Determination of seismic design forces by equivalent static load method

2003 ◽  
Vol 30 (2) ◽  
pp. 287-307 ◽  
Author(s):  
JagMohan Humar ◽  
Mohamed A Mahgoub
Keyword(s):  
Seismic Design ◽  
Static Load ◽  
Base Shear ◽  
Uniform Hazard Spectra ◽  
Uniform Hazard Spectrum ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Equivalent Static Load ◽  
Adjustment Factors ◽  
Mode Vibration

In the proposed 2005 edition of the National Building Code of Canada (NBCC), the seismic hazard will be represented by uniform hazard spectra corresponding to a 2% probability of being exceeded in 50 years. The seismic design base shear for use in an equivalent static load method of design will be obtained from the uniform hazard spectrum for the site corresponding to the first mode period of the building. Because this procedure ignores the effect of higher modes, the base shear so derived must be suitably adjusted. A procedure for deriving the base shear adjustment factors for different types of structural systems is described and the adjustment factor values proposed for the 2005 NBCC are presented. The adjusted base shear will be distributed across the height of the building in accordance with the provisions in the current version of the code. Since the code-specified distribution is primarily based on the first mode vibration shape, it leads to an overestimation of the overturning moments, which should therefore be suitably adjusted. Adjustment factors that must be applied to the overturning moments at the base and across the height are derived for different structural shapes, and the empirical values for use in the 2005 NBCC are presented.Key words: uniform hazard spectrum, seismic design base shear, equivalent static load procedure, higher mode effects, base shear adjustment factors, distribution of base shear, overturning moment adjustment factors.

Application of uniform hazard spectra in seismic design of multistorey buildings

2000 ◽  
Vol 27 (3) ◽  
pp. 563-580 ◽  
Author(s):  
J L Humar ◽  
M A Rahgozar
Keyword(s):  
Seismic Design ◽  
Reduction Factor ◽  
Degree Of Freedom ◽  
Base Shear ◽  
Uniform Hazard Spectra ◽  
Single Degree Of Freedom ◽  
Building Frames ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Adjustment Factors

The use of uniform hazard spectra for obtaining the seismic design forces is being considered for the next version of the National Building Code of Canada. Such spectra provide the spectral accelerations of a single-degree-of-freedom system for a range of periods but for a uniform level of hazard. One of the issues that need to be resolved before uniform hazard spectra are used in the design of multistorey buildings is the adjustment required in the base shear to account for the higher mode effects present in a multi-degree-of-freedom system. This issue is examined through analytical studies of the response of idealised elastic and inelastic multistorey building frames to ground motions representative of the seismic hazard in the eastern and western regions of Canada. Representative values are obtained for the adjustment factors that must be applied to the design base shear and to the base overturning moment.Key words: seismic design base shear, uniform hazard spectra, higher mode effects, base shear adjustment factor, base overturning moment reduction factor.

Seismic Response Analysis and Design for Concrete Nuclear Structures: A Comparative Study of the Time History, Response Spectrum, and Equivalent Static Load Methods

2016 ◽  
Author(s):  
Michael O’Leary ◽  
William Godfrey
Keyword(s):  
Seismic Design ◽  
Static Load ◽  
Response Spectrum ◽  
Time History ◽  
Response Analysis ◽  
Seismic Response Analysis ◽  
Equivalent Static Load ◽  
Fixed Base ◽  
Time Histories ◽  
Nuclear Structures

A partially buried fixed-base finite element model of a typical safety-related nuclear structure is analyzed for earthquake loads by the time history method, the response spectrum method, and the equivalent static load method. The spectra-consistent artificial time histories are generated with seed time histories in accordance with Standard Review Plan 3.7.1: Seismic Design Parameters [1] with target spectra based on Regulatory Guide 1.60: Design Response Spectra for Seismic Design of Nuclear Power Plants [2]. The response spectrum analyses are performed with the same target spectra used in generating the artificial time histories. The equivalent static loads are based on the nodal zero period accelerations from the fixed-base time history analyses. The seismic responses in a column in the structure are combined using algebraic sum, square root of the sum of the squares (SRSS), and the 100-40-40 rule in accordance with Regulatory Guide 1.92: Combining modal responses and spatial components in seismic response analysis [3]. The equivalent static load method is applied according to ASCE 4-15: Seismic Analysis of Safety-Related Nuclear Structures [4]. The resulting design forces and required reinforcement for a column in the structure are compared for each method along with the corresponding computational demand.

