Short Notes: Tension Members | Short Notes for Civil Engineering - Civil Engineering (CE) PDF Download

 Page 1


Design of Tension Members 
 
1.0 Introduction 
The Tension member considered for the design is a linear member which 
carries an axial pull. The members undergo extension due to this axial pull. This 
is one of the common types of force transmitted in the structural system. 
Tension members are very efficient since the entire cross section carries 
uniform stress unlike flexural members. The tension members do not buckle 
even when stressed beyond the elastic limit. Hence the design is not effected 
by the type of section used i.e., Plastic, Compact or Semi-compact. Some of the 
common examples of tension members in structures are; Bottom chord of pin 
jointed roof trusses, bridges, transmission line and communication towers, 
wind bracing system in multi-storey buildings, etc. 
The objective of this exercise is to determine the tensile strength of a given 
member having a specified end connection. The strength of these members is 
influenced by several factors such as the length of connection, type of 
connection (by bolts or welds), connection eccentricity, size and shape of 
fasteners, net area of cross-section and shear lag at the end connection. 
2.0 Types of Tension Members 
The tension members may be made of single structural shapes.  The standard 
structural shapes of typical tension members are: 
• Angle section • Tee section 
• Channel section • Box section 
• I section • Tubular section 
Page 2


Design of Tension Members 
 
1.0 Introduction 
The Tension member considered for the design is a linear member which 
carries an axial pull. The members undergo extension due to this axial pull. This 
is one of the common types of force transmitted in the structural system. 
Tension members are very efficient since the entire cross section carries 
uniform stress unlike flexural members. The tension members do not buckle 
even when stressed beyond the elastic limit. Hence the design is not effected 
by the type of section used i.e., Plastic, Compact or Semi-compact. Some of the 
common examples of tension members in structures are; Bottom chord of pin 
jointed roof trusses, bridges, transmission line and communication towers, 
wind bracing system in multi-storey buildings, etc. 
The objective of this exercise is to determine the tensile strength of a given 
member having a specified end connection. The strength of these members is 
influenced by several factors such as the length of connection, type of 
connection (by bolts or welds), connection eccentricity, size and shape of 
fasteners, net area of cross-section and shear lag at the end connection. 
2.0 Types of Tension Members 
The tension members may be made of single structural shapes.  The standard 
structural shapes of typical tension members are: 
• Angle section • Tee section 
• Channel section • Box section 
• I section • Tubular section 
The sections can also be built up using a number of the above structural 
shapes. 
Single angle members are economical but the connection produces eccentric 
force in the member. These are generally used in towers and in trusses. Double 
angle members are more rigid than single angle members. They are used in 
roof trusses. Since there exists a gap of about 6 to 10 mm between the two 
members (which depends on the thickness of the gusset plate), they are 
generally interconnected at regular intervals so that they act as one integral 
member. In the members of bridge trusses the tensile forces developed are 
very large and hence require more rigid members. In these structures single 
channel, single I-section, built-up channels, or built-up I-sections will be 
generally used.  
3.0 Behaviour of Tension Members 
The load-deformation behavior of members subjected to uniform tensile stress 
is similar to the load-deflection behavior of the corresponding basic material. 
The typical stress-strain behavior of mild steel under axial tensile load is shown 
in Fig. 1. The upper yield point is merged with the lower yield point for 
convenience. The material shows a linear elastic behavior in the initial region 
(O to A). The material undergoes sufficient yielding in portion A to B. Further 
deformation leads to an increase in resistance, where the material strain 
hardens (from B to C). The material reaches its ultimate stress at point C. The 
stress decreases with increase in further deformation and breaks at D. The high 
strength steel members do not exhibit the well defined yield point and the 
yield region (Fig. 1). For such materials, the 0.2 percent proof stress is usually 
taken as the yield stress (E). 
Page 3


Design of Tension Members 
 
1.0 Introduction 
The Tension member considered for the design is a linear member which 
carries an axial pull. The members undergo extension due to this axial pull. This 
is one of the common types of force transmitted in the structural system. 
Tension members are very efficient since the entire cross section carries 
uniform stress unlike flexural members. The tension members do not buckle 
even when stressed beyond the elastic limit. Hence the design is not effected 
by the type of section used i.e., Plastic, Compact or Semi-compact. Some of the 
common examples of tension members in structures are; Bottom chord of pin 
jointed roof trusses, bridges, transmission line and communication towers, 
wind bracing system in multi-storey buildings, etc. 
The objective of this exercise is to determine the tensile strength of a given 
member having a specified end connection. The strength of these members is 
influenced by several factors such as the length of connection, type of 
connection (by bolts or welds), connection eccentricity, size and shape of 
fasteners, net area of cross-section and shear lag at the end connection. 
2.0 Types of Tension Members 
The tension members may be made of single structural shapes.  The standard 
structural shapes of typical tension members are: 
• Angle section • Tee section 
• Channel section • Box section 
• I section • Tubular section 
The sections can also be built up using a number of the above structural 
shapes. 
Single angle members are economical but the connection produces eccentric 
force in the member. These are generally used in towers and in trusses. Double 
angle members are more rigid than single angle members. They are used in 
roof trusses. Since there exists a gap of about 6 to 10 mm between the two 
members (which depends on the thickness of the gusset plate), they are 
generally interconnected at regular intervals so that they act as one integral 
member. In the members of bridge trusses the tensile forces developed are 
very large and hence require more rigid members. In these structures single 
channel, single I-section, built-up channels, or built-up I-sections will be 
generally used.  
3.0 Behaviour of Tension Members 
The load-deformation behavior of members subjected to uniform tensile stress 
is similar to the load-deflection behavior of the corresponding basic material. 
The typical stress-strain behavior of mild steel under axial tensile load is shown 
in Fig. 1. The upper yield point is merged with the lower yield point for 
convenience. The material shows a linear elastic behavior in the initial region 
(O to A). The material undergoes sufficient yielding in portion A to B. Further 
deformation leads to an increase in resistance, where the material strain 
hardens (from B to C). The material reaches its ultimate stress at point C. The 
stress decreases with increase in further deformation and breaks at D. The high 
strength steel members do not exhibit the well defined yield point and the 
yield region (Fig. 1). For such materials, the 0.2 percent proof stress is usually 
taken as the yield stress (E). 
 
Fig. 1 Typical stress-strain diagram for mild steel and high strength steel 
4.0 Slenderness Ratio 
Apart from strength requirement, the tension members have to be checked for 
minimum stiffness by stipulating the limiting maximum slenderness ratio of the 
member. This is required to prevent undesirable lateral movement or 
excessive vibration. The slenderness limits specified in IS: 800-2007 for tension 
members are given in Table 1. 
Table 1  Maximum values of effective slenderness ratio as per IS: 800-2007 
Member 
Maximum effective 
slenderness ratio (l/r) 
A tension member in which a reversal of direct stress 
occurs due to loads other than wind or seismic forces 
180 
A member subjected to compressive forces resulting 
only from a combination of wind/earthquake actions, 
provided the deformation of such a member does not 
adversely affect the stresses in any part of the 
structure 
250 
A member normally acting as a tie in a roof truss or a 
bracing member, which is not considered effective 
when subject to reversal of stress resulting from the 
action of wind or earthquake forces 
350 
Page 4


Design of Tension Members 
 
1.0 Introduction 
The Tension member considered for the design is a linear member which 
carries an axial pull. The members undergo extension due to this axial pull. This 
is one of the common types of force transmitted in the structural system. 
Tension members are very efficient since the entire cross section carries 
uniform stress unlike flexural members. The tension members do not buckle 
even when stressed beyond the elastic limit. Hence the design is not effected 
by the type of section used i.e., Plastic, Compact or Semi-compact. Some of the 
common examples of tension members in structures are; Bottom chord of pin 
jointed roof trusses, bridges, transmission line and communication towers, 
wind bracing system in multi-storey buildings, etc. 
The objective of this exercise is to determine the tensile strength of a given 
member having a specified end connection. The strength of these members is 
influenced by several factors such as the length of connection, type of 
connection (by bolts or welds), connection eccentricity, size and shape of 
fasteners, net area of cross-section and shear lag at the end connection. 
2.0 Types of Tension Members 
The tension members may be made of single structural shapes.  The standard 
structural shapes of typical tension members are: 
• Angle section • Tee section 
• Channel section • Box section 
• I section • Tubular section 
The sections can also be built up using a number of the above structural 
shapes. 
Single angle members are economical but the connection produces eccentric 
force in the member. These are generally used in towers and in trusses. Double 
angle members are more rigid than single angle members. They are used in 
roof trusses. Since there exists a gap of about 6 to 10 mm between the two 
members (which depends on the thickness of the gusset plate), they are 
generally interconnected at regular intervals so that they act as one integral 
member. In the members of bridge trusses the tensile forces developed are 
very large and hence require more rigid members. In these structures single 
channel, single I-section, built-up channels, or built-up I-sections will be 
generally used.  
3.0 Behaviour of Tension Members 
The load-deformation behavior of members subjected to uniform tensile stress 
is similar to the load-deflection behavior of the corresponding basic material. 
The typical stress-strain behavior of mild steel under axial tensile load is shown 
in Fig. 1. The upper yield point is merged with the lower yield point for 
convenience. The material shows a linear elastic behavior in the initial region 
(O to A). The material undergoes sufficient yielding in portion A to B. Further 
deformation leads to an increase in resistance, where the material strain 
hardens (from B to C). The material reaches its ultimate stress at point C. The 
stress decreases with increase in further deformation and breaks at D. The high 
strength steel members do not exhibit the well defined yield point and the 
yield region (Fig. 1). For such materials, the 0.2 percent proof stress is usually 
taken as the yield stress (E). 
 
