---
title: "Warehouse exterior wall, wind 860 N/m2, anchored"
subject: "Concrete Technology and Masonry Structure"
chapter: 9
key: "semester_5/concrete_technology_and_masonry_structure:wind-wall-warehouse-860-floor-roof"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/wind-wall-warehouse-860-floor-roof
site: BCT Engineering
---

# Warehouse exterior wall, wind 860 N/m2, anchored

Concrete Technology and Masonry Structure · Chapter 9: Masonry structures under lateral loads

- Asked in: 2071 Chaitra, 12 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/wind-wall-warehouse-860-floor-roof
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-9

## Question

Design an exterior wall of a single storey warehouse of 3.5 m height. The loading on the wall consists of a vertical load of 25 kN/m from the roof and wind pressure of 860 N/m$^2$. The wall is tied with metal anchor at the floor and roof level.

## Short answer

A 230 mm thick wall is required. Use bricks with minimum compressive strength 3.5 N/mm² and cement mortar grade M1 (1:5) or richer. The maximum and minimum stresses at mid-height are 0.291 N/mm² and -0.007 N/mm²; the slight tension is within the 0.07 N/mm² flexural tension limit.

## Answer

#### Data and assumptions

- Exterior wall of a single-storey warehouse, 3.5 m high, tied by metal anchors at floor and roof levels (simply supported vertically). $P=25$ kN/m (axial); wind pressure 860 N/m$^2$.
- Anchors give lateral restraint only: $h_{ef}=1.0H$ (Table 4 Sl. 3).
- Design by IS 1905:1987 cl. 5.4.1, 5.4.2, 5.5.2, 5.5.3 (NBC 109 follows the same method). Unit weight of masonry 19 kN/m$^3$. Per metre run of wall.

```text
     roof anchor (support)
        |<-- wind w
  ------+-----------   load P=25
        |   |
        | wall, H=3.5 m
        |   |  M = wH^2/8 at mid-height
  ------+-----------
        floor anchor (support)
```

#### Step 1: Wind moment

$$
\begin{aligned} w &= 0.860\ \text{kN/m (per m of wall)}\\ M &= 0.860\times3.5^2/8 = 1.317\ \text{kNm/m} \end{aligned}
$$

#### Step 2: Trial thickness 230 mm, load and slenderness

$$
\begin{aligned} \text{Self weight of wall} &= 0.230\times3.50\times19 = 15.30\ \text{kN/m}\\ N\ (\text{at mid-height}) &= 25 + 15.30/2 = 32.65\ \text{kN/m}\\ h_{ef} &= 1.0\times3.5=3.5\ \text{m} \\ SR &= \frac{3.500}{0.230} = 15.22\ (<27) \end{aligned}
$$

#### Step 3: Stresses at the mid-height section

$$
\begin{aligned} \sigma_a &= \frac{N}{A}=\frac{32.65\times10^3}{230\times10^3} = 0.1419\ \text{N/mm}^2\\ \sigma_b &= \frac{6M}{t^2} = \frac{6\times1.317\times10^6}{1000\times230^2} = 0.1494\ \text{N/mm}^2\\ \sigma_{max} &= \sigma_a+\sigma_b = 0.2913,\qquad \sigma_{min} = \sigma_a-\sigma_b = -0.0075\ \text{N/mm}^2 \end{aligned}
$$

$\sigma_{min}$ is a small tension of about 0.0075 N/mm$^2$ (resultant $e/t=0.175>1/6$). This is below the permissible flexural tension of 0.07 N/mm$^2$ for vertical bending with mortar M1 or better (IS 1905 cl. 5.4.2), so the wall is safe against cracking provided the mortar is M1 or richer.

