The document summarizes the design of batten plates connecting back-to-back channel sections in a built-up column using both bolt and weld connections. For the bolt connection, 420x340x8mm end batten plates and 420x300x8mm intermediate batten plates are designed to transmit shear and bending forces using four 20mm diameter bolts per connection. For the weld connection, 360x270x6mm end batten plates and 360x220x6mm intermediate batten plates are designed using full penetration welds on all sides to transmit the forces. Both connections are checked to verify the capacities of the bolts/welds are not exceeded.
2. Example: A batten column of 10-m long is carrying a factored
load of 1150 kN. The column is restrained in position but not in
direction at both ends. Design a built up column using channel
sections placed back to back.
Design batten plates using bolt connection.
3. Let us try two ISMC 350 @ 413 N/m
Relevant properties of ISMC 350 [ Table II SP 6 (1): 1964]
๐ด = 5366 mm2, ๐๐ง๐ง = 136.6 mm,
๐๐ฆ๐ฆ = 28.3 mm ๐ก๐ = 13.5 mm
๐ผ๐ง๐ง = 10008 ร 104 mm4 ๐ผ๐ฆ๐ฆ = 430.6 ร 104 mm4
๐๐ฆ๐ฆ = 24.4 mm ๐ = 100 mm
Solution:
Design of column:
๐ = 1150 kN = 1150 ร 103 N
L = 1.0 ร 10 ร 103 = 10000 mm
Let design axial compressive stress for the column be 125 MPa
Required area =
1150ร103
125
= 9200 mm2
4. For
๐พ๐ฟ
๐ ๐
= 80.53, ๐๐ฆ = 250 MPa and buckling class c, the
design compressive stress from Table 9c of IS 800 :2007
๐๐๐ = 136 โ
136โ121
10
ร 0.53 = 135.2 MPa
Therefore load carrying capacity = ๐ด๐๐๐๐
= 10732 ร 135.2 ร 10โ3
= 1451 kN > 1200 kN, OK
Area provided = 2 ร 5366 = 10732 mm2
๐ฟ
๐๐ง๐ง
=
10000
136.6
= 73.21
The effective slenderness ratio,
๐พ๐ฟ
๐ ๐
= 1.1 ร 73.21
= 80.53 < 180; ok
5. Spacing of channels:
2๐ผ๐ง๐ง = 2 ๐ผ๐ฆ๐ฆ + ๐ด
๐
2
+ ๐ถ๐ฆ๐ฆ
2
or 2 ร 10008 ร 104 = 2 ร 430.6 ร 104 + 5366
๐
2
+ 24.4
2
โ ๐ = 218.4 mm
Let us keep the channels at a spacing of 220 mm
Spacing of battens:
As per clause 7.7.3 of IS 800: 2007,
๐ถ
๐๐ฆ๐ฆ
< 0.7๐
๐๐ ๐ถ < 0.7 ร ๐ ร ๐๐ฆ๐ฆ = 0.7 ร 80.53 ร 28.3 = 1595.3 mm
Also
๐ถ
๐๐ฆ๐ฆ
< 50 or ๐ถ < 50 ร 28.3 = 1415 mm
Hence, provide battens at a spacing of 1400 mm.
6. Size of end battens (cl. 7.7.2.3 of IS 800 :2007):
Provide 20 mm bolts.
Edge distance = 1.5 ร โ๐๐๐ ๐๐๐๐๐๐ก๐๐ [Cl. 10.2.4.2 IS 800:2007]
= 1.5 ร 20 + 2 = 33 mm
Effective depth = ๐ + ๐ถ๐ฆ๐ฆ
= 220 + 2 ร 24.4 = 268.8 mm > 2 ร 100 mm
Hence, chosen effective depth is safe.
Overall depth = 268.8 + 2 ร 33 = 334.8 mm
Required thickness of batten =
1
50
ร 220 + 2 ร 50 = 6.4 mm
Length of batten = 220 + 2 ร 100 = 420 mm
Provide 420ร340ร8 mm end batten plates.
