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RE: axial braking load for bridges

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: axial braking load for bridges
• From: "Chris Towne" <ctowne(--nospam--at)chaptech.com>
• Date: Wed, 17 May 2006 16:12:53 -0400

>bend you knees quickly & then stop your decent next you're on a bathroom scale.....

I agree with you that the scale would show more "weight" when I stopped the decent.  This increase would be the resultant of my stopping force which would be vertical (once again, the direction of travel).

When a vehicle comes to an abrupt stop, the front suspension dives down and the rear suspension "lifts up" as a resultant of the moment generated from the breaking force times the height of the vehicle c.g.  No additional gravity loads are present, unless of course you are driving down hill when you hit the breaks.

Chris
-----Original Message-----
From: Robert Kazanjy [mailto:rkazanjy(--nospam--at)gmail.com]
Sent: Wednesday, May 17, 2006 2:28 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: axial braking load for bridges

On 5/17/06, Chris Towne <ctowne(--nospam--at)chaptech.com> wrote:
Dynamics really never was my thing, but how does braking increase the vertical load of the truck?  Sure it will change the distribution of the loading in the front and rear axle, but not the total vertical load.  The resultant force in breaking is in the direction of travel (horizontal), not vertical.

Chris Towne
-----Original Message-----
From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca]
Sent: Wednesday, May 17, 2006 1:56 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: axial braking load for bridges

Scott,

I can't answer your question about where in the code the stopping load is but 25% to 30% may not be enough.  It might do in combination with a lane load governing situation but if a single truck governs you should probably consider a panic stop for the truck.

Panic stop breaking generates about 70% of the vertical load for stopping force.

Regards,

H. Daryl Richardson
----- Original Message -----
Sent: Tuesday, May 16, 2006 6:22 PM
Subject: axial braking load for bridges

I have a old structural engineering manual and I thought I read in there that it said that bridge foundations need to be designed for an axial breaking load equal to 25% or 30% of the live load neglecting impact.  Is this right?  Where is this located in the AASHTO Bridge Design Specifications.

Thanks.
Scott.
Chris-