The code for the 3d cantilever beam using solid elements is shown below.

```
from dolfin import *
L = 5000.
H = 600.
W = 300.0
mesh = BoxMesh(Point(0, 0, 0), Point(6, 2, 1), Nx, Ny, Nz)
E = Constant(1e5)
nu = Constant(0.3)
mu = E/2/(1+nu)
lmbda = E*nu/(1+nu)/(1-2*nu)
def eps(u):
return sym(grad(u))
d = mesh.topology().dim()
def sigma(v):
return lmbda*tr(eps(v))*Identity(d) + 2.0*mu*eps(v)
V = VectorFunctionSpace(mesh, 'Lagrange', degree=1)
u = TrialFunction(V)
v = TestFunction(V)
rho_g = 1e-3
f = Constant((0, -rho_g,0))
a = inner(sigma(u), eps(v))*dx
l = inner(f, v)*dx
def left(x, on_boundary):
return near(x[0], 0.)
bc = DirichletBC(V, Constant((0.,0.,0)), left)
u_sol = Function(V, name="Displacement")
solve(a == l, u_sol, bc)
```

Can you pls share some references for modifying it for the beam element?