Tamil Nadu HSE Second Year Basic Civil Engineering cheat sheet

Standard brick size in India is 190 × 90 × 90 mm (modular); with mortar the nominal size becomes 200 × 100 × 100 mm.

Good burnt clay brick: water absorption under 20% (first-class under 15%), compressive strength of first-class brick not less than 10 N/mm², and a sharp metallic ringing sound when struck.

Efflorescence test: bricks soaked in water and dried showing white salt patches are graded nil, slight, moderate, heavy or serious; heavy and serious grades are rejected.

Lime is classified as fat lime (rich, high calcium, slakes readily, used for whitewashing) and hydraulic lime (contains clay, sets under water).

Ordinary Portland cement grades in India are 33, 43 and 53, the number being the 28-day compressive strength in N/mm² of a 1:3 cement-sand mortar cube.

Initial setting time of OPC is not less than 30 minutes; final setting time not more than 600 minutes.

Timber seasoning reduces shrinkage, increases strength and prevents decay; air seasoning is slow, kiln seasoning is fast and controllable.

Mortar ratio 1:3 (cement:sand) is used for load-bearing masonry and 1:6 for general plastering; richer mixes give higher strength but more shrinkage cracking.

Damp-proof course (DPC) is laid at plinth level, typically 1:2 cement mortar with waterproofing compound, or bitumen felt, projecting to full wall width.

Chain surveying uses only linear measurements; it suits small, fairly level, open areas and is divided into triangles (well-conditioned when no angle is below 30° or above 120°).

Metric chain lengths are 20 m and 30 m; a 30 m chain has 150 links of 0.2 m each, and the tally is fixed at every 10 links.

Ranging is fixing intermediate points on a straight line between two stations; direct ranging needs intervisibility, indirect ranging is used when stations are not intervisible.

Obstacles to chaining: a river is crossed by the similar-triangle or sine rule method; a building is bypassed by the perpendicular offset or triangle method.

Levelling terms: benchmark (BM) is a fixed reference of known reduced level (RL); height of instrument (HI) = RL of station + backsight reading.

Rise and fall method: rise = previous staff reading − current reading; fall = current reading − previous reading; RL of next station = RL of previous ± rise or fall.

Collimation or height-of-instrument method: RL of any point = HI − intermediate or foresight reading; arithmetic check is ΣBS − ΣFS = last RL − first RL.

The level tube axis must be parallel to the line of collimation; the two-peg test detects and corrects this collimation error.

Contour lines join points of equal elevation; closely spaced contours indicate steep ground, widely spaced contours indicate gentle slope, and they never cross except at an overhanging cliff.

Minimum room height for a habitable room is 3.0 m (2.75 m for a bath or store); minimum carpet area for a habitable room is 9.5 m².

Minimum widths: 0.9 m for a habitable room door, 1.2 m for a main entrance door, 0.6 m for a bath door; stair width at least 0.9 m with riser not more than 190 mm and tread not less than 250 mm.

Setback (open space around a building) is measured from the plot boundary and depends on plot area and building height as per local development rules.

Orientation rule: in the northern hemisphere, the long axis of the building should run east-west so maximum wall area faces north and south, reducing heat gain.

FAR (floor area ratio) = total floor area of all floors ÷ plot area; ground coverage = built-up area on plot ÷ plot area.

A line plan shows walls, openings and room names without dimensions or details; a detailed plan shows dimensions, thicknesses, and door/window schedules.

Vastu/general planning principles: kitchen in the south-east, pooja in the north-east, master bedroom in the south-west; cross-ventilation through opposite openings is preferred.

Aspects of planning: privacy, grouping (zoning of related rooms), circulation, sanitation, lighting and ventilation, and economy of construction.

Stress σ = P/A (N/mm²); strain ε = δL/L (dimensionless); Young's modulus E = σ/ε within the elastic limit (Hooke's law).

Poisson's ratio μ = lateral strain ÷ longitudinal strain, typically 0.25 to 0.33 for steel and concrete; μ cannot exceed 0.5 for isotropic materials.

A simply supported beam with central point load W and span L has maximum bending moment WL/4 at midspan and maximum shear force W/2 at supports.

A cantilever with point load W at free end: maximum BM = WL at the fixed end, maximum deflection = WL³/(3EI).

Bending equation: M/I = σ/y = E/R, where I is the second moment of area and y is the distance from the neutral axis.

Shear stress τ = VQ/(Ib); for a rectangular section the maximum shear stress is 1.5 times the average, occurring at the neutral axis.

Moment of inertia: rectangle about centroidal axis = bd³/12; circle = πd⁴/64; triangle about base = bh³/12.

A section modulus Z = I/y_max; a beam is designed so that M/Z does not exceed the permissible bending stress.

