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Archives for Engineering Resources

Steel Beam Design Specifications: Getting the Answers You Need

When you are looking for steel beam design specifications, where do you go? If you have a degree in structural engineering or architecture, you may be able to perform the calculations required for a steel beam design specifications yourself. However, most of the population requires some form of assistance in order to compile steel beam design specifications for building projects.

Steel Beam Design Specifications: Resources Available to Some

Some individuals have access to a team of professionals capable of calculating steel beam specifications and any other construction related calculation needed. Students may have access to an engineering library complete with tables, equations, and values necessary to calculate steel beam design specifications.

For a price, some structural analysts and architects provide consultation services for steel beam design specifications and other construction problems. (These fees may vary greatly and are not regulated.)

Steel Beam Design Specifications: Resources Available to Everyone

A structural engineer in the field, a civil engineer in an office, or a homeowner planning a remodeling project all may need to calculate steel beam design specifications. One option is to obtain this information through a professional. Some architects and structural engineers offer their consultations services to the public for a fee.

Another option is to post your question on a structural engineering or construction related discussion forum and hope you receive a reliable answer in a timely manner. This option has obvious drawbacks and may be a good choice for obtaining a general answer, but is not reliable enough for construction and application purposes.

The most reliable option for obtaining steel beam design specifications is a structural analysis software program. Many companies offer a trial version of this type of software if you only plan to use the software to solve a single steel beam design problem.

For others who require repeated steel beam design specifications, investing in a structural analysis software program is a wise choice. Structural analysis software programs range in price and features, with a program to fit nearly any structural analysis need. Take the time to research which structural analysis software program is right for you.

Steel beam design specifications can come from a variety of different sources and the perfect source for you may well be a structural analysis software program. A fee trial of a structural analysis program can provide the solution to your steel beam design specifications.

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The Most Used Engineering Terminology Defined

The most used engineering terminology can be confusing to the average consumer. Understanding the common jargon used in structural engineering can help you communicate with your architect, engineer, or construction manager more effectively.

Beam
A structural member, usually horizontal, with a main function to carry loads cross-ways to its longitudinal axis. These loads usually result in bending of the beam member. Examples of beams are simple, continuous, and cantilever.

Beam-Column
This is a structural member whose main function is to carry loads both parallel and transverse to the longitudinal axis.

Cantilever
Cantilever refers to the part of a member that extends freely over a beam, which is not supported at its end.

Collateral Load

Collateral load is additional dead loads (not the weight of people and not the weight of the building itself), such as plumbing, duct work, ceilings, and other components of the structure.

Column
A column is a main vertical member that carries axial loads from the main roof beams or girders to the foundation parallel to its longitudinal axis.

Continuity
Continuity is the term given to a structural system describing the transfer of loads and stresses from member to member as if there were no connections.

Damping
Damping is the rate of decay of amplitude for floor vibrations.

Dead Load
Dead load describes the loads from the weight of the permanent components of the structure.

Deflection
Deflection is the displacement of a structural member or system under a load.

Dynamic Load
This type of load varies over time.

Footing
A footing is a slab of concrete under a column, wall, or other structural to transfer the loads of the member into the surrounding soil.

Foundation
A foundation supports a building or structure.

G-Type Joist Girder
A type of Joist Girder using joists located at panel points where diagonal webs intersect the top chord of the joist only.

Gable
A gable is located above the elevation of the eave line of a double-sloped roof.

Gage
Gage can refer to the thickness of a sheet of material or the distance between centerlines in a set of holes, usually perpendicular to the joist or joist girder.

Girder
A girder is the main horizontal member spanning between two main supports and carries other members or vertical loads within the structure.

Grade
The ground elevation of the soil.

Header
A member that carries other supporting members and is placed between other beams.

Hip Roof
A roof sloping from all four sides of a building.

Joist
A structural load-carrying member with an open web system which supports floors and roofs utilizing hot-rolled or cold-formed steel and is designed as a simple span member.

Kip
1000 pounds.

Live Load
Non-permanent loads on a structure created by the use of the structure.

Load
An outside force that affects the structure or its members.

Modulus of Elasticity (E)
The value is usually 29,000 ksi for structural steels and is also called Young’s Modulus. It calculates the slope of the straight-line portion of the stress-strain curve in the elastic range.

Moment
Moment is the tendency of a force to cause a rotation about a point or axis which in turn produces bending stresses.

Moment of Inertia (I)
A measure of the resistance to rotation offered by a member’s geometry and size.

Pitch
Pitch is the slope of a member defined as the ratio of the total rise to the total width

Reaction
Reaction is the force or moment developed at the points of a support.

Seismic Load
Loads produced during the seismic movements of an earthquake.

Shear
Forces resulting in two touching parts of a material to slide in opposite directions parallel to their plane of contact.

Span
The distance between supports.

Structural Steels
Steels suitable for load-carrying members in a structure.

Strut
A structural brace that resists axial forces.

Stud
A vertical wall member used to attach other structures, such as walls.

Torsion Loads
A load that causes a member to twist about its longitudinal axis. A couple or moment in a plane perpendicular to the axis produces simple torsion.

These most used structural engineering terminology definitions provide a baseline understanding of engineering jargon for the average consumer. Detailed definitions can be obtained from visiting a professional engineering website or professional journal.

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Flitch Beam Bolting

In a separate article entitled “Accurate Flitch Beam Design Made Easier with Software” there was an allusion to the difficulty associated with designing the connection between the solid sawn members and the steel members of a flitch beam.  In this article there will be a more in depth discussion on the methodology for attaching the different materials of a flitch beam so that all the materials act as one solid member.

Flitch beams must be connected together to appropriately transfer loads to the wood and steel portions of the beam in proportion to the relative stiffness of each material.  Most structural engineering software packages don’t provide this calculation; two sample methods are provided below for determining this connection.

Empirical Method

The first method is an empirical method, which is purely based on what has worked well in the past.  An example of a regular bolting pattern might be 1/2 inch diameter or 5/8 inch diameter bolts spaced 16 inches on center.  Stagger the bolts and make sure the bolts are placed a minimum of 2 1/2 inches from the edge of the beam.

Rational Method

The alternative to the empirical method is the rational method.  Using the rational method the load transfer between the steel and wood members is actually calculated.  The first step in the rational method is determining the percentage of load that is carried by both the steel and wood portions of the beam.  If structural engineering software was used to size the flitch beam then somewhere within the software there should be a display of the load transfer percentages.  If the flitch beam was sized by hand, then the load transfer percentages can be determined from the modular ratio that was calculated.  The load carried by the steel plate can then be determined by multiplying the percentage of load carried by the steel plate by the total load on the beam.  After the load has been determined bolts can then be sized by using tables found in the National Design Specification.

Example Calculation

 Flitch Beam Bolting

Now, determine capacity of 5/8 inch diameter bolts for loads traveling perpendicular to the grain of the wood.  For simplicity, use table 11B of the National Design Specification.  This is a table for single shear bolt capacities.  This is conservative since the flitch beam being sized actually has bolts in double shear.  Higher values can be calculated using the six yield equations.

 Flitch Beam Bolting Bolt

End bolts required to transfer steel plate load to wood members for bearing are required unless the steel plate bears on a steel bearing plate.

Flitch Beam Bolting Number of Bolts

Final Considerations

This is just one example of how to design the bolting for a flitch beam; there are certainly other valid methods and assumptions that will provide an adequate design.  When doing any kind of beam design, especially a flitch beam using structural design software will greatly ease the entire process of calculating adequacy.  There are several different engineering design software packages available for beams, columns, or foundation design.  StruCalc, Enercalc, Risa, and BeamChek are all examples of such software.

James DiNardo, P.E.
Josh Parker, E.I.T.
Cascade Design Group

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Normal Stress, Bending Stress, & Shear Stress

Stresses in Beams
In a separate article entitled “Structural Analysis of a Beam” there was a brief discussion of stresses and their function in structural analysis.  In this article there will be a more in dept discussion of normal, bending, and shear stress.

Normal Stress
A normal stress is a stress that occurs when a member is loaded by an axial force.  The value of the normal force for any prismatic section is simply the force divided by the cross sectional area.

