Hi friends,

On last week's newsletter, we learned how to calculate and design reinforced concrete beams by hand. Today, I'll show you how to use structural design software to achieve the same.

As I said last week, knowing and learning the formulas from Eurocode or other standards is important, as you need to know what inputs you need to insert into the software. And you need to evaluate if the results make sense.

Garbage in equals garbage out!

But if you are familiar with the formulas, structural design software is very powerful. It's indispensable in today's structural engineering projects.

I am very happy and proud that ClearCalcs sponsors this episode of the Structural Basics newsletter.

As a Structural Basics reader, you also get a special deal. You get a 3-month free trial, instead of 1 month, if you sign up for a free trial by using the Structural Basics referral link: https://app.clearcalcs.com/?referralCode=2sGhr3a7c6rxKYhP&utm_source=structuralbasics&utm_medium=partnership&utm_campaign=newsletter-sponsorship​

This partnership is great, because I can show and teach you how to use structural design software.

In this newsletter, I’ll show you how to use the ClearCalcs concrete beam calculator to design and verify reinforced concrete beams. We first, input geometry parameters like the cross-sectional dimensions, material parameters of the concrete and reinforcement, then loads and deflection criterias. Finally, we check out the results and evaluate them.

Let's get into it..

1. Sign-up and open the Concrete Beam Calculator

ClearCalcs is a web-based software, which makes it easier and faster to get started, because we don't need to install anything.

→ Sign up here and claim your 3-month free trial. ←

You can sign up with your Google or Microsoft account. Or if you don't want that, just with your e-mail.

Next, open the Concrete Beam Calculator.

Once we are in the ClearCalcs project folder, click on Create a new project or if you already created a project for the beam analysis two weeks ago, you can also use that project.

If you create a new project, then fill out the project details (project name, project number, building standard → Eurocode for me) and click on Add a calculation. I already did this in the newsletter 2 weeks ago. You can fill out a project address if you want. This is beneficial if you design exterior walls, or roof rafters, because ClearCalcs automatically calculates the wind and snow loads based on the project address. For now, I just selected the address of the football stadium I used to play in.

Next, we click on Rectangular Concrete Beam.

2. Properties of the beam

First, we enter all the key properties of the beam such as cross-sectional dimensions, concrete strength, span, type and positions of the supports.

1. Depth and Width of Cross-Section: This is self-explanatory. In this tutorial, I use h=500mm as the cross-sectional height and b=300mm as the width.

2. Concrete Strength Class: When you click on this input field or click on Select, you can choose the concrete strength. C25/30 or C30/37 are most common for reinforced concrete beams.

3. Length of Member: In this example, we'll use 7m =7000mm as the length.

4. Supports: We have a simply supported beam with 2 pinned supports. In theory, one of the supports should be a roller support. But because the beam isn't inclined and will not be exposed to a normal force 2 pins are also ok. If you need to learn about supports and reaction forces, then check out this YouTube tutorial.

5. Nominal Concrete Cover: The concrete cover depends on the exposure class of the beam. The cover "safes" the reinforcement from external influences which can destroy it, such as fire and water.

6. Cracked or Uncracked Concrete: Once the tensile stress of concrete is reached, concrete cracks. This happens for most reinforced concrete elements. The result is that the structural element is less stiff (= E-modulus is reduced). Therefore, we select Cracked.

7. Partial and Reduction Factors of Concrete and Reinforcement: We use the partial factors from EN 1992-1-1 Table 2.1N. But these can be defined differently in your National Annex.

3. Reinforcement of the beam

Next, we select the longitudinal and shear reinforcement of the beam.

Longitudinal Reinforcement at Midspans (Positive Moment Regions)

1. Bottom Reinforcement Type: Here you select the diameter of the bottom reinforcement. For simply supported beams this is the critical reinforcement to resist bending moments. When you click on Select, you can choose all the different diameters. And another advantage of ClearCalcs is that you even get a summary of the utilisation for each rebar diameter. We use d=16mm.

2. Number of Bottom Reinforcement Bars: We use 7 rebars in the bottom.

3. Top Reinforcement Present: I recommend always using rebars in beams. I have never seen a concrete beam without rebars. So, we select Yes.

4. Top Reinforcement Type: This is the same input as 1. just for the top reinforcement. The top reinforcement must at least fullfill the minimum reinforcement requirements. But often that is not enough to fullfill the crack width requirements.

5. Number of Bottom Reinforcement Bars: We use 5 rebars in the top.

Longitudinal Reinforcement at Supports (Negative Moment Regions)

This is kind of the same input as for the longitudinal reinforcement at midspan.

Transverse Shear Reinforcement at Supports

1. Angle of Shear Stirrups: Stirrups that are placed vertically have an angle of 90 degrees.

2. Cotangent of the Anlge Inclination of the Compression Struts: According to EN 1992-1-1 6.2.3 (6.7N) this value should be between 1 and 2.5, but may be defined differently in the National Annex. I usually use 2.5.

