Question 1

Purpose of a column splice in steel construction: what is the primary functional reason for providing a splice in a column shaft?

Accepted Answer

Introduction / Context: Columns are often fabricated and transported in manageable lengths. Splices are introduced to assemble the full-height column on site and to align storey levels accurately. Given Data / Assumptions: Fabrication/transport limits necessitate splitting long members. Splice plates and fasteners/welds are provided at accessible elevations (near floors). Concept / Approach: The primary function of a column splice is to join adjacent lengths of column to achieve the required storey height—i.e., to increase the effective length of the member by connecting two pieces. Although splices must be designed to carry forces safely, they are not intended to boost the inherent strength or area beyond that of the connected sections. Step-by-Step Solution: Identify construction need: columns exceed transportable length.Place splices near beam levels for ease of erection and to minimize bending effects.Design splice to transfer axial load, shear, and any small moment as required by code. Verification / Alternative check: Review typical detailing: splices are commonly located 0.6–1.0 m above floor level to facilitate tightening/welding and inspection. Why Other Options Are Wrong: Splices do not inherently increase section strength or area; buckling length is governed by end restraint and bracing, not the mere existence of a splice. Common Pitfalls: Ignoring alignment and fit-up tolerance; under-designing the splice for construction-stage loads (e.g., imperfect alignment or temporary eccentricities). Final Answer: To increase the length of the column by joining two pieces

Question 2

Steel design – lacing bars: In a built-up compression member with double lacing, what is the minimum required thickness t of flat lacing in relation to the length between inner end rivets L? (Assume guidance as per standard steel design practice; ex…

Accepted Answer

Introduction / Context: Lacing bars connect the main components of a built-up compression member so that the parts act as a single column. Correct detailing prevents premature buckling of the lacing system and ensures that the whole member carries load efficiently. Double lacing requires specific minimum thickness to resist in-plane and out-of-plane forces and to provide adequate stiffness. Given Data / Assumptions: A built-up steel compression member employing double lacing. L is the length between the inner end fasteners (rivet/bolt/weld) of a lacing bar. We seek the minimum thickness t of flat lacing as a ratio of L in standard practice. Concept / Approach: Design standards require minimum thickness limits to control slenderness of lacing bars, limit local buckling, and provide robustness during fabrication and erection. For double lacing, the usual prescription is less severe than for single lacing because load paths are shared. A commonly adopted rule is t not less than L/60 for double lacing (compared with t not less than L/40 for single lacing). Step-by-Step Solution: Identify lacing configuration: double lacing.Recall standard minimum thickness: t ≥ L/60 for double lacing.Select from options: “t ≥ L/60”. Verification / Alternative check: Handbooks and teaching texts consistently list t ≥ L/60 for double lacing and t ≥ L/40 for single lacing to maintain an acceptable bar slenderness and prevent undue flexibility or damage during handling. Why Other Options Are Wrong: t ≥ L/40 or L/50: appropriate or conservative for single lacing; unnecessarily thick for double lacing. t ≥ L/70 or L/80: too thin and prone to buckling; does not meet typical codal recommendations. Common Pitfalls: Confusing single and double lacing requirements. Measuring L incorrectly (use the length between inner end fasteners along the bar). Ignoring corrosion allowance or fabrication tolerances that may require slightly thicker plates in practice. Final Answer: t ≥ L/60.

Question 3

Built-up beams: When sizing cover plates, what percentage allowance should be added to the calculated area of cover plates to account for rivet (or bolt) holes in a traditional riveted built-up beam?

