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# Re: Which method do you like for calculating deflection

• To: seaint-seaosc(--nospam--at)mail-list.com
• Subject: Re: Which method do you like for calculating deflection
• From: TJ Fu <tzujfu(--nospam--at)gmail.com>
• Date: Thu, 21 Mar 2013 15:20:38 -0400
• List-subscribe: <mailto:SEAINT-SEAOSC-on@mail-list.com>

```For Example:  Calculate the max. +M in span 1 of 100'-125'-100' Continuous
Spans ....

·         Attached is the M&V influence lines for 100'-125'-100' spans

·         The maximum moment coefficient will be 20.76 at 0.4 point

·         Apply the maximum wheel load , say 100k, at 1.4 point: +M1= 100k
x 20.76 = 2,076 'k

·         Apply 2nd wheel load, say 80k, at 10' away --> Location = 1.4 +-
10' / 100' = 1.3 or 1.5 point

·         The moment coefficient will be --> 15.37 at 1.3 point, and 16.39
at 1.5 point (governs)

·         The moment for 2nd wheel load will be: +M2 = 80k x 16.39 = 1,311
'k

·         Apply all the other wheel loads from all the cranes

·         Final +M = M1 + M2 + M3 ....

Similarly, you can calculate the maximum moments at any other locations -
maximum -M at interior supports and maximum +M in span 2.

TJ
On Thu, Mar 21, 2013 at 11:39 AM, Gary L. Hodgson and Assoc. <
design(--nospam--at)hodgsoneng.ca> wrote:

> I don't see how influence lines can help me with rolling loads. I know
> bridges are subject to rolling loads but how do you choose the worst
> location for 2 or 3 cranes each with different wheel loads and variable
> spacing between them.
>
> I have a customer now who has a 15 ton crane and 7.5 ton crane and wants
> to know how close he can operate them while fully loaded and then only
> 50% loaded for one or the other.
>
> Gary
>
>
> On 2013/03/16 3:16 PM, TJ Fu wrote:
>
>> Dealing with moments and shears for continuous spans (constant I), I
>> always use M&V influence coefficients from AISC “Moments, Shears and
>> Reactions for Continuous Highway Bridges”. That will give you
>> maximum/minimum M&V at any point. For any odd span combinations or
>> variable I spans, you could use my programs.
>>

Truncated 1002 characters in the previous message to save energy.

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