--- title: "Design steps of axially loaded brick column" subject: "Concrete Technology and Masonry Structure" chapter: 8 key: "semester_5/concrete_technology_and_masonry_structure:axially-loaded-column-vs-wall" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/axially-loaded-column-vs-wall site: BCT Engineering --- # Design steps of axially loaded brick column Concrete Technology and Masonry Structure · Chapter 8: Design of masonry walls for gravity loads - Asked in: 2082 Baisakh, 5+3 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/axially-loaded-column-vs-wall - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-8 ## Question Explain in detail the design steps of an axially loaded brick masonry column. How does it differ from the design of an axially loaded brick masonry wall? ## Short answer Assume column size, compute effective height (0.75H if fully restrained), ensure slenderness ratio ≤12, obtain basic compressive stress fb, apply stress reduction factor ks, area reduction factor ka (0.7+1.5A for A<0.2 m²), and shape factor kp, then check σ = P/A ≤ fb·ks·ka·kp. A column differs from a wall: SR limit 12 vs 27, uses greater slenderness of two directions, area reduction normally applies, and design treats the whole section, not per metre length. ## Answer #### Design steps for an axially loaded brick masonry column (IS 1905) 1. **Assume** column size (least dimension not less than about 200 to 230 mm and area as needed) and unit and mortar grade. 2. **Loads:** find axial load $P$ from roof or floor, add self weight of column. 3. **Effective height** (cl. 4.3.2): actual height for the direction in which it is laterally supported, twice the height for an unsupported direction; $0.75H$ if fully restrained at both ends (Table 4). 4. **Slenderness ratio** $SR = h_{ef}/t$ in each principal direction; take the greater. It must not exceed 12 for a column (Table 7). 5. **Basic compressive stress** $f_b$ for the unit strength and mortar grade (Table 8). 6. **Factors:** stress reduction factor $k_s$ from Table 9 for $SR$ and $e=0$; area reduction factor $k_a=0.7+1.5A$ when $A<0.2$ m$^2$; shape factor $k_p$ for the unit height-to-width ratio (Table 10). 7. **Permissible stress** $f_c=f_bk_sk_ak_p$. 8. **Check:** $\sigma = P/A \le f_c$. If not satisfied, increase size or unit/mortar strength and repeat. 9. Detail: stagger joints, use header courses, tie to beam or slab, avoid chases. #### Difference from an axially loaded wall | Point | Column | Wall | |---|---|---| | Slenderness limit | $SR\le12$ (Table 7) | $SR\le27$ for cement mortar (20 for lime mortar) | | Slenderness ratio | Greater of the two directions, $h_{ef}/t$ | Lesser of $h_{ef}/t$ and $L_{ef}/t$ (horizontal stiffening by cross walls) | | Effective length | Not used | Used; depends on cross walls, piers or buttresses | | Area reduction factor $k_a$ | Usually applies ($A<0.2$ m$^2$) | Normally 1.0 (analysed per metre run, 0.2 m$^2$ or more) | | Design unit | Whole section | Per metre length of wall | | Effective thickness | Actual thickness of column | Actual thickness; stiffening coefficient where piers or cross walls (Table 6) | | Effective height | Based on lateral support in both directions | Based on top and bottom restraint (Table 4) | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the maximum slenderness ratio allowed for a column compared with a wall in cement mortar? A. Column 27, wall 12 B. Column 12, wall 27 C. Both 20 D. Column 12, wall 20 Answer: B. Columns are limited to SR 12 (Table 7); walls in cement mortar to 27. (Key point: Slenderness limit) 2. How is the slenderness ratio taken for a column versus a wall? A. Column: lesser of the two; wall: greater of the two B. Both use the greater value C. Column: greater of the two directions; wall: lesser of h_ef/t and L_ef/t D. Both use only h_ef/t Answer: C. A column uses the worse direction, whereas a wall benefits from horizontal stiffening by cross walls. (Key point: Governing slenderness ratio) 3. When does the area reduction factor k_a = 0.7 + 1.5A apply? A. When the cross-sectional area A is less than 0.2 m^2, as in most columns B. When A is more than 0.2 m^2 C. Only for walls per metre run D. Only when eccentricity is zero Answer: A. Small sections lose strength, so k_a applies to A < 0.2 m^2; walls normally have k_a = 1.0. (Key point: Area reduction factor) 4. What is the final check in designing an axially loaded column? A. P/A must exceed f_c for safety B. Only the slenderness ratio is checked C. Check that k_s equals 1 D. sigma = P/A must not exceed f_c = f_b k_s k_a k_p, otherwise increase size or strength Answer: D. If the actual stress exceeds permissible stress the size or unit/mortar strength is increased and the design repeated. 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