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// CODE SNIPPET

3107F.2.7.1 Joint Shear Capacity

Los Angeles Building Code > 31F [SLC] Marine Oil Terminals > 3107F Structural Analysis and Design of Components > 3107F.2 Concrete Deck With Concrete or Steel Piles > 3107F.2.7 Pile/Deck Connection Strength > 3107F.2.7.1 Joint Shear Capacity
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The joint shear capacity shall be computed in accordance with ACI 318 [7.7]. For existing MOTs, the method [7.1, 7.2] given below may be used:

  1. Determine the nominal shear stress in the joint region corresponding to the pile plastic moment capacity.

    (7-23)

    where:

    vj = Nominal shear stress

    Mp = Over strength moment demand of the plastic hinge (the maximum possible moment in the pile) as determined from the procedure of Section 3107F.2.5.7.

    ldv = Vertical development length, see Figure 31F-7-9

    Dp = Diameter of pile

    FIGURE 31F-7-9
    DEVELOPMENT LENGTH

  2. Determine the nominal principal tension pt, stress in the joint region:

    (7-24)

    where:

    (7-25)

    is the average compressive stress at the joint center caused by the pile axial compressive force N and hd is the deck depth. Note, if the pile is subjected to axial tension under seismic load, the value of N, and fa will be negative.

    If pt < 5.0 √ f 'c, psi, joint failure will occur at a lower moment than the column plastic moment capacity Mp. In this case, the maximum moment that can be developed at the pile/deck interface will be limited by the joint principal tension stress capacity, which will continue to degrade as the joint rotation increases, as shown in Figure 31F-7-10. The moment capacity of the connection at which joint failure initiates can be established from Equations (7-27) and (7-28).

    FIGURE 31F-7-10
    DEGRADATION OF EFFECTIVE PRINCIPAL TENSION STRENGTH WITH JOINT SHEAR STRAIN (rotation) [7.1, pg. 564]

    For pt = 5.0 f ' c , determine the corresponding joint shear stress, vj:

    (7-26)

  3. The moment capacity of the connection can be approximated as:

    (7-27)

    This will result in a reduced strength and effective stiffness for the pile in a pushover analysis. The maximum displacement capacity of the pile should be based on a drift angle of 0.04 radians.

    If no mechanisms are available to provide residual strength, the moment capacity will decrease to zero as the joint shear strain increases to 0.04 radians, as shown in Figure 31F-7-11.

    FIGURE 31F-7-11
    REDUCED PILE MOMENT CAPACITY

    If deck stirrups are present within hd/2 of the face of the pile, the moment capacity, Mc,r, at the maximum plastic rotation of 0.04 radians may be increased from zero to the following (see Figure 31F-7-12):

    (7-28)

    As = Area of slab stirrups on one side of joint

    hd = See Figure 31F-7-9 (deck thickness)

    dc = Depth from edge of concrete to center of main reinforcement

    In addition, the bottom deck steel (As, deckbottom) area within hd/2 of the face of the pile shall satisfy:

    (7-29)

    FIGURE 31F-7-12

    JOINT ROTATION

  4. Using the same initial stiffness as in Section 3107F.2.5.4, the moment-curvature relationship established for the pile top can now be adjusted to account for the joint degradation.

    The adjusted yield curvature, ϕ'y, can be found from:

    (7-30)

    Mn is defined in Figure 31F-7-4.

    The plastic curvature, ϕp, corresponding to a joint rotation of 0.04 can be calculated as:

    (7-31)

    Where Lp, is given by Equation (7-5).

    The adjusted ultimate curvature, ϕ'u, can now be calculated as:

    (7-32)

    Note that Mc,r = 0 unless deck stirrups are present as discussed above. Examples of adjusted moment curvature relationships are shown in Figure 31F-7-13.

FIGURE 31F-7-13
EQUIVALENT PILE CURVATURE

Related Code Sections


3107F.2.7.1 [SLC] Marine Oil Terminals, Joint Shear Capacity
The joint shear capacity shall be computed in accordance with ACI 318 [7.7]. For existing MOTs, the method [7.1, 7.2] given below may be used ...
Los Angeles Building Code > 31F [SLC] Marine Oil Terminals > 3107F Structural Analysis and Design of Components > 3107F.2 Concrete Deck With Concrete or Steel Piles > 3107F.2.7 Pile/Deck Connection Strength > 3107F.2.7.1 Joint Shear Capacity
2306.7.9.1.4 Motor Fuel-Dispensing Facilities and Repair Garages, Flexible Joints and Shear Joints
Flexible joints shall be installed in accordance with Section 5703.6.9. An approved shear joint shall be rigidly mounted and connected by a union ...
2017 LA City Fire Code > 23 Motor Fuel-Dispensing Facilities and Repair Garages > 2306 Flammable and Combustible Liquid Motor Fuel-Dispensing Facilities > 2306.7 Fuel-Dispensing Systems for Flammable or Combustible Liquids > 2306.7.9 Vapor-Recovery and Vapor-Processing Systems > 2306.7.9.1 Vapor-Balance Systems > 2306.7.9.1.4 Flexible Joints and Shear Joints
Section A103 Guidelines for the Seismic Retrofit of Existing Buildings, Definitions
] CROSSWALL. A new or existing wall that meets the requirements of Section A111.3. A crosswall is not a shear wall. [BS] CROSSWALL SHEAR CAPACITY ...
Los Angeles Existing Building Code > A Guidelines for the Seismic Retrofit of Existing Buildings > A103 Definitions
A111.3.2 Guidelines for the Seismic Retrofit of Existing Buildings, Crosswall Shear Capacity
Within any 40 feet (12 192 mm) measured along the span of the diaphragm, the sum of the crosswall shear capacities shall be at least 30 percent ...
Los Angeles Existing Building Code > A Guidelines for the Seismic Retrofit of Existing Buildings > A111 Special Procedure > A111.3 Crosswalls > A111.3.2 Crosswall Shear Capacity
A111.3.2 Guidelines for the Seismic Retrofit of Existing Buildings, Crosswall Shear Capacity
Within any 40 feet (12 192 mm) measured along the span of the diaphragm, the sum of the crosswall shear capacities shall be not less than 30 percent ...
Los Angeles Existing Building Code > A Guidelines for the Seismic Retrofit of Existing Buildings > A111 Special Procedure > A111.3 Crosswalls > A111.3.2 Crosswall Shear Capacity
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