Page 68 - Between light and shade

between light and shade, TRANSPARENCy and reflection

Any form of surface (with zero, positive or
negative Gaussian curvature) 65 is geometrically
achievable using triangles or trapezoids (with flat
glass, as in the following examples, or conical, as
for Europa’s “lantern”, being the usual approxi-
mation).

Nevertheless, the use for which a glass canopy
is intended, its size and the physical perfor-
mances 66 that are expected of it, as well as the
quest for the lightest possible structure (within
the bounds of flexibility imposed by the fragility
of the glass) restrict this freedom.

Furthermore, the structure must be neither
too slender vertically nor too low profile to limit
the effects of wind, on the one hand (horizontal
force of the order of 1 kN/m²), and dead load, on

65 TgRrlwaaeh2hrdnkeitiecnuogrhosaetwilohosffnmeotchtareuaemstrnrtpvgyhoraeeoftonudapftrurasepicunclatracunofniardpfevcatReeahl.dt2ec,Teuslihaaturstcevrthsrafemeatroufcoa(ferKlreilietesss=,.sdftTp1o,e/ohrmfiReiqnne1Gutae×sasad,udu1o/brrsreiRyscdiba2Rsy)pnu1d,e1rc/riefutpafRsriecn1vlneaaaesdnrtsg(iudctterhhus1eee-/t,
three-dimensional equivalents of two-dimensional ellipses,
pelalripabtiocl,ahsyoprehrybpoelircboorlaps)aKrab=o0licwchyelrienRde1 risoirnfaincoitne,eaws for an
> 0 where R ith an
elliptical base; K an ellipsoid, 1aannedlliRpt2 iacrpeaoranbtohloe isdaomr ea side of
the surface, as for hyper-
bofotlohiedsoufrftawcoe,barsafnocrhaehs;yKpe<rb0owlohideroefRo1naenbdrRan2 cahre(aodnieaabcohlos)idoer
a hyperbolic paraboloid (a saddle), illustrations and equations
available at www.wikipédia “quadric”. This is also defined as
mean cur vature: t1o/Rfimre=b(e1h/ aRv1i+ou1r/. R2) /2.
66 This also relates

68