Category: Design of Steel Structures Objective Questions

Design of Steel Structures online test on “Plastic Design of Portal Frames, Effect of Axial and Shear force on Plastic Moment Capacity”.

1. Single bay portal frames with fixed bases have _______
a) two redundancies
b) three redundancies
c) four redundancies
d) zero redundancies
Answer: b
Clarification: Single bay portal frames with fixed bases have three redundancies and require four hinges to produce a mechanism.

2. If order of indeterminacy is r, then minimum number of plastic hinges required for total collapse is _______
a) r-1
b) r
c) r+1
d) r+2
Answer: c
Clarification: If order of indeterminacy is r, then minimum number of plastic hinges required for total collapse is r+1.

3. Which method is used when mechanism is applied to structures with sloping members?
a) method of instantaneous centre
b) method of centre
c) method of seismic centre
d) method of metacentre
Answer: a
Clarification: When mechanism is applied to structures with sloping members, the determination of displacements in the direction of applied forces is required. It is done using method of instantaneous centre or centre-of-rotation technique.

4. Which of the following relation is correct for pin based frames?
a) M_p =γ_L(wL²/8)[1-k+(1+k)^0.5].
b) M_p =γ_L(wL²/8)[1+k+(1-k)^0.5].
c) M_p =γ_L(wL²/8)[1+k-(1+k)^0.5].
d) M_p =γ_L(wL²/8)[1+k+(1+k)^0.5].
Answer: d
Clarification: When gravity load governs the design, a good estimate of required section may be obtained by using following formulae :
For pin based frames : M_p =γL(wL²/8)[1+k+(1+k)^0.5]
For fixed=-base frame : M_p =γL(wL²/8)[1/[1+0.5k+(1+k)^0.5]], where γ_L = 1.7 global load factor, k = h₂/h₁.

5. Which of the following statement is true?
a) combined mechanism is combination of elementary mechanism
b) elementary mechanism is combination of combined mechanism
c) combined mechanism is not combination of elementary mechanism
d) elementary mechanism is combination of elementary and combined mechanism
Answer: a
Clarification: The possible mechanisms can be classified into two types : elementary and combined mechanism. Elementary mechanism is independent of each other, combined mechanism is linear combination of elementary mechanisms.

6. The presence of axial equation implies that _________
a) sum of tension forces is always zero
b) sum of compression forces is always zero
c) sum of tension and compression forces is not zero
d) sum of tension and compression forces is zero
Answer: c
Clarification: The presence of axial equation implies that sum of tension and compression forces is not zero and hence following equation is used : ∫A f_ydA – P = 0, where P is the axial force.

7. Which of the following relation is correct for rectangular section of width b and depth d subjected to axial force N together with moment M?
a) (M_pr/M_p) + (N/N_p)² = 1
b) (M_pr/M_p) – (N/N_p)² = 1
c) (M_pr/M_p) + (N/N_p) = 1
d) (M_pr/M_p) – (N/N_p) = 1
Answer: a
Clarification: For a rectangular section of width b and depth d subjected to axial force N together with moment M, (M_pr/M_p) + (N/N_p)2 = 1, where M_pr is moment with axial force, M_p is moment with axial force, N_p is axial force without any moment.

8. Which of the following relation is correct for I- section of width b and depth d subjected to axial force N together with moment M?
a) (N/N_p) – (1/1.18)(M/M_p) ≤ 1, when N/N_p > 0.15
b) (N/N_p) – (1/1.18)(M/M_p) ≤ 1, when N/N_p < 0.15
c) (N/N_p) + (1/1.18)(M/M_p) ≤ 1, when N/N_p < 0.15
d) (N/N_p) + (1/1.18)(M/M_p) ≤ 1, when N/N_p > 0.15
Answer: d
Clarification: For I- section subjected to axial force N together with moment M,
(N/N_p) + (1/1.18)(M/M_p) ≤ 1, when N/N_p > 0.15
M = M_p, when N/N_p < 0.15 .

9. When a member is subjected to uniaxial tensile or compressive stress in presence of shear stress τ , yield occurs when ___
a) f_y² = f² – 3 τ
b) f_y² = f² + 3 τ²
c) f_y² = f² – 3 τ²
d) f_y² = f² + 3 τ
Answer: b
Clarification: When a member is subjected to uniaxial tensile or compressive stress in presence of shear stress τ, yield occurs when f_y² = f² + 3 τ².

