Q: Fluid kinematics (2-D incompressible flow): If the x-component of velocity is u(x,y) = y^2 + 4xy and the y-component v(x,y) = 0 at y = 0, determine the expression for v(x,y).

Introduction / Context: For incompressible 2-D flow, continuity requires that the divergence of velocity is zero. Given one component, the other can be found (up to a function of the remaining variable) by integrating the continuity equation and applying a boundary condition. Given Data / Assumptions: u(x,y) = y^2 + 4xy. Incompressible 2-D: du/dx + dv/dy = 0. Boundary condition: v(x,0) = 0 for all x. Concept / Approach: From continuity, dv/dy = −du/dx. Differentiate u with respect to x, integrate with respect to y to obtain v, and then apply the boundary condition to fix the integration “constant” (a function of x). Step-by-Step Solution: Compute du/dx = ∂(y^2 + 4xy)/∂x = 4y.From continuity: dv/dy = −4y.Integrate: v(x,y) = ∫(−4y) dy = −2y^2 + f(x).Apply v(x,0) = 0 ⇒ f(x) = 0.Thus v(x,y) = −2y^2. Verification / Alternative check: Check: dv/dy = −4y and du/dx = 4y ⇒ du/dx + dv/dy = 0, satisfying incompressibility. Why Other Options Are Wrong: 4y, 2xy: Wrong functional dependence and ignore boundary condition. 2y^2: Sign error; would violate continuity. −4xy: Not supported by integration of −4y. Common Pitfalls: Forgetting the integration function f(x). Not applying the boundary condition properly. Final Answer: -2y^2

Q: Limit state design per IS 456: Unfactored bending moments at a beam section from frame analysis are 50, 80, 120, and 180 kNm due to dead, live, wind, and earthquake loads respectively. What is the design (factored) moment for collapse in flexure?

Introduction / Context: IS 456 (limit state method) specifies load combinations and partial safety factors to obtain design actions. For beams, the governing factored moment is the maximum among prescribed combinations including gravity plus wind or earthquake, and combined cases (1.2 combination) when lateral loads act with gravity. Given Data / Assumptions: M(D) = 50 kNm, M(L) = 80 kNm, M(W) = 120 kNm, M(E) = 180 kNm (unfactored). Use IS 456 load combinations for ultimate limit state. Consider both wind and earthquake combinations. Concept / Approach: Relevant combinations include: 1.5(D+L); 1.5(D+W) or 1.5(D+E); 1.2(D+L+W) or 1.2(D+L+E); and 0.9D ± 1.5W or 0.9D ± 1.5E for stability. The design moment is the maximum absolute value from these combinations at the section. Step-by-Step Solution: 1.5(D+L) = 1.5*(50+80) = 195 kNm.1.5(D+W) = 1.5*(50+120) = 255 kNm.1.5(D+E) = 1.5*(50+180) = 345 kNm.1.2(D+L+W) = 1.2*(50+80+120) = 300 kNm.1.2(D+L+E) = 1.2*(50+80+180) = 372 kNm.0.9D + 1.5W = 45 + 180 = 225 kNm; 0.9D + 1.5E = 45 + 270 = 315 kNm.Maximum is 372 kNm. Verification / Alternative check: Since earthquake governs over wind here, the 1.2(D+L+E) combination produces the highest value; check opposite signs if applicable at other sections. Why Other Options Are Wrong: 195 from 1.5(D+L), 250/255 not governing, 345 from 1.5(D+E) is lower, 315 from 0.9D + 1.5E is lower. Common Pitfalls: Ignoring the 1.2 combination which often governs when lateral loads are large. Forgetting the 0.9D combinations meant for stability checks. Final Answer: 372

Q: Capacity standards: what are the typical capacities for (i) a one-way 1.5 m wide sidewalk (persons per hour) and (ii) a one-way 2-lane urban road with no frontage access, no standing vehicles, and very little cross traffic (PCU per hour)?

Introduction / Context: Planning and traffic engineering rely on benchmark capacities to size facilities. For pedestrian sidewalks and multi-lane urban roads, conventional design manuals provide typical one-way capacities under specified assumptions (unobstructed flow, good surface, limited conflicts). This question tests recall of standard order-of-magnitude values used for preliminary design checks. Given Data / Assumptions: Sidewalk width = 1.5 m, one-way pedestrian movement. Urban road: 2 lanes in one direction, minimal frontage access, no standing vehicles, very low cross traffic. Capacities expressed as persons per hour (sidewalk) and PCU per hour (road). Concept / Approach: Pedestrian facility capacity depends on flow density, desired speed, and comfort level; a 1.5 m one-way sidewalk commonly carries about 1200 persons/hour comfortably. A one-way 2-lane urban road without side frictions typically carries about 2400 PCU/hour (≈1200 PCU per lane) under good conditions. Step-by-Step Solution: Match sidewalk width (1.5 m) to standard pedestrian flow rates to obtain ≈1200 persons/hour.Apply per-lane urban road capacity of ≈1200 PCU/hour; with two lanes in one direction, total ≈2400 PCU/hour.Select the pair that aligns with both computed values. Verification / Alternative check: Cross-check with level-of-service tables; values fall within typical ranges for uninterrupted flow and adequate level of service. Why Other Options Are Wrong: Other pairs either understate sidewalk capacity or over/understate the two-lane urban road capacity compared to norms. Common Pitfalls: Confusing two-way sidewalk flow with one-way capacity; ignoring side frictions that can reduce practical capacity. Final Answer: 1200 and 2400

Question 1

Conjugate beam method (structural analysis): For a two-span real beam that contains an internal hinge, identify the correct conjugate beam using the standard mapping rules—fixed end ↔ free end; end pin/roller ↔ same end pin/roller; internal hinge in…

Accepted Answer

Introduction / Context: The conjugate beam method transforms a bending problem into a statics problem by mapping the real beam to a conjugate beam whose shear and reactions represent slopes and deflections. Correctly creating the conjugate beam support conditions is essential; otherwise, the computed slopes and deflections will be wrong. Given Data / Assumptions: Real member: a continuous (two-span) beam. There is an internal hinge between the spans. Standard conjugate-beam mapping applies. Flexural rigidity is uniform enough to apply the usual E I curvature loading concept. Concept / Approach: Mapping rules are: (1) a fixed end in the real beam becomes a free end in the conjugate beam; (2) a pin/roller support at an end remains a pin/roller at the same end in the conjugate beam; (3) an internal hinge in the real beam becomes an internal simple support in the conjugate beam. The loading on the conjugate beam is the M/EI diagram of the real beam; the conjugate-beam reactions correspond to real-beam rotations/deflections. Step-by-Step Solution: Identify supports in the real beam (fixed/pinned/roller) and apply the mapping to each end.Locate the internal hinge in the real beam and replace it with an internal simple support in the conjugate beam.Keep end pins/rollers unchanged, convert fixed ends to free ends, and insert the internal support at the hinge location.Select the option that follows exactly this construction. Verification / Alternative check: At internal hinges, the real beam allows moment release (zero moment, finite rotation). In the conjugate beam, this state is modeled by a simple support (zero deflection, free slope reaction analogy), validating the mapping. Why Other Options Are Wrong: Rigidifying the internal hinge or removing it contradicts the mapping rule. Converting all ends to free ends ignores the pin/roller mapping at ends. Leaving fixed ends fixed violates the fixed↔free mapping. Common Pitfalls: Forgetting to change internal hinges to internal supports. Mixing up slope/deflection analogies for conjugate beam shear/reactions. Final Answer: A two-span conjugate beam of the same length with end pins/rollers kept as pins/rollers, fixed ends (if any) changed to free ends, and an INTERNAL SIMPLE SUPPORT placed exactly at the real beam’s internal hinge

Question 2

In soil mechanics and geotechnical engineering, the slow recovery of structural strength in remoulded clay due to an isothermal gel–soil–gel transformation (after agitation and subsequent rest) is known as which property?

Accepted Answer

Introduction / Context: Clays exhibit time-dependent behavior influenced by their microstructure and pore-fluid chemistry. When a clay is remoulded, its structure collapses and undrained shear strength drops. Over time at constant temperature and moisture, some strength can recover due to structural reformation—an important concept for construction staging and stability assessments. Given Data / Assumptions: Material: clayey soil. Process: agitation/remoulding followed by rest at roughly constant temperature (isothermal). Observation: partial strength recovery with time. Concept / Approach: The term for this reversible, time-dependent decrease in apparent viscosity/strength under shear and recovery at rest is thixotropy. In soils, thixotropy is linked to rearrangement and flocculation of clay particles and the rebuilding of the diffuse double layer, which restores some interparticle bonding. Step-by-Step Solution: Recognize remoulding → initial loss of structure and strength.At rest (isothermal), microstructure rebuilds → partial strength returns.Match phenomenon to definition → thixotropy. Verification / Alternative check: Field vane tests comparing peak and remoulded strengths often show increased strength after waiting periods, consistent with thixotropic gain. Why Other Options Are Wrong: Isotropy/anisotropy: Directional properties, not time-dependent recovery. Allotropy: Applies to elements with different structural forms, not soils. Rheopexy: Strength increases with continued shear (opposite behavior). Common Pitfalls: Confusing consolidation (drainage/time) with thixotropy (structure/time at constant water content). Final Answer: Thixotropy

Question 3

According to reinforced concrete design practice (IS 456 context), the minimum area of tension reinforcement required in a beam must be greater than which expression?

Accepted Answer

Introduction / Context: Minimum tension steel in beams is provided to ensure ductility, crack control, and to prevent sudden failure after concrete cracking. Codes specify a formula linking minimum steel to beam dimensions and steel strength so that a small but necessary reinforcement area is always present, even when flexural demand is low. Given Data / Assumptions: Beam breadth b and effective depth d are design dimensions. fy is the characteristic yield strength of the reinforcement. We seek the standard minimum tension steel requirement. Concept / Approach: A common code expression for beams is Ast,min ≥ 0.85 * b * d / fy. This ensures the reinforcement percentage decreases with stronger steel (higher fy) yet maintains a floor for post-cracking capacity. The expression has proper dimensions of area and scales with section size. Step-by-Step Solution: Recall the minimum tension steel expression used in IS practice.Check dimensional consistency: 0.85 * b * d / fy has units of area.Select the matching option: 0.85 bd/fy. Verification / Alternative check: Design examples across textbooks use this expression for various grades of steel, producing typical minimum percentages around 0.2% to 0.3% of the concrete area for common fy values. Why Other Options Are Wrong: 0.87 fy/bd: Inverse dimensions (stress divided by area) and not an area. 0.04 bd or 0.4 bd/y: Arbitrary/incorrect forms not tied to fy; may be unconservative or excessive. 0.12 bd/fck: Relates to concrete strength rather than steel yield; not the standard minimum steel formula. Common Pitfalls: Forgetting to compare provided Ast with both minimum and maximum limits. Using gross depth instead of effective depth d. Final Answer: 0.85 bd/fy

Question 4

In IS 456 design for reinforced concrete beams, the span-to-depth ratio limits are specified primarily to ensure which serviceability criterion is respected?

Accepted Answer

Introduction / Context: Serviceability governs how a structure performs in use—particularly deflections and crack widths. IS 456 specifies span/depth (L/d) limits for beams to control excessive long-term and short-term deflections without detailed calculations, ensuring occupant comfort, finish integrity, and line-of-sight performance in floors and roofs. Given Data / Assumptions: Reinforced concrete beam spans and depths are design variables. Code provides L/d limits with modification factors for tension steel percentage and compression reinforcement. We are asked for the primary reason for these limits. Concept / Approach: The code’s basic L/d limits act as a prescriptive deflection control. While crack width has separate detailing provisions, and shear failure is addressed by shear design, the span/depth limits directly address the risk of excessive deflection under service loads, including creep and shrinkage effects. Step-by-Step Solution: Identify the serviceability concern directly controlled by L/d → deflection.Note that crack control uses bar spacing and cover rules, not L/d directly.Hence, select the deflection option. Verification / Alternative check: IS 456 tables list basic L/d values (e.g., 20 for simply supported beams, etc.) modified for reinforcement percentages, confirming a deflection-control intent. Why Other Options Are Wrong: Crack width is managed via bar diameter/spacing and tensile stress limits. Shear failure is prevented by shear design (Vc + Vs), not by L/d limits. Allowable stresses relate to limit state checks, not prescriptive L/d limits. Common Pitfalls: Ignoring long-term deflection from creep and shrinkage when near the limit. Final Answer: deflection of the beam is below a limiting value

Question 5

Hydrology—Unit hydrograph theory: Compared to the peak discharge of a 4-hour unit hydrograph for the same basin, the peak discharge of the instantaneous unit hydrograph (IUH) will be:

Accepted Answer

Introduction / Context: Unit hydrographs describe a basin’s direct runoff response to a unit depth of effective rainfall over a specified duration. As the rainfall duration shortens, runoff is concentrated in time, making the hydrograph sharper and peakier. The theoretical limit is the instantaneous unit hydrograph (IUH). Given Data / Assumptions: Same basin, linear system assumption. Comparison between a finite-duration (4-hour) unit hydrograph and IUH. Unit depth of effective rainfall in both cases. Concept / Approach: Reducing rainfall duration for the same unit depth compresses runoff timing and increases peak discharge while preserving total volume (area under hydrograph). Hence, IUH, as the zero-duration limit, has the most concentrated response and the highest peak. Step-by-Step Solution: Recognize: area under UH = unit runoff volume (constant).Shorter duration → narrower base for similar area → higher peak.Therefore, IUH peak > 4-hour UH peak. Verification / Alternative check: Constructing UHs of varying duration from an IUH via convolution shows peaks decrease as duration increases, confirming the relationship. Why Other Options Are Wrong: Equal or lesser contradicts the concentration principle; equal is only a degenerate case. Common Pitfalls: Confusing peak discharge with total volume (which stays constant for a unit depth). Final Answer: greater

Question 6

Irrigation planning: A tube well delivers 4 m^3/hour and operates 20 hours per day during the season. If the irrigation interval is 20 days and the required depth per irrigation is 7 cm, what is the maximum command area (in m^2)?

