for general theory of shell and plates "theory of plats and shells" by S.timoshenko is recomendable. there you can find drivation of governing equations of deflection of circular plates on elastic foundation which is the basis for tubesheet design. However for a detail underestanding of UHX procedure more resources are requierd. some othere usefull papers and books are:
:Paper) Basis of the tubesheet heat exchanger design rules used in the french pressure vessel code. Osweiller, F.,Trans. ASME, J . Pressure Vessel Technol., 114, 124-131 (1992)
:BOOK) Heat Exchanger Design Handbook ,Kuppan T. ,Marcel Dekker, Inc., - New York BOOK)
:Book) Mechanical design of heat exchangers and Pressure vessule components. Singh K. P. and Soler A. I.Arcturus, 1984.