Accepted Answer

Introduction / Context: In classic riveted or bolted built-up girders, cover plates over the flanges are pierced by fastener holes. These holes reduce the net area available to carry stress. A practical allowance is therefore added to the calculated required area so that the gross plate supplied still delivers the needed net capacity after deducting holes. Given Data / Assumptions: Traditional riveted/bolted construction with cover plates. Allowance sought as a percentage of the calculated required area. Hole deduction approach based on standard practice. Concept / Approach: The net area equals gross area minus area lost due to holes. Rather than detailing every hole in preliminary design, a rule-of-thumb percentage is added to the required area. A widely used allowance is 15% for cover plates, which adequately compensates for typical hole patterns without being excessively conservative. Step-by-Step Solution: Compute required net area based on strength.Apply allowance for holes to obtain gross area.Use standard allowance 15% → choose 15% from options. Verification / Alternative check: Older steel manuals and exam standards consistently quote 15% as a practical additive for cover plates in riveted/bolted built-up beams, streamlining preliminary sizing before detailing exact hole layouts. Why Other Options Are Wrong: 10% or 13%: may under-account for typical hole lines. 18% or 20%: often overly conservative at preliminary stage. Common Pitfalls: Forgetting to recheck net capacity after final hole layout. Using the same allowance for flange angles or webs without considering different hole densities. Final Answer: 15%.

Question 4

Slenderness limits: For a compression member carrying dead load plus superimposed load (no significant dynamic effects), what is the maximum permissible slenderness ratio (effective length / least radius of gyration) according to common steel design…

Accepted Answer

Introduction / Context: Compression members must satisfy slenderness limits to control buckling risk and ensure service performance. Different categories of loading (e.g., dead + superimposed, wind/earthquake, members carrying stress reversals) may have distinct permissible limits in design standards. Given Data / Assumptions: Member is primarily in compression under dead load plus superimposed load. No special conditions like solely wind bracing or temporary erection members. Slenderness ratio kL/r is to be checked against a maximum limit. Concept / Approach: Typical steel design provisions (working-stress tradition and echoed in guidance tables) restrict slenderness for always-in-compression members to about 180. Tighter or looser limits may apply for tension-only members, wind-only struts, or secondary bracing, but for gravity-loaded compression members, 180 is the widely cited maximum. Step-by-Step Solution: Identify member category: dead + superimposed compression.Recall standard maximum slenderness value: about 180.Select 180 from the options provided. Verification / Alternative check: Design handbooks list 180 for compression members in buildings under steady gravity actions, with other categories (e.g., members under wind only) sometimes permitted higher limits (such as 250 or more), which are not applicable here. Why Other Options Are Wrong: 200–350: typically associated with exceptional cases (e.g., wind-only bracing, secondary/temporary members) and not recommended for gravity-carrying columns. Common Pitfalls: Applying wind-bracing limits to main gravity columns. Using r about the wrong principal axis (minimum r must be used). Final Answer: 180.

Question 5

Terminology: The permissible design stress to which a structural member may be subjected in service (based on the chosen design philosophy and partial/overall safety factors) is commonly called ________.

Accepted Answer

Introduction / Context: Engineers distinguish between material strengths (yield, ultimate) and the allowable stress used for design under expected service conditions. In traditional working-stress design, members are proportioned so that service stresses do not exceed a specified allowable value, sometimes called the working or permissible stress. Given Data / Assumptions: General structural member under service loads. Terminology sought for the permissible (allowable) stress level used in design checks. Context fits classic working-stress approach; concept also maps to design-strength limits in limit-state methods via factors. Concept / Approach: Working stress is the allowable service stress derived by applying a factor of safety to a reference strength (often yield for ductile metals). Under limit-state design, we often check serviceability using combinations that keep service stresses/deflections within acceptable limits; the historical term remains useful in exams and practice discussions. Step-by-Step Solution: Identify the requested term for permissible design stress.Match to standard terminology: “working stress”.Therefore select “Working stress”. Verification / Alternative check: Textbooks consistently define working stress as the allowable stress at service loads, typically equal to yield stress divided by factor of safety for ductile metals in the older design method. Why Other Options Are Wrong: Bearing, tensile, compressive, buckling stresses: these describe types of stresses, not the allowable design limit itself. Common Pitfalls: Confusing “design strength” (limit-state) with “working stress” (service-level allowable) without noting the methodology. Final Answer: Working stress.

Question 6

Riveted joints – hole oversize: For rivet diameters over 25 mm, by how much is the rivet hole diameter typically made larger than the nominal rivet diameter to allow for insertion and driving?

