not be significantly reduced from the elastic strength supplies corresponding to the elastic design base shears, Ve. Tso and Naumoski (1991) have suggested a period-dependent force modification factor in the short-period range, which would reduce the ductility demands for short-period structures to an acceptable level. Finally, the mean maximum interstorey shears for the M4S frames, each subjected to the appropriate A/ Vgroup of ground motions, are shown in Fig.…”

Section: Dynamic Analysis Resultsmentioning

confidence: 99%

Seismic performance of reinforced concrete ductile moment-resisting frame buildings located in different seismic regions

Zhu¹,

Tso²,

Heidebrecht³

1992

Can. J. Civ. Eng.

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Seismic areas in Canada are classified into three categories for three different combinations of acceleration and velocity seismic zones (Z, < Z,, Z, = Z,,, and Za > Z,), and ground motions in different zonal combination areas are expected to have different frequency characteristics. The National Building Code of Canada specifies different levels of seismic design base shear for short-period buildings located in areas with different zonal combinations. The specification of seismic design base shear for long-period buildings is directly tied to zonal velocity, irrespective of seismic zonal combination. This paper evaluates the seismic performance of both high-rise long-period and low rise short-period reinforced concrete ductile moment-resisting frame buildings located in seismic regions having Z, < Z,, Z, = Z,, and Z, > Z,. Two frame buildings have 10 and 18 storeys were used as structural models for high-rise buildings, while a set of four-storey buildings were used to represent low-rise buildings. All buildings were designed to the current Canadian seismic provisions and concrete material code. Three groups of earthquake records were selected as representative ground motions in the three zonal combination regions. The inelastic responses of the designed buildings to the three groups of ground motions were analyzed statistically. The results indicate that the distribution of inelastic deformations is significantly different for high-rise frame buildings situated in seismic regions with Z, < Z,, Za = Z,, and Z, > Z,. Inelastic deformation is concentrated in the lower storeys for high-rise buildings located in Z, < Z, areas, whereas significant inelastic deformation can develop in the upper storeys for high-rise buildings situated in Z, > Z, regions.The use of three different levels of seismic design base shear for short-period structures improves the consistency of ductility demands on low-rise buildings situated in the three different zonal combination regions. Despite the use of appropriate design base shears for different seismic regions, the ductility demands for these low-rise buildings are relatively high. T o avoid excessive ductility demands, it is suggested that the seismic strengths for low-rise short-period buildings should not be significantly reduced from their elastic design base shears.Au Canada, les zones sismiques sont classees en trois categories selon trois differentes combinaisons de zones sismiques de vitesse et d'acceleration (Z, < Z,, Z, = Z, et Z, > Z,), et les mouvements du sol dans les regions ayant des combinaisons de zones differentes devraient avoir des caracteristiques de frequence differentes. Le Code national du bfitiment du Canada propose divers niveaux de cisaillement de calcul a la base pour les bdtiments avec periode courte situes dans des regions ayant des combinaisons de zones differentes. L'exigence de cisaillement de calcul a la base pour les bdtiments avec periode longue est directement liee a la vitesse zonale, sans tenir compte de la combinaison de zones sismiques. Cet a...

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Section: Dynamic Analysis Resultsmentioning

confidence: 99%

Seismic performance of reinforced concrete ductile moment-resisting frame buildings located in different seismic regions

Zhu¹,

Tso²,

Heidebrecht³

1992

Can. J. Civ. Eng.

