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Bridge Engineering lec > LOADS ON BRIDGES: DESIGN LOADS > Flashcards

LOADS ON BRIDGES: DESIGN LOADS Flashcards

1
Q

Effect of acceleration, including that of due to gravity, imposed deformation or volumetric change

A

LOAD

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2
Q

An arbitrary selected design load level

A

NOMINAL LOAD

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3
Q

Coefficient expressing the probability of variations in the nominal load for
the expected service life of the bridge

A

LOAD FACTOR

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4
Q

Deformation or stress resultant (i.e. shear, torque/moment) caused by applied loads, imposed deformation or volumetric change

A

FORCE EFFECTS

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5
Q

IMPORTANCE OF LOAD PREDICTION

A

A structural engineer has to make a structure safe against failure

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6
Q

Reasons for structure being susceptible to failures are:

A

▪ Loads that structure will be called upon to sustain CANNOT be predicted with certainty

▪ The strength of various components CANNOT be assessed with full assertion

▪ The condition of structure may deteriorate with time causing it to lose strength

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7
Q

design of the bridge superstructure is based on a set of loading conditions which the component or element must withstand

A

DESIGN LOADS

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8
Q

Variety of loads are taken into consideration based on

A

▪Duration (permanent or temporary)
▪Direction (vertical, longitudinal, etc)
▪Deformation (creep, expansion)
▪Effect (shear, bending, torsion)

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9
Q

The following ___________________ shall be considered for design of bridges where applicable. The load provisions may also be applied to the structural evaluation of existing bridges

A

permanent and transient loads and forces

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10
Q

Categories of Loads:

A

▪PERMANENT LOAD
▪TRANSIENT LOADS

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11
Q

▪Loads that always remain and act on a bridge throughout its life

A

PERMANENT LOAD

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12
Q

▪TEMPORARY LOAD
▪Placed on bridge for only a short time

A

▪TRANSIENT LOADS

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13
Q

DD

A

DownDrag force

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14
Q

DC

A

Dead load of structural Components and nonstructural attachments

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15
Q

DW

A

Dead load of Wearing surfaces and utilities

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16
Q

EH

A

Horizontal Earth pressure load

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17
Q

EL

A

Miscellaneous Locked-in force Effects resulting
from construction process, including jacking
apart of cantilevers in segmental construction

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18
Q

ES

A

Earth Surcharge load

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19
Q

EV

A

Vertical pressure from dead load of Earth fill

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20
Q

PS

A

Secondary forces from Post-tensioning for
Strength limit states; total Prestress forces for
Service limit states

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21
Q

SH

A

Force effects due to SHrinkage

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22
Q

CR

A

Force effects due to CReep

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23
Q

BL

A

BLAST LOADING

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24
Q

BR

A

VEHICULAR BRAKING FORCE

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25
Q

CE

A

VEHICULAR CENTRIFUGAL FORCE

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26
Q

CT

A

VEHICULAR COLLISION FORCE

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27
Q

CV

A

VESSEL COLLISION FORCE

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28
Q

EQ

A

EARTHQUAKE

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29
Q

FR

A

FRICTION LOAD

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30
Q

IC

A

ICE LOAD

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31
Q

IM

A

VEHICULAR DYNAMIC LOAD ALLOWANCE

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32
Q

LL

A

VEHICULAR LIVE LOAD

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33
Q

LS

A

LIVE LOAD SURCHARGE

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34
Q

PL

A

PEDESTRIAN LIVE LOAD

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35
Q

SE

A

FORCE EFFECT DUE TO SETTLEMENT

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36
Q

TG

A

FORCE EFFECT DUE TO TEMPERATURE GRADIENT

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37
Q

TU

A

FORCE EFFECT DUE TO UNIFORM TEMPERATURE

38
Q

WA

A

WATER LOAD AND STREAM PRESSURE

39
Q

WL

A

WIND ON LIVE LOAD

40
Q

WS

A

WIND ON STRUCTURE

41
Q

CATEGORIES OF PERMANENT LOADS:

A
  1. DEAD LOAD
  2. SUPERIMPOSED LOAD
  3. PRESSURE
42
Q

▪Aggregate weight of all superstructure elements

A

DEAD LOAD

43
Q

▪Loads placed on superstructure after the deck has cured and begun to work with primary members in resisting loads

A

SUPERIMPOSED LOAD

44
Q

▪Pressure due to earth or water
▪Note: Though it primarily affect substructure elements, it has potential of
affecting superstructure elements as wells

A

PRESSURE

45
Q

▪Include the weight of all components of the structure, appurtenances and
utilities attached thereto, earth cover, wearing surface, future overlays, and
planned widening

A

DEAD LOAD

46
Q

deadload of structural components and nonstructural attachments

A

DC

47
Q

▪Refer to the elements that are part of load resistance system

A

▪STRUCTURAL COMPONENT

48
Q

▪Refers to items such as curbs, parapets, barriers, rails, signs, etc
▪Weight of such items can be estimated by using unit weight of material and its geometry

A

▪NONSTRUCTURAL ATTACHMENTS

49
Q

▪Include the weight of all components of the structure, appurtenances and
utilities attached thereto, earth cover, wearing surface, future overlays, and
planned widening

A

DEAD LOAD

50
Q

deadload of wearing surfaces and utilities

A

▪DW

51
Q

▪Estimated by taking the unit weight times the thickness of the surface
▪This value is combined with DC loads
▪Weight of utilities carried by the bridge is also included
▪Example: include pipes for sewage, oil, gas, communication wires, etc

A

DW

52
Q

DL for wearing surfaces and utilities are treated as separate DL group which have higher load factors due to its _______

A

larger uncertainty

53
Q

dead load of earth fill

A

EV

54
Q

▪Represents vertical earth pressure applied to substructure components by refill after the components are completed and buried as designed
▪Typical bridge component subjected to EV is the footing of an abutment or pier
▪MUST be considered for buried structures such as culverts
▪Determined by multiplying the unit weight time the depth of the materials

A

EV

55
Q

▪Includes earth loads

A

PRESSURE

56
Q

ES

A

earth surcharge load

57
Q

▪Refers to those loads and their effects on a wall buried in soil due to forces applied on the surface of backfill soil behind the wall
▪Calculated like EV loads with the only difference being in load factors
▪Difference is attributed to variability
▪Part of all load could be removed in future or surcharge material loads could be change

A

ES – earth surcharge load

58
Q

DD

A

downdrag

59
Q

▪Force exerted on a pile or drilled shaft due to soil movement around the element
▪Typically increases with time

A

DD – downdrag

60
Q

▪Example situations where possible downdrag
will be evaluated

A

▪Sites are underlain by compressible
material such as clay, silts or organic soils ▪Fill will be or has recently been placed
adjacent to the piles or shafts, such as
frequently the case of bridge approach fills ▪Groundwater can be substantially lowered ▪Liquefaction of loose sandy soil can occur

61
Q

EH

A

Horizontal Earth Pressure Load

62
Q

Refers to the horizontal earth
pressure normally relevant to the
substructure components such as
an abutment

A

EH – Horizontal Earth Pressure Load

63
Q

▪Refers to loads due to moving vehicles that are dynamic
▪Loads that change their positions with respect to time
▪For modern bridges, service lives are generally decades or even more than a hundred years
▪For highway bridges, the live load includes vehicle load and sidewalk load

A

LIVE LOADS

64
Q

▪hypothetical design vehicles based on truck loadings developed by AASHTO

A

VEHICLE LIVE LOAD (LL)

65
Q

VEHICLE LIVE LOAD (LL)
▪Three Categories:

A

▪Design Truck Load
▪Design Tandem Load
▪Design Lane Load

66
Q

1935 AASHO LOADING SCHEME

A

❏ H20-35
❏ H15-35

67
Q

▪1944 AASHTO LOADING SCHEME

A

❏ H10-44
❏ H15-44 ❏ HS15-44
❏ H20-44 ❏ HS20-44

68
Q

▪To account for higher loading conditions
▪25% increase in loading over the HS 20 -44 truck (90,000lb or 400kN)

