Question 1

Formwork – Time for Removal of Props (RCC) Choose the correct schedule for removal of props under slabs and beams, assuming ordinary Portland cement and normal ambient conditions.

Accepted Answer

Introduction / Context: Formwork striking and removal of props must balance safety and construction speed. Removing props too early can cause excessive deflection or cracking; too late delays cycle times and increases cost. Given Data / Assumptions: Cement type: ordinary Portland cement. Normal ambient temperature and curing conditions. Members: slabs and beams with specified span ranges. Concept / Approach: Codes provide minimum periods for removal of props based on member type and span. Beams require longer support due to higher flexural stiffness demands and slower stiffness gain compared to slabs. Step-by-Step Solution: 1) For slabs up to 4.5 m, typical prop removal time is 7 days.2) For slabs over 4.5 m, increase to about 14 days.3) For beams up to 6 m, about 14 days are required.4) For beams over 6 m, extend to around 21 days. Verification / Alternative check: Project specifications may modify times based on cement type, admixtures, or accelerated curing. However, the listed figures represent widely taught baseline values. Why Other Options Are Wrong: Options a to d are individually correct but partial. Only option e consolidates the full correct schedule. Common Pitfalls: Ignoring temperature effects and high early strength cements, which can shorten times, or cold weather that requires longer durations. Final Answer: All the above

Question 2

Steel Girders – Web Stiffeners (Spacing and Definitions) Which of the following statements regarding web stiffeners in plate girders is correct?

Accepted Answer

Introduction / Context: Web stiffeners are provided in plate girders to prevent web buckling under shear and to control panel aspect ratios. They can be vertical (transverse) or horizontal, and their spacing relates to the clear web depth d. Given Data / Assumptions: Plate girder with thin web subjected to shear and bending. d denotes clear web depth as defined for the stiffener type considered. Design intent: avoid local buckling and ensure panel stability. Concept / Approach: Empirical and code-based limits govern stiffener spacing to maintain web panel efficiency. Vertical stiffeners subdivide the web to limit shear buckling length. Horizontal stiffeners raise buckling resistance by reducing clear depth between a horizontal line and the flange. Step-by-Step Solution: 1) Vertical stiffeners: spacing limits often expressed as 0.33 d ≤ s ≤ 1.5 d to control slenderness.2) For vertical stiffeners, d is the distance between flanges (clear depth between flange angles).3) For horizontal stiffeners, d is measured from the stiffener to the tension flange to capture the effective panel depth in buckling. Verification / Alternative check: Design handbooks and standard practice confirm these definitions to ensure consistent panel sizing and buckling checks. Why Other Options Are Wrong: Each statement a, b, c is individually correct within its definition domain. Therefore the combined correct choice is option d: All the above. Common Pitfalls: Mixing the definition of d between vertical and horizontal stiffeners leads to incorrect spacing and ineffective web panelization. Final Answer: All the above

Question 3

Continuous Slab–Beam Systems – Bending Moment Signs for Filler Joists Identify the correct sign convention for bending moments in filler-joist construction at typical locations along end and interior spans.

Accepted Answer

Introduction / Context: In continuous flooring systems with filler joists, bending moment signs follow the usual convention: sagging is positive and hogging is negative. Recognizing where moments are positive or negative is crucial for placing bottom and top reinforcement appropriately. Given Data / Assumptions: Continuous spans with joists or beams supported over multiple supports. Sign convention: sagging (+) at midspan, hogging (-) over supports. Load primarily uniformly distributed. Concept / Approach: For a continuous system, moments reverse sign between spans and supports. End spans exhibit sagging near midspan and hogging near the interior support, while interior spans sag at midspan and hog at interior supports. Step-by-Step Solution: 1) End span: near midspan, deflection is downward, so bending moment is positive (sagging).2) Next support inboard from the end: restraint causes hogging, so moment is negative.3) Interior spans: gravity loading produces positive moment at midspan.4) Other interior supports: continuity creates negative (hogging) moments. Verification / Alternative check: Classical slope–deflection or moment distribution methods produce the same sign pattern, confirming the qualitative picture. Why Other Options Are Wrong: Options a to d are all correct individually; only option e captures the complete set. Common Pitfalls: Mixing sign conventions or forgetting that support regions in continuous members attract top reinforcement due to negative moments. Final Answer: All the above

Question 4

Concrete Workability for Heavily Reinforced Sections Without Vibration When placing concrete in heavily congested reinforcement where vibration is not feasible, what level of workability is required to ensure proper filling and compaction?

Accepted Answer

Introduction / Context: Workability measures how easily fresh concrete can be mixed, placed, and compacted without segregation. In heavily reinforced members, achieving full compaction without segregation is challenging, especially when mechanical vibration is not possible. Given Data / Assumptions: Member has closely spaced bars and congested detailing. Vibration is not feasible due to access limitations or risk of bar movement. Objective: choose an appropriate workability level. Concept / Approach: Higher workability (higher slump or flow) allows the concrete to pass through narrow gaps around reinforcement. Mix design must maintain cohesion by using suitable fines content, water–binder ratio, and admixtures such as superplasticizers to avoid segregation. Step-by-Step Solution: 1) Identify placement constraints: congested reinforcement and no vibration.2) Select high workability to ensure flow into all voids and around bars.3) Use admixtures to achieve flowability at controlled water–binder ratio, preserving strength and durability. Verification / Alternative check: Field trials using high-slump mixes or self-compacting concrete demonstrate superior filling ability in congested regions without external vibration. Why Other Options Are Wrong: Very low or low: Inadequate flow, risk of honeycombing. Medium: May still be insufficient in heavy congestion without vibration. Common Pitfalls: Increasing water alone to raise slump leads to segregation and reduced strength. Instead, adopt admixtures and proper grading to maintain cohesiveness. Final Answer: High

Question 5

Steel Riveted Joints – Select the single correct detailing rule that ensures strength and serviceability: • Use codal limits for rivet pitch and gauge in tension and compression members. • Apply realistic maxima/minima so plates are neither under-co…

Accepted Answer

Introduction: Riveted (and by extension bolted) joints in steel structures are governed by pitch, gauge, and edge-distance limits to prevent tearing, shear failure, and poor force transfer. This question checks knowledge of codal limits and the reasoning behind them. Given Data / Assumptions: Flat plates joined by rows of rivets. t denotes connected plate thickness. Design aims: prevent tearing between holes and ensure adequate shear transfer. Concept / Approach: Pitch limits control the net cross-section and crack/arrest behavior; minimum pitch avoids hole weakening due to crowding; edge/adjacent-line spacing prevents edge tearing and buckling of narrow strips. Step-by-Step Solution: 1) Tension members require closer spacing: max pitch = min(16 * t, 200 mm).2) Compression members have a different restriction; using a blanket 203 mm regardless of 12 * t is unsafe because 12 * t may be smaller for thick plates.3) Minimum pitch ≥ 2.5 * hole diameter avoids weakening due to overlapping stress fields.4) For outer plates, adjacent line spacing ≤ min(100 mm + 4 * t, 200 mm) limits edge tearing. Verification / Alternative check: If t = 10 mm, tension pitch ≤ 160 mm and also ≤ 200 mm; hence 160 mm governs, illustrating the codal intent. Why Other Options Are Wrong: Option B incorrectly allows 203 mm even when 12 t is smaller, violating compression-member limits. Option E is false because not all statements are simultaneously correct. Options C and D are true but the question requires a single correct choice, so we select one codal-true statement that is unambiguous (Option A). Common Pitfalls: Using a fixed pitch (e.g., 200 mm) irrespective of thickness, ignoring edge/line spacing, or confusing hole diameter with rivet shank diameter. Final Answer: In tension members, max pitch along stress ≤ 16 t or 200 mm, whichever is less.

Question 6

Flexural Design – Beam end partially restrained in a built-up wall: Design the beam for negative (hogging) moment at the face of support under a design load W and clear span L.