7. Size of intermediate battens (cl. 7.7.2.3 of IS 800 :2007):
Effective depth =
3
4
ร (220 + 2 ร ๐ถ๐ฆ๐ฆ)
=
3
4
ร (220 + 2 ร 24.4) = 201.6 mm
> 2 ร 100 = 200 mm
Hence adopt an effective depth of 210 mm
Overall depth = 210 + 2 ร 33 = 276 mm
Therefore, provide a 420ร300ร8 mm batten plates @1400 mm
c/c.
8. Design forces:
Transverse shear, ๐ =
2.5
100
ร ๐ =
2.5
100
ร 1150 ร 103
= 28750 N
Longitudinal shear ๐๐ =
๐๐ถ
๐๐
Spacing of battens, C = 1400 mm
N = No of parallel planes of battens = 2
S = minimum transverse distance between the centroid of the
bolt/weld group = 220 + 2 ร 50 = 320 mm
โด ๐๐ =
28750ร1400
2ร320
= 62891 N
Moment, ๐ =
๐๐ถ
2๐
=
28750ร1400
2ร2
= 10.06 ร 106 N-mm
10. Connection:
The connection should be designed to transmit both shear and
bending moment.
Assuming 20 mm diameter bolts.
Strength of bolt in single shear
=
๐ด๐๐ร๐๐ข๐
3ร๐พ๐๐
=
0.78ร
๐ร202
4
ร400
3ร1.25
ร 10โ3= 45.27 kN
Minimum pitch, p = 2.5d=2.5ร20=50 mm
Minimum end distance, e = 1.5 d0 =1.5ร22=33 mm
Provide p = 60 mm and e = 35 mm
kb is smaller of 35/(3ร22), 60/(3ร22)-0.25, 400/410, 1
Kb = 0.53
11. Strength of bolt in bearing = 2.5๐๐๐๐ก๐๐ข/๐พ๐๐
= 2.5 ร 0.53 ร 20 ร 8 ร
410
1.25
ร 10โ3 = 69.5 kN
Hence, strength of bolt = 45.27 kN
Number of bolts required =
62891
45.27ร103 = 1.39
Let us provide four bolts to take account the stresses due to
bending moments as well.
Check for combined action: For end battens
Force in each bolt due to shear =
62891
4
= 15723 N
Pitch provided = (D-2e)/3= (340-2ร35)/3 = 90 mm.
๐2 = 2[(90/2)2+(90+90/2)2) = 2[452+1352] = 40500 mm2
12. Force due to moment =
๐๐
๐2 =
10.06ร106ร135
40500
= 33533 N
Resultant force = 157232 + 335332
= 37036 N = 37 kN < 45.26 kN
Hence safe.
Check for combined action: For intermediate battens
Force in each bolt due to shear =
62891
4
= 15723 N
Pitch provided = (D-2e)/3= (300-2ร35)/3 = 77 mm.
๐2 = 2[(77/2)2+(77+77/2)2) = 2[38.52+115.52] = 29645 mm2
Force due to moment =
๐๐
๐2 =
10.06ร106ร115.5
29645
= 39195 N
Resultant force = 157232 + 391952
= 42231N = 42.23 kN < 45.26 kN
Hence safe.
13. ISMC 350
350 mm
220 mm
220 mm
1400
mm
Intermediate batten
420 mmร300 mmร8 mm
End batten
420 mmร340 mmร8 mm
20 mm bolt
Channels back-to-back connected by bolts:
15. Example: A batten column of 10-m long is carrying a factored
load of 1150 kN. The column is restrained in position but not in
direction at both ends. Design a built up column using channel
sections placed back to back.
Design batten plates using weld connection.
