from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The upper or exterior curve of an arch.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The outer or upper curve of an arch.
from the GNU version of the Collaborative International Dictionary of English
- n. The exterior curve of an arch; esp., the upper curved face of the whole body of voussoirs. See intrados.
from The Century Dictionary and Cyclopedia
- n. The upper or convex surface of an arch or of a vault.
- n. The outer curve of a voussoir. See arch, 2.
- n. In mech., the locus of the lower ends of wires, of uniform weight per unit of length, hanging down from points on a cord which is perfectly flexible, inextensible, and without weight. When the wires are equally distant from one another and of equal length, the extrados is a parabola.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the exterior curve of an arch
The drawing of the arches, on the elevation, also shows exactly how the thickness of the arches is included within a precise number of earth block courses, from the intrados at the springpoint to the extrados at the keystone.
These spans are dictated by the coursing of the arches: the aim is to achieve high quality masonry with the height of the arch, from the intrados at the spring point to the extrados at the key-stone, contained within the height of two courses of earth blocks.
Infilling the extrados of the vaulting using stabilized cement mortar should also be carried out in such a way as to ensure a correct balance of the post-compression which will finally stabilize the vaulting.
The reinforcement consists of arch and transverse bars; the arch bars are spaced 6 ins. on centers 2½ ins. from both extrados and intrados, and the transverse bars are spaced 24 ins. on centers inside both lines of arch bars.
The four sides of the mold formed the extrados, the intrados, and the two ends of the block; the other two sides being left open.
The concrete was then carried up to the springing lines, the arch centers in two pieces were placed; the arch bar of the reinforcement was placed and the extrados forms erected up to the 45° lines, all as shown by Fig. 259.
In laying the brick in the arch, the five courses of the ring were carried up as high as the void between the extrados and the rock would permit and still leave a working space in which to place the water-proofing.
A small ditch lined with loose 6-in. vitrified half pipe was provided in the top of the sand-wall to collect the water from the extrados of the arch and lead it to the top of the drains.
By reference to Plate XII it will be seen that the water-proofing, which in the concrete-roof tunnels extended the full height of the sides to the 15° line, was carried in the brick-roof tunnels completely around the extrados of the arch.
The concrete arch was placed in sections, from 25 to 50 ft. in length, with a rather wet mixture and a back form on the steep slope of the extrados.