Inelastic seismic response of concrete shear walls consideringP–delta effects

2001 ◽  
Vol 28 (4) ◽  
pp. 640-655 ◽  
Author(s):  
R Tremblay ◽  
P Léger ◽  
J Tu
Keyword(s):  
Plastic Hinge ◽  
Design Procedure ◽  
Building Code ◽  
Stability Factor ◽  
Dynamic Shear ◽  
Shear Forces ◽  
Inelastic Response ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Wall Structures

The inelastic response of a typical 12-storey ductile reinforced concrete flexural wall is examined under strong earthquake ground motions to determine the importance of P–delta effects and assess the seismic demand in shear and flexure. According to the stability factor approach of the National Building Code of Canada (NBCC) to account for P–delta effects, the flexural strength of the wall has to be increased by as much as 29%. However, the inelastic dynamic analyses indicate that P–delta effects on lateral deformations and curvature ductility demand are negligible for walls that meet the 2% NBCC interstorey drift requirement. The current NBCC stability factor approach to consider P–delta effects is thus overly conservative for shear wall structures, which respond significantly in their second and higher modes of vibration. The analyses also indicate that the magnitude and distribution of shear forces and bending moments in the wall are different from those obtained using the NBCC static design procedure. Plastic hinges can occur above the base of the wall, although the probable moment resistance diagram exceeds the assumed moment envelope after plastic hinge formation at the base. Dynamic amplification of shear forces due to higher mode effects was also observed, which must be accounted for in design. Dynamic shear amplification factors proposed for wall structures in the commentary to the current standard for design of concrete structures in Canada compared well with the results of this study.Key words: seismic, flexural wall, P–delta effects, stability coefficient, inelastic response, National Building Code of Canada, dynamic shear force amplification, higher mode effects.

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.

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.

Bending Stiffener Design Through Structural Optimization

2009 ◽  
Author(s):  
Rafael Loureiro Tanaka ◽  
Lauro Massao Yamada da Silveira ◽  
Joa˜o Paulo Zi´lio Novaes ◽  
Eduardo Esterqui de Barros ◽  
Clo´vis de Arruda Martins
Keyword(s):  
Optimization Problem ◽  
Design Procedure ◽  
Complex Task ◽  
Load Case ◽  
Shear Forces ◽  
Design Variables ◽  
Curvilinear Coordinate ◽  
Regular Design ◽  
Curvature Deformation ◽  
Flexible Risers

Bending stiffeners are very important ancillary equipments of umbilicals or flexible risers, since they protect the lines from overbending. Their design however is a complex task, since many load cases must be taken into account; the structure itself has a section that is variable with curvilinear coordinate. To aid the designer in this task, optimization algorithms can be used to automate the search for the best design. In this work an optimization algorithm is applied to the design of the bending stiffener. First, a bending stiffener model is created, which is capable of simulating different load case conditions and provide, as output, results of interest such as maximum curvature, deformation along the stiffener, shear forces and so on. Then, a bending stiffener design procedure is written as an optimization problem and, for that, objective function, restrictions and design variables defined. Study cases were performed, comparing a regular design with its optimized counterpart, under varying conditions.

Inelastic seismic shear amplification due to higher mode effects in reinforced concrete coupled walls

2021 ◽  
pp. 875529302110533
Author(s):  
Gabriel Rivard ◽  
Steeve Ambroise ◽  
Patrick Paultre
Keyword(s):  
Reinforced Concrete ◽  
Parametric Study ◽  
Numerical Study ◽  
Plastic Hinge ◽  
Experimental Studies ◽  
Physical Parameters ◽  
Intensity Level ◽  
Shear Forces ◽  
Coupled Walls ◽  
Seismic Shear

Recent numerical and experimental studies on reinforced concrete shear walls and coupled walls have shown shear forces greater than expected when the walls are subjected to earthquakes at an intensity level that does not exceed the design values. This amplification of shear forces is attributable to the effects of higher modes after the walls develop a plastic hinge at the base. These effects have been recently recognized in North American design codes for cantilever walls and is currently neglected in the design of ductile coupled walls. As part of the research program described in this article, a parametric study was carried out on coupled wall systems to identify the geometric and physical parameters having the greatest influence on the seismic shear amplification. Using the results of this parametric study, an extensive numerical study was conducted on classes of ductile coupled walls subjected to seismic excitation representative of Western and Eastern Canada. This extensive study led to the establishment of shear amplification prediction equations for use in building codes.

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.

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