16. Let us try two ISMC 350 @ 413 N/m
Relevant properties of ISMC 350 [ Table II SP 6 (1): 1964]
๐ด = 5366 mm2, ๐๐ง๐ง = 136.6 mm,
๐๐ฆ๐ฆ = 28.3 mm ๐ก๐ = 13.5 mm
๐ผ๐ง๐ง = 10008 ร 104 mm4 ๐ผ๐ฆ๐ฆ = 430.6 ร 104 mm4
๐๐ฆ๐ฆ = 24.4 mm ๐ = 100 mm
Solution:
Design of column:
๐ = 1150 kN = 1150 ร 103 N
L = 1.0 ร 10 ร 103 = 10000 mm
Let design axial compressive stress for the column be 125 MPa
Required area =
1150ร103
125
= 9200 mm2
17. For
๐พ๐ฟ
๐ ๐
= 80.53, ๐๐ฆ = 250 MPa and buckling class c, the
design compressive stress from Table 9c of IS 800 :2007
๐๐๐ = 136 โ
136;121
10
ร 0.53 = 135.2 MPa
Therefore load carrying capacity = ๐ด๐๐๐๐
= 10732 ร 135.2 ร 10;3
= 1451 kN > 1200 kN, OK
Area provided = 2 ร 5366 = 10732 mm2
๐ฟ
๐๐ง๐ง
=
10000
136.6
= 73.21
The effective slenderness ratio,
๐พ๐ฟ
๐ ๐
= 1.1 ร 73.21
= 80.53 < 180; ok
18. Spacing of channels:
2๐ผ๐ง๐ง = 2 ๐ผ๐ฆ๐ฆ + ๐ด
๐
2
+ ๐ถ๐ฆ๐ฆ
2
or 2 ร 10008 ร 104 = 2 ร 430.6 ร 104 + 5366
๐
2
+ 24.4
2
โ ๐ = 218.4 mm
Let us keep the channels at a spacing of 220 mm
Spacing of battens:
As per clause 7.7.3 of IS 800: 2007,
๐ถ
๐๐ฆ๐ฆ
< 0.7๐
๐๐ ๐ถ < 0.7 ร ๐ ร ๐๐ฆ๐ฆ = 0.7 ร 80.53 ร 28.3 = 1595.3 mm
Also
๐ถ
๐๐ฆ๐ฆ
< 50 or ๐ถ < 50 ร 28.3 = 1415 mm
Hence, provide battens at a spacing of 1400 mm.
19. Size of end battens (cl. 7.7.2.3 of IS 800 :2007):
Overall depth of batten = 220 + 2 ร ๐ถ๐ฆ๐ฆ
= 220 + 2 ร 24.4 = 268.8 โ 270 mm
Required thickness of batten =
1
50
ร 220 = 4.4 mm
Adopt battens with the thickness of 6-mm
Let provide a 70 mm overlap of battens on channel flange for
welding.
[Overlap > 4 t = 4 ร 6 = 24 mm] OK
Length of batten = 220 + 2 ร 70 = 360 mm
Provide 360ร270ร6 mm end batten plates.
20. Size of intermediate battens (cl. 7.7.2.3 of IS 800 :2007):
Overall depth =
3
4
ร (220 + 2 ร ๐ถ๐ฆ๐ฆ)
=
3
4
ร (220 + 2 ร 24.4) = 201.6 mm
> 2 ร 100 = 200 mm
Hence adopt overall depth of 220 mm
Therefore, provide a 360ร220ร6 mm batten plates.
21. Design forces:
Transverse shear, ๐ =
2.5
100
ร ๐ =
2.5
100
ร 1150 ร 103
= 28750 N
Longitudinal shear ๐๐ =
๐๐ถ
๐๐
Spacing of battens, C = 1400 mm
N = No of parallel planes of battens = 2
S = minimum transverse distance between the centroid of the
bolt/weld group = 220 + 2 ร 50 = 320 mm
โด ๐๐ =
28750ร1400
2ร320
= 62891 N
Moment, ๐ =
๐๐ถ
2๐
=
28750ร1400
2ร2
= 10.06 ร 106 N-mm
23. Design of weld:
Welding is done on all the four sides as shown in the figure.
Let ๐ก = throat thickness of weld.
๐ผ๐ง๐ง = 2 ร
70 ร ๐ก3
12
+ 70 ร ๐ก ร
220
2
2
+
2 ร ๐ก ร 2203
12
Neglecting the term 2 ร
70ร๐ก3
12
being insignificant.
