Performance based plastic design method for steel concentric braced

PERFORMANCE - BASED PLASTIC
DESIGN METHOD FOR STEEL
CONCENTRIC BRACED FRAMES
Presented by- Under the guidance of-
Deepak Sharma Dr.(Mrs) P. M. Alandkar
Work by- • M. R. Banihashemi •A. R. Mirzagoltabar • H. R.
Tavakoli
Int J Adv Struct Eng (2015) 7:281–293
DOI 10.1007/s40091-015-0099-0

INTRODUCTION
 This paper presents a performance-based plastic design (PBPD)
methodology for the design of steel concentric braced frames.
 The design base shear is obtained based on energy–work
balance equation using pre-selected target drift and yield
mechanism.
 To achieve the intended yield mechanism and behavior, plastic
design is applied to detail the frame members.
 For validity, three baseline frames (3, 6, 9-story) are designed
according to AISC (Seismic Provisions for Structural Steel
Buildings, American Institute of Steel Construction, Chicago,
2005) seismic provisions (baseline frames).
 These frames are subjected to extensive nonlinear dynamic time-
history analyses.

PERFORMANCE-BASED PLASTIC DESIGN (PBPD)
METHODOLOGY
 Plastic design method is applied to provide the
desirable strength, ductility and yield
mechanism.
 PBPD method does not require such factors
that are based on numerous engineering
judgments which are axiomatically debatable.
 In PBPD method, the drift control and the
selection of yield mechanism are initially
assumed in the design process. It leads to
elimination or minimization of the required of
lengthy iterations to achieve a suitable final
design.

DESIGN BASE SHEAR
 To determine the design base shear for a
particular hazard level, the work required to
push the structure monotonically up to the
target drift (push over analysis is not a
necessity) is equated to the demanded
energy by the same level of EP-SDOF to
reach the same state

DETERMINATION OF DESIGN BASE SHEAR IN
PBPD METHOD
 Obtaining the design base shear for a pre-
determined hazard level is a key factor in
PBPD method. It is calculated by equating
the work needed to push the structure
monotonically up to the target drift (no
pushover analysis needed) to that required
by an equivalent EP-SDOF system to
achieve the same state.

WORK-ENERGY EQUATION
 (Ee + Ep)= γE = ½γMSv
2 = ½γM(T/2∏ . Sa.
G)
where-
 Ee and Ep are, respectively, the elastic and plastic components of
the energy needed as the structure is pushed up to the target drift
 γ is an energy modification factor that is dependent on the
ductility (μ)
 Sa is the pseudo-spectral acceleration,
 Sv is the design pseudo-velocity,
 M is the total mass of the system and
 T is the natural period

CONSIDERING P-∆ EFFECT IN THE LATERAL
FORCES
 P-∆ effect has great influence on seismic performance
and stability of structures, especially when the height of
the building increases.
 Therefore, to provide necessary strength to counter the
overturning due to gravity loads, P-∆ effect is considered
to determine the required shear capacity of braces. It is
performed by adding P-∆ lateral force, to the basic design
force.
 It is well recognized that when the height of braced
frames increases, the flexural deformations in braced
frame increase. So, the P- ∆ effect can lead to severe
damage in the structures, especially in the lower stories.
Therefore, to keep the stability of structure from
overturning, P- ∆ effect is considered in determining the
design base shear and in designing the structural
members in PBPD method.

CONSIDERING P-∆ EFFECT IN THE LATERAL
FORCES
 The strength distribution along the height of the
structure should be according to the lateral force
distribution obtained from nonlinear dynamic analysis.
 This guarantees that the input energy will dissipate
and will prevent the concentration damage in a story.
 To decrease the possibility of inelastic deformation in
a particular part of the structure, it is suitable to
distribute the bracing member strength along the
building height nearly following the design story shear
distribution.

ADDITIONAL LATERAL FORCES DUE TO P-∆
EFFECT

OVERALL DESIGN PROCEDURE IN PBPD
METHOD
 Design of structural members in PBPD method
depends on the type of intended yield mechanism.
 In steel concentric braced frames, the braces are
taken as design yielding members.
 The other members such as beams and columns
should remain elastic, until the structure reaches the
target drift. These members are called non-yielding
members.
 A basic comprehension of plastic design method is
adequate for designing yielding members in the
structures designed by PBPD method. Plastic design
method is applied to provide the desirable strength,
ductility and yield mechanism.

CONTINUED…..
 The strength distribution along the height of the
structure should be according to the lateral force
distribution obtained from non-linear dynamic
analysis.
 This guarantees that the input energy will dissipate
and will prevent the concentration damage in a story.
 To decrease the possibility of inelastic deformation in
a particular part of the structure, it is suitable to
distribute the bracing member strength along the
building height nearly following the design story shear
distribution.
 Non-yielding member’s design, such as beams and
columns, is carried out on the basis of capacity
design approach. The non yielding member’s design
must tolerate the combined forces of gravity loads

PLASTIC HINGE DISTRIBUTIONS FOR 9-STORY (A)PBPD FRAME,
(B) BASELINE FRAMES UNDER GROUND MOTION

MODELING THE STRUCTURE IN SOFTWARE
OPENSEES
 Nonlinear time-history analysis and modeling
the structures are carried out using the
OpenSees software.
 This software is finite element software which
has been specifically designed in
performance systems of soil and structure
under earthquake

REFERENCES
 www.springerlink.com
 Chao S-H, Goel SC, Lee S-S (2007) A Seismic
design lateral force distribution based on
inelastic state of structures. Earthq Spectra
23(3):547–569.
 Goel SC, Chao S-H (2009) Performance-based
plastic design— earthquake resistant steel
structures. International Code Council (ICC),
Falls Church, p 261.
 Performance Based Analysis of Steel
Buildings, Matthew Joseph Williams November
2009.

Performance based plastic design method for steel concentric braced

Performance based plastic design method for steel concentric braced

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