Quantifying higher mode effects in rocking systems considering shear-flexural behavior

Structures ◽  
2020 ◽  
Vol 27 ◽  
pp. 542-558
Author(s):  
Hedayat Veladi ◽  
Bahman Farahmand Azar ◽  
Saeed Rahimi Gendeshmin
Keyword(s):  
Flexural Behavior ◽  
Higher Mode Effects ◽  
Mode Effects

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.

scholarly journals An Optimal Seismic Force Pattern for Uniform Drift Distribution

Buildings ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 231 ◽  
Author(s):  
Rosario Montuori ◽  
Elide Nastri ◽  
Bonaventura Tagliafierro
Keyword(s):  
Low Cycle Fatigue ◽  
Force Distribution ◽  
Premature Failure ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Seismic Force ◽  
Uniform Drift ◽  
Load Pattern ◽  
Set Up ◽  
Cyclic Damage

The force distribution proposed by codes, which in many cases is framed in the equivalent static force procedure, likely leads to design structures with non-uniform drift distribution in terms of inter-storey drift and ductility demands. This can lead to an unbalanced drift demand at certain storeys. This phenomenon may also amass cyclic damage to the dissipative elements at this very storey, therefore increasing the probability of premature failure for low-cycle fatigue. This work proposes a new force design distribution that accounts for higher mode effects and limits the displacement concentration at any storey thus improving the dissipative capacity of the whole structures. The main advantage of the proposed method stands in its formulation, which allows to spare any previous set up with structural analyses. The proposed force distribution has been applied to multi-degree-of-freedom systems to check its effectiveness, and the results have been compared with other proposals. In addition, in order to obtain a further validation of the proposed force distribution, the results obtained by using a genetic algorithm have been evaluated and compared. Additionally, the results provided in this work validate the proposed procedure to develop a more efficient lateral load pattern.

Investigation of Soil-Structure Interaction and Higher-Mode Effects on Dynamic Response of Base-Isolated Structure Founded on Half Space

2013 ◽  
Author(s):  
C. S. Tsai ◽  
H. C. Su
Keyword(s):  
Closed Form ◽  
Soil Structure ◽  
Dynamic Responses ◽  
Soil Structure Interaction ◽  
Entire System ◽  
Higher Mode Effects ◽  
Closed Form Solutions ◽  
Structure Interaction ◽  
Mode Effects ◽  
Isolated Structures

This paper attempts to investigate the effects of soil-structure interaction (SSI) and higher modes on the dynamic responses of base-isolated structures through closed-form solutions for a superstructure, seismic isolator, and soil system under various conditions, comprising the cases of rigid and half-space foundations. The proposed system considers continuum media for both the superstructure and soil foundation, which can take the effects of higher modes into account, along with a discontinuous layer with a governing equation that interprets the mechanical behavior of the base-isolation system. Then, the closed-form solutions in terms of well-known frequency and impedance ratios under various conditions of soil foundations were obtained through rigorous mathematical derivations and validations by collapsing the entire system to a single degree-of-freedom system in structural dynamics and well-known cases of wave propagation in elastic solids. The closed-form solutions derived in this study explicitly revealed the characteristics of the SSI and higher mode effects in influencing the seismic behavior of base-isolated structures. Furthermore, the SSI effects on the dynamic responses of the entire system were extensively evaluated. The conclusive results of this paper will be useful for understanding the SSI and higher mode effects on the dynamic responses of base-isolated structures.

scholarly journals Base isolation

1978 ◽  
Vol 11 (4) ◽  
pp. 219-233
Author(s):  
D. M. Lee ◽  
I. C. Medland
Keyword(s):  
Base Isolation ◽  
Shear Forces ◽  
Isolation System ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Effective Form ◽  
Base Isolation System ◽  
Standard Set ◽  
Isolated Structures

In this paper the evolution of a technique for protecting a structure from earthquake attack is traced from its beginning through to its currently most effective form, and this form, the Base Isolation System, is compared to other currently available techniques. The influence of higher mode effects in base isolated multi-storey structures is investigated and shown to be of considerable significance in determining the shear forces in the upper levels of a structure. Because of these higher mode effects the responses of appendages on isolated structures, while still being less than those for appendages on unisolated structures, can be significantly larger than previous 1-D analyses had suggested. A standard set of distributions of inter-storey shear up a multi-storey structure is presented with each distribution being defined by a parameter which varies from zero to unity.

scholarly journals Column strength requirements in multi-storey seismic frames

1989 ◽  
Vol 22 (3) ◽  
pp. 135-144
Author(s):  
E. L. Blaikie
Keyword(s):  
Flexural Strength ◽  
Ground Motions ◽  
Design Procedure ◽  
Capacity Design ◽  
Design Code ◽  
Factors Affecting ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Column Design ◽  
Future Evaluation

This paper examines factors affecting the strength requirements of columns in multi-storey frames responding to seismic ground motions. The examination is carried out using an inelastic static analysis approach and the concept of an "equivalent condensed frame". In particular, the influence of higher modes and the effect of varying the pattern of beam flexural strength over the frame height are evaluated. It is suggested that the current capacity design approach of the NZ Concrete Design Code overstates the importance of higher mode effects while neglecting the potentially more important influence of the beam flexural strength pattern that is provided for a frame. Some tentative modifications to the current column design procedure are suggested for future evaluation under inelastic dynamic response conditions.

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