PART 2 PRELIM Flashcards
GENERAL REQUIREMENTS
The American Association of State
Highway and Transportation Officials
(AASHTO) specifications require highway
bridges be designed for:
_____, ______, and
______, with due regard to issues
of _____,______, and _____
constructability, safety, and
serviceability
inspectability, economy, and
aesthetics.
primary approach
recommended by AASHTO for both
bridge design and evaluation.
Load and Resistance Factor Design
(LRFD) method
a reliability-based design
approach
LRFD
account for
uncertainties in applied loads.
Load Factors
reflect material
variability and construction tolerances.
Resistance Factors
a condition beyond which
a structure or its components cease to
perform their intended function safely
and efficiently.
Limit states
defines the boundary between
acceptable and unacceptable
performance in terms of strength,
serviceability, and other criteria.
Limit state
used to ensure that bridges remain safe
and functional under various loads and
conditions throughout their service life.
Limit states
The limit states specified in the AASHTO
codes are intended to provide a
buildable and serviceable bridge
capable of safely carrying the design
loads for the specified life span of _____
years.
75
A bridge design must satisfy all relevant
limit states to be considered safe and
effective.
Strength Limit State
Serviceability Limit State
Fatigue and Fracture Limit State
Extreme Event State
ensures that the
bridge has sufficient capacity to resist
the maximum expected loads without
experiencing structural failure, such as
collapse or excessive yielding of
materials.
Strength limit state
Prevents catastrophic failure.
Ensures public safety under worst-case
loading conditions.
Strength limit state
Guarantees the bridge’s ability to
support expected traffic and
environmental loads.
Strength limit state
The strength limit state accounts for:
Dead Loads
Live Loads
Environmental Loads
Impact Loads
Stability
ensures
that the bridge remains functional,
comfortable, and durable under normal
operating conditions, without excessive
deflections, vibrations, or cracking.
serviceability limit state
Maintains user comfort and operational
efficiency.
Prevents service interruptions due to
excessive deformations.
Enhances long-term durability by
minimizing material damage.
serviceability limit state
The serviceability limit state accounts for:
Deflections
Vibrations
Crack Control
Creep and Shrinkage
Thermal Expansion
evaluates the bridge’s ability to
withstand repeated cyclic loading over
its lifetime without experiencing
progressive material damage, such as
cracking in steel or concrete.
fatigue and fracture limit state
Prevents failure due to cumulative
damage over time.
Ensures long-term structural integrity
under repeated loading.
Addresses concerns in high-traffic or
heavily loaded bridges.
fatigue and fracture limit state
Fatigue and fracture evaluation takes into
account:
Repeated Traffic Loads
Material Stress Cycles
Crack Propagation
Detailing and Connections
ensures
that the bridge can withstand rare but
severe events such as earthquakes,
floods, hurricanes, or vehicle collisions
without collapsing.
extreme event limit state
Protects human life and critical
infrastructure during emergencies.
Ensures resilience and functionality
after extreme events
Helps in planning emergency response
and recovery
extreme event limit state
Extreme Event limit state takes into account
for:
Seismic Forces
Floods and Scour
Fire Hazards
Accidental Loads
Extreme Weather
refers to the ability to
successfully complete the construction
of the bridge being designed.
Constructability
Its goal is to
optimize the bridge design to minimize
construction time, reduce costs,
enhance safety, and ensure quality.
Constructability
When designing a bridge with
constructability in mind, engineers must
consider:
Site Conditions
Materials Selection
Construction Methods
Labor and Equipment Availability
Traffic Management
Construction Sequencing
Weather and Seasonal Impacts
a critical aspect of
bridge design that ensures the bridge
remains functional, safe, and
comfortable for users over its lifespan.
Serviceability
address various aspects of serviceability to
ensure that bridges remain functional,
comfortable, and durable throughout their
service life.
