Accounting for overstrength in seismic design of steel structures

1998 ◽  
Vol 25 (1) ◽  
pp. 1-15 ◽  
Author(s):  
M A Rahgozar ◽  
J L Humar
Keyword(s):  
Seismic Design ◽  
Slenderness Ratio ◽  
Steel Structures ◽  
Building Structures ◽  
Braced Frames ◽  
Concentrically Braced Frames ◽  
Moment Resisting Frames ◽  
Moment Resisting ◽  
Design Loads ◽  
Reserve Strength

Observations during many earthquakes have shown that building structures are able to sustain without damage earthquake forces considerably larger than those they were designed for. This is explained by the presence in such structures of significant reserve strength not accounted for in design. Relying on such overstrength, many seismic codes permit a reduction in design loads. The possible sources of reserve strength are outlined in this paper, and it is reasoned that a more rational basis for design would be to account for such sources in assessing the capacity rather than in reducing the design loads. As an exception, one possible source of reserve strength, the redistribution of internal forces, may be used in scaling down the design forces. This is because such scaling allows the determination of design forces through an elastic analysis rather than through a limit analysis. To assess the extent of reserve strength attributable to redistribution, steel building structures having moment-resisting frames or concentrically braced frames and from 2 to 30 storeys in height are analyzed for their response to lateral loading. A static nonlinear push-over analysis is used in which the gravity loads are held constant while the earthquake forces are gradually increased until a mechanism forms or the specified limit on interstorey drift is exceeded. It is noted that in moment-resisting frames the reserve strength reduces with an increase in the number of storeys as well as in the level of design earthquake forces. The P→Δ effect causes a further reduction. In structures having braced frames the main parameter controlling the reserve strength is the slenderness ratio of the bracing members. In these structures, reserve strength is almost independent of both the height of the structure and the effect of building sway. Key words: seismic design, overstrength factor, reserve strength owing to redistribution, steel moment-resisting frames, steel-braced frames, push-over analysis.

Seismic design of steel buildings: lessons from the 1995 Hyogo-ken Nanbu earthquake

1996 ◽  
Vol 23 (3) ◽  
pp. 727-756 ◽  
Author(s):  
Robert Tremblay ◽  
Andre Filiatrault ◽  
Michel Bruneau ◽  
Masayoshi Nakashima ◽  
Helmut G. L. Prion ◽  
...  
Keyword(s):  
Seismic Design ◽  
Steel Structures ◽  
Structural Systems ◽  
Braced Frames ◽  
Steel Buildings ◽  
Concentrically Braced Frames ◽  
Framed Structures ◽  
Concentrically Braced ◽  
Moment Resisting ◽  
Column Bases

Past and current seismic design provisions for steel structures in Japan are presented and compared with Canadian requirements. The performance of steel framed structures during the January 17, 1995, Hyogo-ken Nanbu earthquake is described. Numerous failures and examples of inadequate behaviour could be observed in buildings of various ages, sizes, and heights, and braced with different structural systems. In moment resisting frames, the damage included failures of beams, columns, beam-to-column connections, and column bases. Fracture of bracing members or their connections was found in concentrically braced frames. The adequacy of the current Canadian seismic design provisions is examined in view of the observations made. Key words: earthquake, seismic design, steel structures.

scholarly journals A Comparative Study on the Behavior of Steel Moment-Resisting Frames with Different Bracing Systems Based on a Response-Based Damage Index

2018 ◽  
Vol 4 (6) ◽  
pp. 1354 ◽  
Author(s):  
Kamran Karsaz ◽  
Seyed Vahid Razavi Tosee
Keyword(s):  
Damage Index ◽  
Steel Structures ◽  
Braced Frames ◽  
Initial Stiffness ◽  
Concentrically Braced Frames ◽  
Braced Frame ◽  
Under Five ◽  
Seismic Rehabilitation ◽  
Moment Resisting Frames ◽  
Moment Resisting

Seismic rehabilitation of existing buildings is one of the most effective ways to reduce damages under destructive earthquakes. The use of bracings is one of techniques for seismic rehabilitation of steel structures. In this study we aimed to investigate the seismic performance of three 5, 10 and 15-storey steel structures with moment-resisting frames designed three dimensionally in ETABS 2015 application based on first edition of Iranian Standard 2800. Their damage under five ground motions was evaluated using response-based damage model proposed by Ghobara et al. (1999). Then, the structures were rehabilitated with different bracing systems (X, eccentric and concentric V and inverted-V) and, again, their damage under five earthquakes were evaluated and compared with those of moment resisting frames. The pushover analysis results indicated that X-braced frame was the least ductile system but had highest initial stiffness and yield stress. In low-rise building, X-braced frames showed better performance among studied bracing systems compared to moment resisting frames, while mid and high-rise buildings with eccentrically braced  frame (EBF) showed the best behavior against earthquakes with the least damage. Moreover, it was found out that EBFs’ performance increases by increasing storey height, but for concentrically braced frames (CBFs) it was decreased. We concluded that the use of response-based damage models can be a suitable procedure for estimating the vulnerability of steel structures rehabilitated with bracing system.

