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Although this forum discusses about very advanced level issues of structure designing of concrete and steel. I have a very basic sort of question which i was unable to find in literature so any help from anyone will be highly appreciated. The misunderstanding in my mind is that when we test concrete cylinder in compression testing machine as per ASTM standards. The dimensions of cylinders are 1 foot height by 6" diameter. We use this concrete strength of concrete in designing of beam and designing of any structure of concrete regardless of stress/strain pattern. f'c used in designing formula is as per strength of cylinder of ASTM. If we change the size of cylinder as we use 8" height and 4" diameter the strength of concrete cylinder increases a bit and it is further increased if we use cubes instead of cylinders. Some testing standards allow to use specimen other than ASTM. Conclusively, the strength of concrete is highly dependent upon the type and dimensions of concrete specimen. My questions are 1)- What will be f'c of cylinders sizes other than ASTM sizes used in designing formulas? 2)- If ASTM cylinder size truly depicts the concrete actual strength in structure then is there any literature available on this or some research paper? Regards

Assalam o alaikum. ACI 21.1.4.2 says, Specified compressive strength of concrete should not be less than 3000psi. I am confused whether is it just for FRAME MEMBERS and members resisting lateral forces or this is for all members i.e. slabs etc?