BE Civil Engineering (IOE, TU) Building Technology (IOE, CE 502) Question Paper 2079 Nepal

Given: wall load $w = 180\ \text{kN/m}$, wall thickness $t = 250\ \text{mm} = 0.25\ \text{m}$, safe bearing capacity $q_s = 150\ \text{kN/m}^2$, footing+soil allowance $= 10\%$.

(a) Required width of footing

Total load on soil per metre run, including footing self-weight allowance:

$$P = w \times 1.10 = 180 \times 1.10 = 198\ \text{kN/m}$$

Required width per metre run (length considered $= 1\ \text{m}$):

$$B_{req} = \frac{P}{q_s \times 1} = \frac{198}{150} = 1.32\ \text{m}$$

Provide a footing width $B = 1.40\ \text{m}$ (rounded up to a convenient construction dimension; this keeps the actual pressure $< q_s$, which is safe).

Check: actual pressure $= 198 / 1.40 = 141.4\ \text{kN/m}^2 < 150\ \text{kN/m}^2$ ✓

(b) Net upward soil pressure for design

For structural bending design, only the structural (wall) load produces a net upward reaction on the projecting slab; the footing self-weight is balanced by the soil directly beneath it. Using the structural load over the provided width:

$$p_{net} = \frac{w}{B} = \frac{180}{1.40} = 128.57\ \text{kN/m}^2$$

Net upward design pressure $p_{net} \approx 128.6\ \text{kN/m}^2$.

(c) Maximum bending moment at the face of the wall

Projection (cantilever) of the footing beyond each face of the wall:

$$l = \frac{B - t}{2} = \frac{1.40 - 0.25}{2} = \frac{1.15}{2} = 0.575\ \text{m}$$

The projection behaves as a cantilever carrying the net upward pressure. Maximum moment per metre run at the wall face:

$$M = p_{net}\times \frac{l^2}{2} = 128.57 \times \frac{(0.575)^2}{2}$$ $$M = 128.57 \times \frac{0.330625}{2} = 128.57 \times 0.16531 = 21.25\ \text{kN\,m/m}$$

Maximum bending moment $M \approx 21.3\ \text{kN\,m per metre run}$.

Pressure distribution (ASCII):

        wall (0.25 m)
        |#####|
   _____|#####|_____      <- footing, width B = 1.40 m
  |<-0.575->|<-0.575->|   (projections)
  ^  ^  ^  ^  ^  ^  ^  ^   uniform upward soil pressure
  p_net = 128.6 kN/m^2 (net)

The uniform upward pressure acts on each cantilevering projection, producing tension on the bottom face — hence main reinforcement is placed transversely near the bottom of the footing.

Given: floor-to-floor height $H = 3.60\ \text{m}$, riser $R = 150\ \text{mm}$, tread $T = 270\ \text{mm}$.

(a) Number of risers and treads / arrangement

$$\text{No. of risers} = \frac{H}{R} = \frac{3600}{150} = 24$$

Number of treads (one less than risers in a continuous rise) $= 24 - 1 = 23$.

For an open-well stair the flights run around a central open space (the well). A convenient symmetrical arrangement is three flights of 8 risers each ($8+8+8 = 24$), separated by two landings around the well. This gives equal, comfortable flights and the central well permits a lift or natural light.

(b) Comfort checks (step proportion rules)

Rule 1 — $2R + T$ should lie between $550$ and $700\ \text{mm}$:

$$2R + T = 2(150) + 270 = 300 + 270 = 570\ \text{mm} \quad (550\text{–}700)\ ✓$$

Rule 2 — $R + T$ should be about $400$–$450\ \text{mm}$:

$$R + T = 150 + 270 = 420\ \text{mm}\ ✓$$

Rule 3 (product check) — $R \times T$ should be about $40000$–$42000\ \text{mm}^2$:

$$R \times T = 150 \times 270 = 40500\ \text{mm}^2\ ✓$$

All three rules are satisfied, so the step $150\times270\ \text{mm}$ is comfortable.

