Panel Zone and Rigid Offsets •

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• Added by Truly Guzman, last edited by Truly Guzman on May 26, 2011

ETABS has the capability to model both, rigid offsets and Panel zones. In order to illustrate the

correct use of both options the following simple examples have been created, all frames have

the same steel frame sections and a lateral load of 10kips applied at the top floor, the rigid

offsets and panel zone have been modified as follows:

Model 1.- Default rigid offsets , rigid zone

factor 0, No panel zone

X-Deflection= 0.133in

This model is the simplest one, and

represents the higher bound for deflections

(conservative) but the lower bound for

moments.

Model 2.- Default rigid offsets, rigid zone

factor 1, No panel zone

X-Deflection=0.104in

This model assume fully rigid offsets,

reports the smallest deflection which is

generally unconservative and is not

recommended. Results for moments are

the highest of the four models

(conservative)

Model 3.- Default rigid offsets, rigid zone

factor 0, Panel zone from column

X-Deflection=0.152in

This model assumes no rigid zone and

panel zone modeled based on column

properties. Deflections are extremely high

due to the fact that flexibility is being

duplicated at joints. Moment is the smallest

of the four models, and is also not

recommended due to unconservative

results.

Model 4.- Default rigid offsets, rigid zone

factor 1, Panel zone from column

X-Deflection=0.128in

This model has fully rigid offsets, and panel

zone modeled based on column properties.

In this case flexibility of joint is correctly

modeled. Results for deflections report a

value in between the upper and lower

bound. Moments as well indicate a good fit

in between extreme bounds. Therefore; this

is generally the best modeling assumption.

NOTES:

• If the first model would be modeled using the user defined lengths option as 0,0 for rigid

offsets instead of default based on connectivity, results will be identical except for the

fact that moments will be reported at end of elements (not a column/beam face)

• A fully rigid zone should never be used in steel frames, usually for concrete frames a

value of 0.5 is recommended. Which I turn indicates that 50% of the actual offset will be

consider rigid

• Rigidity will only affect bending in the 3 axis of the frame, not torsion, not axial

properties.