One way Slab – Types, Farmula and Reinforcement details
One kind of reinforced concrete slab is known as the one way slab. The main purpose of the slab is to resist bending in a single direction. In simple terms, “one-way” means that the slab is strengthened to support loads that are largely transported in one direction, typically the shorter span. One way slab and two way slabs are much different.
What is One Way Slab?
If loads are distributed along one direction or way of a slab and these loads are carried by two opposite sides (longer side), then the slab is called a one-way slab.
In the figure (L) is long direction and (W) is short direction of the slab. If L/W> 2, then the slab is one way and the deflection occurs in one direction only.
Definition of the One way slab:
In one way slab, the ratio of a longer span (L) to a shorter span (W) is equal or greater than 2. However, when a longer span (L) to a shorter span (W) is equal or greater than 2, then the slab will bend in one direction i.e. short direction.
Types of one way slab?
- One-way solid slab (with beams)
- One-way ribbed slab (with beams)
- One-way ribbed slab with integral beams
One Way Slab Formula:
Longer span(L) /Shorter span (W)>= 2
One way slab Example:
L= 6
W= 2
L/W=6/2=3>2
What is the One Way Slab reinforcement details?
In one-way slabs, reinforcement works to compete with tensile forces. It improves the slab’s resistance to bending and prevents failure or splitting under loads. It changes the brittle concrete into a composite material that is more durable and ductile.
Beam: Structure element to carry load In one way slab one direction beam is used.
Slab Formwork: A temporary framework named slab formwork is used to support and shape concrete slabs while they are being built.
Concrete Cover: The layer of security for concrete reinforcement from corrosion and environmental effects.
Bottom Main Bars: The main sidebars and the main cranked bars are placed in shorter spans only. As deflection and bending occur in short direction in one way slab, the rebars required along short direction to prevent the bending are known as the Main bar.
Bottom Crank Bar: Minimum rebars for temperature and shrinkage, provided along long directions are known as distribution bars.
Bottom Distributed Bars: The extra distributed bars provided on the upper part of the bottom crank bar are just provided to support the cranked portion of the main steel bars.
Top Bars: Reinforcement bars are inserted in the upper part of a concrete element to provide it with more strength and support.
How to design the One Way Slab?
The ACI 318-19 criteria must be followed when building a one-way slab. This includes calculating the concrete’s compressive strength, slab thickness according to support conditions, and the concrete cover’s capability to maintain reinforcement.
Concrete features and steel yield strength both have a direct effect on the maximum and minimum reinforcement ratios. Therefore, these are significant considerations. An economical design is shaped through factors such as carefully placed steel bar spacing, crack prevention, and bar size decision-making.
All factors that balance handling capability and manufacturing costs. Through cost-effective construction, this comprehensive method maintains the one-way slab’s strength and structural integrity. Moreover, to know the whole details about how to design the one way slab view the video.
Thickness of the One way slab:
According to the ACI-318 table, the minimum height of the slab is given below.
Support Condition | Minimum Height h(min) |
---|---|
Simply Supported slab | L/20 |
One end Continuous Slab | L/24 |
Both End Continuous Slab | L/28 |
Cantilever Slab | L/10 |
How to calculate the load of the one way slab?
The load distribution can be calculated by examining the slab’s deflection and bending moments. In the case of one-way slabs, the load is distributed in proportion to the tributary area that each wall or beam supports.
Here are the general steps mentioned to distribute the load of the one-way slab. Also, you can watch the tutorial to better understand.
- Determine the type of the slab:
- Calculate the load on the slab:
- Determine the slab’s flexural behavior:
- Calculate the bending moments:
- Determine the load distribution:
- Check the deflection:
Frequently Asked Question:
How do you know if a slab is one-way?
If you see a rectangular slab that is supported on all four sides but the ratio of the longer side to the shorter side is greater or equal 2. So, the slab is the one way slab.
What depth of a one way slab?
The slab’s depth, as determined by the span to depth formula of span/30, is primarily between 4″ and 10″ (10.2-25.4 cm).
What size is a one way slab?
Conventional spans of 6′-20′ (1.83-6.1 m) and post-tensioned spans of 13′-28′ (3.96-8.53 m) are the two standard sizes for One-Way Slab Concrete Floor construction.
Wrapping Up:
A one-way slab is used in constructions where support in one direction is required. Remember that slab design requires structural consideration. Engineers are experts and they use many methods to design structural integrity.