by Tom Kujawa

Designing a steel beam is not as complicated as you may think. There are essentially 6 Steps to design most steel beams:

- Material - Choose the appropriate grade of steel for the beam you will be designing.
- Shape - Select the shape of steel beam you would like to design.
- Span - Enter the distance you are trying to span.
- Bracing - Not to be overlooked! Bracing is critical in determining the capacity of a beam.
- Load - Enter loads based on their type and load case.
- Design - In the United States, there are two common methods of beam design (ASD and LRFD). Select the method you would like to use and specify deflection limits.

In the WebStructural beam design app each of these steps has an associated icon to allow you to efficiently work through the design process.

There are many different grades of steel, but usually one common
grade for each shape type. There are also many different shape
types used in steel construction including: W, HSS, C, and angles
to name a few. One of the most commonly used shape types for I-beams
in steel construction is the W (wide flange) shape. W Shapes are
usually made from Grade A992 steel. For our example, we'll be
designing a W shape steel I-beam. Let's start by selecting the
appropriate material for this shape. Click the **"Edit material..."**
link to launch the **Material Dialog** and select A992 from the
material list.

Next, let's select our W shape from WebStructural's extensive shape
library. Click the **"Edit shape..."** link to launch the **Shape Dialog**
and select W8X15 from the list (you might need to scroll the list a little to find it).
This beam is roughly 8" deep (or tall), that's the first number in
the shape name. The beam weighs 15 lbs/ft, the second number in
the shape name. Typically, the lighter the beam, the less it will cost,
so to design the most cost-effective beam, you'll want to choose one
that weighs the least but meets your design criteria. After we enter
all the design criteria and analyze our beam, we can always change the
shape and material if it's not adequate for our loads (demand).

Span is the distance between points of support for a beam. A beam
is often just a single span supported at both ends. However, that's
not always the case. Beams can be supported anywhere along their
length or they can be cantilevered beyond their end supports. To
add or edit span length in WebStructural, simply click **Edit spans...**
or click the span dimension on the drawing and add a span to the
left or right, then enter the length of your second span.

For our example, add a span to the right and make it 4'-0". Adjust the first span to equal 12'-0".

Beam support conditions can also be changed in WebStructural by simply
clicking on a support (the gray triangle under the beam). Cliking a
support will toggle through three support types (support conditions):
Pinned, Fixed, or Free. For our example, change the right most support to **Free**
by clicking the right-most gray triangle in the drawing. This will
create a cantilever (overhang) on the right side of the beam.

Bracing is an incredibly important, yet often overlooked aspect of beam design.
When a beam is bent, tension and compression forces are introduced.
For a simple span beam (one spanning between two pinned supports),
the top of the beam will be in compression. It is these compression
forces that can cause a beam to buckled out-of-plane
(called lateral torsional buckling or LTB). To understand this type
of buckling, think of compressing a short ruler between your hands.
Now think of compressing a yard stick. Which one is more likely to
flex and twist when you compress it? Clearly the longer, more slender one.
It is this slenderness that is directly related to buckling.
If we are able to brace a beam against this type of buckling, then
we can often achieve greater bending strength. **WebStructural**
allows you to specify bracings in many different common configurations.
Span supports are automatically assumed to be bracing locations.
Remember, continuous bracing assumes that the compression side of
the beam is braced. If you need to find the compression side of your
beam just take a look at the moment diagram. The compression side
will be the inside of the curve where ever you see areas of high
curvature (moment). If you're unsure about bracing conditions you
can always conservatively assume the beam is completely unbraced.

A beam can carry loads from many different sources. Below is a list of some of the more common types of Load Cases:

**Dead loads (D)** are those which are always present.
Think of a concrete slab, or the weight of a wall. Those loads are always present
and do not change.

**Live Loads (L)** are typically occupancy type loads. You
are a type of Live Load in the structure you are in right now. American
Society of Civil Engineers publishes a book (ASCE 7) with guidance for the
amount of live load that should be used for different structures.

**Roof Live Loads (Lr)** are similar to Live Loads, but are
specific to the roof and are typically related to construction or maintenance
activities.

**Snow Loads (S) **are exactly want they sound like, loads
cause by snow. Local building codes often dictate the appropriate ground or
design snow loads to use. These are typically basic loads. Drift and
unbalanced conditions should be accounted for as needed.

**Other Loads** are less common in beam design but can include
Wind (W), Seimic or Earthquake (E), Rain (R), Lateral Earth (H), etc.

Beams can be loaded in many ways, but most loadings that cause flexure can be described as either:

**Uniform Loads** These loads have units of force per unit length.
With WebStructural, the default units for Uniform Loads is kips per foot (1 kip = 1000 lbs.).
Uniform loads are often used to simplify repetitive and closely spaced point
loads such as floor joists or roof rafters. To calculate the appropriate
uniform load to apply to a beam, simply multiply the beams tributary area by
the appropriate area load. Area loads and other structural loads are
established by the American Society of Civil Engineers ASCE7 document and are
given as pounds per square foot (psf).