(c) Going and pitch of one flight (8 risers)

A flight of $8$ risers has $8 - 1 = 7$ treads.

$$\text{Going of flight} = 7 \times T = 7 \times 0.270 = 1.89\ \text{m}$$ $$\text{Rise of flight} = 8 \times R = 8 \times 0.150 = 1.20\ \text{m}$$

Slope (pitch):

$$\tan\theta = \frac{\text{rise}}{\text{going}} = \frac{1.20}{1.89} = 0.6349 \Rightarrow \theta = \tan^{-1}(0.6349) = 32.4^{\circ}$$

Going per flight $= 1.89\ \text{m}$; pitch $\approx 32.4^{\circ}$ (within the comfortable $25^{\circ}$–$40^{\circ}$ range).

(d) Open-well vs dog-legged stair

Plan (ASCII):

  +----------+----------+
  | Flight 1 |  Landing |
  +----------+    --+   |
  | Landing  | WELL |F3 |
  +----+-----+------+   |
  | F2 |   Landing      |
  +----+---------------+

(a) Number of bricks

Volume of wall:

$$V_{wall} = L \times H \times t = 4.5 \times 3.0 \times 0.30 = 4.05\ \text{m}^3$$

Volume occupied by one brick including its share of mortar (nominal size $240\times120\times80\ \text{mm}$):

$$V_{brick} = 0.240 \times 0.120 \times 0.080 = 0.0023040\ \text{m}^3$$

Number of bricks:

$$N = \frac{V_{wall}}{V_{brick}} = \frac{4.05}{0.0023040} = 1757.8 \approx \mathbf{1758\ bricks}$$

(In practice a wastage allowance of about $5\%$ is added, giving $\approx 1758 \times 1.05 \approx 1846$ bricks to order.)

(b) Cavity wall vs solid wall

• Solid wall: a single continuous thickness of masonry (e.g., one-brick / $230\ \text{mm}$ or $300\ \text{mm}$ thick) with no internal gap. Moisture and heat can transmit directly through the mass.
• Cavity wall: two separate leaves (an outer and an inner leaf, each usually a half-brick thick) separated by a continuous air gap (cavity) of about $50$–$75\ \text{mm}$, tied together at intervals by non-corrosive wall ties.

Solid wall          Cavity wall
 [#######]          [###] | [###]
 one mass           outer  air  inner
                    leaf  gap  leaf
                       (ties span the gap)

Advantages of a cavity wall:

1. The air gap prevents rain penetration to the inner leaf, keeping the interior dry.
2. The trapped air gives better thermal and sound insulation than a solid wall of equal weight.

(c) Function and location of DPC

A damp-proof course (DPC) is an impervious barrier (e.g., dense cement concrete with waterproofer, bitumen, or a polymer membrane) provided to prevent the upward (and lateral) migration of moisture by capillary action from the ground into the superstructure.

It is provided horizontally at plinth level (above ground level, typically $150\ \text{mm}$ above finished ground) across the full width of all walls, and is continued around openings and under floors where moisture can enter.

(a) Classification of roofs

Roofs are broadly classified as:

1. Flat roofs — roof slope generally less than about $10^{\circ}$ (RCC slab roofs, Madras terrace, etc.).
2. Pitched (sloping) roofs — appreciable slope to drain rain/snow quickly (lean-to, couple, couple-close, collar-beam, king-post, queen-post trusses).
3. Curved / shell roofs — domes, vaults, shells, folded plates, etc.

King-post truss — principal components:

              ridge
               /\
   principal  /||\  principal
    rafter   / || \   rafter
            /  ||  \
   strut-> /  king   \ <-strut
          /   post    \
  wall   /_____________\  wall
  plate     tie beam     plate

• Tie beam: the lowest horizontal member; ties the feet of the rafters together and resists the outward thrust (in tension).
• Principal rafters: inclined members carrying the purlins and transmitting load to the walls.
• King post: the central vertical member connecting the ridge/apex to the middle of the tie beam; prevents the tie beam from sagging (in tension).
• Struts: inclined members from the foot of the king post to the principal rafters; support the rafters at mid-length (in compression).
• Ridge, purlins, common rafters, wall plate complete the assembly and carry the covering.

(b) Roof geometry and surface area

Span $= 6\ \text{m}$, so half-span (horizontal run of one rafter) $= 3\ \text{m}$; rise $= 1.8\ \text{m}$.

