Lecture 2 Flashcards
Highways with 1-2 lanes have a ______width
12’
Highways with 4 lanes have a ______wide right shoulder
10’
Highways with 4 lanes have a ______wide right shoulder
10’
Highways with 4 lanes have a ______wide left shoulder
4’
Highways with 6-8 lanes have a ______wide left shoulder
10’
The minimum median width is obtained by…
adding two left shoulder width in table 3.10 AASHTO to give 10’ for 4 lane and 22’ for 6 and 8
for freeways and arterial systems a minimum vertical clearance is
16’ plus an allowance for about 6 inches of resurfacing
A general statement for assuring safety in design is that
the resistance of the components supplied must exceed the demands placed on them by the loads
A limit state can be defined as
a condition beyond which a bridge system or component ceases to fulfil the function for which it was designed
The value to be used for the strength limit state ductility factors in non ductile components and connections is…
ηd = 1.05
The value to be used for the strength limit state ductility factors in ductile components and connections is…
ηd = .95
Ductility is importannt to the safety of the bridge because
If ductility is present, overloaded portions of the structure can redistribute the load to other portions that have reserve strength.
What is the redistribution of the load from ductility dependent on?
the ability of the overloaded component and its connections to develop inelastic deformations WITHOUT failure
When is a structure statically indeterminant?
When it has more restraints than necessary to satisfy conditions of equilibrium
Benefits of Redundancy in a bridge system
To increase its margin of safety and its reflected strength limit state redundancy factors
What is the redundancy factor for non-redundant members?
ηR= 1.05
What is the redundancy factor for redundant members?
ηR= .95
What is the redundancy factor for conventional redundant members?
ηR= 1.00
True/False Single load paths or non redundant bridge systems are encouraged
False, they are not
Extreme limit state and strength limit state have a importance factor of ________for non ductile components
ηi= 1.05
Extreme limit state and strength limit state have a importance factor of ________for ductile components
ηi= .95
Limit states to consider in bridge design
- service limit state
- fatigue limit state
- strength limit state
- extreme limit state
Service limit state pertains to?
restrictions on stresses, deflections, and crack width of bridge components
For service limit state resistance factor Φ and load factor γi are =
1.0
How many service limit state conditions are there?
4
Define service limit state 1
refers to the load commination elating to normal operational use of the bridge with 55 mph wind
Define service limit state 2
this service limit state refers to the load combination relating to steel structures and is intended to control yielding and slip critical connections
Define service limit state 3
This limit state refers to the load combination relating to tension in pre-stressed concrete superstructure with the objective of crack control.
Define service limit state 4
This limit state refers to the load combination relating to tension in pre-stressed concrete substructure with the objective of crack control.
AASHTO defines __#____ fatigue limit states
2
The fatigue limit state refers to restrictions on…
stress range caused by a design truck
The fatigue and fracture limit state Φ
1.0
What limit state defines ΦRn >= η Σ Υi Qi
Strength limit state
Strength limit state defines the evaluation of the resistance to…
Bending
Shear
Torsion
Axial Load
Define strength limit state 1
this is the basic load combination relating to the normal vehicular use of the bridge without wind
Define strength limit state 2
this is the basic load combination relating to use of the bridge by permit vehicles without wind
Define strength limit state 3
This strength limit is the basic load combination relating to the bridge exposed to wind velocity exceeding 55mph
Define strength limit state 4
This strength limit is the basic load combination relating to very high dead load/live load force effect ratios
Define strength limit state 5
This strength limit is the basic load combination relating to the normal vehicular use of the bridge with wind of 55mph velocity. It differs from strength 3 b the presence of the live load on the bridge, wind on the live load and reduced wind on the structure.
Extreme event limit state defnes
Refers to the structural survival of a bridge during a major earthquake or floods or when collided by a vessel, vehicle or ice flow. (apply separately)
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