BRIDGE ANALYSIS

1
BRIDGE ANALYSIS

• Data you must obtain
• Span and height dimensions
• Number of lanes
• Deck width and depth
• Tower width and depth
• Main cable or arch rib diameter
• Spacing between hangers/struts/stays

2
LOADS

• Wind pressure (may decrease for openings)
• Highway lane 0.64kip/ft 9.34KN/m
• Railroad track 7.2kip/ft 105KN/m
• Steel 490pcf 76.9KN/m3
• Reinforced concrete 150pcf 23.6KN/m3
• Dead deck load 150psf 7.18KN/m2

3
MATERIAL PROPERTIES

• High-strength steel cables
• Strength 256ksi (1763MPa)
• E29000ksi (200GPa)
• Structural steel, tubes (assume 1 thick)
• strength 60ksi (413MPa)
• E29000ksi (200GPa)
• Structural concrete
• strength 8.72ksi (60MPa)
• E 6000ksi (41.3GPa)

4
DECK STRUCTURE

• Obtain Adeck by wind stress with safety factor of
  1.5
• Check safety factor for gravity stress
• Iteration required for cable-stayed bridges

5
HANGERS OR STRUTS

• 1) Obtain Ahanger or Astrut by gravity stress
  with safety factor of 2

6
MAIN CABLE OR ARCH RIB

• For suspension bridges, check stress safety
  factor for main cables under all gravity loads
• For arches, check stress safety factor for rib
  tube only under its own weight, and for rib tube
  plus fill under all gravity loads
• For cable-stayed bridges, assume safety factor is
  2 for stay cables

7
SUSPENSION MAIN CABLENEGATIVE FOR ARCH RIBS

• w includes weight of deck, load, and cables
• V wL
• T wL2/2H (horizontal reaction for arch rib)
• Max tension

8
STAY CABLE NEGLECTING ITS OWN WEIGHT

• Deck compression
• Cable tension

9
STAY CABLE INCLUDING ITS OWN WEIGHT

• Deck compression
• Cable tension

10
QUADRATIC EQUATION

• If w bT then solve the following for T/V
• Then get F/V

11
TOWER STRUCTURE

• Obtain Atower by combined wind and gravity stress
  with safety factor of 1.5
• Check safety factors for both in-plane and
  out-of-plane buckling

12
SUPPORT REACTIONS

• Calculate support reactions at all external cable
  anchorages, tower supports, and arch rib supports