BE Civil Engineering (IOE, TU) Building Technology (IOE, CE 502) Question Paper 2076 Nepal

(a) Functions of a foundation

A foundation is the lowest part of a structure (substructure) in direct contact with the soil. Its functions are:

1. To distribute the superstructure load over a larger area so that the intensity of pressure on the soil is within its safe bearing capacity.
2. To transfer loads (dead, live, wind, seismic) safely to the supporting strata.
3. To provide a level, hard surface for building up the superstructure.
4. To anchor the structure and give lateral stability against overturning and sliding.
5. To prevent differential settlement and distribute load uniformly.

Requirements of a good foundation:

• Located on sound strata at adequate depth (below zone of seasonal volume change / scour).
• Must safely carry the load without shear failure of soil and without excessive settlement.
• Settlement (total and differential) within permissible limits.
• Resistant to deterioration (sulphate attack, moisture, frost).
• Economical and constructable.

(b) Footing size for $q_a = 150\ \text{kN/m}^2$

Required area:

$$A = \frac{P}{q_a} = \frac{800\ \text{kN}}{150\ \text{kN/m}^2} = 5.333\ \text{m}^2$$

For a square footing of side $B$:

$$B = \sqrt{A} = \sqrt{5.333} = 2.309\ \text{m}$$

Provide $B = 2.35\ \text{m}$ (rounded up to a practical size).

Check: $A_{prov} = 2.35^2 = 5.52\ \text{m}^2$, pressure $= 800/5.52 = 144.9\ \text{kN/m}^2 < 150\ \text{kN/m}^2$. OK.

Provide a $2.35\ \text{m} \times 2.35\ \text{m}$ square footing.

(c) Footing size for $q_a = 100\ \text{kN/m}^2$

$$A = \frac{800}{100} = 8.0\ \text{m}^2 \implies B = \sqrt{8.0} = 2.828\ \text{m}$$

Provide $B = 2.85\ \text{m}$ square footing ($A_{prov}=8.12\ \text{m}^2$, pressure $=98.5\ \text{kN/m}^2$ < 100). OK.

Comment: As the bearing capacity drops the footing grows rapidly (area $\propto 1/q_a$). If the load increases substantially the isolated footings may overlap or become uneconomical; in that case a raft (mat) foundation is preferred when footing area exceeds about 50% of the plan area, or a pile foundation if a firm stratum lies at depth and the surface soil is weak/compressible.

(a) Definitions

• Rise (R): vertical distance between the top faces of two consecutive treads.
• Going / Tread (G): horizontal distance between the faces of two consecutive risers (the usable depth of a step).
• Waist slab: the inclined structural slab of uniform thickness that spans between landings/supports and on which the steps rest.
• Landing: a horizontal platform provided at the end of a flight, used for change of direction and rest.
• Pitch: the angle the line of nosings (slope of the stair) makes with the horizontal.

(b) Number of steps

Total rise $= 3.30\ \text{m} = 3300\ \text{mm}$.

$$\text{Number of risers} = \frac{3300}{150} = 22$$

For a dog-legged stair the 22 risers are split into two flights of 11 risers each.

Number of treads $=$ risers $- 1$ per straight run; since there is a mid-landing, each flight of 11 risers has $11 - 1 = 10$ treads. Total treads $= 20$.

Design-rule check:

$$2R + G = 2(150) + 250 = 550\ \text{mm}$$

This lies within $550$–$600\ \text{mm}$. OK (comfortable step).

(c) Flight width, length and layout check

For a dog-legged stair the two flights run side by side. With a hall width of $2.60\ \text{m}$, allow a small central gap/string of $\approx 100\ \text{mm}$:

$$\text{Width of each flight} = \frac{2.60 - 0.10}{2} = 1.25\ \text{m}$$

This exceeds the minimum $\approx 0.90\ \text{m}$ for residential stairs. OK.

Horizontal length of stepped portion of one flight (10 treads):

$$L_{steps} = 10 \times 250\ \text{mm} = 2500\ \text{mm} = 2.50\ \text{m}$$

Provide a mid-landing of width $1.20\ \text{m}$. Total going length used along the $5.00\ \text{m}$ direction:

$$2.50\ (\text{flight}) + 1.20\ (\text{landing}) + 1.20\ (\text{upper landing/entry}) = 4.90\ \text{m} < 5.00\ \text{m}$$

Layout fits the available hall.

Pitch:

$$\tan\theta = \frac{R}{G} = \frac{150}{250} = 0.60 \implies \theta = 30.96^\circ \approx 31^\circ$$

This is within the recommended $25^\circ$–$40^\circ$ range. Pitch $\approx 31^\circ$.

