Design of Compression Members with Lacing and Battens | Civil Engineering Optional Notes for UPSC PDF Download

 Page 1


   
 
                                          
 
 
A structural member loaded axially in compression is generally called a compression 
member. Vertical compression members in buildings are called columns, posts or 
stanchions. A compression member in roof trusses is called struts and in a crane is 
called a boom. Columns which are short are subjected to crushing and behave like 
members under pure compression. Columns which are long tend to buckle out of the 
plane of the load axis. 
COMPRESSION MEMBERS COMPOSED OF BACK-TO-BACK 
COMPONENTS 
A compression member composed of two angles, channels or tees, back to back, in 
contact or separated by a small distance should be connected together by riveting, 
bolting or welding so that the slenderness ratio of each member between the 
connections is not greater than 40 nor greater than 0.60 times the most unfavourable 
slenderness ratio of the strut as a whole. In no case, the spacing of tacking rivets in 
a line exceed 600mm for such members. For other types of built-up compression 
members, where cover plates are used, the pitch of tacking rivets should not exceed 
32t or 300mm, whichever is less, where t is the thickness of the thinner outside plate. 
Where plates are exposed to bad weather conditions, the pitch should not exceed 16 
t or 200mm whichever is less. The rivets, welds and bolts in these connections should 
be sufficient to carry the shear force and bending moments, if any, specified for 
battened struts. The diameter of the connecting rivets should not be less than the 
minimum diameter given in the table below: 
Page 2


   
 
                                          
 
 
A structural member loaded axially in compression is generally called a compression 
member. Vertical compression members in buildings are called columns, posts or 
stanchions. A compression member in roof trusses is called struts and in a crane is 
called a boom. Columns which are short are subjected to crushing and behave like 
members under pure compression. Columns which are long tend to buckle out of the 
plane of the load axis. 
COMPRESSION MEMBERS COMPOSED OF BACK-TO-BACK 
COMPONENTS 
A compression member composed of two angles, channels or tees, back to back, in 
contact or separated by a small distance should be connected together by riveting, 
bolting or welding so that the slenderness ratio of each member between the 
connections is not greater than 40 nor greater than 0.60 times the most unfavourable 
slenderness ratio of the strut as a whole. In no case, the spacing of tacking rivets in 
a line exceed 600mm for such members. For other types of built-up compression 
members, where cover plates are used, the pitch of tacking rivets should not exceed 
32t or 300mm, whichever is less, where t is the thickness of the thinner outside plate. 
Where plates are exposed to bad weather conditions, the pitch should not exceed 16 
t or 200mm whichever is less. The rivets, welds and bolts in these connections should 
be sufficient to carry the shear force and bending moments, if any, specified for 
battened struts. The diameter of the connecting rivets should not be less than the 
minimum diameter given in the table below: 
   
 
                                          
 
 
LACINGS AND BATTENS FOR BUILT-UP COMPRESSION MEMBERS 
  
As per Indian Standard, IS 800-1984, the following specifications are used for the 
design of lacing and batten plates. 
In a built-up section, the different components are connected together so that they 
act as a single column. Lacing is generally preferred in case of eccentric loads. 
Battening is normally used for axially loaded columns and in sections where the 
components are not far apart. Flat bars are generally used for lacing. Angles, 
channels and tubular sections are also used for lacing of very heavily columns. Plates 
are used for battens. 
Lacings 
  
Page 3


   
 
                                          
 
 
A structural member loaded axially in compression is generally called a compression 
member. Vertical compression members in buildings are called columns, posts or 
stanchions. A compression member in roof trusses is called struts and in a crane is 
called a boom. Columns which are short are subjected to crushing and behave like 
members under pure compression. Columns which are long tend to buckle out of the 
plane of the load axis. 
COMPRESSION MEMBERS COMPOSED OF BACK-TO-BACK 
COMPONENTS 
A compression member composed of two angles, channels or tees, back to back, in 
contact or separated by a small distance should be connected together by riveting, 
bolting or welding so that the slenderness ratio of each member between the 
connections is not greater than 40 nor greater than 0.60 times the most unfavourable 
slenderness ratio of the strut as a whole. In no case, the spacing of tacking rivets in 
a line exceed 600mm for such members. For other types of built-up compression 
members, where cover plates are used, the pitch of tacking rivets should not exceed 
32t or 300mm, whichever is less, where t is the thickness of the thinner outside plate. 
Where plates are exposed to bad weather conditions, the pitch should not exceed 16 
t or 200mm whichever is less. The rivets, welds and bolts in these connections should 
be sufficient to carry the shear force and bending moments, if any, specified for 
battened struts. The diameter of the connecting rivets should not be less than the 
minimum diameter given in the table below: 
   