Seismic loading for buildings with setbacks

1994 ◽  
Vol 21 (5) ◽  
pp. 863-871 ◽  
Author(s):  
C. M. Wong ◽  
W. K. Tso
Keyword(s):  
Dynamic Analysis ◽  
Fundamental Mode ◽  
Load Distribution ◽  
Static Load ◽  
Seismic Loading ◽  
Seismic Load ◽  
Base Shear ◽  
Reasonable Estimate ◽  
Equivalent Static Load ◽  
Irregular Buildings

Dynamic analysis is in general accepted as the best method to obtain the seismic load distribution for buildings with a setback. However, most building codes require the base shear obtained by dynamic analysis to be calibrated by the static base shear obtained using the code's equivalent static load procedure. In obtaining the code static base shear, two issues often arise among the design professionals. First, it is unclear whether the code static base shear is applicable for buildings with setbacks because the period prescribed by the code to be used in the base shear formula is in general not pertinent to buildings with setbacks. Second, it is uncertain whether the higher mode period should be used in computing the base shear when the modal weight of a higher mode is larger than that of the fundamental mode — a case often encountered in designing buildings with setbacks. This paper is an attempt to resolve the above issues. For the first issue, modification factors were derived for adjusting the code period formula so that it can provide a more reasonable estimate for the period of a building with a setback. For the second issue, it was demonstrated in this paper that for cases where the modal weight of a higher mode is larger than that of the fundamental mode, using the higher mode period for base shear calculation will result in unnecessarily conservative design. Key words: earthquake, seismic, irregular buildings, setback, dynamic analysis.

Overview of seismic provisions of the proposed 2005 edition of the National Building Code of Canada

2003 ◽  
Vol 30 (2) ◽  
pp. 241-254 ◽  
Author(s):  
Arthur C Heidebrecht
Keyword(s):  
Seismic Design ◽  
Urban Areas ◽  
Building Code ◽  
Structural Systems ◽  
Base Shear ◽  
Site Factors ◽  
Higher Mode Effects ◽  
Explicit Recognition ◽  
History Of ◽  
The Impact

The proposed 2005 edition of the National Building Code of Canada (NBCC) will contain very significant changes in the provisions for seismic loading and design. A brief history of the NBCC seismic provisions is presented followed by a discussion of the reasons for introducing such major changes in the next edition of the code. The major changes to the seismic provisions are summarized; this includes updated hazard in spectral format, change in return period (probability of exceedance), period-dependent site factors, delineation of effects of overstrength and ductility, modified period calculation formulae, explicit recognition of higher mode effects, rational treatment of irregularities, triggers for special provisions incorporated directly in classification of structural systems, and placing dynamic analysis as the normal "default" method of analysis for use in seismic design. The impact of these changes on the seismic level of protection is considered by comparing the 2005 NBCC and 1995 NBCC base shear coefficients for a selection of common structural systems located on a range of site conditions in three urban areas having low to high levels of seismic hazard, i.e., Toronto, Montréal, and Vancouver.Key words: seismic, design, loading, code, hazard, buildings, structures, foundations, period, analysis.

Vector-Valued Uniform Hazard Spectra

2012 ◽  
Vol 28 (4) ◽  
pp. 1549-1568 ◽  
Author(s):  
Shun-Hao Ni ◽  
De-Yi Zhang ◽  
Wei-Chau Xie ◽  
Mahesh D. Pandey
Keyword(s):  
Seismic Hazard ◽  
Seismic Design ◽  
Hazard Analysis ◽  
Occurrence Rate ◽  
Simultaneous Occurrence ◽  
Uniform Hazard Spectra ◽  
Design Spectrum ◽  
Performance Based Seismic Design ◽  
Design Earthquake ◽  
Vector Valued

Uniform hazard spectra (UHS) have been used as design earthquakes in several design codes. However, as the results from scalar probabilistic seismic hazard analysis (PSHA), UHS do not provide knowledge about the simultaneous occurrence of spectral accelerations at multiple vibration periods. The concept of a single “design earthquake” is then lost on a UHS. In this study, a vector-valued PSHA combined with scalar PSHA is applied to establish an alternative design spectrum, named vector-valued UHS (VUHS). Vector-valued seismic hazard deaggregation (SHD) is also performed to determine the design earthquake in terms of magnitude, distance, and occurrence rate for the VUHS. The proposed VUHS preserves the essence of the UHS and can also be interpreted as a single design earthquake. To simplify the procedure for generating the VUHS, so that they can be easily incorporated into performance-based seismic design, an approximate method is also developed.

scholarly journals Numerical Simulation of Dynamic Response and Evaluation of Flexural Damage of RC Columns under Horizontal Impact Load

2021 ◽  
Vol 11 (23) ◽  
pp. 11223
Author(s):  
Bin Hu ◽  
Jian Cai ◽  
Jiabin Ye
Keyword(s):  
Static Load ◽  
Impact Load ◽  
Bending Moment ◽  
Internal Force ◽  
Displacement Curve ◽  
Fe Model ◽  
Damage State ◽  
Rc Columns ◽  
Equivalent Static Load ◽  
The Impact

By using the ABAQUS finite element (FE) model, which has been verified by experiments, the deformation and internal force changes of RC columns during the impact process are investigated, and a parametric analysis is conducted under different impact kinetic energies Ek. According to the development path of the bottom bending moment-column top displacement curve under impact, the member is in a slight damage state when the curve rebounds before reaching the peak and in a moderate or severe damage state when the curve exceeds the peak, in which case the specific damage state of the member needs to be determined by examining whether there is a secondary descending stage in the curve. Accordingly, a qualitative method for evaluating the bending failure of RC column members under impact is obtained. In addition, the damage state of RC columns under impact can also be quantitatively evaluated by the ratio of the equivalent static load Feq and the ultimate static load-bearing capacity Fsu.

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