Nailing schedule for 2x10x16 treated fir beam

[cpy911]

I am trying to figure out the nailing schedule to combine two treated fir 2"x10"x16' boards together. Application is for three of these 2' feet apart, total of 4' wide for an ATV bridge spanning 12' allowing for 2' supported portion on each end. So far, the best I can come up with is use a nail rated for treated boards. (Not sure gauge or type of nail). Nail about 1.5" from the edges with another nail in the middle and do so at 16" intervals. I plan to put in construction adhesive before nailing it together. Do the nails go in on one side, alternate or does it matter?
CAD drawing below showing dimensions to the points that represent nails.

 

[dik]

I don't know if there is a standard... I've generally run with two lines of fasteners at 2'o/c, staggered 1'. I don't do much stuff in lumber, though...


-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SWComposites]

Based on gut feel, nails are too close to the end (potential splitting), and should be spaced closer together down the length.

How are you bracing these laterally?

 

[cpy911]

I will move the start of the pattern off the ends to about 4" and could do 12" on center pattern. I did read about staggering, but did not get much definitive information on if that makes a difference.

The bridge will be braced laterally similar to the design below...2x10 on the ends and in the middle. Was going to fasten those pieces on via 3" deck screws. Note the beams are 2x10 with plywood sandwiched in between. I am going to forgo that step as my loads will be way less than what this was designed for.

I will then put on 2x6 decking similar to the image below.

Below is what I am going to cross. I built up the sides with the landscape stones with soil and a layer of gravel behind the stones to allow for drainage.

 

[dvd]

[ol 1]
[li]Center span is more heavily loaded.[/li]
[li]No way to answer this question without understanding the loading, including dynamic loading from an ATV hitting the bridge at high speed and bottoming suspension.[/li]
[li]Choose whatever number you want, then load test the bridge after you are done.[/li]
[li]Use proper fasteners for the wood type - i.e., if pressure treated lumber, use a fastener which does not corrode.[/li]
[li]In general, this thing is more of a sculpture than a bridge.[/li]
[li]Why not get some tree trunks that are overly big to build your bridge?[/li]
[/ol]