Definition of secondary members
Definition of secondary members
(OP)
I am working on a steel box truss for an overhead sign structure. I am using the AASHTO "LTS-3" design code along with the AASHTO Standard Specs for Highway Bridges, since this is an ASD design (lucky me). I am also referring to the AISC code.
My question is about the connection for web angles bolted to gusset plates, which are welded to a tubular chord member. The AASHTO Std code §10.24.1.6 states "Bolted bearing-type connections ... shall be limited to members in compression and secondary members."
Can webs be considered as secondary members in a truss? I cannot find any solid definitions regarding "secondary members" in the AISC or AASHTO Std codes. The AASHTO LTS-3 code mentions it once in §1.9.2 .
The peak loads are about 50 kips tensile force, and the 'standard' design calls for only two bolts per web. As a result, I will require 1-3/8" A325 bolts if limited to friction-type connections. As the design requires 5x5x½ angles, this violates AASHTO Std code §10.24.4.2, requiring the fastener diametre to be 25% or less of the leg width.
Thanks for you input!
My question is about the connection for web angles bolted to gusset plates, which are welded to a tubular chord member. The AASHTO Std code §10.24.1.6 states "Bolted bearing-type connections ... shall be limited to members in compression and secondary members."
Can webs be considered as secondary members in a truss? I cannot find any solid definitions regarding "secondary members" in the AISC or AASHTO Std codes. The AASHTO LTS-3 code mentions it once in §1.9.2 .
The peak loads are about 50 kips tensile force, and the 'standard' design calls for only two bolts per web. As a result, I will require 1-3/8" A325 bolts if limited to friction-type connections. As the design requires 5x5x½ angles, this violates AASHTO Std code §10.24.4.2, requiring the fastener diametre to be 25% or less of the leg width.
Thanks for you input!





RE: Definition of secondary members
Primary member: Takes calculated stresses - on the load path of your structure.
Secondary member: Does not take calculated stresses on the load paths, but simply provides bracing to the primary members to keep the primary members from buckling.
RE: Definition of secondary members
Secondary members as you are probably aware can be connected with bearing type connections. This should ease your 1-3/8" bolt issue.
RE: Definition of secondary members
This confirms my thoughts that the webs are essentially holding the chords apart, and are indeed secondary members.