Solved Problems

1. Base Plate Bearing Area Without Confinement

A W10x49 steel column (Fy=50F_y = 50 ksi) is supported by a concrete pier (fc=3f'_c = 3 ksi). The pier dimensions exactly match the required base plate dimensions (A1=A2A_1 = A_2). The column carries an LRFD factored axial load Pu=300 kipsP_u = 300 \text{ kips}. Determine the minimum required area (A1A_1) for the base plate.

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2. Base Plate Bearing Area With Confinement

The same W10x49 column carrying Pu=300 kipsP_u = 300 \text{ kips} is now supported by a massive concrete spread footing where the concrete support area A2A_2 is significantly larger than A1A_1. Assume the maximum confinement multiplier applies. Determine the new minimum required area (A1A_1).

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3. Base Plate Required Thickness

A base plate is sized at B=14 inB = 14 \text{ in} and N=14 inN = 14 \text{ in} to support a W10x49 column (d=10.0 ind = 10.0 \text{ in}, bf=10.0 inb_f = 10.0 \text{ in}). The factored load is Pu=300 kipsP_u = 300 \text{ kips}. The plate is A36 steel (Fy=36 ksiF_y = 36 \text{ ksi}). Calculate the required plate thickness, tpt_p.

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4. Anchor Rod Tensile Design

Determine the required LRFD nominal tensile strength (PnP_n) of an anchor rod. The factored uplift force on the column is Tu=120 kipsT_u = 120 \text{ kips}. There are 4 anchor rods in the base plate layout, and the load is distributed equally among them. Assume the threads are included in the shear plane (though this is pure tension).

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5. Flange Force Extraction in Moment Connections

A fully welded moment connection is used to connect a W18x50 beam to a W14x90 column flange. The factored bending moment at the connection is Mu=240 kipftM_u = 240 \text{ kip}\cdot\text{ft}. The depth of the beam is d=18.0 ind = 18.0 \text{ in}, and the flange thickness is tf=0.570 int_f = 0.570 \text{ in}. Calculate the required factored force (PufP_{uf}) that the top flange weld must resist in tension.

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Case Studies & Practical Considerations

Case Study 1: Large Base Plate Leveling

A contractor is setting a massive W14x311 column on a concrete foundation for a heavy industrial facility. The concrete foundation is rarely perfectly level, and the heavy base plate (3 inches thick) must be set to an exact elevation. How is this practically achieved?

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Case Study 2: Resisting High Base Shear

A rigid frame building is designed to resist extreme lateral wind loads. The calculated lateral shear force at the base of the column exceeds the combined shear capacity of the anchor rods and the friction between the base plate and the grout.

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Case Study 3: Overturning Moments & Prying Action

A tall slender column is subjected to a large lateral wind load, creating a significant overturning moment at the base plate in addition to its axial load.

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6. Base Plate Bearing Pressure Under Axial Load Plus Small Moment

A base plate (N=20 inN = 20 \text{ in}, B=20 inB = 20 \text{ in}) is subjected to an axial load Pu=400 kipsP_u = 400 \text{ kips} and a small overturning moment Mu=1000 kipinM_u = 1000 \text{ kip}\cdot\text{in}. Assume the eccentricity is small (eN/6e \le N/6). Calculate the maximum bearing pressure on the concrete.

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7. Moment Connection Simple Web Yielding Check

A moment connection transfers a flange tension force of Puf=165 kipsP_{uf} = 165 \text{ kips} into the column. The column is a W14x90 (dc=14.0 ind_c = 14.0 \text{ in}, tw=0.440 int_w = 0.440 \text{ in}, kdes=1.31 ink_{des} = 1.31 \text{ in}). The specified yield stress of the column is Fyc=50 ksiF_{yc} = 50 \text{ ksi}. Determine if the column web yields locally under this concentrated force. Assume the force is applied at a distance greater than the column depth from the column end.

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8. Anchor Rod Shear Capacity Calculation

Calculate the LRFD nominal shear strength (ϕvRn\phi_v R_n) of a single 1-inch diameter ASTM F1554 Grade 36 anchor rod. The threads are included in the shear plane.

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9. Shear Lug Basic Bearing Capacity

A shear lug measuring 10 inches wide by 3 inches deep (embedded into the grout/concrete) is used to transfer a lateral shear force of Vu=80 kipsV_u = 80 \text{ kips}. The foundation concrete has fc=4 ksif'_c = 4 \text{ ksi}. Check if the bearing pressure on the concrete face of the lug is acceptable.

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10. Base Plate Bearing Pressure Under Axial Load Plus Large Moment

A base plate (N=20 inN = 20 \text{ in}, B=20 inB = 20 \text{ in}) is subjected to an axial load Pu=200 kipsP_u = 200 \text{ kips} and a large overturning moment Mu=1200 kipinM_u = 1200 \text{ kip}\cdot\text{in}. Assume the eccentricity is large (e>N/6e > N/6). Calculate the maximum bearing pressure on the concrete.

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11. Shear Transfer: Friction vs Shear Lugs

A column base must resist an axial load of Pu=150 kipsP_u = 150 \text{ kips} and a lateral shear force of Vu=40 kipsV_u = 40 \text{ kips}. The coefficient of friction between the steel base plate and concrete is μ=0.40\mu = 0.40. Determine if friction alone is sufficient, or if a shear lug is required.

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