# Slab Punching Shear Calculator

The SkyCiv Punching Shear Design Software allows users to estimate the punching shear capacity of a reinforced concrete slab panel subject to point loading. Punching shear checks are used to ensure that a concrete slab is capable of resisting local forces concentrated around columns (under) or applied forces (over). Punching shear is a brittle failure mode, meaning that it can lead to structural collapse if not accounted for in design. In some cases, the minimum required slab thickness can be governed by punching shear resistance, rather than bending capacity or deflection.

SkyCiv offers tools to calculate punching shear resistance for the following codes:

- ACI 318-19: Building Code Requirements for Structural Concrete
- AS 3600:2018 Concrete Structures

The below calculator allows engineers to conduct punching shear checks and provides detailed, code referenced calculation reports explaining the results.

## About Punching Shear

## What is Punching Shear?

Punching shear refers to a mode of structural slab failure that occurs around concentrated load-bearing points. The most common causes of punching shear failure are punching of a column (under) or a point load (over) through a slab. Punching shear occurs as a "cone" failure through a slab (refer graphic below), where the slab cracks diagonally outwards from the point load/slab interface.

The failure "cone" through which punching shear occurs is referred to as the "critical shear perimeter". This perimeter is proportional to the dimensions of the applied load, and the thickness of the slab supporting it. The larger the critical shear perimeter, the greater capacity against punching shear failure. Design to strengthen a slab against punching shear often includes increasing the size of this perimeter or strengthening it with reinforcement.

Bending moments within a slab can contribute to punching shear failure, as flexure cracking can exacerbate punching shear cracking. Hence the interaction of shear and bending needs to be taken into account in capacity calculations.

## How to Prevent Punching Shear Failure?

Special detailing is required around columns and point loads to reinforce the slab against punching shear failure. Punching shear capacity can be increased by any of the following methods:

- Increasing slab depth
- Distributing point loads over a larger area
- Incorporating punching shear reinforcement over supports
- Local slab thickenings at supports (i.e. drop panels)
- Increasing concrete strength

These methods are all focused on either increasing the size of the critical shear perimeter or increasing the strength of the concrete section at the critical shear perimeter.

## How to Calculate Punching Shear Capacity?

Punching shear capacity is calculated in the following sequence:

- Calculate critical shear perimeter, based on point load area and slab thickness.
- Calculate concrete shear strength, taking into account the critical shear perimeter and any bending moments within the slab.
- Calculate contribution of shear reinforcement to section shear capacity.
- Calculate overall concrete section shear capacity.

Calculation methods vary slightly across regions but are based in similar logic. SkyCiv offers calculation tools that support American (ACI) and Australian (AS) design standards.

## Punching Shear Software - Frequently Asked Questions

**What does the SkyCiv Punching Shear Software do?**

This punching shear calculator determines the punching shear capacity of a slab panel subject to high local shear force in accordance with ACI 318-19 and AS 3600.

**What type of concrete types are supported?**

The ACI 318-19 calculator supports both normal weight as well as light weight concrete. The AS 3600 calculator supports normal weight concrete only.

**What type of shear reinforcements are supported?**

The ACI 318-19 calculator can consider either stirrups or headed studs in the form of shear reinforcement. The AS 3600 calculator focuses on concrete capacity only but allows users to specify whether a shear head is provided.

**What punching shear strength cases are checked?**

The following cases are checked in the ACI 318-19 Punching Shear Calculator:

- Concentrated Load Transferred at the Interior of the Slab Panel
- Concentrated Load Transferred at the Edge of the Slab Panel
- Concentrated Load Transferred at the Corner of the Slab Panel

The AS 3600 Punching Shear Calculator checks interior slab loading only.

**What inputs are required by the calculator?**

Inputs are required for the column dimensions, slab dimensions, the concrete properties and the reinforcement/shear head properties.

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## About SkyCiv

SkyCiv offers a wide range of Cloud Structural Analysis and Design Software for engineers. As a constantly evolving tech company, we're committed to innovating and challenging existing workflows to save engineers time in their work processes and designs.