ASDIP CONCRETE is a structural engineering software for the design of concrete members. ASDIP CONCRETE includes the design of two-way slab systems based on the latest ACI 318 provisions. This document is a step-by-step design example of a beam-supported two-way slab using ASDIP CONCRETE.
The design of two-way slabs may become cumbersome and time-consuming, since it involves the calculation of moments and shears in both directions, and the application of the Code provisions to design the reinforcement.
Two-Way Slab Example
As an example, determine the required reinforcement in an interior design strip of the beam-supported two-way slab system shown below, with a 7" thick slab, 28" by 24" beams, and 24" by 24" columns. Assume concrete f'c = 4 ksi and Grade 60 reinforcement. Superimposed DL = 10 psf, LL = 65 psf.
Two-Way Slab Geometry
In the Geometry tab select the slab type as Beam-supported. From the given information, the slab thickness is 7" and the beam size is 28" wide x 24" deep. The spans can be modelled as five spans @ 25'-0" in X, and four spans @ 23'-6" in Y.
The image below shows the Geometry tab at the left, and a summary view with the most relevant result information in the At-a-Glance tab at the right. Note that the results update automatically with any input changes.
Calculating the Moments
Go to the Loads tab to enter the loads provided in the statement of the example. In this case enter uniform dead and live loads of 10 and 65 psf respectively, in addition to the self-weight. Note that these are unfactored loads, and the program will combine them per the specified load combinations.
The software calculates the factored moments for an interior design strip in X and in Y, per the Direct Design Method of the ACI, including column strip, middle strip, and beams. It also calculates the factored shears along the beams. In this example the slab is beam-supported, therefore the punching shear is not critical at any of the columns, and the slab thickness is checked for serviceability requirements only.
The image below shows the Loads tab, and a view of the Condensed tab, showing detailed calculations organized by topic in a tabular format This is an excellent tool for a deeper check of the design as you go.
Specifying the Reinforcement
Go to the Reinforcement tab to specify the rebars for the slab and beams. ASDIP CONCRETE has multiple options to customize the reinforcement. In this example, we specified slab bars #4 @ 12" and 5 bars #6 for the beams. Typical 3-leg stirrups #3 @ 10".
The Detailed tab shows a step-by-step set of calculations, with exposed formulas and references to the design code. This is an excellent tool for a granular check of the full design.
The image below shows the Reinforcement tab and a construction view of the two-way slab design example. The rebar size and spacing are shown for column strip and middle strip in each direction.
Optimizing the Design
As you enter the information, the program calculates the bending moments and shear forces, and it compares these values versus the structural capacity. These design ratios are shown immediately in the At-a-Glance tab, so the user can change the input accordingly to improve the design.
In this example the maximum slab bending ratio is 0.98 at the middle strip in the Y-direction. This ratio can be reduced easily by reducing the rebar spacing in that area as required. The maximum beam bending ratio is 0.89. The minimum slab thickness ratio is 0.94. These ratios indicate that the design fully utilized the structural capacity in this example.
Takeaway
ASDIP CONCRETE includes the design of two-way slabs. This step-by-step design example shows how fast the design can be completed and optimized using ASDIP CONCRETE. The results are shown instantly in both text and graphics format for an immediate granular check.
For our collection of blog posts about concrete design please visit Concrete Design.
Detailed information is available about this structural engineering software by visiting ASDIP CONCRETE. You are invited to download the Free 15-day Software Trial or go ahead and Place your Order.
Best regards,
Javier Encinas, PE
ASDIP Structural Software
I cant use this email install, the text comes up tinny.
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