Tuesday, November 1, 2011

RE: Standard Portal Frame Analysis

Back in the 1970's, I was trained by engineers who did not know computers.  They used graphical methods and other approximate methods to calculate lateral drift.  I came in on my white horse and was going to teach the old hands how to calculate lateral drift the computer way.  They could do it faster by a long shot, and we were well within about 5% of my "modern" ways.  ...I was not worthy. 
I have collected many approximate methods in order to calculate lateral drift quickly with only a calculator (or even a slide rule). 
These are some additional very good tools:
  Kleinlogel had a book of formulas for frames in the 1950's
  Hool & Kinne wrote " Stresses in Framed Structures"
  AISC "Single Span Rigid Frames in Steel" in 1948
  AISC published a really neat little one page frame drift tool in Modern Steel Construction, Steel Interchange in April 1993.  It was based on Kleinlogel.
I have used a similar method that you list below.  I think you will be surprised how accurate the approximate methods are. 

Regards, Harold Sprague

From: vicpeng@telus.net
To: seaint@seaint.org
Subject: Standard Portal Frame Analysis
Date: Mon, 31 Oct 2011 11:28:31 -0700

I'm doing stuff I should done in school J


1)      I am reviewing how to quickly arrive at sway in a rectangular (or any, for that matter) portal using simple portal frame equations.

2)      I calculate the moments from the std equations and then release the top corners to arrive at a flagpole concept tied at tops by a strut/beam.

3)      The resulting base moments are approx by iterative moment distribution.

4)      If I use a partial, or offset, load on the beam I expect sway.

5)      My question is, "Is it too simplistic to take the resulting moment difference at the bases and apply slope-deflection arithmetic to arrive at an estimate of the sway?"




Thor A. Tandy P.Eng, C.Eng, Struct.Eng, MIStructE
Victoria, BC, V8T 1Z1

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