×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Structural Effects of a Lightning Strike
2

Structural Effects of a Lightning Strike

Structural Effects of a Lightning Strike

(OP)
Does a lightning strike apply any additional forces to a structure?

I have done some research on this and have come across: "Any conductor carrying lightning current will be subject to an electromagnetic force F=Bli in Newtons."
B = the component of the magnetic field at right angles to the conductor
l = length of the conductor (meter)
i = the current (ampere)

Would this be the only force applicable? Is there another known way to quantify this? We are designing a tall structure and want to ensure there are no additional loads from a lightning strike that would affect the structure, even though we can't imagine it would be enough to even consider.

Thank you!

RE: Structural Effects of a Lightning Strike

I'd imagine some thermal stresses at the location of the strike, but otherwise the effects should dissipate rapidly as you move away from the strike location.

Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com

RE: Structural Effects of a Lightning Strike

(OP)
Thanks @TehMightyEngineer

RE: Structural Effects of a Lightning Strike

Exactly, thermal forces. There's probably an analogy to the short circuit force that is checked in substation bus (electrical bus, not automotive bus) structures.

RE: Structural Effects of a Lightning Strike

(OP)
Thank you @Lomarandil,that sounds pretty close. I found an equation for the short circuit force in substation bus structures and will apply it to approximate.

RE: Structural Effects of a Lightning Strike

(OP)
Thanks @TehMightyEngineer. "When lightning strikes a lightning rod, a large lightning current flows into the ground through the lightning rod conduction wires and the steel framework of the building."...wonder what would happen to the steel structure if there was no lightning rod?

RE: Structural Effects of a Lightning Strike

I have seen a building have to be rewired and replumbed after a lightning strike.
They pulled out long lengths of wire, and 30' down the wall was where it found an easier path and blew the insulation off, and arced a hole in the water line.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Structural Effects of a Lightning Strike

In addition to the electrical motive force, there will also be a thermally-induced air-pressure shock wave (a big "boom", for those of you in Rio Linda!). bigsmile Depending on where the strike occurs, and what materials surround the strike site, you could very well see shock-displaced structural (and non-structural) members and elements.
Dave

Thaidavid

RE: Structural Effects of a Lightning Strike

(OP)
Does load factoring take this as an extreme event like seismic?

RE: Structural Effects of a Lightning Strike

I don't know that I have ever seen "lightning strikes" listed as a specific IBC or ASCE load. wink I do think that you are probably on the right track in accounting for it as an "extreme event", to be evaluated as an ultimate load, to be compared to ultimate tensile strength limits.
Dave

Thaidavid

RE: Structural Effects of a Lightning Strike

I would imagine a bigger concern than the load would be the risk of fire.

Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com

RE: Structural Effects of a Lightning Strike

(OP)
Thanks for the help folks thumbsup2

RE: Structural Effects of a Lightning Strike

I forgot to mention that, for the aspects of this design related to the structural effects, you might want to approach this from the same standpoint as weapons blast effects on structures. These is a wealth of that information from the military codes and guides on the WBDG website.

Thaidavid

RE: Structural Effects of a Lightning Strike

(OP)
Interesting approach, I will take a look at those codes. Thanks for the reference!

RE: Structural Effects of a Lightning Strike

Properly constructed steel framed buildings conduct lightning to ground without affect; however, poorly constructed steel framed buildings where gaps exist at connections and there is "looseness" in the connection have a potential for arcs and welding at those locations. That is particulary problematic for high-strength bolts.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources