BE Civil Engineering (IOE, TU) Building Technology (IOE, CE 502) Question Paper 2080 Nepal

(a) Function and proportioning criteria of a footing

A footing is the enlarged base of a foundation that spreads the concentrated load from a wall or column over a larger area of soil so that the resulting bearing pressure does not exceed the safe bearing capacity (SBC) of the soil, and settlement remains within tolerable limits.

Proportioning criteria:

• Area of base chosen so that soil pressure $\le$ SBC (prevents shear failure / excessive settlement).
• Depth/thickness chosen so the footing can transfer load safely (for PCC, by $45^\circ$ load dispersion; for RCC, by bending, one-way & two-way shear).
• The base must be centred under the resultant load so pressure is uniform (no tilting).

(b) Required width of strip footing

For a continuous footing, consider $1\ \text{m}$ run.

$$\text{Load per metre run} = 180\ \text{kN/m}$$ $$\text{Required area per metre} = \frac{\text{Load}}{\text{SBC}} = \frac{180}{150} = 1.20\ \text{m}^2 \text{ per metre run}$$

Since length per run is $1\ \text{m}$, the width is:

$$B = \frac{1.20\ \text{m}^2}{1\ \text{m}} = 1.20\ \text{m}$$

Required footing width $B = 1.20\ \text{m}$ (1200 mm).

(c) Minimum depth of PCC footing (45° dispersion)

The load from the $300\ \text{mm}$ wall must spread out to the full footing width of $1200\ \text{mm}$. The projection (offset) on each side beyond the wall face:

$$\text{Offset} = \frac{B - t_{wall}}{2} = \frac{1200 - 300}{2} = \frac{900}{2} = 450\ \text{mm}$$

For a $45^\circ$ dispersion line, $\tan 45^\circ = 1$, so depth = offset:

$$D = \text{Offset} \times \tan 45^\circ = 450 \times 1 = 450\ \text{mm}$$

Minimum PCC footing depth $D = 450\ \text{mm}$.

Sketch of load dispersion:

        |<-- 300 -->|   (wall)
   =====+===========+=====
        \           /        ^
         \   45°   /         |  D = 450 mm
          \       /          v
  ========+======+=========+========
  |<-450->|<-300->|<-450->|
  |<------ B = 1200 mm ----------->|

The $45^\circ$ lines from each wall face must reach the footing edges, confirming $D = 450\ \text{mm}$.

(a) Definitions

• Riser: the vertical face of a step; the riser height is the vertical distance between two consecutive treads.
• Tread: the horizontal upper surface of a step on which the foot is placed.
• Going: the horizontal distance between the faces of two consecutive risers (effective tread depth, excluding nosing).
• Flight: an unbroken series of steps between two landings.
• Landing: the level platform provided at the top, bottom, or between flights to allow rest and change of direction.

(b) Number of risers and treads

$$\text{Number of risers} = \frac{\text{Floor-to-floor height}}{\text{Riser}} = \frac{3300}{165} = 20\ \text{risers}$$

For a dog-legged stair with two equal flights:

$$\text{Risers per flight} = \frac{20}{2} = 10$$

Number of treads is always one less than the risers in each flight (the last riser lands on the landing/floor):

$$\text{Treads per flight} = 10 - 1 = 9$$ $$\text{Total treads} = 9 \times 2 = 18$$

20 risers total; two flights of 10 risers each, 9 treads per flight.

(c) Width of flight, going length, and fit check

Width available = $2.50\ \text{m}$, shared by two parallel flights with no central gap:

$$\text{Width of each flight} = \frac{2.50}{2} = 1.25\ \text{m}$$

This exceeds the $0.90\ \text{m}$ minimum for residential stairs — acceptable.

Length occupied by the going of one flight (9 treads):

$$L_{going} = 9 \times 270 = 2430\ \text{mm} = 2.43\ \text{m}$$

Stairwell length = $5.00\ \text{m}$. The single flight going (2.43 m) plus a landing of, say, $1.25\ \text{m}$ at the turn:

$$2.43 + 1.25 = 3.68\ \text{m} < 5.00\ \text{m}$$

There is ample room (a generous landing or a small entry space of $5.00 - 3.68 = 1.32\ \text{m}$ remains). The staircase fits comfortably within the stairwell.

