SUPRAÎNĂLŢÁRE s.f. 1. Acţiunea de a supraînălţa şi rezultatul ei. ♦ Diferenţă de nivel între cele două margini ale unei şosele sau căi ferate în curbă pentru diminuarea sau anularea forţei centrifuge. 2. (Constr.) Mărire a săgeţii unui arc de boltă prin aşezarea capetelor arcului deasupra nivelului zidurilor de sprijin. [< supraînălţa].

http://dexonline.ro/search.php?cuv=suprainaltare

În contextul tău cel mai probabil este vorba de al doilea sens, ceea ce este "stilting" în engleză.

stilted arch
(arc supraînălţat)
An arch whose curve begins above the impost line.

http://www.answers.com/topic/stilted-arch-1
(este şi o imagine acolo)


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Note added at 30 mins (2009-03-06 11:20:19 GMT)
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This stilting of the longitudinal arches was from the beginning almost invariable in France; structurally, it concentrated the vault thrust on a comparatively narrow vertical line, where it could be easily handled by the flying buttress; it permitted the largest possible window area in the clerestory, while the composition of lines and the delicately waved or twisted surfaces were so beautiful in themselves that, once discovered, they could not beabandoned by the logical and beauty-loving Franks.

http://www.newadvent.org/cathen/06665b.htm

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Note added at 32 mins (2009-03-06 11:21:34 GMT)
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n England vaults were generally constructed with continuous level ridges, instead of in this domical form, and the difference in height between diagonal and transverse ribs in a square vaulting compartment was equalised by " stilting " the latter or by making the diagonal rib a segment of a larger circle than that of the longitudinal and transverse ribs, which were semicircular as explained on the illustration

http://www.oldandsold.com/articles23/architecture-54.shtml