I try to write simple code to solve simple frame structure using 6 degrees of
freedom bar elements.

I use Excel functions to assemble stiffness matrix. Inputs are columns of
element properties.
Sheet works OK on Excel 2003 and later. My friends can not run it on Excel 2000.
Problem might be in variable declaration of function k_global_sum input/output.
Inputs are columns of numbers and output is matrix.

Option Base 1 ' Set default array subscripts to 1.

Function k(E As Double, A As Double, i As Double, L As Double)
Dim KK(1 To 6, 1 To 6) As Double
KK(1, 1) = E * A / L
KK(1, 2) = 0
KK(1, 3) = 0
KK(1, 4) = -E * A / L
KK(1, 5) = 0
KK(1, 6) = 0
KK(2, 1) = 0
KK(2, 2) = 12 * E * i / L ^ 3
KK(2, 3) = 6 * E * i / L ^ 2
KK(2, 4) = 0
KK(2, 5) = -12 * E * i / L ^ 3
KK(2, 6) = 6 * E * i / L ^ 2
KK(3, 1) = 0
KK(3, 2) = 6 * E * i / L ^ 2
KK(3, 3) = 4 * E * i / L
KK(3, 4) = 0
KK(3, 5) = -6 * E * i / L ^ 2
KK(3, 6) = 2 * E * i / L
KK(4, 1) = -E * A / L
KK(4, 2) = 0
KK(4, 3) = 0
KK(4, 4) = E * A / L
KK(4, 5) = 0
KK(4, 6) = 0
KK(5, 1) = 0
KK(5, 2) = -12 * E * i / L ^ 3
KK(5, 3) = -6 * E * i / L ^ 2
KK(5, 4) = 0
KK(5, 5) = 12 * E * i / L ^ 3
KK(5, 6) = -6 * E * i / L ^ 2
KK(6, 1) = 0
KK(6, 2) = 6 * E * i / L ^ 2
KK(6, 3) = 2 * E * i / L
KK(6, 4) = 0
KK(6, 5) = -6 * E * i / L ^ 2
KK(6, 6) = 4 * E * i / L
k = KK
End Function

Function t_matrix(c As Double, s As Double)
Dim T(1 To 6, 1 To 6) As Double
For m = 1 To 6
For n = 1 To 6
T(m, n) = 0
Next n
Next m
T(1, 1) = c
T(1, 2) = s
T(2, 1) = -s
T(2, 2) = c
T(3, 3) = 1
T(4, 4) = c
T(4, 5) = s
T(5, 4) = -s
T(5, 5) = c
T(6, 6) = 1
t_matrix = T
End Function

Function k_global_sum(E, A, i, L, n1, n2, c, s)
'Dim ke(1 To 6, 1 To 6) As Double

'Dim ke_global(1 To 6, 1 To 6) As Double
Dim ke_global As Variant
Dim ke As Variant
Dim kk_global() As Double
'Dim T(1 To 6, 1 To 6) As Double
Dim T As Variant
Dim k_size As Integer
Dim el_no As Integer
Dim n_1 As Variant
Dim E_u As Double, A_u As Double, I_u As Double, L_u As Double
Dim c_u As Double, s_u As Double
n_1 = n1

k_size = Application.Max(n1, n2) * 3
el_no = UBound(n_1, 1)
ReDim kk_global(k_size, k_size)
For m = 1 To k_size
For n = 1 To k_size
kk_global(m, n) = 0
Next n
Next m
For u = 1 To el_no
'local stiffnes matrix see Pg.: 266
E_u = E(u, 1)
A_u = A(u, 1)
I_u = i(u, 1)
L_u = L(u, 1)
ke = k(E_u, A_u, I_u, L_u)

'transformation of local to global stifness matrix
c_u = c(u, 1)
s_u = s(u, 1)
T = t_matrix(c_u, s_u)
ke_global = Application.MMult(Application.MMult(Application.Transpose(T), ke),
T)

'index of elemnt DOF in global coord
index_global = Array(3 * n1(u, 1) - 2, 3 * n1(u, 1) - 1, 3 * n1(u, 1), 3 * n2(u,
1) - 2, 3 * n2(u, 1) - 1, 3 * n2(u, 1))
For m = 1 To 6
For n = 1 To 6
kk_global(index_global(m), index_global(n)) = kk_global(index_global(m),
index_global(n)) + ke_global(m, n)
Next n
Next m
Next u
k_global_sum = kk_global

End Function