Fig. 1 Typical stress-strain diagram for mild steel and high strength steel 
4.0 Slenderness Ratio 
Apart from strength requirement, the tension members have to be checked for 
minimum stiffness by stipulating the limiting maximum slenderness ratio of the 
member. This is required to prevent undesirable lateral movement or 
excessive vibration. The slenderness limits specified in IS: 800-2007 for tension 
members are given in Table 1. 
Table 1  Maximum values of effective slenderness ratio as per IS: 800-2007 
Member 
Maximum effective 
slenderness ratio (l/r) 
A tension member in which a reversal of direct stress 
occurs due to loads other than wind or seismic forces 
180 
A member subjected to compressive forces resulting 
only from a combination of wind/earthquake actions, 
provided the deformation of such a member does not 
adversely affect the stresses in any part of the 
structure 
250 
A member normally acting as a tie in a roof truss or a 
bracing member, which is not considered effective 
when subject to reversal of stress resulting from the 
action of wind or earthquake forces 
350 
Members always in tension (other than pre-tensioned 
members) 
400 
 
5.0 Shear Lag 
The tensile force to a tension member is transferred by a gusset plate or by the 
adjacent member connected to one of the legs either by bolting or welding. 
This force which is transferred to one leg by the end connection locally gets 
transferred as tensile stress over the entire cross section by shear. Hence, the 
distribution of tensile stress on the section from the first bolt hole to the last 
bolt hole will not be uniform. Hence, the connected leg will have higher 
stresses at failure while the stresses in the outstanding leg will be relatively 
lower. However, at sections far away from the end connection, the stress 
distribution becomes more uniform. Here the stress transfer mechanism, i.e., 
the internal transfer of forces from one leg to the other (or flange to web, or 
from one part to the other), will be by shear and because one part ‘lags’ 
behind the other, the phenomenon is referred to as ‘shear lag’. 
The shear lag reduces the effectiveness of the component plates of a tension 
member that are not connected directly to a gusset plate. The efficiency of a 
tension member can be increased by reducing the area of such components 
which are not directly connected at the ends. The shear lag effect reduces with 
increase in the connection length. 
6.0 Modes of Failure 
The different modes of failure in tension members are  
1. Gross section yielding 
2. Net section rupture 
3. Block shear failure 
Page 5


Design of Tension Members 
 
1.0 Introduction 
The Tension member considered for the design is a linear member which 
carries an axial pull. The members undergo extension due to this axial pull. This 
is one of the common types of force transmitted in the structural system. 
Tension members are very efficient since the entire cross section carries 
uniform stress unlike flexural members. The tension members do not buckle 
even when stressed beyond the elastic limit. Hence the design is not effected 
by the type of section used i.e., Plastic, Compact or Semi-compact. Some of the 
common examples of tension members in structures are; Bottom chord of pin 
jointed roof trusses, bridges, transmission line and communication towers, 
wind bracing system in multi-storey buildings, etc. 
The objective of this exercise is to determine the tensile strength of a given 
member having a specified end connection. The strength of these members is 
influenced by several factors such as the length of connection, type of 
connection (by bolts or welds), connection eccentricity, size and shape of 
fasteners, net area of cross-section and shear lag at the end connection. 
2.0 Types of Tension Members 
The tension members may be made of single structural shapes.  The standard 
structural shapes of typical tension members are: 
• Angle section • Tee section 
• Channel section • Box section 
• I section • Tubular section 
The sections can also be built up using a number of the above structural 
shapes. 
Single angle members are economical but the connection produces eccentric 
force in the member. These are generally used in towers and in trusses. Double 
angle members are more rigid than single angle members. They are used in 
roof trusses. Since there exists a gap of about 6 to 10 mm between the two 
members (which depends on the thickness of the gusset plate), they are 
generally interconnected at regular intervals so that they act as one integral 
member. In the members of bridge trusses the tensile forces developed are 
very large and hence require more rigid members. In these structures single 
channel, single I-section, built-up channels, or built-up I-sections will be 
generally used.  
3.0 Behaviour of Tension Members 
The load-deformation behavior of members subjected to uniform tensile stress 
is similar to the load-deflection behavior of the corresponding basic material. 
The typical stress-strain behavior of mild steel under axial tensile load is shown 
in Fig. 1. The upper yield point is merged with the lower yield point for 
convenience. The material shows a linear elastic behavior in the initial region 
(O to A). The material undergoes sufficient yielding in portion A to B. Further 
deformation leads to an increase in resistance, where the material strain 
hardens (from B to C). The material reaches its ultimate stress at point C. The 
stress decreases with increase in further deformation and breaks at D. The high 
strength steel members do not exhibit the well defined yield point and the 
yield region (Fig. 1). For such materials, the 0.2 percent proof stress is usually 
taken as the yield stress (E). 
 
