ECIV 320 Structural Analysis I Influence Lines. LAST TIME ANALYSIS OF FORCES DUE TO LIVE LOADS Live...
-
Upload
brittany-campbell -
Category
Documents
-
view
225 -
download
2
Transcript of ECIV 320 Structural Analysis I Influence Lines. LAST TIME ANALYSIS OF FORCES DUE TO LIVE LOADS Live...
LAST TIME ANALYSIS OF FORCES DUE TO
LIVE LOADS
Live or Moving Loads• Variable point of Application• Temporary Loads
Common Structures
• Bridges• Industrial Crane Rails• Conveyors• Floor Girders• any other structure where
loads move across its span
INFLUENCE LINESVariation of
Reaction, Shear, Moment or Deflection
at a SPECIFIC POINT
due to a concentrated force moving on member
LAST TIMEProcedures
Tabulate Values• Place UNIT LOAD at a number of fixed locations
Perform a series of static analyses to determine the value of reaction/shear/moment/deflection at the specific point. Tabulate Values
Influence Line Equations• Place UNIT LOAD at a variable location x
Perform a static analysis to determine the function of reaction/shear/moment/deflection at the specific point as a function of x.
LAST TIME
HINTS:
Beware of Points of Discontinuities
Influence lines of statically determinate beams consist of straight line segments
Place unit load at points representing the end points of these segments
Qualitative Influence Lines
Muller-Breslau PrincipleInfluence Line for a function is to the same scale as the
deflected shape of the beam when the beam is acted upon by the function
Live Loads for Highway BRIDGES
•Caused by Traffic•Heaviest: Series of Trucks
Specifications: AASHTO American Association of State and Highway Transportation Officials
Load Desigantions
H 15-44 HS 20-44
2 Axle Truck
15 Tons (10-20)
Year ofSpecifications
20 Tons
2 Axle Truck &1 Axle Semitrailer
Year of Specifications
Simplification: Uniform Load plus a Concnetrated force placed at critical locations
Live Loads for Railroad BRIDGES
Specifications: AREA American Railroad Engineers Associations
Load Desigantions
E-72
Devised by Theodore Cooper 1894
Loading on Driving Axle
M-72
Devised by D.B. Steinman
Loading on Driving Axle
Impact Loads
Moving Vehicles Bounce as they move over Bridge=> Impact Loads
Calculated as % of Live Loads - Impact Factor I
125
50
LI
Maximum Influence due to a Series of Concentrated Loads - Shear
125.025.5375.521 V
875.2375.55.232 V
Maximum Influence due to a Series of Concentrated Loads - Shear
To compute change
12 xxPsV
Sloping Line
12 yyPV
Jump