June_1967 — Page 17

Rebar compression struts AISC

spec.

Deformed reinforcing bars

18,000 psi

28-day concrete strength: Caissons 3,000 psi

Others 2,500 psi

M

There are 12 cylindrical caissons, each 320 cm outside diameter and 40 cm shell thickness, In view of the low bearing capacity of the foun- dation bedrock, a caisson bell was created to enlarge the bottom bearing area. The depths (H) varied between 7.1 and 18.6 metres.

Boring was conducted during sink- ing of the caisson to ensure proper setting and cores were taken and test- ed to show that the allowable bearing capacity on foundation bedrock was safe. The caisson foundation was sealed with concrete by drop-bottom bucket. The cement factor was 81⁄2

bags per cu. metre with slump 6-8 in. The sealing concrete reached 1 to 4 metres into the shaft to help resist water pressure, enabling the sea water to be pumped out before concrete was poured in the dry. The cement factor of the shaft filling concrete was 3.5 bags per cu. metre with slump ap- proaching zero in.

Framework

In a corner of the first shed com- partment is a two-storey office build- ing which has an independent raft foundation, bordering upon but not connected with the lower flange beams of the transit shed girder walls. This is in order to allow any settlement of the newly filled site to be as even as possible without interfering with the main structure.

Figure 6 shows the layout of the

structures with one compartment as a unit. The two three-hinged para- bolic main arches take the diagonal directions and meet at the centre. The span is 66.6 metres and the rise-span ratio 1 10. Secondary arches TX and TY are placed longitudinally and transversely, respectively, at every eighth point.

Between the TX's and TY's are purlins. The central purlins and every other purlin that is an extension of either TX's or TY's are stiffener purlins. The TX and TY parabolas are the horizontal projections of the main arches on X-X and Y-Y vertical planes respectively. Consequently all vertices of the parabolic arches occupy the same elevation and the two para- bolic surfaces, orthogonally intersected form the roof of the structure.

The stress analysis for dead load of Rebar arches is comparatively simple

ST# FENER PURLINS

TXI

TX2

TX3

TX3

TX2

TXI

STIFFENER PURLINS

50

Fig. 6. Layout of Rebar structures

1

]

L

+ PLAN

TY3

PARAPET

EXTERIOR WILL SECTION

Fig. 8. Girder wall plan and elevation

Far East Architect & Builder June, 1967

EXT.

INT.

CROSS HALL SECTION

t-

(4)

X

<1>

(2)

X

E

:5

(1) 4 Roof area loaded

6

(3)

Y

(2) 1⁄2 Roof area loaded, X direction (3) 1⁄2 Roof area loaded, Y direction

(4) X Direction earthquake

(5) Y Direction earthquake

(6) X Direction wind load

(7) Y Direction wind load

Fig. 7. Arrangement of L. L. for Rebar structure design analysis

NO. 3

NO. 1,

NO. 2,

4

5

Fig. 9. Expansion joints plan

STEEL TENSION RODS

COMPARTMENT NO 2.4

EXP JOINTS

Fig. 10. Expansion joints and tension rods of compartments 2 and 4

39

x