farhhhan

Let me explain my question in a different posture.. Suppose we have three bar sizes #8, #4 and # 11 for grade 60 steel. If we experiment over the Yielding strength, it will come out to be 60 ksi for all sizes and we use this strength in our design formulas and all. But in the case of concrete we use ASTM Standard cylindrical strength in all our design formulas, like strength of column is 0.85 x f'c x a x b (let a and b be the column dimensions). Here f'c will be 28 days cylindrical strength. But changing the cylinder dimensions will be change the strength of concrete specimen suppose we have standards of 6" cube, then strength will be different and using above formula for column will over estimate the columns nominal strength. Does we have any reduction factors if we use different concrete specimen?? Does the ASTM Cylinder size truly depicts the actual strength of concrete in actual structure? If it do so then is there any research paper over it?

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