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RM E Prestressing Basic Part2 AASHTO Imp

Jan 16, 2016

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  • RM Bridge Professional Engineering Software for Bridges of all Types

    RM Bridge V8i

    March 2011

    TRAINING PRESTRESSING BASIC

    ANALYZER PART 2: AASHTO [IMP. UNITS]

  • RM Bridge

    Training Prestressing Basic - ANALYZER - Part 2: AASHTO [IMPERIAL UNITS] I

    Bentley Systems Austria

    Content

    1 General ................................................................................................................... 1-1

    1.1 Design Code ................................................................................................... 1-1

    1.2 Design Loadings: ........................................................................................... 1-1

    1.2.1 Permanent actions and Creep & Shrinkage ............................................... 1-1

    1.2.2 Live Load ................................................................................................... 1-1

    1.2.3 Braking Loads ............................................................................................ 1-3

    1.2.4 Wind Loads ................................................................................................ 1-3

    1.2.5 Thermal Forces .......................................................................................... 1-4

    1.2.6 Creep and Shrinkage .................................................................................. 1-5

    1.2.7 Pier settlement ............................................................................................ 1-5

    1.3 Load combinations ......................................................................................... 1-6

    1.4 Design checks ................................................................................................ 1-7

    1.4.1 Servicebility limit state .............................................................................. 1-7

    1.4.2 Ultimate limit state ..................................................................................... 1-7

    2 Lesson 13: Definition of Additional Loads ........................................................... 2-1

    2.1 Definition of Settlement Load Cases ............................................................. 2-1

    2.2 Definition of Temperature Load Case ........................................................... 2-2

    2.3 Definition of Wind Load Case ....................................................................... 2-4

    2.4 Definition of Braking Forces ......................................................................... 2-6

    3 Lesson 14: Calculation and Superposition of Additional Loads ........................... 3-1

    3.1 Calculation and superposition of Settlement loads ........................................ 3-1

    3.2 Calculation and superposition of temperature loads ...................................... 3-3

    3.3 Calculation and superposition of wind loads ................................................. 3-4

    3.4 Calculation and superposition of braking loads ............................................. 3-5

    4 Lesson 15: Traffic Loads ....................................................................................... 4-7

    4.1 Traffic Definition ........................................................................................... 4-7

    4.2 Definition of Traffic Lanes ............................................................................ 4-9

    4.3 Traffic Loads ................................................................................................ 4-11

    4.4 Traffic Calculation ....................................................................................... 4-12

    4.4.1 Calculation of influence lines .................................................................. 4-12

  • RM Bridge

    Training Prestressing Basic - ANALYZER - Part 2: AASHTO [IMPERIAL UNITS] II

    Bentley Systems Austria

    4.4.2 Combining Influence Lines with Load Trains ......................................... 4-13

    4.5 Traffic Superposition ................................................................................... 4-15

    5 Lesson 16: Load Combinations ............................................................................. 5-1

    5.1 Definition of the Load Combination .............................................................. 5-1

    5.2 Calculation of the load combinations ............................................................ 5-3

    6 Lesson 17: Fiber Stress Check ............................................................................... 6-1

    7 Reinforced concrete checks General ................................................................... 7-3

    8 Lesson 18: Ultimate Load Capacity Check ........................................................... 8-1

    9 Lesson 19: Shear Capacity Check ......................................................................... 9-1

    10 Lesson 20: Fatigue Check .................................................................................... 10-2

    11 Lesson 21: Lists and Plots ................................................................................... 11-4

  • RM Bridge

    Training Prestressing Basic - ANALYZER - Part 2: AASHTO [IMPERIAL UNITS] 1-1

    Bentley Systems Austria

    1 General

    1.1 Design Code

    This example is designed in accordance with AASHTO LRFD 2007.

    1.2 Design Loadings:

    1.2.1 Permanent actions and Creep & Shrinkage

    See Prestressing Basic Training Analyzer Part 1; Chapter 1.7.

