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.

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.

The Research on Hysteretic Energy in the Equivalent System Schemes between Multi Degree of Freedom System and Single Degree of Freedom System

2012 ◽  
Vol 166-169 ◽  
pp. 2177-2181
Author(s):  
Ming Qiang Sheng ◽  
Ying Liu
Keyword(s):  
Seismic Design ◽  
Seismic Waves ◽  
Good Alternative ◽  
Cumulative Damage ◽  
Degree Of Freedom ◽  
Equivalent System ◽  
Single Degree Of Freedom ◽  
Hysteretic Energy ◽  
Single Degree ◽  
Comparison And Analysis

The cumulative damage produced by severe earthquake is significant to the structural dilapidation and collapse. Most design methods based on force or displacement can’t reflect the effect of cumulative damage. Energy-based seismic design is known as a good alternative design. At present the research on the hysteretic energy of single-degree of freedom system(SDOF) is abundant, but real buildings can only be simplified as multi-degree of freedom systems(MDOF) mostly. Therefore how to acquire suitable equivalent single-degree of freedom system(ESDOF) is a key program. In this paper 12 equivalent system schemes(ESS) have been put forward, then the ratio of hysteretic energy(RH) of 6-floors framework was calculated with 30 typical seismic waves. Based on the comparison and analysis between calculations of 3 typical ESS, by the way of envelope fitting, the expression of RH related to earthquake characteristic value a/v was established.

Vertical Response of Multi-Story Structures at the Instance of Maximum Horizontal Response

2002 ◽  
Author(s):  
Tomoyo Taniguchi
Keyword(s):  
Modal Analysis ◽  
Seismic Design ◽  
Equations Of Motion ◽  
Normal Modes ◽  
Degree Of Freedom ◽  
Response Analysis ◽  
Governing Equations ◽  
Single Degree Of Freedom ◽  
Shear Modes ◽  
Direct Numerical Integration

A vertical response of a multiple degree of freedom system vibrating in axial modes at the instance of its maximum horizontal response vibrating in shear modes is analyzed by superposition of normal modes. The coincident vertical response acceleration at the instance of the maximum horizontal response acceleration between two independent single degree of freedom systems indicated probabilistic properties. It is of interest to extend concepts of the response coincidence in the response analysis of multi-story structures. Nevertheless, the distribution of the coincident vertical response along the building height may be the most important in connection with the seismic design. Its probable distribution and an approximate upper bound are investigated to determine an analysis constant. The analysis constant enables the computation of the coincident vertical response of multi-story structures at the instance of the maximum horizontal response by the modal analysis. The results of the proposed method and the direct numerical integration of governing equations of motion are compared, and conclusions are drawn about the use of the modal analysis to the coincident vertical response of multi-story structures.

The Inelastic Input Energy Spectra for Main Shock–Aftershock Sequences

2016 ◽  
Vol 32 (4) ◽  
pp. 2149-2166 ◽  
Author(s):  
Changhai Zhai ◽  
Duofa Ji ◽  
Weiping Wen ◽  
Weidong Lei ◽  
Lili Xie ◽  
...  
Keyword(s):  
Seismic Design ◽  
Main Shock ◽  
Degree Of Freedom ◽  
Energy Spectra ◽  
Site Conditions ◽  
Input Energy ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Earthquake Records ◽  
Aftershock Sequences

This study investigates the input energy spectra for inelastic single-degree-of-freedom (SDOF) systems under main shock–aftershock sequences. The input energy spectra quantitatively reveal the effects of aftershocks on input energy, which verifies the necessity of incorporating aftershocks in energy-based seismic design. The investigation selects the sequences including one aftershock or two aftershocks respectively, according to the proposed criteria for selecting earthquake records. Then, the input energy for sequences is normalized by mass, m, and expressed in terms of the equivalent velocity, V E, seq. Next, the variation of V E, seq is studied in consideration of the hysteretic models, ductility values, periods of vibration, site conditions, relative intensities of aftershocks and number of aftershocks. The results indicate that the effects of aftershocks on input energy are significant in almost the whole period region. Finally, a simplified expression of input energy is proposed for incorporating aftershocks in energy-based seismic design.

scholarly journals Seismic forces in base-isolated masonry structures

1977 ◽  
Vol 10 (2) ◽  
pp. 55-68 ◽  
Author(s):  
M. J. N. Priestley ◽  
R. L. Crosbie ◽  
A. J. Carr
Keyword(s):  
Base Isolation ◽  
Substantial Reduction ◽  
Shear Walls ◽  
Degree Of Freedom ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Short Period ◽  
Margin Of Safety ◽  
Isolation Systems ◽  
Seismic Forces

Dynamic analyses of four, eight and twelve storey masonry shear walls supported on base-isolation systems are described. Each wall was modelled as a multi-degree-of-freedom cantilever. Results are presented which indicate behaviour is more complex due to the significance of higher mode effects, than was previously believed on the basis of simple single-degree-of-freedom models. The influence of different types of base-isolation, and of the stiffness of the gravity supporting system, are discussed. Tentative design recommendations are proposed which provide a substantial reduction in design forces for short period structures while still maintaining an adequate margin of safety against the formation of wall hinges.

Simplified Model of High-Rise Isolated Structure for Earthquake Response Analysis

2011 ◽  
Vol 250-253 ◽  
pp. 2007-2010
Author(s):  
Wei Qing Fu ◽  
Fei Chen ◽  
Wen Guang Liu
Keyword(s):  
High Order Mode ◽  
Degree Of Freedom ◽  
Equivalent Model ◽  
Response Analysis ◽  
Original Structure ◽  
Base Shear ◽  
Isolation Technique ◽  
Single Degree Of Freedom ◽  
High Rise ◽  
Single Degree

Kelly and Xiyuan Zhou research on upper single-degree-of–freedom model of regular isolated building, and give necessary computing formulas. For various middle or low isolated building, the result is satisfied by using the model. Recently isolation technique was applied to high-rise buildings. For isolated building systems with large aspect ratio, high-order mode parts of upper structure can not be ignored. It brings large errors to use single-degree-of–freedom model. In the paper, according to the equivalent rules of equal structure period and total base shear, the computing formula of structure parameters is deduced. After numerical analysis for some regular buildings, a simplified method for equivalent model is given. By analyzing the earthquake responses of equivalent model and original structure, it is proved that the equivalent method is simple and feasible.

Efficacy of Importance Factor in Seismic Design of Indian Buildings

2016 ◽  
Vol 857 ◽  
pp. 71-75
Author(s):  
V. Sukumar ◽  
J. Arunachalam ◽  
D.C. Haran Pragalath
Keyword(s):  
Seismic Design ◽  
Reduction Factor ◽  
Seismic Load ◽  
Base Shear ◽  
Public Buildings ◽  
Response Reduction Factor ◽  
Rc Frames ◽  
Time Period ◽  
Importance Factor ◽  
Load Evaluation

At present, seismic load evaluation for design of Indian buildings are carried out using Indian seismic code. In which, building Time period, Response Reduction factor and Importance factor alters design base shear majorly. Currently IS code defines Importance factor differently as “1” for general buildings and “1.5” for public buildings. This factor makes public buildings as heavier sections as it increases design base shear. However there are no evidence that, how this importance factor affects/alters/improves the seismic behavior of buildings. In this present study, four storey RC frames are designed with different importance factors. Pushover analyses are carried out to find its effects on over strength factor and response reduction factor.

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.

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