Rule check:

$$2R + T = 2(165) + 270 = 330 + 270 = 600\ \text{mm}$$

Since $550 \le 600 \le 700$, the combination is comfortable and satisfies the rule.

(a) Flat roof vs pitched roof

Flat roofs are preferred in (i) dry/warm climates and (ii) where roof terrace/future vertical extension is needed. Pitched roofs are preferred in (i) heavy rainfall/snowfall regions and (ii) for large-span sheds and traditional sloped-roof architecture.

(b) Rafter geometry

Half span (horizontal run of one rafter):

$$\text{run} = \frac{8}{2} = 4\ \text{m}$$

Rise:

$$\text{rise} = \text{run} \times \tan 30^\circ = 4 \times 0.5774 = 2.309\ \text{m}$$

Slope (rafter) length:

$$L = \frac{\text{run}}{\cos 30^\circ} = \frac{4}{0.8660} = 4.619\ \text{m}$$

Rafter slope length $\approx 4.62\ \text{m}$, rise $\approx 2.31\ \text{m}$.

(c) Roof area and number of CGI sheets

Each sloping plane has dimensions $L \times (\text{ridge length}) = 4.619\ \text{m} \times 12\ \text{m}$.

Area of one plane:

$$A_1 = 4.619 \times 12 = 55.43\ \text{m}^2$$

Total for two planes:

$$A = 2 \times 55.43 = 110.86\ \text{m}^2$$

Add $10\%$ for laps and wastage:

$$A_{net} = 110.86 \times 1.10 = 121.94\ \text{m}^2$$

Number of sheets:

$$N = \frac{121.94}{1.8} = 67.7 \Rightarrow 68\ \text{sheets (round up)}$$

Total roof area $\approx 110.86\ \text{m}^2$; required CGI sheets = 68.

(d) King-post truss

Principal members: tie beam (bottom horizontal member), two principal rafters (sloping top members), the central king post (vertical tension member from ridge to mid-span of tie beam), and two struts connecting the king post to the principal rafters. The ridge and purlins rest on the rafters.

A king-post truss is economical for spans up to about $5\text{–}8\ \text{m}$. For the present $8\ \text{m}$ span it is suitable; larger spans use a queen-post or steel truss.

(a) Functions and wall types

Two functions of a wall: (i) to enclose/divide space and provide privacy, security and protection from weather; (ii) to support and transmit floor/roof loads to the foundation (in load-bearing construction) and resist lateral loads.

• Load-bearing wall: carries its self-weight plus floor/roof loads down to the foundation; thickness governed by load and slenderness. Cannot be removed without structural support.
• Partition wall: a thin, non-load-bearing wall used only to divide interior space; carries only its self-weight.

(b) Net masonry volume

Gross wall area:

$$A_{gross} = 6.0 \times 3.0 = 18.0\ \text{m}^2$$

Openings:

$$A_{door} = 1.0 \times 2.1 = 2.1\ \text{m}^2, \quad A_{window} = 1.2 \times 1.5 = 1.8\ \text{m}^2$$ $$A_{openings} = 2.1 + 1.8 = 3.9\ \text{m}^2$$

Net area:

$$A_{net} = 18.0 - 3.9 = 14.1\ \text{m}^2$$

Net volume (wall thickness $0.23\ \text{m}$):

$$V = 14.1 \times 0.23 = 3.243\ \text{m}^3$$

Net masonry volume $= 3.243\ \text{m}^3$.

(c) Number of bricks and mortar volume

Volume of one modular brick including its mortar joint (nominal size):

$$v = 0.200 \times 0.100 \times 0.100 = 0.002\ \text{m}^3$$

Number of bricks (nominal volume fills the wall completely):

$$N = \frac{V}{v} = \frac{3.243}{0.002} = 1621.5 \Rightarrow 1622\ \text{bricks}$$

Mortar (dry) volume at $25\%$ of gross masonry volume:

$$V_{mortar} = 0.25 \times 3.243 = 0.811\ \text{m}^3$$

Bricks required $\approx 1622$; dry mortar volume $\approx 0.81\ \text{m}^3$.

