October_1966 — Page 72

designed by using the method of moment distribution.

The typical pier designed for most of these bridges consisted of the necessary number of piles, varying from six to nine, in one row, extend- ing up into a reinforced concrete cap. None of the typical piers was suffi- ciently high to require lateral bracing, but the two end piles were battered outward on a slope of 1:6 for added transverse rigidity.

Prestressed Beams

Several types of prestressed beam sections were considered. The box section was selected as a deck made up of box beams requires no expen- sive formwork if a concrete slab or bituminous surfacing is to be placed on it.

A dimension of 1 metre was select- ed as a convenient width for all beams. Mild steel reinforcement was used to carry the tensile stress at the top. near the ends of the beams. to allow the use of straight-line pre- stressing, and to simplify production of the beams. A full length wedge- shaped groove 10 cm. deep, was pro-

vided along both sides at the top of each beam.

For transverse connection of beams, No. 7 U-shaped bars were set into the beams, with the bottom of the U projecting into these grooves. These same bars from adjacent beams were welded together before filling the groove with cement grout to form a positive shear key between beams, and thus assure load transfer and unit action of the deck.

Neoprene bearing pads were speci- fied for use on this project. The neoprene bearing pads assure uniform bearing on the concrete caps, and per- mit longitudinal movement due to temperature changes. The required thickness of the bearing pads was 2.50

cm.

The length of each pad was 91.40 cm. The width needed to main- tain a safe bearing stress on the con- crete seat was 12.50 cm.

Two types of bridge railing were used. Cast-in-place concrete posts and railings were used on all bridges where asphalt surfacing was laid. A prestressed concrete barrier railing was designed and specified for use in the four-lane portion of the highway. Cast-in-place concrete posts were used

Dual four-lane pavement at Km. 14.70, section D

to support the bridge railing. One rail was used at safety curbs with two rails at sidewalks.

To provide for vertical curvature, piers and abutments were set at pro- per elevations and the thickness of slab or surfacing was varied along each span. The typical embankment

in front of an abutment consisted of a narrow berm about 1 metre below the bottoms of bridge beams, and on a 2:1 slope normal to the abutment face.

At single 6-metre span bridges it was decided to omit the use of a berm, while at several bridge sites local conditions necessitated the use of variable slopes.

Contractors

Construction began first at Saraburi in February 1961, under a contract with Construction Syndicate Co., Ltd. This portion of the new highway, from Saraburi 21 km. south to the town of Nongkhae, was completed in Decem- ber 1962.

The next portion of the new road to be completed was from Nongkhae south to Rangsit, a distance of 55 km., on which construction started in December 1961 and was completed three years later, in October 1964. This was constructed by Phitsanu- Koster Registered Ordinary Partner- ship.

The final portion of the road, 28 km. from Rangsit to Bangkok, serv- ing the Don Muang Airport, was constructed by Sakok Sthapat Co., Ltd. between August 1961 and June 1965.

The temporary bituminous surface course between Saraburi and Rangsit was improved with a high-type bitu- minous asphalt-cement pavement, 76 km. long, between January and De- cember 1965, by Thai Asphalt Co. Ltd.

Each contract was more costly and took considerably longer to complete than the engineers originally estimat- ed. None of the contractors had previous experience of road construc- tion on this scale or to such design concepts and tight specifications. Per- sonell generally were inexperienced and modern road-making plant was not available. Plant breakdowns were in fact a daily occurrence.

However many Thai inspectors and engineers received on-the-job training throughout the project and these found ready employment elsewhere long before the highway was com pleted.

Part of section A; bituminous concrete surfacing with bituminous sealed shoulders

66

Far East Architect & Builder October, 1966