Fig. 1 Typical stress-strain diagram for mild steel and high strength steel 
4.0 Slenderness Ratio 
Apart from strength requirement, the tension members have to be checked for 
minimum stiffness by stipulating the limiting maximum slenderness ratio of the 
member. This is required to prevent undesirable lateral movement or 
excessive vibration. The slenderness limits specified in IS: 800-2007 for tension 
members are given in Table 1. 
Table 1  Maximum values of effective slenderness ratio as per IS: 800-2007 
Member 
Maximum effective 
slenderness ratio (l/r) 
A tension member in which a reversal of direct stress 
occurs due to loads other than wind or seismic forces 
180 
A member subjected to compressive forces resulting 
only from a combination of wind/earthquake actions, 
provided the deformation of such a member does not 
adversely affect the stresses in any part of the 
structure 
250 
A member normally acting as a tie in a roof truss or a 
bracing member, which is not considered effective 
when subject to reversal of stress resulting from the 
action of wind or earthquake forces 
350 
Members always in tension (other than pre-tensioned 
members) 
400 
 
5.0 Shear Lag 
The tensile force to a tension member is transferred by a gusset plate or by the 
adjacent member connected to one of the legs either by bolting or welding. 
This force which is transferred to one leg by the end connection locally gets 
transferred as tensile stress over the entire cross section by shear. Hence, the 
distribution of tensile stress on the section from the first bolt hole to the last 
bolt hole will not be uniform. Hence, the connected leg will have higher 
stresses at failure while the stresses in the outstanding leg will be relatively 
lower. However, at sections far away from the end connection, the stress 
distribution becomes more uniform. Here the stress transfer mechanism, i.e., 
the internal transfer of forces from one leg to the other (or flange to web, or 
from one part to the other), will be by shear and because one part ‘lags’ 
behind the other, the phenomenon is referred to as ‘shear lag’. 
The shear lag reduces the effectiveness of the component plates of a tension 
member that are not connected directly to a gusset plate. The efficiency of a 
tension member can be increased by reducing the area of such components 
which are not directly connected at the ends. The shear lag effect reduces with 
increase in the connection length. 
6.0 Modes of Failure 
The different modes of failure in tension members are  
1. Gross section yielding 
2. Net section rupture 
3. Block shear failure 
The strength of tension members under the different modes are failure, i.e., 
design strength due to yielding of gross section, T
dg
, rupture of critical section, 
T
dn
 and block shear T
db
 are first determined. The design strength of a member 
under axial tension, T
d
, is the lowest of the above three values. 
 
6.1 Gross section yielding 
Steel members (plates, angles, etc.) without bolt holes can sustain loads up to 
the ultimate load without failure. However, the members will elongate 
considerably (10 to 15 % of its original length) at this load, and hence make the 
structure unserviceable. Hence the design strength T
dg
 is limited to the yielding 
of gross cross section which is given by 
T
dg
 = f
y
 A
g
 /?
m0 
where  
f
y
 = yield strength of the material in MPa 
A
g
 = gross area of cross section in mm
2
 
?
m0  
 = 1.10 = partial safety factor for failure at yielding 
 
6.2 Net section rupture 
This occurs when the tension member is connected to the main or other 
members by bolts. The holes made in members for bolts will reduce the cross 
section, and hence net area will govern the failure in this case. Holes in 
members cause stress concentration at service loads. From the theory of 
elasticity, the tensile stress adjacent to a hole will be about two to three times 
the average stress on the net area (Fig. 2a). This depends on the ratio of the