In the formulation of Euler-Bernoulli Beam Theory, there are two degrees of freedom at a point, w and dw/dx. Typically, the finite element model of this theory uses cubic polynomial for interpolation of $w$ using a two noded element as given in Chapter 5 of this book [1]. This element is a subparametric because the geometry is represented by low-order elements than those used to approximate the dependent variable. I need a reference where I can find the FE model for this problem using isoparametric elements. [1]: https://www.amazon.com/dp/0072466855/?tag=pfamazon01-20
Have you researched any of the beam element formulations for specific FEA packages? Ansys's element documentation is fairly robust for example, you can read more about them here: Sharcnet.ca: ANSYS Beam and Link Elements