If we output this bending moment then it completely creates a haywire in our design. This flipping in the moment values is to account our change in local axis. As you can see the bending moment is completely flipped in the opposite direction for member 2 compared to member 1. Figure 5: Bending Moment Plotįigure 5 is the bending moment diagram for the above beam. This is a crucial information for us to determine whether a beam or a column or diagonal member is in negative or positive force or moment state even if local axes are flipped. This concludes that SAP2000’s deflection is independent of local axis modification. SAP2000 output is U3 at some negative value. The beam should deflection downward with a parabolic curve with vertex at the midspan of each section, thus the value should be a negative value in Z axis. So X = U1, Y=U2 and Z=U3 direction is the naming for the deflection axis.
SAP2000 uses global axis for the deflection diagram. Fig 3: Deflection diagram with max deflection value on first memberįig 4: Deflection diagram with max deflection value on second memberįrom Figure 3 and 4, we can see the deflection values at the max deflection point of member 1 and member 2. Upon loading 1 kip-ft of uniformly distributed load in this beam, below is the deflection diagram of the beam. The behavior in terms of deflection, shear and moments. Then for our study purpose, we rotate the local axes of the second member by 180 degrees with respect to local axes 1 (red axis), you can see the change in the local axes in the above diagram.Īs from theoretical concept, if we apply loading in this beam, no matter what be the local axes, the structure should behave same for the loading condition. First they are kept with default local axis direction given by SAP2000. 2 member continuous beam in SAP2000Ī 2 member continuous beam is taken in consideration for our example. Importance of global and local coordinate system is a talk of another day, but this article is about how local axes affects the required parameters in SAP2000. That’s why, local coordinate system was referred to used to analyse any parameter efficiently. Whether be it in deflection, bending moment, shear forces, torsion, strains or stresses, the directional polarity should be consistent.įor finite element structure, if we use global coordinates the uniformity in the direction is observed but it will be too computationally complicated to analyse in global coordinate. Directional polarity has been the most fundamental thing one should learn before digging deep into the numerical values of any problem.