(a) Load-bearing vs partition wall

Three common brick bonds:

1. Stretcher bond: all bricks laid as stretchers (long face showing); used only for half-brick (115 mm) walls; weak for thicker walls.
2. Header bond: all bricks laid as headers (short face showing); used for one-brick curved walls and footings; gives good transverse strength.
3. English bond: alternate courses of headers and stretchers; the strongest bond, with a queen closer placed next to the quoin header to develop the lap. Widely used for load-bearing walls. (Flemish bond — headers and stretchers alternating in the same course — may also be cited; better appearance, slightly weaker than English bond.)

(b) Number of bricks

Volume of wall (one-brick = 230 mm thick):

$$V_{wall} = 4.0 \times 3.0 \times 0.23 = 2.76\ \text{m}^3$$

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

$$V_{brick} = 0.20 \times 0.10 \times 0.10 = 0.0020\ \text{m}^3$$

Number of bricks:

$$N = \frac{V_{wall}}{V_{brick}} = \frac{2.76}{0.0020} = 1380$$

Adding about 2% for wastage: $1380 \times 1.02 \approx 1408$.

Approximately $1380$ bricks (≈ $1410$ including wastage).

(a) Classification of roofs and choice of pitched roof

Roofs are broadly classified as:

1. Flat roofs — slope $\leq 10^\circ$ (RCC slab roofs, used as terraces).
2. Pitched / sloping roofs — appreciable slope (single, double/gable, hipped, etc.).
3. Curved / shell roofs — domes, vaults, shells for large spans.

Why pitched roofs suit much of Nepal: Nepal's hills and Terai receive heavy monsoon rainfall and the hills have snow at altitude. A pitched roof sheds water and snow rapidly, reducing leakage and dead load from ponding. Pitched roofs (CGI/tile) are light, quick to erect, easily repaired, and provide an attic/insulating air space against heat and cold. Flat roofs, while giving usable terrace space, are more prone to leakage and need careful waterproofing in high-rainfall zones.

(b) Members of a king-post truss and functions

• Tie beam (lower chord): the main horizontal member; takes tension and prevents the walls from spreading.
• Principal rafters (upper chords): inclined members carrying the roof load; in compression.
• King post: central vertical member connecting ridge to tie beam; in tension, it supports the tie beam at mid-span and prevents it from sagging.
• Struts: inclined members from foot of king post to principal rafters; in compression, they support the rafters at mid-length.
• Ridge / purlins / common rafters / battens: carry the covering and transfer loads to the trusses.

(c) Sloping roof surface area

The roof is a symmetrical double (gable) roof, ridge along the 12 m length. The horizontal projection of each slope $= 9.0/2 = 4.5\ \text{m}$.

True sloping length of each rafter run:

$$L_{slope} = \frac{4.5}{\cos 30^\circ} = \frac{4.5}{0.8660} = 5.196\ \text{m}$$

Area of one slope (length along ridge $= 12.0\ \text{m}$):

$$A_1 = 5.196 \times 12.0 = 62.35\ \text{m}^2$$

Two slopes:

$$A = 2 \times 62.35 = 124.7\ \text{m}^2$$

Allowing ~5% extra for overlaps and eaves projection: $124.7 \times 1.05 \approx 131\ \text{m}^2$.

Total sloping roof area to cover $\approx 124.7\ \text{m}^2$ (≈ $131\ \text{m}^2$ with laps/overhang).

(a) Building byelaws

Definition: Building byelaws are the legal rules and regulations framed by a local authority (municipality / urban development authority) to control and regulate building activities — covering plot coverage, setbacks, height, FAR, light/ventilation, fire safety, parking and structural safety — within its jurisdiction.

Four objectives:

1. To ensure safety of occupants against fire, structural failure and earthquake.
2. To provide adequate light, air and ventilation by controlling open spaces and setbacks.
3. To achieve orderly, planned development and prevent haphazard, congested construction.
4. To safeguard public health, sanitation and amenity, and protect the rights of neighbouring properties.

(b)(i) Buildable footprint

From setbacks: the plot is $15.0\ \text{m} \times 20.0\ \text{m}$.

• Buildable width $= 15.0 - (1.0 + 1.0) = 13.0\ \text{m}$
• Buildable depth $= 20.0 - (3.0 + 1.5) = 15.5\ \text{m}$

$$A_{setback} = 13.0 \times 15.5 = 201.5\ \text{m}^2$$

From ground coverage (60% of plot area):

$$A_{coverage} = 0.60 \times 300 = 180.0\ \text{m}^2$$

The footprint must satisfy both; the smaller value governs:

$$A_{coverage} = 180.0\ \text{m}^2 < A_{setback} = 201.5\ \text{m}^2$$

Ground coverage governs; maximum footprint $= 180.0\ \text{m}^2$.

