- Depth (H)
- Angle of rupture

**Fig.1: Sectional View of a Bunker**

Contents:

**Design Consideration of Bunkers **

**1. ****Design of Bunkers with Rectangular or Square Bottom**

The main structural elements that constitutes a bunker are shown in figure-2. They comprise of
- Vertical walls
- Hopper Bottom
- Edge Beam (At the top level)
- Supporting Columns

**Fig.2: Structural Elements of a bunker**

**Step 1: Design of Vertical Walls**

Based on Rankine's Theory, the lateral pressure applied on the vertical wall can be given by the formula
**Where,**

*P*= Lateral pressure intensity that is acting at a height of 'h'. L = Length of the bunker B = Breadth of the bunker

_{a}*a*= Angle of surcharge (The material slope as shown in figure-3)

*w*= density of the material stored in the bunker

**Fig.3: Representation of angle of surcharge (?) and pressure component acting on walls (p).**

*p*is acting in the direction parallel to angle of surcharge. So, the pressure that is applied on the vertical walls are the horizontal component of

_{a}*p*. Let it be p as shown in figure-3.

_{a}**Design Moments:**

a) Negative Moments at the supports
**Direct Tension:**

a) Tension in long walls
**b) Tension in Short walls**

**Effective depth:**

The effective depth is given by the formula
*A*), is arranged in the horizontal direction. Minimum distribution reinforcement is provided in the vertical direction. Minimum cross section of 300mm x 300mm edge beams are provided at the top, to facilitate attachments used by conveyor supports.

_{st}**Step 2: Design of Hopper Bottom**

The hopper bottom is designed for direct tension caused due to:
a) Self weight of the material
b) Self weight of sloping slab
**Fig. 4: Sloping slab in the hopper subjected to direct tension**

**Fig.5: Sloping Slab in Hopper Bottom Subjected to bending**

*wt*= weight of material

**Calculation of Direct tension**

**Calculation for Bending Moment**

To determine the maximum moments at the supports and the center of the sloping slab, we need to determine the normal pressure intensity which is the sum of normal pressure due to material weight and the self-weight of the slab
**a) Due to material weight**

If *w*= density of the material

*h*= average height at the center of the slope of bottom

*L*= Effective span at the center of the slope, as shown in figure-5 Then, Normal pressure intensity for depth h is

**b) Due to self-weight of slab**

Let*W*be the self-weight of slab Its normal component with respect to plane of slab is given by,

_{d}

**2. ****Design consideration of Bunkers with Circular Bottom**

For design of bunkers with circular cross section, vertical walls are subjected to a hoop tension along the diameter of the bunker. The value of hoop tension is given by the formula
*T _{h} = 0.5p_{h} .D*

*p*= horizontal component of pressure at a depth

_{h}*h*from the top The reinforcement details are provided to resist the hoop tension for this a minimum thickness of 120mm is recommended. The hopper bottom is designed for both direct and hoop tension due to normal pressure on the sloping slabs. Minimum vertical reinforcement is provided based on the bar used.