Function
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Using the interaction of the base shear and the displacements calculated from the results of a Pushover analysis, the capacity curve and capacity spectrum of a structure are calculated. The demand spectrum is also generated for a design seismic load using the design response spectrum.
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The Performance Point, which represents the state of maximum inelastic capacity of the structure, is found through the cross point of the Capacity Spectrum and Demand Spectrum for a given damping ratio.
Call
From the main menu, select [Poshover] tab > [Pushover Results] group > [Pushover Curve]
Input
Pushover Curve dialog box
Pushover Load Case
Select a load case applied to pushover analysis.
If Pushover Load Case acting in GCS Z-direction is specified, only Load Factor vs. Displacement becomes activated in Plot Type.
Plot Type
Select the type of pushover result curve to be produced.
Base Shear vs. Displacement
Shear Coefficient vs. Displacement : Shear coefficient (Lateral load/Total weight) vs. Displacement
Shear Coefficient vs. Drift : Shear coefficient vs. inter-story Drift
Load Factor vs. Displacement
If Load Factor vs. Displacement is specified in Plot Type, Capacity Spectrum becomes inactivated. Pushover Curve due to vertical (gravity) load can be produced. An example of application may be an arch structure subjected to vertical displacement in relation to the total reaction.
Additional Curves at other Nodes : Nodes numbers for which additional curves will be produced
Capacity Spectrum : Load (Base Shear) - Displacement of the pushover analysis is transformed into the Spectral Acceleration (Sa) vs. Spectral Displacement (Sd) curve.
Demand Spectrum
Define Design Spectrum... : In order to apply the design response spectrum to prepare the demand spectrum, define a design spectrum specified in a design standard.
Demand Spectra at Damping Ratios(%)
Using the specified damping ratio, produce the demand spectrum.
Constant Period Lines at Period (sec)
Produce the corresponding period lines for the specified periods.
Evaluation of Performance Point
Using the effective damping ratios suggested in ATC-40, evaluate the inelastic demand spectrum and compare it with the capacity spectrum to find the performance point.
Procedure-A : The effective damping ratio for inelastic behavior of a structure is evaluated first, and a corresponding demand spectrum is created. The performance point is found through a repetitive process.
Procedure-B : Assuming the ductility demand curve and using the corresponding effective period and effective damping ratio, the path of the performance point is evaluated and the intersection with the capacity spectrum is found.
Damping Parameters
Enter the parameters determining the effective damping ratio.
Inherent + Additional Damping (%) : Specify the total damping ratio (%) reflecting the inherent damping ratio and additional damping resulting from physical devices installed in the structure.
Structural Behavior Type : Select A, B or C to obtain a reduction factor applicable for effective damping.
Performance Point
It provides the information on the performance point on the spectrum and the performance point transformed into a multi-degree of freedom system.
V, D : Maximum base shear and maximum displacement of the inelastic structure by the performance point
Sa, Sd : Spectral Acceleration (Sa) and Spectral Displacement (Sd) at the performance point
Teff, Deff : Inelastic effective period and effective damping at the performance point
Text Output : Pushover analysis result graphs can be saved as text files.
Draw : Display the capability spectrum generated by the performance point on the screen.
The result for the step generated by the Additional Step is additionally output after the Reference Step.