Steel Bracing Design
Steel Bracing Design
(OP)
I am designing a steel bldg. with chevron and "x-bracing" using a structural analysis/design computer program.
The bldg. columns have been analyzed with the bracing "inactive" to insure they will support all the gravity load. My question is do I need to design the compression bracing for gravity load in addidtion to the lateral loads? If I were designing the bldg. with tension-only bracing I would not be concerned with "failure" of the compression side brace in, for instance, an x-braced bay, but when I am relying on compression bracing to share the load with the tension brace it seems the compression brace needs to support all load it will see--including gravity loads. Is this correct thinking? Thanks for any suggestions.
The bldg. columns have been analyzed with the bracing "inactive" to insure they will support all the gravity load. My question is do I need to design the compression bracing for gravity load in addidtion to the lateral loads? If I were designing the bldg. with tension-only bracing I would not be concerned with "failure" of the compression side brace in, for instance, an x-braced bay, but when I am relying on compression bracing to share the load with the tension brace it seems the compression brace needs to support all load it will see--including gravity loads. Is this correct thinking? Thanks for any suggestions.





RE: Steel Bracing Design
1) The compression braces are not designed to carry gravity loads. The compression braces are expected to buckle in a large seismic event and the gravity loads they were initially supporting will be transferred to the adjacent beams and columns.
2) The compression braces are designed for gravity loads. This is a conservative approach. If used, the beams and columns should still be designed to support the entire gravity load in recognition of the fact that the braces may buckle.
RE: Steel Bracing Design
RE: Steel Bracing Design
If seismic design is required and you follow the code minimum design requirements, your compression braces will indeed buckle in a design-level event. The lateral system is designed with a reduction factor that reflects the ductility and energy dissipation capacity of the system. The design forces would have to be multiplied several times in order to preclude buckling.