#### Step 4: Required basic compressive stress

Resultant eccentricity ratio $e/t = M/(Nt) = 0.175$. From Table 9: $k_s=0.653$ ($SR=15.22$, $e/t=0.175$; the factor is lower than for a smaller eccentricity at the same slenderness). $k_a=1$, $k_p=1$. Conservatively, the 25 percent increase allowed for $e/t>1/6$ (with the tension area disregarded) is not taken.

$$
f_b \ge \frac{\sigma_a}{k_sk_ak_p\times1.00} = \frac{0.1419}{0.653\times1.00} = 0.217\ \text{N/mm}^2
$$

#### Step 5: Brick and mortar (IS 1905 Table 8)

| Mortar (IS 1905 Table 1) | Min. unit strength (N/mm²) | Table 8 $f_b$ (N/mm²) |
|---|---|---|
| M2 (cement:sand 1:6) | 3.5 | 0.35 |
| M1 (cement:sand 1:5) | 3.5 | 0.35 |
| H2 (cement:sand 1:4) | 3.5 | 0.35 |
| H1 (cement:sand 1:3) | 3.5 | 0.35 |

For comparison, IS 1905 Table 11 (free-standing walls; 860 N/m$^2$ gives $H/t=5$) applies to walls without anchors: it would need $t=3.5/5=0.70$ m, which shows the importance of the anchors.

**Answer: 230 mm thick wall; bricks not less than 3.5 N/mm$^2$ in cement mortar of grade M1 (1:5) or richer** (needed for the 0.07 N/mm$^2$ flexural tension allowance); practical choice 5 N/mm$^2$ bricks with 1:5 mortar. Stresses at mid-height: $\sigma_{max}=0.291$ and $\sigma_{min}=-0.007$ N/mm$^2$; slenderness ratio 15.2.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the wind moment for w = 0.860 kN/m, H = 3.5 m, simply supported?
   A. 1.317 kNm/m
   B. 5.26 kNm/m
   C. 2.63 kNm/m
   D. 0.439 kNm/m
   Answer: A. M = wH^2/8 = 0.860 x 12.25/8 = 1.317 kNm/m. (Key point: Wind moment)

2. sigma_min = -0.0074 N/mm^2 here. Why is the wall still acceptable?
   A. Tension is ignored in masonry
   B. The tension is below the permissible flexural tension of 0.07 N/mm^2 for M1 or richer mortar
   C. The wall is thickened to remove it
   D. Wind load is reduced by 25 percent
   Answer: B. IS 1905 cl. 5.4.2 allows 0.07 N/mm^2 flexural tension in vertical bending with M1 or better mortar, so the wall does not crack. (Key point: Tension at mid-height)

3. Why is the factor 1.25 not applied in Step 4?
   A. It applies only to free-standing walls
   B. e/t = 0.175 exceeds 1/6, so the increase is not allowed
   C. The wall is too slender
   D. Mortar is M2
   Answer: B. The 25 percent increase is allowed only for 1/24 < e/t <= 1/6; here e/t = 0.175 > 1/6, so f_b = 0.1419/0.653 = 0.218. (Key point: No 25% increase)

4. Why must the mortar be M1 (1:5) or richer?
   A. To meet slenderness limit
   B. To give the 0.07 N/mm^2 flexural tension allowance used
   C. To raise brick strength to 10 N/mm^2
   D. To avoid the use of anchors
   Answer: B. The small tension is safe only if the mortar can carry the permissible flexural tension, which needs M1 or richer. (Key point: Mortar choice)

## Close variants set in other exams

- [Warehouse exterior wall, wind 750 N/m2](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awind-wall-warehouse-750) — Concrete Technology and Masonry Structure, chapter 9, asked 3×
- [Warehouse exterior wall, wind 860 N/m2, fixed base](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awind-wall-warehouse-860-fixed-base) — Concrete Technology and Masonry Structure, chapter 9, asked 3×

## Related in other subjects

- [Multi-storey wall: stresses at each level](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Athree-storey-wall-base-stress-check) — Design of Timber and Masonry Structures, chapter 5