Structural Concrete - Hassoun

642 Chapter 17 Design of Two-Way Slabs
6. Determine the distribution factors for the positive and negative moments in the longitudinal
and transverse directions for each column and middle strip in both interior and exterior panels
as follows:
a. For interior panels, use the moment factors given in Table 17.4 or Fig. 17.15.
b. For exterior panels without edge beams, the panel moment factors are given in Table 17.2
or Fig. 17.14 (Case 5). For the distribution of moments in the transverse direction, use
Table 17.6 or Fig. 17.15 for column-strip ratios. The middle strip will resist the portion of
the moment that is not assigned to the column strip.
c. For exterior panels with edge beams, the panel moment factors are given in Table 17.2
or Fig. 17.14 (Case 4). For the distribution of moments in the transverse direction, use
Table 17.5 for the column strip. The middle strip will resist the balance of the panel
moment.
7. Determine the steel reinforcement for all critical sections of the column and middle strips and
extends the bars throughout the slab according to Fig. 17.16.
8. Compute the unbalanced moment and check if transfer of unbalanced moment by flexure is
adequate. If not, determine the additional reinforcement required in the critical width. (Refer
to Section 17.10.)
9. Check if transfer of the unbalanced moment by shear is adequate. If not, increase h or provide
shear reinforcement. (Refer to Section 17.10.)
Case 2. Slabs with interior and exterior beams.
1. Check the limitation requirements as explained in Section 17.8.1.
2. Determine the minimum slab thickness (h) to control deflection using Eqs. 17.1 through 17.3.
In most cases Eq. 17.2 controls.
3. Calculate the factored load, W u .
4. Check the slab thickness, h, according to one-way and two-way shear requirements. In general,
shear is not critical for slabs supported on beams.
5. Calculate the total static moment, M 0 in both directions (Eq. 17.17).
6. Determine the distribution factors for the positive and negative moments in the longitudinal
and transverse directions for each column and middle strips in both interior and exterior panels
as follows:
a. For interior panels, use moment factors in Fig. 17.14 (Case 3) or Fig. 17.12. For the distribution
of moments in the transverse direction, use Table 17.3 for column strips. The middle
strips will resist the portion of the moments not assigned to the column strips. Calculate
α 1 from Eq.17.12.
b. For exterior panels, use moment factors in Table 17.2 or Fig. 17.14 (Case 3). For the
distribution of moments in the transverse direction, use Table 17.5 for the column strip.
The middle strip will resist the balance of the panel moment.
c. In both cases (a) and (b), the beams must resist 85% of the moment in the column strip
when α f1
(l 2 ∕l 1 ) ≥ 1.0, whereas the ratio varies between 85 and 0% when α f1
(l 2 ∕l 1 ) varies
between 1.0 and 0.
7. Determine the steel reinforcement for all critical sections in the column strip, beam, and middle
strip; then extend the bars throughout the slab according to Fig. 17.16.
8. Compute the unbalanced moment and then check the transfer of moment by flexure and shear.
(Refer to Section 17.10.)