Civil engineering basics: 50 core concepts

All 50 cards

1. 1
   Structural engineering
   Designing buildings, bridges, towers and other structures to carry their loads safely and stay fit for use
2. 2
   Geotechnical engineering
   Applying the behavior of soil and rock to foundations, slopes, retaining walls, tunnels and earthworks
3. 3
   Transportation engineering
   Planning, designing and operating roads, railways, airports and transit so people and goods move safely and efficiently
4. 4
   Water resources engineering
   Managing water: dams, canals, pipelines, flood control and irrigation

   Its core sciences are hydraulics (how water flows) and hydrology (where water comes from and how much).
5. 5
   Environmental engineering
   Protecting health and the environment: drinking water treatment, wastewater, solid waste and air quality
6. 6
   Dead load
   The permanent weight of the structure and everything fixed to it: beams, slabs, walls, finishes and fixed equipment

   It can be estimated well from member sizes and densities. Reinforced concrete, for example, weighs about 24 to $25\ \mathrm{kN/m^3}$.
7. 7
   Live load
   Variable gravity load from use and occupancy: people, furniture, movable equipment and stored goods

   Building codes set minimum values for each type of occupancy, usually as a uniform floor pressure.
8. 8
   Wind load
   Pressure and suction from wind on a structure’s surfaces, acting mainly sideways, plus uplift on roofs

   Pressure grows with the square of the wind speed: $q = \tfrac{1}{2}\rho v^2$.
9. 9
   Snow load
   The weight of snow on a roof, based on the site’s ground snow load and adjusted for roof slope, exposure and drifting
10. 10
    Seismic load
    Inertial forces from earthquake ground shaking, acting mainly horizontally

    They grow with the building’s mass, so heavier structures attract larger seismic forces.
11. 11
    Point load vs uniformly distributed load
    A point load acts at one spot ($\mathrm{kN}$); a uniformly distributed load is spread evenly along a length ($\mathrm{kN/m}$) or over an area ($\mathrm{kN/m^2}$)
12. 12
    Tension
    Forces that pull a member apart and lengthen it

    Cables, hangers and ties work in tension.
13. 13
    Compression
    Forces that push on a member and shorten it

    Columns and struts work in compression; long, slender ones can fail by buckling sideways.
14. 14
    Shear
    Forces acting parallel to a cross-section that tend to slide one part of a member past the next
15. 15
    Bending
    Loads across a member’s length make it curve, putting one face in compression and the other in tension

    In a simply supported beam under gravity load, the top is in compression and the bottom in tension.
16. 16
    Normal stress
    $\sigma = \dfrac{F}{A}$

    Force per unit area of cross-section. $1\ \mathrm{MPa} = 1\ \mathrm{N/mm^2}$.
17. 17
    Young’s modulus
    $E = \dfrac{\sigma}{\varepsilon}$, the ratio of stress to strain in the elastic range

    Strain $\varepsilon = \Delta L / L$ has no units. For steel, $E \approx 200\ \mathrm{GPa}$.
18. 18
    Beam
    A member, usually horizontal, that carries loads across its length mainly by bending and shear
19. 19
    Column
    A vertical member that carries load mainly in axial compression
20. 20
    Truss
    A framework of straight members joined at their ends into triangles; with loads applied at the joints, each member carries only tension or compression

    Triangles keep it rigid: a triangle can’t change shape unless one of its sides changes length.
21. 21
    Pin support
    Prevents movement in both directions but allows rotation: two reaction forces, no moment
22. 22
    Roller support
    Prevents movement perpendicular to the surface only: one reaction force, normal to the surface

    It lets the member expand and contract freely. A beam on a pin at one end and a roller at the other is simply supported.
23. 23
    Fixed support
    Prevents movement and rotation: two reaction forces and a reaction moment

    A cantilever is a beam fixed at one end and free at the other.
24. 24
    Equations of static equilibrium in 2D
    $\sum F_x = 0,\quad \sum F_y = 0,\quad \sum M = 0$

    Three equations, so statics alone can find up to three unknown reactions on a single rigid body.
25. 25
    Ingredients of concrete
    Cement, water, fine aggregate (sand) and coarse aggregate (gravel or crushed stone), often with admixtures

    Aggregates fill about 60–75% of the volume; the cement paste binds them together.
26. 26
    Portland cement
    A hydraulic cement: it sets and hardens by reacting chemically with water (hydration), even under water

