BRIDGE

Taranaki Daily News, 28 August 1930, Page 15

BRIDGE

: . THE ARCH. .../triumph for. builders. Two flags flying ■ from the creeper cianes nearly oOUft above the Sydney harbour on August 19 proclaimed'to the world'that the'two-sections of the arch of-‘the great harbour bridge had been joined. \ : For the previous 10 days, disturbed only by the vagaries of Sydney’s temperature, the process of lowering the . two halves of the arch had slowly pro-, gie'ssed. On Monday, August 18, the gap between the pilot pins ,on the south arm and the sockets into which they are now locked on the north side decreased from' iP/jin to Gin. Most of this conduction was caused by rising temperatures between 8 aim. rind 4 p.m. Although the controlling cables were still further released during the night tin cold night temperatures had made tl e gap Bin wide when dawn broke on Tuesday., By noon the loxy.ering process and. the higher temperatures had reduced to 3in. By. four o’clock in the afterjmon only three-eighths of an inch separated the two arms. .. : Until the Tuesday only the tapered points of the powerful lOin-square pilot pins of the south arm, so fixed that they eduld be driven forward into the corresponding square sockets in the north' arm, had been allowed to rest in the openings. On the all-important day, when the gap was reduced to about Gin, the pins were forced home with great hydraulic jacks and the two parts of the structure were joined. This was a Tremendous task, infinitely complicated by the effect of the fickle sun-rays on the arch. ' Standing on the south side, one could almost see their effect on the more directly exposed right arm, says the Sydney Morning Herald. The heat expanded tho steel by nearly 2in at the extreme end, and the relatively’ higher temperature of the top chord made it sag downward. At the same time, the more intense heat on one side tended to produco a lateral bend. With’the half arches temporarily in a somewhat flexible condition, and influenced, too, by the ' temperature of the anchorage cables themselves, the disturbance of vertical and horizontal alignment made the process of forcing home the pins an unexpectedly difficult business. At one' moment the alignment would bo correct. A quarter of an hour later there would bo aii apparent error in, one sjde’s level of ,as much as an inch, although the other side would .still bo: true. Sweating, in brilliant sunshine far above tho scudding ferry boats, men heaved then at gigantic tackle, strained and thrust, and heaved again. Slowly tho steel yielded to their will, and the two half arches were in horizontal alignment. Quick-footed, they made good their work with temporary clamps. Meanwhile the workmen on the north sido had ceased to lower their cables. Those on tho south kept on to counteract the sagging tendency of the northern arm. At five o’clock, Mr. Lawrence Ennis, the bridge builder, and Mr. Ralph Freeman, tho designer, reached solid earth with flushed, triumphant faces. Their eyes told a story of tremendous strain suddenly relaxed. The lowering process had not been completed, but the anxiety was over. The pins would never move completely apart again. The last stage developed into a race between the men who were releasing the cables and the falling temperature. After five o’clock the steelwork contracted so-'rapidly That the slackening cables could not keep the arch arms together, although tho pilot pins were still in their sockets. Under the glare of arc lights, with whistles shrilling and telephones ringing, the slow battle dragged on, hour by hour until toward midnight the arms began again to approach each other. In the early morning hours human patience won. Tho arms touched, the pins thrust firmly into their sockets, and the terrific strain of all that steel rested no longer on the cables, but on the bearings that will hold its weight for long years to come. Above the sleeping city tho bridgebuilders . smiled, shook hands, and then went homo to bed. -Tho job was done.