VETRI VINAYAHA COLLEGE OF ENGINEERING AND TECHNOLOGY

DEPARTMENT OF CIVIL ENGINEERING

Third years

CE6603 - DESIGN OF STEEL STRUCTURES

UNIT – I - CONNECTIONS – RIVETED, WELDED & BOLTED 1. Mention the advantages and disadvantages of steel structures?

Advantages: Ability to resist high loads

Due to its high density, steel is completely non-

porous Durability Easy to disassembling or replacing some steel members of a structure

Disadvantages:

Corrosion

At high temperature steel loses most of its strength, leading to deformation or failure

2. What is meant by Girder? Girder means a major beam frequently at wide spacing that supports small beams. 3. What is meant by joists?

It is a closely spaced beam supporting the floors and roofs of buildings. 4. What is meant by Purlins?

It is a roof beam usually supported by truss.

5. What is meant by Rafters?

It is a roof beam usually supported by purlin. 6. What is meant by Lintel?

It is a beam over window or door openings that support the wall

above. 7. What is Girts?

It is horizontal wall beams used to support wall covering on the side of an industrial

building. 8. What is meant by Spandrel beam?

It is beam around the outside perimeter of a floor that supports the exterior walls and the outside edge of the floor.

9. Name the different types of connections? Riveted connections

Welded connections

Bolted connections

Pinned connection

10. Name the types of riveted connections? Lap Joint - single riveted and double riveted

Butt joint – single cover and double cover

11. What is meant by rivet value?

The least of the strengths in shearing and bearing is the rivet value.

12. What is meant by gauge distance?

The perpendicular distance between two gauge lines, is called gauge distance. 13. Name the different modes of failure of a riveted joint?

Tearing failure of the plate

Shear failure of the plate

Shear failure of the rivet

Bearing failure of the rivet

Splitting failure of plate

14. As per the American practice where the neutral axis lie in the rivet group?

It is assumed that the line of rotation lies at a distance of 1/7 th of the effective bracket

depth from the bottom of the bracket

15. What are the factors that govern will govern the structural design? Foundation movements

Elastic axial shortening

Soil and fluid pressures

Vibration Fatigue

Impact (dynamic effects)

16. What are the load combinations for the design purposes? Dead load + Imposed Load (Live load)

Dead Load + Imposed Load + Wind Load or earthquake load

Dead Load + Wind Load or Earthquake load

17. What are the steps involved in structural design?

Forces or loads Structural arrangement and material selection analyzing

Internal stresses proportioning of members

PART – B 1.Determine the strength of a double cover butt cover butt joint used to connect two flats 200

F.The thickness of each cover plate is 8 mm. flat shave been joined by 9 rivets in chain riveting

at a gauge of 60 mm. What is the efficiency of the joint? 2. A load of 150 kN is applied to a bracket plate at an eccentricity of 300mm.sixteen rivets of 20

mm nominal diameter are arranged in two rows with 8rivets per row. The two rows are 200 mm apart and the pitch is 80 mm. if the bracket plate is 12.5 mm thick, investigate the safety of the

connection. Given,s = 100 N / mm2,fb = 300 N / mm

2 and ft = 150 N / mm

2.

3. What are the types of load to be account for steel design? 4. A bridge truss carries an axial pull of 400 KN. It is to be a gusset plate22mm thick by a double

cover butt joint with 22 mm diameter power driven rivets. Design an economical joint.

Determine the efficiency of the joint 5. Two plates 12 mm and 10 mm thick are joined by a triple riveted lap joint, in which the pitch of the central row of rivets is 0.6 times the pitch of rivets in the outer rows. Design the joint

and find its efficiency. Take óat = 150 N/mm2&ópf= 250 N/mm

2. (May / June 2007)

6.A double riveted double cover butt joint is used to connect plates 12 mm thick. Using Unwin’s

formula, determine the diameter of rivet; rivet value, gauge and efficiency of joint. Adopt the

following stresses: Working stress in shear in power driven rivets = 100 N / mm

2 (MPa)

Working stress in bearing in power driven rivets = 300 N / mm

2 (MPa)

Working stress in axial tension in plates = 0.6 fy 7. A bracket carrying a load of 100 kN is connected to column by means of two horizontal fillet

welds, of 130 mm effective length and 10 mm thick. The load acts at 70 mm from the face of

the column as shown. Find the throat stress. (May / June 2007) 8. A tie member 75 mm X 8mm is to transmit a load of 90 kN. Design the fillet weld

and calculate the necessary overlap. (Nov / Dec 2007) 2. A single bolted double cover butt joint is used to connect two plates 8mmthick. Assuming

20mm bolts at 50mm pitch calculate the efficiency of the joint. The thickness of cover plate

is 4mm 3. The figure shows the joint in the bottom chord continuous member of the truss. Design

the connection using M16 black bolt of property class 4.6 and grade Fe410 steel. Assume

edge distance of 35 mm and minimum pitch. 4. Design the seat angle connection between the beam ISMB 250 and column ISHB 250 for

a reaction from beam equal to 85 KN. Use M16 black bolt of property class 4.6 and grade

Fe410 steel with fy =250 MPa. 5. A beam ISWB 550 having equal flange width to that of column, transfers a factored

end reaction of 275 KN to the flange of the column ISSC 250. Design the stiffened seat

angle connection using 20 mm bolts of grade 4.6, fy =250MPa.

6. A plate in which the axial tension is 520Kn is to be provided with a splice joint. The size

of the plate is 400mm x 20mm. Design a suitable rivet joint. 7. Design a double riveted cover butt joint to connect 2 plates of 12mm thick. Adopt power

driven rivets. Take fy = 250MPa. Find also the efficiency of the joint.

UNIT – II - TENSION MEMBERS

1. Tie member – Explain.

Tie member or a tension member is a structural element carrying an axial tensile force.

For the tensile force to be axial it is necessary that the load be applied through centroid of the

section of the member. But under axial tension the member gets straightened and eccentricity of

the force decreases.

The member is almost straight at the yield point and the distribution of the stress over the

section becomes uniform.

2. How the tension members are classified?

It is classified according to its shape and size and it depends upon the type of structures.

Wires and cables – Used in hoists, derricks, suspenders in suspension bridges

Rods and bars – Used in radio tower, small spanned roof trusses with different

cross-sections such as round, rectangular or square

3. What is meant by single section member?

Structural sections such as I-section, T-section, angle, and channel are used as tension

members. As the structural shapes provide more rigidity than cables or rods, their buckling

tendency under compression load is reduced and so can be used where reversal of stress takes

place.

4. Under what circumstances you would go for Built-up members?

When single structural sections fail to provide required strength and stiffness to carry

tension as well as compression in case of reversal of stresses, built-up members are used.

5. How the tension members are selected?

It depends upon the various factors such as type of fabrication, type of structure, type of

loading, i.e. whether the member undergoes reversal of stresses, and the maximum tension to be

carried by the member.

6. Sketch the different forms a single section member.

7. How is net effective area of single angle used as tension member calculated?

Effective area = A1 + A2K

A1- Net area of connected leg

A2- area of outstanding leg

K =

3A1

3A1x A2

8. What is net sectional area of a tension member? How it is calculated in chain riveting?

The gross sectional area of the tension member minus the sectional area of the maximum

number of rivet/bolt holes is known as net sectional area. In case of chain riveting,anet= (b – nd)

t

9. What is Lug angle?

A larger length of the tension member and the gusset plate may be required sometimes to

accommodate the required number of connection rivets. But this may not be feasible and

economical. To overcome this difficulty lug angles are used in conjunction with main tension

members at the ends.

It provides extra gauge lines for accommodating the rivets and thus enables to reduce the

length of the connection. They are generally used when the members are of single angle, double

angle or channel sections.

10. What are the main objectives of the lug angles?

They produce eccentric connections, due to rivets placed along lug angle. The centroid

of the rivet system of the connection shifts, causing eccentric connection and bending moments.

Stress distribution in the rivets connecting lug angles is not uniform.

It is preferred to put a lug angle at the beginning of the connection where they are more effective

and not at the middle or at the end of the connection.Rivets on the lug angles are not as efficient

as those on the main member.

The out-standing leg of the lug angle usually gets deformed and so the load shared by the

rivets on the lug angles is proportionately less.

11. What is meant by Tension splice?

Splicing of tension members is necessary when the required length of the member is

more than the length Available or when the member has different cross-sections for different

parts of its length. If actual member

is to be of

. Greater length, two or more lengths shall have to

be spliced at the joints.

12. What is the net effective area of a pair of angles placed back to back connected by one

leg of each angle subjected to tension?

Anet = A1 + A2 K

A1 - effective cross – section area of connected legs

A2 – Gross area of outstanding legs

K =A 2 +5A

13. What is the permissible stress in axial tension?

As per IS: 800 – 1984, the permissible stress in axial

tension σat = 0.6 fy N/mm2

fy = minimum yield stress in steel in N /mm2.

14. How will you join the member of different thickness in a tension member?

When tension member of different thickness are to be jointed, filler plates may

be used to bring the member in level.

15. What happens when a single angle with one leg is connected to a gusset plate, which is

subjected to an eccentric load?

The rivets connecting the angle to the gusset plate does not lie on the line of action of

load. This gives rise to an eccentric connection due to which the stress distribution becomes non-

uniform.

The net cross-sectional area of such a section is reduced to account for this non-uniform

stress distribution resulting from eccentricity.