EVALUATION OF THE DYNAMIC CHARACTERISTICS FOR SEISMIC DESIGN OF MULTI-STORY BUILDINGS

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Aya Aboelhamd ◽  
Aman Mwafy ◽  
Suliman Gargoum
Keyword(s):  
Reinforced Concrete ◽  
Seismic Design ◽  
Building Codes ◽  
Fundamental Period ◽  
Braced Frames ◽  
Data Set ◽  
Structural Dynamic ◽  
Moment Resisting Frames ◽  
Moment Resisting ◽  
Period Data

The fundamental period of vibration is a critical structural dynamic characteristic in seismic design. Several expressions for the calculation of the fundamental period have been recommended by different building codes and previous studies. However, further studies are still needed to evaluate the design expressions used for the calculation of the fundamental periods and assess the need for further refinement. In this study, comprehensive fundamental period data from two sources is collected and compared with different formulas from building codes and previous studies. The first data set is obtained from 147 instrumented buildings with various lateral force resisting systems (LFRSs). The second set of period data are collected from the dynamic response simulations of selected structures. Different LFRSs are considered, including steel moment resisting frames (SMRFs), reinforced concrete moment resisting frames (RCMRFs), reinforced concrete shear walls (RCSWs), concentrically braced frames (CBFs), eccentrically braced frames (EBFs), masonry structures and pre-cast structures. The correlations between the derived period expressions with those recommended by the design provisions show that the code approach is conservative enough for SMRFs, CBFs, masonry buildings and pre-cast structures. For RCMRFs, EBFs and RCSWs, the design code is slightly unconservative for low-rise buildings. The outcomes of the study help to arrive at more efficient and cost-effective seismic design of buildings with different characteristics.

Code-Oriented Methodology for the Seismic Design of Regular Steel Moment-Resisting Braced Frames

2014 ◽  
Vol 30 (4) ◽  
pp. 1683-1709 ◽  
Author(s):  
Edgar Tapia-Hernández ◽  
Arturo Tena-Colunga
Keyword(s):  
Seismic Design ◽  
Time History ◽  
Federal District ◽  
Design Parameters ◽  
Braced Frames ◽  
Steel Buildings ◽  
Moment Frames ◽  
Concentrically Braced Frames ◽  
Design Spectrum ◽  
Moment Resisting

In order to help improve the seismic design of regular steel buildings structured with ductile moment-resisting concentrically braced frames (MRCBFs) using the general design methodology of Mexico's Federal District Code (MFDC-04), suitable design parameters were first assessed using the results of pushover analyses of 13 regular MRCBFs. In order to insure collapse mechanisms consistent with the assumptions implicit in a code-based design (strong-column/weak-beam/weaker-brace), it is proposed to relate the minimum strength ratio for the resisting columns of the moment frames and the bracing system. Improved equations are proposed for a more realistic assessment of ductility and overstrength factors. In a second stage, the effectiveness of the improved methodology was assessed with the design of six regular steel buildings with MRCBFs. Buildings were evaluated by performing both pushover and nonlinear time-history analyses under ten selected artificial ground motions related to the corresponding design spectrum.

Steel structures damage from the Christchurch earthquake series of 2010 and 2011

2011 ◽  
Vol 44 (4) ◽  
pp. 297-318 ◽  
Author(s):  
Charles Clifton ◽  
Michel Bruneau ◽  
Greg MacRae ◽  
Roberto Leon ◽  
Alistair Fussell
Keyword(s):  
Steel Structures ◽  
Braced Frames ◽  
Concentrically Braced Frames ◽  
Eccentrically Braced Frames ◽  
Satisfactory Performance ◽  
Concentrically Braced ◽  
Earthquake Series ◽  
Moment Resisting ◽  
Industrial Storage ◽  
Storage Racks

This paper presents preliminary field observations on the performance of selected steel structures in Christchurch during the earthquake series of 2010 to 2011. This comprises 6 damaging earthquakes, on 4 September and 26 December 2010, February 22, June 6 and two on June 13, 2011. Most notable of these was the 4 September event, at Ms7.1 and MM7 (MM as observed in the Christchurch CBD) and most intense was the 22 February event at Ms6.3 and MM9-10 within the CBD. Focus is on performance of concentrically braced frames, eccentrically braced frames, moment resisting frames and industrial storage racks. With a few notable exceptions, steel structures performed well during this earthquake series, to the extent that inelastic deformations were less than what would have been expected given the severity of the recorded strong motions. Some hypotheses are formulated to explain this satisfactory performance.

scholarly journals Performance of steel structures during the 1994 Northridge earthquake

