One-Way Slab Classification Criteria

A reinforced concrete slab is classified based on how it distributes the applied loads to the supporting beams or walls. This distribution is primarily influenced by the slab's geometry, specifically the ratio of its longer span to its shorter span.

Distinguishing One-Way vs. Two-Way Slabs

• One-Way Slab: Behaves as if it bends primarily in one direction. Loads are mainly supported by the two parallel sides.
• Two-Way Slab: Bends in two directions. Loads are supported by all four sides.

Span Ratio Condition for One-Way Slabs

The primary criterion to determine if a slab is a one-way slab is the ratio of the longer span to the shorter span. Let $L_y$ represent the longer span and $L_x$ represent the shorter span.

A slab is generally considered a one-way slab if the ratio $\frac{L_y}{L_x}$ is greater than 2.

Mathematically, the condition is:

$ \frac{L_y}{L_x} > 2 $

Applying the Condition to Options

Based on the established engineering principle:

• Option 1: $\frac{L_y}{L_x} \le 1$. This implies $L_y \le L_x$, which contradicts $L_y$ being the longer span, unless $L_y = L_x$. If $L_y = L_x$, it's a square slab, typically considered two-way.
• Option 2: $\frac{L_y}{L_x} \le 2$. This range includes slabs that behave as two-way slabs (ratio close to 1) up to the threshold.
• Option 3: $\frac{L_y}{L_x} > 2$. This condition correctly identifies slabs that predominantly bend along the shorter span, behaving as one-way slabs.
• Option 4: $\frac{L_y}{L_x} = 1$. This represents a square slab, which is typically classified as a two-way slab.

Therefore, the condition for a slab to be considered a one-way slab is $\frac{L_y}{L_x} > 2$.