(b)(ii) Maximum floor area and storeys

Maximum permissible total floor area from FAR:

$$A_{floor} = \text{FAR} \times \text{plot area} = 2.5 \times 300 = 750\ \text{m}^2$$

Maximum number of storeys using the governing footprint:

$$n = \frac{A_{floor}}{A_{footprint}} = \frac{750}{180.0} = 4.17$$

Since a partial storey is not built to full FAR efficiency, the maximum full storeys at the governing footprint $= 4$ storeys, using $4 \times 180 = 720\ \text{m}^2$, leaving $30\ \text{m}^2$ that could be added on a 5th (reduced) floor within the FAR cap.

Maximum permissible floor area $= 750\ \text{m}^2$; about $4$ full storeys at the $180\ \text{m}^2$ footprint (a small 5th floor permissible within FAR).

(b)(iii) Height-limit check

Take the 4 full storeys from (ii). Building height:

$$H = (4 \times 2.9) + 0.6 = 11.6 + 0.6 = 12.2\ \text{m}$$ $$12.2\ \text{m} < 16.0\ \text{m} \quad \textbf{OK}$$

Even a 5th storey would give $H = (5 \times 2.9) + 0.6 = 15.1\ \text{m} < 16.0\ \text{m}$, which is also within the height limit. Therefore the FAR (not the height limit) governs the number of storeys here: the building is limited to about $4$ full storeys plus a partial 5th floor by FAR, and this is well within the $16.0\ \text{m}$ height cap.

Dampness: the presence of unwanted/excess moisture in building components (walls, floors, roofs) that finds its way into the structure through capillarity, leakage or condensation.

Main causes:

• Rising of ground moisture by capillary action through foundations/walls.
• Rain penetration through walls, roofs and around openings.
• Defective construction — poor joints, bad slopes, inadequate DPC.
• Condensation of water vapour on cold surfaces.
• Leaking/defective plumbing and drainage.

Ill-effects:

• Unsightly patches, efflorescence and peeling of plaster/paint.
• Decay of timber, corrosion of reinforcement and metal fittings.
• Growth of mould/fungus → health hazards.
• Softening and crumbling of masonry; reduced durability and warmth.

Methods of damp proofing:

1. Damp-proof course (DPC): an impervious horizontal/vertical barrier (bitumen, mastic asphalt, PCC with waterproofing compound, or polythene sheet) laid in walls at plinth level (typically $\approx 150\ \text{mm}$ above ground) to block rising capillary moisture. Vertical DPC is provided to basement walls.
2. Integral / surface treatment: adding water-proofing admixtures to concrete and mortar, or applying guniting / cement-based or bituminous coatings, plus providing good slopes, weep holes and cavity walls to drain water away.

(Other valid methods: membrane/integral waterproofing, cavity-wall construction, proper site drainage.)

(a) Objectives of plastering

• To provide a smooth, even, durable finished surface for decoration.
• To conceal defective workmanship, joints and porous masonry.
• To protect surfaces from rain, atmospheric agencies and dampness.
• To provide a base for paint/whitewash and improve hygiene (easy to clean).

Two common finishes: smooth-cast (trowelled) finish and rough-cast (pebble-dash) finish. (Sand-faced and textured finishes are also acceptable.)

(b) Mortar estimate

Plaster area $= 5.0 \times 3.0 = 15.0\ \text{m}^2$. Thickness $= 12\ \text{mm} = 0.012\ \text{m}$.

Wet volume of mortar:

$$V_{wet} = 15.0 \times 0.012 = 0.18\ \text{m}^3$$

Dry volume (apply bulking/voids factor $1.27$):

$$V_{dry} = 0.18 \times 1.27 = 0.2286\ \text{m}^3 \approx 0.229\ \text{m}^3$$

(For information — split for $1:6$: total parts $=7$; cement $= 0.2286/7 = 0.0327\ \text{m}^3$, i.e. $\approx 0.0327 \times 1440/50 \approx 0.94$ bags; sand $= 6 \times 0.0327 = 0.196\ \text{m}^3$.)

Wet mortar $= 0.18\ \text{m}^3$; dry mortar $\approx 0.229\ \text{m}^3$.

(a) Components of a panelled door

A panelled door consists of a timber frame enclosing one or more panels. Principal components:

• Door frame: the surrounding frame fixed to the wall, made of two vertical posts (jambs) and a horizontal head (and sometimes a sill).
• Stiles: the outer vertical members of the door shutter.
• Top rail, lock (middle) rail, bottom rail: horizontal members of the shutter; the lock rail carries the handle/lock.
• Muntin (mullion): intermediate vertical member dividing panels.
• Panels: the infill boards (timber/glass/ply) set in grooves of stiles and rails.
• Hinges, hold-fasts, fittings: fix the shutter to the frame and the frame to the wall.

