Pushover Analysis
(Pushover analysis) is the preferred tool for seismic
performance evaluation of structures by the major rehabilitation guidelines and
codes because it is conceptually and computationally simple. Pushover analysis
allows tracing the sequence of yielding and failure on member and structural
level as well as the progress of overall capacity curve of the structure.
The main output of the pushover analysis is in the form of a
force-displacement curve, called pushover curve.
Pushover analysis is a simplified,
static, nonlinear procedure in which a
predefined pattern of earthquakes loads
is applied incrementally to frameworks
until a collapse mechanism is reached.A pushover analysis is a series of
incremental static
analysis carried out to develop a capacity curve for the
building. Based on the
capacity curve, a target displacement which is an
estimate of the displacement
that the design earthquake will produce on the
building is determined. The
extent of damage experienced by the structure at
this target displacement is
considered representative of the damage
experienced by the building when
subjected to design level ground shaking.For Hinge Property we have to follow ATC-40(RCC building) & FEMA-273(STEEL building) guideline.
Performance Point is the point where Capacity Curve intersects Demand Curve.
Theoretically, the
plastic hinges are assumed to form at points at
which plastic rotations occur. In
a simply supported beam with central
concentrated load, the maximum bending moment occurs at the centre of the
beam.
As the load is increased gradually, this moment reaches the fully plastic
moment of the section Mp and a plastic hinge is formed at the
centre.
Introduction of Performance Level
•This is the performance level related
to functionality and any required repairs are minor.
A) Operational
Level
•This
corresponds to the most widely used criteria for essential facilities. The
building’s spaces and systems are expected to be reasonably usable .
B) Immediate
Occupancy level
•This
level is intended to achieve a damage state that presents an extremely low
probability of threat to life safety, either from structural damage or from
falling or tipping of nonstructural building component.
C) Life
Safety Level
•This
damage state addresses only the main building frame or vertical load carrying
system and requires only stability under vertical loads.
D) Collapse Prevention Level
The above deffinition of Performance Level are given by FEMA-273.
Analysis & interpretation of PUSHOVER CURVE data to real life situation,I have choosen a 11-storied Commercial Building Project as an example.
First of all, I have to compare PUSHOVER ANALYSIS SHEAR with DESIGNED SHEAR.
For Performance Point Storey Shear is 609.11 kip & Designed Shear is 423.31 kip ,which implies that Design is SAFE.It also implies that any certain increment of load second plastic hinge will be formed & building will collapse.
From above Figure we see Capacity is well above Demand which means DESIGN is safe.Next Figure will illustrates Formated Plastic Hinge.
From next FIGURE ,You can assess Building Performance under Seismic ground shaking.
Where,Number of formated Hinge is 1798 and among these total hinge minimum hinge formated at B-IO range ,which implies Building Performance will be discussed in Immediate Occupancy Level (B-IO range).
(THANKS)
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