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RE: Lateral Force from Pedestrian Movement

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One of the problems with balconies is that there can be excessive vibration
if the natural frequency of the structure is similar to the frequency of
the excitation from people dancing or stamping.  This vibration even if it
dosen't cause a structural problem can cause people to freak out and
potentially panic.  

The best solution is to stiffen the structure so that the natural frequency
of the structure is significantly higher than the exciting motion.  It is
my understanding that frequency of people dancing or jumping up and down is
limited to about 3 Hz.  If you design the balcony to have a natural
frequency of at least 7 to 9 Hz you should not have a problem.

Mark Gilligan

Message text written by INTERNET:seaint(--nospam--at)

Watching people climb extension ladders illustrates the amount of sidesway 
that can occur accidently.  When I design stairs, I include 10 percent of
gravity live load as a horizontal sidesway load.

A balcony in a college area:  Double the code specified live load, and add 
the weight of all the full kegs of beer that are consumed in one week plus 
the weight of all the bottles of whiskey that are consumed, then find the 
weight of the heaviest statue in town particularly one that is anchored
so it can't be stolen, compare it to the weight of the rival school's
use the heavier weight and assume that it will be permanently on the

Other than this, use good judgement.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Ron Martin wrote:

>>Does anyone have a good method of estimating the lateral force from the 
movement of pedestrians if they were somewhat walking or swaying in the

I have a client with a free-standing balcony.   They have already built it 
and now need some help.  We are assuming this large balcony could get
dancing or swaying at some time in the future.   We are not in a high
zone, so I was not sure what kind of loading we are looking at.  The only 
equation we have now is "college town + college kids+alcohol+ thinking you 
can sing/dance=problems".  Currently it is a food establishment, but I can 
easily see it becoming a bar in the future.<<