Accepted Answer

Introduction / Context: Command area calculations translate discharge and operating schedule into the land area that can be adequately irrigated at a specified interval and depth. This is essential for sizing well fields and planning water distribution. Given Data / Assumptions: Discharge Q = 4 m^3/hour. Operating time = 20 hours/day. Irrigation interval = 20 days. Depth per irrigation = 7 cm = 0.07 m. Concept / Approach: Total volume available per interval equals discharge × operating time over the interval. Command area A = Volume / required depth. Uniform application and negligible losses are assumed. Step-by-Step Solution: Compute daily volume: V_day = 4 * 20 = 80 m^3/day.Compute interval volume: V = 80 * 20 = 1600 m^3.Depth requirement: d = 0.07 m.Area: A = V / d = 1600 / 0.07 = 22857.14 m^2 ≈ 2.29 × 10^4 m^2. Verification / Alternative check: Units check: m^3 / m = m^2 → correct. Result matches option D. Why Other Options Are Wrong: Values smaller or larger than 2.29 × 10^4 m^2 result from arithmetic errors (wrong interval volume or depth conversion). Common Pitfalls: Forgetting to convert 7 cm to 0.07 m. Multiplying instead of dividing by depth when computing area. Final Answer: 2.29 × 10^4 m^2

Question 7

Reinforced concrete columns (elastic theory): A column has longitudinal steel equal to 1% of the net concrete area. With modular ratio m = 10, if Ps and Pc are the loads carried by steel and concrete respectively, what is the ratio Ps/Pc expressed a…

Accepted Answer

Introduction / Context: Under the elastic (transformed section) theory, steel and concrete in a short column share load in proportion to their moduli and areas because they undergo the same strain. The modular ratio m = Es/Ec scales the steel area to an equivalent concrete area, letting us apportion the load between materials. Given Data / Assumptions: Percentage of longitudinal steel As = 1% of net concrete area Ac. Modular ratio m = 10. Short column behavior; same strain in steel and concrete. Concept / Approach: Because strain is common, stresses relate as σs = m * σc. Load carried: Ps = As * σs, Pc = Ac * σc. Therefore, Ps/Pc = (As * m * σc) / (Ac * σc) = m * (As/Ac). With As = 0.01 Ac, Ps/Pc = 10 * 0.01 = 0.10 = 10%. Step-by-Step Solution: Write ratio: Ps/Pc = m * (As/Ac).Substitute As/Ac = 0.01.Compute: 10 * 0.01 = 0.10.Express as percent: 0.10 × 100 = 10. Verification / Alternative check: Transformed section: Aeq = Ac + m As = Ac + 10(0.01 Ac) = 1.10 Ac. Steel carries 0.10 Ac worth of equivalent area; steel share vs. concrete share is 0.10:1.00 → 10%. Why Other Options Are Wrong: 0.1 or 1 or 1.1 represent 0.1%, 1%, or 1.1%—not consistent with m = 10 and 1% steel. 11 overstates due to rounding; exact is 10% with given data. Common Pitfalls: Treating 1% as of gross area including steel instead of net concrete area; here definition explicitly uses concrete area, giving a clean 10% result. Final Answer: 10

Question 8

For fully developed laminar flow in a circular pipe, what is the kinetic energy correction factor (α) used in energy equations to account for the non-uniform velocity profile?

Accepted Answer

Introduction / Context: The kinetic energy correction factor α adjusts the V^2/2g term in the Bernoulli/energy equation to account for non-uniform velocity distributions across a cross-section. For laminar flow in circular pipes, the parabolic profile makes α significantly larger than 1.0. Given Data / Assumptions: Flow is steady, incompressible, and fully developed. Laminar regime (Re < 2000 in a circular pipe). Velocity profile is parabolic: u(r) = umax(1 − r^2/R^2). Concept / Approach: α is defined as (∫A ρ u^3 dA) / (ρ A V^3). For a parabolic profile, integration yields α = 2.0. In contrast, for turbulent flows with flatter profiles, α is closer to 1.0 (often 1.03–1.10 in engineering practice). Step-by-Step Solution: Use parabolic profile in the definition of α.Integrate u^3 over the cross-section and divide by A V^3.Result for laminar circular pipe → α = 2.00. Verification / Alternative check: Textbook derivations universally report α = 2 for laminar circular flow; momentum correction factor β for the same case is 4/3 ≈ 1.33. Why Other Options Are Wrong: 1.00 pertains to perfectly uniform velocity, not laminar parabolic. 1.33 is the momentum (not kinetic energy) correction factor in laminar flow. 1.50 and 1.67 do not match the exact integral result. Common Pitfalls: Confusing α (energy) with β (momentum) correction factors. Final Answer: 2.00

Question 9

Fluid kinematics (2-D incompressible flow): If the x-component of velocity is u(x,y) = y^2 + 4xy and the y-component v(x,y) = 0 at y = 0, determine the expression for v(x,y).

