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

LOADS ON BRIDGES: DESIGN LOADS Flashcards

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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
CE
VEHICULAR CENTRIFUGAL FORCE
26
CT
VEHICULAR COLLISION FORCE
27
CV
VESSEL COLLISION FORCE
28
EQ
EARTHQUAKE
29
FR
FRICTION LOAD
30
IC
ICE LOAD
31
IM
VEHICULAR DYNAMIC LOAD ALLOWANCE
32
LL
VEHICULAR LIVE LOAD
33
LS
LIVE LOAD SURCHARGE
34
PL
PEDESTRIAN LIVE LOAD
35
SE
FORCE EFFECT DUE TO SETTLEMENT
36
TG
FORCE EFFECT DUE TO TEMPERATURE GRADIENT
37
TU
FORCE EFFECT DUE TO UNIFORM TEMPERATURE
38
WA
WATER LOAD AND STREAM PRESSURE
39
WL
WIND ON LIVE LOAD
40
WS
WIND ON STRUCTURE
41
CATEGORIES OF PERMANENT LOADS:
1. DEAD LOAD 2. SUPERIMPOSED LOAD 3. PRESSURE
42
▪Aggregate weight of all superstructure elements
DEAD LOAD
43
▪Loads placed on superstructure after the deck has cured and begun to work with primary members in resisting loads
SUPERIMPOSED LOAD
44
▪Pressure due to earth or water ▪Note: Though it primarily affect substructure elements, it has potential of affecting superstructure elements as wells
PRESSURE
45
▪Include the weight of all components of the structure, appurtenances and utilities attached thereto, earth cover, wearing surface, future overlays, and planned widening
DEAD LOAD
46
deadload of structural components and nonstructural attachments
DC
47
▪Refer to the elements that are part of load resistance system
▪STRUCTURAL COMPONENT
48
▪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
▪NONSTRUCTURAL ATTACHMENTS
49
▪Include the weight of all components of the structure, appurtenances and utilities attached thereto, earth cover, wearing surface, future overlays, and planned widening
DEAD LOAD
50
deadload of wearing surfaces and utilities
▪DW
51
▪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
DW
52
DL for wearing surfaces and utilities are treated as separate DL group which have higher load factors due to its _______
larger uncertainty
53
dead load of earth fill
EV
54
▪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
EV
55
▪Includes earth loads
PRESSURE
56
ES
earth surcharge load
57
▪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
ES – earth surcharge load
58
DD
downdrag
59
▪Force exerted on a pile or drilled shaft due to soil movement around the element ▪Typically increases with time
DD – downdrag
60
▪Example situations where possible downdrag will be evaluated
▪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
EH
Horizontal Earth Pressure Load
62
Refers to the horizontal earth pressure normally relevant to the substructure components such as an abutment
EH – Horizontal Earth Pressure Load
63
▪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
LIVE LOADS
64
▪hypothetical design vehicles based on truck loadings developed by AASHTO
VEHICLE LIVE LOAD (LL)
65
VEHICLE LIVE LOAD (LL) ▪Three Categories:
▪Design Truck Load ▪Design Tandem Load ▪Design Lane Load
66
1935 AASHO LOADING SCHEME
❏ H20-35 ❏ H15-35
67
▪1944 AASHTO LOADING SCHEME
❏ H10-44 ❏ H15-44 ❏ HS15-44 ❏ H20-44 ❏ HS20-44
68
▪To account for higher loading conditions ▪25% increase in loading over the HS 20 -44 truck (90,000lb or 400kN)
HS -25
69
“design vehicular live load”
HL – 93 loading
70
▪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)
▪HL – 93 loading
71
▪Former Highway semitrailer 20-ton design truck (HS 20-44)
DESIGN TRUCK LOAD
72
▪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)
DESIGN TANDEM LOAD
73
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
DESIGN TANDEM LOAD
74
▪Number of lanes a bridge may accommodate must be established
DESIGN LANE LOAD
75
▪The number of lanes of traffic that the traffic engineer plans to route across the bridge
TRAFFIC LANE
76
▪A lane width is associated with a traffic lane and is typically __ m
3.6
77
▪Lane designation used by bridge engineer for live load placement ▪Design lane width may or may not be the same as traffic lane
▪DESIGN LANE
78
Number of Design lanes
= 𝐈𝐧𝐭𝐞𝐠𝐞𝐫 𝐨𝐟 𝐰/𝟑𝟔𝟎𝟎𝐦𝐦 ≥ 𝐧𝐮𝐦𝐛𝐞𝐫 𝐨𝐟 𝐚𝐜𝐭𝐮𝐚𝐥 𝐭𝐫𝐚𝐟𝐟𝐢𝐜 𝐥𝐚𝐧e
79
▪For roadway width from __ m to ___ m, there should be 2 design lanes
6 to 7.2
80
______ is used in conjunction with design truck or tandem
lane load
81
Lane load is spread over a 3m wide are in a standard __ m lane
3.6
82
▪no dynamic allowance (IM) for this load
DESIGN LANE LOAD
83
▪Live loads created by pedestrians and/or bicycles
PEDESTRIAN LOAD (PL)
84
▪ A _________ is applied to sidewalks simultaneous with the vehicular live load
0.075 KSF (3.6 kPa)
85
a design live load of ______________ is used if bridge is designed only for pedestrian (including bicycle traffic)
0.085 ksf (4.07 kPa)
86
▪If sidewalk is designed for vehicular load, ________ need not to be considered concurrently
pedestrian load
87
No IM factor (neglect dynamic effect of pedestrians)
PEDESTRIAN LOAD
88
▪Accounts for the dynamic effects of vehicle riding over a structure ▪An impact factor is used as multiplier for certain structural elements
IMPACT (DYNAMIC LOAD ALLOWANCE, IM)
89
2 Sources of IMPACT (DYNAMIC LOAD ALLOWANCE, IM)
1. Hammering Effect 2. Dynamic response of bridge as a whole to passing vehicles
90
Dynamic response of the wheel assembly to riding surface discontinuities, such as deck points, cracks, potholes and delamination
Hammering Effect
91
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
Dynamic response of bridge as a whole to passing vehicles

Bridge Engineering lec (7 decks)

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