EASWARI ENGINEERING COLLEGE, RAMAPURAM

Transcription

MAHALAKSHMI
ENGINEERING COLLEGE
TIRUCHIRAPALLI - 621213.
QUESTION BANK WITH ANSWER
DEPARTMENT: CIVIL
SUBJECT CODE /NAME: CE 2352/DESIGN OF STEEL STRUCTURES
SEMESTER: 06
YEAR: III
UNIT V – ROOFTRUSSES AND INDUSTRIALSTRUCTURES
PART - A (2 marks)
1. What are the loads to be considered for the design of gantry girder?
(NOV/DEC 11)
The reaction from the crane girder, acting vertically downwards.
The longitudinal thrust, due to starting or stopping of crane, acting in the longitudinal
direction.
The lateral thrust, due to starting of the crab acting horizontally, normal to the gantry
girder.
2. Give general guidelines for fixing spacing of roof trusses.
(NOV/DEC 11)
The spacing between trusses is determined by the required column spacing and by
considerations of minimum cost for the structure as a whole. The usual economical spacing
ranges between 4 and 8m, with the lower limit for short truss spans and the higher limit for long
spans of about 30m or over.
3. With a neat sketch show the various components in a steel roof truss. (MAY/JUNE 12)
4. State the purpose of gantry girders.
(MAY/JUNE 12)
Gantry girders are designed as laterally unsupported beams unless the compression flange
is laterally supported by either a catwalk or by additional member.
06 Semester Civil CE2352 Design of steel structures. by M.Alaguraj AP / Civil
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5. What are the considerations for selection of a suitable type of truss? (MAY/JUNE 12)
The followings are the considerations for selection of a suitable roof truss
Roof coverings
Fabrication and transportation
Aesthetic
climate
.
6. Name the commonly used roof coverings.
(MAY/JUNE 12)
The two materials are used as roof coverings:
GI sheet
A.C. sheet
7. What are the types of roof trusses?
Kingpost truss
Queen post truss
French truss
North light truss
(NOV/DEC 12)
8. Name the components of steel roof truss.
Strut
Principal rafter
Sling
Principle tie
Tie
Purlins
GI or A.C. sheet
(NOV/DEC 12)
9. How to calculate the deflection of trusses?
The deflection of a pin jointed truss can be calculated using the strain energy method. The
deflection at a node is given by.
Δ=ΣPuL/AE
Where,
P=force in a truss member due to applied load
u=force in a truss member due to unit load applied at the node
L=Length of the truss member
A=Area of a truss member
E=young’s modulus of elasticity
10. What are main benefits of using composite floors with profiled steel decking?
i. Savings in steel weight are typically 30% to 50% over non-composite Construction
ii. Greater stiffness of composite beams results in shallower depths for the same span.
Hence lower storey heights are adequate resulting in savings in cladding costs, reduction
in wind loading and savings in foundation costs.
iii. Faster rate of construction.
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11. Explain about the importance of steel decking.
• It supports loads during construction and acts as a working platform
• It develops adequate composite action with concrete to resist the imposed loading Steel
• It transfers in-plane loading by diaphragm action to vertical bracing or shear walls
• It stabilizes the compression flanges of the beams against lateral buckling, until concrete
hardens.
• It reduces the volume of concrete in tension zone
• It distributes shrinkage strains, thus preventing serious cracking of concrete
12. What is meant by Composite Beam Stage?
The composite beam formed by employing the profiled steel sheeting is different from
the one with a normal solid slab, as the profiling would influence its strength and stiffness. This
is termed ‘composite beam stage’. In this case, the profiled deck, which is fixed transverse to
the beam, results in voids within the depth of the associated slab.
13. Write short notes on composite slab stage
The structural behavior of the composite slab is similar to that of a reinforced concrete
beam with no shear reinforcement. Steel sheeting provides adequate tensile capacity in order to
act with the concrete in bending. However, the shear between the steel and concrete must be
carried by friction and bond between the two materials. The mechanical keying action of the
indents is important. This is especially so in open trapezoidal profiles, where the indents must
also provide resistance to vertical separation.
14. What are economical considerations for industrial truss?
• Method of fabrication and erection to be followed, facility for shop fabrication available,
transportation restrictions, field assembly facilities. Steel f Technology Madras
• Preferred practices and past experience.