Slope length of one rafter side (rafter length):

$$L_s = \sqrt{(\text{run})^2 + (\text{rise})^2} = \sqrt{3.0^2 + 1.8^2} = \sqrt{9.0 + 3.24} = \sqrt{12.24} = 3.499\ \text{m} \approx 3.50\ \text{m}$$

Pitch angle:

$$\tan\theta = \frac{\text{rise}}{\text{run}} = \frac{1.8}{3.0} = 0.6 \Rightarrow \theta = \tan^{-1}(0.6) = 30.96^{\circ} \approx 31^{\circ}$$

Total sloping surface area (two slopes), with roof length $= 10\ \text{m}$:

$$A = 2 \times (L_s \times \text{length}) = 2 \times (3.499 \times 10) = 2 \times 34.99 = 69.98\ \text{m}^2$$

Slope length $\approx 3.50\ \text{m}$, pitch $\approx 31^{\circ}$, total roofing area $\approx 70.0\ \text{m}^2$ (add overhang/eaves allowance for actual covering).

Given: plot $= 15\ \text{m} \times 18\ \text{m}$, FAR $= 2.5$, ground coverage $= 60\%$, set-backs: front $1.5\ \text{m}$, other three sides $1.0\ \text{m}$ each.

Plot area:

$$A_{plot} = 15 \times 18 = 270\ \text{m}^2$$

(a) Definitions

• FAR (Floor Area Ratio): ratio of the total covered floor area of all storeys to the plot area, i.e. $\text{FAR} = \dfrac{\text{total floor area}}{\text{plot area}}$. It limits the total built-up bulk on a plot.
• Ground coverage: the proportion (percentage) of the plot area that may be covered by the building footprint at ground level.
• Set-back: the minimum mandatory open distance to be left between the plot boundary and the building line on each side, for light, ventilation, fire access and privacy.

(b) Maximum permissible floor area and ground footprint

Maximum total floor area (from FAR):

$$A_{floor,max} = \text{FAR} \times A_{plot} = 2.5 \times 270 = 675\ \text{m}^2$$

Maximum ground-floor footprint (from ground coverage):

$$A_{ground,max} = 0.60 \times 270 = 162\ \text{m}^2$$

(c) Fit within set-back (buildable) area

Buildable plan dimensions after deducting set-backs:

• Along the $18\ \text{m}$ length (front $1.5$ + rear $1.0$): $18 - (1.5 + 1.0) = 15.5\ \text{m}$
• Along the $15\ \text{m}$ width ($1.0$ each side): $15 - (1.0 + 1.0) = 13.0\ \text{m}$

Buildable area:

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

Since $A_{ground,max} = 162\ \text{m}^2 < A_{build} = 201.5\ \text{m}^2$, the maximum permissible ground footprint comfortably fits within the set-back limits — here the ground coverage (not the set-backs) governs the footprint.

(d) Minimum number of storeys for full FAR

If each storey uses the maximum allowed footprint of $162\ \text{m}^2$:

$$n = \frac{A_{floor,max}}{A_{ground,max}} = \frac{675}{162} = 4.17$$

Since a fractional storey is not possible, a minimum of 5 storeys would be required to consume the full FAR of $675\ \text{m}^2$ (four full storeys of $162\ \text{m}^2 = 648\ \text{m}^2$, plus a fifth partial storey of $675 - 648 = 27\ \text{m}^2$).

(a) Dampness — definition and causes

Dampness is the presence and movement of unwanted moisture (water) within the components of a building — in walls, floors, roofs or foundations — which damages the structure and finishes and harms the health/comfort of occupants.

Common causes/sources (any four):

1. Rising damp — capillary rise of ground water from the foundation/soil into walls and floors.
2. Rain penetration — rain striking exposed walls, parapets, copings and through defective roofs.
3. Defective plumbing / leaking pipes and fittings allowing water into walls and floors.
4. Condensation of water vapour on cold internal surfaces (poor ventilation).
5. Defective construction / poor workmanship — bad joints, plinth sloping toward the wall, absence of DPC.

