A Treatise On The Principles And Practice Of Dock Engineering

MONIER SYSTEM. 377 under ordinary conditions, considered exclusively of any wearing surface, may be 1J inches for flat floors and interior roofs and 2 inches for arched floors and exterior roofs, while 3 and 8 feet may be considered as minimum spacings for flat and arched floors respectively. Arched floors are generally constructed with a rise of only one-tenth the span; the thrust, where much weight is supported, is therefore considérable. Provision for the thrust may be supplied by tie-rods in the end bays of a floor or by horizontal end girders suitably anchored to the walls—the latter method, where possible, being preferable. Fürther, when a series of arches succeed one another, care should be taken that their centre lines meet on the vertical centre lines of the girders which carry them, for a very small divergence will cause an appreciable tendency to twist. This tendency may be further guarded against by embedding the girders in concrete. It is customary with ordinary flooring arches (which probably partake more of the nature of a girder than an arch) to allow a series to finish with its end mernber resting simply on a brick corbel ; this should not be attempted with Monier arches, but a shallow, wide joist should be used as a wall-plate.”* Fig. 363. —Monier Floor. k...-............ "J e" .................. 1 Fig. 364. —Monier Floor. Examples of floors constructed on the Monier system are reproduced in figs. 363 and 364, from Mr. Walter Beer’s paper, from which quotations have been already made, and in which the student will find a very interest- ing investigation of the nature and amount of the stresses set up in the varions parts. These stresses, which have engaged the attention of several eminent mathematicians, are too complicated for analysis in these pages. Joints are formed by causing the ends of the bars to overlap by a certain amount, which depends on the tensile strength of the bars and the coefficient of adhesion between iron and concrete, the latter being about 300 Ibs. per square inch of surface. After the bars have been laid the concrete is deposited in layers, not less than 1^ inches thick, and well raramed. Thin slabs need a closer mesh than thick slabs, owing to there being greater liability to local failure. * Beer on “ The Monier System of Construction,” Min. Proc. Inst. C.E., vol. cxxxiii.