Accepted Answer

Introduction / Context: For incompressible 2-D flow, continuity requires that the divergence of velocity is zero. Given one component, the other can be found (up to a function of the remaining variable) by integrating the continuity equation and applying a boundary condition. Given Data / Assumptions: u(x,y) = y^2 + 4xy. Incompressible 2-D: du/dx + dv/dy = 0. Boundary condition: v(x,0) = 0 for all x. Concept / Approach: From continuity, dv/dy = −du/dx. Differentiate u with respect to x, integrate with respect to y to obtain v, and then apply the boundary condition to fix the integration “constant” (a function of x). Step-by-Step Solution: Compute du/dx = ∂(y^2 + 4xy)/∂x = 4y.From continuity: dv/dy = −4y.Integrate: v(x,y) = ∫(−4y) dy = −2y^2 + f(x).Apply v(x,0) = 0 ⇒ f(x) = 0.Thus v(x,y) = −2y^2. Verification / Alternative check: Check: dv/dy = −4y and du/dx = 4y ⇒ du/dx + dv/dy = 0, satisfying incompressibility. Why Other Options Are Wrong: 4y, 2xy: Wrong functional dependence and ignore boundary condition. 2y^2: Sign error; would violate continuity. −4xy: Not supported by integration of −4y. Common Pitfalls: Forgetting the integration function f(x). Not applying the boundary condition properly. Final Answer: -2y^2

Question 10

Limit state design per IS 456: Unfactored bending moments at a beam section from frame analysis are 50, 80, 120, and 180 kNm due to dead, live, wind, and earthquake loads respectively. What is the design (factored) moment for collapse in flexure?

Accepted Answer

Introduction / Context: IS 456 (limit state method) specifies load combinations and partial safety factors to obtain design actions. For beams, the governing factored moment is the maximum among prescribed combinations including gravity plus wind or earthquake, and combined cases (1.2 combination) when lateral loads act with gravity. Given Data / Assumptions: M(D) = 50 kNm, M(L) = 80 kNm, M(W) = 120 kNm, M(E) = 180 kNm (unfactored). Use IS 456 load combinations for ultimate limit state. Consider both wind and earthquake combinations. Concept / Approach: Relevant combinations include: 1.5(D+L); 1.5(D+W) or 1.5(D+E); 1.2(D+L+W) or 1.2(D+L+E); and 0.9D ± 1.5W or 0.9D ± 1.5E for stability. The design moment is the maximum absolute value from these combinations at the section. Step-by-Step Solution: 1.5(D+L) = 1.5*(50+80) = 195 kNm.1.5(D+W) = 1.5*(50+120) = 255 kNm.1.5(D+E) = 1.5*(50+180) = 345 kNm.1.2(D+L+W) = 1.2*(50+80+120) = 300 kNm.1.2(D+L+E) = 1.2*(50+80+180) = 372 kNm.0.9D + 1.5W = 45 + 180 = 225 kNm; 0.9D + 1.5E = 45 + 270 = 315 kNm.Maximum is 372 kNm. Verification / Alternative check: Since earthquake governs over wind here, the 1.2(D+L+E) combination produces the highest value; check opposite signs if applicable at other sections. Why Other Options Are Wrong: 195 from 1.5(D+L), 250/255 not governing, 345 from 1.5(D+E) is lower, 315 from 0.9D + 1.5E is lower. Common Pitfalls: Ignoring the 1.2 combination which often governs when lateral loads are large. Forgetting the 0.9D combinations meant for stability checks. Final Answer: 372

Question 11

In highway engineering, flexible pavements achieve their structural stability primarily through which mechanism? Choose the most complete combination that reflects how granular layers and bituminous binders work together.

Accepted Answer

Introduction / Context: Flexible pavements distribute wheel loads through a layered granular system topped by a bituminous surfacing. Unlike rigid pavements that rely on slab action, flexible systems mobilize aggregate interlock, friction, and binder-related cohesion to resist shear and rutting. This question checks your understanding of the fundamental stability mechanism in asphalt/bituminous pavements used in civil engineering practice. Given Data / Assumptions: Typical flexible pavement structure: surface (bituminous mix), base and sub-base (granular or treated), subgrade. Load transfer occurs by grain-to-grain contact and matrix action, not by bending as a beam. Bitumen provides adhesion and some cohesion but does not replace aggregate skeleton stability. Concept / Approach: Stability in flexible pavements arises mainly from the aggregate skeleton. Angular particles lock together (aggregate interlock) while normal forces generate frictional resistance; the bituminous binder coats and glues particles, adding cohesion and durability. The layered system gradually reduces stresses with depth by spreading the load over a larger area, preserving subgrade performance. Step-by-Step Solution: Identify the load path: wheel load → surface mix → base → sub-base → subgrade.Recognize that the surface and base layers rely on aggregate interlock and friction for shear resistance.Acknowledge that bitumen contributes cohesion and waterproofing, enhancing the aggregate skeleton's stability.Conclude that the complete mechanism combines interlock + friction + cohesion, not any single factor alone. Verification / Alternative check: Marshall and gyratory mix designs target stability and flow by optimizing aggregate gradation (skeleton) and binder content (cohesion, durability), confirming the combined mechanism. Why Other Options Are Wrong: Cohesion alone ignores the dominant role of aggregate skeleton.Binder's adhesive power alone is insufficient without proper gradation and interlock.Flexural strength of surface course suggests rigid-slab behavior, not applicable to flexible pavements. Common Pitfalls: Over-asphalting mixes, which reduces interlock; or using rounded aggregates that impair friction and stability. Final Answer: Aggregate interlock, particle-to-particle friction, and a measure of cohesion within the bituminous matrix

Question 12

Capacity standards: what are the typical capacities for (i) a one-way 1.5 m wide sidewalk (persons per hour) and (ii) a one-way 2-lane urban road with no frontage access, no standing vehicles, and very little cross traffic (PCU per hour)?