10. Yield in pure shear occurs when ______
a) 0.58 f_y
b) 1.58 f_y
c) 2.8 f_y
d) 3.5 f_y
Answer: a
Clarification: Yield in pure shear occurs when τ_y = f_y/√3 = 0.58 f_y.

11. At full plasticity, the stress in web is given by
a) f_w = f_y√[1+(τ_w/τ_y)² ].
b) f_w = f_y√[(τ_w/τ_y)² ].
c) f_w = f_y√[1-(τ_w/τ_y)² ].
d) f_w = f_y√[1+2(τ_w/τ_y)² ].
Answer: c
Clarification: When full plasticity is produced, the stress in web will be equal to f_w, f_w =√(f_y² -3τ_w² ) = f_y√[1-(_w/τ_y)² ] where τ_y is shear strengths when yield is in pure shear.

12. Loss of web capacity is given by ___
a) Z_pw / (f_y – f_w)
b) Z_pw (f_y – f_w)
c) Z_pw (f_y + f_w)
d) Z_pw /(f_y + f_w)
Answer: b
Clarification: Loss of web capacity is given by Z_pw (f_y – f_w) = Z_pw f_y { 1-√[1-(τ_w/τ_y)2] }.

Design of Steel Structures for online tests,

Design of Steel Structures Multiple Choice Questions on “Lateral Torsional Buckling”.

1. What is lateral torsional buckling?
a) buckling of beam loaded in plane of its weak axis and buckling about its stronger axis accompanied by twisting
b) buckling of beam loaded in plane of its strong axis and buckling about its weaker axis accompanied by twisting
c) buckling of beam loaded in plane of its strong axis and buckling about its weaker axis and not accompanied by twisting
d) buckling of beam loaded in plane of its weak axis and buckling about its stronger axis and not accompanied by twisting
Answer: b
Clarification: The buckling of beam loaded in plane of its strong axis and buckling about its weaker axis accompanied by twisting (torsion) is called as torsional buckling. The load at which such beam buckles can be much less than that causing full moment capacity to develop.

2. Critical bending moment capacity of a beam undergoing lateral torsional buckling is a function of
a) does not depend on anything
b) pure torsional resistance only
c) warping torsional resistance only
d) pure torsional resistance and warping torsional resistance
Answer: d
Clarification: Critical bending moment capacity of a beam undergoing lateral torsional buckling is a function of pure torsional resistance and warping torsional resistance.

3. Elastic critical moment is given by
a) (π/L){√[(EI_yGI_t) + (πE/L)²I_wI_y]}
b) (π/L){√[(EI_yGI_t) – (πE/L)²I_wI_y]}
c) (π/L){√[(EI_yGI_t) + (πE/L) I_wI_y]}
d) (π/L){ [(EI_yGI_t) – (πE/L)²I_wI_y]}
Answer: a
Clarification: Elastic critical moment is given by M_cr = (π/L){√[(EI_yGI_t) + (πE/L)2I_wI_y]}, where EI_y = flexural rigidity(minor axis), GI_t = torsional rigidity, I_t = St.Venant torsion constant, I_w = St.Venant warping constant, L = unbraced length of beam subjected to constant moment in plane of web.

4. Lateral torsional buckling is not possible to occur if
a) moment of inertia about bending axis is twice than moment of inertia out of plane
b) moment of inertia about bending axis is greater than moment of inertia out of plane
c) moment of inertia about bending axis is equal to or less than moment of inertia out of plane
d) moment of inertia about bending axis is equal to or greater than moment of inertia out of plane
Answer: c
Clarification: I_t is not possible for lateral torsional buckling to occur if moment of inertia of section about bending axis is equal to or less than moment of inertia out of plane.

5. Limit state of lateral torsion buckling is not applicable to
a) square shapes
b) doubly symmetric I shaped beams
c) I section loaded in plane of their webs
d) I section singly symmetric with compression flanges
Answer: a
Clarification: Lateral torsional buckling is applicable to doubly symmetric I shaped beams, I section loaded in plane of their webs, I section singly symmetric with compression flanges. I_t is not possible for lateral torsional buckling to occur if moment of inertia of section about bending axis is equal to or less than moment of inertia out of plane. So, limit state of lateral torsion buckling is not applicable for shapes bent about their minor axis for shapes with Iz ≤ I_y or for circular or square shapes.

