DOI : 10.17577/IJERTCONV4IS23057
- Open Access
- Total Downloads : 12
- Authors : Divya Vishnoi, Sameer Mohammad, Rishikesh Sharma, Ravi Tiwari, Ramnarayan Choudhary
- Paper ID : IJERTCONV4IS23057
- Volume & Issue : NCACE – 2016 (Volume 4 – Issue 23)
- Published (First Online): 24-04-2018
- ISSN (Online) : 2278-0181
- Publisher Name : IJERT
- License:
This work is licensed under a Creative Commons Attribution 4.0 International License
The Comparative Analysis of Strength and Cost of Connections using LSM and WSM Method
Divya Vishnoi, Sameer Mohammad, Rishikesh Sharma, Ravi Tiwari, Ramnarayan Choudhary
Department of Civil Engineering Poornima Group of Institutions, Jaipur
Abstract Connections are very important part of steel structure and are designed more than members in number.The connections are classified as, riveted connections, bolted connection, welded connections.Riveted connections were once very popular and are still used in some cases but designed to follow only Working stress method not on limit state method. In this research paper we did a comparative study of various connections as per IS800:2007 and IS800:1984.In this paper mainly focuses on connections is economical, reliable and have good strength. We talk to bearing strength, shearing strength, and design strength of connection.
Keywords Stress, throat, weld, shear, design.
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INTRODUCTION
A civil engineering designer has to ensure that the structure and facilities he designs arefit for their purpose and Safe and Economical. We all know very well L.S.M (IS800:2007) working on plastic method and W.S.M (IS800:1984) working on Elastic method and both codes are used for analysis and designing for structure element and connections members. In this paper we have analyzed differences between and results of connection members. We have choose ISA100×75×8mm and ISA100×75×10mm angle section for design Welded connections and vary thickness of angle section like 6mm, 8mm, 10mm for analysis differences of results through both L.S.M and W.S.M method for several loading condition. In bolted and Welded connections we analyze which method are safely and suitable for connection members through numerical analysis.
Concept of Elastic Method
In the elastic method of design, many combinations of loads is ascertained and the member are proportioned on the basis of working stress. These stresses should never exceed the permissible as the codal provision.
Working stress permissible stress
Concept of Limit State Method
For achieving the design criteria, the design shall be based on codal provisions of IS800:2007 values for material strengths and applied loads (actions).
Design action Design strength
Welding – Welding is the process of connecting and joining two pieces of metal by creating a strong bond between them by heating gases. It is most of the oldest and good methods of joining between two pieces of materials.
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DESIGN OF WELDED CONNECTION BY LIMIT
STATE METHOD
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Fillet Welds
Permissible stresses – Shear stress shall not exceed more 110MPa or nor as calculated using methods [1].
Effective throat thickness – Shall not be < 3mm and not > 0.7t, Where t is the thickness of the thinner plate. For stresses calculation in fillet welds joining faces inclined to each other, effective throat thickness shall be taken as K times the fillet size as to codal provision, where K is a constant.
Effective length – Shall be the overall length of weld left end returns in case of Fillet welds and shall be the overall length of weld including end returns for Butt welds.
Minimum weld length – Shall be not less than 4 times of size of weld.
Minimum size of weld – Minimum size of weld shall be not less than 3mm.
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Butt Weld`
Permissible stresses – Stresses shall not more than those permitted in parent metal.
Minimum size of weld – Specified by the effective throat thickness.
Effective throat thickness – Shall be taken as thickness of thinner part joined. For an incomplete penetration, effective throat thickness shall be taken as the minimum thickness of the weld metal common to the parts joined, excluding reinforcement not more than the thickness of the thinner part joined.
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DESIGN WELDED CONNECTION BY WORKING STRESS METHOD
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Fillet Welds
Permissible stresses – Shear stress shall not exceed 110MPa.
Effective throat thickness – Shall not be < 3 mm and not > 0.7t, where t is the thickness of the thinner plate. For stresses calculation, the effective throat thickness shall be taken as K times the fillet size, where K is a constant.
Effective length – Shall be the overall length of the weld+ 2(weld size).
Minimum weld length – Shall not be less than 4(size of the weld).
Minimum size of weld – Shall not be less than 3 mm
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Butt Welds
Permissible stresses – Stresses in weld shall not exceed those permitted in the parent metal.
Minimum size of weld – Size of butt weld shall be specified by the effective throat thickness.
Effective throat thickness – For complete penetration effective throat thickness shall be taken as the thickness of thinner part joined according codal provision.
For incomplete penetration, effective throat thickness shall be taken as the thickness of the weld metal common to the parts joined as codal provision, excluding reinforcement.
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DESIGN BOLTED CONNECTION BY LIMIT STATE
METHOD (IS800:2007)
Permissible stresses – No particular value is prescribed. Specific Procedure given for calculation of permissible loads (Axial Tension, Shear &Bearing).
Combined shear tension in bolts – No particular value is provided. Procedure given for calculation of permissible loads
Minimum pitch – Shall not be less than 2.5 times the nominal diameter of the bolt.