(b) Methods of damp-proofing (any three)

1. Membrane damp-proofing (DPC): providing a continuous impervious layer (bitumen felt, polythene, mastic asphalt, or rich cement concrete with waterproofer) horizontally at plinth level and around openings to cut off capillary moisture.
2. Integral / surface waterproofing treatment: adding waterproofing compounds to the concrete/mortar mix, or applying water-repellent surface coatings and cement-based renderings to resist penetration.
3. Guniting / pressure grouting: forcing rich cement mortar (under pressure) onto or into the surface/cracks to form an impervious skin (used on water-retaining and below-ground surfaces).
4. Cavity wall construction: the air gap between two leaves prevents moisture from crossing to the inner leaf.

(c) Common DPC materials (any two): mastic asphalt, bitumen/bituminous felt, dense cement concrete (1:2:4) with integral waterproofer, polythene/PVC sheet, or engineering bricks/slates.

Given: room $4.0 \times 3.0\ \text{m}$, height $3.0\ \text{m}$, plaster thickness $= 12\ \text{mm} = 0.012\ \text{m}$, mix $1:6$.

(a) Net plaster area

Gross internal wall area (perimeter × height):

$$\text{Perimeter} = 2(4.0 + 3.0) = 14.0\ \text{m}$$ $$A_{gross} = 14.0 \times 3.0 = 42.0\ \text{m}^2$$

Deductions for openings:

$$\text{Door} = 1.0 \times 2.0 = 2.0\ \text{m}^2$$ $$\text{Windows} = 2 \times (1.2 \times 1.2) = 2 \times 1.44 = 2.88\ \text{m}^2$$ $$\text{Total deduction} = 2.0 + 2.88 = 4.88\ \text{m}^2$$

Net plaster area $= 42.0 - 4.88 = 37.12\ \text{m}^2$.

(b) Dry mortar volume

Wet mortar volume:

$$V_{wet} = A_{net} \times t = 37.12 \times 0.012 = 0.4454\ \text{m}^3$$

Dry volume (add $30\%$):

$$V_{dry} = 1.30 \times 0.4454 = 0.5791\ \text{m}^3$$

Dry mortar volume $\approx 0.579\ \text{m}^3$.

(c) Cement quantity

For a $1:6$ mix, total parts $= 1 + 6 = 7$. Cement fraction $= \tfrac{1}{7}$.

$$V_{cement} = \frac{1}{7} \times 0.5791 = 0.08273\ \text{m}^3$$

Number of bags ($1$ bag $= 0.0347\ \text{m}^3$):

$$N = \frac{0.08273}{0.0347} = 2.38\ \text{bags} \approx \mathbf{3\ bags}$$

Cement required $\approx 0.083\ \text{m}^3 \approx 3$ bags (rounding up); sand $= \tfrac{6}{7}\times 0.5791 = 0.496\ \text{m}^3$.

(a) Components of a panelled door (any four)

  +=====================+  <- head / top rail
  ||  panel  | panel   ||
  ||---------|---------||  <- intermediate (lock) rail
  ||  panel  | panel   ||
  +=====================+  <- bottom rail
  ^ stile      ^ mullion (vertical)
  (frame: jambs + head fixed to wall; shutter hung on the frame)

1. Frame (jambs and head): the fixed surrounding member built into the wall opening; the shutter is hung from it.
2. Stiles: the outer vertical members of the shutter to which rails and panels are fixed.
3. Rails: horizontal members of the shutter — top rail, lock/intermediate rail, bottom rail — connecting the stiles.
4. Panels: the thin boards (timber/glass/ply) fitted into grooves between stiles and rails, filling the shutter.
5. Mullion: a vertical member dividing the shutter into panels (optional).
6. Sill/threshold: the bottom horizontal member at the base of the opening.

(b) Door vs window (function)

• A door is a movable barrier in an opening that provides access/egress (entry and exit) of people and goods into and between spaces, while giving privacy and security.
• A window is an opening (with a glazed shutter) in a wall mainly to admit natural light and air (ventilation) and to provide vision/outlook; it is not normally used for passage.

(c) When a ventilator is preferred (any two)

1. In bathrooms, toilets, kitchens and store rooms, where privacy is needed but stale/humid air must escape — a small high-level ventilator removes air without exposing the interior.
2. Above doors or windows (fanlights) in rooms with high ceilings, to let hot air escape near the ceiling while maintaining wall space and security.

