Section H. 

 ENGINEERING AND ARCHITEGTUI 



l._\VIND PRESSURE. 



Bij W. C. KERXOT, M.A., C.E., F.R.G.S., Professor of Er.gineerhuj, 

 TJriiversiti) of Melbourne. 



Ill order that bridges, viaducts, chimney shafts, towers, elevated 

 water tanks, roofs, and other structures of an engineering nature 

 may be scientifically designed and the opposite evils of weakness 

 and undue expense both avoided, it is necessary that all forces 

 acting upon them should be known within a comparatively narrow 

 margin of error. As far as vertical forces are concerned this 

 condition is in all ordinary cases satisfactorily complied with. 

 The weight of the bridge, viaduct, chimney, tower, tank, or roof, 

 and also that of the railway train, crowd of people, or mass of 

 water, constituting what is usually called the live load, can be, 

 and is usuall}^ determined with a maximum error of not move 

 than 1 or 2 per cent. With regard, however, to the horizontal 

 forces due to that ubiquitous agent, the wind, and which in multi- 

 tudes of cases are the only important horizontal forces the structures 

 are called upon to endure, the present state of knowledge is most 

 unsatisfactory and discreditable. Publications professing to be 

 scientific authorities give arbitrary, inconsistent, and occasionally 

 unintelligible directions, while an examination of engineering 

 practice as exhibited in large and costly structures in Australia 

 and elsewhere reveals the most extraordinary inconsistencies. 

 Structures in exposed positions and offering large surface to the 

 wind are not infrequently absolutely devoid of wind bracing, 

 while others placed in sheltered localities and offering but little 

 surface are filled with costly lateral members having no possible 

 utility except as aids against wind pressure. 



Not many years ago a bridge over the Yarra, in Melbourne, 

 occupying a very sheltered position, was condemned as liable to 

 be overturned by the wind, and altered at great cost, although it 

 would have taken 90lbs. to the square foot to move it according 

 to the correct calculation, and 56lbs. to the square foot according 

 to the engineer that reported upon it, while chimneys and railway 

 vehicles that would overturn with not more than 30lbs. per square 

 foot were continually to be found in positions infinitely more 

 exposed. Furthermore, at the very time this lamentable waste of 