PART – B 1.Using a lug angle, design a suitable joint for 100 mm x 65mm x 10 mm angle, used as a

tension member .use 20 mm diameter rivets and thickness of gusset plate 8 mm. 2. The bottom tie of roof truss is 4m long .in addition to an axial tension of1000 kN, it has to

support at its Centre a shaft of load of 3600N. The member is composed of two angles 100 mm

x 7. mm x 10 mm with the longer legs turned down and placed back to back on either side of

10 mm gusset plate. The angles are tack riveted at 92 mm centres with 20 mm diameter

rivets.

3.Design a horizontal tension member carrying a load 600 KN, The length of the member is 3

m. The member is connected to 4.5 mm thick gusset plate with 20 mm rivets. 4.Design the tension strength of a roof truss diagonal 100 X 75 X 10 mm connected to the gusset

plate by 20 mm diameter power driven rivets in one row along the length of the member. The

short leg of the angle is kept outstanding. (NOV/DEC 2007) 5.A bridge truss diagonal carries an axial pull of 300 KN .Two mild steel flats250 ISF 10 and

ISF 18 of the diagonal are to be jointed together. Design a suitable splice

6.Design a double angle tension member carrying axial tensile force of 300kN in addition to

this, it is also subjected to a uniformly distributed load of 0.4kN/m throughout its length,

including self weight. The centre to centre distance between the end connections is 2.7 m.

(MAY/JUNE2007)

7.Design a tension splice to connect two plates of size 220 mm X 20 mm and200 mm X 10 mm,

for a design load of 220 kN. Also sketch the details of the riveted joint. (MAY/JUNE2007

8. The main tie of a roof truss consists of ISA 150 X 115 X 8 mm and is connected to a

gusset plate by 18 mm diameter rivets. Find out the maximum load it can carry. 9. A double angle ISA 75mm x 75mm x 8mm back to back welded to one side of a 12mm gusset

have allowable stress 150MPa. Determine the allowable tensile load on the members and weld

length and overlap length of gusset plate. 10. An ISA 100mm x 100mm x 12mm is used as a tie riveted to a gusset plate with 24mm

rivets arranged in one row along the length of the angle. Determine the allowable tension on the

angle if the allowable tensile stress is 150 MPa.

UNIT – III - COMPRESSION MEMBERS

1. What do you mean by compression members?

Compression members are the most common structural elements and it is termed

as columns, struts, posts or stanchions. They are designed to resist axial compression.

2. Name the modes of failures in a column.

Failure of the cross-section due to crushing or yielding Failure by buckling,

due to elastic instability mixed mode of failure due to crushing and buckling.

3. Define slenderness ratio.

It is defined as the ratio of effective length l of the column to the least radius

of gyration r of the column section.

4. Classify the columns according to the slenderness ratios.

Short columns - l/r <60

Medium columns - 60< l/r <100

Long columns - l/r >100

5. Distinguish column and strut.

Columns are the vertical members which carry the loads to the beams, slabs etc,

generally they are used in ordinary buildings.

Struts are commonly used for compression members in a roof truss; it may either be

in vertical position or in an inclined position.

6. What is meant by stanchions?

These are the steel columns made of steel sections, commonly used in

7. What is Post?

It is loosely used for a column, but in truss bridge girders, end compression

members are called end posts.

8. What is a boom?

It is the principal compression member in a crane.

9. State the assumptions that made in Euler’s theory.

The axis of the column is perfectly straight when unloaded. The line of thrust coincides

exactly with the unstrained axis of the strut. The flexural rigidity EI is uniform the material is

isotropic.

10. Why the lateral systems are provided in compound columns?

If the plates are not connected throughout their length of the Built up sections, lateral

systems may be provided, which act as a composite section. In such cases the load carrying

elements of the built-up compression member in the relative position, without sharing any axial

load. However when the column deflects, the lateral system carries the transverse shear force.

11. Name the lateral systems that are used in compound columns and which is the mostly

used one?

Lacing or latticing, Battening or batten plates, perforated cover plates.

Lacing or latticing is the most common used lateral system and the sections are flats,

angles and channels.

12. What will be the thickness for the single and double lacing bars?

The thickness of flat lacing bars shall not be less than one-fortieth of the length between

the inner end rivets or welds for single lacing, and one-sixtieth of the length for double lacing.

13. What is the purpose of providing battens in compound steel columns?

Batten plates consist of flats or plates, connecting the components of the built-up columns

in two parallel planes.

These are used only for axial loading. Battening of the composite column should not be

done if it is subjected to eccentric loading or a applied moment in the plane of battens.

14. What is the thickness of a batten plate?

The thickness of batten plate shall not be less than one fiftieth of the distance between the

inner most connecting lines of rivets or welds. This requirement eliminates lateral buckling of

the batten.