6. Which of the following assumptions were not made while deriving expression for elastic critical moment?
a) beam is initially undisturbed and without imperfections
b) behaviour of beam is elastic
c) load acts in plane of web only
d) ends of beam are fixed support
Answer: d
Clarification: The following assumptions were made while deriving expression for elastic critical moment: (i) beam is initially undisturbed and without imperfections, (ii) behaviour of beam is elastic,(iii) beam is loaded with equal and opposite end moments in plane of web, (iv) load acts in plane of web only, (v) ends of beam are simply supported vertically and laterally, (vi) beam does not have residual stresses.

7. For different loading conditions, the equation of elastic critical moment is given by
a) M_cr = c₁ (EI_yGI_t) γ
b) M_cr = c₁ [(EI_yGI_t)²] γ
c) M_cr = c₁ [√(EI_yGI_t)] γ
d) M_cr = c₁ (EI_y /GI_t) γ
Answer: c
Clarification: For different loading conditions, the equation of elastic critical moment is given by M_cr = c₁ [√(EI_yGI_t)] γ, where c₁ = equivalent uniform moment factor or moment coefficient, EI_y = flexural rigidity(minor axis), GI_t = torsional rigidity, γ = (π/L){√[1 + (πE/L)²I_wI_y]}, I_t = St.Venant torsion constant, I_w = St.Venant warping constant, L = unbraced length of beam subjected to constant moment in plane of web.

8. Which of the following is not true about moment coefficient?
a) for torsionally simple supports the moment coefficient is greater than or equal to unity
b) for torsionally simple supports the moment coefficient is less than unity
c) moment coefficient accounts for the effect of differential moment gradient on lateral torsional buckling
d) it depends on type of loading
Answer: b
Clarification: The moment coefficient accounts for the effect of differential moment gradient on lateral torsional buckling and depends on type of loading. For torsionally simple supports the moment coefficient is greater than or equal to unity.

9. √EI_yGI_t depends on
a) shape of beam only
b) material of beam only
c) shape and material of beam
d) does not depend on anything
Answer: c
Clarification: √EI_yGI_t depends on shape and material of beam, where = flexural rigidity(minor axis), GI_t = torsional rigidity.

10. Which of the following is true?
a) sections with greater lateral bending and torsional stiffness have great resistance to bending
b) sections with lesser lateral bending and torsional stiffness have great resistance to bending
c) sections with greater lateral bending and torsional stiffness have less resistance to bending
d) lateral instability of beam cannot be reduced by selecting appropriate shapes
Answer: a
Clarification: Lateral instability of beam can be reduced by selecting appropriate shapes. Sections with greater lateral bending and torsional stiffness have great resistance to bending.

11. In the equation M_cr = c₁ [√(EI_yGI_t)] γ, γ depends on
a) load on beam
b) shape of beam
c) material of beam
d) length of beam
Answer: d
Clarification: In the equation M_cr = c₁ [√(EI_yGI_t)] γ, c₁ varies with loading and support conditions, [√(EI_yGI_t)] varies with material properties and shape of beam and γ varies with length of beam.

12. Which of the following is true?
a) long shallow girders have high warping stiffness
b) short and deep girders have very low warping resistance
c) long shallow girders have low warping stiffness
d) short and shallow girders have very low warping resistance
Answer: c
Clarification: Short and deep girders have very high warping stiffness while long shallow girders have low warping stiffness or resistance.

13. Elastic critical moment for long shallow girders is given by
a) (π/L){√(EI_yGI_t)}
b) (πL){√(EI_yGI_t)}
c) (π/L){√(EI_y /GI_t)}
d) (πL){√(EI_y /GI_t)}
Answer: a
Clarification: Long shallow girders have low warping stiffness or resistance. So, elastic critical moment for long shallow girders is given by (π/L){√(EI_yGI_t)}, where EI_y = flexural rigidity(minor axis), GI_t = torsional rigidity, L = unbraced length of beam subjected to constant moment in plane of web.

Design of Steel Structures Multiple Choice Questions on “Stiffeners”.

1. The function of bearing stiffener is to
a) improve buckling strength of web
b) preclude any crushing of web
c) restrain against torsional effects
d) increase buckling resistance of web
Answer: b
Clarification: The function of bearing stiffener is to preclude any crushing of web at locations of heavy concentrated loads. Thus, they transfer heavy reactions or concentrated loads to the full depth of web. They are placed in pairs on the web of plate girders at unframed girder ends and where required for concentrated loads.