Accepted Answer

Introduction / Context: In riveted construction (and analogously for some bolted work), holes are made slightly larger than the fastener to account for fabrication tolerances and ease of installation. The recommended oversize depends on the fastener diameter. Given Data / Assumptions: Traditional hot-driven rivets in structural steel. We focus on rivet diameters > 25 mm. Looking for the standard oversize value used in shop drawings and inspection. Concept / Approach: Common practice sets the hole oversize to about 1.5 mm for rivet diameters up to and including 25 mm; for larger rivets (over 25 mm) the oversize is typically 2.0 mm. This maintains adequate net section while ensuring practical driving and proper fit-up under field conditions. Step-by-Step Solution: Confirm rivet category: diameter over 25 mm.Apply standard hole oversize rule: +2.0 mm.Choose 2.0 mm from the options. Verification / Alternative check: Tabulated values in traditional steel design texts and specifications list +1.5 mm for ≤25 mm and +2.0 mm for >25 mm rivets, balancing fit-up and net-section loss considerations. Why Other Options Are Wrong: 1.0–1.5 mm: used for smaller rivets; insufficient for large diameters. 2.5–3.0 mm: overly large, causing unnecessary reduction in net area and potential alignment issues. Common Pitfalls: Using a single oversize value for all diameters without checking the transition at 25 mm. Failing to account for net-section reduction in tension members due to holes. Final Answer: 2.0 mm.

Question 7

Basic definitions: The factor of safety (FoS) in traditional working-stress design is defined as the ratio of ________ to the working (allowable) stress.

Accepted Answer

Introduction / Context: Factor of safety is a foundational concept that links material strength to the stress permitted in service. In working-stress design, FoS is applied to yield (or ultimate) strength to derive an allowable stress that ensures elastic behaviour and sufficient margin against failure under uncertainties. Given Data / Assumptions: Traditional working-stress methodology. Allowable (working) stress = reference strength / FoS. For ductile metals like structural steel, reference strength commonly taken as yield stress. Concept / Approach: For structural steel under service loading, the working stress is typically derived from yield stress divided by a chosen factor of safety. Hence, FoS = yield stress / working stress. While limit-state design uses partial factors on loads and resistances, the underlying safety philosophy still aims for comparable reliability. Step-by-Step Solution: Recall definition: FoS = strength / allowable stress.For ductile steel, “strength” is generally yield stress.Therefore, FoS is the ratio of yield stress to working stress. Verification / Alternative check: Standard textbooks define working stress = yield stress / FoS for steel; for brittle materials, ultimate strength may be used instead, but the exam convention for steel is yield-based. Why Other Options Are Wrong: Options b, c, d use actual service stresses, which are not the numerator in FoS definition. Option e is a mismatched ratio not generally used. Common Pitfalls: Confusing FoS with load factors from limit-state design. Using ultimate instead of yield for ductile steel in working-stress contexts without noting the convention. Final Answer: Yield stress.

Question 8

Choice of tension members for long lengths: In steelwork, when a tension member is required over a very long length (e.g., roof bracing or long ties), which form is most commonly adopted for practicality, weight saving, and ease of tensioning?

Accepted Answer

Introduction / Context: Long tension members are frequently required in roofs, trusses, temporary works, and cable-supported structures. The choice of form affects dead weight, erection convenience, and the ability to adjust tension on site. Cables and rods are typical solutions, with cables (wire ropes) preferred where very long, flexible ties are needed. Given Data / Assumptions: Member primarily carries tension over a long clear length. Serviceability (sag, vibration) can be controlled by adequate prestress/tensioning. Connections and end fittings are available for the selected member type. Concept / Approach: Wire ropes (cables) provide high strength-to-weight ratio, ease of coiling/transport, and straightforward on-site tensioning with turnbuckles or jacks. Round rods can also be used but become heavy and unwieldy at long lengths; bars and single angles are stiffer and heavier, better suited to shorter bracing lengths or where compression might occur (then they risk buckling). For very long pure tension ties, cables are standard practice in both building and bridge applications. Step-by-Step Solution: Identify governing considerations: weight, handling, and tension adjustment.Compare candidate forms: cables excel in long lengths; rods/bars are heavier and harder to tension over long spans.Select: “A wire rope (cable)”. Verification / Alternative check: Architectural trusses, large-span roofs, and guy systems frequently use cables as the long tension element, confirming industry practice. Why Other Options Are Wrong: Solid round rod: usable, but heavy and less convenient for very long runs. Flat bar/single angle: heavier; angles suffer from handling/twist and offer no advantage in pure tension over very long spans. Plate girder flange strip: inappropriate for a discrete long tie. Common Pitfalls: Ignoring end anchorage and turnbuckle detailing for adjustability. Allowing excessive sag by under-tensioning long cables. Final Answer: A wire rope (cable).

