385 



GIRDERS. 



GIRONDINS. 



breadth and depth vary, the vertical section should present a cubical 

 parabola. 2. If the beam should only have its own weight to support, 

 it should present in vertical section a double parabola, whose depth 

 should be as the square of the length. 3. If the beam should be 

 evenly loaded upon its surface, arid the upper surface be horizontal, 

 the lower surface should be a straight line meeting the upper surface 

 at the extremity ; the depth at the point of support being the one 

 required to resist the effort of the load and of its leverage ; and if an 

 additional load be placed at the extremity of the beam, the under 

 surface should present a parabolic curvature. 



For beams supported at both ends : 1. If the beam be loaded at 

 only one point, it should present a parabolic vertical section, falling 

 each way from the loaded point. 2. If the beam be loaded uniformly, 

 the upper surface should be elliptical, and the lower one straight. 

 3. In flanged beams evenly loaded, the upper surface should be made 

 parabolic instead of elliptical, and the sides of the flanges in plan 

 .should also present a parabolic curvature. 



In modern construction the openings between the points of support 

 and the loads to be supported, are often so far in excess of the powers 

 of wooden beams that it is necessary to resort to the use of iron in one 

 or another of ita forms ; and, practically, this is effected by the use of 

 .some modification of the flanged section. Numerous experiments have 

 been made for the purpose of ascertaining the best proportion to be 

 given to metal girders, a description of which will be found in Warr's 

 ' Dynamics ' before quoted ; in Barlow, on ' Materials and on Con- 

 struction,' 1851; Moseley's 'Engineering and Architecture,' 1843; 

 Weisbach's 'Mechanics of Engineering and Machinery,' 1848; Tate, 

 on the ' Strength of Materials,' 1850 ; Fairburn.on ' Cast and Wrought 

 Iron for Building Purposes,' 1854 ; Hodgkinson's new edition of 

 Tredgold, 1856; Morin, 'Lecons de Mcchanique Pratique,' 1846, c. 

 &e. From these authors it would appear, 1st, that the power of cast- 

 iron to resist a tensile strain is, when compared to its power of resisting 

 an effort of compression, as 1 to about 5707; 2nd, that the strength of 

 cast-iron girders is nearly in the direct ratio of their bottom flanges ; 

 3rd, that everything else being equal, the strength is nearly as the 

 depth. Mr. Fairbairn resumes the inquiry into the best form of iron 

 girder by giving the following formula for ascertaining the breaking 



weight: w = f , hi which w= the breaking weight applied in the 



centre ; a, the area of the bottom flange, which is made 6 times that of 

 the top one; d, the depth of the beam in inches; /, the distance 

 between the supports in inches ; and c, a constant, ascertained ex- 

 perimentally to be = 26. In the best cast-iron girders the proportions 

 of the other respective parts than the top and bottom flanges are, a. 

 the width of the bottom flange is made rather less than half the depth 

 of the girder in the centre ; b. the thickness of the centre web is made 

 < (jual to one half that of the bottom web, when that theoretical con- 

 dition can be attained without compromising the solidity of the casting, 

 or the quality of the metal. 



Compound cast-iron girders, in which the strength is obtained by a 

 combination of the resistances of cast and wrought iron, have been 

 found practically to be liable to so many objections, on account of the 

 different physical properties of the two states of the metal, as to have 

 led to the abandonment of their use. Cast-iron beams are frequently 

 cast in lengths of 40 feet, and even occasionally of 70 feet, though at 

 Home risk. Beyond those lengths, it is necessary to resort to the use 

 if either the arched construction, if cast-iron be used, to some descrip- 

 tion of framed girder, or to the use of wrought iron. 



In wrought-iron girders it is found that the proportionate resistance 

 of the top and bottom flanges to the efforts of compression and 

 extension differ notably from those which were previously stated to 

 prevail in cast-iron ; for the resistance of wrought iron to compression 

 ii only one half of its powers to resist extension, and the top flanges of 

 wrought-iron girders, therefore, should be made about double the 

 isectional area of the bottom flanges, instead of being as in cast-iron 

 girders only J of that dimension. Mr. Fairbairn gives the formula for 



the breaking weight of a wrought-iron girder, as follows; w = ^-_f, 



in which the same notation is followed as in the formula for cast-iron 

 girders ; but singularly enough hi working out his examples, instead of 

 making a=the area of the bottom flange, he attributes to it a value 

 derived from the mdlh. The coefficient, r, becomes, according to Mr. 

 Fairbairn, 75, when ordinary plate-iron girders are used, and 80, when 

 lioxwl girders are adopted; and, from the experiments he records, it 

 would seem that the coefficient of a lattice girder is nearly the same as 

 that of a plate girder. Exactly, it would appear to be 72. One of the 

 l>es$ rules for proportioning box girders is, firstly, to make the area of 

 the top equal to twice that of the bottom ; to make the thickness of 

 the sides from ,',, to ,!,-, of the depth of the tube, according to the 

 facilities for giving it lateral stiffness ; and then, as the span and the 

 depth are often given, to calculate the dimensions of the bottom flange 

 from the ratio, s : d :: i: w; in which 8= the span; rf=the depth; 

 ji=the cohesive strength of the bottom flange, calculated on the 

 assumption that it is equal to 1 5 tons on the superficial inch ; and w = 

 leaking weight in tona. This would, of course, give the weight 

 under which the girder would instantaneously break, and it should 

 'ore never be approached in practice. Indeed, if the girder 

 ABTH A.VD SCI. DIV. VOL. IV. 



should be exposed to rolling weights, or to sudden shocks, it should 

 present a resistance at least six times that of the maximum load able 

 to produce instantaneous fracture. 