2. Match the following

	Stiffeners				Function
A) Load carrying stiffener		(i) increases buckling resistance of web
B) Torsional stiffener			(ii) local strengthening of web
C) Diagonal stiffener			(iii) prevent local buckling of web
D) Tension stiffener			(iv) restrain against torsional effects
E) Longitudinal stiffener		(v) transmit tensile forces

a) A-i, B-ii, C-iii, D-iv, E-v
b) A-v, B-iv, C-iii, D-ii, E-i
c) A-iv, B-v, C-i, D-ii, E-iii
d) A-iii, B-iv, C-ii, D-v, E-i
Answer: d
Clarification: Load carrying stiffener prevents local buckling of web due to any concentrated load. Torsional stiffener are provided at supports to restrain girders against torsional effects. Local strengthening of web under the combination of shear and bending is provided by diagonal stiffeners. The tensile forces from the flange are transmitted to the web through the tension stiffener. A longitudinal stiffener increases the buckling resistance of web.

3. The outstand of stiffener from face of web is restricted to
a) 20t_q/ε
b) 120t_qε
c) 20t_qε
d) 50t_qε
Answer: c
Clarification: Unless the outer edge is continuously stiffened, the outstand of stiffener from face of web should not exceed 20t_qε,where t_q is thickness of stiffener. When the outstands of web is between 14t_qε and 20t_qε, then the stiffener design should be on the basis of a core section with an outstand of 14t_qε.

4. What is the stiff bearing length?
a) length which cannot deform appreciably in bending
b) length which deform appreciably in bending
c) length of outer end of flange
d) length of web
Answer: a
Clarification: The stiff bearing length of any element b₁ is that length which cannot deform appreciably in bending. To determine b₁, the dispersion of load through a steel bearing element should be taken as 45˚ through solid material, such as bearing plates, flange plates, etc.

5. The effective length of web on each side of centreline of stiffeners for interior stiffeners is limited to
a) 10 t_w
b) 50 t_w
c) 40 t_w
d) 15 t_w
Answer: c
Clarification: The effective length of web on each side of centreline of stiffeners is limited to 20 times the web thickness, i.e. 40t_w for interior stiffeners and 20t_w for end stiffeners . The effective section is the full area or core area of stiffener together with effective length of web on each side of centreline of stiffeners.

6. The effective length of intermediate transverse stiffener is taken as
a) 2 times the length of stiffener
b) 0.7 times the length of stiffener
c) 1.4 times the length of stiffener
d) 0.5 times the length of stiffener
Answer: d
Clarification: The effective length of intermediate transverse stiffener is taken as 0.7 times the length of stiffener. The intermediate transverse stiffener is provided mainly to improve shear buckling resistance of the web.

7. The second moment of area of transverse web stiffeners not subjected to external loads or moments is given by
a) I_s ≤ 0.75dt_w²
b) I_s ≥ 0.75dt_w²
c) I_s ≤ 1.5dt_w²
d) I_s ≥ 12.5dt_w
Answer: b
Clarification: Transverse stiffeners not subjected to external loads or moments should have second moment of area Is about centreline of the web, if stiffeners are on both sides of the web and about face of the web, if stiffener is on only one side of the web such that Is ≥ 0.75dt_w² for c/d ≥ √2 and Is ≥ 1.5dt_w²/c² for c/d < √2.

8. Which of the following buckling check is applied to stiffeners?
a) [(V+V_c)/γ_m0] ≤ F_qd
b) [(V+V_c)γ_m0] ≥ F_qd
c) [(V-V_c)/γ_m0] ≤ F_qd
d) [(V-V_c)γ_m0] ≥ F_qd
Answer: c
Clarification: Stiffeners not subjected to external loads or moments should be checked for buckling for a force F_d = [(V-V_c)/γ_m0] ≤ F_qd, where F_qd is design resistance of intermediate stiffeners, V is factored shear force adjacent to the stiffener, V_cr is shear buckling resistance of the web panel designed without using tension field action. This check is required for intermediate stiffeners only when tension field action is utilized in webs.