Therefore, ๐ผ๐ง๐ง = 346.87 ร 104๐ก mm4
๐ผ๐ฆ๐ฆ = 2 ร
๐ก ร 703
12
+ 2 ร
220 ร ๐ก3
12
+ 2 ร 220 ร ๐ก ร
70
2
2
Neglecting the term 2 ร
220ร๐ก3
12
being insignificant.
Therefore, ๐ผ๐ฆ๐ฆ = 59.62 ร 104๐ก mm4
24. ๐ผ๐ = ๐ผ๐ง๐ง + ๐ผ๐ฆ๐ฆ = 346.87 ร 104
๐ก + 59.62 ร 104
๐ก
= 406.49 ร 104
๐ก mm4
๐ =
220
2
2
+
70
2
2
= 115.43 mm
๐๐๐ ๐ =
35
115.43
= 0.30
Direct shear stress (cl. 10.5.9 of IS 800:2007)
=
62891
2ร70:2ร220 ๐ก
=
108.43
๐ก
N/mm2
Shear stress due to bending moment =
10.06ร106ร115.43
406.49ร104๐ก
=
285.67
๐ก
N/mm2
25. Combined stress due to shear and bending
=
108.43
๐ก
2
+
285.67
๐ก
2
+ 2 ร
108.43
๐ก
ร
285.67
๐ก
ร 0.3
=
334.59
๐ก
<
410
3 ร 1.25
= 189.4
or ๐ก = 1.77 mm
Size of weld = 1.77/0.7 = 2.5 mm
The size of weld should not be less than 5 mm for 13.5 mm
flange.
Hence provide a 5 mm weld to make the connection.
26. ISMC 350
350 mm
220 mm
220 mm
1400
mm
Intermediate batten
360 mmร220 mmร6 mm
End batten
360 mmร270 mmร6 mm
5 mm weld
Channels back-to-back connected by welding:
28. Splices
โข A joint when provided in the length of a member is called
splices.
โข If a compression member is loaded concentrically,
theoretically no splice is required.
โข However, the load is never truly axial and the real column has
to resist bending due to this eccentrically applied load.
Column sections can be spliced in the following cases:
1. When the length of the column is more than the length of
the column section available.
2. In case of multistorey buildings, the section of the column
required for the various storey may be different, as the
load goes on increasing for columns of the lower storeys.
29. Specifications for the design of splices
โข Where the ends of the compression members are faced
for complete bearing over the whole area, these should be
spliced to hold the connected members accurately in
position, and to resist any tension when bending is
present.
โข Where such members are not faced for complete bearing,
splices should be design to transmit all the forces to
which these are subjected.
โข Splices are designed as short columns.
31. Steps for the design of splice
1. For axial compressive load the splice plates are provided
on the flanges of the two column sections to be spliced.
If the column has machined ends, the splice is designed only
to keep the columns in position and to carry tension due to the
bending moment to which it may be subjected. The splice
plate and the connection should be design to carry 50% of the
axial load and tension.
If the ends are not machined, the splice and connections are
design to resist the total axial load and any tension, if present
due to the bending moment.
32. Steps for the design of splice
โข The load for the design of splice and connection due to axial
load,
๐๐ข1 =
๐๐ข
4
(for machined ends)
๐๐ข1 =
๐๐ข
2
(for non machined ends)
Where, ๐๐ข is the axial factored load.
โข The load for the design of splice and connection due
bending moment,
๐๐ข2 =
๐๐ข
๐๐๐ฃ๐๐ ๐๐๐
Where, lever arm is the c/c distance of the two splice plates and
๐๐ข is the factored bending moment.
33. Steps for the design of splice
2. Splice plates are assumed to act as short columns (with zero
slenderness ratio). So these plates will be subjected to yield
stress (๐๐ฆ).
3. The cross-sectional area of the splice plate is calculated by
dividing the appropriate portion of the factored load coming
over the splice by the yield stress.
c/s area required =
๐๐ข1+๐๐ข2
๐๐ฆ
4. The width of splice plate is usually kept equal to the width of
the column flange.
Width of splice = ๐๐ (width of flange)
The thickness of the splice plate can be found by dividing the
c/s area of the plates with its width.
