Post on 29-Apr-2022
1
IABSE 2006 May 16
By Peter G. Buckland, C.Eng.
Increasing the Load Capacityof Major Bridges
As time passes ….bridges deterioratetraffic loads increase (heavier
vehicles)traffic volume increases (more
lanes)more lanes = more eccentricity
Strengthening can be very expensive
What can we do?
And how can we do it?
keep peak traffic runningshort periods of occupancytwo deadlines per dayno time to correct problemsdesign must be tolerant of misfitalso improve seismic, wind,
maintenance
Examples
leading to
Suggested Guidelines
1/28
2
North ViaductNorth Viaduct
6 hours per night
88391220 1220
2/28
3
2000 200010668
3/28
4
4/28
5
Increase capacity from HS 20 loading to CS-600
Widen from 7.3m to 10.0mNew deck made composite
Rock Creek Canyon Bridge
Typical Deck Section
old new
5/28
6
Hagwilget Bridge, Canada
6/28
7
Replace deck system
Change load from 1 x 13.5t to 2 x 55t
10 hours per night, plus always access to hospital
7/28
8
8/28
9
9/28
10
10/28
11
Belgo Bridge, Canada Tower overstressed,
D/C = 2.75
11/28
12
Increase capacity by changing from a suspension bridge
into cable-stayed
6 weeks each summer,
keep conveyor running
12/28
13
Seaway International Bridge, Canada - USA Stiffening truss overloaded by modern trafficReplace chords with high strength steel
13/28
14
14/28
15
15/28
16
Port Mann Bridge, CanadaFour lanes five,
modern traffic loads
16/28
17
Originally, load factor = 1.75R≥1.75(D+L)
Now 0.9R≥1.1Df+1.5Dw+1.7L
For an existing bridge0.9R≥1.1Df+1.2Dw+1.65L
Lions’GateBridge,Canada
17/28
18
ObjectivesObjectivesReplace corroded deck Widen traffic lanes Widen sidewalksProvide barriers Provide pavingProvide drainsReduce maintenanceIncrease load capacity Improve aerodynamic stability
ConstraintsConstraintsMaintain same weightCarry traffic during constructionReplace each section in 10 hours 20:00 to 06:00Very limited access
Solution:Solution:
Replacement of Entire Suspended Structure
12 200
3 SP'S @ 2900 = 8700 13001300
18/28
19
2000
2700
12 192
16 762
2000
27003 LANES @ 3556 = 10 668
ORNAMENTALLIGHTS
HANDSTRANDS
19/28
20
20/28
21
Guidelines
GuidelinesDetermine current stress state
GuidelinesDetermine current stress state
(survey and analyze)
21/28
22
GuidelinesDetermine current stress stateDetermine loads accurately
GuidelinesDetermine current stress stateDetermine loads accuratelyEstablish load & resistance factors
GuidelinesDetermine current stress stateDetermine loads accuratelyEstablish load & resistance factorsMinimize weight
GuidelinesDetermine current stress stateDetermine loads accuratelyEstablish load & resistance factorsMinimize weightImprove load paths
22/28
23
GuidelinesDetermine current stress stateDetermine loads accuratelyEstablish load & resistance factorsMinimize weightImprove load pathsShort occupancy → constructibility
GuidelinesDetermine current stress stateDetermine loads accuratelyEstablish load & resistance factorsMinimize weightImprove load pathsShort occupancy → constructibilitySolve gravity loads first
GuidelinesDetermine current stress stateDetermine loads accuratelyEstablish load & resistance factorsMinimize weightImprove load pathsShort occupancy → constructibilitySolve gravity loads firstImprove maintenance
GuidelinesDetermine current stress stateDetermine loads accuratelyEstablish load & resistance factorsMinimize weightImprove load pathsShort occupancy → constructibilitySolve gravity loads firstImprove maintenanceAnalysis last - think first!
23/28
24
Be creative
… and be careful.
Think first!
Some ideas …Accurately determine conditionReview loads and load factorsSubstitute lighter materialMake deck composite“Prestress” suspension bridgeAlter load pathsConvert the form of a bridgeAlter steel grade
24/28
25
25/28
26
Churn Creek Bridge
Fraser River, Canada
Churn Creek Bridge - before
5t limit
Churn Creek Bridge - after
30t limit
26/28
27
Increase capacity from 5t to 30t Replace wood with steel between Replace wood with steel between 08:3008:30--12:00 & 13:0012:00 & 13:00--16:3016:30 dailydaily
27/28
28
28/28