Structural Concrete - Hassoun

CHAPTER23
REVIEW PROBLEMS ON CONCRETE
BUILDING COMPONENTS
In order to achieve the desired strength of concrete in structural elements, it is particularly important
to follow the proper procedure of determining member dimensions and the necessary reinforcement
required. This chapter mainly focuses on the general process of designing various building components,
such as slabs, beams, columns, and footings, with compliance to ACI Code 318-14. The first
step is to calculate the required strength of each of these elements by multiplying the actual applied
loads by load factors. These loads then develop external forces, such as bending moment, shear,
axial forces, or torsion, depending on how these loads are being applied to the structure. Once the
strength requirements are determined, the proper reinforcement, along with the appropriate dimensions
of each element, can then be developed. The final design of structural elements must account
for three main items: structural safety, deflection, and cracking conditions.
Example 23.1
A simply supported beam has a 30 ft span and carries a service uniform dead load of 2 K/ft (including
self-weight) and a uniform live load of 0.5 K/ft.
′
Given: b = 14 in., d = 26 in., f c = 5ksi,f y = 60 ksi.
a. Design the section for flexural reinforcement.
b. Design for shear reinforcement.
c. Check for development length.
Solution:
a. Design the section for flexural reinforcement
Check for minimum thickness to satisfy the deflection criterion: (ACI Code, Section 24.2.3.1)
Minimum thickness for simply supported beams =L16=30 × 1216 = 22.5 in. < 29 in. (OK)
Determine the design moment strength: (ACI Code, Section 5.3.1)
M u = 1.2M DL + 1.6M LL
M u = 1.2 w DL × L2
8
+ 1.6 w LL × L2
8
M u = 1.2 2 × 302 0.5 × 302
+ 1.6
8
8
M u = 360 K ⋅ ft = 4, 320 K ⋅ in.
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