Accepted Answer

Introduction: When a beam end is built into or partially restrained by a wall, some fixity develops. This produces a negative (hogging) moment at the face of the support that must be resisted in design to avoid cracking and rotation at the bearing. Given Data / Assumptions: Uniformly distributed design load W on span L. End provides partial restraint due to embedment in a built-up wall. Design convention uses a codal negative moment coefficient at the face. Concept / Approach: End restraints reduce mid-span sagging moment and introduce end hogging. Classical coefficients for a partially fixed end commonly adopt an equivalent negative moment of W L / 12 at the face. This is a conservative and widely used detailing/design value. Step-by-Step Solution: 1) Identify that restraint exists at the support → negative moment must be provided for.2) Adopt design coefficient for partial fixity at wall face → M_support = W * L / 12.3) Provide top bars (or compression steel for steel beams provide flange adequacy) to resist hogging near the face. Verification / Alternative check: In the limiting cases, simply supported gives zero end moment; fully fixed would give a larger negative moment. The value W L / 12 sits between these, aligning with partial fixity practice. Why Other Options Are Wrong: W L / 8 and W L / 10 overestimate typical partial fixity; W L / 16 and W L / 24 underestimate the required end capacity, risking cracks. Common Pitfalls: Ignoring end fixity in detailing, placing insufficient top bars at supports, or checking only mid-span sagging moment. Final Answer: W L / 12

Question 7

Steel Slab Base Plates – Permissible bending stress (Pbet) selection for base plate bending under column load.

Accepted Answer

Introduction: Base plates under steel columns act as short cantilevers between the column footprint and the compression on concrete. The plate is designed in bending, so we must select the correct permissible bending stress for the steel plate material. Given Data / Assumptions: Mild steel or equivalent structural steel base plate. Permissible stresses expressed in kg/cm2 per traditional working-stress design. Concrete bearing pressure is treated separately. Concept / Approach: In working-stress design, the permissible bending stress for mild steel plates is typically taken around two-thirds of the yield stress. For fy ≈ 2500 kg/cm2 (≈ 250 MPa), 0.66 * 2500 ≈ 1650 kg/cm2, which is commonly used for base plate bending checks. Step-by-Step Solution: 1) Identify plate as bending element with maximum fiber stress = M * y / I.2) Select permissible bending stress for steel plate ≈ 1650 kg/cm2 in WSD terms.3) Check thickness so computed bending stress ≤ 1650 kg/cm2 under factored/working load as per method used. Verification / Alternative check: Cross-check against codal tables for base plate design examples; values align with standard practice for mild steel under bending in working-stress format. Why Other Options Are Wrong: 1500 kg/cm2 is conservative but not the common permissible; 1800 and 1890 kg/cm2 are higher than typical WSD value; 2100 kg/cm2 is overly high. Common Pitfalls: Confusing steel bending stress with concrete bearing stress, or mixing limit-state and working-stress numbers. Final Answer: 1650 kg/cm2

Question 8

Concrete Technology – Achieving low permeability in hardened concrete: Choose the most comprehensive set of measures that reduce ingress of water and aggressive ions.

Accepted Answer

Introduction: Permeability governs durability. Lower permeability reduces penetration of chlorides, sulfates, and carbon dioxide, extending service life of reinforced concrete by slowing corrosion and chemical attack. Given Data / Assumptions: Normal-weight concrete with ordinary Portland cement. Durability focus (water and ion ingress). Site practices influence pore structure. Concept / Approach: Permeability is controlled by capillary pore continuity and microcracking. Aggregates, w/c ratio, curing, and compaction each affect pore refinement and connectivity. Best performance comes from combining all good practices. Step-by-Step Solution: 1) Dense aggregates reduce weak ITZ zones and microvoids.2) Low w/c ratio decreases capillary porosity: fewer continuous pores.3) Proper curing promotes continued hydration → pore refinement.4) Proper compaction expels entrapped air → reduces permeability pathways. Verification / Alternative check: Rapid chloride permeability or sorptivity tests show pronounced improvement when all measures are adopted together rather than one measure alone. Why Other Options Are Wrong: Options A–D individually help but are incomplete. The most correct is the combined approach. Common Pitfalls: Relying solely on low w/c without curing, or over-vibrating and causing segregation. Final Answer: All the above (combined measures)

Question 9

Construction Tolerances – Formwork depth tolerance for a footing with specified thickness 100 cm.

