April_1966 — Page 40

gives a high standard of riding quality, since expansion joints occur only at every sixth span.

The bridge supports consist of 30in. diameter prestressed concrete piles, precast on the site.

The piles are jetted into position and the sand in the surrounding area is then mechanically compacted. The piles are joined by an in-situ concrete pile cap which connects with the in-situ concrete diaphragms linking the deck beams.

The main earthquake supports of each group of six spans consist of two rows of six piles each, intermediate supports of a single row. Provision has been made for jacking the structure at any support in the event of dif- ferential settlement in a severe earthquake.

The bridge over the Maipo will provide an entirely new crossing of the river, at a height of 20ft. It has twelve equal spans of 100ft., giving a total length of 1.200ft. The total width of 66ft. is made up of a dual, two lane carriageway, a median strip, and footpaths at both sides.

The superstructure will be similar to that for the Bio-Bio bridge but using six pretensioned concrete girders per span, at a greater spacing of 11ft. 6in. These girders are 10ft. shorter than those for the Bio-Bio bridge, but identical in section and prestress. British prestressing equipment and materials will be used for both bridges.

Largest Suspended Steel

Roof System

TULSA, Oklahoma, claims to have the largest suspended steel roof system ever constructed. Spanning 484,000 sq. ft., it is being built to frame the US$4 million Tulsa Exposition Centre.

The structure is 1,200 ft. long and 404 ft. wide. Exhibitors will have 360.000 sq. ft. of column-free area at their disposal, a feat made possible by the unusual combination of box columns, built-up girders and pre- stretched cable.

The horizontal framing for the structure spans 304 ft. without column support. A series of cables and out- side columns carry the suspended roof system load.

The structure will have two rows of 27 ft. high triangular-shaped side-wall columns, 41 on each side of the building. In addition, there will be 82 interior columns, or masts, located 50 ft. in from the outside members and spaced 30 ft. apart.

These masts are 80 ft. high tapered columns canted on a 9 degree angle toward the outside of the structure.

In erection procedure, the mast is raised first. Then the welded box girders, shipped to the site in three sec- tions, are erected. The first of these sections, 52 ft. long and preconnected to the outside column. is slipped through a rectangular hole in the mast and pinned. column part of this section is welded to a base plate which is held in tension by a series of high-strength wires extending from the plate down to the foundation caissons.

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Welded box girder, 52 ft. long, being positioned

The

The remaining two sections of the girder, 58 ft. and 95 ft. long, are spliced by welding on the ground, then raised and held in place by a crane until field spliced by welding to the previously erected section of girder at the The suspension cables are also attached at this time. Each of these girders, 41 on each side of the build- ing, cantilevers 152 ft. into the centre of the structure.

mast.

The pre-stretched galvanized bridge strands aid the tensioned outside columns in supporting the cantilevered girders. The strand is attached to the top of the mast, 45 ft. above the roof, and then connected to the girder.

The girders are connected at the building centre point by hydraulic dampers equipped with plungers that permit the roof to "breathe" under wind loads.

Steel acoustical decking will form the roof. The decking will be coated with a layer of insulation, in turn covered with asphalt impregnated felt. The final cover- ing will be white marble chips.

The slanted roof design provides 50 ft. of height clearance in the centre of the structure sloping to 25 ft. at the masts and to 15 ft. at the outside columns,

The centre is designed by David R. Graham and Associates, Inc., engineers, and Bert E. Griffin, architect. of Tulsa. United States Steel supplied the steel and Flint Steel Corp. are responsible for fabrication and erection.

UK Authority Approves 29 Building Systems

BRITAIN'S National Building Agency has issued its first appraisal certificates for industrialised building systems. Twenty-nine low-rise housing systems, among them the Ministry of Housing's own 5M. have been given the go- ahead by the agency.

Appraisals of other systems are in hand, and further certificates will be issued as assessments are completed. They will include systems in the high-rise category.

The NBA said that a certificate, valid for one year, indicates that a particular system has been fully examined by them and is suitable for use by local authorities in England and Wales, on the basis of a 60-year loan period. Separate certificates are being issued for their use in Scot- land, because of the different building regulations.

The granting of a certificate will also mean that the system can produce dwellings at reasonable initial and maintenance costs, it is capable of producing dwellings which comply with the necessary technical and space re- quirements, and that it is sufficiently flexible to be cap- able of producing an adequate environment in the hands of competent designers.

It will also mean that condensation problems are not likely to be encountered under normal conditions and that the system is at least equal to traditional construction in this respect, the productivity is adequate, the quality of at least one available plan type is adequate, and that an inspection of the prototype has revealed no serious defect.

Certificates will be reviewed periodically as relevant information is updated, whether in regard to design, pro- duction or management techniques. Copies of the certi- ficates will be issued under copyright to sponsors and to local authorities.

Huge Residential Town Planned Near Tokyo

PROBABLY the biggest residential town in the world is to be built in the western suburbs of Tokyo by 1973 by the Japan Housing Corporation in co-operation with the Tokyo Prefectural Government,

To be called Tama New Town, the town will accom- modate 300,000 people in 80,000 dwelling units. The total cost is estimated at US$1,250 million; this covers the apartments, three universities and three railways as well as amusement facilities for the residents. Some 3,300 retail shops and stores are also planned.

The town will cover an area of about 3,200 hectares. Its site is well known to Japanese archeologists as a re- sidental area during the Jomon era of 2,000 to 6,000 years ago.

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Far East Architect & Builder April, 1966

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