TO DO (see labels for assignee): Provide numerically solved example: 3 span continuous beam with uniform and point loads, check mispan moment.
The purpose of Pattern Live Load Factor (PLLF) is to enable modeling of moment redistribution due to yielding. When nonzero PLLF is specified for a frame object, the program treats the member as if it is simply supported for resisting the applied live loads (this applies only for calculating the positive design moments; the moments obtained from the analysis are not affected). The PLLF then enables to specify what percentage of the live load should be applied to the frame object for which no continuity is assumed. This enables to model a condition when negative moments are redistributed and thereby increasing the positive mid-span moments. You can specify zero PLLF if you wish not to consider this moment redistribution.
The Pattern Live Load Factors can be assigned to individual elements by using "Design > Steel Frame Design (or Concrete Frame Design) > View/Revise Preferences" menu command:
Example
The maximum midspan moment due to uniform live load would be calculated as:
Mpos_
= f1*MDL+(f2*Pllf*LL*l^2)/8
where
- Unknown macro: {math}= dead load factor multiplier as per code (i.e 1.2)
f1
- Unknown macro: {math}= live load factor multiplier as per code (i.e 1.6)
f2
- Unknown macro: {math}= Live load pattern factor of ETABS (i.e 0.75)
Pllf
- Unknown macro: {math}= length of the element
l
- Unknown macro: {math}= Distributed Live load
LL
- Unknown macro: {math}= Positive moment from analysis with actual boundary conditions due to dead load only
MDL
- Unknown macro: {math}... maximum midspan (positive) moment (calculated assuming no continuity; simply supported condition is assumed)
Mpos_
Unknown macro: {max}
For point loads, the span positive moments would be calculated similarly as for uniform loads: the frame object would be assumed as simply supported and the specified factor would be applied to the live loads.
Related emails:
- Unknown macro: {email}