15. Where the perforated cover plates are used and mention its advantages?

They are mostly used in the box sections, which consist of four angle sections so

that the interior of column remains accessible for painting and inspection.

Advantages: They add to the sectional area of column and the portions beyond the perforation

share axial load to the extent of their effective area.

There is economy and fabrication and maintenance

Perforations conveniently allow the riveting and painting work on the inside portion

16. Name the types of column base?

Slab Base, which is a pinned base.

Gusseted base, which is a rigid base.

17. State the purpose of column base?

The base of the column is designed in such a way to distribute the concentrated column load over

a definite area and to ensure connection of the lower column end to the foundation.

It should be in adequate strength, stiffness and area to spread the load upon the concrete or other

foundations without exceeding the allowable stress.

18. Give the difference between slab base and gusseted base for steel columns.

Slab base is a thick steel base plate placed over the concrete base and

connected to it through anchor bolts.

The steel base plate may either be shop-welded to the stanchion, or else can

be connected at the site to the column through cleat angles.

19. What is slab base and for what purpose is it provided?

The base plate connected to the bottom of the column to transfer over wider area is

known as slab base. Column end is machined to transfer the load by direct bearing. No gusset

materials are required.

20. When the slenderness ratio of compression member increases, the permissible stress

decreases. Why?

The section must be so proportioned that it has largest possible moment of inertia for the

same cross-sectional area. Also the section has approximately the same radius of gyration about

both the principal axes.

21. State the possible failure modes of an axially loaded column.

Local buckling failure

Squashing

Overall flexural buckling

Torsional and flexural Torsional buckling

22. What is meant by slenderness ratio?

Slenderness ratio is defined as the ratio of effective length of compression member

to its last radius of gyration. It is denoted by λ. Slenderness ratio λ=Effective

length (KL)/least radius of gyration(r).

23. What is the allowable slenderness ratio for compression members?

Sl.no Member Maximum effective

ratio(KL/r)

1. A member carrying compressive loads resulting from dead

load and imposed loads.

180

2. A tension member in which a reversal of direct stress

occurs due to loads other than wind load or seismic forces.

180

3. A member subjected to compression forces resulting only

from combination with wind/earthquake action, provided

the deformation of such member does not adversely affect

the stress in any part of the structure.

250

4. Compression flange of a beam against lateral Torsional

buckling.

300

5. A member normally acting as a tie in a roof truss or a

bracing system not considered effective when subjected to

possible reversal of stress into compression resulting from

the action of wind or earth quake forces.

350

24. Under what circumstances lacings are provided.

For economical design of heavily loaded long columns the least radius of gyration

of column section is increased to maximum (r y ≥ r z). To achieve the rolled

sections are kept away the centroidal axis of the column and are concentrated by

some connecting system knows as lattice system.

25. What do you mean by latticed columns .

The size and shape of standard rolled steel sections are limited because of the

limitations of rolling mills. What rolled sections do not furnish the required

sectional area when a special shape or large radius of gyration is required in two

different directions a built –up section is fabricated.

26. What is the purpose of lacing in a built up laced column?

The purpose of lacing is to hold the varies parts a column straight, parallel, at a correct

distance apart and to equalizer the stress distribution between parts.

27. Where should the splice plate be located in a column?

A splice plate should be located at the point of contra flexure of the column. If the

column ends are restrained in direction and position, this point will be at the middle

of the column due to wind stress. However due to direct load there will be two

points of contra flexure varying from the middle of column to the points above or

below the middle depending upon the amount of wind stresses.

28. What are assumptions made while designing a column?

The axis of the column is perfectly straight when unloaded.

The line of thrust coincides exactly with the unstrained axis of the strut.

The flexural rigidity EI is uniform

The material is isotropic.

29. Write any two limitations of euler’s formula.

Material is isotropic and homogeneous and is assumed to be perfectly elastic.

The column is initially straight and the load acts along the centroidal axis.

30. Define effective length.

The effective length of a compression member is the distance between the

points of contra flexures of a buckled column. It depends on the actual length

and the end condition in regards to restrained against rotation and transverse

displacement

31. List the limiting slenderness ratio of compression member carrying dead load and live

load.

Si.no Member Maximum effective

slenderness ratio (KL/r)

1. A member carrying compressive loads

resulting from dead load and imposed loads.

180

32. Define radius of gyration.

Radius of gyration is a geometrical property of a section and is denoted by

‘r’. it is given by r=

33. Define single lacing and double lacing.

Single laced systems, on opposite faces of the components being laced

together shall preferably be in the same direction so that one is the shadow of

other, instead of being mutually opposed in direction.

Double laced system, on opposite faces of the components being laced together shall preferably

be in mutual opposed in direction.

