Collapse Mechanisms of Controlled Rocking Steel Braced Frames: Base Rocking Joint vs. Capacity-Protected Frame Members

2018 ◽  
Vol 763 ◽  
pp. 669-677
Author(s):  
Taylor C. Steele ◽  
Lydell D.A. Wiebe
Keyword(s):  
Numerical Models ◽  
Ground Motions ◽  
Braced Frames ◽  
Capacity Design ◽  
Higher Mode Effects ◽  
Collapse Prevention ◽  
Mode Effects ◽  
Collapse Mechanisms ◽  
Seismic Force ◽  
Collapse Assessment

Controlled rocking steel braced frames (CRSBFs) have been proposed as a low-damage seismic force resisting system with reliable self-centering capabilities. The frame members in CRSBFs are selected to remain elastic during design-level earthquakes, so they must be designed to resist the peak forces from at least the first-mode pushover response. However, several researchers have shown that higher mode effects can contribute significantly to the peak member forces. Some collapse assessment studies on CRSBFs have included member yielding and buckling in the numerical models, but the studies have not examined a range of possible design intensities for the higher modes, and have not separated the influence on the collapse risk of the capacity design from that of the design of the base rocking joint. This paper presents the collapse assessment results for 12-story CRSBFs that were designed either excluding the higher-mode forces, or including the higher-mode forces at the DBE level, MCE level 1.5 times the MCE level, and 2.0 times the MCE level. The ground motions were selected conditionally based on the first-mode period of each example frame. The probability of collapse during an MCE-level event was computed for the frames when buckling and yielding of the frame members was modeled, and compared to the probabilities of collapse when the members were modeled as elastic. The results indicate that the base rocking joint design was more conservative than required to provide adequate collapse prevention compared to the design of the frame members. Including the higher-mode forces at the MCE level for capacity design seems appropriate from a collapse prevention perspective.

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.

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.

A Discussion on some Key Issues for Seismic Design of Concentrically Braced Frames According to Canadian and Chinese Codes

2010 ◽  
Vol 163-167 ◽  
pp. 211-221
Author(s):  
Wen Yuan Zhang ◽  
Constantin Christopoulos
Keyword(s):  
Seismic Design ◽  
Braced Frames ◽  
Capacity Design ◽  
Concentrically Braced Frames ◽  
Main Design ◽  
Seismic Force ◽  
Concentrically Braced ◽  
Key Issues ◽  
Design Requirements ◽  
Insight Into

To gain further insight into the seismic design of concentrically braced frames as defined by the Canadian and Chinese codes, a comparison of the main design requirements contained in each code is carried out in this paper. The comparison emphasizes on the differences existing in these two code provisions, and the reasons behind them. The issues that are examined include the seismic force resisting systems for braced frames, the height restrictions, the force transferred to the beams in chevron configurations, the slenderness ratios of the bracing members, the width-to-thickness ratios of the brace sections, and the influence of brace connections on the columns. Some additional issues that still remain undefined on the seismic response of these systems and some proposals for further studies are also discussed. It is concluded through this comparison that a number of modifications are still required in order to fully implement a capacity design approach of these systems in both codes.

Higher-mode effects for soil-structure systems under different components of near-fault ground motions

2014 ◽  
Vol 7 (1) ◽  
pp. 83-99 ◽  
Author(s):  
Faramarz Khoshnoudian ◽  
Ehsan Ahmadi ◽  
Sina Sohrabi ◽  
Mahdi Kiani
Keyword(s):  
Soil Structure ◽  
Ground Motions ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Near Fault

Seismic force demand on ductile reinforced concrete shear walls subjected to western North American ground motions: Part 2 — new capacity design methods

2012 ◽  
Vol 39 (7) ◽  
pp. 738-750 ◽  
Author(s):  
Yannick Boivin ◽  
Patrick Paultre
Keyword(s):  
Shear Strength ◽  
Reinforced Concrete ◽  
Ground Motions ◽  
Plastic Hinge ◽  
Shear Walls ◽  
Companion Paper ◽  
Design Methods ◽  
Design Codes ◽  
Capacity Design ◽  
Seismic Force

This paper proposes for the Canadian Standards Association (CSA) standard A23.3 new capacity design methods, accounting for higher mode amplification effects, for determining, for a single plastic hinge design, capacity design envelopes for flexural and shear strength design of regular ductile reinforced concrete cantilever walls used as seismic force resisting system for multistorey buildings. The derivation of these methods is based on the outcomes from a review on various capacity design methods proposed in the current literature and recommended by design codes and from the extensive parametric study presented in the companion paper. A discussion on the limitations of the proposed methods and on their applicability to various wall systems is presented.

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.

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