9. The interaction expression for stiffeners subjected to external loads or moments is given by
a) [(F_q-F_s)/F_qd]+(F_s/F_sd)+(M_q/M_yq) < 1
b) [(F_q-F_s)/F_qd]+(F_s/F_sd)+(M_q/M_yq) > 1
c) [(F_q-F_s)/F_qd]-(F_s/F_sd)-(M_q/M_yq) < 1
d) [(F_q+F_s)/F_qd]-(F_s/F_sd)-(M_q/M_yq) > 1
Answer: a
Clarification: Stiffeners subjected to external loads and moments should meet the conditions of load carrying stiffeners. In addition, they should satisfy the following interaction equation: [(F_q-F_s)/F_qd]+(F_s/F_sd)+(M_q/M_yq) q is stiffener force, F_qd is design resistance of intermediate stiffeners corresponding to buckling about axis parallel to the web, F_s is external load or reaction at stiffener, F_sd is design resistance of load carrying stiffener corresponding to buckling about axis parallel to the web, Md is moment on the stiffener due to eccentrically applied load and transverse load, M_yq is yield moment capacity of stiffener based on its elastic modulus about its centroidal axis parallel to the web.

10. Which of the following is not true regarding longitudinal stiffeners?
a) longitudinal stiffeners increase buckling resistance considerably as compared to transverse stiffeners
b) they consist of plane section for welded plate girder
c) first horizontal stiffener is provide at one-fifth of distance from compression flange
d) first horizontal stiffener is provide at neutral axis
Answer: d
Clarification: Longitudinal stiffeners are also called horizontal stiffeners. They increase buckling resistance considerably as compared to transverse stiffeners when the web is subjected to buckling. They consist of angle section for riveted/bolted plate girder and plane section for welded plate girder and are provided in the compression zone of the web. The first horizontal stiffener is provide at one-fifth of distance from compression flange to tension flange. If required another stiffener is provided at the neutral axis.

11. The connection of intermediate transverse stiffeners are designed for shear of
a) t_wb_s
b) t_w²/5b_s
c) t_w²5b_s
d) t_w5b_s
Answer: b
Clarification: Intermediate transverse stiffeners not subjected to external loading should be connected to the web so as to withstand a shear between each component of the stiffener and the web not less than t_w²/5b_s, where t_w is thickness of web, b_s is outstand width of stiffener.

12. The second moment of area of torsional stiffeners about center line of the web is given as
a) I_s ≤ αs_sD³
b) I_s ≤ 0.34α_sD³T_cf
c) I_s ≥ 0.34α_sD³T_cf
d) I_s ≥ α_sD³
Answer: c
Clarification: When bearing stiffeners are required to provide torsional restraint at the support of the beams, the second moment of area of the stiffener section about center line of the web should be such that I_s ≥ 0.34α_sD³T_cf , where αs = 0.006 for L_LT/r_y ≤50, 0.3/( L_LT/r_y) for 50LT/r_y≤100, 30/( L_LT/r_y)² for L_LT/r_y ≥100, D = overall depth of beam at the support, T_cf = maximum thickness of compression flange in the span under consideration, KL = laterally unsupported effective length of compression flange of beam, r_y = radius of gyration of the beam about minor axis.

Design of Steel Structures Multiple Choice Questions on “Types of Steel”.

1. Which of the following is the property of high carbon steel?
a) high toughness
b) reduced ductility
c) high strength
d) reduced strength
Answer: b
Clarification: High carbon steel contains high carbon content. Hence it has reduced ductility, toughness and weldability.

2. High carbon steel is used in ______________
a) transmission lines and microwave towers
b) structural buildings
c) fire resistant buildings
d) for waterproofing
Answer: a
Clarification: High carbon steel is used in transmission lines and microwave towers where relatively light members are joint by bolting.

3. What is the permissible percentage of micro-alloys in medium and high strength micro-alloyed steel?
a) 0.1%
b) 0.5%
c) 0.25%
d) 1.0%
Answer: c
Clarification: Medium and High strength micro-alloyed steel have low carbon content, but alloys such as niobium, vanadium, titanium or boron are added to achieve high strength.

4. Fire resistant steels are also called as ____________
a) Stainless steel
b) Weathering steel
c) High strength steel
d) Thermomechanically treated steel
Answer: d
Clarification: Fire resistant steels are also called as thermomechanically treated steel. They perform better than ordinary steel under fire.

5. What is the minimum percentage of chromium and nickel added to stainless steel?
a) 0.5%, 10.5%
b) 2%, 20%
c) 10.5%, 0.5%
d) 30%, 50%
Answer: c
Clarification: Stainless steel are low carbon steels to which a minimum of 10.5% chromium (maximum 20%) and 0.5% nickel is added.

