D-1Restrained slabs

D-1.0

When the corners of a slab are prevented from lifting, the slab may be designed as specified in D-1.1 to D-1.11.

D-1.1

The maximum bending moments per unit width in a slab are given by the following equations:

$M_{x}=\alpha_{x} w$

$M_{y}=\alpha_{y} w$

where

$\alpha_{x}$ and $\alpha_{y}$ are coefficients given in Table 26,

$w=$ total design load per unit area,

• $\begin{aligned} M_{x}, M_{y} & =\text { moments on strips of unit width } \\ & \text { spanning } l_{x} \text { and } l_{y} \text { respectively, } \\ & \text { and }\end{aligned}$
• $l_{\mathrm{x}}$ and $l_{\mathrm{y}}=$ lengths of the shorter span and longer span respectively.

D-1.2

Slabs are considered as divided in each direction into middle strips and edge strips as shown in Fig. 25 the middle strip being three-quarters of the width and each edge strip one-eight of the width.

D-1.3

The maximum moments calculated as in D-1.1 apply only to the middle strips and no redistribution shall be made.

D-1.4

Tension reinforcement provided at mid-span in the middle strip shall extend in the lower part of the slab to within 0.25 l of a continuous edge, or 0.15 l of a discontinuous edge.

D-1.5

Over the continuous edges of a middle strip, the tension reinforcement shall extend in the upper part of the slab a distance of 0.15 / from the support, and at least 50 percent shall extend a distance of 0.3 /.

D-1.6

At a discontinuous edge, negative moments may arise. They depend on the degree of fixity at the edge of the slab but, in general, tension reinforcement equal to 50 percent of that provided at mid-span extending 0.1 l into the span will be sufficient.

D-1.7

Reinforcement in edge strip, parallel to that edge, shall comply with the minimum given in Section 3 and the requirements for torsion given in D-1.8 to D-1.10.

D-1.8

Torsion reinforcement shall be provided at any corner where the slab is simply supported on both edges meeting at that corner. It shall consist of top and bottom reinforcement, each with layers of bars placed parallel to the sides of the slab and extending from the edges a minimum distance of one-fifth of the shorter span. The area of reinforcement in each of these four layers shall be three-quarters of the area required for the maximum mid-span moment in the slab.

D-1.9

Torsion reinforcement equal to half that described in D-1.8 shall be provided at a corner contained by edges over only one of which the slab is continuous.

D-1.10

Torsion reinforcements need not be provided at any corner contained by edges over both of which the slab is continuous.

D-1.11

Torsion $l_{y} / l_{x}$ is greater than 2 , the slabs shall be designed as spanning one way.