**Linear Loads** Linear Loads are very similar to uniform
loads, but rather than having a constant magnitude, vary along their length.
Linear Loads also have units of force per length. Linear loads can be used to
represent triangular snow drifts or beams with joists framing in at a skewed
angle, or many other triangular and trapezoidal type loading.

**Point Loads** Point loads have units of force. The default in
WebStructural is Kips (1 kip = 1000 lbs.). Point loads can be as
simple as a reaction from another member such as a beam framing into another
beam, or a column sitting on a beam.

**Moments** Moments are loads which cause rotation in the
axis of a beam and have units of force times length. The default in WebStructural
is kip-feet. Moments are more complex to those less familiar with them,
but consider a column welded to the top of a steel beam. If a force is applied to top of
the column, it will cause the beam it is attached to bend
as well, just like a lever. This bending type reaction is a moment. If the
force is in the direction of the beam axis (or span direction), it can be input
as a moment in WebStructural. If the force applied is perpendicular to the
beam axis, then a torsional moment will be introduced. WebStructural does not
currently allow for torsional loads to be input.

For our example, let's use a dead load **D = 0.63 k/ft ** and a
live load **L = 1.5 k/ft** Also, we'll make sure to **Include
Self Weight**. You can edit loads by clicking any load on the drawing
or by clicking the **Edit Loads...** text above the drawing or from the
menu **Edit → Loads...**

We'll start by clicking **Edit Loads...**. That will pull up the
**Loads Dialog**. The **Loads Dialog** allows you to add new
loads or edit existing loads by clicking on a row from the
**Current Loads** table.

Let's go ahead and edit our dead load by clicking on the first
(and only) row in the **Current Loads** table. The first thing
we need to do is adjust the load so that it covers the entire length
of our beam. You can do this by clicking the button that says
**Right End**. This will change the end position of the load
to the end of the beam.

Now let's add our **live load**. Since our live load is the same
length as our dead load we can simply add a magnitude for the
**Live Load** case for our current uniform load. In the Uniform
Dialog note the check box that says **Show All Load Cases**.
Click that box to show the **Load Case** table. Enter 0.63 in
the dead load box (box **D**) and 1.5 in the live load box (box **L**).

**What about Load Factors?** Depending on which design method you choose, (see below) the
loads you enter will be factored appropriately. Simply enter the service
(unfactored) loads.

Structural steel can either be designed by Load or
Resistance Factor Design (LRFD) and Allowable Stress Design (ASD). Both
methods yield similar results. Engineers have their opinions about the pros
and cons of each method, but both are currently allowed in the United States.
Simply click **Edit design...** and choose the method you would
like to use.

WebStructural will automatically factor your loads and apply them in the appropriate design equations. You can view these equation and exclude ones you don't want to include in analysis if you wish.

To exclude specific equations click on one in the equation table to toggle it.

Deflection is an important measure of beam performance. Beams that have excessive deflection can be strong enough to carry their design loads, but perform poorly in service. Excessive deflections can lead to user complaint including bouncy floors, cracked building finishes, instability for mechanical equipment, etc. The International Building Code (IBC) dictates the minimum deflection for various members and load types. Deflections are typically described as a ratio or L (span) over some value to allow for comparison and standardization. Example: The deflection ratio for 0.5" delection in a 12' beam equals L/288 = 12ftx12in/ft (span) 0.5" (deflection). Now consider a beam that deflects 0.75" and is 18' long. It has an equivalent deflection ratio or L/288. In theory, these beams have the same deflection performance even though the longer span beam has a greater deflection. That is because the deflection is less noticeable over the greater distance. L/100 is often considered to be near the limit of deflection that is detectable to the human eye. L/360 is usually considered a minimum accepatlbe deflection due to live loads on floors, but that is just a minimum.

Once you have input all of your criteria, all you have to do
is click that **big green Calculate button** that I know you've been
itching to click. WebStructural will perform a finite element
analysis for your beam model. It will determine design forces and calculate
the design capacities of the beam using the American Institute of
Steel Construction (AISC) standards. If you originally selected an
appropriate beam size, you will see a lot of green and bending, shear,
and deflection capacity ratios will be less than 1.0. These values are
a percentage of capacity. For example, if your report reads "Bending 0.88"
the beam configuration you selected is at 88% of it's flexural capacity
(according to AISC).

If your report is red, then your capacity ratios are greater than
1.0 and the beam does not meet the design criteria. This means you
need a bigger beam! Simply choose a different shape (larger moment
of inertia) and click the **Calculate** button.

At WebStructural we strive to give you high quality design calculations with transparent reports that you can rely on. If you found this how-to useful please share it with your colleagues.

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Happy Engineering,

The WebStructural Team