Worked Base-Connection Examples

Example 1: Concrete Bearing Without Confinement

A concentrically loaded plate carries Pu=300 kipsP_u=300\text{ kips} on concrete with fc′=3.0 ksif'_c=3.0\text{ ksi}. The plate covers the entire similar supporting area, so A2=A1A_2=A_1. For this teaching example use ϕ=0.65\phi=0.65.

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Example 2: Maximum Confinement Effect

Use the same load and concrete, but suppose the permitted similar concentric supporting area provides the maximum confinement multiplier of 2.0.

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Example 3: Concentric Plate Thickness Is a Different Limit State

A selected plate is 14 in by 14 in under a concentric column. The concrete bearing check passes.

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Example 4: Full-Contact Eccentric Bearing Screening

A 20 in by 20 in plate carries P=400 kipsP=400\text{ kips} and M=1000 kip-inM=1000\text{ kip-in} about the 20 in dimension. Assume the full-contact linear bearing model is valid.

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Example 5: When Full Contact Is Lost

For a different load case, e=M/P>N/6e=M/P>N/6.

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Example 6: Anchor Rod Tension Is Not Only a Steel-Rod Calculation

Four anchors share a calculated factored tensile action of 120 kips before prying/redistribution effects, giving a preliminary 30 kips per anchor.

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Example 7: Base Shear and Friction

A column base has significant shear and compression.

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Example 8: Moment-Connection Flange Force as a Force-Path Approximation

A beam connection carries Mu=240 kip-ft=2880 kip-inM_u=240\text{ kip-ft}=2880\text{ kip-in}. The beam depth is 18.0 in and flange thickness is 0.57 in.

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Example 9: Seismic Base/Connection Scope

A base or moment connection passes ordinary static AISC 360 strength checks but belongs to the seismic force-resisting system.

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Key Takeaways
  • Concrete bearing area and base-plate thickness are independent checks.
  • The A2/A1A_2/A_1 confinement benefit uses only the permitted similar/concentric supporting area.
  • Full-contact bearing formulas are valid only while the computed contact pressure remains nonnegative.
  • Anchor design requires both steel and concrete anchorage checks and a defensible load distribution.
  • Friction must use the correct maintained interface compression for the governing shear combination.
  • Moment-connection flange-force couples are useful force-path approximations, not complete connection designs.