(d) Cement and sand for the 1:6 mortar

Using the dry mortar volume $V_{mortar} = 0.811\ \text{m}^3$ with ratio $1:6$ (total 7 parts):

Cement volume:

$$V_c = \frac{1}{7} \times 0.811 = 0.1159\ \text{m}^3$$ $$m_c = 0.1159 \times 1440 = 166.9\ \text{kg} = \frac{166.9}{50} = 3.34 \Rightarrow 4\ \text{bags}$$

Sand volume:

$$V_s = \frac{6}{7} \times 0.811 = 0.695\ \text{m}^3$$

Cement $\approx 166.9\ \text{kg}$ (4 bags); sand $\approx 0.695\ \text{m}^3$.

(a) Dampness and its sources

Dampness is the presence and movement of unwanted moisture within the components of a building (walls, floors, roofs), usually drawn in from the ground or admitted through defective construction.

Four sources of dampness:

1. Rising damp — ground moisture rising by capillary action through foundations/walls.
2. Rain penetration — through roofs, parapets, defective joints, and exposed wall faces.
3. Leaking/condensation — from defective plumbing, sanitary fittings, or condensation of water vapour on cold surfaces.
4. Poor drainage / improper slope allowing water to accumulate against walls.

(b) Four defects/ill-effects of dampness

1. Efflorescence — white salt deposits on plaster/masonry, causing disintegration of the surface.
2. Deterioration of finishes — blistering, flaking and softening of paint, plaster and distemper.
3. Decay of timber & corrosion of steel — rot/warping of doors, windows and joists; rusting of reinforcement and fixtures.
4. Unhealthy living conditions — growth of mould/fungi, musty smell, and breeding of mosquitoes; promotes disease.

(c) Working of horizontal DPC at plinth level

A continuous, impervious horizontal layer (the DPC) is laid in the wall at plinth level (about $150\ \text{mm}$ above ground level) and throughout the basement floor, breaking the capillary path so ground moisture cannot rise into the superstructure.