PART – B

1. Design a rolled steel beam section column to carry an axial load 1100 KN. The column

is 4 m long and adequately in position but not in direction at both ends. 2. A rolled steel beam section HB 350 @ 0.674 kN/m is used as a stanchion. If the

unsupported length of the stanchion is 4 m, determine safe load carrying capacity of the

section. 3. A double angle discontinuous strut ISA 125 mm x 95 x mm x10 mm longlegs back to

back is connected to both sides of a gusset plate 10 mm thick with 2 rivets. The length of strut

between centre-to-centre of intersections is 4m. Determine the safe load carrying capacity of

the section.

4. A steel column 12 m long carries an axial load of 1000 kN. The column is hinged at both

ends. Design an economical built-up section with double lacing. Design the lacing also. 5. Design a built-up column consisting of two channels connected by batten to carry an

axial load of 800 KN; the effective length of the column is 6 m. 6. Design a built up column 8m long to carry a load of 400kN. The column is

restrained in position but not in direction at both the ends. Provide single angle lacing

system with riveted connections. (Nov/Dec 2007) 7. Design a built up column 6m long to carry a load of 400kN. The column is

provided with Batten system. The ends of the columns are pinned. Design the battens.

(Nov/Dec 2007)

8. A discontinuous strut consists of two ISA 90X75X10mm placed to the same side of a

gusset plate 10mm thick with its longer leg back to back, with one rivet on each angle at the

ends. The effective length of the strut is 2.5m.Determine the allowable load. What is the safe

load if the strut is continuous? Take fy = 250N/mm2. The angles are connected with tack

rivets along the length. (May/June 2007) 9. A built up column consists ISHB 400@ 77.40 kg/m with one 300mm x 12mmflange

plate on each side. The column carries an axial load of 2600kN. Design a gusseted base, if the

column is supported on concrete pedestal with a bearing pressure of 5N/mm2. (May/June

2007)

10. Design a laced column for an axial load of 1200kn with an effective span of 7.5m has

one end fixed and other end hinged. Use channels for main members and an angle for lacing

bars. 11. A column of ISMB 400 is subjected to an axial force of 750kn. Design suitable base

plate. Assume necessary data required.

UNIT –IV BEAMS

1. Distinguish between laterally restrained and unrestrained beams.

Laterally restrained beam :

The laterally supported beams are also called laterally restrained beams. When

lateral deflection of the compression flange of a beam is prevented by

providing effective lateral support, the beam is said to be laterally supported.

Laterally unrestrained beam :

Beams with major axis bending and compression flange not restrained against

lateral bending fail by lateral torsional buckling before attaining their bending

strength. The effect of torsional buckling need not be considered.

2. What are the checks to be performed for beam member design?

A trail section assuming it is going to be plastic section

Then it is checked for the class it belongs.

Check for bending strength.

Check for shear strength.

Check for deflection.

3. Why to compression flanges require lateral support?

Beams are normally used so as to bend about major (z-z) axis rather than to bend about

minor (y-y) axis, since they have higher value of moment of inertia about that axis.

In such cases when the compression flange is not supported , it has a tendency to bend in

the lateral direction with twisting as shown in fig. Bending of compression flange with

twisting reduce the load carrying capacity of the section.

4. How flange plate curtailment done in plate girders?

The section of a plate girder is to be designed first at mid span. The bending moment

will goes on decreasing towards the supports. Hence the flange plates, provided at the maximum

section can be curtailed.

5. What are built up beams?

These are used for sections, for which readymade available beam section are not

sufficient. The additional requirement of moments are compensated by using additional plate

connected to the flanges of available I or channel section and they are called as built-up beams.

6. Define bi axial bending of beams.

When a beam is subjected to a loading condition that produces bending about both

the major and the minor axis, the beam undergoes bi axial bending.

7. What do you mean by web buckling?

A heavy concentrated load produces a region of high compressive stresses in the

web either at support or under the load. This causes the web either to buckle or to cripple

Web buckling occurs when the intensity of the compressive stress near the centre of the section

exceeds the critical buckling stress of the action as a struct.

8. What do you mean by castellated beam?

A rolled beam with increased depth is to be castellated. To obtain such sections, a

zigzag line is cut along the beam by an automatic flame cutting machine.

The two halves thus produced are rearranged so that the teeth match up and teeth are

then welded together.

9. What is the function of a load bearing stiffener in a plane girder?

The function of a bearing stiffer to produce any crushing of the web at locations of

heavy concentrated loads, thus bearing stiffeners transfer heavy reactions or concentrated loads

to the full depth of the web.

They are placed in pairs on the web of plate girders at unframed girder ends and

where required for concentrated loads.

They should fit tightly against the flanges being loaded and extend out towards the

edges of flange plate as far as possible.

