Advanced calculation inputs
Enter geometry, material values, and factored shear
This calculator performs a preliminary ACI-style two-way shear check for rectangular supports. It assumes a centered gravity reaction, nonprestressed concrete, and no punching shear reinforcement.
Example data table
Typical interior slab-column input set
| Input | Example value | Purpose |
|---|---|---|
| Factored shear, Vu | 180 kips | Gravity demand at the critical perimeter. |
| Concrete strength, f′c | 4,000 psi | Concrete shear resistance input. |
| Column size | 18 in × 18 in | Determines β and the critical perimeter. |
| Slab thickness | 10 in | Supports effective depth estimation. |
| Cover and bar diameter | 0.75 in and 0.625 in | Used to estimate d when overrides are blank. |
| Strength factor, φ | 0.75 | Reduces nominal capacity to design capacity. |
Formula used
Two-way shear equations and check sequence
The method evaluates three candidate concrete shear stresses and uses the smallest value. It uses a rectangular critical perimeter, a depth size-effect factor, and support-location coefficient αs.
Critical perimeter and demand
US customary expressions
Metric expressions
The calculator uses αs = 40 for interior columns, 30 for edge columns, and 20 for corner columns. It limits the square-root concrete-strength term to the selected method cap.
How to use this calculator
Complete the puncture shear check
- Choose US customary or metric units before entering values.
- Enter the governing factored vertical shear at the support.
- Select the support location and enter the rectangular column dimensions.
- Enter thickness, cover, and bar diameter. Add d1 and d2 only when known.
- Use b0 override when an engineer has defined a special critical section.
- Press Calculate puncture shear. Review stress, capacity, and demand ratio.
- Download the CSV or PDF report for project records. Verify final design separately.
Design guidance
Concrete puncture shear basics
Understand the local action
Concrete puncture shear is a local two-way shear check. It applies near columns, reactions, and concentrated loads. The concrete can fail rapidly around a closed perimeter. That perimeter sits near the support face. A sudden failure can occur with little warning.
Define the critical section
The first task is identifying the governing critical perimeter. For a rectangular interior column, the perimeter lies d/2 from each face. Effective depth d measures the distance to tension steel. The calculation uses the average effective depth when directions differ. A smaller depth reduces the available shear area.
Compare demand and resistance
Factored shear force creates the demand. Divide Vu by b0 times d. The result is the factored shear stress. Concrete strength creates the nominal resistance. The resistance depends on f'c, density factor, support location, depth, and column shape. A strength reduction factor then gives the available design strength.
Use the report wisely
A rectangular column needs its long-to-short ratio. This ratio is beta. A long column changes the shear field. The procedure evaluates three concrete stress expressions. The lowest expression controls. Interior, edge, and corner supports use different alpha values. Edge and corner perimeters are shorter. They often need closer review.
This calculator automates a gravity-only, nonprestressed check. It uses a rectangular support and no punching shear reinforcement. It can estimate effective depth from total thickness, cover, and bar diameter. You may enter directional depths when they are already known. A perimeter override is available for an engineer-defined section.
The screen result shows demand stress, nominal stress, design capacity, and utilization. A utilization at or below one indicates the calculated check passes. A higher value indicates inadequate concrete-only capacity. Do not treat a pass as complete slab design. Flexure, deflection, development, minimum reinforcement, and load transfer still matter.
Openings near a support can remove part of the perimeter. Drop panels and capitals create extra critical sections. Unbalanced moments create nonuniform shear stress. Shear studs or stirrups change the applicable resistance method. Prestressed slabs also require separate conditions. These cases need a full code-based review.
Use consistent factored loads and dimensions. Keep the chosen unit system unchanged during entry. Confirm cover and bar size from the actual detail. Check the support location carefully. Save the report with project assumptions. Always verify final design with a licensed structural engineer.
Frequently asked questions
Concrete puncture shear answers
1. What is concrete puncture shear?
It is two-way shear around a column, reaction area, or concentrated load. The support can appear to push through the slab or footing if the surrounding concrete cannot resist the demand.
2. What load should be entered as Vu?
Enter the governing factored vertical shear crossing the selected critical perimeter. Use the relevant load combination. Do not enter an unfactored service reaction unless the check method specifically requires service loads.
3. Does this calculator include unbalanced moment transfer?
No. It assumes centered gravity shear. Unbalanced moments create nonuniform stress around the perimeter. Use a complete slab-column connection procedure when wind, seismic, frame action, or eccentric loading transfers moment.
4. Why does effective depth matter?
Effective depth controls the shear area b0d. It also affects the size-effect factor. A small change in d can change demand stress, capacity, and the final utilization ratio.
5. What is the critical perimeter b0?
It is the calculated path around the support where punching shear is checked. For ordinary rectangular supports, it is commonly located d/2 from the support face. Irregular geometry may require an engineer-defined perimeter.
6. Which support location should I choose?
Select interior when the column is surrounded by slab. Select flush edge or flush corner only when the column face aligns with a free slab edge. Use an override for different edge geometry.
7. When should I use the perimeter override?
Use it after a qualified designer determines b0 for openings, drop panels, capitals, nonrectangular supports, or other special conditions. The override replaces the page’s simplified geometric perimeter.
8. Does this page design shear studs or stirrups?
No. It checks concrete-only capacity. Shear reinforcement requires additional strength equations, detailing limits, spacing rules, anchorage checks, and an outer critical-section review.
9. Can I use it for a footing?
It can provide a preliminary two-way shear check for a rectangular footing reaction area. You must still verify soil pressure, one-way shear, flexure, development, reinforcement, and all footing-specific code requirements.
10. Does the result cover nearby openings?
No. Openings near a support can reduce the effective critical perimeter. Define the required perimeter using the adopted design standard, then enter that value through the b0 override field.
11. Is a passing result a final design approval?
No. It is a preliminary screening result. Always verify final design with a licensed structural engineer.