The above value of kc is valid only if a > 0, since the deduction assumes that there is a part of the cross section which is in compression. In order to approximate kc in the following figure the value of a=z/h is plotted against the adimensional axial force v = -Ne±- within a range of +0.03 to -0.22. Over bhfck
0.03, there is no compression block and under -0.22 there is no need to provide minimum reinforcement according to the principle established above. Factor alpha=z/h as a function of adimensional axial force
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