Accepted Answer

Introduction: Tolerances ensure constructability without compromising performance. For massive elements like footings, small dimensional variations are inevitable but must be limited to avoid capacity or cover issues. Given Data / Assumptions: Footing specified thickness = 100 cm. Checking allowable formwork depth deviation. Standard good-practice tolerance bands are considered. Concept / Approach: Depth deviations affect bearing area, cover, and reinforcement position. A pragmatic yet tight tolerance for a 1 m thick footing is within ±5 mm for formwork depth, aligning with quality control expectations on major foundations. Step-by-Step Solution: 1) Identify element scale → thick footing, not a thin slab.2) Adopt a realistic tolerance that site teams can achieve with steel/ply formwork and proper leveling.3) Choose ±5 mm as acceptable without affecting bearing safety significantly. Verification / Alternative check: Rebar cover checks and cube level measurements typically keep variation within this band for heavy foundations when supervised. Why Other Options Are Wrong: ±2–4 mm are impractically tight for 1 m thickness; ±10 mm may be permissible in some specs, but is looser than the recommended tolerance here. Common Pitfalls: Neglecting settlement or uplift of formwork during concreting and not re-checking levels after initial pour. Final Answer: -5 mm to +5 mm

Question 10

Reinforced Concrete – Effective depth of a shallow beam: Identify the correct definition used for flexural design and detailing.

Accepted Answer

Introduction: Effective depth is a key geometric parameter in flexural design. It directly influences the lever arm, moment capacity, and deflection predictions in reinforced concrete beams. Given Data / Assumptions: Shallow, singly reinforced beam. Tension steel placed near the soffit (bottom) with adequate cover. Compression at the top fibre under sagging moments. Concept / Approach: By definition, effective depth d is measured from the most compressed fibre to the centroid of the tension reinforcement. This standard definition is used in design equations for ultimate and serviceability checks. Step-by-Step Solution: 1) Locate maximum compression fibre → top surface under sagging.2) Locate centroid of main tension steel → typically at bar centerline below neutral axis.3) Measure vertical distance between these two → this is the effective depth d. Verification / Alternative check: Section analysis formulas for moment of resistance use d, not overall depth or NA distance, confirming the definition's role. Why Other Options Are Wrong: A and C mix up fibres or use NA; B uses NA which is not the definition; E is incorrect since a standard definition exists. Common Pitfalls: Confusing overall depth with effective depth, or measuring to bar surface instead of its centroid. Final Answer: Distance from maximum compression fibre to the centroid of tension reinforcement

Question 11

Aggregates and Moisture – Typical maximum surface water content in moist sand by mass.

Accepted Answer

Introduction: Moist sand carries free (surface) water that affects batching by volume and workability. Estimating typical surface moisture helps adjust water content and sand bulking corrections. Given Data / Assumptions: Fine aggregate is natural sand. State considered is moist, not oven-dry or fully saturated slurry. Mass-based percentage is requested. Concept / Approach: Surface moisture in sand commonly varies from about 2% to 8% by mass depending on grading and weather. A widely cited upper typical value for moist sand is around 7.5% before the material becomes obviously saturated. Step-by-Step Solution: 1) Recognize that finer sands hold more surface water due to higher specific surface area.2) Adopt conservative upper typical estimate for moist condition → 7.5%.3) Use this to correct mix water and apply bulking factor if batching by volume. Verification / Alternative check: Field tests (bulking test in a jar) and periodic moisture content checks align with 5%–8% ranges; 7.5% is a reasonable upper typical value. Why Other Options Are Wrong: 1.25% and 2.5% are too low for typical moist sand; 5% can occur but is not the upper typical value; 10% is higher than usual for ‘‘moist’’ and indicates very wet conditions. Common Pitfalls: Ignoring moisture corrections causing variable slump or strength; not recalibrating volumetric batching. Final Answer: 7.5%

Question 12

Masonry Walls – Slenderness check: When should the slenderness effect of a wall be considered based on effective height to thickness ratio?

