D I S T R I B U T I O N F A C T O R S

Question 1

INFLUENCNG PARAMETERS

Answer 1

• Type of floor (deck)
• Depth of deck (thickness)
• Span length
• Spacing between stringers
• Spacing of secondary members
• Stiffness of primary members
• Stiffness of secondary members
• Type of bracing employed (if any
• Size and position of loads

Question 2

INFLUENCNG PARAMETERS of AASHTO Standard Specification (DF)

Answer 2

• Type of floor (deck)
• Spacing between stringers

Question 3

INFLUENCNG PARAMETERS of AASHTO LRFD Specification (DF)

Answer 3

• Type of floor (deck)
• Depth of deck (thickness)
• Span length
• Spacing between stringers
• Stiffness of primary members

Question 4

▪ are computed for (live load) moment, shear, and reactions for interior and exterior girders
▪ computed for strength, service, extreme event, and the fatigue limit state

Answer 4

DISTRIBUTION FACTORS

Question 5

DISTRIBUTION FACTORS

Answer 5

▪ AASHTO Standard Specifications
▪ AASHTO LRFD Specifications

Question 6

▪ Applied to wheel loads
▪ Vary depending on whether longitudinal or transverse members are analyzed

Answer 6

AASHTO Standard Specifications

Question 7

▪ Provides more accurate and sophisticated formula for DF
▪ Uses axle load AND lane load
▪ HL-93 truck forces uses
▪ 8k 32k 32k (35kN 145kN 145kN)
▪ Identical to HS-20 force loads

Answer 7

AASHTO LRFD Specifications

Question 8

DIFFERENT TYPES OF LOAD DISTRIBUTION

Answer 8

1. INTERIOR LONGITUDINAL MEMBERS
2. EXTERIOR LONGITUDINAL MEMBERS
3. TRANSVERSE MEMBERS
4. MULTIBEAM CONCRETE DECKS (Concrete Panels)

Question 9

As discussed, not only the floor type and stringer spacing are considered,

Answer 9

▪ The orientation (transverse or longitudinal) of member and
▪ its position (interior or exterior) are also considered

Question 10

• Other load distribution factors are determined from AASHTO LRFD Table 4.6.2.2.2b-1
• This accounts for lateral distribution of loads ONLY
• NO longitudinal distribution of wheel loads is allowed
• LL Bending moments are computed using the whole truck multiplied by the
  distribution factor

Answer 10

INTERIOR LONGITUDINAL MEMBERS

Question 11

• Depends on longitudinal arrangement, outside girders are subjected to heavier loads compared to interior
• Superimposed DL can be distributed equally among all primary members

Answer 11

EXTERIOR LONGITUDINAL MEMBERS

Question 12

This is for easy future widening purposes

Answer 12

Exterior girders IN NO CASE must be designed smaller than interior girders

Question 13

If an exterior girder is under a sidewalk, the girder should be designed for truck load
on the sidewalk

Answer 13

EXTERIOR LONGITUDINAL MEMBERS

Question 14

-specifications do not allow any lateral distribution for transverse members (Floor beams)
- Applied when no longitudinal members are present and deck is supported entirely by
the floor beam
- DF is outlined in AASHTO LRFD Table 4.6.2.2.2f-1

Answer 14

TRANSVERSE MEMBERS

Question 15

For concrete bridges: DF for shear and moment is ___ (English) or____ (metric)

Answer 15

S/6
S/1.8

Question 16

If ________, DF can be calculated by positioning the LL to obtain maximum
reaction at floor beam

Answer 16

S > 6 feet (1.8m)

Question 17

-either RC or prestressed
- Same as other longitudinal members, no longitudinal distribution of wheel load is
allowed
- For moment in interior and exterior beams, use AASHTO LRFD Tables 4.6.2.2.2b-1 and
4.6.2.2.2d-1
- For shear interior and exterior beams, use Table 4.6.2.2.3a-1 and 4.6.2.2..3b-1

Answer 17

MULTIBEAM CONCRETE DECKS (Concrete Panels)

Question 18

in MULTIBEAM CONCRETE DECKS (Concrete Panels):
- ___ is greatly dependent on the cross sectional geometry of the panel
- _________ and _________ are functions of type of panel/beam used

Answer 18

DF
Moment of Inertia
torsional constant