Question 9

Structural steel – Typical application of bulb angles In steel construction practice, bulb angles are most commonly used in which type of construction because of their excellent flange stiffness and compact geometry?

Accepted Answer

Introduction / Context: Bulb angles are a special rolled steel section where an unequal angle has a thickened, rounded “bulb” along one leg. This shape offers high stiffness-to-weight ratio and better resistance to local buckling in thin plating applications. Understanding where such sections are predominantly used helps students connect section properties with practical design contexts. Given Data / Assumptions: The question asks for the most common application domain of bulb angles. We compare typical structural sectors: buildings, bridges, ships, and water tanks. No numerical calculations are required; the concept is application-based. Concept / Approach: Bulb angles are particularly well-suited to stiffen thin plates, as found in hulls and decks. Their geometry allows efficient welding and riveting to plating, reducing stress concentrations and providing torsional and out-of-plane stiffness. This is why naval architecture standards and shipyards specify bulb flats/angles extensively for longitudinal and transverse stiffeners. Step-by-Step Solution: Identify where thin plates dominate structural components → ship hulls and decks.Recall that ship framing uses bulb flats/angles as primary stiffeners to plating.Conclude that bulb angles are most commonly used in ship building. Verification / Alternative check: Look at classification society details (general knowledge): scantling rules and shipyard catalogues list extensive bulb flat/angle sizes for hull stiffening, confirming the typical application. Why Other Options Are Wrong: Column building and water tank building rarely need plate stiffeners of this type. Bridge building uses standard I/H sections, channels, and plates; bulb angles are uncommon. Industrial shed purlins are typically cold-formed Z/C or channels, not bulb angles. Common Pitfalls: Confusing bulb angles with normal equal/unequal angles; assuming any “angle” is interchangeable across sectors without considering plating needs. Final Answer: Ship building

Question 10

Riveted splice with packing (> 6 mm) – code-based increase in number of rivets According to IS 800:1971, in a splice plate where the calculated shear is transmitted through a packing thicker than 6 mm, the required number of rivets should be increas…

Accepted Answer

Introduction / Context: When load in a riveted (or bolted) splice is transferred through a packing piece instead of direct plate-to-plate bearing, deformation and secondary effects can reduce the effectiveness of the fasteners. Older code provisions (IS 800:1971 working stress design) therefore specify an increase in the number of rivets as the packing thickness grows. Given Data / Assumptions: Packing thickness exceeds 6 mm. Increase in rivet count is expressed as a percentage per unit thickness. Provision cited is specific to IS 800:1971 practice. Concept / Approach: Load path through a compressible packing introduces additional eccentricity/deformation. A small percentage increase in rivet count offsets this potential reduction in joint efficiency. The code quantifies this as 2.5% per mm of extra packing thickness over 6 mm. Step-by-Step Solution: Identify threshold: packing > 6 mm → apply increase rule.Quantify increase: 2.5% per 1.0 mm beyond 6 mm.Select the option matching 1.0 mm increment. Verification / Alternative check: Historical steel design handbooks repeating IS 800:1971 guidance show the same 2.5% per mm increase where shear passes through packing. Why Other Options Are Wrong: 1.5 mm, 2.0 mm, 2.5 mm, or 3.0 mm increments would misstate the prescribed rate, leading to unconservative or overly conservative designs. Common Pitfalls: Forgetting the rule applies only to thickness beyond 6 mm; applying the percentage to shear force instead of the number of rivets; ignoring that more modern limit-state codes handle such effects differently. Final Answer: 1.0 mm of packing (beyond 6 mm)

Question 11

Compression member – effective sectional area for design For a riveted or bolted compression member, the effective sectional area used in design is taken as:

Accepted Answer

Introduction / Context: Compression members (columns, struts, lacing members) often have holes for rivets or bolts at their connections. These holes reduce the net cross-sectional area resisting compression. For working stress design and many practical checks, an effective (net) area is used to compute compressive stress and slenderness-based capacities. Given Data / Assumptions: Member is built-up or connected using rivets/bolts. Holes pass through the section in the connection zone considered critical. We wish to determine the area adopted in stress computations. Concept / Approach: The effective compressive area is conservatively taken as the gross area minus the deduction for fastener holes. This aligns with the concept of net area used in tension members and avoids overestimating capacity in zones weakened by holes. Some codes allow limited exceptions if holes are filled tightly and are away from buckling-critical zones, but the standard safe approach is to deduct. Step-by-Step Solution: Compute gross area Ag from dimensions.Determine total deduction Ah for the governing hole line (diameter taken as nominal hole dia).Effective area Ae = Ag − Ah for capacity checks. Verification / Alternative check: Design examples in steel handbooks commonly subtract hole area for compression members at connections, matching the conservative practice embedded in older codes and many specifications. Why Other Options Are Wrong: Adding hole area is physically meaningless; multiplying areas has no dimensional coherence; ignoring holes can overrate capacity. Common Pitfalls: Using bolt nominal diameter instead of hole diameter; neglecting stagger correction where relevant; applying deductions over lengths where holes are absent. Final Answer: Gross sectional area minus the area of rivet (bolt) holes

Question 12

Effect of carbon content on mechanical properties of steel With an increase in the percentage of carbon in steel (keeping other factors constant), which property decreases most notably for structural applications?

Accepted Answer

Introduction / Context: Carbon is the primary alloying element that controls the balance between strength, hardness, and ductility in plain carbon steels. As the carbon percentage rises, microstructural changes shift steel from more ductile ferrite-pearlite to harder, stronger phases, affecting formability and toughness. Given Data / Assumptions: Comparative, qualitative property change with carbon percentage. No heat treatment variations considered. Room-temperature behavior for structural use. Concept / Approach: Higher carbon content increases strength and hardness but reduces ductility and toughness. For structural members that must deform plastically to redistribute stresses, ductility is valuable; hence, structural steels typically keep carbon content modest (e.g., < 0.25%). Step-by-Step Solution: As carbon ↑ → tensile strength ↑.As carbon ↑ → hardness ↑.As carbon ↑ → brittleness ↑ (i.e., toughness ↓) and ductility ↓.Therefore, the property that decreases most notably is ductility. Verification / Alternative check: Stress-strain curves for steels with increasing carbon show lower elongation at fracture and reduced uniform elongation, confirming reduced ductility. Why Other Options Are Wrong: Strength and hardness generally increase with carbon; brittleness increases (so it does not decrease); elastic modulus is largely insensitive to composition changes in steels. Common Pitfalls: Confusing toughness with hardness; assuming all properties improve together with alloying. Final Answer: Ductility

Question 13

Deflection of a simply supported steel beam – midspan point load A simply supported steel beam of span L carries a concentrated load W at its centre. What is the central deflection in terms of W, L, E, and I (second moment of area)?

Accepted Answer

Introduction / Context: Deflection control is a key serviceability criterion in beam design. The classical elastic curve solution for a simply supported beam under a central point load is a staple result, used to check deflection limits against code-prescribed span ratios. Given Data / Assumptions: Beam is prismatic with constant E and I. Boundary conditions: simple supports at both ends (no end fixity). Loading: a single concentrated load W at midspan. Small deflections and linear elastic behavior. Concept / Approach: Use the standard integration of the Euler–Bernoulli beam equation: E * I * d^2y/dx^2 = M(x). For a central point load, the bending moment diagram is triangular, peaking at W * L / 4 at midspan. Integrating twice with appropriate boundary conditions yields the closed-form deflection at midspan. Step-by-Step Solution: Write maximum bending moment at midspan: Mmax = W * L / 4.Integrate beam equation over half-span, apply symmetry (slope zero at midspan, deflection zero at supports).Obtain central deflection: δ = (W * L^3) / (48 * E * I). Verification / Alternative check: Compare with tabulated deflection coefficients: for central point load on simply supported beam, coefficient = 1/48, matching the derived expression. Why Other Options Are Wrong: 1/24 overestimates deflection by a factor of 2; (W * L^2)/(8 * E * I) has wrong dimensions; 5/384 corresponds to uniformly distributed load, not point load; (W * L)/(4 * E * I) is dimensionally inconsistent. Common Pitfalls: Mixing up the coefficient with that for uniformly distributed loads; forgetting to use consistent units for E and I. Final Answer: δ = (W * L^3) / (48 * E * I)