Euler buckling load for a column: P = π²EI/L²; effective length depends on end conditions (both ends pinned L, fixed-fixed 0.5L, fixed-free 2L).

Nominal concrete mixes: M5 (1:5:10), M7.5 (1:4:8), M10 (1:3:6), M15 (1:2:4), M20 (1:1.5:3), M25 (1:1:2) as cement:sand:coarse aggregate by volume.

The number in M20 is the characteristic compressive strength in N/mm² at 28 days measured on 150 mm cubes; the target mean strength adds 1.65 times standard deviation.

Water-cement ratio governs strength and durability; a lower w/c ratio gives higher strength, but workability must be maintained, typically w/c 0.4 to 0.6.

Slump test measures workability of fresh concrete; typical values are 25-75 mm for normal RCC work, and a true slump indicates a cohesive mix.

Compaction by vibration removes entrapped air; curing keeps moisture for hydration and should continue for at least 7 days (14 days for cement with pozzolana).

Bulking of sand is the increase in volume of moist sand (up to 20-30% for fine sand) and must be accounted for when batching by volume.

Grades M20 and above are used for reinforced concrete; M10 and M15 are used for mass concrete and lean concrete.

Segregation is separation of coarse aggregate from mortar; bleeding is upward migration of water to the surface of freshly placed concrete.

Per capita water demand in Indian towns is commonly taken as 135 litres per head per day for domestic use; total demand adds industrial, commercial and public uses.

Design period for water supply components is typically 30 years for dams and mains, and 15 years for distribution systems.

Sources of water: surface sources (river, lake, reservoir) and subsurface sources (spring, well, infiltration gallery); groundwater is generally freer of turbidity.

Water treatment sequence: screening, aeration, coagulation-flocculation (alum), sedimentation, filtration (rapid sand filter), disinfection (chlorination).

Rapid sand filters have a filtration rate around 100-150 litres per m² per minute; slow sand filters are around 100-200 litres per m² per hour.

Residual chlorine of 0.2 mg/l should remain after the contact period; chlorine demand is the difference between dose applied and residual.

Sewer design uses self-cleansing velocity of about 0.6-0.9 m/s and a maximum of about 3 m/s; sewers are laid with a minimum gradient to maintain flow.

Septic tank is a combined sedimentation and digestion unit, while a soak pit or dispersion trench disposes of the effluent; minimum capacity is usually 1-2 m³.

One-pipe and two-pipe plumbing systems: the two-pipe system separates soil (from WCs) and waste (from sinks, baths) pipes for better ventilation and reuse.

Road classification in India: National Highways, State Highways, Major District Roads, Other District Roads and Village Roads (Nagpur classification).

Camber or cross slope is provided for drainage; typical values are 2% for cement concrete and high-type bituminous, 3% for other bituminous, and 4% for earth roads.

Superelevation e = V²/(127R) (V in km/h, R in m) with friction neglected; the maximum permissible superelevation is 7% (10% for hill roads).

Stopping sight distance = lag distance + braking distance = 0.278 Vt + V²/(254f), where t is reaction time in seconds and f is the coefficient of friction.

Transition curve (spiral) length is governed by rate of change of centrifugal acceleration and by superelevation introduction; a spiral is preferred in India.

Bituminous construction types: WBM (water-bound macadam) is a base course, while WMM, DBM and BC are bituminous layers; SDBC and BC are wearing courses.

CBR (California Bearing Ratio) is the ratio of load on a soil to that on standard crushed stone, expressed in percent, and is used for flexible pavement design.

Bridges: the span is the distance between supports; a culvert has span up to 6 m, a minor bridge up to 60 m, and a major bridge above that.

Pier supports the bridge superstructure between spans, while abutment supports the end of the span and retains the approach embankment.

Approximate estimate methods: plinth area rate, cubic content, unit rate (per km, per seat), and percentage of similar completed work.

Detailed estimate: measure quantities from drawings, multiply by rates (with the rate analysis) and add contingency, work-charged establishment and departmental charges.

Plinth area estimate = plinth area × plinth area rate; the plinth area is measured at the floor level of the ground floor, including walls.

Deduction rules for plastering: no deduction for openings up to 0.5 m²; for larger openings deduct the full area, and add the jambs, soffits and sills.

For brickwork, no deduction is made for openings up to 0.1 m²; for larger openings deduct the full area, but add the area of the jambs and soffits.

Contingency in a detailed estimate is usually 3-5% of the estimated cost; work-charged establishment is 1-2%.

Depreciation methods: straight line (constant annual amount) and sinking fund (annual amount invested at compound interest to replace the asset).

Valuation terms: market value, book value, scrap value, salvage value and sinking fund; capitalised value = net income ÷ rate of interest.

Standard rent is fixed under rent control as a percentage return on the cost of construction plus land value, and is used in valuation of rented property.