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

# Warehouse exterior wall, wind 860 N/m2, fixed base

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

- Asked in: 2080 Baisakh, 7 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-fixed-base
- 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 fixed at base and tied with metal anchor at the roof level.

## Short answer

230 mm thick wall, bricks ≥3.5 N/mm² in M1 (1:5) mortar. Propped cantilever, base moment wH²/8 = 1.317 kNm/m. Maximum compressive stress 0.325 N/mm², no tension. Slenderness ratio 12.9 <27. Fix base with dowels, anchor at roof.

## Answer

#### Data and assumptions

- Exterior wall of a single-storey warehouse, 3.5 m high, fixed at base (continuous with the foundation) and tied with a metal anchor at roof level: a propped cantilever. $P=25$ kN/m (axial); wind 860 N/m$^2$.
- Fixed at the base and laterally supported (not rotationally restrained) at the top: $h_{ef}=0.85H$ (Table 4 Sl. 2). Maximum moment is at the fixed base, $M=wH^2/8$ (hogging); sagging moment $9wH^2/128$ is smaller.
- 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=860 N/m2
  ------+-----------   load P=25 kN/m
        |   |
        | wall, H=3.5 m
        |   |  M = wH^2/8 at the fixed base
  ======+===========   foundation (fixed)
```

#### 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

$$
\begin{aligned} \text{Self weight of wall} &= 0.230\times3.50\times19 = 15.30\ \text{kN/m}\\ N\ (\text{at base}) &= 40.30\ \text{kN/m}\\ h_{ef} &= 0.85\times3.5=2.975\ \text{m} \\ SR &= \frac{2.975}{0.230} = 12.93\ (<27) \end{aligned}
$$

#### Step 3: Stresses at the base section

$$
\begin{aligned} \sigma_a &= \frac{N}{A}=\frac{40.30\times10^3}{230\times10^3} = 0.1752\ \text{N/mm}^2\\ \sigma_b &= \frac{6M}{t^2} = \frac{6\times1.317\times10^6}{1000\times230^2} = 0.1494\ \text{N/mm}^2\\ \sigma_{max} &= \sigma_a+\sigma_b = 0.3246,\qquad \sigma_{min} = \sigma_a-\sigma_b = 0.0258\ \text{N/mm}^2 \end{aligned}
$$

$\sigma_{min}>0$: the whole section is in compression, no tension (the resultant eccentricity $e=M/N=0.0327$ m, $e/t=0.142<1/6$).

#### Step 4: Required basic compressive stress

Resultant eccentricity ratio $e/t = M/(Nt) = 0.142$. From Table 9: $k_s=0.753$ ($SR=12.93$). $k_a=1$, $k_p=1$. Since $1/24<e/t\le1/6$, a 25 percent increase is allowed (cl. 5.4.1.4 a).

$$
f_b \ge \frac{\sigma_a}{k_sk_ak_p\times1.25} = \frac{0.1752}{0.753\times1.25} = 0.186\ \text{N/mm}^2
$$

#### 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 |

**Answer: 230 mm thick wall; bricks not less than 3.5 N/mm$^2$ with cement mortar M1 (1:5) or richer (practically 5 N/mm$^2$ bricks, 1:5 mortar).** Base section: $\sigma_{max}=0.325$, $\sigma_{min}=0.026$ N/mm$^2$ (all compression). Anchor the roof to the wall and tie the wall to the footing with dowels to ensure fixity.

## Check yourself

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

1. What structural model applies to a wall fixed at base and tied at roof?
   A. Simply supported beam
   B. Cantilever
   C. Propped cantilever
   D. Fixed-fixed beam
   Answer: C. Fixed base plus roof anchor gives a propped cantilever, with maximum moment wH^2/8 at the fixed base. (Key point: Support condition)

2. What effective height is used and why?
   A. 1.0H, both ends hinged
   B. 0.85H, fixed at base and laterally supported at top
   C. 1.5H, free top
   D. 0.75H, fixed at both ends
   Answer: B. IS 1905 Table 4 Sl. 2 gives h_ef = 0.85H = 2.975 m, so SR = 12.93. (Key point: Effective height)

3. Where is the stress check made and why?
   A. At mid-height, since sagging moment is largest
   B. At the base, where hogging moment wH^2/8 and axial load are both greatest
   C. At the roof, where load is applied
   D. At the top anchor
   Answer: B. The base has the largest moment (1.317 kNm/m) and largest N (40.30 kN/m), so it governs. (Key point: Critical section)

4. How is the required f_b obtained?
   A. f_b = sigma_a / (k_s k_a k_p x 1.25)
   B. f_b = sigma_max x k_s
   C. f_b = sigma_b / k_s
   D. f_b = sigma_a x k_s x 1.25
   Answer: A. Basic compressive stress is the axial stress divided by the stress reduction factors, with a 25 percent increase since e/t is between 1/24 and 1/6, giving 0.186 N/mm^2. (Key point: Required brick strength)

## Close variants set in other exams

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

## 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