Minimum edge distance – Should be less 1.7 times hole dia. for sheared or hand flame cut edges, less than>1.5 times hole dia. for rolled, machine-flame cut, sawn and planed edges, from the centre of the hole..
Maximum pitch – Shall not exceed 32×thickness of thinner outside of plate or 300mm whichever is less.
Maximum edge distance – Shall not exceed 12t, where t is the thickness of the thinner router plate, and = (250/fy)
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DESIGN BOLTED CONNECTION BY WORKING
STRESS METHOD (IS800:1984)
Permissible stresses
Axial tension 120MPa Shear strength 80MPa Bearing strength 250MPa
Combined shear tension in bolts –
Individual stresses should not exceed the pre define values and combined stress ratio should not exceed 1.40.
Minimum pitch – Shall not be less than 2.5 times the nominal diameter of the bolt
Minimum edge distance – Distance from the centre of hole to the edge of a plate shall not be less than that specified in Table 8.2 in code IS800:1984 When two or more parts are connected and joined together, a line of bolts shall be provided at a distance of not more than 37 mm+ 4× thickness
of thinner plate from the nearest edge in mm. In case of work not exposed to weather, this may be increased to 12t.
Maximum pitch – Shall not exceed 32 times of thickness of thinner outside plate or 300mm whichever is less
Maximum edge distance – No specific criteria are mentioned.
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NUMERICAL ANALYSIS
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Welded Connection By Limit State Mathod
Consider a single angle section ISA 100×75×8mm. Some axial load applied on a section interval like 140kn, 160kn, 180kn, 200kn, 220kn at a 20kn load interval.10mm gusset plate used.
fwd = fwn / m and fwn = fu/3
Where fu = smaller of the ultimate stress of the weld and the parent metal and
m= partial safety factor (=1.25 for shop welds and = 1.5 for field welds)
fwd= L×t× fu/(3×1.25)
t= 0.75×s
t= thickness of weld.
S=3/4×t
Thickness of weld is 8mm than s= 6mm. Take partial safety factor= 1.25
Table I. Length of weld for ISA10075×8mm by LSM
Load(KN)
Fwd(KN)
Lw(mm)
L1(mm)
L2(mm)
140
210kn
264
182
82
160
240kn
302
208
94
180
270kn
340
234
106
200
300kn
378
260
118
220
330
415
286
129
This table values show the result for welded connection for ISA 100×75×8mm single angle section. Now change the thickness of section and consider ISA100×75×10mm single angle section and calculate value for this section and show in table.
t= 0.7×s = 0.7×7.5 = 5.25mm
Table 2. Length of weld for ISA100×75×10mm by LSM
LOAD
Fwd(KN)
LW(MM)
L1(MM)
L2(MM)
140kn
210kn
212
144
68
160kn
240kn
242
164
78
180kn
270kn
272
185
87
200kn
300kn
302
205
97
220kn
330kn
332
226
106
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Welded Connection By Working Stress Method
Consider single angle section ISA 100×75×8mm and same loading applied on a angle as applied in LSM.
Min. size of weld=0.75×8=6mm S=0.7×6×110=462N
Max length of end weld=2×31=62mm Strength of end weld=62×462=28.64KN
Table III. Length of weld for ISA100×75×8mm by WSM
Load (KN)
P1 (KN)
P2 (KN)
Lw(mm)
L1(mm)
L2(mm)
140
63.16
76.83
303
137
166
160
69.36
90.63
346
150
196
180
75.56
104.43
389
163
226
200
81.76
118.23
433
177
256
220
87.96
132.03
476
190
286
Now change the thickness of plate 10 and consider a single angle section ISA 100×75×10mm.
t=0.75×10 = 7.5mm S=0.7×7.5×410 = 577.5N.
Max length of end weld=2×31.9 = 68.1mm Strength of end weld= 68.1×577.5 =36.84KN.
Table IV. Length of weld for ISA100×75×10mm by WSM
LOAD (KN)
P1 (KN)
P2 (KN)
Lw(mm)
L1(mm)
L2(mm)
140
69.75
70.25
243
121
122
160
76.13
83.87
277
132
145
180
82.51
97.49
312
143
169
200
88.89
111.11
346
154
192
220
95.27
124.73
381
165
216
SPACING (mm)
SPACING (mm)
The above table shows the variation of length of weld through LSM and WSM show for ISA 100×75×8mm and ISA 100×75×10 mm respectively.
ISA 100×75×8 mm
ISA 100×75×8 mm
500
400
300
200
100
0
LSM
WSM
500
400
300
200
100
0
LSM
WSM
140 160 180 200 220
LOAD(KN) Fig.(1)
140 160 180 200 220
LOAD(KN) Fig.(1)
Fig I. Graph for Length of weld for varying loading
The above graph shows the variation in length of weld for single angle section by both LSM and WSM method.
ISA100×75×10 mm
ISA100×75×10 mm
500
400
300
200
100
0
LSM
WSM
500
400
300
200
100
0
LSM
WSM
140 160 180 200 220
LOAD(KN)
Fig(2)
140 160 180 200 220
LOAD(KN)
Fig(2)
SPACING (mm)
SPACING (mm)
Fig II. Graph for length of weld at varying loading
The above graph represents variation in length of weld through LSM and WSM method for ISA 100×75×10mm angle section.