Accepted Answer

Introduction: Slenderness influences stability and compression capacity of masonry walls. Beyond a certain height-to-thickness ratio, second-order effects and risk of buckling increase and must be considered in design. Given Data / Assumptions: Load-bearing or partition wall, effective height considered. Thickness = wall thickness including plaster if allowed by code. Design per typical masonry codes using slenderness limits. Concept / Approach: Effective height to thickness ratio (He/t) indicates slenderness. Many codes flag slenderness effects when He/t exceeds around 12 for walls, triggering reductions in compressive strength and additional checks. Step-by-Step Solution: 1) Compute effective height considering end restraints.2) Compute He/t.3) If He/t > 12, apply slenderness reduction factors and verify stability and eccentricity limits. Verification / Alternative check: For He/t ≤ 12, walls behave as stocky members with negligible second-order effects; above this, sensitivity rises markedly. Why Other Options Are Wrong: 8 and 10 are conservative thresholds but not typical triggers; 16 and 20 delay consideration of slenderness, which could be unsafe. Common Pitfalls: Using clear height instead of effective height, or overlooking partial fixity at slab supports. Final Answer: Exceeds 12 times the thickness

Question 13

Floor Systems – Filler joists supporting slabs: When may their spans be treated as approximately equal for analysis and detailing?

Accepted Answer

Introduction: In joisted slabs, small variations in joist span may be ignored to simplify analysis. Recognizing an acceptable tolerance avoids unnecessary differentiation in design loads and reinforcement. Given Data / Assumptions: Parallel filler joists supporting a slab. Uniform loading and similar boundary conditions. Interest: how close spans must be to assume equality. Concept / Approach: When the longest span does not exceed the shortest span by more than about 10%, stiffness and deflection differences are modest. Treating spans as equal is typically acceptable for pragmatic design and layout. Step-by-Step Solution: 1) Measure shortest and longest spans.2) Compute percentage difference = (longest − shortest) / shortest * 100.3) If ≤ 10%, proceed with equal-span assumptions for design tables and detailing. Verification / Alternative check: Elastic deflection and moment comparisons show small deviations within ±10% length variation under uniform loading. Why Other Options Are Wrong: 5% is overly restrictive; 15% and 20% may lead to noticeable redistribution; exact equality is unnecessary in practice. Common Pitfalls: Ignoring differences in support conditions or load patterns; using equal span assumption when one bay is much longer. Final Answer: If longest span is within 10% of the shortest

Question 14

Reinforcement Anchorage – Standard U-hook anchorage value for a bar of diameter d in tension.

Accepted Answer

Introduction: Anchorage length ensures that a reinforcing bar develops its design stress without pullout. Hooks provide additional anchorage where straight embedment is limited. Given Data / Assumptions: Standard U-type (180-degree) hook in tension zone. Bar diameter = d. Normal concrete, adequate cover, and spacing. Concept / Approach: A standard U or 180-degree hook contributes an equivalent anchorage value commonly taken as 16 d for tension bars, supplementing the straight development length as permitted by code. Step-by-Step Solution: 1) Identify need for hook due to limited available straight length.2) Assign hook value = 16 * d.3) Compute required development length and ensure straight length + hook value ≥ required. Verification / Alternative check: Detailing guides map 180-degree hook to ≈ 16 d anchorage contribution; site practice confirms improved pullout resistance. Why Other Options Are Wrong: 4 d and 8 d underestimate anchorage; 12 d is still low; 20 d is conservative but not the standard value used for U-hooks. Common Pitfalls: Counting hook value without ensuring adequate concrete cover or confining reinforcement; ignoring bar bend radii. Final Answer: 16 d

Question 15

Base (cap) plate thickness for a solid round steel column In the standard base-plate thickness formula, identify what d represents.

Accepted Answer

Introduction: In steel column base design, the thickness of a rectangular cap/base plate is determined from a bearing and bending check. The commonly used formula contains a diameter term d when the supported member is a solid round steel column. This question tests whether you know what that d physically represents. Given Data / Assumptions: Solid round steel column supported on a rectangular base plate. Plate thickness is set by bending from bearing pressure under the footprint of the column. Symbol d appears in the thickness expression. Concept / Approach: Base plates distribute axial load from the column to the concrete pedestal or foundation. The bending strip model uses the projection of the plate beyond the loaded area and the bearing pressure. For a round column, the loaded area is a circle defined by the column's effective (reduced) diameter at the interface after deducting machining tolerances or corrosion allowances. Hence, d refers to the column's reduced diameter, not the base dimensions. Step-by-Step Solution: 1) Identify the loaded (bearing) area: circular area under the column end.2) Bending in the plate is governed by projection beyond this loaded circle.3) Therefore d must characterize the column's loaded circle, i.e., the reduced diameter.4) Base or top diameters of the plate are irrelevant to the bending calculation for the inner loaded area. Verification / Alternative check: Derivations treat the inner edge of the bending strip at the column–plate interface. Replacing d with base dimension would grossly overestimate thickness needs. Why Other Options Are Wrong: Base dimension or base diameter describe outer plate size, not the loaded circle. The top diameter is not a design variable for the plate's inner loaded area. Common Pitfalls: Confusing external plate size with internal loaded patch; ignoring machining allowance when selecting d. Final Answer: the reduced diameter of the column