• Availability of materials and sections to be used in fabrication.
• Erection technique to be followed and erection stresses.
• Method of connection preferred by the contractor and client (bolting, welding or riveting).
• Choice of as rolled or fabricated sections.
• Simple design with maximum repetition and minimum inventory of material.
15. Write about basics of plastic analysis?
In plastic analysis and design of a structure, the ultimate load of the structure as a whole
is regarded as the design criterion. The term plastic has occurred due to the fact that the
ultimate load is found from the strength of steel in the plastic range.
This method is rapid and provides a rational approach for the analysis of the structure. It
also provides striking economy as regards the weight of steel since the sections required by this
method are smaller in size than those required by the method of elastic analysis.
16. What is meant by first yield moment?
As W is increased gradually, the bending moment at every section increases and the
stresses also increase. At a section close to the support where the bending moment is
maximum, the stresses in the extreme fibers reach the yield stress. The moment corresponding
to this state is called the first yield moment My, of the cross section.
17. Write about Principles of plastic analysis
(i) Mechanism condition: The ultimate or collapse load is reached when a mechanism is
formed. The number of plastic hinges developed should be just sufficient to form a mechanism.
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(ii) Equilibrium condition: ΣFx = 0, ΣFy = 0, ΣMxy = 0
(iii) Plastic moment condition: The bending moment at any section of the structure should not
be more than the fully plastic moment of the section.
18. State that Uniqueness theorem
If both the above criteria are satisfied, then the resulting load factor corresponds to its
value at rigid plastic collapse (λp).
19. Explain about Crane gantry girders
The function of the crane girders is to support the rails on which the traveling cranes
move. These are subjected to vertical loads from crane, horizontal lateral loads due to surge of
the crane, that is, the effect of acceleration and braking of the loaded crab and swinging of the
suspended load in the transverse direction, and longitudinal force due to acceleration and
braking of the crane as a whole.
20. What are the different types of floors used in steel-framed buildings?
a) Concrete slabs supported by open-web joists?
b) One-way and two-way reinforced concrete slabs supported on steel beams
c) Concrete slab and steel beam composite floors
d) Profiled decking floors
e) Pre-cast concrete slab floors.
21. What are the advantages of steel-decking floors?
(i) They do not need form work
(ii) The lightweight concrete is used resulting in reduced dead weight
(iii) The decking distributes shrinkage strains, thus prevents serious cracking
(iv) The decking stabilizes the beam against lateral buckling, until the concrete
(v) The cells in decking are convenient for locating services.
22. Write about Pre-cast concrete floors
Pre-cast concrete floors offer speedy erection and require only minimal formwork.
Light-weight aggregates are generally used in the concrete, making the elements light
and easy to handle. Typical pre-cast concrete floor slab sections are shown in Fig. It
is necessary to use cast in place mortar topping of 25 to 50 mm before installing other
Floor coverings. Larger capacity cranes are required for this type of construction when
compared with those required for profiled decking. Usually pre-stressing of the pre-cast
an element is also done.
23. What are assumptions are made for arrangement of live load in the analysis of
frames?
a) Consideration is limited to combination of:
i) Design dead load on all spans with full design live load on two adjacent spans and
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ii) Design dead load on all spans with full design live load on alternate pans.
b) When design live load does not exceed three-fourths of the design dead load, the load
arrangement of design dead load and design live load on all the spans can be used.
24. Explain about Drift Analysis
Drift in building frames is a result of flexural and shear mode contributions, due to the
column axial deformations and to the diagonal and girder deformations, respectively. In low-rise
braced structures, the shear mode displacements are the most significant and, will largely
determine the lateral stiffness of the structure.
In medium to high-rise structures, the higher axial forces and deformations in the
columns, and the accumulation of their effects over a greater height, cause the flexural
component of displacement to become dominant.
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PART B (16 MARKS)
1. Explain detail the steps involved in the design of channel purlin of a steel roof truss.
(MAY/JUNE 12)
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2. i) list out the various elements of the roof truss and mark all its significance.
(MAY/JUNE 12)
Principal rafter
Purlins
Sheeting’s
Principal tie
Struts
Principal rafter
Principal rafter is the top chord member of the truss and is subjected to compressive forces
when the loads from purlins are transferred at the nodes.