Question 14

Plate girder terminology: When no horizontal stiffeners are provided, the distance between the vertical legs of the top and bottom flange angles (i.e., the clear distance between the inner faces of the flange angles) of a plate girder is called what?

Accepted Answer

Introduction / Context: In steel plate girders, three different depth terms are routinely used in design and detailing: overall depth, clear depth, and effective depth. Examiners often test whether learners can correctly identify each from a verbal description or a simple sketch. This question focuses on the name for the distance between the inner faces of the flange angles when horizontal stiffeners are not present. Given Data / Assumptions: A riveted/bolted plate girder with angle sections forming the top and bottom flanges. No horizontal stiffeners are used along the web. We are referring specifically to the distance between the vertical legs of the flange angles. Concept / Approach: Overall depth is the total depth of the girder, typically measured between the outermost surfaces of the top and bottom flanges or cover plates. Effective depth is the distance between the centroids of the compression and tension resultants (often approximated to the distance between the centroids of flange areas for preliminary design). The distance strictly between the inner faces of the flange angles is termed the clear depth. This dimension is frequently used for checking web slenderness and spacing of vertical stiffeners. Step-by-Step Solution: Identify the two reference faces: inner faces of the vertical legs of top and bottom flange angles.Recognize that this excludes any cover plates, fillets, or external projections.The standard term for this measurement is clear depth. Verification / Alternative check: Design handbooks define clear depth as the net web panel height available between flange connections. This is the controlling panel dimension for stiffener spacing checks and web buckling calculations in plate girders without horizontal stiffeners. Why Other Options Are Wrong: Overall depth: includes flange thicknesses and any cover plates; it is larger than the inner-to-inner distance. Effective depth: relates to internal force couple arm, not a simple inner-face-to-inner-face measurement. None of these: incorrect because a standard term (clear depth) exists. Common Pitfalls: Confusing clear depth with web plate height; fillets and connection geometry can create slight differences. Using overall depth in web slenderness checks where clear depth is appropriate. Final Answer: clear depth

Question 15

Fillet weld orientation: A fillet weld whose longitudinal axis is parallel to the direction of the applied load is referred to as which type of fillet weld?

Accepted Answer

Introduction / Context: Correct terminology for weld orientation is essential in steel detailing and quality control. In lap joints and cover-plate connections, fillet welds can be arranged either parallel or perpendicular to the line of action. Their names reflect this orientation and help designers compute the correct throat lengths and capacities. Given Data / Assumptions: A fillet weld is loaded by a force acting in a known direction. The weld’s longitudinal axis is parallel to this load direction. Standard structural steel terminology is used. Concept / Approach: In common steelwork language: side fillet welds run alongside the load path, so their axes are parallel to the direction of the applied force. End fillet welds are located across the ends of a lap or plate, so their axes are perpendicular to the load. “Diagonal” is not a standard orientation term in basic detailing specifications for this simple case. Step-by-Step Solution: Identify load direction in the joint.Determine weld orientation relative to load: here, axes are parallel to load.Name for parallel orientation: side fillet weld. Verification / Alternative check: Most handbooks and code commentaries illustrate lap joints with longitudinal (side) fillets and transverse (end) fillets. Parallel-to-load welds are consistently labeled as side fillets in these references. Why Other Options Are Wrong: End fillet weld: axis perpendicular to the load in a typical lap joint layout. Diagonal fillet weld: not a standard naming convention for basic parallel orientation. All the above: mutually contradictory options cannot all be correct. Common Pitfalls: Mixing up “end” and “side” when both types are present in the same connection. Forgetting that weld design strength depends on orientation due to directional components of shear. Final Answer: side fillet weld

Question 16

Column buckling – effective length: For a compression member held in position and restrained in direction at both ends (i.e., effectively fixed at both ends), the effective length is approximately equal to which of the following?