34. Steps for the design of splice
5. Nominal diameter of bolts for connection is assumed and the
strength of the bolt is computed.
6. In case of bearing plate is to be designed between two
column sections, the length and width of the plate are kept
equal to the size of lower-storey column and the thickness is
computed by equating the ultimate moment due to the factored
load to the moment of resistance of plate section.
35. Example: A column ISHB 300 @ 576.8 N/m is to support a
factored axial load of 500 kN, shear force of 120 kN and
bending moment of 40 kNm. Design the splice plate and
connection using 4.6 grade bolts. Use steel of grade Fe 410.
Solution:
For steel of grade Fe 410: ๐๐ข = 410 MPa, ๐๐ฆ = 250 Mpa
For bolts of grade 4.6: ๐๐ข๐ = 400 MPa
Partial safety factors for material:(Table 5 IS 800:2007)
๐พ๐0 = 1.10 ๐พ๐๐ = 1.25
The relevant properties of ISHB 300 @ 576.8 N/m are (Table I,
SP 6-1)
๐ด = 7485 mm2 ๐๐ = 250 mm,
๐ก๐ = 10.6 mm ๐ก๐ค = 7.6 mm
36. Assume the ends of the column sections to be machined for
complete bearing. As the column ends are flush, it is assumed that
50% of the load is transferred directly and 50% is transferred
through the splice and fastenings. Therefore,
The direct load on each splice plate = 50% ๐๐
500
2
= 125 kN
Load on splice due to moment =
๐๐ข
๐๐๐ฃ๐๐ ๐๐๐
=
40ร103
300+6
= 130.72 kN
(Assuming 6 mm thick splice plate, the lever arm = 300 + 6 mm)
Total design load for splice, ๐๐ = 125 + 130.72 = 255.72 kN
Sectional area of splice plate required =
๐๐
๐๐ฆ
=
255.72ร103
250
= 1022.9 mm2
37. Width of the splice plate should be kept equal to the width of
the flange.
Here, the width of the splice plate = 250 mm
Hence, thickness of splice plate =
1022.9
250
= 4.09 mm โฎ 6 mm
Provide a 250ร6 mm splice plate.
The length of the splice plate depends upon the number of
bolts in vertical row.
Let us provide 20 mm diameter bolts of grade 4.6.
Strength of 20 mm diameter bolt in single shear (cl. 10.3.3, IS
800:2007)
=
๐ด๐๐
๐๐ข๐
3
๐พ๐๐
=
245ร
400
3
1.25
ร 10โ3 = 45.26 kN
38. Strength of bolt in bearing = 2.5๐๐๐๐ก๐๐ข/๐พ๐๐ (cl. 10.3.4, IS
800:2007)
For 20 mm diameter bolts the minimum edge distance,
๐ = 1.5 ร ๐0 = 1.5 ร 20 + 2 = 33 mm
The minimum pitch, p = 2.5 ร 20 = 50 mm
Let us provide an edge distance (e) of 35 mm and pitch (p) of
60 mm.
๐๐ is smaller of
๐
3๐0
=
35
3ร22
= 0.53 ,
๐
3๐0
โ 0.25 =
60
3ร22
โ 0.25 = 0.66 ,
๐๐ข๐
๐๐ข
=
400
410
= 0.98 and 1.0
Hence ๐๐ = 0.53
39. โด Strength in bearing = 2.5 ร 0.53 ร 20 ร 6 ร
410
1.25
ร 10โ3
= 52.15 kN
Hence, the strength of bolt (Bv) = 45.26 kN
Number of bolts required, n =
๐๐
๐ต๐ฃ
=
255.72
45.26
= 5.65 โ 6
Provide 6 bolts for each splice.
Length of the splice plate = 2 ร (2 ร 60 + 2 ร 35) = 380 mm
Provide a splice plate 380ร250ร6 mm on column flanges as
shown in the figure.
41. Example: A column ISHB 300 @ 576.8 N/m is to support a
factored axial load of 500 kN, shear force of 120 kN and
bending moment of 40 kNm. Design the splice plate and
connection using 4.6 grade bolts. Use steel of grade Fe 410.