AASHTO LRFD Bridge Design Specifications
The key serviceability considerations
include:
Clearance
Durability
Maintainability
Rideability
Controlled Deformation
Facilitating Utilities
Allowance for Future Widening
refers to the vertical and horizontal
space provided beneath and around the bridge to
accommodate traffic, pedestrians, utilities, and
future expansions.
Clearance
Ensures safe passage for vehicles, trains, ships,
and pedestrians.
Accommodates oversized vehicles and
emergency services.
Reduces the risk of vehicle or vessel collisions.
Allows for future upgrades or changes in traffic
requirements
Clearance
Vertical clearance above the roadway shall not
be less than _____meters over the entire roadway
width to which an allowance of _____ meter shall
be added for future additional road surfacing.
4.88
0.15
Roadway clearance for trucks and high vehicles
(typically _____ to _____meters for highways).
4.3-4.9
Pedestrian footbridges over roads on the other
hand shall be _____meter greater than the vertical
clearance to reduce the risk of truck impact
against pedestrian bridges which have low load
capacity.
0.30
The clear height/headroom
between the pedestrian bridge
walking surface and the bottom
of the girder of the structure
above it shall not be less than
____meters.
2
According to standard design practices, the
vertical clearance from the roadway to the
overhead cross bracing of through trusses
should be a minimum of _____meters.
5.3
____&____ in cable ducts in concrete
members are required in the AASHTO specifications to be
grouted or otherwise protected against corrosion.
Prestressing strands or tendons
_____&____used in wood construction are
required to be of stainless steel, malleable iron, aluminum, or
galvanized steel, cadmium plated, or otherwise coated.
Attachments and fasteners
____products shall be electrically insulated from steel
and concrete components to be protected from possible
corrosion.
Aluminum
To prevent water from remaining near the edge of a concrete
deck, ________ is required along the deck’s
underside at a distance less than _____mm from the edge.
continuous drip groove
250
refers to the ease with which the
bridge can be inspected, repaired, and
maintained during its service life.
Maintainability
Reduces downtime and disruption to traffic
during maintenance.
Ensures safety of maintenance personnel.
Minimizes long-term operational costs.
Maintainability
The AASHTO specifications require that the
following considerations be identified in the
contract documents:
a contemporary or future protective overlay
a future deck replacement
supplemental structural resistance
Asphalt concrete overlay at about ____ to ___ years
of slab life for improved rideability.
15-20
Removal of asphalt overlay and certain depth of
top concrete and then overlay of concrete at
about ___ to ___ years of slab life to improve
structural performance and rideability.
20-30
Replacement of slab at about ___ to ___ years of
slab in a rehabilitation of the bridge.
30-40
refers to the smoothness and comfort
of travel over the bridge for vehicles and
pedestrians.
Rideability
ensures that the bridge
maintains acceptable levels of movement,
deflection, and vibration under service loads
without compromising safety or comfort.
Controlled deformation
Prevents excessive movements that could
damage the structure.
Ensures user comfort and safety under normal
operations.
Protects structural elements from stress
concentrations.
Controlled deformation
Recommended deflection limits for steel,
aluminum, and concrete structure
Vehicular load , general ……..
Span / 800
Recommended deflection limits for steel,
aluminum, and concrete structure
Vehicular and pedestrian loads ———————–
Span/1000
Recommended deflection limits for steel,
aluminum, and concrete structure
Vehicular load on cantilever arms ———–
Span/300
Recommended deflection limits for steel,
aluminum, and concrete structure
Vehicular and pedestrian loads on cantilever arms ——-
Span/375
Recommended deflection limits for wood
structures
Vehicular and pedestrian loads———–
Span/425
Vehicular load on wood planks and panels——–
0.10 inch
Provides infrastructure support without affecting
bridge aesthetics and functionality.
Reduces the need for future modifications or
retrofitting.
Allows for efficient maintenance and expansion
of utility services.
Facilitating utilities
ensures that the
bridge design considers potential traffic growth
and expansion needs by providing options for
future widening.
Allowance for future widening
