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Module 1: Eccentric Connections

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Eccentric Loading in Plane of Bolted Joint
 

In an eccentric connection, the center of gravity of connection and that of the load are in different positions. Because of this, the eccentricity will develop, thus leading to an extra moment. When an eccentric joint is being designed, the direct load and eccentricity must be considered.

 


The design of a bolt group due to an eccentric load lying in the plane of the joint is done by a trial and error method.
A Basic Design Procedure for eccentric load lying in the plane of bolt groups are:



Assume a suitable diameter for the bolt


Find the strength of one bolt in shear and bearing, and get bolt value


Determine the number of bolts


Increase the number of bolts and decide the arrangement of bolts


Calculate the resultant force for the critical bolt


Check to ensure resultant force in the critical bolt is less than the bolt value


Eccentric Load in Plane of Welded Joint
 

When designing an eccentric connection where a load is lying on the plane of a welded joint, the stresses due to direct force and due to moment must be calculated. Then, resultant forces are determined. If the resultant stress is less than the weld strength, then the design factor is safe. Otherwise, the length or width of the weld will have to be changed.

 
Eccentric Load Perpendicular to Plane of Bolted Joint
 
The Nine Design Steps to determining the number of bolts that should be provided in an eccentric connection where a load is lying perpendicular to the plane of the bolted joint are:
 
1)   Select the nominal diameter of the bolt and provide pitch and edge distance suitably

2)   Calculate the design shear strength of the bolt
3)   Select number of bolt lines and external moment due to eccentricity
4)   Find the approximate number of bolts per line
5)   Compute the shear force in each bolt
6)   Calculate the design tensile strength of the bolt group
7)   Calculate the tensile force in the extreme critical bolt
8)   Check for developed shear and tension individually
9)   Check the connection against combined shear and tension.
 

Eccentric Load Lying Perpendicular to Plane of Welded Joint
 
Basic steps to design an eccentric connection where a load is lying perpendicular to the plane of a welded joint:
 


Select a suitable size of weld and then compute effective thickness and weld strength
Calculate the depth of weld
Increase depth to a certain percentage to accommodate shear stress 
Calculate direct shear stress which should be less than weld strength
Compute stress due to bending which should be less than weld strength
Calculate equivalent stress which should be less than weld strength
If the equivalent stress exceeds the design weld strength, the length of the weld should be
increased and the above process be repeated until the checks are satisfied.