BR0
Structural
- Nov 10, 2010
- 54
I have never had any luck trying to use the provisions in ACI 318 Chapter 17.10.6.3 to limit the design force to less than the over-strength (omega) times the applied force. I was wondering if others have the same experience or am I missing something?
In (a), you can limit the force to what a ductile yield mechanism can deliver, considering over-strength and strain hardening. I typically use the over-strength values in ASIC 341, table A3.1 for these values. If my steel is A36, than Ry = 1.6 and Rt = 1.2. The ultimate strength 1.2 * Fu always is higher than omega*F.
In (b), I have been a bit baffled by these requirements. As an example, if I am trying to use a force-limiting mechanism from the crushing of a wood member from a fastener, that yield mode is typically 3 to 5 times higher than the Fastener Yield mode that governs the Fastener design. If I design the concrete anchorage portion by the member crushing load, it is always higher than omega*F.
Is (b) intended to allow you to limit to the design yield mode, in my case, the fastener yield, as long as there is this force-limiting mechanism?
In (a), you can limit the force to what a ductile yield mechanism can deliver, considering over-strength and strain hardening. I typically use the over-strength values in ASIC 341, table A3.1 for these values. If my steel is A36, than Ry = 1.6 and Rt = 1.2. The ultimate strength 1.2 * Fu always is higher than omega*F.
In (b), I have been a bit baffled by these requirements. As an example, if I am trying to use a force-limiting mechanism from the crushing of a wood member from a fastener, that yield mode is typically 3 to 5 times higher than the Fastener Yield mode that governs the Fastener design. If I design the concrete anchorage portion by the member crushing load, it is always higher than omega*F.
Is (b) intended to allow you to limit to the design yield mode, in my case, the fastener yield, as long as there is this force-limiting mechanism?
