Engineering: Civil and Structural
Forces, materials, design constraints, and safety in the built environment
Engineering: Civil and Structural
Forces, materials, design constraints, and safety in the built environment
Engineering - Grade 9-12
- 1
A simply supported beam is 6.0 m long and carries a single 12,000 N point load at its center. What is the upward reaction force at each support?
For a centered load on a symmetric simply supported beam, divide the total load by 2.
Each support provides an upward reaction force of 6,000 N. Because the load is centered and the beam is symmetric, the total load of 12,000 N is shared equally by the two supports. - 2
A steel tension member carries a force of 45,000 N. Its cross-sectional area is 0.0030 m². Calculate the tensile stress in pascals.
Use stress = force ÷ area.
The tensile stress is 15,000,000 Pa. Stress equals force divided by area, so 45,000 N divided by 0.0030 m² equals 15,000,000 Pa, or 15 MPa. - 3
A concrete column supports a compressive load of 800,000 N. The column has a square cross section that is 0.40 m by 0.40 m. What is the compressive stress in the column?
The compressive stress is 5,000,000 Pa. The area is 0.40 m times 0.40 m, which equals 0.16 m². Stress equals 800,000 N divided by 0.16 m², so the stress is 5 MPa. - 4
A structural member has an original length of 2.00 m. Under load, it stretches by 0.0015 m. Calculate the strain.
Strain is a ratio, so the meters cancel out.
The strain is 0.00075. Strain equals change in length divided by original length, so 0.0015 m divided by 2.00 m equals 0.00075. Strain has no units because it is a ratio. - 5
A material has a stress of 120 MPa and a strain of 0.00060 while still behaving elastically. Estimate its Young's modulus.
The Young's modulus is 200,000 MPa, or 200 GPa. Young's modulus equals stress divided by strain, so 120 MPa divided by 0.00060 equals 200,000 MPa. - 6
A bridge deck must support dead load and live load. Explain the difference between dead load and live load, and give one example of each for a highway bridge.
Think about what stays on the bridge all the time and what can move on or off the bridge.
Dead load is the permanent weight of the structure itself, such as the bridge deck, beams, and railings. Live load is a changing load, such as cars, trucks, pedestrians, or wind acting on the bridge. - 7
A truss bridge uses many triangles instead of rectangles. Explain why triangles are useful in structural design.
Triangles are useful because they are geometrically stable and resist changing shape when forces are applied. A rectangular frame can deform into a parallelogram more easily unless it is braced, but a triangle keeps its shape if its members do not fail. - 8
A design code requires a factor of safety of 2.5. If a cable is expected to carry a working load of 20,000 N, what minimum breaking strength should the cable have?
Factor of safety compares failure strength to expected working load.
The cable should have a minimum breaking strength of 50,000 N. The required strength equals the working load times the factor of safety, so 20,000 N times 2.5 equals 50,000 N. - 9
A building is planned for an area with soft clay soil. Name two foundation strategies engineers might consider and explain why foundations are important.
Engineers might consider deep piles that transfer load to stronger soil or rock, or a mat foundation that spreads the building load over a large area. Foundations are important because they transfer loads safely to the ground and help limit settlement, tilting, and structural damage. - 10
A beam bends too much under service loads, even though it does not break. Explain why excessive deflection can still be a serious engineering problem.
Strength is not the only requirement. Think about how the structure feels and functions.
Excessive deflection can crack finishes, damage nonstructural parts, make doors and windows stick, create drainage problems, or make people feel unsafe. A structure must be strong enough to avoid failure and stiff enough to perform properly during normal use. - 11
A civil engineering team is choosing between steel, reinforced concrete, and timber for a small pedestrian bridge. List one advantage and one limitation of each material.
Steel is strong and can span long distances, but it can corrode if not protected. Reinforced concrete is durable and strong in compression, but it is heavy and can crack. Timber is renewable and relatively light, but it may require protection from moisture, insects, and fire. - 12
A retaining wall holds back soil on a sloped site. Describe two forces or failure modes the engineer must consider when designing the wall.
Soil does not only push downward. It can push sideways too.
The engineer must consider lateral earth pressure pushing the wall outward and the possibility of sliding or overturning. The engineer may also consider bearing failure under the base, water pressure behind the wall, and drainage needs. - 13
A structure in an earthquake zone must be designed for lateral loads. Explain what a lateral load is and name two building features that can help resist lateral loads.
A lateral load is a sideways force, such as force from wind or earthquake motion. Braced frames, shear walls, moment-resisting frames, and base isolation systems can help a building resist lateral loads. - 14
A rectangular concrete slab is 5.0 m long, 3.0 m wide, and 0.20 m thick. If the density of concrete is about 2400 kg/m³, estimate the mass of the slab.
First find volume, then multiply by density.
The mass of the slab is about 7,200 kg. The volume is 5.0 m times 3.0 m times 0.20 m, which equals 3.0 m³. The mass equals density times volume, so 2400 kg/m³ times 3.0 m³ equals 7,200 kg. - 15
A city wants to replace an old bridge. Identify three constraints or criteria civil engineers should consider before choosing a final design.
Engineers should consider safety, cost, construction time, environmental impact, traffic disruption, expected lifespan, maintenance needs, site conditions, accessibility, and code requirements. A strong design must balance technical performance with real-world constraints.