AASHTO Deck Span?

[scottsman]

REF: NCEES Structural 1 Sample Questions & Solutions © 2008, problem 129

AASHTO 4th edition with 2008 interm sections

Problem 129, effective span between bridge girders question is not consistent from what I have found in the 4th edition with Interm 2008 sections. The practice book references the 3rd edition but I'm not confident that what I have found in the 4th edition is the right answer. Nor can I find in chapter 4 within the 4th edition the same method that they used to solve the problem.

In the 4th edition section 9.7.2.3, Effective length is the distance between flange tips + the flange overhang, taken as the distance from the extreme flange tip to the face of the web. Basically for a W shape this is centerline of beam to centerline of beam.

The answer provided for problem 129 takes the clear span 8' - 16.5 (flange width) + 16.5/2 ~ 7'-4".

Can anyone point me to the correct section in the 4th edition that would correctly answer this problem?

Thank you

 

[Hromis1]

Scottsman, watch the EQ problems as well. many changes there.

the section you referenced is only for empirical design. look at page 4-24. Extreme bottom of the page. Center to center of beam spaceing minus 1/2 bf...(if both beams are the same). This is only for certain types of bridge cross sections.

of course I am not a bridge person...I could be mis-understanding this.

hromis1

 

[IL_Struct_Eng]

page 4-24 is indeed the place to find the effective spans for the different types shown in Table 4.6.2.2.1-1

 

[scottsman]

Thank you for the Reply!

I reviewed page 4-24 and i can't find were it addresses effective span. It addresses how to determine the distribuition of wheel loads on an equivalant strip of deck and how to apply this to the primary/secondary beam structure.

Other than for the emperical design method of 9.7.2, where does AASHTO state what should be used as the span between bridge beams when designing reinforcement?

Im coming to the conclusion it is the center to center spacing of the supports.

Any feedback would be great!

 

[deviationz]

Read the bullet points on page 4-24 very carefully. It tells you where the moment occurs. Center to center spacing - (2* this distance) = effective span length. It appears very clear. Think it over, its pretty straight forward.

 

[SNP]

Sorry i may not answer the original question here.

but please Refer to NCEES Errata. That question/solution is revised in Errata.

http://www.ncees.org/Exams/Study_materials/Errata.php

There are lot of erros in this book.