    1.2.2 Live Load

    Traffic loads will be in accordance with AASHTO 3.6.1 and 3.6.2. Centrifugal force is

    not considered in this example. Three lanes will be considered, and multiple presence

    factors will be applied as required.

    A simplification is made which assumes that the axial load trains stay at a fixed location

    transversely within the notional lane. Varying the load positions in the transverse direc-

    tion would have no effect on the longitudinal bending moment and shear force for cal-

    culations on the global one-beam system*. In order to produce the worst case torsional

    moments, all of the load trains could be shifted to one side of their respective notional

    lanes.

    During the live load superposition, the dynamic impact factor 1.33 will be applied

    where necessary according to AASHTO 3.6.2. Also for the negative bending region, a

    factor of 90% will be applied to the double truck load train.

    The optional live load deflection evaluation is not checked in this example.

    The following figures show the necessary load trains for HL-93 loading. A more de-

    tailed description of how they will be superimposed is presented in Section 4.1.

    *This is not true of a grillage model where position of the load train transversely within the

    notional lane must be considered for longitudinal bending.

  • RM Bridge

    Training Prestressing Basic - ANALYZER - Part 2: AASHTO [IMPERIAL UNITS] 1-2

    Bentley Systems Austria

    1.2.2.1 Load train 1 Lane

    1.2.2.2 Load train 2 Truck

    1.2.2.3 Load train 3 Tandem

  • RM Bridge

    Training Prestressing Basic - ANALYZER - Part 2: AASHTO [IMPERIAL UNITS] 1-3

    Bentley Systems Austria

    1.2.2.4 Load train 4 Double Truck

    1.2.2.5 Load train 5 Fatigue Truck

    1.2.3 Braking Loads

    Braking load will be calculated in accordance with AASHTO 3.6.4, and is taken as the

    greater of:

    - 25% of the axle weights of the design truck or tandem

    - 5% of the design truck/tandem plus the lane load

    In this example, 25% of the design truck is the governing condition:

    (32 kip + 32 kip + 8 kip)x0.25 = 18 kip

    It is assumed that all three lanes are loaded and multiple presence factors are applied.

    Because the lanes are symmetric about the centerline of the bridge, the braking load will

    be applied as a single uniform line load located 1.8m above the surface of the deck. The

    load will have the following magnitude:

    18kip x 3(lanes) x 0.85 (mult. presence) / 455ft (length of bridge) = 0.1 kip/ft

    1.2.4 Wind Loads

    AASHTO 3.8.1.2 will be used to determine the wind pressure to be applied on the struc-

    ture. In the absence of information about the wind velocity for a bridge taller than 30 ft,

    design wind velocity is assumed to be 100mph. Therefore, the wind pressure is as fol-

    lows:

  • RM Bridge

    Training Prestressing Basic - ANALYZER - Part 2: AASHTO [IMPERIAL UNITS] 1-4

    Bentley Systems Austria

    = 0.05 kip/ft2

    Wind pressure will be applied to the concrete box, and it is also assumed to act on a

    barrier that is 3 ft tall.

    Wind load on the live load according to AASHTO 3.8.1.3 is also applied.

    Wind on Live Load: 0.1 kip/ft (6 ft above the deck)

    1.2.5 Thermal Forces

    Uniform temperature and temperature gradient loads will be applied to the structure.

    The initial temperature is assumed to be 68oF.

    According to AASHTO 3.12.2.1 the temperature range for uniform temperature diffe-

    rence will be 0.0oF to 80

    oF (table 3.12.2.1-1). For an initial temperature of 68

    oF this

    gives:

    - Uniform temperature postitive = 12oF - Uniform temperature negative = -68oF

    Thermal Coefficient: 6 x 10e-6 per F

    The non-linear temperature gradient is done according to AASHTO 3.12.3. The struc-

    ture is assumed to be in temperature zone 3, thus the values for T1 and T2 are given in

    table 3.12.3-1. T3 is

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