        Wall (superstructure)
        ||||||||||||||||||
  GL    =====DPC=========   <- horizontal DPC at plinth (~150 mm above GL)
  ~~~~~~|              |~~~~~~  ground level
        | plinth/found |
        |   masonry    |
  ------+--------------+------
  ::::::: basement floor DPC :::::::  <- floor membrane turned up to meet wall DPC
  ====== PCC bed / footing ======

The wall DPC and the floor membrane are lapped/turned up so that the moisture barrier is continuous at the wall–floor junction; this is essential, otherwise damp bypasses the DPC at the corner.

Suitable DPC materials: bituminous felt / bitumen mastic, dense cement concrete (1:2:4) with waterproofing compound, or polythene/PVC sheet. Typical thickness: mastic/bitumen layer $\approx 2.5\ \text{mm}$; cement-concrete DPC course $\approx 25\text{–}40\ \text{mm}$.

(d) Requirements of an ideal damp-proofing material

1. It should be impervious (completely watertight).
2. It should be durable and last the life of the structure, resisting wear and chemical/biological attack.
3. It should be strong enough to bear the imposed loads without crushing and be dimensionally stable (free from cracks).
4. It should be flexible/workable, capable of being laid continuously and lapped at joints, and reasonably economical.

Plaster area (perimeter × height):

$$P = 2(4.0 + 5.0) = 18.0\ \text{m}$$ $$A = P \times h = 18.0 \times 3.0 = 54.0\ \text{m}^2$$

Wet mortar volume (thickness 12 mm = 0.012 m):

$$V_{wet} = 54.0 \times 0.012 = 0.648\ \text{m}^3$$

Dry mortar volume (add 20%):

$$V_{dry} = 0.648 \times 1.20 = 0.7776\ \text{m}^3$$

Cement volume (ratio 1:5, so cement = 1/6 of dry volume):

$$V_{cement} = \frac{1}{1+5} \times 0.7776 = \frac{0.7776}{6} = 0.1296\ \text{m}^3$$

Mass and bags of cement:

$$m = 0.1296 \times 1440 = 186.6\ \text{kg}$$ $$\text{Bags} = \frac{186.6}{50} = 3.73 \Rightarrow 4\ \text{bags}$$

Wet mortar $\approx 0.648\ \text{m}^3$; cement required $\approx 186.6\ \text{kg} = 4$ bags.

(a) Labelled panelled door (ASCII)

  +==========================+   <- Lintel above
  | head/top rail            |
  |  +------+   +------+      |
  |  |panel |   |panel |      |  <- Stiles (vertical members) at left & right edges
  |  +------+   +------+      |  <- Mullion (central vertical) between panels
  |  ---- lock/intermediate rail ----
  |  +------+   +------+      |
  |  |panel |   |panel |      |
  |  +------+   +------+      |
  | bottom rail              |
  +==========================+
     ^Frame (jambs) all around; hinges on one stile; handle/lock on the other.

Labelled components: (1) Frame/jamb, (2) Top (head) rail, (3) Bottom rail, (4) Stile, (5) Mullion, (6) Panel, (7) Lock/intermediate rail, (8) Hinges.

(b) Functions

Door: (i) provides access/exit and connection between spaces; (ii) gives privacy, security and control of light/sound/heat when closed.

Window: (i) admits natural light and ventilation (fresh air); (ii) gives outside view and helps regulate light/air while providing weather protection.

(c) Common sizes

• Single-leaf main entrance door: about $1.0\ \text{m} \times 2.1\ \text{m}$ (1000 mm × 2100 mm).
• Internal room door: about $0.9\ \text{m} \times 2.1\ \text{m}$ (900 mm × 2100 mm); bathroom/WC door: about $0.75\ \text{m} \times 2.0\ \text{m}$.

(a) Components of a ground floor (bottom to top)

1. Subgrade / compacted earth (well-rammed natural soil).
2. Sub-base / soling — sand or compacted hardcore/brick-bat soling.
3. Base course — lean cement concrete (e.g. 1:4:8) bed.
4. Floor finish / topping — the wearing surface (cement screed, tiles, terrazzo, etc.). A DPC membrane is provided below the base course to stop rising damp.

(b) Comparison of flooring finishes

Summary: cement-concrete is cheapest and best for rough/utility use; terrazzo gives a decorative, very durable monolithic finish; ceramic tiles give a hygienic, water-resistant finish ideal for wet areas.

(a) Definitions

• Ground coverage: the percentage of the plot area covered by the building's footprint at ground level $=\dfrac{\text{built-up area at ground floor}}{\text{plot area}}\times 100$.
• Floor Area Ratio (FAR): the ratio of the total covered (built-up) floor area of all storeys to the plot area $=\dfrac{\text{total floor area}}{\text{plot area}}$.

(b) Maximum permissible areas

Ground-floor built-up area:

$$A_{ground} = 0.60 \times 250 = 150\ \text{m}^2$$

Maximum total built-up (floor) area:

$$A_{total} = \text{FAR} \times \text{plot area} = 2.5 \times 250 = 625\ \text{m}^2$$

Ground coverage $= 150\ \text{m}^2$; total permissible floor area $= 625\ \text{m}^2$.

(c) Maximum number of storeys

If each storey has the full ground-coverage area of $150\ \text{m}^2$:

$$n = \frac{A_{total}}{A_{ground}} = \frac{625}{150} = 4.17$$

Since a partial storey is not built, round down:

$$n = 4\ \text{storeys}$$

Maximum number of storeys $= 4$ (using $4 \times 150 = 600\ \text{m}^2 \le 625\ \text{m}^2$; a 5th full storey would give $750\ \text{m}^2 > 625$, not allowed).

(a) Shallow vs deep foundation

(b) Situations requiring a pile foundation

1. When the upper soil layers are weak/compressible (soft clay, loose fill, made-up ground) and firm strata lie deep, piles transfer load to the deeper hard layer.
2. When heavy concentrated loads must be carried, the water table is high, or uplift/lateral forces (e.g. from waterfront, expansive soils, bridge piers) make spread footings impractical.

(a) Bond in brick masonry

A bond is the systematic arrangement of bricks in successive courses so that the vertical (continuous) joints are broken/staggered and adjacent bricks overlap.

Importance: it prevents continuous vertical joints, ties the masonry together so that the load is distributed over a larger area, and gives the wall strength, stability and a good appearance. Without proper bonding the wall would behave as independent columns of brick and could fail.

(b) English bond vs Flemish bond

In short, English bond is preferred where strength matters, while Flemish bond is chosen where appearance and economy of facing bricks matter.