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Bolted Connection By Lsm
Take dia of bolts is 16mm and 18mm and determine shearing and bearing capacity.
Vnpb = 2.5dtfu
fu = ultimate tensile stress of the bolt and the ultimate tensile stress of the plate
d = nominal diameter of the bolt
t =The thicknesses of the connected plates. Set load interval 20 an dia 16mm and 18mm.
Calculation show by table. d=16, bolt value=29, Kb=0.49
d=18, bolt value=36.67, Kb=0.41
Load (KN)
D(mm)
No of bolt
Min pitch(mm)
Min edge distance(m m)
70
16
3
40
30
90
16
4
40
30
110
16
4
40
30
130
16
5
40
30
70
18
2
50
30
90
18
3
50
30
110
18
3
50
30
130
18
4
50
30
Load (KN)
D(mm)
No of bolt
Min pitch(mm)
Min edge distance(m m)
70
16
3
40
30
90
16
4
40
30
110
16
4
40
30
130
16
5
40
30
70
18
2
50
30
90
18
3
50
30
110
18
3
50
30
130
18
4
50
30
Table IV. No of bolts at a varying loading condition by LSM
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Bolted Connection By Wsm Shear=100mpa, Bearing=300mpa, Shearing capacity=Area×100Mpa
For 16mm, shearing capacity=60.31KN For 18mm, shearing capacity=76.34KN Bearing capacity=Area×300Mpa
For 16mm, bearing capacity=20.01KN For 18mm, bearing capacity=25.44KN
Table V. No of bolts for varying loading by WSM
Load (KN)
Dia (mm)
No of
bolts
Min pitch(mm)
Min edge distance(mm)
70
16
4
40
30
90
16
5
40
30
110
16
6
40
30
130
16
7
40
30
70
18
3
45
30
90
18
4
45
30
110
18
5
45
30
130
18
6
45
30
NO. OF BOLTS
NO. OF BOLTS
The above table shows the number of bolts at different loading condition for 16 diameter of bolt.
8
6
4
2
LSM
WSM
8
6
4
2
LSM
WSM
0
0
70KN 90KN 110KN 130KN
LOADS
Fig(3)
70KN 90KN 110KN 130KN
LOADS
Fig(3)
Fig III. No of bolts at varying loading for 16mm dia
The Graph represents the value of shearing strength and bearing strength for different dia of bolt by LSM method
120
100
80
60
40
20
0
16 18 20
22
SHEARING
STRENGTH
BEARING STRENGTH
120
100
80
60
40
20
0
16 18 20
22
SHEARING
STRENGTH
BEARING STRENGTH
DIA OF BOLT (mm)
Fig(5)
DIA OF BOLT (mm)
Fig(5)
STRENGTH (KN)
STRENGTH (KN)
Fig V. Shearing and Bearing strength at varying dia by IS800:2007
STRENGTH(KN)
STRENGTH(KN)
The above graph represents the Bearing and Shearing strength at different dia of bolt by WSM method.
150
100
50
0
16 18 20
22
SHEARING
STRENGTH
BEARING STRENGTH
150
100
50
0
16 18 20
22
SHEARING
STRENGTH
BEARING STRENGTH
DIA OF BOLT (mm)
Fig(6)
DIA OF BOLT (mm)
Fig(6)
Fig VI. Shearing and Bearing strength at varying dia of bolt by IS800:1984
The above graph shows the strength variation in Bearing and Shearing strength with the suitable number of diameter of bolts.
NO OF BOLTS
NO OF BOLTS
This graph also shows the no of bolts at different loading condition for 18 diameters of bolts.
7
6
5
4
3
2
1
0
LSM
WSM
7
6
5
4
3
2
1
0
LSM
WSM
70KN 90KN 110KN 130KN
LOADS
Fig(4)
70KN 90KN 110KN 130KN
LOADS
Fig(4)
Fig IV. No of bolts at varying loading for 18mm dia
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RESULTS
In this study we found the 30%variation in shearing strength of bolts for 16mm, 18mm,20mm diameter of bolts through both IS800:2007 and IS800:1984 codes. We found the variation in Bearing strength of bolts for 16mm, 18mm,20mm diameter of bolts is 21%, 13%, 3% respectively through analysis between IS800:2007 and IS800:1984 codes. The paper study shows that the bolted connections are 25% economical for 16mm dia of bolt and welded connections are 12% economical through IS800:2007 as compare to IS800:1984..
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CONCLUSION
The process will be done and results show the variation in LSM and WSM both methods values. It means LSM is a more reliable and economical for steel structure as compare to WSM and fulfill criteria of serviceability.
REFERENCE
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Dr. N. Subramanian, Code Of Practice On Steel Structures -A Review Of IS 800: 2007, Computer Design Consultants, Gaithersburg, MD 20878, USA.
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IS 800:2007 Indian Standard General Construction in Steel Code of Practice.
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Duggal S.K. Limit State Design of Steel StructuresTata McGraw Hill EducationPrivate Limited. New Delhi, 2010, 3 rd. edition.