10. What is plate girder?

A plate girder is basically an I-beam built from plates using riveting or welding. It is

a deep flexural member used to carry loads that cannot be economically carried by rolled beams.

Standard rolled sections may be adequate for many of the usual structures; but in situations

where the loads are heavier and the span is also large.

11. Write down the simple bending equation?

M/I=f/y=E/R

Where, M= Bending moment in the section

I= Moment of inertia of the section about N.A

R= Radius of curvature

Y= Distance of extreme fibre from N.A

E= Young’s modulus of elasticity

12. What is meant by lateral buckling of beam?

A long beam with laterally unrestrained compression flange when incrementally

loaded, first defects downwards and when load exceeds a particular value; it tilts sideway due to

instability of compression flange; and rotates about longitudinal axis. This phenomenon is

known as laterally buckling or torsional buckling of beam.

13. What are effects of larger deflection in beams?

Beams that deflect too much may not normally load to a structural failure, but

nevertheless endanger the functioning of the structure.

14. How the flange area of a plate girder is designed?

Flanges are designed from the consideration of strength and rigidity. For a non

pomposite plate girder, the ratio of width of the flange plate and the depth of the section may be

chosen as 0.3. A f = [M z γ mo/f y d]

15. What is a beam?

A beam is a structural member, which carries a load normal to the axis. The load

produces bending moment and shear force in the beam.

16. How the beams are failed?

Bending failure

Shear failure

Deflection failure

The designs are based on these three failures which are to be determined.

17. What do you mean by bending failure? Bending failure may be due to crushing of compression flange or fracture of the tension

flange of the beam. Instead of failure due to crushing, the compression flange may fail by a

column like action with sideways or lateral buckling. Collapse would follow the lateral

buckling

18. What is the maximum deflection that to be allowed in steel beams?

The deflection of a member shall not be such as to impair the strength or efficiency of

the structure and lead to finishing. The deflection is generally should not exceed 1/325 of the

span.

19. What is web crippling?

Web crippling is the localized failure of a beam web due to introduction of an

excessive load over a small length of the beam.

It occurs at point of application of concentrated load and at point of support of a

beam. A load over a short length of beam can cause failure due to crushing and due to

compressive stress in the web of the beam below the load or above the reaction.

This phenomenon is also known as web crippling or web crushing.

20. What are laterally supported beams?

The beams which are provided with the lateral supports either by embedding the

compression flange in the concrete slab or by providing effective intermediate (support)

restraints at a number of points to restrain the lateral buckling is called laterally supported

Beam.

21. Under what situations the plated beams are used?

When a bending moment is large which cannot be resisted by the largest

available rolled beam section.

The depth of the beam is restricted due to headroom requirements.

22. Why intermediate stiffeners are required for plate girders?

The web of the plate girder relatively being tall and thin it is subjected to buckling.

Hence it is stiffened both vertically and horizontally using intermediate stiffeners.

23. What do you mean by curtailment of flanges?

The section of a plate girder is to be designed first at mid span. The bending moment

will goes on decreasing towards the supports. Hence the flange plates, provided at the

maximum section can be curtailed.

24. What is the purpose of providing the bearing stiffener?

It prevents the web from crushing and buckling sideways, under the action of

concentrated loads.

It relieves the rivets connecting the flange angles and web, from vertical shear.

PART – B 1. Design a simply supported beam to carry uniformly distributed load of 44 kN/m.The

effective Span of beam is 8 m. The effective length of compression flange of the beam is also 8

m. The ends of beam are not to free to rotate at the bearings. 2. The effective length of compression flange of simply supported beam MB 500 @0.869

kN/m. Determine the safe uniformly distributed load per metre length which can be placed over

the beam having an effective span of 8 m. The ends of beam are restrained against rotation at

the bearings.

3. ISMB 550 @1.037 kN/ m has been used as simply supported over a span of 4 m. The ends

of beam are restrained against torsion but not against lateral bending. Determine the safe UDL

per metre, which the beam can carry. 4.Design rolled steel I- sections for a simply supported beam with a clear span of 6m .it carries

a UDL of 50 KN per metre exclusive of self-weight of the girder .the beam is laterally

unsupported. 5. Check the beam section WB 500 @1.45 kN/m against web crippling and web buckling if reaction at the end of beam is 179.6 KN, The length of bearing plate at the support is 120

mm. Design bearing plate. The bearing plate is set in masonry. 6. A beam simply supported over an effective span of 7m, carries a uniformly distributed load

of 50kN/m inclusive of its own weight. The depth of the beam is restricted to 450mm. design

the beam, assuming that the compression flange of the beam is laterally supported by a floor

construction. Take fy = 250N/mm2 and E =2X105N/mm2. Assuming width of the support is

230mm. (May/June 2007). 7. Design a bearing stiffener for a welded plate girder with the following specifications. Web = 1000mm X 6mm thick. Flanges = 2 Nos. of 350X20mm plate on each side.