  ____Head (frame)____
 |  ___top rail___    |
 |J| panel | panel |  |J   <- Jambs / posts
 |a|--lock rail-----|  |a
 |m| panel | panel |  |m
 |b|__bottom rail___|  |b
 |________sill________|

(b) Window-area thumb rule

Empirical rule: the total window (glazed) area should be about $\tfrac{1}{8}$ to $\tfrac{1}{10}$ of the floor area of the room (often taken as $\geq 10\%$ of floor area) for adequate light and ventilation.

Floor area $= 4.0 \times 5.0 = 20.0\ \text{m}^2$.

Required window area:

$$A_{win} = \frac{1}{8} \times 20.0 = 2.5\ \text{m}^2 \quad\text{to}\quad \frac{1}{10} \times 20.0 = 2.0\ \text{m}^2$$

Provide window area of about $2.0$–$2.5\ \text{m}^2$ (e.g. one window $1.2\ \text{m} \times 1.5\ \text{m} = 1.8\ \text{m}^2$ plus a small ventilator, or two windows).

(a) Requirements of a good floor

• Hard-wearing / durable and able to resist abrasion and loads.
• Damp-proof and impervious to moisture.
• Easy to clean and maintain; non-absorbent and hygienic.
• Fire-resistant and reasonably sound/heat insulating.
• Smooth but non-slippery, with good appearance.
• Economical in initial cost and maintenance.

(b) Layers of a ground-floor cement-concrete floor (bottom to top)

1. Subgrade (earth base): the natural/compacted soil, well rammed and consolidated to give a firm, even base.
2. Sub-base / soling: a layer of compacted granular fill or brick-bat/stone soling (≈ 75–100 mm) to spread the load and break capillary rise.
3. Base concrete (PCC): lean cement concrete, e.g. $1:4:8$ or $1:3:6$, about $75$–$100\ \text{mm}$ thick, providing the main load-bearing slab and a rigid bed.
4. Damp-proofing layer (where needed): a polythene membrane or DPC over the base to stop rising damp.
5. Topping / wearing surface: a $40$–$50\ \text{mm}$ rich cement-concrete topping ($1:2:4$) or a cement screed, finished smooth (trowelled), forming the wearing surface.

Each upper layer rests on and is supported by the layer below; together they transfer floor loads to the subgrade while keeping the surface dry, level and hard-wearing.

Rankine's minimum depth formula:

$$D_{min} = \frac{p}{\gamma}\left(\frac{1-\sin\phi}{1+\sin\phi}\right)^2$$

where $p$ = intensity of bearing pressure, $\gamma$ = unit weight of soil, $\phi$ = angle of internal friction.

Substituting values: $\sin 30^\circ = 0.5$

$$\frac{1-\sin\phi}{1+\sin\phi} = \frac{1-0.5}{1+0.5} = \frac{0.5}{1.5} = 0.3333$$ $$\left(0.3333\right)^2 = 0.1111$$ $$D_{min} = \frac{200}{18}\times 0.1111 = 11.111 \times 0.1111 = 1.235\ \text{m}$$

Minimum depth of foundation $\approx 1.24\ \text{m}$.

Assumption: Rankine's theory assumes the soil is dry, cohesionless (granular) and homogeneous, the ground surface is horizontal, and the foundation imparts pressure such that the soil is on the verge of a Rankine active/passive state (it neglects cohesion and surcharge).

(a) Cavity wall

A cavity wall consists of two parallel leaves (skins) of masonry separated by a continuous air gap (cavity) of about $50$–$75\ \text{mm}$, tied together at intervals by metal wall ties. The cavity may be kept empty or partly filled with insulation; weep holes drain any water at the base. Advantages: excellent thermal insulation (air gap reduces heat transfer), good sound insulation, prevents rain/damp penetration to the inner leaf (moisture in the outer leaf drains out via weep holes), and lighter/economical compared with a solid wall of equal performance.

(b) Lintel vs arch

(c) Scaffolding vs shoring

• Scaffolding: a temporary working platform (with standards, ledgers, putlogs/transoms, braces) erected to support workers and materials during construction/repair at height. Its purpose is access and support of workmen, not support of the permanent structure.
• Shoring: temporary support given to an unsafe or weakened structure (raking shores, flying shores, dead/vertical shores) to prevent collapse during repairs, demolition of adjacent buildings, or when walls bulge/crack. Its purpose is to support the existing structure until permanent repairs are done.

(Answer any two; full marks for two correctly explained notes.)