Question 16

Actual length of a steel column with cap and base Between which two faces is the physical (actual) length measured?

Accepted Answer

Introduction: Columns are often provided with a base plate at the bottom and a cap plate (or beam seat) at the top. The physical or actual length is the clear dimension that the steel member occupies between its supporting and supported plates. This question checks that you select the correct reference faces. Given Data / Assumptions: Steel column with a base plate at bottom and a cap plate at top. We are asked for actual (physical) length, not effective length for buckling. Plates are horizontal and well-seated. Concept / Approach: Actual length is the physical distance occupied by the member. For a column with cap and base, the relevant faces are the top (upper surface) of the base plate and the underside (bottom surface) of the cap plate because those bound the steel shaft length that will be fabricated and erected. Step-by-Step Solution: 1) Identify the lower reference surface: top of the base plate.2) Identify the upper reference surface: underside of the cap plate.3) Measure the clear distance between these two faces.4) This is the actual length used for detailing and shop drawings. Verification / Alternative check: Effective length for buckling depends on boundary conditions and is different (K * L). The question asks purely for physical length, which is clear between plate contact faces. Why Other Options Are Wrong: Options including the bottom of the base or top of the cap extend beyond the column shaft into plate thicknesses, which is not the member's actual length. Common Pitfalls: Mixing up actual and effective length; measuring to the wrong plate faces. Final Answer: top of the base and underside of the cap

Question 17

Flat single lacing — minimum thickness criterion Let l be the effective length of a flat lacing bar; choose the correct rule for thickness.

Accepted Answer

Introduction: Lacing bars tie together main components of built-up compression members and must be sufficiently stiff and strong. Design codes specify minimum thickness and slenderness limits for lacing to prevent local buckling and to ensure adequate shear transfer between components. Given Data / Assumptions: Flat single lacing bars are used. l denotes effective length of an individual lacing bar between node points. We seek the minimum thickness rule for flat single lacing. Concept / Approach: The minimum thickness requirement controls plate-like local buckling and ensures adequate stiffness. A practical empirical rule relates thickness to the effective length segment: t should not be too small compared to l. For flat single lacing, the conventional rule is t ≈ l/40 (minimum), together with separate limits on bar slenderness (L/r) and minimum width. Step-by-Step Solution: 1) Identify that a flat, single lacing configuration is used.2) Apply the standard minimum thickness rule for such lacing.3) Take t(min) = l / 40.4) Check separately that L/r does not exceed the code limit for single lacing and that shear capacity is adequate. Verification / Alternative check: Design handbooks tabulate lacing proportioning rules; l/40 sits within the accepted range used in traditional steelwork practice for single lacing. Why Other Options Are Wrong: l/30 is unnecessarily thick; l/50 and l/60 may be too thin, risking local buckling and excessive flexibility. Common Pitfalls: Using the same rule for double lacing; ignoring end connections and rivet/bolt weld details that also control stiffness. Final Answer: t = l / 40 (minimum)

Question 18

Limit on clear web panel dimension without stiffeners For a web of thickness t, the greater clear dimension should not exceed:

Accepted Answer

Introduction: Thin webs in plate girders and built-up members are susceptible to shear buckling. Codes therefore limit the clear panel size between stiffeners in terms of web thickness to ensure adequate stability under shear and combined stresses. Given Data / Assumptions: Unstiffened web panel of thickness t. We are selecting the upper limit on the greater clear dimension. Elastic buckling considerations govern the limit. Concept / Approach: Critical shear buckling stress is inversely proportional to the square of panel aspect ratio and directly to plate thickness. To prevent premature buckling, the greater clear dimension a is restricted to a ≤ 180 t (typical conservative limit), unless intermediate stiffeners are provided or the web is thicker. Step-by-Step Solution: 1) Identify web as a thin plate subject to shear.2) Apply code-based dimensional limit for panel size.3) Choose a(max) = 180 t to satisfy stability without stiffeners.4) If a larger spacing is needed, provide intermediate stiffeners or use a thicker web. Verification / Alternative check: Shear buckling checks or tension-field action design may permit larger panels with stiffeners; without them, 180 t provides a safe bound. Why Other Options Are Wrong: 200 t, 240 t, 270 t relax the limit and can be unsafe for slender webs without additional stiffening. Common Pitfalls: Measuring overall rather than clear distance; ignoring cut-outs and openings that further reduce stability. Final Answer: 180 t

Question 19

Underwater concreting — select the correct set of requirements (Workability, cement content, aggregate proportions, and dewatering practice.)

Accepted Answer

Introduction: Underwater concreting requires special provisions to control washout of cement paste and to maintain cohesion and workability. This question validates understanding of mix adjustments and construction practice when placing concrete below water level. Given Data / Assumptions: Concrete is placed under water using tremie, pump, or bucket methods. Washout risk and segregation must be minimized. Workability must be higher than for dry placement. Dewatering during and immediately after placement is prohibited. Concept / Approach: To resist washout, cement content is typically increased and fines proportion improved. Slump is kept high (about 100–180 mm) for continuous flow. Coarse aggregate volume is commonly 1.5–2.0 times that of fine aggregate to maintain grading without harshness. Dewatering induces flow through fresh concrete, promoting segregation and should be avoided for at least 24 h. Step-by-Step Solution: 1) Select a well-graded mix with higher paste content (≥10% more cement).2) Target slump 100–180 mm for tremie/pumped flow without segregation.3) Maintain coarse:fine aggregate volume between 1.5 and 2.0.4) Prohibit dewatering during placement and for about 24 h afterwards. Verification / Alternative check: Field guides for tremie concreting specify anti-washout measures (higher cement/fines, admixtures), and strict controls on water movement. Why Other Options Are Wrong: Options B–D contradict best practice on cement content, slump, aggregate proportion, or dewatering, and would risk segregation and washout. Option E cannot be correct because the sets conflict. Common Pitfalls: Using low slump; starting or resuming dewatering too early; allowing free fall through water; inadequate continuous flow in tremie pipe. Final Answer: At least 10% more cement than dry work; coarse aggregate 1.5–2 times fine aggregate; slump 100–180 mm; no dewatering during placement or for 24 h thereafter.

Question 20

Cut-off (termination) distance in bundled bars Four 30 mm bars are bundled; the lower two continue to the end supports. Keep the distance between the cut-off points of the upper bars equal to:

Accepted Answer

Introduction: Bundled reinforcement is used to accommodate large steel areas within limited beam width. When bars in a bundle are curtailed at different locations, codes specify minimum stagger distances between bar end points to avoid abrupt changes in stiffness and bond demand. Given Data / Assumptions: Bundle of 4 bars, diameter 30 mm each. Lower two bars continue to end supports (not curtailed). Upper two bars are curtailed and must terminate at separated points. Concept / Approach: Staggering bar cut-offs ensures that anchorage forces are distributed and splitting cracks are limited. A typical prescriptive minimum stagger for heavy bars in a bundle is about 0.75 m along the member length, preventing simultaneous loss of steel area over a very short region. Step-by-Step Solution: 1) Identify that two bars in the bundle are to be curtailed.2) Apply the minimum longitudinal stagger rule for bundled bar cut-offs.3) Provide at least 0.75 m between successive cut-off points.4) Detail adequate development length beyond theoretical cut-off sections. Verification / Alternative check: Stagger distances of ~0.75 m are widely adopted in detailing guides to mitigate bond stress concentration. Why Other Options Are Wrong: Zero defeats the purpose of staggering; 0.9 m and 1.2 m are conservative but not the standard minimum asked; selecting the code-typical minimum 0.75 m is correct. Common Pitfalls: Ending multiple bars at the same section; omitting hooks/anchorage; ignoring shear and moment envelopes when choosing curtailment. Final Answer: 0.75 m

Structural Design Specifications Questions