no. 1

The obstacle problem for the biharmonic operator
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 6 (1979) no. 1, pp. 151-184. 
@article{ASNSP_1979_4_6_1_151_0,
     author = {Caffarelli, Luis and Friedman, Avner},
     title = {The obstacle problem for the biharmonic operator},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {151--184},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 6},
     number = {1},
     year = {1979},
     zbl = {0405.31007},
     mrnumber = {529478},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1979_4_6_1_151_0/}
}
Caffarelli, Luis A.; Friedman, Avner. The obstacle problem for the biharmonic operator. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 6 (1979) no. 1, pp. 151-184. http://www.numdam.org/item/ASNSP_1979_4_6_1_151_0/

[1] H. Brézis - G. Stampacchia, Remarks on some fourth order variational inequalities, Ann. Scuola Norm. Sup. Pisa, 4 (4) (1977), pp. 363-371. | Numdam | MR 481472 | Zbl 0422.35043

[2] L. Carleson, Selected Topics on Exceptional Sets, Van Nostrand, Princeton, 1967. | MR 225986 | Zbl 0189.10903

[3] J. Frehse, Zum Differenzierbarkeitsproblem bei Variationsungleichungen höherer Ordnung, Hamburg Univ. Math. Sem., Abhand., 36 (1971), pp. 140-149. | MR 330754 | Zbl 0219.35029

[4] J. Frehse, On the regularity of the solution of the biharmonic variational inequality, Manuscripta Math., 9 (1973), pp. 91-103. | MR 324208 | Zbl 0252.35031

[5] O.D. Kellogg, Foundations of Potential Theory, Dover Publications, New York, 1953. | Zbl 0053.07301

[6] N.S. Landkof, Foundations of Modern Potential Theory, Springer-Verlag, Berlin, 1972. | MR 350027 | Zbl 0253.31001

[7] J.L. Lions, Quelques Méthodes de Résolution des Problèmes aux Limites Non Linéaires, Dunod, Gauthier-Villars, Paris, 1969. | MR 259693 | Zbl 0189.40603

[8] J.L. Lions - E. Magenes, Problèmes aux limites Non Homogènes et Applicacations, vol. 1, Dunod, Paris, 1968. | MR 247243 | Zbl 0165.10801

[9] J.L. Lions - G. Stampacchia, Variational inequalities, Comm. Pure Appl. Math., 20 (1967), pp. 493-519. | MR 216344 | Zbl 0152.34601

[10] L. Schwartz, Théorie des Distributions, vol. 1, Herman, Paris, 1957. | MR 107812 | Zbl 0037.07301

[11] G. Stampacchia, Su una disequazione variazionale legata al comportamento elastoplastico delle travi appoggiate agli estremi, Boll. U.M.I., 11 (4) (1975), pp. 444-454. | MR 408406 | Zbl 0317.49033

[12] G. Cimatti, The constrained elastic beam, Meccanica, 8 (1973), pp. 119-129. | MR 337110 | Zbl 0281.73032