A	Cross-sectional area
E	Elastic modulus
F x1/2	Axial load at the two element ends
Fy1/2, Fz1/2	Load in y-direction and z-directions, respectively
G	Shear modulus
I	Moment of inertia
Ip,S = ∫ρS2dA	Polar moment of inertia about the shear center
Iyy, Izz	Moments of inertia about the y-axis and z-axis, respectively
I ωω	Warping constant
J	St. Venant torsion constant
[Ke]	Element stiffness matrix
[Ks]	Structural stiffness matrix
k tor	Torsional stiffness
L	Element length
My1/2, Mz1/2	Bending moments about the y-axis and z-axis, respectively
P	Axial compressive force
P cr	Buckling axial force
Q1, Q2, Q3, Q4 (Q1t, Q2t, Q3t, Q4t)	Deformation combination factors defining the possible deformation curve
Tc/t, Qc/t, Sc/t, Cc/t, TF, φc/t	Coefficients in the element stiffness matrix as functions of λc/t
T mid	Applied midspan torque
Ts, Tw	St. Venant torque and warping restraint torque, respectively
T(x), Bω(x)	Torque and bimoment at the cross-section considered, respectively
T1/2, Bω1/2	Torques and bimoments at the two element ends, respectively
uy1/2, uz1/2	Translational displacements in y-direction and z-direction, respectively
Δ, Fext	Element-end deformation vector and corresponding stress resultant vector
θy1/2, θz1/2	Rotation angles in the X-Z plane and X-Y plane, respectively
λc/t	Factor for the effect of axial force and St. Venant torsion
λc,cr	Factor for axial force and St. Venant torsion at the buckling state
λy, λz	Factors for axial force associated with the y-axis bending and z-axis bending, respectively
ρ S	Distance of a point in the cross-section to the shear center
σn	Assumed uniformly-distributed axial stress from the axial force
τ	Distributed torque
φ,ω	Angle and rate of twist, respectively
φ1/2, ω1/2	Angles and rates of twist at the two element ends, respectively