Purlins
As far as possible purlins should be located on panel points of top chord members. However it
depends upon the type of roofing materials also. Generally the spacing of purlins varies from
1.35 to 2.0m.
Sheeting’s
Commonly used sheeting’s are GI and A.C.
GI sheets
Corrugated iron sheets are galvanized for protection against corrosion and are used as
roof coverings. The common sizes of GI sheets are:
8 corrugations, 75mm wide and 19mm deep which have overall width of 660mm.
10 corrugations, 75mm wide and 19mm deep, which have overall width of 810mm.
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A.C.sheets
Asbestos cement sheets are better insulators for sun’s heat compared to GI sheet. They
are used commonly in the factories and godowns. They are available in two common shapes,
corrugated and traffold.
Principal tie
The lower chord of the truss is principal tie and carries tension. The long middle tie member of
the truss may sag because of its self weight and to check this sag tie may be provided.
Struts
Struts are the members of the truss which are under compression while those bearing tension
are called ties.
ii) Explain the design principles of gantry girder.
(MAY/JUNE 12)
The step by step design procedure of a gantry girder is as follows:
The maximum wheel load is determined.
The maximum bending moment in the gantry girder due to vertical loads.
The maximum shear force is computed.
This consists of shear force due to wheel load and dead loads from the gantry girder and
rails. The shear due to the wheel load is maximum when one of the wheels is at the support.
The lateral forces on the girder and the maximum bending moments and shear due to
these are calculated. The position of the wheels should be same as that in step 1 and
step3.
The plastic section modulus of the trial section is determined by
Mp=fyx2XA/2Xy=ZPfy
ZP,REQ=(1.4 to 1.5)Mu/fy
Section is classified.
The girder is checked for moment capacity.
Local moment carrying capacity of the girder is checked.
The girder is checked for buckling resistance.
The section is checked for shear capacity.
Buckling of the web under wheel load is checked.
The girder is checked for bearing.
Rivets/bolts or welds connecting the channel to the I section are designed.
Deflection of the gantry girder is checked.
The girder is checked for fatigue strength.
The bracket and the connection with column are designed.
3. Design an I section purlin for an industrial building to support a galvanized corrugated
iron sheet roof.
Given:
Spacing of the trusses=5.0m
Spacing of purlins=1.5m
Inclination of main rafter to horizontal=300
Weight of galvanized sheet taking into account laps and connecting bolts=130N/m2
Imposed load=1.5kN/m2
Wind load= 1.0kN/m2
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4. Design angle purlin for the following data by simplified method:
Spacing of trusses=4m
Spacing of purlins=1.6m
Weight of A.C sheets including laps and fixtures=0.205kN/m2
Live load=0.6 kN/m2
Wind load=1 kN/m2
Inclination of main rafter of truss=210
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5. Design a welded plate girder of span 30m to carry on superimposed load of 35kN/m.
avoid use of bearing and intermediate stiffeners. Use Fe415 steel.
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6. Design a welded plate girder of span 30m to carry on superimposed load of 35kN/m.
use intermediate stiffeners. Use Fe415 steel.
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7. design a simply supported gantry girder to carry one electric overhead travelling
crane, given
Span of the gantry crane=6.5m
Span of the crane girder=16m
Crane capacity=250kN
Self weight of crane excluding trolley=280 kN
Self weight of the trolley=50 kN
Minimum hook approach=1.0m
Distance between wheels=3.5m
Self weight of rails=0.3 kN/m
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8. A roof truss shed is to be built in lucknow for an industry. The size of shed is
24mx40m.the height of building is 12m at the eves. Determine the basic wind pressure.
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9. A power plant structure having maximum dimension more than 60m is proposed to
build on downhill side near dehradun. The height of the hill is 400m with a slope of 1 in
3.the location is 250m from the crest of the hill on downward slope, and its eve board is
at a height of 9m, determine the design wind pressure.
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10. Design a truss of span 15m spacing 4m to be built near Visakhapatnam with the
following details:
Class of building=general with life of 50 years
Terrain: category 2
Max.dimension:40m
Width of building: 15m
Height at eve level: 8m
Topography: less than 300
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EASWARI ENGINEERING COLLEGE, RAMAPURAM

Transcription

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