Last Updated on February 14, 2026 by Maged kamel
The Effective Area for a Built-Up Section.
This post will check a practice problem for a built-up section, problem no.3-19, quoted from Prof. Mccormack’s book, fifth edition. It is required to compute the effective net area of the built-up section shown in Fig 3-19. The holes are punched for 3/4 inches. The U factor is set to 0.90.
The gross area for a Built-Up Section.
The built-up section consists of two C10x25 channels and two 1/2×11-inch plates. Each plate is 1/2 inch thick and 11 inches long.
We will estimate these four elements. Since we have two channels, we can estimate the gross area for one channel and multiply it by two. Similarly, we can find the area of one plate and then multiply it by 2.
From Table 1-5, the table of channel areas, we find that section C10x25 has an area of 7.35 in^2.
It is easy to estimate the area of a rectangle (1/2″x 11 “) for a plate. The area of one plate is equal to (1/2) × 11, which is 5.50 in^2.
The areas of the two channels are equal to (2×7.35)=14.70 inch^2.
The area of the two plates equals (2*5.50) = 11.0 in^2.
The sum of the areas gives a total of 14.70 in^2; please refer to the next image for more details.
The bolts used are of diameter 3/4 inches, to get the hole diameter we add 1/8 inch to the bolt diameter so the diameter of the hole will be equal to 7/8 inches.
The net area for a Built-Up Section.
For the Effective Area of a Built-Up Section, we need to find the net areas of the two channels and the two plates.
1-for the net area for plates, use section (1-1). We have 4 bolts, and the area of these 4 bolts equals the hole diameter multiplied by the number of bolts and by the plate thickness; this value will be deducted from the gross area of the plates.
We can use the same section, 1-1, to get the net area of the two channels. Again, we have four bolts connecting the flanges of the two channels to the upper and lower plates.
We estimate the area of the holes by multiplying the hole diameter by 4 and by the thickness of the C channel flange.
The final net area of the built-up section equals 22.42 square inches. The net area for channels is 13.74 square inches. The net area for the two plates is 9.25 square inches. Please refer to the next slide image for more details.
The Effective Area for a Built-Up Section.
The final value for the effective area for a built-up section will be equal to U*An, where U is given as equal to 0.90; then the effective area of a built-up section will be equal to the product of (UxAn) or 0.9x(13.174+9.25)=20.18 inch^2.
The PDF file for this post can be viewed or downloaded from the following link.
For staggered connection, please refer to posts 16 and 17 for the details of a solved problem, Problem 3-4-3 for the MC section-staggered bolts.
For more information about block shear for beams, please refer to Block Shear-Coped Beam Problems.
This post is included within the list of tension members’ posts- part 3.
A useful external link –Tensile yielding and tensile rupture. A Beginner’s Guide to the Steel Construction Manual, 14th ed.
A useful external link –Tensile yielding and tensile rupture. A Beginner’s Guide to the Steel Construction Manual, 15th ed.
A useful external link –Tensile yielding and tensile rupture. A Beginner’s Guide to the Steel Construction Manual, 16th ed.