1995 ◽  
Vol 22 (2) ◽  
pp. 338-360 ◽  
Author(s):  
Robert Tremblay ◽  
André Filiatrault ◽  
Peter Timler ◽  
Michel Bruneau
Keyword(s):  
Current Knowledge ◽  
Steel Frames ◽  
Steel Structures ◽  
Northridge Earthquake ◽  
Braced Frames ◽  
Concentrically Braced Frames ◽  
Load Paths ◽  
Concentrically Braced ◽  
Moment Resisting ◽  
Observed Damage

The performance of concentrically braced steel frames and moment resisting steel frames during the January 17, 1994, Northridge, California, earthquake is examined. Most of the observations made during the reconnaissance visits confirmed the current knowledge on the inelastic response of these structural systems. This permits the anticipation of proper seismic behavior for buildings designed according to the seismic provisions that have been recently introduced in the Canadian building code and standard for steel structures. In some cases, however, the observed damage raised concerns that should be addressed in future investigations or next editions of these codes. Preventing potentially hazardous nonstructural damage, avoiding premature nonductile failures anywhere along the lateral load paths, limiting structural and nonstructural damage due to brace buckling, and accounting for the vertical ground motion are among those issues. Key words: earthquake, seismic, steel, concentrically braced frames, moment resisting frames, weld.

scholarly journals On California Structural Steel Seismic Design

1986 ◽  
Vol 2 (4) ◽  
pp. 703-727 ◽  
Author(s):  
Egor P. Popov
Keyword(s):  
Structural Steel ◽  
Seismic Design ◽  
Steel Frames ◽  
Steel Structures ◽  
Concentrically Braced Frames ◽  
Concentrically Braced ◽  
Moment Resisting ◽  
The Usa ◽  
Major Attention ◽  
Eccentric Bracing

A number of new code developments, largely initiated in California, are taking place in the USA for the seismic design of steel structures. The principal ones are reviewed and commented upon in the paper. Key experimental support for some of the changes is indicated. Major attention is directed to the three main types of steel construction: moment-resisting frames, concentrically braced steel frames, and, the relatively new method for seismic design, eccentric bracing. Some of the proposed and possible practical improvements in moment-resisting connections are given; the reasons for some concern over the use of concentrically braced frames for severe seismic applications are discussed; and a brief overview on the application of eccentrically braced steel frames is presented. The paper concludes with a few remarks on future trends and needs in structural steel seismic design.

scholarly journals On California structural steel seismic design

1987 ◽  
Vol 20 (1) ◽  
pp. 7-21
Author(s):  
Egor P. Popov
Keyword(s):  
Structural Steel ◽  
Seismic Design ◽  
Steel Frames ◽  
Steel Structures ◽  
Concentrically Braced Frames ◽  
Concentrically Braced ◽  
Moment Resisting ◽  
The Usa ◽  
Major Attention ◽  
Eccentric Bracing

A number of new code developments, largely initiated in California, are taking place in the USA for the seismic design of steel structures. 
The principal ones are reviewed and commented upon in the paper. Key experimental support for some of the changes is indicated. Major attention is directed to the three main types of steel construction: moment resisting frames, concentrically braced steel frames, and, the relatively new method for seismic design, eccentric bracing. Some of the proposed and possible practical improvements in moment-resisting connections are given: the reasons for some concern over the use of concentrically braced frames for severe seismic applications are discussed; and a brief overview on the application of eccentrically braced steel frames is presented. The paper concludes with a few remarks on future trends and needs in structural
steel seismic design.

scholarly journals Concentrically braced frames

1985 ◽  
Vol 18 (4) ◽  
pp. 351-354
Author(s):  
W. R. Walpole
Keyword(s):  
Seismic Design ◽  
Steel Structures ◽  
Study Group ◽  
Braced Frames ◽  
Concentrically Braced Frames ◽  
Concentrically Braced

This paper is the result of deliberations of the Society's Study Group for the seismic design of steel structures.

scholarly journals A Capacity Design Procedure for Columns of Steel Structures with Diagonals Braces

2014 ◽  
Vol 8 (1) ◽  
pp. 196-207 ◽  
Author(s):  
M. Bosco ◽  
A. Ghersi ◽  
E.M. Marino ◽  
P.P. Rossi
Keyword(s):  
Design Procedure ◽  
Steel Structures ◽  
Building Structures ◽  
Axial Deformation ◽  
Braced Frames ◽  
Capacity Design ◽  
Concentrically Braced Frames ◽  
Design Spectrum ◽  
Internal Forces ◽  
Seismic Forces

According to modern seismic codes, in concentrically braced frames the seismic input energy should be dissipated by means of the hysteretic behaviour of braces while all the other members (i.e. beams and columns) have to remain elastic. Accordingly, the design internal forces of braces are determined in these codes by elastic analysis of the structure subjected to seismic forces obtained by the design spectrum. The internal forces of the non-dissipative members, instead, are calculated by means of specified rules for the application of capacity design principles. According to some recent numerical analyses, the yielding or buckling of columns may take place before braces achieve their axial deformation capacity. This paper investigates the reasons of this unsatisfactory behaviour and proposes technological suggestions and a design procedure to improve the seismic performance of columns of building structures with diagonal braces.

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