Søgning i bogen
Den bedste måde at søge i bogen er ved at downloade PDF'en og søge i den.
Derved får du fremhævet ordene visuelt direkte på billedet af siden.
Digitaliseret bog
Bogens tekst er maskinlæst, så der kan være en del fejl og mangler.
CHAPTER VI.
BREAKWATER DESIGN.
Importance of Breakwaters—Régime— The Sea Ware—Form, Height, and Length—
Breaking Waves—Dynamical Value—Measurement of Wave Stroke—Dynamometers—
Recorded Pressures— Instances of Wave Action—Classification of Breakwaters—Com-
parison in Cost of Construction and Maintenance and in Efficiency—Conditions of
Stability—Stresses in Wall Breakwaters—Summation of Type Characteristics—Ex-
amples of Breakwater Design at Genoa, Marseilles, Algiers, Sandy Bay, and Tynemouth.
Thk most important work, as also the most prominent and fundamental
feature, in connection with artificially sheltered harbours and roadsteads, is
the Breakwater. As the name implies, its function is to break up and
disperse heavy seas, preventing them from exerting their destructive influence
upon the area inclosed for the reception of shipping. Manifestly, then, a
breakwater must be characterised by great strength and stability. The
safety of helpless vessels and the efficiency of the harbour as a place of
refuge are bound up in the essential permanence and immobility of the
breakwater.
Before proceeding to an investigation of the principles which underlie the
design of breakwaters and by which these objects may be attained, we have
to pass in review the conditions and environment to which such structures
must conform and the general circumstances attending their construction and
maintenance.
Régime of Breakwaters.—Structures erected within the domain of the
sea and submerged for the greater part of their bulk, if not altogether, are
subjected to physical experiences of a nature very different from those which
are characteristic of structures on land. The fact of immersion materially
modifies the effect of gravity upon a body, reducing its apparent weight to a
very considerable extent. That this condition must be applicable to mari-
time structures is obvious, unless, indeed, the foundation be absolutely
impervious and there be an entire absence of duets for the penetration of
water—conditions which, in many cases, are quite unrealisable, and in most
are so imperfectly guaranteed as to render them inacceptable as working
hypothèses. The solvent properties of water combined with the extreme
mobility of its particles, cause it to act in a most prejudicial and injurious
manner upon much of the material used in breakwaters, as well as upon the
foundation itself, and these merely mechanical effects are supplemented and