Normal Stress

A normal stress will occur when a member is placed in tension or compression.  Examples of members experiencing pure normal forces would include columns, collar ties, etc.

Bending Stress

Beam Design

When a member is being loaded similar to that in figure one bending stress (or flexure stress) will result.  Bending stress is a more specific type of normal stress.  When a beam experiences load like that shown in figure one the top fibers of the beam undergo a normal compressive stress.  The stress at the horizontal plane of the neutral is zero.  The bottom fibers of the beam undergo a normal tensile stress.  It can be concluded therefore that the value of the bending stress will vary linearly with distance from the neutral axis.

Bending Stress

Calculating the maximum bending stress is crucial for determining the adequacy of beams, rafters, joists, etc.

Shear Stress
Normal stress is a result of load applied perpendicular to a member.  Shear stress however results when a load is applied parallel to an area.  Looking again at figure one, it can be seen that both bending and shear stresses will develop.  Like in bending stress, shear stress will vary across the cross sectional area.

Shear Stress

Calculating the maximum shear stress is also crucial for determining the adequacy of beams, rafters, joists, etc.

Final Considerations
When doing any kind of beam design using structural design software will greatly ease the entire process of calculating stresses.  There are several different engineering design software packages available for beams, columns, or foundation design.  StruCalc, Enercalc, Risa, and BeamChek will all take in to account normal and shear stresses when doing any kind of beam design.

Josh Parker, E.I.T.
Cascade Design Group

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Structural Analysis of a Beam

The process used for determining the adequacy of a wood, steel, or even a concrete beam is essentially the same. Once a beam has been selected the method is as follows:

  • Determine the loads
  • Calculate the stresses
  • Check the allowable stresses against the actual stresses.

Determine the Loads
The first step in the structural analysis of a beam is determining the amount of load, or weight the beam is going to support.  There are two major categories of loads:

Live Loads – A live load is a type of load that is temporarily placed on a structure (i.e. loads from snow, wind, vehicles, etc.).  The magnitude of live loads will be defined or referenced in a local building code.

Dead Loads – are loads permanently attached to a structure (i.e. loads from building materials, furniture, etc.).  Sometimes the weights of materials are exactly known and can be added together to determine the total dead load.  More often the dead load is assumed and given an approximate weight.

Calculating the Stresses
There are two types of stresses that are typically calculated when performing a beam design: bending stress and shear stress.  A more complete definition of both bending stress and shear stress can be found here.  In order to calculate the bending and shear stresses it will be first necessary to calculate the maximum bending moment and maximum shear that occurs in the beam.

The maximum moment and shear will most likely occur at different locations, and the process used to determine their value will be defined in a separate article.  The other two pieces of information needed to determine the stresses will be the section modulus and cross sectional area of the beam being used.  The section modulus and cross sectional area can be calculated, or in most cases can be looked up in tables (like in the National Design Specification (NDS) for wood beams, or the AISC Steel Manual for steel beams).  Once all the information has been tabulated the following equations can be used to determine the nominal maximum bending stress and nominal maximum shear stress:

structuralanalysisofabeamcalculatingthestresses.png

Compare Actual Stresses against Allowable Stresses
In most cases the allowable stresses are tabulated in a design manual of some sorts (like in the NDS for wood, or the AISC Steel Manual for steel).  Once the allowable stresses have been located determining the adequacy of a beam is simply a matter of comparing the actual stresses to the allowable stresses.  So, a beam is adequate if the following is true:

Actual Stresses Versus Allowable Stresses

Other Considerations
One major consideration not discussed in this article is that of deflection, or sag in the beam.  A beam might be strong enough structurally, but might deflect so much that it effects the actual performance of the beam.  Deflection is a calculation that is very important and will be addressed in a separate article.

Another consideration when doing any kind of beam design is that of using structural design software.  There are several different engineering design software packages available for beams, columns, or foundation design.  StruCalc, Enercalc, Risa, and BeamChek are a few examples of those structural design software packages.

Josh Parker, E.I.T.
Cascade Design Group

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