Support reaction = 350kN.Width of the support = 300mm.. (May/June 2007).

8. A simply supported steel joist with a 4.0m effective span carries a udl of 40kN/mover its

span inclusive of self weight. The beam is laterally unsupported. Design a suitable section.

Take fy = 250N/mm2. (Nov/Dec 2007) 9. Design the step by step procedure for design of vertical and horizontal stiffeners in a plate

girder. (Nov/Dec 2007)

10. Design a built up beam section for a span of 8m to carry a uniformly distributed load of

15 kN/m and a central concentrated load of 100 kn. The beams is laterally supported through

out. Show the curtailment of plates also. 11.A plate girder of span 15m is made-up of web plates of 1600mm x 8mm flange angles

150mmx 115mm x 10mm and two flange plates 480mm x 10mm it carries a uniformly

distributed load of 100kn/m including its own weight. Design and sketch the web splices at 5m

from one end.

10. Design a simply supported (laterally supported) of effective span 12m to carry a

factored load of 70kN/m. The depth of the beam is restricted to 500mm.

UNIT – V – ROOF TRUSSES AND INDUSTRIAL BUILDINGS

1. Name the types of roofing systems.

Flat roofing consists of either RCC construction or RSJ

slab

construction Sloping roofing

2. List the different types of roof trusses.

King post truss

Compound fink truss

Compound fan truss

Pratt truss

Simple fink truss

Simple fan truss

Howe truss

North light truss

3. What are the loads acting on the roof truss and for what load combinations should it be

designed?

Types of loads:

Dead loads

Imposed loads (live load)

Wind loads

Other loads if any like snow loads

Load combination:

Dead load +live load

Dead load +snow load

Dead load +wind load

Dead load +live load +wind load

4. List the factors affecting the economical spacing of roof truss.

Spacing of trusses is small : The cost of trusses per unit area increases . Roof

coverings cost high .

Spacing of trusses is large : The cost of these trusses per unit area decreases

but the cost of purlins increases . Roof coverings cost high.

5. What is the function of purlins ?

Purlins are beams provided over trusses to support the roofing between the

adjacent trusses.

These are placed in a tilted position over the principal rafters of the trusses.

6. What is difference between purlins and girts ?

Purlin : A roof beam usually supported by roof trusses is called as purlins

and itg usually consists of channels, angle sections or I sections.

Girt : Girts are normally used to take the floor loads in case of a flat roof .

7. List the steel section normally used in steel trusses.

Rolled steel single or double angles

T-sections

Hollow circular section

Square or rectangular section

Channel section

I – section

8. What is the use of sag rod?

These rods reduce the moment Mvv and result in a smaller purlin section. In

addition to this, sag rods can serve other useful purposes.

First, they can be provided lateral support for the purlins Second, they are

useful in keeping the purlins in proper alignment during the erection.

9. List the components of truss.

Principal rafter or top chord

Bottom chord or main tie

Ties

Struts

Sag tie

Purlins

Rafters

Ridge line

Eaves

Panel points

Roof covernings

Shoe angle

Anchor bolts

10. What are the loads to be considered for the design of gantry girder?

Vertical load from the cranes

Impact loads from crane

Longitudinal horizontal force along the crane rail

Lateral thrust across the crane rail

11. Give general guidelines for fixing spacing of roof trusses.

As a guide, the spacing of the roof trusses can be kept

¼ of the span up to 15m

1/5 of the span 15m-30m

12. Define pitch of a roof?

The pitch of a truss is the ratio of rise to the span. When the pitch of a roof

truss is less, the wind force acting on it is less.

A pitch of ¼ is very common where the roofs are to carry snow loads in

addition to wind load.

13. How do you calculate the self-weight of truss when the pitch of the roof is ¼ and the

roof covering is GI sheeting?

This formula applicable for roof truss with GI sheet and pitch is ¼ and for 4m

spacing of truss.

W= (1/100)((L/3)+5) KN/m2

L= Span of truss in meter

14. Which section is bested for purlin?

Channels, angle sections and cold formed c or z sections are widely used as

purlins.

15. Describe the assumptions made in analysis of roof trusses.

The roof truss is not restrained by reactions.

The axes of members meeting at a joint intersect at a common point.

The bolt /riveted joints in roof trusses act as friction less hinges.

16. How is economical spacing of roof trusses obtained?

The economical range of spacing of trusses is 1/5 to 1/3 of span 1.

Spacing of 3-4 for span up to 15m and 4.5-6m for spans of 15-30m for trusses

may result in economy.

