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International Design Codes

ACI 318-19 : Longitudinal Reinforcement (SwRD)

TSC 2018 :

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Notation in ACI 318-19

A_g = gross area of concrete section, in²
A_st = total area of nonprestressed longitudinal reinforcement, in²
b_w = web width or diameter of circular section, in.
d = distance from extreme compression fiber to centroid of longitudinal tension reinforcement, in.
d_b = nominal diameter of bar, wire, or prestressing strand, in
√f_c‘ = square root of specified compressive strength of concrete, psi
f_y = specified yield strength of nonprestressed reinforcement,psi
f_yt = specified yield strength of transverse reinforcement, psi
h = overall thickness, height, or depth of member, in.
h_sx = story height for story x, in.
h_w = height of entire wall from base to top, or clear height of wall segment or wall pier considered, in.
l_d = development length in tension of deformed bar, deformed wire, plain and deformed welded wire reinforcement, or pretensioned strand, in.
l_w = length of entire wall, or length of wall segment or wall pier considered in direction of shear force, in.
M_u= factored moment at section, in.-lb
s = center-to-center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.
V_u = factored shear force at section, lb
ϕ = strength reduction factor

According to ACI 11.7.2.1; maximum spacing of longitudinal reinforcement bars in shear walls is the lesser of 3h and 18 inches. If shear reinforcement is required for in-plane strength, maximum longitunal reinforcement spacing is l_w/3.

According to ACI 11.7.4.1; logitudinal reinforcement should be laterally supported bu transverse reinforcement if the following two conditions are satified;

• A_st > 0.01A_g

• longitudinal reinforcement is required

Earthquake Reistant Structures

Special structural walls

According to ACI 18.10.2.3; longitudinal reinforcement in structural walls shoud be satisfied the reqirements in titles Development of Reinforcement and Splices as well as the following conditions;

• Except at the top of a wall, longitudinal reinforcement shall extend at least 12 ft above the point at which it is no longer required to resist flexure but need not extend more than l_d above the next floor level.

• At locastions where longitudinal reinforcement yielding is likely to occur due to lateral displacements , development lengths of longitudinal reinforcement should be 1.25 times the values calculated for f_y in tension.

• At locations where yielding of longitudinal reinforcement is likely to occur due to lateral displacements, lap splices of longitudinal reinforcement within boundary regions should not be permitted over a height equal to h_sx above, and l_d below. The maximum value of h_sx is 20 ft.

According to ACI 18.10.2.4; walls or wall piers with h_w/l_w ≥ 2.0 that are effectively continuous from the base of structure to top of wall and are designed to have a single critical section for flexure and axial loads should have longitudinal reinforcement at the ends of a vertical wall segment that satisfies conditions given below;

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minimum longitudinal reinforcement ratio in the area 0.15l_w from the end of a vertical wall segment, and over a width equal to the wall thickness, should be 6√f_c‘/f_y.

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longitudinal reinforcement should extend vertically above and below the critical section at least the greater of l_w and M_u/3V_u.

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