3. Shear Reinforcement Type: This is the diameter of the shear reinforcement. We use d=8mm.

4. Number of Legs per Stirrup Bundle: A stirrup has 2 vertical legs/rebars. Therefore we set this value to 2.

5. Longitudinal Spacing of Stirrups: This is the distances between the stirrups. We set it to 200mm.

4. Loads

Next, we'll apply loads on the beam. ClearCalcs has many options for loads, like triangular loads, moments, axial loads, etc. You can even link loads from a previous calculation. In 95% of beam calculations, we only need line and point loads. But line loads often come from area loads that are applied to slabs. In ClearCalcs we can define the area loads and then the spacing between beams. It then calculates the line load from it.

Note that ClearCalcs doesn't use kN/m2 as unit but kPa (1 kN/m2 = 1 kPa).

1. Name of the line load: I just called it Floor Load. Feel free to use a different name.

2. Start Location: This is the location on the beam, starting from the left, where the load value defined in 5. starts. We use a line load on the entire length of the beam. We therefore set it to 0.

3. End Location x: This is the location on the beam, starting from the left, where the load value defined in 5. ends. We use a line load on the entire length of the beam. We therefore set it to 7000 (7m away from the start of the beam).

4. Start and End Load Width: This is the influence load width of the beam meaning how much of the area load the beam takes up. We set it to 2000. This means that the spacing of the beams is 2m.

5. Load Magnitude w: This is the area load values on the floor. We use 3 kPa (=3 kN/m2) as the dead load and 1.5 kPa (=1.5 kN/m2) as the live load. Btw in the top of this section the calculated loads on the beam are visualised (see picture above).

6. Location x: We also add a point load. Location x is the location on the beam, starting from the left, where the point load is applied. We set it to 3500 which means that it's applied at midspan of the beam.

7. Load Magnitude: This is the load value of the point load in kN. We set the live load to 20.

8. Building Category for imposed Load: This is the live load category. It's important for the automatic load combination calculation. The different categories have different psi factors. The beam is part of a residential building. We therefore set the category to A.

9. Include Self Weight: We select Yes. The self-weight of reinforced concrete beams can be quite large.

5. Design Criteria

Finally, we define the deflection criterias.

1. Deflection Limit Absolute Criterion: This is a very important criteria. For example in schools or in other buildings, you often have the criteria that the deflection due to live loads is max. 10mm because there are partition walls which would be damaged with bigger deflections. In our example we use 20 mm.

2. - 4. Characteristic, frequent and quasi-permanent deflection: These criteria depend on the country you work in, the building type and the client. In almost every project I have different deflection criteria. L/250 is a good value to work with.

We now have inserted all the required inputs..

6. Results of the beam analysis

The calculation happens automatically. We instantly get the results like positive and negative bending moment, shear forces, deflection, bending verification, shear verification etc.

In ClearCalcs there are a few options to view the results.

Below the input sections, we get the calculation and results of each verification. Even the design load which are calculated in load combinations:

• Load Case Analysis
• Unfactored Load Analysis
• ULS: Flexural Analysis at Midspan
• ULS: Flexural Analysis at Supports
• ULS: Shear Analysis at Supports
• SLS: Crack Control and Widths
• SLS: Deflection Control
• Deflection Analysis

When we click on a design verification we can see all the that were used in the calculation. It's not a black box which is great!

As an example, let's look into ULS: Flexural Analysis at Midspan. If you want to see how a variable was calculated, click on it's name. There's even an explanation added.

At the end of each verification section you see the utilisation ratio. In our example the bending verfication at midspan is 66%.

And then there is also the summary on the right side of the interface and at the very top. That's great when you are adding or removing reinforcement to quickly see if the beam is still verified. It also has shear, moment and deflection diagrams which are interactive. Simply click on one of the diagrams and the values are shown.

7. Export as a PDF

As a structural engineer, you also need and want to document your calculations as PDF files.

And of course, we can also export the ClearCalcs calculations as a PDF. Simply click on the print button in the top right corner, select your Print Mode and Paper size of choice, and click on Export.

Final words

Now you have your first structural calculation report of a reinforced concrete beam in PDF, which you can attach to your Structural Design report.

Let me know how you like ClearCalcs' concrete beam designer. Or if it was the first time you used a structural design tool let me know how much you like these tools instead of calculating with paper and pen. 😄

I hope you like these guides about how to use software in structural engineering. This is how structural engineers really do their work 80% of the time.

Thank you, ClearCalcs, for sponsoring this episode of the Structural Basics newsletter.

See you next Wednesday my friends.

Let’s design better structures together,

Laurin.

P.S.: In case you missed the ClearCalcs trial link, here’s another chance to claim your 3-month free trial and get started with structural design software today.

​