42. Solution:
For steel of grade Fe 410: ๐๐ข = 410 MPa, ๐๐ฆ = 250 Mpa
For bolts of grade 4.6: ๐๐ข๐ = 400MPa
Partial safety factors for material:(Table 5 IS 800:2007)
๐พ๐0 = 1.10๐พ๐๐ = 1.25
The relevant properties of ISHB 300 @ 576.8 N/m are (Table I,
SP 6-1)
๐ด = 7485 mm2๐๐ = 250 mm,
๐ก๐ = 10.6mm ๐ก๐ค = 7.6 mm
43. Assume the ends of the column sections to be machined for
complete bearing. As the column ends are flush, it is assumed that
50% of the load is transferred directly and 50% is transferred
through the splice and fastenings. Therefore,
The direct load on each splice plate = 50% ๐๐
500
2
= 125 kN
Load on splice due to moment =
๐๐ข
๐๐๐ฃ๐๐ ๐๐๐
=
40ร103
300+6
= 130.72 kN
(Assuming 6 mm thick splice plate, the lever arm = 300 + 6 mm)
Total design load for splice, ๐๐ = 125 + 130.72 = 255.72 kN
Sectional area of splice plate required =
๐๐
๐๐ฆ
=
255.72ร103
250
= 1022.9mm2
44. Width of the splice plate should be kept equal to the width of
the flange.
Here, the width of the splice plate = 250 mm
Hence, thickness of splice plate =
1022.9
250
= 4.09 mm โฎ 6 mm
Provide a 250ร6 mm splice plate.
The length of the splice plate depends upon the number of
bolts in vertical row.
Let us provide 20 mm diameter bolts of grade 4.6.
Strength of 20 mm diameter bolt in single shear (cl. 10.3.3, IS
800:2007)
=
๐ด๐๐
๐๐ข๐
3
๐พ๐๐
=
245 ร
400
3
1.25
ร 10โ3
= 45.26 kN
45. Strength of bolt in bearing = 2.5๐๐๐๐ก๐๐ข/๐พ๐๐(cl. 10.3.4, IS
800:2007)
For 20 mm diameter bolts the minimum edge distance,
๐ = 1.5 ร ๐0 = 1.5 ร 20 + 2 = 33 mm
The minimum pitch, p = 2.5 ร 20 = 50 mm
Let us provide an edge distance (e) of 35 mm and pitch (p) of
60 mm.
๐๐ is smaller of
๐
3๐0
=
35
3ร22
= 0.53 ,
๐
3๐0
โ 0.25 =
60
3ร22
โ 0.25 = 0.66 ,
๐๐ข๐
๐๐ข
=
400
410
= 0.98 and 1.0
Hence ๐๐ = 0.53
46. โด Strength in bearing = 2.5 ร 0.53 ร 20 ร 6 ร
410
1.25
ร 10โ3
= 52.15kN
Hence, the strength of bolt (Bv) = 45.26 kN
Number of bolts required, n =
๐๐
๐ต๐ฃ
=
255.72
45.26
= 5.65 โ 6
Provide 6 bolts for each splice.
Length of the splice plate = 2 ร (2 ร 60 + 2 ร 35) = 380 mm
Provide a splice plate 380ร250ร6 mm on column flanges as
shown in the figure.
47. Splice plates for shear:
The splice plate for the shear force is provided on the web. A pair
of splice plate (one on each side of web) are provided.
Let us provide 20 mm diameter bolts of grade 4.6.
Strength of bolt in double shear = 45.26 ร 2 = 90.52 kN
Strength in bearing = 2.5๐๐๐๐ก๐๐ข/๐พ๐๐
Where, ๐๐ = 0.53 (taking ๐ = 35 mm and p = 60 mm),
๐ก = 7.6 mm (web thickness)
โด Strength in bearing = 2.5 ร 0.53 ร 20 ร 7.6 ร
410
1.25
ร 10โ3 =
66.06 kN
Hence, strength of 20 mm bolt = 66.06kN
48. Shear force in the web, ๐ = 120 kN
Number of bolts required =
120
66.06
= 1.8 โ 2
Provide 2, 20 mm diameter bolts on each side of the splice.