6. Match the pair of Type of steel with its ultimate tensile strength :

	TYPE OF STEEL					ULTIMATE TENSILE CAPACITY
(A) Carbon Steel 					(i) 700-950 MPa
(B) High Strength Carbon Steel				(ii) 440-590 MPa
(C) Weathering Steel					(iii) 410-440 MPa
(D) High Strength quenched & tempered steel		(iv) 480 MPa
(E) Medium and High strength microalloyed steel	        (v) 480-550 MPa

a) A-i, B-ii, C-iii, D-iv, E-v
b) A-v, B-iv, C-iii, D-ii, E-i
c) A-iii, B-v, C-iv, D-i, E-ii
d) A-ii, B-iii, C-v, D-i, E-iv
Answer: c
Clarification: Ultimate tensile strength is the capacity of material to withstand loads tending to elongate. It is the maximum stress that a material can withstand while being stretched or pulled. The ultimate tensile strength for Carbon Steel is 410-440 MPa, 480-550 MPa for High Strength Carbon Steel, 480 MPa for Weathering Steel, 700-950 MPa for High Strength quenched & tempered steel, 440-590 MPa for Medium and High strength microalloyed steel.

7. What is weathering steel?
a) low-alloy atmospheric corrosion-resistant steel
b) low-carbon steel
c) high strength quenched and tempered steel
d) fire resistant steel
Answer: a
Clarification: Weathering steel are low-alloy atmospheric corrosion-resistant steel. They are often left unpainted. They have an ultimate tensile strength of 480 MPa.

8. Match the pair of Type of steel with its yield strength:

	TYPE OF STEEL					YIELD STRENGTH
(A) Carbon Steel 					(i) 300-450 MPa
(B) High Strength Carbon Steel				(ii) 350 MPa
(C) Weathering Steel					(iii) 350-400 MPa
(D) High Strength quenched & tempered steel		(iv) 230-300MPa
(E) Medium and High strength microalloyed steel	        (v) 550-700 MPa

a) A-i, B-ii, C-iii, D-iv, E-v
b) A-i, B-iii, C-v, D-iv, E-ii
c) A-v, B-iv, C-iii, D-ii, E-i
d) A-iv, B-iii, C-ii, D-v, E-i
Answer: d
Clarification: Yield Strength is the stress that a material can withstand without any permanent deformation i.e. the point of stress at which any material starts to deform plastically. The yield strength of carbon steel is 230-300MPa, 350-400 MPa for High Strength Carbon Steel, 350 MPa for Weathering Steel, 550-700 MPa for High Strength quenched & tempered steel, 300-450 MPa for Medium and High strength microalloyed steel.

Design of Steel Structures Multiple Choice Questions on “Types and Properties of Welding”.

1. Arrange the following welds in ascending order as per their usage in structural engineering applications.
a) fillet weld, groove weld, slot and plug weld
b) slot and plug weld, groove weld, fillet weld
c) groove weld, fillet weld, slot and plug weld
d) fillet weld, slot and plug weld, groove weld
Answer: b
Clarification: Fillet welds are used extensively (about 80%) followed by groove welds (15%). Slot and plug welds are rarely used (less than 5%) in structural engineering applications.

2. Which of the following type of weld is most suitable for lap and T-joints?
a) Fillet weld
b) Groove weld
c) Slot weld
d) Plug weld
Answer: a
Clarification: Fillet welds are suitable for lap and T-joints and groove welds are suitable for butt, corner, and edge joints.

3. Which of the following is true about back-up strip provided at bottom of single-V grooves?
a) Back-up strips are commonly used when welding is done from both the sides
b) Back-up strips are commonly used when root opening is sufficient
c) It creates a problem of burn-through
d) It introduces a crevice into the weld geometry
Answer: d
Clarification: Back-up strip is provided at the bottom of single-V/bevel/J or U grooves. It is commonly provided when welding is done from one side or when the root opening is excessive. It introduces a crevice into the weld geometry and prevents the problem of burn-through.

4. The size of root gap and root face for groove weld does not depend on :
a) type of welding process
b) welding position
c) type of metal plate
d) volume of deposited material
Answer: c
Clarification: For groove weld, the root opening or gap is provided for the electrode to access the base of the joint. The size of root gap and root face depends on the following : (i) type of welding process, (ii) welding position, (iii) volume of deposited material, (iv)cost of preparing edges, (v)access for arc and electrode, (vi)shrinkage and distortion.

