Kindly share any material on how to design a tunnel on sap2000. Attached is a pic of a model i found somewhere. this person has braced the tunnel by using "link supports" which I have no idea about since i have ever used them. Whats the purpose of these supports? Its properties have terms like coupled or uncoupled stiffness. and factors for line area and solid springs etc. That image is attached too and the values this person has entered are 1000 and 1000000. Its going above my head. Please guid