Last Updated on September 10, 2026 by Maged kamel
The Effective Area for a Built-Up Section.
This post will review a practice problem for a built-up section, problem no. 3-19, quoted from Prof. McCormack’s book, fifth edition. Compute the effective Area of the built-up section shown in Fig. 3-19. The holes are punched for 3/4 inches. Set the U factor to 0.90.
The gross Area for a Built-Up Section.
The built-up section consists of two C10x25 channels and two 1/2 x 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 in^2.
The Area of the two plates equals (2*5.50) = 11.0 in^2.
The sum of the areas is 14.70 in^2; please refer to the next image for more details.
The bolts are 3/4 in. in diameter; to find the Hole diameter, add 1/8 in. to the Bolt diameter, so the Hole diameter is 7/8 in.
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 of the 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 the plate thickness; we will deduct this value 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, four bolts connect the flanges of the two channels to the upper and lower plates.
We estimate the Hole Area by multiplying the Hole diameter by 4 and 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 the 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.
You can view or download the PDF file for this post from the following link.
For staggered connections, please refer to posts 16 and 17 for details on a solved problem, and Problem 3-4-3 for the MC section on 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.