Length of the splice plate = 4 ร 35 = 140 mm
Width of the splice plate = 60 + 2 ร 35 = 130 mm
Design shear strength of splice plate (cl. 8.4, IS 800:2007),
๐๐ =
๐๐ฆ
3 ร ๐พ๐0
ร โ ร ๐ก
=
250
3 ร 1.1
ร 130 ร 2๐ก๐ ร 10โ3
= 34.12 ๐ก๐ kN
49. Now, ๐๐ > ๐
or 34.12 ๐ก๐ > 120
Thickness of the splice plate required,
๐ก๐ =
120
34.12
= 3.52 mm โฎ 6mm
So provide a pair of 140ร130ร6 mm shear splice plates on each
side of the web as shown in the figure.
52. INTRODUCTION
โข Flexural members or bending members are commonly called
BEAMS.
โข A beam is a structural member subjected to transverse loads
i.e., loads perpendicular to the longitudinal axis.
โข The load produce Bending moment & Shear forces.
54. DIFFERENT TYPES OF BEAMS
โข JOIST: A closely spaced beams supporting floors or roofs of
building but not supporting the other beams.
โข GIRDER: A large beam, used for supporting a number of
joists.
โข PURLIN: Purlins are used to carry roof loads in trusses.
โข STRINGER: In building, beams supporting stair steps; in
bridges a longitudinal beam supporting deck floor & supported
by floor beam.
โข FLOOR BEAM: A major beam supporting other beams in a
building; also the transverse beam in bridge floors.
55. โข SPANDREL BEAM: In a building, a beam on the outside
perimeter of a floor, supporting the exterior walls and outside
edge of the floor
โข GIRT: A horizontal beam spanning the wall columns of
industrial buildings used to support wall coverings is called a
GIRT.
โข RAFTER: A roof beam usually supported by purlins.
โข LINTELS: This type of beams are used to support the loads
from the masonry over the openings .
DIFFERENT TYPES OF BEAMS
56. NATURE OF FORCES ACTING ON BEAMS
โข It is assumed that the beam is subjected to only transverse
loading.
โข All the loads and sections lie in the plane of symmetry.
โข It follows that such a beam will be primarily subjected to
bending accompanied by shear in the loading plane with no
external torsion and axial force.
57. โข The problem of torsion can not completely be avoided in a
beam even if the beam shape is symmetrical and loads are in
the plane of symmetry.
โข The reason is the instability caused by compressive stresses.
Such instability is defined as LATERAL BUCKLING .
When it is involving only local components of a beam it is
called LOCAL BUCKLING.
โข Local buckling is a function of width-thickness ratio.
NATURE OF FORCES ACTING ON BEAMS
58. Primary modes of failure of beams are as follows:
1. Bending failure
2. Shear failure
3. Deflection failure
1. Bending failure: Bending failure generally occurs due to
crushing of compression flange or fracture of tension flange of
the beam.
2. Shear failure: This occurs due to buckling of web of the beam
near location of high shear forces. The beam can fail locally
due to crushing or buckling of the web near the reaction of
concentrated loads.
3. Deflection failure: A beam designed to have adequate strength
may become unsuitable if it is not able to support its load
without excessive deflections.
MODES OF FAILURE
61. CONSIDERATIONS IN DESIGN OF BEAMS
โข Beams should be proportioned for strength in bending
keeping in view of the lateral and local stability of the
compression flange.
โข The selected shape should have capacity to withstand
essential strength in shear and local bearing .
โข The beam dimension should be suitably proportioned for
stiffness, keeping in mind their deflections and deformations
under service conditions .
62. LIMITATIONS OF ANGLES , T-SECTIONS AND
CHANNELS
โข Angles and T-sections are weak in bending.
โข Channels only be used for light loads.
โข The rolled steel channels and angle sections are used in those
cases where they can be designed and executed satisfactory.
โข This is because the load is not likely to be in the plane, which
removes torsional eccentricities .
โข Also, it is complicated to calculate the lateral buckling
characteristics of these sections .