    It is made by heating limestone and clay in a kiln to form clinker, which is ground with a little gypsum.
27. 27
    Water–cement ratio
    The mass of water divided by the mass of cement in a mix

    Lower ratios give stronger, more durable concrete; extra water makes it easier to place but leaves pores. Typical structural mixes are about 0.4 to 0.6.
28. 28
    Curing concrete
    Keeping fresh concrete moist and warm enough after placing so hydration continues

    Good curing raises strength and durability and reduces shrinkage cracking; it typically lasts at least 7 days.
29. 29
    Slump test
    A workability test for fresh concrete: fill a standard cone, lift it off and measure how far the concrete sinks

    A higher slump means a more fluid mix.
30. 30
    Age at which concrete strength is usually specified
    28 days

    Measured by crushing standard cylinders or cubes. Typical structural concrete is about 20 to $40\ \mathrm{MPa}$.
31. 31
    Tensile strength of concrete
    Low: roughly 10% of its compressive strength

    Concrete cracks easily in tension, which is why steel is added to carry it.
32. 32
    Reinforced concrete
    Concrete with embedded steel bars (rebar) that carry the tension, while the concrete carries the compression

    In a simply supported beam the main bars go near the bottom, where bending causes tension. Ribs on the bars help them bond to the concrete.
33. 33
    Concrete cover
    The layer of concrete between the reinforcement and the surface

    It protects the steel from corrosion and fire and lets the bars bond. Typically about 20 to $75\ \mathrm{mm}$, more for harsher exposure.
34. 34
    Why an I-beam is shaped like an I
    Most of the steel sits in the flanges, far from the middle of the section, where it resists bending best; the thin web carries the shear
35. 35
    Common structural steel shapes
    Wide-flange (I or H) sections, channels, angles, tees and hollow structural sections (tubes)
36. 36
    Yield strength of steel
    The stress at which steel starts to deform permanently

    Common structural grades yield at about 250 to $355\ \mathrm{MPa}$.
37. 37
    Soil types from coarsest to finest
    Gravel, sand, silt, clay

    Gravel and sand are coarse-grained; silt and clay are fine-grained. Size limits differ between classification systems, but clay particles are typically under $0.002\ \mathrm{mm}$.
38. 38
    Cohesive vs granular soils
    Cohesive soils (clays) stick together and are plastic when moist; granular soils (sands and gravels) get their strength from friction between grains and drain freely
39. 39
    Shallow foundation
    Spreads the load into soil near the surface: strip footings under walls, pad footings under columns, or a raft under the whole building

    Its depth is typically no greater than its width.
40. 40
    Deep foundation
    Piles or drilled shafts that carry load down through weak soil to stronger soil or rock
41. 41
    End-bearing vs friction piles
    An end-bearing pile carries load mainly through its tip into a firm layer; a friction pile carries it mainly by friction along its shaft
42. 42
    Differential settlement
    Uneven settlement between parts of a structure

    It distorts and cracks a building far more than the same amount of uniform settlement.
43. 43
    Leveling
    Finding differences in height between points with a level and a graduated staff

    The staff is also called a rod.
44. 44
    Benchmark
    A permanent point of known elevation used as the reference for leveling
45. 45
    Height of instrument method
    $\mathrm{HI} = \text{known elevation} + \text{backsight}$, then $\text{new elevation} = \mathrm{HI} - \text{foresight}$

    A backsight is a staff reading on a point of known height; a foresight is a reading on a point whose height you want.
46. 46
    Contour line
    A line on a map joining points of equal elevation

    Closely spaced contours mean a steep slope; widely spaced ones mean a gentle slope.
47. 47
    Road crown
    The cross slope from the center of a road down to its edges, so rain drains off the surface

    Typically about 2% on paved roads.
48. 48
    Culvert
    A pipe or box that carries a stream or drainage water under a road, railway or embankment
49. 49
    Storm sewer vs sanitary sewer
    A storm sewer carries rainwater runoff; a sanitary sewer carries wastewater from buildings to a treatment plant

    A combined sewer carries both, and can overflow in heavy rain.
50. 50
    Layers of an asphalt road, from the top down
    Surface course, base course, subbase, subgrade

    The subgrade is the prepared soil underneath; each layer spreads the wheel load before it reaches the one below.