A

HS -25

69
Q

“design vehicular live load”

A

HL – 93 loading

70
Q

▪composed of a design truck or tandem (identical to HS – 20 or tandem) which ever gives a larger force, combined with a 0.64 k/ft (9.34kN/m) design lane load
▪Design tandem : 2 - 25k axles spaced at 4.0 ft (1.2m)

A

▪HL – 93 loading

71
Q

▪Former Highway semitrailer 20-ton design truck (HS 20-44)

A

DESIGN TRUCK LOAD

72
Q

▪Consist of two 110-kN axles spaced at 1.20 m on center
▪Transverse spacing of wheels shall be taken as 1.8 m
▪Need to multiply this by dynamic allowance
factor (IM)

A

DESIGN TANDEM LOAD

73
Q

Lead to larger moment than the HS 20 truck for simple support beam with span length less 13. m
▪*tandem
– can be defined as two closely spaced and mechanically interconnected axles of equal weight

A

DESIGN TANDEM LOAD

74
Q

▪Number of lanes a bridge may accommodate must be established

A

DESIGN LANE LOAD

75
Q

▪The number of lanes of traffic that the traffic engineer plans to route across the bridge

A

TRAFFIC LANE

76
Q

▪A lane width is associated with a traffic lane and is typically __ m

A

3.6

77
Q

▪Lane designation used by bridge engineer for live load placement
▪Design lane width may or may not be the same as traffic lane

A

▪DESIGN LANE

78
Q

Number of Design lanes

A

= 𝐈𝐧𝐭𝐞𝐠𝐞𝐫 𝐨𝐟 𝐰/𝟑𝟔𝟎𝟎𝐦𝐦
≥ 𝐧𝐮𝐦𝐛𝐞𝐫 𝐨𝐟 𝐚𝐜𝐭𝐮𝐚𝐥 𝐭𝐫𝐚𝐟𝐟𝐢𝐜 𝐥𝐚𝐧e

79
Q

▪For roadway width from __ m to ___ m, there should be 2 design lanes

A

6 to 7.2

80
Q

______ is used in conjunction with design truck or tandem

A

lane load

81
Q

Lane load is spread over a 3m wide are in a standard __ m lane

A

3.6

82
Q

▪no dynamic allowance (IM) for this load

A

DESIGN LANE LOAD

83
Q

▪Live loads created by pedestrians and/or bicycles

A

PEDESTRIAN LOAD (PL)

84
Q

▪ A _________ is applied to sidewalks simultaneous
with the vehicular live load

A

0.075 KSF (3.6 kPa)

85
Q

a design live load of ______________ is used if bridge is designed only for pedestrian (including bicycle traffic)

A

0.085 ksf (4.07 kPa)

86
Q

▪If sidewalk is designed for vehicular load, ________ need not to be considered concurrently

A

pedestrian load

87
Q

No IM factor (neglect dynamic effect of pedestrians)

A

PEDESTRIAN LOAD

88
Q

▪Accounts for the dynamic effects of vehicle riding over a structure
▪An impact factor is used as multiplier for certain structural elements

A

IMPACT (DYNAMIC LOAD ALLOWANCE, IM)

89
Q

2 Sources of IMPACT (DYNAMIC LOAD ALLOWANCE, IM)

A
  1. Hammering Effect
  2. Dynamic response of bridge as a whole to passing vehicles
90
Q

Dynamic response of the wheel assembly to riding surface discontinuities, such as deck points, cracks, potholes and delamination

A

Hammering Effect

91
Q

Due to long undulations in the roadway pavements such as caused by settlement of fill, resonant excitation as result of similar frequencies of vibration between bridge and vehicle. Frequency of vibration of bridge should not exceed 3 Hz

A

Dynamic response of bridge as a whole to passing vehicles

Bridge Engineering lec (7 decks)

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