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“…The design structural overstrength is considered an inherent part of the structural overstrength, which is implicitly or explicitly accounted as a source of earthquake resisting capacity to reduce the elastic spectrum. This idea is generally accepted and it form part of the state of knowledge in earthquake engineering, see for example, ATC-10 (1982), ATC-19 (1995), ATC 34 (1995, Charney and Bertero (1982), Moehle and Diebold (1984), Miranda and Bertero (1989), Osteraas and Krawinkler (1989), Hadjian (1989), Shahrooz and Moehle (1990), Fischinger and Fajfar (1990), Nassar and Krawinkler (1991), Tso and Naumoski (1991), Zhu et al (1992), Uang (1992), Mitchell and Paultre (1994), Elnashai and Broderick (1996), Broderick and Elnashai (1996), Whittaker et al (1999) and Balendra et al (1999). In fact, values of reduction factors of modern seismic codes from 5 to 12 can only be justified if the design structural overstrength is included.…”

Section: Numerical Example Of Code Calibrationmentioning

confidence: 99%

“…Based on this observation, a second source of earthquake-resisting capacity has been identified: the structural overstrength. In previous years, the importance of structural overstrength to resist earthquakes and its possible sources have been widely studied and reported in the technical literature (Hadjian 1989;ATC-10 1982;Miranda and Bertero 1989;Osteraas and Krawinkler 1989;Fischinger and Fajfar 1990;Shahrooz and Moehle 1990;Tso and Naumoski 1991;Zhu et al 1992;Uang 1992;Mitchell and Paultre 1994;ATC-19 1995;ATC-34 1995;Humar and Rahgozar 1996;and Rahgozar and Humar 1998).…”

Section: Introductionmentioning

confidence: 99%

Implications of structural overstrength on the calibration of seismic codes

Sanchez-Ricart

2011

Bull Earthquake Eng

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A computer program is developed to test the influence of the structural overstrength to calibrate seismic codes. The program automatically performs an iterative design-evaluation process to calibrate the seismic code. A numerical example is performed in order to test the different approaches. The virtual simulation shows that the force reduction factor cannot be directly deduced from building performance in past earthquakes. This custom of deducing the force reduction factor from the building performance under past earthquakes artificially increases the ratios elastic spectrum to design spectrum due to the design structural overstrength. The similitude of the simulation with the historical calibration of the design spectrum in the seismic codes in the United States of America (USA) is evident.

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“…In NBC 1990 the force modification factor can be interpreted as the product of a global ductility factor varying from 1 to 4 and a constant overstrength factor, R,, with U = 1/R, (Tso and Naumoski 1991;Fischinger and Fajfar 1990). The overstrength, that is, the supplied strength in excess of the seismic design base shear, can be attributed to member oversize, minimum code detailing requirement, multiple load combinations, nonstructural components, ... (Uang 1991).…”

Section: Response Spectra From the 1988 Saguenay Earthquakementioning

confidence: 99%

“…In this case, Tl was defined from [8]. Tso and Naumoski (1991) recently proposed the adoption by the NBC of a perioddependent force modification factor, defined by [4] and [5], with T I = 0.5 s, to reduce the high ductility demand associated with short-period structures.…”

Section: Period-dependent Force Modification Factormentioning

confidence: 99%

Seismic analysis of short-period structures subjected to the 1988 Saguenay earthquake

Léger¹,

Romano²

1992

Can. J. Civ. Eng.

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This paper presents elastic and inelastic response spectra of strong motion accelerograms recorded during the 1988 Saguenay earthquake. Comparisons are made with the National Building Code of Canada (NBC) 1990 lateral forces requirements for the seismic resistant design of short-period structures. The use of a period-dependent force modification factor is proposed to take advantage of the energy dissipation capacity of short-period structures on a more rational basis. The seismic response of a typical low-rise steel building designed according to the NBC 1990 and CAN3-S16.1-M89 is then investigated. It is shown that to obtain a realistic picture of the ductility demand of low-rise buildings, the structural overstrength, that is, the supplied strength in excess of the seismic design base shear, should be explicitly considered in the design process.

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Period-dependent seismic force reduction factors for short-period structures

Cited by 13 publications

References 5 publications

Seismic performance of reinforced concrete ductile moment-resisting frame buildings located in different seismic regions

Seismic performance of reinforced concrete ductile moment-resisting frame buildings located in different seismic regions

Implications of structural overstrength on the calibration of seismic codes

Seismic analysis of short-period structures subjected to the 1988 Saguenay earthquake

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