 
                                          
 
 
LACINGS AND BATTENS FOR BUILT-UP COMPRESSION MEMBERS 
  
As per Indian Standard, IS 800-1984, the following specifications are used for the 
design of lacing and batten plates. 
In a built-up section, the different components are connected together so that they 
act as a single column. Lacing is generally preferred in case of eccentric loads. 
Battening is normally used for axially loaded columns and in sections where the 
components are not far apart. Flat bars are generally used for lacing. Angles, 
channels and tubular sections are also used for lacing of very heavily columns. Plates 
are used for battens. 
Lacings 
  
   
 
                                          
 
 
A lacing system should generally conform to the following requirements: 
  
i. The compression member comprising two main components laced and tied 
should, where practicable, have a radius of gyration about the axis 
perpendicular to the plane of lacing not less than the radius of gyration at right 
angles to that axis. 
ii. The lacing system should not be varied throughout the length of the strut as 
far as practicable. 
iii. Cross (except tie plates) should not be provided along the length of the column 
with lacing system, unless all forces resulting from deformation of column 
members are calculated and provided for in the lacing and its fastening. 
iv. The single-laced systems on opposite sides of the main components should 
preferably be in the same direction so that one system is the shadow of the 
other. 
v. Laced compression members should be provided with tie plates at the ends of 
the lacing system and at points where the lacing system are interrupted. The 
tie plates should be designed by the same method as followed for battens. 
 
 
Page 4


   
 
                                          
 
 
A structural member loaded axially in compression is generally called a compression 
member. Vertical compression members in buildings are called columns, posts or 
stanchions. A compression member in roof trusses is called struts and in a crane is 
called a boom. Columns which are short are subjected to crushing and behave like 
members under pure compression. Columns which are long tend to buckle out of the 
plane of the load axis. 
COMPRESSION MEMBERS COMPOSED OF BACK-TO-BACK 
COMPONENTS 
A compression member composed of two angles, channels or tees, back to back, in 
contact or separated by a small distance should be connected together by riveting, 
bolting or welding so that the slenderness ratio of each member between the 
connections is not greater than 40 nor greater than 0.60 times the most unfavourable 
slenderness ratio of the strut as a whole. In no case, the spacing of tacking rivets in 
a line exceed 600mm for such members. For other types of built-up compression 
members, where cover plates are used, the pitch of tacking rivets should not exceed 
32t or 300mm, whichever is less, where t is the thickness of the thinner outside plate. 
Where plates are exposed to bad weather conditions, the pitch should not exceed 16 
t or 200mm whichever is less. The rivets, welds and bolts in these connections should 
be sufficient to carry the shear force and bending moments, if any, specified for 
battened struts. The diameter of the connecting rivets should not be less than the 
minimum diameter given in the table below: 
   
 
                                          
 
 
LACINGS AND BATTENS FOR BUILT-UP COMPRESSION MEMBERS 
  
As per Indian Standard, IS 800-1984, the following specifications are used for the 
design of lacing and batten plates. 
In a built-up section, the different components are connected together so that they 
act as a single column. Lacing is generally preferred in case of eccentric loads. 
Battening is normally used for axially loaded columns and in sections where the 
components are not far apart. Flat bars are generally used for lacing. Angles, 
channels and tubular sections are also used for lacing of very heavily columns. Plates 
are used for battens. 
Lacings 
  
   
 
                                          
 
 
A lacing system should generally conform to the following requirements: 
  
i. The compression member comprising two main components laced and tied 
should, where practicable, have a radius of gyration about the axis 
perpendicular to the plane of lacing not less than the radius of gyration at right 
angles to that axis. 
ii. The lacing system should not be varied throughout the length of the strut as 
far as practicable. 
iii. Cross (except tie plates) should not be provided along the length of the column 
with lacing system, unless all forces resulting from deformation of column 
members are calculated and provided for in the lacing and its fastening. 
iv. The single-laced systems on opposite sides of the main components should 
preferably be in the same direction so that one system is the shadow of the 
other. 
v. Laced compression members should be provided with tie plates at the ends of 
the lacing system and at points where the lacing system are interrupted. The 
tie plates should be designed by the same method as followed for battens. 
 
