Design Information
Standard Sections
Planks

SCI precast prestressed plank units are the simplest of all of the basic bridge construction elements. They find widespread use in short to medium span bridges and it is noteworthy that some plank bridges are achieving spans in excess of 20m spans.



For the smaller spans up to 12m the planks are solid. Above this span the planks are voided with circular voids to reduce self weight and increase structural efficiency.

The planks may be either composite or non-composite with their deck wearing surface depending upon the design of the bridge.



Seven standard depths are readily available ranging from 240mm to 700mm. Current design philosophy employs a mix of prestressed and non tensioned reinforcement, although the most economical designs use prestressing strands only. These are placed horizontally on a 50mm x 50mm grid, 25mm each side of plank centreline and debonded locally as required at each end to control concrete stresses to within acceptable design limits.

Two strands are always placed near the top of the section to support the stirrups within the planks and to assist in control of concrete stresses at time of transfer of prestress. Concrete of grade S50 at 28 days and strength at transfer of prestress 35 Mpa is commonly specified.





Type A
(mm²)
Ixx
(mm4)
Yb
(mm)
Zt
(mm³)
Zb
(mm³)
P240 128.5x10³
642.7x106 116 5.19x106 5.54x106
P300 164.5x10³
1254.0x106 144 8.05x106 8.70x106
P380 212.5x10³
2540.0x106 183 12.87x106 13.91x106
P455 209.9x10³
4177.3x106 218 17.61x106 19.18x106
P535 234.8x10³
6700.0x106 256 24.05x106 26.13x106
P600 275.6x10³
9656.0x106 288 30.95x106 33.53x106
P700 335.6x10³
15630.0x106 338 43.18x106 46.25x106


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