Accepted Answer

Introduction / Context: Effective length, Le, is a key concept for column buckling. It converts actual member length and end restraints into an equivalent pin-ended length for use in Euler-type stability checks or code-based slenderness limits. Knowing standard Le factors for typical end conditions speeds preliminary design and checking. Given Data / Assumptions: Prismatic column, uniform cross-section. End conditions: held in position and restrained in rotation at both ends (fixed–fixed idealization). Elastic buckling concept underlying effective length. Concept / Approach: The relation is Le = K * L. For typical end conditions: pinned–pinned K ≈ 1.0; fixed–free K ≈ 2.0; fixed–pinned K ≈ 0.7–0.8; fixed–fixed commonly ≈ 0.65–0.70. Many examination problems adopt 0.67 L as a practical rounded value for fixed–fixed restraint to account for real-world semi-rigidity. Step-by-Step Solution: Recognize end restraint: both ends held and restrained in direction.Adopt K ≈ 0.67 for fixed–fixed boundary.Compute Le = 0.67 L → select the listed option 0.67 L. Verification / Alternative check: Comparative capacity: Buckling load is proportional to 1 / Le^2. Fixed–fixed with Le ≈ 0.67 L provides about (1 / 0.67^2) ≈ 2.2 times the Euler load of a similar pinned–pinned column, matching engineering expectations. Why Other Options Are Wrong: L: corresponds to pinned–pinned. 0.85 L: closer to fixed–pinned or partial restraint. 1.5 L or 2 L: represent weak-end or cantilever conditions, not both ends restrained. Common Pitfalls: Assuming perfect fixity; real joints may justify slightly higher K values. Confusing “held in position” (translation fixity) with “restrained in direction” (rotation fixity). Final Answer: 0.67 L

Question 17

Riveted joint limit states: A riveted structural joint may fail by which of the following mechanisms under load?

Accepted Answer

Introduction / Context: Although high-strength bolts dominate modern practice, many legacy bridges and buildings use riveted joints. Understanding all plausible failure modes remains important for assessment and retrofits. A riveted joint has multiple interacting limit states involving both the fasteners and the connected plates. Given Data / Assumptions: Lap or butt type riveted joint under static shear and bearing. Standard shop or field-driven rivets with proper heads and holes. Plates in single or double shear configurations. Concept / Approach: Principal limit states include: shear failure of the rivet shank; bearing (crushing) of plate or rivet material at the interface; and tearing or shear-out of the plate (including net-section tension and block shear). Each can govern depending on plate thickness, edge distance, hole diameter, and rivet spacing. Step-by-Step Solution: Check rivet shear capacity against factored shear demand.Check plate and rivet bearing stress: bearing = load / (hole diameter * plate thickness).Check plate net-section tension and block shear using net area after hole deductions.Identify the lowest capacity among all; that mode governs failure. Verification / Alternative check: Worked examples in steel handbooks show cases where any of these limit states can control depending on detailing. Conservative design ensures none of the capacities is exceeded. Why Other Options Are Wrong: Options a–d each describe a single mechanism; in reality all are possible, so the comprehensive answer is “all the above.” Common Pitfalls: Ignoring block shear and net tension, which can be critical with large holes or short edge distances. Assuming rivet shear alone governs without checking bearing stresses. Final Answer: all the above

Question 18

Built-up members – use of perforated cover plates: Perforated cover plates are particularly suitable for built-up compression/tension members made from which of the following component arrangements?