17. List the various forces acting on a gantry girder.

Loads transmitted through the cranes acting vertically over the girder.

Impact loads passed from the girder due to dynamic motion and sudden

stopping of the crane with loads.

Longitudinal horizontal forces along the crane rail.

18. Where the steel roof trusses are used?

Industrial buildings, workshop buildings, storage godowns, warehouse and even for

residential buildings, school buildings, offices where the construction work is to be

completed in a short duration of time.

19. Mention the advantages of a roof truss.

Its mid-span depth is the greatest especially where bending moment in the span is the

maximum Great economy.

Sloping faces of trusses facilitate in easy drainage of rainwater.

20. What is the factor that is considered in the roof truss and why?

The factor, which is considered in the roof truss, is pitch, it is defined as the ratio of the span length

to the depth of the truss, is governed by the roofing material and other Requirements such as

ventilation and light.

21. What is gantry girder and what are the forces that are acting on it?

A gantry girder, having no lateral support in its length, has to withstand vertical loads

from the weight of the crane, hook load and impact and horizontal loads from crane surge.

22. What is meant by purlins?

Purlins are structural members which are supported on the principal rafter, and which

run transverse to the trusses. The span of the purlins is equal to the center-to-center spacing

of the trusses. The purlins support the roof covering either directly or through common

rafters. They are usually made of either an angle section or a channel section and are

therefore subjected to unsymmetrical bending.

23. Why the bracings are provided?

Bracing is required to resist horizontal loading in pin-jointed buildings, including roof

trusses. Bracing of roof trusses and supporting columns provide still rigid structure. When

wind blows normal to the inclined surface of the trusses, it is efficiently resisted by all the

members of the truss and the wind forces are transferred to the supports at the ends of the

truss.

24. Name the most common roof covering materials.

Slates Glass

Tiles Corrugated aluminum sheets

Lead sheets Galvanized corrugated iron sheets (G.I. sheets)

Zinc sheets Asbestos cement sheets (A.C. sheets)

25. Write the equation to calculate the design wind pressure.

Design pressure is p 0.6V 2 k k k V

2

z z 1 2 3 b

Vb = Basic wind speed in m/s at 10 m height

k1 = Probability factor (or risk coefficient)

k2 = Terrain, height and structure size factor

k3 =Topography factor

PART – B 1. A roof truss- shed is to be built Jodhpur city area for an industrial use. Determine the

basic wind pressure .The use of shed 18 m* 30 m 2. An industrial roof shed of size 20 m* 30 m is proposed to be constructed at Mangalore

near a hillock of 160 m and slope is 1 in 2.8. The roof shed is to be built at a height of 120 m

from the base of the hill. Determine the design wind pressure on the slope. The height of roof

shed shall be 12m 3.A communications tower of 80 m height is proposed to be built hill top height 520 m with a

gradient of 1in 5. The horizontal approach distance is 2.8 m km from the level ground .The

tower is proposed at Abu mount .Determine the design wind pressure. 4. Design a purlin for a roof truss having the following

data: Span of the truss = 6.0m

Spacing of truss = 3m c/c. Inclination of roof = 30

o\ Spacing of Purlin = 2m c/c Wind pressure = 1.5 kN/m2

Roof coverage= A.C Sheeting weighing 200 N/m2 Provide a channel section Purlin. (Dec 2007). 8. Design a gantry girder to be used in an industrial building carrying an EOT crane for the

following data: Crane capacity = 200 kN. Total self weight of all components = 240 kN. Minimum approach at the carne hook of gantry girder = 1.2m Wheel base = 3.5m C/C distance between gantry rails = 16m C/C distance between columns = 8m

Self weight of rail section = 300 N/m

Yield stress = 250 N/mm2 Design the main gantry section. Connection design not required. . (Dec 2007). Design the angle purlin for the following specifications:

Span of truss = 9m c/c.

Pitch = 1/5 of span Spacing of purlin = 1.4 c/c.

Load from roofing material = 200 N/m2.

Wind load = 1200 N/m2.

Determine the dead load, live load and wind load on a ‘Fink’ type truss for the following

data and mark the loads on the nodes of the truss. Span = 12m

Pitch = ¼ of span

Height at eves level = 10m from the ground

Spacing of truss = 5m c/c.

8.In an industrial building, the trusses of 16m span and 4m rise are spaced at 8m apart. The

building is in medium wind zone in an industrial area of plain land. Design the purlin. 9.i) List out various elements of the roof truss and mark all its significance.

Explain the design principles of Gantry girder. 10.Design a channel section purlin for the following data:

Spacing of trusses =4.2m Spacing of purlin= 2m Live load on galvanized iron roofing sheets = 0.6 kN/m

2

Wind load = 1.4 kN/m2

Slope of main rafter = 310