Understanding Lug Angles in Steel Structures

Lug angles are short lengths of angles or other structural shapes used to connect outstanding legs of tension members, like angles or channels, to the gusset plate or other connecting component. Their primary purpose is to reduce the shear lag effect and distribute the load more evenly among the different legs of the tension member. This leads to a shorter connection length required to transfer the full load.

Analysis of Statement (i): Reduced Connection Length

Statement (i) says "The length of end connection is reduced". This is a key benefit of using lug angles. By providing an additional connection point for the outstanding leg, the load is transferred to the gusset plate over a shorter distance along the main member's connected leg. This reduces the effective length of the connection required to develop the full strength of the member, making the overall joint more compact.

Therefore, statement (i) is correct.

Analysis of Statement (ii): Saving in Gusset Plate

Statement (ii) says "By using lug angles there will be saving in the gusset plate". While reducing the connection length might sometimes allow for a slightly smaller gusset plate, this is not a guaranteed or primary outcome. The main purpose of the lug angle is connection efficiency and reducing shear lag, which leads to a shorter connection length. Using a lug angle adds material (the angle itself) and fasteners. Any potential saving in the gusset plate size might not outweigh the added cost and material of the lug angle and additional fasteners. In many cases, the gusset plate size is determined by other factors like bolt spacing, edge distances, and overall geometry, rather than solely the connection length along the main member.

Therefore, statement (ii) is generally considered incorrect as a primary or guaranteed benefit.

Analysis of Statement (iii): Cost of Connection Increases

Statement (iii) says "Cost of connection increases due to additional fasteners and angle required". This statement is correct. When you use a lug angle, you need to purchase and fabricate the lug angle itself, and you need additional bolts or welds to connect the lug angle to both the main tension member and the gusset plate. These extra materials and labor directly increase the overall cost of the connection compared to a similar connection without a lug angle that would require a longer joint length.

Therefore, statement (iii) is correct.

Evaluating the Statements about Lug Angles

Based on the analysis:

• Statement (i) is correct because lug angles reduce the required length of the tension member connection.
• Statement (ii) is incorrect because saving in the gusset plate is not a guaranteed outcome and the cost often increases overall.
• Statement (iii) is correct because the additional material and fasteners for the lug angle increase the cost of the connection.

Thus, only statements (i) and (iii) are correct regarding the use of lug angles in tension members.

Revision Table: Lug Angle Characteristics

Additional Information: Steel Tension Member Connections

Connecting tension members in steel structures is crucial for transferring tensile forces safely. When connecting angle or channel sections, shear lag can occur, where the stress is higher in the connected leg than in the outstanding leg. This reduces the efficiency of the connection. Lug angles are a common method to mitigate shear lag and ensure that the full cross-section of the member is effective in resisting the tensile load. While they add complexity and cost to the connection, they allow for shorter joint lengths, which can be beneficial in reducing the overall size of the connection region and potentially the size of the gusset plate, although the latter is not a primary guarantee as discussed.