AASHTO Bridge Question - Appendix A

[gipper]

Hi - I've got a question about Appendix A in the Standard Specifications for Highway Bridges, 17th Edition. The appendix title indicates the moments and shears are for simple spans, one lane. In some of the examples I've read, the values obtained from this appendix are divided by 2. Is this because it's a two-lane highway, or 1/2 the load is distributed to each girder?

 

[scottiesei]

Hi - I've got a question about Appendix A in the Standard Specifications for Highway Bridges, 17th Edition. The appendix title indicates the moments and shears are for simple spans, one lane. In some of the examples I've read, the values obtained from this appendix are divided by 2. Is this because it's a two-lane highway, or 1/2 the load is distributed to each girder?

It would help to have an example of what you are talking about. The girder distribution depends on the spacing.

 

[gipper]

I've attached the problem I'm referring to. Thanks for your help!

 

[DFMIL]

The live load moment is divided by 2 because the loads in Appendix A are Truck loadings (total HS-20 Truck load). The Wheel Load Distribution Factors (S/5.5 of this case AASHTO Table 3.23.1) were developed to maximize the loading to an interrior girder without preforming a transverse load distribution analysis. The load is for wheel loads which are 1/2 an axle load (or Truck Load). If you refer Figure 3.7.7 it may help to clarify Truck Loadings (I think the references stated above are correct).

 

[gipper]

Thanks for the info DFMIL, I appreciate it very much!

 

[JoeBoone82]

DFMIL hit it right on. You always have to watch that. Gives you an axle load, and sometimes need the wheel load or vice versa. It can get mixed up easily if you do not pay attention. I've had to have it explained to me a couple of times to make sure I get it right.

 

[Preparation Hell]

AASHTO has a new code for spring 08' exam