(a) Requirements of a good floor (any four)

1. Durability / hardness — should resist wear, abrasion and indentation under traffic.
2. Damp resistance / impermeability — should keep ground moisture out and stay dry.
3. Ease of cleaning and maintenance — smooth, non-absorbent, hygienic surface.
4. Adequate strength and stability — must carry imposed loads without cracking/settling.
5. Good appearance and a non-slip surface; reasonable thermal/sound insulation and economy.

(b) Layers of a typical ground floor (bottom → top)

  ---- floor finish (terrazzo / marble / CC topping)   <- top
  ---- bedding / screed (cement mortar)
  ---- floor concrete / base slab (1:2:4 or 1:4:8, ~75-100 mm)
  ---- DPC / damp-proof membrane (polythene or bitumen)
  ---- sub-base: compacted hardcore / soling (broken stone/brick)
  ---- compacted natural soil / earth fill              <- bottom

1. Compacted earth/sub-grade — natural soil rammed and consolidated.
2. Sub-base (hardcore/soling) — layer of broken stone or brick ballast, well compacted, to give a firm bed and break capillary rise.
3. Damp-proof membrane — polythene sheet or bitumen layer to stop rising damp.
4. Base concrete — lean/plain cement concrete bed (about $75$–$100\ \text{mm}$).
5. Bedding/screed — cement-mortar leveling layer.
6. Floor finish — the wearing surface (terrazzo, marble, tiles or cement-concrete topping).

(c) Comparison of finishes (any two)

Cement-concrete is the cheapest and adequately durable for utility areas; marble is the costliest with the best appearance; terrazzo gives a good balance of durability and cost for halls and lobbies.

(a) Substructure vs superstructure

• Substructure: the part of the building below the plinth/ground level that transfers all loads from the superstructure safely to the soil. Examples: foundation footings, plinth/foundation walls, basement and the DPC at plinth level.
• Superstructure: the part of the building above the plinth level that is used and seen. Examples: walls, columns, beams, floors, doors, windows, stairs, roof.

(b) Lintel — definition, function, materials

A lintel is a horizontal structural member (a small beam) placed across the top of an opening (door, window, ventilator) to support the masonry and other loads coming over the opening and transfer them to the supporting walls/jambs on either side.

Function: it spans the opening, carries the wall load above and keeps the shutter frame free of that load.

Materials (any two): reinforced cement concrete (RCC), timber/wood, stone, brick (reinforced), or steel (rolled sections).

(c) Lintel vs arch (load transfer)

• A lintel spans the opening as a beam in bending: the load above produces bending and shear in the lintel, which are resisted by its flexural strength and carried down to the jambs. It works largely in bending/tension (hence RCC needs steel at the bottom).
• An arch spans the opening as a curved system in compression: the load is transmitted along the curve as compressive thrust from voussoir to voussoir down to the abutments, which must resist an inclined (horizontal + vertical) thrust. The arch works in compression, so it can use materials weak in tension (brick/stone).

(a) Settlement of foundations — causes and types

Settlement is the vertical downward movement of a foundation under load. Causes: compression/consolidation of soil under load, lowering of the water table, vibration, loading of adjacent structures, poorly compacted fill, and inadequate foundation depth. Types:

• Uniform settlement — the whole structure sinks equally (least harmful).
• Differential settlement — unequal settlement between different parts (most harmful; causes cracking and tilting).
• Tilting — settlement varying linearly across the structure causing it to lean.

(b) Functions of a foundation

1. Distribute the superstructure load over a larger soil area so the soil pressure stays within its safe bearing capacity.
2. Provide a level, firm base for the superstructure.
3. Anchor the structure and give stability against sliding, overturning and wind/earthquake forces.
4. Reduce/avoid differential settlement and protect against soil movement and undermining.

(c) Shallow vs deep foundations

(d) Bearing capacity and factors affecting it

Bearing capacity is the load per unit area that the soil can safely carry without shear failure or excessive settlement. The safe bearing capacity (SBC) is the ultimate bearing capacity divided by a factor of safety. Factors affecting it: type and density of soil, soil cohesion and angle of internal friction, depth and width of the foundation, position of the water table, and the nature of the loading.