Shear-friction design method or Appendix D? Both?
Shear-friction design method or Appendix D? Both?
(OP)
I have a question on when to use the shear-friction method or Appendix D. One particular instance I can think of would be for a suspended concrete slab on top of a concrete basement wall. It seems to me like shear friction could be used, but there are no reductions for edge distances, etc. ACI 318-08 11.1.6 states that it can be applied at "an interface between two concretes cast at different times". So my questions are:
1. Is the shear friction method acceptable for both in plane and out of plane forces on our hypothetical basement wall? If I try to make this work with appendix D I will get much tighter dowel spacing than with the shear-friction method.
2. If the incorrect dowels are installed and I have to come back and epoxy additional dowels then Appendix D would have to be used, right?
Any input is appreciated. I am just trying to define when one method can be used versus another.
1. Is the shear friction method acceptable for both in plane and out of plane forces on our hypothetical basement wall? If I try to make this work with appendix D I will get much tighter dowel spacing than with the shear-friction method.
2. If the incorrect dowels are installed and I have to come back and epoxy additional dowels then Appendix D would have to be used, right?
Any input is appreciated. I am just trying to define when one method can be used versus another.





RE: Shear-friction design method or Appendix D? Both?
RE: Shear-friction design method or Appendix D? Both?
RE: Shear-friction design method or Appendix D? Both?
RE: Shear-friction design method or Appendix D? Both?
Thanks for the response. So then for this situation it sounds like shear friction would be ok. If we did have to add dowels after the fact and epoxy per appendix D, how would you arrive at the appropriate tension force to design for? Is there a way you could back calculate it from the friction factor?
RE: Shear-friction design method or Appendix D? Both?
RE: Shear-friction design method or Appendix D? Both?
"When moment acts on a shear plane, the flexural tension stresses and flexural compression stresses are in equilibrium. There is no change in the resultant compression Avf fy acting across the shear plane and the shear-transfer strength is not changed. It is therefore not necessary to provide additional reinforcement to resist the flexural tension stresses, unless the required flexural tension reinforcement exceeds the amount of shear-transfer reinforcement provided in the flexural tension zone. This has been demonstrated experimentally."
Lets say your
Required Avf = 0.14 in^2
Required Ast = 0.16 in^2
Required Asmin = 0.31in^2 T & B(in say a 2' deep slab cold joint)
Now you're providing a # 5 for temperature where you could've gotten by with a # 4 for shear and moment. I would match the dowels with # 5 reinforcing for ease of construction.
Would i interpret 11.6.8 to mean i need to develop this # 5? - No
The bar that needs to be developed for fy is the bar that's providing the clamping force Avf Fy. Since bars only come discrete sizes, in order to ensure that my Avf develops Fy, i am going to develop the bar for T = Avf x fy... Not a (#5)0.31 x fy
11.6.8 applies for Avf only unless your Ast requirements are significantly higher than your Avf in which case you may want to develop the differential (Ast - Avf) per Chapter 12
RE: Shear-friction design method or Appendix D? Both?
ACI 318 11.6.8 requires that shear friction reinforcement be anchored for fy, so the 12.2.5 reduction for ld does not apply. The commentary in R11.6.8 is very clear about "full tensile anchorage on both sides".
--
In order for the assembly to remain ductile, you must fully develop the bars used, not just the amount of load expected. If ductility is not a concern and the appropriate factors are used, you may not need to fully develop the bar, but be aware that the behavior will not be the same as a fully developed bar of smaller diameter.
RE: Shear-friction design method or Appendix D? Both?
I havent thought about it the way you stated it. So your saying if my avf required was half of Ast required then I would only end up developing 1/2fy?