Page 180 - Civil Engineering Formulas

CONCRETE FORMULAS 117

TENSILE STRENGTH OF CONCRETE

The tensile strength of concrete is used in combined-stress design. In normal-
weight, normal-density concrete the tensile strength can be found from

2
f r 7.5 2 c lb/in in USCS units (5.5)
f
f
f r 0.7 2 c MPa in SI units
REINFORCING STEEL

American Society for Testing and Materials (ASTM) specifications cover ren-
forcing steel. The most important properties of reinforcing steel are

2
1. Modulus of elasticity E , lb/in (MPa)
s
2
2. Tensile strength, lb/in (MPa)
2
3. Yield point stress f , lb/in (MPa)
y
4. Steel grade designation (yield strength)
5. Size or diameter of the bar or wire
CONTINUOUS BEAMS AND ONE-WAY SLABS

The ACI Code gives approximate formulas for finding shear and bending
moments in continuous beams and one-way slabs. A summary list of these for-
mulas follows. They are equally applicable to USCS and SI units. Refer to the
ACI Code for specific applications of these formulas.

For Positive Moment

End spans
If discontinuous end is unrestrained wl n 11
2
2
If discontinuous end is integral with the support wl n 14
Interior spans wl n 16
2
For Negative Moment

Negative moment at exterior face of first interior
support
2
Two spans wl n 9
2
More than two spans wl n 10
Negative moment at other faces of interior supports wl n 11
2