# node local coordinate system

**Question:**

Dear sir,

Refer to the model attached.

I defined the nodal local coordinate system at the abutment supports such that it lines up with the bridge skew.

I then defined the restraints at these nodes to be free in local x.

When I ran the analysis, I see some reaction in local x, say, under "testing lateral load". How could this be possible?

thanks

**Answer:**

Hi,

It is happening because of numerical error caused by huge modulus of elasticity of material "4: Rigid". It is 2e+15 kN/m2. Usually, it is rigid enough if you define 1000 times of normal modulus of elasticity. For example, the modulus of elasticity for Conc C30 is 2.497e+7 kN/m2. Then, 2e+10 kN/m2 would be sufficient to represent rigid material property and also it can avoid the numerical error.

After the change above, I can see zero reactions in the local x direction as shown below.

Regards,

DK Lee

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DataImage2.jpeg | ||

DataImage93.jpeg | ||

Model 3.mcb |