The above remarks have been designedly made as practical, and as 

 devoid of abstract theory as possible, leaving that part of the investiga- 

 tion to RESISTANCE OF MATERIALS ; NEUTRAL Axis ; TUBULAR BEAMS. 

 The reader who may desire to study the theory of the subject 

 is, moreover, referred to the author before quoted ; or to Clark's 

 ' Britannia and Conway Tubular Bridges.' Framed girders are described 

 under TRUSS. 



GIRDLE, a band of leather, or some other substance, to gird up the 

 loins : from the Anglo-Saxon gyrdel or gyrdl, and that from r/yrdan, to 

 encircle or bind around. Girdlestead is an old English word for tho 

 waist, or place of the girdle. 



There are many passages in Scripture, as well as among the Greek 

 and Roman writers, illustrative of the girdle. It appears to have been 

 rarely worn by the Hebrews, except upon a journey. Elijah, we are 

 told, girded up his loins, and ran before Ahab. Girdles of sackcloth, 

 too, were used among the Hebrews as marks of humiliation and 

 sorrow. 



As a military ornament, it is noticed in Homer (' II.' iv. 135; v. 539, 

 &c.) ; and so universal was its use among the Greek and Roman 

 warriors, that Pitiscus, in his Lexicon, says, " Et Cinyulum pro ipsa 

 militia usurpatur." Military girdles were often given as rewards for 

 bravery. The magister equitum of the Romans wore a red girdle as a 

 distinctive badge. 



A girdle, or zone, was always worn by young women before marriage. 

 Hence, " Zonam solvere virgineam," to loose the maiden's girdle, in the 

 language of Catullus, was a phrase appropriate to the marriage cere- 

 mony. Festus says, " Ciugulum quo nupta cingebatur vir in leeto 

 solvebat." This girdle was usually of wool. The cestus of Venus was 

 the zone or girdle. It was worn round the lower part of the waist, 

 and concealed by the falling of the tunic. 



The term girdle was in ancient times very frequently used to express 

 the purse. An epigram in the ' Authologia ' shows that this was the 

 custom among the Greeks ; and it is in this sense that we must under- 

 stand the fragment of Gracchus's speech to the senate, upon his return 

 from Sardinia, quoted in Aulus Gellius, lib. xv., c. 12 : " Itaque Quirites, 

 quum Romam profectus sum, zonas, quas plenas argenti extuli, eas ex 

 provincia inanes retuli." 



In Mark vi. 8, when our Saviour sent his Apostles out to preach, he 

 commanded them to take no scrip, no bread, no money in their purse : 

 the Anglo-Saxon version reads, ne fcsh on /tyra yyrdlum, " nor money 

 in their girdles." Hence probably arose the custom, formerly used in 

 England, for bankrupts or other insolvent persons to put off and 

 surrender their girdles in open court. 



Various passages in the classic writers might be adduced to show 

 that to go without the girdle was considered disreputable, and bespoke 

 a dissolute person. Aubrey, in one of his manuscripts, says that 

 " Ungirt, unblessed," was an English proverb before the civil wars of 

 Charles I. 



Among the ancient companies of London, that of the Girdlers was 

 incorporated as early as August 6, 1449, 27 Henry VI., and it has been 

 supposed that these were the makers of girdles. Their armorial ensigns 

 are, ' Per fess, az. and or, a pale counter-changed, each piece of the first 

 charged .with a gridiron of the second. Crest, the demi-effigy of St. 

 Lawrence, holding in the right hand a gridiron, and in the left a book." 

 Strype, in his edition of Stow's ' Survey,' conjectures, from their arms, 

 that the girdlers were originally a fraternity of St. Lawrence. But, as 

 Mr. Thorns, in his edition of Stow, suggests, these arms seem to indicate 

 pretty clearly that the girdlers were really makers of the girdles, or 

 griddles, still used for baking oaten cakes ill every household in 

 Scotland and much of the north of England. 



GIRONDINS was the name given to a political party which formed 

 a section of the second National Assembly of France, called " Legis- 

 latif," in contradistinction to the first or " Constituante," which 

 framed the constitution of 1791. The members of this party were 

 mostly returned by the departments of the west and south ; and as 

 their leaders, Vergniaud, Guadet, Gensonne', &c., represented the 

 department of La Gironde (Bordeaux), the party took the name of 

 Girondins. They showed themselves from the first hostile to the 

 monarchy, and they stood opposed to the constitutionalists, who wished 

 to maintain the constitution of 1791. Tho Girondins were republicans, 

 who had formed notions of liberty on classical models, such as they 

 were then conceived by ardent young men. They had among them 

 some brilliant orators, and several accomplished and amiable indivi- 

 duals ; but as a political party they placed themselves in a false posi- 

 tion, and they did great mischief to others. By their opposition to the 

 constitutionalists they weakened the strength of the middling classes, 

 and left the field open to those who, like Danton, addressed themselves 

 to the passions of the lower orders. They at one time obliged the 

 king to choose a ministry from among themselves, including Roland, 

 Servan, Claviere, and Dumouriez, and they seemed for awhile recon- 

 ciled to the constitutional monarchy ; but a schism broke out among 

 them, and they resigned. Soon after came the scenes of June and 

 August, 1792, which the Girondins indirectly sanctioned, and which 

 destroyed the monarchy in France. In the Convention the Girondina 

 for the most part voted for the death of the king ; they tried indeed to 



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