5. Which of the following groove weld is used for plates of thickness more than 40mm?
a) Double-bevel
b) Single-J
c) Single-U
d) Double-U
Answer: d
Clarification: The groove is made of double-bevel or double-V for plates of thickness more than 12mm, and made of double-U or double-J for plates of thickness more than 40mm. For plates of thickness between 12-40mm, single-J and single-U grooves may be used.

6. Groove welds should have ________ strength as member they join.
a) same
b) less
c) greater
d) half
Answer: a
Clarification: Groove welds will transmit full load of the members they join, so they should have the same strength as the members they join.

7. Which of the following is not true regarding fillet welds?
a) They require less precision in fitting up two sections
b) They are adopted in field as well as shop welding
c) They are assumed to fail in tension
d) They are cheaper than groove welds
Answer: c
Clarification: Fillet welds require less precision in fitting up two sections. They are adopted in field as well as shop welding. They are assumed to fail in shear and are cheaper than groove welds.

8. Which of the following is true about slot and plug welds?
a) They are extensively used in steel construction
b) They are assumed to fail in shear
c) The inspection of these welds is easy
d) They are normally used to connect members carrying tensile loads
Answer: b
Clarification: Slot and plug welds are not extensively used in steel construction. They are used to fill up holes in connections. They are assumed to fail in shear. The inspection of these welds is difficult. They are useful in preventing overlapping parts from buckling.

9. Choose the correct option regarding weld metal.
a) Weld metal is same as parent metal
b) Weld metal is same as steel
c) It has higher yield to ultimate ratio
d) It has higher ductility compared to structural steel
Answer: c
Clarification: Weld metal is a mixture of parent metal and steel melted from electrode. The solidified weld metal has properties characteristic of cast steel. It has higher yield to ultimate ratio but lower ductility compared to structural steel.

10. Which of the following is not true regarding pre-heating of heat affected zone ?
a) Pre-heating does not help to reduce heat affected zone cracks
b) Pre-heating increases the cost of welding
c) It is done to remove surface moisture in highly humid conditions
d) It is done to disperse hydrogen away from weld pool and heat affected zone
Answer: a
Clarification: Pre-heating of joints help to reduce heat affected zone cracks but increases the cost of welding. It is done to remove surface moisture in highly humid conditions, to disperse hydrogen away from weld pool and heat affected zone, to bring steel to ambient temperature in cold climates.

Design of Steel Structures Multiple Choice Questions on “Local Buckling of Plates”.

1. Buckling occurs to members or elements mainly subjected to ________
a) seismic forces
b) tensile forces
c) compressive forces
d) shear forces
Answer: c
Clarification: Buckling may be defined as structural behavior in which mode of deformation develops in direction or plane perpendicular to that of bending which produces it. Such deformation changes rapidly with increase in magnitude of applied loading. It occurs mainly members or elements that are subjected to compressive forces.

2. The critical stress of infinite plate having width b and thickness t loaded by compressive forces acting on simply supported sides is given by
a) (kπ²E)/ [12(1-μ²)(b/t)].
b) (kπ²E)/ [12(1-μ²)(b/t)²].
c) (kπ²E)/ [12(1+μ²)(b/t)].
d) (kπ²E)/ [12(1+μ²)(b/t)²].
Answer: b
Clarification: The critical stress of infinite plate having width b and thickness t loaded by compressive forces acting on simply supported sides is given by
f_cr = (kπ²E)/ [12(1-μ²)(b/t)²],
where μ is Poisson’s ratio of material, b/t is width-to-thickness ratio of plate, k is buckling coefficient and E is Young’s modulus of rigidity of material. The value of coefficient k depends on constraints along non-loaded edges of plate.

3. Which of the following statement is correct?
a) stiffened elements are supported along one edge perpendicular to axial stress
b) un-stiffened elements are supported along one edge perpendicular to axial stress
c) stiffened elements are supported along one edge parallel to axial stress
d) un-stiffened elements are supported along one edge parallel to axial stress
Answer: d
Clarification: Unstiffened elements are supported along one edge parallel to axial stress (eg : legs of single angles, flanges of beams, and stems of T-section). Stiffened elements are supported along both the edges parallel to axial stress (eg: flanges of square and rectangular hollow sections, perforated cover plates, and webs of I-sections and channel sections).

4. Lowest value of buckling coefficient for simply supported plates is _____
a) 4.0
b) 2.0
c) 5.0
d) 3.0
Answer: a
Clarification: The lowest value of buckling coefficient for simply supported plates is 4.0. The buckilng stress depends upon buckling coefficient.

