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    Benkelman Beam Deflection Studies: Transportation Engineering Section

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    Prashant Garg
    The document discusses Benkelman beam deflection studies, which is a test procedure used to evaluate the structural capacity of existing pavements. It involves measuring the deflection of the pavement surface under a standard wheel load using a Benkelman beam. The deflection measurements are then used to estimate the need for and design of overlays to strengthen weak pavements. The procedure involves selecting test points, placing the Benkelman beam and measuring the initial, intermediate, and final readings as the loaded truck is driven over the beam at the test point. Corrections are applied to standardize deflection values. Overlay design is based on a statistical analysis of deflection measurements across a given road section.

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    Benkelman Beam Deflection Studies: Transportation Engineering Section

    Uploaded by

    Prashant Garg
    109 views33 pages
    The document discusses Benkelman beam deflection studies, which is a test procedure used to evaluate the structural capacity of existing pavements. It involves measuring the deflection of the pavement surface under a standard wheel load using a Benkelman beam. The deflection measurements are then used to estimate the need for and design of overlays to strengthen weak pavements. The procedure involves selecting test points, placing the Benkelman beam and measuring the initial, intermediate, and final readings as the loaded truck is driven over the beam at the test point. Corrections are applied to standardize deflection values. Overlay design is based on a statistical analysis of deflection measurements across a given road section.

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    The document discusses Benkelman beam deflection studies, which is a test procedure used to evaluate the structural capacity of existing pavements. It involves measuring the deflection of the pavement surface under a standard wheel load using a Benkelman beam. The deflection measurements are then used to estimate the need for and design of overlays to strengthen weak pavements. The procedure involves selecting test points, placing the Benkelman beam and measuring the initial, intermediate, and final readings as the loaded truck is driven over the beam at the test point. Corrections are applied to standardize deflection values. Overlay design is based on a statistical analysis of deflection measurements across a given road section.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    109 views33 pages

    Benkelman Beam Deflection Studies: Transportation Engineering Section

    Uploaded by

    Prashant Garg
    The document discusses Benkelman beam deflection studies, which is a test procedure used to evaluate the structural capacity of existing pavements. It involves measuring the deflection of the pavement surface under a standard wheel load using a Benkelman beam. The deflection measurements are then used to estimate the need for and design of overlays to strengthen weak pavements. The procedure involves selecting test points, placing the Benkelman beam and measuring the initial, intermediate, and final readings as the loaded truck is driven over the beam at the test point. Corrections are applied to standardize deflection values. Overlay design is based on a statistical analysis of deflection measurements across a given road section.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 33

    Benkelman Beam Deflection

    Studies

    Transportation Engineering
    Section
    Introduction
    Benkelman Deflection Studies
    (IRC-81:1997)

    Static Load Test Procedure

    wheel

    Pavement
    Benkelman Beam

    Evaluation Of Structural Estimation And Design Of


    Over Lay
    Capacity Of
    For Strengthening Of Weak
    Existing Pavement Pavement
    Need of Evaluation
    • Pavement deteriorate functionally and
    structurally with time due to traffic loading and
    the different climatic condition.
    • It is necessary to evaluate the condition of
    existing pavement in terms of functionally and
    structurally.
    OVERLAY
    • Pavement that do not have adequate structural
    strength to carry out the projected future traffic
    will have to be reinforced by providing
    additional pavement layer
    Sub Grade Soil Type And Its
    Moisture Content

    Compaction

    Thickness

    Quality Of Pavement Course

    Drainage Condition Etc.


    • This test procedure covers the determination of
    the rebound deflection of a pavement under a
    standard wheel load and tyre pressure.
    Deflected Pavement Structure Bounce Back To
    Original Shape

    L L
    O O
    A A
    D D

    Deflected Surface Load removed Original Position


    1. Benkelman beam –
    • Consist of slender beam of length 3.66 m.
    • Pivoted at 2.44 m from probe.
    • distance from pivot to dial gauge 1.22 m.
    • Distance from pivot to front leg 25 cm.
    • Distance from pivot to rear leg 1.66 m.
    2. Loaded truck
    • Weight of truck 12 t
    • Rear axle load 8170 kg(dual tyre)
    • Spacing between tyres 30-40 mm.
    • Inflation pressure 5.6 kg/sq.cm.
    3. Accessories –
    • Tyre pressure measuring gauge.
    • Thermometer(0-100 °c) with 1 ° division.
    • Measuring tape.etc
    Deflection Survey

    1 .Pavement Condition Done As Per


    Survey IRC-81:1997

    2.Measurement Of Deflection
    • Deflection Measurement –
    • Point selection –
    • 1 km road stretch .
    • Minimum 10 points at 50 m interval .
    • Location Of Point –

    • Lane Width(m)
    • Distance From Lane Edge(cm)
    • Less than 3.5
    • 60
    • More than 3.5
    • 90
    A 2.7 m B 9m C
    1. Select the points and marked.
    2. The dual wheel of the truck is centered above the mark.
    3. The probe of the benkelman beam is placed between the dual
    tyres at the marked position.
    4. Dial gauge is set at 1 cm.
    5. Initial reading (s) is recorded when rate of deformation is less
    than or equal to .025 mm/min.
    6. Truck is slowly driven (at speed 8-10 m/s appr.)
    at a distance of 2.7 m. and stopped.
    7. Intermediate reading (I) is recorded.
    8. Truck is driven forward a further 9 m.
    9. Final reading (F) is recorded.
    10.Pavement temperature is recorded atleast once
    in each hour.
    11.Tyre pressure is checked at 2-3 hrs interval
    during a day.
    •Find (S-I) & (S-F)

    • If deferential Reading ≤ 0.025 mm (2.5 Divisions), then


    True Rebound Deflection At Temp. T Is
    XT = 2(S-F)

    •If deferential reading ≥ 0.025mm, then

    XT = 2(S-F) + 5.82 (I-F)

    The pavement rebound deflection at a standard temperature


    of 20°C shall be calculated
    • Standard temp 35 °c.
    • Correction is applied when min thickness of the pavement
    is 40 mm.
    • No correction for
    – thin bituminous surfacing
    – severe cracking in pavement
    – bituminous layer is striped.
    – Cold and high altitude regions where daily temp. < 20 °c
    • Correction will be positive when temp blow stand.
    Temperature
    • Correction will be negative when temperature above
    standard temperature.
    • Correction factor is 0.01mm/ °c variation from standard
    temp.
    Over Lay Design For A Given Section Is Based Not
    On Individual Deflection Value But On Statistical
    Analysis Of All Measurements In The Section

    1.Mean Deflection

    2.Standard Deviation

    3.Charecteristic Deflection

    DC = M + 2S, For NH & SH


    DC = M +S, for other roads
    Concept of Over Lay

    Undulated Surface Cracked Surface

    Over Lay Surface


    Surface

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