Introduction
When designing steel moment connections, ensuring the column web can transfer the applied forces is critical for the overall performance of the connection. One of the key checks is web panel-zone shear, outlined in AISC 360, Chapter J10.6. This design check ensures that the web has enough shear capacity to transfer the forces applied to the flanges of a beam-column connection. In this post, we'll explore the principles of web panel-zone shear, and the example problem provided later will walk through the detailed steps of performing these calculations.
What is Web Panel-Zone Shear?
The web panel-zone of a column is the area between its flanges. In moment connections, this zone experiences shear forces as the applied moments generate opposing forces on the flanges. This condition typically arises when double-concentrated forces are applied to one or both flanges simultaneously, as often occurs in seismic or wind-resistant moment frames.
The AISC 360 design standard, specifically Chapter J10.6, lays out the requirements for checking web panel-zone shear. The goal is to ensure that the column web can safely transfer the moment-induced forces without excessive deformation or failure. The example problem later will demonstrate how to calculate if the web can safely carry these forces. If the web does not have enough capacity, as we’ll see in the example, a web doubler plate may be required to strengthen the panel-zone.
Key Considerations
Here are some of the main considerations when performing a web panel-zone shear check:
Depth of Column: The depth of the column affects the size of the panel-zone and the capacity of the web to resist shear forces. The larger the depth, the more area the web has to resist the applied forces.
Width of Column Flange: A wider flange provides greater resistance to the applied forces. In cases where the flange is narrow, the shear forces on the web can increase, necessitating more robust design.
Thickness of Column Flange: Thicker flanges provide more stiffness and strength to the moment connection. This impacts how forces are distributed to the web, which will be accounted for in the example problem.
Thickness of Column Web: The thickness of the web plays a direct role in determining its shear capacity. In the example problem, we’ll calculate if the web thickness is adequate to resist the shear demands or if a doubler plate is needed.
Depth of Beams: The depth of the connecting beams influences the magnitude of the applied moments, which in turn affects the shear forces in the panel-zone. The example problem will show how beam depth factors into the design process.
Material Strength: The yield strength of the column material determines its ability to resist the panel-zone shear forces. This consideration is critical in determining whether the column’s web can withstand the shear demands.
Panel-Zone Deformation and Frame Stability: Whether or not panel-zone deformations are considered in the frame analysis impacts the overall design. If deformations are accounted for, the column web may be allowed to experience some flexibility, but if not, additional reinforcement may be needed.
Example Problem (Solutions Provided Using CalcBook): Problem Statement:
Step 1: Preliminary Calculations
Step 2: Design Input
Step 3: Determine Capacity Equation
Step 4: Panel-Zone Shear Capacity
Step 5: Determine Controlling DCR
Conclusion:
Checking web panel-zone shear is an essential step in designing robust moment connections in steel structures. When double-concentrated forces are applied to one or both flanges of a beam-column connection, the web must transfer shear forces without excessive deformation. By following the design procedures in AISC 360 Chapter J10.6 and adding doubler plates when necessary, structural engineers can ensure their moment connections meet safety and performance standards. The example problem above demonstrates how these principles come together in a real-world design scenario.