The deviation between the ANSYS forces and the Shigley forces may be reduced if you make a few changes to the ANSYS model.

Change the diameter of the 14 mm bolts to 12 mm to match the other bolts.

Use an End Release on one end of each bolt so it does not carry any moments (forces only).

Make sure the bolt material is different from the I-beam and plate materials.

Edit the I-beam and plate material properties to increase the Young’s Modulus by a factor of 1000.

Please reply with results from these changes and show the new values of Deviation (%).