BS5400:Pt2

LOADING


Click on the Clause No. for the commentary.


INDEX


CLAUSE No

SUBJECT

Type HA loading (Example)


Clause 6.2


Problem:

How do you work out the HA loading and bending moment for a bridge deck ?

Example:

  Carriageway = 7.3m wide
Deck span = 34m (centre to centre of bearings for a simply supported single span)

Design for a metre width of deck :

Clause 3.2.9.3.1.

Number of notional lanes = 2
Notional lane width = 7.3/2 = 3.65m
Clause 6.2.1. Loaded length = 34m
W = 336(1/L)0.67 kN/m (per notional lane)
W = 31.6 kN/m (per notional lane)
Clause 6.2.2. Knife Edge Load = 120 kN (per notional lane)
Clause 6.4.1.1. a2 = 0.0137[bL(40-L)+3.65(L-20)]
a2 = 0.0137[3.65(40-34.0)+3.65(34.0-20)] = 1.0
Note: For loaded lengths less than 20m the load is proportioned to a standard lane width of 3.65m, i.e. 0.274bL = bL/3.65.
For a metre width of deck :
W = (31.6 x 1.0)/3.65 = 8.66 kN/m
KEL = (120 x 1.0)/3.65 = 32.88 kN
Clause 6.2.7. gfL = 1.50 (Ultimate limit state - combination 1)

Design HA loading for a metre width of deck :
W = 1.5 x 8.66 = 12.99 kN/m
KEL = 1.5 x 32.88 = 49.32 kN

Maximum mid span Bending Moment with KEL at mid span = Mult
Mult = (12.99 x 342)/8 + (49.32 x 34)/4
Mult = 1877 + 419 = 2300 kNm
Note: Use of gf3
BS 5400 Pt.3 & Pt.5 - gf3 is used with the design strength so Mult = 2300 kNm.
BS 5400 Pt.4 - gf3 is used with the load effect so Mult = 1.1 x 2300 = 2530 kNm.

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Last Updated : 18/04/2008
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Email: david@childs-ceng.demon.co.uk