Accepted Answer

Introduction / Context: Planning and traffic engineering rely on benchmark capacities to size facilities. For pedestrian sidewalks and multi-lane urban roads, conventional design manuals provide typical one-way capacities under specified assumptions (unobstructed flow, good surface, limited conflicts). This question tests recall of standard order-of-magnitude values used for preliminary design checks. Given Data / Assumptions: Sidewalk width = 1.5 m, one-way pedestrian movement. Urban road: 2 lanes in one direction, minimal frontage access, no standing vehicles, very low cross traffic. Capacities expressed as persons per hour (sidewalk) and PCU per hour (road). Concept / Approach: Pedestrian facility capacity depends on flow density, desired speed, and comfort level; a 1.5 m one-way sidewalk commonly carries about 1200 persons/hour comfortably. A one-way 2-lane urban road without side frictions typically carries about 2400 PCU/hour (≈1200 PCU per lane) under good conditions. Step-by-Step Solution: Match sidewalk width (1.5 m) to standard pedestrian flow rates to obtain ≈1200 persons/hour.Apply per-lane urban road capacity of ≈1200 PCU/hour; with two lanes in one direction, total ≈2400 PCU/hour.Select the pair that aligns with both computed values. Verification / Alternative check: Cross-check with level-of-service tables; values fall within typical ranges for uninterrupted flow and adequate level of service. Why Other Options Are Wrong: Other pairs either understate sidewalk capacity or over/understate the two-lane urban road capacity compared to norms. Common Pitfalls: Confusing two-way sidewalk flow with one-way capacity; ignoring side frictions that can reduce practical capacity. Final Answer: 1200 and 2400

Question 13

In structural steel design, what is the maximum permissible size of a fillet weld placed on the square edge of a plate, considering proper fusion and avoidance of overwelding at the root?

Accepted Answer

Introduction / Context: Fillet weld sizing on square plate edges must respect code rules to ensure sound fusion and to prevent lack-of-fusion defects at the root. Overly large fillets on square edges can trap slag and cause incomplete penetration, compromising connection performance. Given Data / Assumptions: Square (unprepared) plate edge with fillet weld on the edge. Standard structural steel practice and code-based detailing rules. Objective: determine the upper bound of the leg size for such a fillet weld. Concept / Approach: Codes and good practice limit the maximum leg size of a fillet weld on a square edge to slightly less than the plate thickness, typically by 1.5 mm. This provides a small root face to avoid overwelding and assists proper heat distribution for fusion without excessive melt-through or distortion. Step-by-Step Solution: Identify joint type: fillet weld on square edge (no edge preparation).Apply the maximum fillet size rule: maximum leg size = t_plate − 1.5 mm.Choose the option that states this limit explicitly. Verification / Alternative check: Detailing guides from steel codes reflect the same limit to encourage proper root fusion. Why Other Options Are Wrong: Half thickness or full thickness do not address root fusion concerns.More than plate thickness is geometrically and practically unsound.A fixed 3 mm limit is not general and fails for thicker plates. Common Pitfalls: Ignoring edge condition; applying the rule meant for prepared edges to square edges. Final Answer: 1.5 mm less than the plate thickness

Question 14

Minimum tensile steel in an RCC beam as per code intent (IS 456 context): what is the primary purpose of specifying a minimum area of longitudinal reinforcement in flexural members?

Accepted Answer

Introduction / Context: Reinforced concrete beams must maintain integrity after cracking of the tensile concrete. Design codes prescribe a minimum area of tensile reinforcement so that the beam can safely carry moments beyond first cracking and display ductile behavior, providing warnings before failure. Given Data / Assumptions: Flexural member (RCC beam) designed per limit state concepts. Concrete is weak in tension; tensile zone cracks at service loads. Longitudinal steel bridges the cracked zone and provides ductility. Concept / Approach: The minimum tensile steel ensures that the moment of resistance of the cracked section exceeds the cracking moment and that steel yields gradually rather than the member failing in a brittle manner. It also helps control crack widths and deflection under service loads. This is a safety and serviceability requirement, not merely a detailing convenience. Step-by-Step Solution: Recognize that concrete tension capacity is negligible in design; post-cracking capacity must come from steel.Minimum steel area criteria ensure the beam remains under-reinforced and ductile.Select the option emphasizing ductility and prevention of sudden brittle failure. Verification / Alternative check: Load–deflection curves of beams with minimum steel show gradual yielding rather than abrupt loss of capacity at cracking. Why Other Options Are Wrong: Compression failure is undesirable in flexural members; holding stirrups is a secondary detailing purpose; eliminating shear cracks is a separate shear reinforcement issue; steel rupture avoidance is a consequence of adequate ductility but not the primary code intent stated most directly. Common Pitfalls: Confusing minimum tension steel (ductility) with maximum steel limits (over-reinforcement) or with minimum shear links. Final Answer: To provide sufficient ductility and post-cracking capacity so that failure is not sudden and brittle

