Mixed Deck — All BCE Topics Flashcards

Solid waste disposed in a sanitary landfill must be compacted and covered daily primarily to:

Answer: Control odors, vectors, and fire hazards

Daily cover of compacted solid waste controls odors, prevents vector attraction (rodents, flies), reduces fire risk, and controls litter blowing off the site.

What is the definition of the overconsolidation ratio (OCR)?

Answer: Ratio of preconsolidation pressure to current vertical effective stress

OCR = σ'p / σ'v0; OCR = 1 means normally consolidated, OCR > 1 means overconsolidated, indicating the soil has experienced higher stresses in its past.

Which property of a material is measured by the Brinell Hardness Test (BHN)?

Answer: Resistance to plastic indentation

The BHN test measures a material's resistance to permanent surface deformation by pressing a hardened steel ball under a known load.

In plastic analysis, the collapse load of a fixed-fixed beam of span L carrying a central point load P is:

Answer: 8M_p/L

Three plastic hinges form (two at fixed ends, one at midspan); virtual work gives P_collapse = 8M_p/L.

What is the significance of the preconsolidation pressure (σ'p) in soil mechanics?

Answer: Maximum past effective stress the soil has experienced

σ'p is the maximum effective stress the soil has ever been subjected to; stresses below it cause small elastic (recompression) settlements, while stresses above cause larger virgin consolidation settlements.

In rigid pavement design, which type of joint prevents differential settlement between adjacent slabs while allowing horizontal movement?

Answer: Expansion joint

Expansion joints provide space for concrete slabs to expand due to temperature increases while dowel bars transfer load and prevent differential vertical movement.

What should be the bare minimum number of joints necessary for the stability of an equilibrium equation if a structure has a total of 10 joints?

Answer: 10

For a structure to be in stable equilibrium, every part of it, including each joint, must satisfy the conditions of equilibrium. This means that the sum of forces in all directions and the sum of moments must be zero at every joint. Therefore, if a structure has 10 joints, all 10 joints must be considered in the equilibrium equations to ensure the overall stability of the system.

The factor of safety in structural design is defined as the ratio of:

Answer: Ultimate (failure) stress to allowable (working) stress

Factor of safety = ultimate stress / allowable stress (or failure load / working load), ensuring adequate reserve strength.

What is carried by the members of a truss?

Answer: axial load

Trusses are structural frameworks designed such that their members are primarily subjected to axial forces, meaning forces acting along the longitudinal axis of the member. The connections in an ideal truss are assumed to be pinned, which means they do not transfer bending moments. This design principle ensures that members efficiently carry loads in either tension or compression, making trusses highly efficient for spanning large distances.

Which formula gives the minimum radius of a horizontal curve on a railway track based on speed and superelevation?

Answer: R = V² / (127 × (e + f))

The minimum curve radius R = V²/[127(e+f)] relates speed (km/h), superelevation (e), and side friction factor (f) to curve radius in meters.

In structural analysis, an 'indeterminate' structure is one where:

Answer: Equilibrium equations alone are insufficient to find all forces

Statically indeterminate structures have more unknowns than available equilibrium equations, requiring compatibility conditions to solve.

The plastic hinge in a steel beam forms at the section where:

Answer: The bending moment reaches the plastic moment capacity M_p

A plastic hinge forms when the cross-section's bending moment reaches M_p, causing unlimited rotation at constant moment.

In fluid mechanics, the Reynolds number is used to determine:

Answer: Whether flow is laminar or turbulent

The Reynolds number is a dimensionless ratio of inertial to viscous forces that predicts flow regime (laminar vs. turbulent).

In prestressed concrete, post-tensioning differs from pre-tensioning in that:

Answer: Tendons are stressed after the concrete has hardened

In post-tensioning, tendons are placed in ducts and stressed against the hardened concrete after it reaches sufficient strength.

What is the primary function of a weigh-in-motion (WIM) system installed on a highway?

Answer: Measure vehicle axle loads without stopping trucks

WIM systems use embedded sensors to measure dynamic axle loads as vehicles travel at normal speeds, collecting load data for pavement design and enforcement.

Galvanizing steel involves coating it with which metal to provide sacrificial corrosion protection?

Answer: Zinc

Zinc galvanizing provides both a physical barrier and cathodic (sacrificial) protection, oxidizing preferentially to protect the base steel.

For a propped cantilever beam carrying a uniformly distributed load w over its full span L, the prop reaction is:

Answer: 3wL/8

Compatibility analysis of the propped cantilever shows the prop reaction equals 3wL/8, with the fixed end taking the remaining 5wL/8.

What is the primary purpose of a weir in open channel flow measurement?

Answer: To measure discharge by correlating head over the weir

A weir creates a controlled overflow section where the water head above the crest is measured and related to discharge via empirical formulas.

What is the purpose of 'thermal pre-stressing' in continuously welded rail (CWR) installation?

Answer: Lock rail in a stress-neutral state to prevent buckling and breakage

CWR is thermally pre-stressed (or stress-relieved) at a target neutral temperature so it is in neither tension nor compression at that temperature, minimizing buckling and fracture risk.

Which pump type is most commonly used for water supply in civil engineering applications?

Answer: Centrifugal pump

Centrifugal pumps are the most widely used in water supply systems due to their simplicity, reliability, and ability to handle large volumes.