Accepted Answer

Introduction / Context: Built-up members are frequently formed from rolled sections (angles, channels) connected together. Rather than using lacing bars, designers sometimes adopt cover plates to tie the components. Perforated cover plates offer structural connectivity while reducing wind area and self-weight compared with solid plates. Given Data / Assumptions: Built-up section made from channels and/or angles. Cover plates provided in lieu of lacing. Perforations reduce drag and weight yet maintain overall connectivity. Concept / Approach: Perforated plates act as continuous ties between components, enhancing torsional stiffness and load sharing. They are applicable for back-to-back channels, toe-to-toe channels (forming a box-like section), and four-angle box sections. The perforations mitigate wind loading and facilitate inspection while preserving the required shear transfer between elements. Step-by-Step Solution: Identify component arrangement (channels or angles) and whether a box or open section results.Recognize the function of the cover plate: to connect the elements and provide lateral restraint.Note that perforations improve aerodynamics and reduce weight; hence, suitability spans all listed arrangements. Verification / Alternative check: Design guides list perforated plates as acceptable alternatives to lacing for open and box built-up members, provided plate thickness and fastener spacing meet shear flow requirements. Why Other Options Are Wrong: Each of a–c is individually suitable; therefore, the most comprehensive correct choice is “all the above.” Common Pitfalls: Using solid cover plates unnecessarily, increasing wind load and weight. Insufficient perforation edge distances or fastener spacing, compromising shear transfer. Final Answer: all the above

Question 19

Axial tension – thickness reduction factor: In working stress design for steel, the allowable axial tensile stress is usually reduced (thickness factor applied) when the plate thickness exceeds which value?

Accepted Answer

Introduction / Context: Plate thickness influences the ductility and the likelihood of lamellar tearing or through-thickness imperfections affecting performance. Many traditional codes apply a reduction (thickness factor) to the permissible axial tensile stress beyond a certain plate thickness threshold. Given Data / Assumptions: Structural steel plates loaded in direct tension. Working stress or allowable stress design context. Typical legacy Indian practice and common exam conventions. Concept / Approach: For plates thicker than a specified limit, allowable stress is reduced by applying a factor less than unity to account for material through-thickness properties and the statistical likelihood of defects. A commonly cited threshold in classic problems is 20 mm, above which the permissible tensile stress is reduced marginally. Step-by-Step Solution: Identify the threshold plate thickness where reduction begins.Recall standard exam value used in traditional references: 20 mm.Select the option corresponding to 20 mm. Verification / Alternative check: Older editions of steel design texts list a step-down in allowable stress beginning at about 20 mm plate thickness. Modern limit-state codes handle thickness effects via partial factors and material specifications but retain the principle that very thick plates warrant caution. Why Other Options Are Wrong: 10–15 mm: typically below the traditional threshold for reduction. 22 mm: not the standard teaching value used in classic problems. Common Pitfalls: Applying thickness reductions to members where governing limit state is net-section rupture instead of gross yield. Ignoring toughness requirements (e.g., through-thickness properties) in thick plates for heavily restrained joints. Final Answer: 20 mm

Question 20

Column buckling – asymmetric end restraint: For a compression member that is effectively held in position and restrained in direction at one end but neither held in position nor restrained in direction at the other end (i.e., fixed–free), the effect…

Accepted Answer

Introduction / Context: The effective length factor K captures end restraint conditions for columns. The most flexible case is the cantilever (fixed–free), which has the highest effective length and therefore the lowest buckling strength for a given member length and section. Given Data / Assumptions: One end fixed (no translation or rotation), the other end free (no restraint). Prismatic member, elastic buckling considered. Concept / Approach: Standard K values: pinned–pinned K = 1.0; fixed–pinned K ≈ 0.7–0.8; fixed–fixed K ≈ 0.65–0.70; fixed–free K = 2.0. Therefore, the effective length Le = K * L = 2L for the fixed–free (cantilever) case. Step-by-Step Solution: Identify boundary condition as fixed–free.Use K = 2.0.Compute Le = 2.0 * L = 2 L. Verification / Alternative check: Euler buckling solution for a cantilever gives the first buckling mode with a node at the fixed end and a maximum deflection at the free end, corresponding to Le = 2 L when compared to the pinned–pinned baseline. Why Other Options Are Wrong: L, 0.67 L, 0.85 L, 1.5 L: all correspond to more restrained conditions, which would produce higher buckling loads than the cantilever case. Common Pitfalls: Mistaking a partially braced top (e.g., lateral support only) as “free”; true free end has no translational or rotational restraint. Final Answer: 2 L

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