Resistant Moment
===================================
* :math:`d`: Effective depth of the foundation.
* :math:`b`: Width of the foundation.
* :math:`As`: Area of steel in the section.
* :math:`\epsilon_t`: Total strain.
* :math:`\epsilon_{ty}`: Yield strain.




.. math::
   \beta_1 = \left\{
   \begin{array}{lr}
   0.85, & 17 \leq f'_c \leq 28 \\
   0.85 - \frac{0.05(f'_c-28)}{7}, & 28 < f'_c < 55 \\
   0.65, & f'_c \geq 55
   \end{array}
   \right.


.. math::

   \phi = \left\{
   \begin{array}{lr}
   0.65, & \epsilon_t \leq \epsilon_{ty} \\
   0.75 + 0.15 \frac{\epsilon_t - \epsilon_{ty}}{0.005-\epsilon_{ty}}, & \epsilon_{ty} < \epsilon_{t} < 0.005 \\
   0.9, & \epsilon_{t} \geq 0.005
   \end{array}
   \right.


.. math::

   \begin{align*}
   a &= \frac{As f_y}{0.85 f'_c b} \\
   c &= \frac{a}{\beta_1} \\
   \epsilon_t &= 0.003 \frac{d-c}{c}
   \end{align*}


.. math::
   M_u = \phi As f_y \left( d - \frac{As f_y}{1.7 b f'_c} \right)