Gate Design - Dynamic Analysis 3

[dik]

I have a small 8' gate that is used as a guard. Does anyone have a link to a quick design of the hinges and 'stop' for dynamic forces on a small gate? There are two hinges on the one side and a single locking hasp on the other. I plan to support the entire weight on the top hinge with the bottom hinge resisting the horizontal moment force. With the hasp taking an impact equal to the total weight. The other connections will be designed for twice their loads due to impact. It's exterior, so I will add wind loads to it, treating it as a chain link fence. Does anyone have suggestions of an alternate design?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[JoelTXCive]

Dik-

I've done debris screens for water structures that require gates in them.

The potential impact loading from a tree or couch floating down a drainage channel is often unknown. Also, If the channel is 20ft deep, It's cost prohibitive to design a gate that will handle all that head.

For these scenarios, I try and come up with geometry where my gate is LARGER than the actual opening; and then I face mount my hinges to the supporting structure.

The gate spans across across the opening, but I can remove the hinge capacity from my impact design considerations.

In a true catastrophic failure event, the hinges will surely give out, but the gate will just crush against the structure.

I'll dig around for a photo..

-Joel

 

[dik]

Thanks Joel... Impact by a projectile is not an issue... we no not have many tornados (sp?) in the neighbourhood (no trailer parks to attract them). The work's for a consultant, and in the last couple of years I've only done 3 of these. I was wondering how others handle the problem. My approach isn't exact, but it is a 'safe method' I believe. The impact load is from 'slamming' the gate and not from a missile.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[WARose]

If you really want to get fancy you can do some kind of conservation of (rotational) momentum calculation. I.e. see how much force is generated by it swinging. We took on such a problem on this board sometime back. (And I threw in one of several possible solutions)

 

[dik]

Thanks WARose... I couldn't find a link seaching... can you post the link? That's something what I was looking for. I just found out a few minutes ago that the gate is totally indoors... no wind loads, but I will include for it in my SMath program.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[WARose]

Thanks WARose... I couldn't find a link seaching... can you post the link?

This was the thread:

https://www.eng-tips.com/viewthread.cfm?qid=486009

I guess the hard part is knowing how hard someone would slam it.

 

[XR250]

I think just using your gut would the best solution. The amount of extra steel it would take to make this stout AF would easily cost less than you messing around.

 

[dik]

I concur... that 'educated' gut design was what I used... I'm just trying to refine it... I often do that just to see how things are really working.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[GC_Hopi]

I like to the OSHA fall arrest requirements as a guide for an incidental force in the design of some components. So this can be a 3,000 lb or 5,000 lb incidental force. Also using the IBC vehicle load or the OSHA ladder loading is useful depending on the component.

 

[dik]

The design requirements are that it has to be designed as a simple guardrail. not for tying off for fall arrest, but it is a good idea that there is a 'safety anchorage'. I will include that.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[GC_Hopi]

In your OP it was a little unclear if the gate is 8' tall or 8' wide and my experience is with a swing gate in the guardrail but it sounds like you have something custom. I assume you are already checking it for the OSHA guardrail loading of 200 lb point and 50 plf line load.

 

[dik]

Sorry 8' wide and 3'-6 tall... and another added item... to be self closing.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[GregLocock]

The factor of 2 approximation for dynamic loads is widely misunderstood. So far as I can tell it comes from a simple observation about simple harmonic motion (the peak to peak displacement is twice the static deflection) and bears no resemblances to real dynamic loads from things hitting other things, like gates slamming.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[phamENG]

Greg - you can arrive at the factor of 2 by comparing the energy of a falling body to the elastic strain energy of the member it hits. If you take the height from which the body falls as 0, the math works out to F=2xweight of the falling body. This example is in Blodgett's book, and I wonder if that helped to spread the use of 2 as an impact factor, even though it's not always correct?

 

[GC_Hopi]

8' is going to be a pain. Can you talk them into a 8' stretch of removable guardrail and a standard swing gate?

Edit: My reasoning for this is I have only seen swing gate up to 42". They start to get unweldy. The other option is a lift gate like so..

 

[dik]

Thanks Greg, I just wanted to include for some dynamic force... 2 was just a WAG that I can accommodate for strength. The gate has pickets and is fabricated out of HSS 2x2 material and is OK for strength.

Thanks for the link, Warose. I think I will stick with statics and just use the multiplier. I've asked if they want fall restraint built in and also if they want the gate to be self closing... both good ideas, and a couple of things I hadn't considered.

thanks gentlemen...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[ThomasH]

Hi
I would say that it all depends om how accurate you want to be and how much work you want to do.

A fairly simple approach may be to estimate the energy associated with the impact. And then you can check if the gate can support the "damage" made by that energy.

Good Luck

Thomas

 

[dik]

Thanks, Thomas...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[JoelTXCive]

Dik -

If you are still shopping for ideas.... Have a look at this setup....

This is the parking lot gate at my local high school stadium. You could possibly do a scaled down version of this.

Instead of hinges, they did a big sleeve over the post. Also, the square section generates some membrane action and lets them get lots of weld on the post.

I don't know how to make it self-close though..

 

[dik]

Thanks Joel... earlier today I resubmitted my 'design check' and revised my sealed set. I've included the need for a positive latching system. The guard has pickets @ 4" and unlike the gate to the parking lot, there is a shaft on the other side... definitely a safety issue. The gate is designed as a guard in the closed position, with the latch providing the end support for guard loads. Outside the closed position, it is designed as a gate, for gravity dead loads only. I also, on the revised set, noted the design loading.

If the post were tilted, it would tend to be self closing.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik