Lecture XII.

Concluding Summary.

Special types of construction.—Difference of pressures on tunnel and bridge arches.—Tunnel inverts.—Side walls.—Slow setting cement to be used for tunnel arches.—Shingle concrete may be substituted in some cases for brickwork.—Tunnelling in Japan under rivers.—Harbour walls should meet the sea obliquely.—Advantage and disadvantage of parapets.—Effect of form of section on the rising wave.—Jetty Floors: Lifting action of the sea—Oamaru jetty.—Towers: Factory chimneys and lighthouse towers—Factory chimneys, two considerations: design and construction—Calculation of draft—How to build a wash-house chimney—Practical rules for apportioning height and sectional area—Foundations—Fire-brick lining—Chimney at Invercargill gasworks—Force of the wind—Bursting action of hurricanes—Particulars of celebrated chimneys—Lighthouse towers—Different from chimneys in conditions of stability—Combined action of wind and sea—Form of tower now recognised as the best—Defects of old Eddystone tower—Wolf Rock lighthouse—New Eddystone lighthouse—Cost per cubic foot of old and new Eddystone towers—Suggestions for substituting concrete for masonry in future work.

General considerations.—When designing, consider both the nature of the material and the mode of execution.—Study ornamented construction rather than constructed ornament.—Guard against inequality of settlement—Make full provision for contraction and expansion.—Design foundations with reference to the nature of the ground and the weight of the proposed structure.—Have a clear idea where to use lime mortar and where cement.—Suggestions for building concrete arches.—Extended use of cement concrete.—Caution to be used in selecting building stone from the older rocks.—Iron bark piles and wrought iron girders recommended for New Zealand bridge construction.—False bearings to be avoided.—Short bearings recommended in floor construction.—Advantages of flat roofs in towns.—Importance of husbanding our natural resources.—Destruction of native timber.—Wrought iron in trusses or arches the future material for bridges of large span.—Importance of native manufacture of cement.—Concluding remarks: The desirability of establishing technical schools to supplement the training of the workshop.