5. The buckling stress f_cr varies _____
a) inversely as plate slenderness or width-to-thickness ratio
b) directly as plate slenderness or width-to-thickness ratio
c) inversely as square of plate slenderness or width-to-thickness ratio
d) directly as square of plate slenderness or width-to-thickness ratio
Answer: c
Clarification: The buckling stress f_cr varies inversely as square of plate slenderness or width-to-thickness ratio, √(f_y /f_cr) = (b/t)√{(f_y / E)[12(1-μ²)/(π²k)]} .

6. The buckling coefficient for thin flat plate free along one longitudinal edge is given by
a) k = 0.425 + (b/a)
b) k = 0.425 + (b/a)²
c) k = 0.425 + (a/b)²
d) k = 0.425 – (b/a)²
Answer: b
Clarification: For a thin plate simply supported along both transverse edged and one longitudinal edge and free along the other longitudinal edge, the buckling coefficient can be approximated by k = 0.425 + (b/a)².

7. The elastic buckling stress of thin flat plate of length L, depth d and thickness t simply supported along four edges and loaded by shear stresses distributed uniformly along its edges is given by
a) f_cr = kπ²E / [12(1-μ²)(d/t)²].
b) f_cr = kπ²E / [12(1+μ²)(d/t)²].
c) f_cr = kπ²E / [12(1-μ²)(d/t)].
d) f_cr = kπ²E / [12(1+μ²)(d/t)].
Answer: a
Clarification: The elastic buckling stress f_cr of thin flat plate of length L, depth d and thickness t simply supported along all four edges and loaded by shear stresses distributed uniformly along its edges is given by f_cr = kπ2E / [12(1-μ²)(d/t)²], where buckling coefficient can be approximated by k=5.35 + 4(d/L)², when L ≥ d and k = 5.35(d/L)2 + 4, when L ≤ d.

8. The elastic buckling stress for thin flat plate of length L, depth d and thickness t simply supported along four edges and loaded by bending stress distribution is given by
a) f_cr = π²E/k[12(1-μ²)(d/t)²].
b) f_cr = π²E/k[12(1+μ²)(d/t)²].
c) f_cr = kπ²E/[12(1+μ²)(d/t)²].
d) f_cr = kπ²E/[12(1-μ²)(d/t)²].
Answer: d
Clarification: The elastic buckling stress for thin flat plate of length L, depth d and thickness t simply supported along all four edges and loaded by bending stress distribution, which varies linearly across its width is given by f_cr = kπ²E/[12(1-μ²)(d/t)²], where buckling coefficient k depends on aspect ratio L/d and the number of buckles along the plate.

9. Which of following statement is correct?
a) elastic buckling stress may be decreased by using longitudinal stiffeners
b) elastic buckling stress may be decreased by using intermediate stiffeners
c) elastic buckling stress may be increased by using intermediate transverse stiffeners
d) elastic buckling stress is not affected by intermediate or longitudinal stiffeners
Answer: c
Clarification: The elastic buckling stress may be increased by using intermediate transverse stiffeners (which will decrease the aspect ratio L/d, thus increasing the value of buckling coefficient), or by using longitudinal stiffeners to decrease the depth-thickness ratio.

10. Match the following values of limiting b/t or d/t ratio for various cases

	Plates			                 (b/t))√(fy /250) or (d/t)√(fy /250)
 
i. Simply supported plates					A) 17.5
ii. Long plate elements in shear				B) 131.4
iii. Long plate elements free along one longitudinal edge	C) 81.9
iv. Long plate elements in bending				D) 53.8

a) i-A, ii-B, iii-C, iv-D
b) i-D, ii-C, iii-A, iv-B
c) i-C, ii-D, iii-B, iv-A
d) i-D, ii-C, iii-B, iv-A
Answer: b
Clarification: i) For simply supported plates, if material ceases to be linearly elastic at yield stress f_y, the width-to-thickness ratio b/t is given by (b/t)√(f_y /250) = 53.8
ii) For long plate elements simply supported along both transverse edges and one longitudinal edge and free along other longitudinal edge, elastic buckling stress is equal to yield stress if (b/t)√(f_y/250) = 17.5
iii) The elastic buckling stress is equal to yield stress in shear τy = f_y/√3 when (d/t)√(f_y/250) = 81.9
iv) For long plates elements simply supported along four edges and loaded by bending stress distribution, limiting ratio d/t may be given as (d/t)√(f_y/250) = 131.4.