${\mathbf{\beta }}_{\mathbf{1}}\mathbf{=}\mathbf{0.85}$	$\hspace{1em}\mathbf{F}\mathbf{o}\mathbf{r} {\mathbf{f}}_{\mathbf{c}}^{\mathbf{\prime }}\mathbf{\le }\mathbf{28} \mathbf{MPa}$
${\beta }_1=0.80$	$\hspace{1em}For f_c^{\prime }=35 \mathrm{MPa}$
${\beta }_1=0.75$	$\hspace{1em}For f_c^{\prime }=41 \mathrm{MPa}$
${\beta }_1=0.70$	$\hspace{1em}For f_c^{\prime }=48 \mathrm{MPa}$
${\beta }_1=0.65$	$\hspace{1em}For f_c^{\prime }\ge 55 \mathrm{MPa}$