Question 15

A hydraulic turbine develops a discharge of 5 m^3/s under a head of 20 m at a rotational speed of 500 rpm. If the turbine must operate under a reduced head of 15 m for the same discharge (geometrically similar operation), what will be the approximat…

Accepted Answer

Introduction / Context: Turbine similarity (unit quantities) relates speed, discharge, and head. For dynamically similar operation, rotational speed varies with the square root of head. This relation is widely used to predict operating points when head fluctuates in hydropower schemes. Given Data / Assumptions: Initial head H1 = 20 m, speed N1 = 500 rpm, discharge Q is unchanged. New head H2 = 15 m, geometric similarity assumed. Affinity law: N ∝ √H for similar operation. Concept / Approach: For turbines, the specific speed and similarity conditions yield N2 = N1 * √(H2/H1), when comparing points of similar efficiency profiles and geometry. Since only head changes, speed scales by √H. Step-by-Step Solution: Compute head ratio: H2/H1 = 15/20 = 0.75.Take square root: √0.75 ≈ 0.866.Calculate N2: 500 * 0.866 ≈ 433 rpm. Verification / Alternative check: Check unit speed n11 = N * √D / √H (for fixed geometry D constant, n11 roughly constant), confirming the proportionality. Why Other Options Are Wrong: 403 and 388 rpm underestimate the √H scaling; 627 rpm contradicts the reduction in head; 500 rpm implies no scaling with head. Common Pitfalls: Confusing pump and turbine affinity relations or neglecting the square-root dependency on head. Final Answer: 433

Question 16

Soil–water measurement devices: a lysimeter and a tensiometer are used to measure which quantities, respectively, in irrigation and soil physics practice?

Accepted Answer

Introduction / Context: Efficient water management requires measuring both how much water crops consume and how strongly soil holds water. Two classic tools are the lysimeter, which quantifies evapotranspiration (ET), and the tensiometer, which gauges soil water tension (capillary potential) to aid irrigation scheduling. Given Data / Assumptions: Lysimeter: a controlled soil–plant system with measured inflows/outflows to compute ET. Tensiometer: a porous cup connected to a vacuum gauge equilibrating with soil matric suction (low to moderate ranges). Focus is on routine agricultural engineering applications. Concept / Approach: Lysimeters determine ET by mass balance: ET = Inflows − Outflows ± Storage change. Tensiometers measure soil water potential (negative pressure relative to atmosphere) in the suction range where water columns can be maintained (typically up to ~80 kPa), indicating plant availability. Step-by-Step Solution: Identify lysimeter purpose: quantify field ET directly.Identify tensiometer purpose: measure capillary (matric) potential for irrigation control.Match the correct pair to the instruments named. Verification / Alternative check: Compare with psychrometers or gypsum blocks; these measure related potentials but not ET directly like lysimeters. Why Other Options Are Wrong: Permeability is measured via permeameters; velocities via hydrometric or velocimetric methods; vapour pressure is not directly measured by tensiometers. Common Pitfalls: Confusing soil moisture content with potential; ET cannot be inferred from tensiometer alone. Final Answer: Evapotranspiration and capillary potential

Question 17

Rapid single-parameter assessment of river water pollution: which test provides a quick indication of the oxidisable load without waiting for 5-day incubation?

Accepted Answer

Introduction / Context: Regulators and operators often need a rapid measure of organic pollution in rivers and effluents. While BOD5 is biologically meaningful, it requires a 5-day incubation. COD offers a fast, laboratory-based oxidation of organics using a strong chemical oxidant, giving a same-day proxy for oxygen demand. Given Data / Assumptions: Sampling is from a river where prompt decisions are needed. COD test uses dichromate (or equivalent) under acidic conditions with a catalyst. Results approximate the total chemically oxidisable load (often ≥ BOD). Concept / Approach: COD correlates with BOD for many wastewaters and is favored for process control due to speed. DO alone indicates current oxygen level, not the oxidisable load; total organic solids lack specificity to oxygen demand; MPN indicates fecal contamination, not organic load magnitude. Step-by-Step Solution: Select the test that measures oxidisable organics quickly: COD.Note that BOD5 requires 5 days and hence is not 'rapid'.Confirm that COD results help estimate pollutional status promptly. Verification / Alternative check: Compare COD:BOD ratios; abnormal ratios can signal industrial discharges or poor biodegradability. Why Other Options Are Wrong: BOD5 is too slow; DO is instantaneous but not a load metric; solids measures are non-specific; MPN relates to pathogens. Common Pitfalls: Assuming COD always equals BOD; matrix-specific correlations must be established. Final Answer: Chemical Oxygen Demand (COD)

Question 18

A wastewater sample has a 5-day BOD of 190 mg/L with a first-order deoxygenation rate constant k = 0.01 h^-1. What is the ultimate BOD (oxygen demand), in mg/L, of the sample?

