bridge systems by dr medhat kamal - infra consultants
TRANSCRIPT
BRIDGE SYSTEMS
By
Dr. Medhat Kamal
Typical bridges are composed of:• bridge deck,• bearings,• piers • abutments.
Types of Bridge deck
• Solid slabs
• Voided slabs
• Slab and beam system
• Box‐girder
• Precast I‐beams
• Precast T‐beams
• Precast box sections
• Precast V‐sections
BearingsAre support elements that transfer the deck reactions to the sub‐ structure: Elastomeric for low range bearing reactions (≤12000 KN) Pot bearings for high reactions (>12000 KN).
PiersAre vertical elements (columns) that form the intermediate supports of the bridge deck.Their cross section may be rectangular, oblong, and or circular type.
DIFFERENT TYPES OF BRIDGE DECK
1-SLAB TYPE DECK
Solid slabs span 5m→ 10 m,
Voided slabs spans 10 →15
More spans for prestressed slabs
• Span/depth ratio =(simply supported), 15(continuous) 20→24
• Appearance = simple
• Construction time = shortest among cast in‐situ construction
• Maintenance = very li le → regular inspection of deck and bearings.
• Future extension = difficult
Prestressed Concrete Slab Bridges
• Prestressed slab decks are similar to reinforced concrete ones, except that it can cover larger spans
• Voided slab concept can also be utilized
• Span/depth = 15 (simply supported),
20→24 (continuous)
2- SLAB - GIRDER BRIDGE DECK
• L from 10.0m→ 30.0m• Precast beams may be used
instead of cast in‐situ ones as this facilitates erections and minimize construction time.
• Spacing between girders= 2m ‐3.5m
• Tg= L/14 Simple• = L/17 Contin• bg = 30,40,50.. Cm• Ts =25cm min• T asphalt =7‐10cm• Construction time =
complicated form work• Requires good finish.• Traffic obstruction =
formwork blocks traffic. Improves by using precast beams.
• Maintenance = very li le → regular inspection of deck and bearings.
Precast Prestressed Concrete “ I ” , “ T ” and “ Box ” Beams
SPANS = 30m (simply supported), 50m (continuous).
3-BOX GIRDER BRIDGE DECK
Box girder bridges have high torsional strength and good appearance
• Typical spans = 25m (constant depth) ‐60m (variable depth).
• Span/depth = 17.0 (simply supported), 18.0 (continuous)
• Appearance = neat, webs may be vertical or inclined, utilities can be
• Construction time = complicated form work, casting in 3 stages, must leave openings for formwork.
• Traffic obstruction = formwork blocks traffic.
• Cantilever carriage and othertechniques may improve this aspect.
• Maintenance = minimum→ regular inspection of deck and bearings.
Prestressed Box girder bridge deck
Prestressed box girder bridges are used for spans 30 m → 100m in case of constant section depth) Up to spans = 300m if variable depth is used
Variable Depth Post Tensioned PrestressedBox Girder Bridge.
LOAD PATH
LOADS SLABS GIRDERS BEARINGS PIERS FOUNDATIONS and PILES
Forces Acting on Bridges
• Vertical Loads• Longitudinal horizontal loads• Transversal horizontal loads• Restraining movements due to temperaturevariation, shrinkage and creep
Vertical Loads
• Self weight
• Superimposed DL
• Live load (pedestrian, traffic, railway, …)
• Prestressing force
• Prestressing reactions
• Support settlement
• Replacement of bearings
• Temperature variation
Horizontal Loads• Braking force (L)
• Centrifugal force (L & T)
• Temperature variation (L & T)
• Frictional force (L mainly)
• Earth and water pressures ( to surface)
• Wind (L & T, mainly T)
• Earthquake forces (L & T)