 
   
 
                                          
 
GUIDELINES FOR THE DESIGN OF LACING SYSTEM 
  
i. The angle of inclination of the lacing with the longitudinal axis of the column 
should be between  to . 
ii. The slenderness ratio  of the lacing bars should not exceed 145. 
iii. The effective length  of the lacing bar should be according to the table given 
below: 
 
1. For riveted or welded lacing system,  or 0.7 times maximum 
slenderness ratio of the compression member as a whole, whichever is 
less.NHere, L = distance between the centers of connections of the lattice bars, 
and = the minimum radius of gyration of the components of the 
compression member. 
Page 5


   
 
                                          
 
 
A structural member loaded axially in compression is generally called a compression 
member. Vertical compression members in buildings are called columns, posts or 
stanchions. A compression member in roof trusses is called struts and in a crane is 
called a boom. Columns which are short are subjected to crushing and behave like 
members under pure compression. Columns which are long tend to buckle out of the 
plane of the load axis. 
COMPRESSION MEMBERS COMPOSED OF BACK-TO-BACK 
COMPONENTS 
A compression member composed of two angles, channels or tees, back to back, in 
contact or separated by a small distance should be connected together by riveting, 
bolting or welding so that the slenderness ratio of each member between the 
connections is not greater than 40 nor greater than 0.60 times the most unfavourable 
slenderness ratio of the strut as a whole. In no case, the spacing of tacking rivets in 
a line exceed 600mm for such members. For other types of built-up compression 
members, where cover plates are used, the pitch of tacking rivets should not exceed 
32t or 300mm, whichever is less, where t is the thickness of the thinner outside plate. 
Where plates are exposed to bad weather conditions, the pitch should not exceed 16 
t or 200mm whichever is less. The rivets, welds and bolts in these connections should 
be sufficient to carry the shear force and bending moments, if any, specified for 
battened struts. The diameter of the connecting rivets should not be less than the 
minimum diameter given in the table below: 
   
 
                                          
 
 
LACINGS AND BATTENS FOR BUILT-UP COMPRESSION MEMBERS 
  
As per Indian Standard, IS 800-1984, the following specifications are used for the 
design of lacing and batten plates. 
In a built-up section, the different components are connected together so that they 
act as a single column. Lacing is generally preferred in case of eccentric loads. 
Battening is normally used for axially loaded columns and in sections where the 
components are not far apart. Flat bars are generally used for lacing. Angles, 
channels and tubular sections are also used for lacing of very heavily columns. Plates 
are used for battens. 
Lacings 
  
   
 
                                          
 
 
A lacing system should generally conform to the following requirements: 
  
i. The compression member comprising two main components laced and tied 
should, where practicable, have a radius of gyration about the axis 
perpendicular to the plane of lacing not less than the radius of gyration at right 
angles to that axis. 
ii. The lacing system should not be varied throughout the length of the strut as 
far as practicable. 
iii. Cross (except tie plates) should not be provided along the length of the column 
with lacing system, unless all forces resulting from deformation of column 
members are calculated and provided for in the lacing and its fastening. 
iv. The single-laced systems on opposite sides of the main components should 
preferably be in the same direction so that one system is the shadow of the 
other. 
v. Laced compression members should be provided with tie plates at the ends of 
the lacing system and at points where the lacing system are interrupted. The 
tie plates should be designed by the same method as followed for battens. 
 
 
   
 
                                          
 
GUIDELINES FOR THE DESIGN OF LACING SYSTEM 
  
i. The angle of inclination of the lacing with the longitudinal axis of the column 
should be between  to . 
ii. The slenderness ratio  of the lacing bars should not exceed 145. 
iii. The effective length  of the lacing bar should be according to the table given 
below: 
 
1. For riveted or welded lacing system,  or 0.7 times maximum 
slenderness ratio of the compression member as a whole, whichever is 
less.NHere, L = distance between the centers of connections of the lattice bars, 
and = the minimum radius of gyration of the components of the 
compression member. 
   
 
                                          
 
 
 
2. Minimum width of lacing bars in riveted connection should be according to 
the Table given below: 
 
1. Minimum thickness of lacing bars: 
, for single lacing; , for double lacing Where = length between inner 
end rivets. 
1. The lacing of compression members should be designed to resist a transverse 
shear, V=2.5 percent of the axial force in the member. The shear is divided 
equally among all transverse lacing systems in parallel planes. The lacing 
system should also be designed to resist additional shear due to bending if the 
compression member carries bending due to eccentric load, applied end 
moments, and / or lateral loading. 
2. The riveted connections may be made in two ways, as shown in the figure (a) 
and (b).