Accepted Answer

Introduction / Context: Ultimate BOD (L0) represents the total oxygen demand exerted as biodegradable organics are oxidised to completion. The 5-day BOD (at 20°C) measures only a portion of this demand, depending on the reaction rate constant k. Converting BOD5 to L0 is routine in wastewater engineering for mass balance and treatment design. Given Data / Assumptions: BOD5 = 190 mg/L at 20°C. First-order kinetics with k = 0.01 h^-1. Time for BOD5 test t = 5 days = 120 h. Concept / Approach: For first-order BOD decay, the BOD exerted over time t is BOD_t = L0 * (1 − e^(−k * t)). Rearranging gives L0 = BOD_t / (1 − e^(−k * t)). This uses the classic Thomas/first-order model without nitrification adjustment. Step-by-Step Solution: Compute k * t = 0.01 * 120 = 1.2.Evaluate exponential term: e^(−1.2) ≈ 0.301.Compute fraction exerted: 1 − 0.301 = 0.699.Calculate L0 = 190 / 0.699 ≈ 271.8 mg/L ≈ 271 mg/L. Verification / Alternative check: Back-calculate expected BOD5 using L0 = 271 mg/L: 271 * (1 − e^(−1.2)) ≈ 190 mg/L, confirming consistency. Why Other Options Are Wrong: 190 mg/L ignores unexerted demand; 475 mg/L or 3800 mg/L are inconsistent with first-order kinetics and the given k; 225 mg/L underestimates L0. Common Pitfalls: Forgetting to convert 5 days to hours for k in h^-1; using k for a different temperature without adjustment. Final Answer: 271

Question 19

In highway geometric design and traffic engineering, what standard driver reaction time (perception–reaction time) should be assumed for computing stopping sight distance under design conditions?

Accepted Answer

Introduction / Context: Stopping Sight Distance (SSD) is a core safety parameter in highway design. It ensures a driver can perceive a hazard, react, and brake to a stop before reaching the object. The assumed perception–reaction time (also called reaction time) directly influences SSD and thus affects vertical curves, horizontal curves, and placement of roadside features. Given Data / Assumptions: Design is for normal drivers under ordinary conditions. SSD comprises two components: distance traveled during reaction plus braking distance. Standard practice adopts a conservative average reaction time constant for design. Concept / Approach: Highway design manuals (e.g., many national standards) commonly assume a perception–reaction time around 2.5 seconds for design purposes. This value covers typical alert drivers, accounts for recognition and decision lags, and builds in conservatism for real-world variance without being overly restrictive. Step-by-Step Solution: SSD = v * t_r + v^2 / (2 * g * f) where t_r is reaction time.Adopt t_r = 2.5 s for design to cover recognition and movement to the brake.Longer times like 5–10 s are excessive for standard design; shorter like 0.5–1.5 s are non-conservative. Verification / Alternative check: Using t_r = 2.5 s aligns SSD with crash data and the operating speed environment. Sensitivity checks show SSD increases linearly with t_r, so using the standard value maintains consistency across facilities. Why Other Options Are Wrong: 5 s or 10 s: Overly conservative; not representative of normal alert drivers. 0.5 s or 1.5 s: Underestimates human reaction, yielding unsafe SSD. Common Pitfalls: Confusing perception–reaction time with braking time. Ignoring environmental factors (night, rain) that are handled by friction and visibility considerations, not by radically changing t_r. Final Answer: 2.5 secs

Question 20

Flow measurement over a triangular (V-notch) weir: If the head over the notch has a 1% measurement error, what is the approximate percentage error in the computed discharge?

Accepted Answer

Introduction / Context: Triangular (V-notch) weirs are widely used to measure low flows because they are sensitive to small heads. The discharge–head relationship is nonlinear, so small head errors amplify in discharge calculations. Understanding error propagation helps choose proper gauges and establish calibration procedures. Given Data / Assumptions: Triangular V-notch with standard calibration. Head measurement error ΔH/H = 1%. Discharge formula follows Q ∝ H^(5/2). Concept / Approach: For a V-notch, Q = K * H^(5/2). For small errors, percentage error in Q is obtained by logarithmic differentiation: dQ/Q = (5/2) * dH/H. Thus, a 1% head error produces a 2.5% discharge error. This shows the importance of precise head measurement for V-notches compared to rectangular notches with different exponents. Step-by-Step Solution: Write discharge law: Q = K * H^(5/2).Differentiate: dQ/Q = (5/2) * dH/H.Substitute dH/H = 0.01 → dQ/Q = 0.025 = 2.5%. Verification / Alternative check: Numerical check: Increase H by 1%; raise to power 2.5 and compare the ratio; the result is ≈ 1.025 for small errors, confirming 2.5%. Why Other Options Are Wrong: 1.0, 1.5, 2.0: Underestimate error amplification from the 2.5 exponent. 0.5: Not consistent with the exponent. Common Pitfalls: Using linear error scaling (1:1) instead of exponent-based propagation. Neglecting notch coefficient variability, which is a separate systematic effect. Final Answer: 2.5

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