ASCE 7-05Chapter 15, Table 15.4-1 or 2?

[larsacious]

I am reviewing calc's where a 90 foot tall tower is supporting an industrial bridge. The tower consists of 9 levels of a 12 ft x 15 ft frame with inverted chevron bracing on each side.Since it is inverted chevron bracing which is similar to a building, I believe that table 15.4-1 Ordinary Concentrically Braced Frame with unlimited height and R=1.5 would apply. The calc's that I am reviewing are using Table 15.4-2 Trussed Towers with an R=3.0. I believe that this is incorrect because I this table is for structures that behave differently than the typical building structure but I am finding difficulty finding supporting documentation. I believe the trussed tower designation is for large unique shaped transmission structures with a varying moment of inertia that would behave differently. Any thoughts would be appreciated.

 

[Nonlinearer]

Table 15.4-2 refers to structures which are not similar to buildings & are mostly free standing like big vertical cantilevers. Whereas your case is similar to building, means you have vertical element (tower) and then the horizontal element which is your bridge thus more towards the building phenomenon. The stability of bridge and the tower may depend on each other which is also making it a structure similar to buildings. Thus your approach seems to be OK.

IR