Page 252 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 5 LOAD AND RESISTANCE FACTOR RATING AND REDESIGN 227

Figure 5.23 Use of additional pier adjacent
to abutment minimizing sharp skew effects.

following load combinations for hybrid (cast-in-place deck and precast beams or precast panel
decks and cast-in-place beams) cases are expressed as examples using different load factors for
each condition.
AASHTO LRFD Table 3.4.1-1 does not differentiate between primary and secondary
loads/effects. Superstructure and substructure load combinations need to be separated. Earth
pressure, water loads, and most extreme events need to be tabulated separately. In the following
load combinations, the most commonly used loads such as dead load, live load, and wind are

used. For extreme events such as floods, AASHTO Extreme Event II is revised.
Unit weights of cast in place (CIP) wet concrete and precast concrete will be different and
are differentiated. Appropriate factors need to be used.
i
Factors for temperature, creep, and shrinkage will be different for precast construction than

those shown in AASHTO Table 3.4.1-1. For a composite or unified behavior between precast
units and CIP units, AASHTO factors will not be applicable. The probability of vehicle impact
(IM) to happen at the same time as extreme events is very low and is neglected. Construction
load combinations not fully covered by AASHTO Table has been added.

5.8.2 Strength (see Table 5.7)
For strength I load combination with HL-93 live load:
7 R 9 [ (CIP DC1) (CIP DC1) Q CIP 4 (Precast DC1) (Precast DC1) Q Precast 4 DC2 DC2 Q DC2
n
4 WS Q )] 4 [ HL93 (1 4 I) Q HL93 ]
LL
WS
WS
Where I is dynamic load allowance or impact factor.
For strength II load combination with permit live load:
7 R 9 [ (CIP DC1) (CIP DC1) Q CIP 4 (Precast DC1) (Precast DC1) Q Precast 4 DC2 DC2 Q DC2

n
4 WS Q )] 4 [ PERMITL Q PERMITL ]
WS
WS
LL
For strength V load combination with live load:
7 R 9 [ (CIP DC1) (CIP DC1) Q CIP 4 (Precast DC1) (Precast DC1) Q Precast 4 DC2 DC2 Q DC2
n
4 WS Q )] 4 [ (1 4 I) Q ]
WS
LL
LL
WS
LL
For other load combinations:
For strength III load combination with no live load, but wind forces:
7 R 9 [ (CIP DC1) (CIP DC1) Q CIP 4 (Precast DC1) (Precast DC1) Q Precast 4 DC2 DC2 Q DC2
n
4 WS Q )] 4 [ wind wind Q wind ]
WS
WS
5.8.3 Extreme Conditions (see Tables 5.6a and 5.8)
For earthquake load combination with live load:
7 R 9 [ (CIP DC1) (CIP DC1) Q CIP 4 (Precast DC1) (Precast DC1) Q Precast 4 DC2 DC2 Q DC2
n
4 WS Q )] 4 [ Q 4 EQ Q ]
EQ
WS
EQ
WS
LL
LL
For collision load combination with partial live load:
7 R 9 [ (CIP DC1) (CIP DC1) Q CIP 4 (Precast DC1) (Precast DC1) Q Precast 4 DC2 DC2 Q DC2
n
4 WS Q )] 4 [ CV 0.5 Q ]
WS
CV
CV
WS