Earthquate Loading on Falsework 1

[DWHA]

Are there any codes that anyone knows of (preferably AASHTO) that deals with earthquake loads on falsework. I started designing a lot of falsework throughout the country and the person who did this before me told me that he honestly had never thought about it. After talking about it we agreed that it is kind of a judgement call due to the fact that most of the falsework is not up for an extended period of time. But there are some instances where some may be up for a year or so.
Is it strictly Engineering Judgement? Or is there any codes dealing with it?

 

[msucog]

are there life safety issues related to what you reference?

 

[Taro]

I'm not sure about AASHTO, but ASCE 37 "Design Loads on Structures During Construction" might be a useful reference.

 

[DWHA]

MUSCOG
There could be human safety issues. If there are workers on the falsework, which there often are during working hours then there is a safety issue.

 

[DTGT2002]

In the Formwork(Falsework) industry, earthquake loading is typically considered beyond the design scope of a formwork designer.

The ACI guide for formwork, from committee 347, does not include earthquake loading as an expected load to formwork, though it does not specifically exclude it.

In my work, I do not design for earthquake loads, nor do I design for hurricane or tornado loading. The magnitude of the loading is immense and the cost often cannot be justified with the expected return period.

As a side note, the construction dangers of hurricanes and tornadoes are dealt with through safety plans within my company. As seismic zones change, we may need to add an earthquake procedure. However, I cannot forsee designing forming systems for seismic loading in the near future.

All of that said, if you are working in a seismically active zone, you may find yourself compelled to attempt to design for these forces. There is certainly no reason not to other than practicality and economics, but I know of no guide or code reference that will tell you to.

Daniel Toon

 

[msucog]

i agree with DTGT2002.

i think it's unreasonable to design the same as for say a building. if the project has a long time frame, then maybe design accordingly. i suppose you could always look at it from the standpoint that people will be following OSHA and would be tied off if up high for example. maybe the safety system would be designed for the seismic loading and the other not. i see it being up to you to decide.

 

[cvg]

In reviewing Caltrans criteria, there is nothing published regarding falsework, only permanent structures. Even though it is entirely possible and likely that a construction site in many areas of California will experience a small to moderate earthquake during a 6 - 12 month construction period.

However, comparing seismic to tornados and hurricanes is like apples to bananas. Storm events are very predictable, but unfortunately seismic events are not.

 

[DWHA]

cvg
Thanks, I guess if any state would have desing criteria for earthquakes it would be Ca.
I will keep seismic in mind and if I can economically design for it, I will. Otherwise I guess I will just hope for the best.

 

[crossframe]

My version of the Caltrans Falsework Manual dates from 1993, and it indicates (in Section 3-1.04) that the design horizontal load (which can act in any direction) is "the sum of any actual loads due to equipment, construction sequence or other causes, plus an allowance for wind. In no case may the design load be less than two percent of the total supported dead load at the location under consideration."

It goes on to say that the bracing should be designed to resist the horizontal design load with the falsework in either the loaded or unloaded condition.

Continuing, it says that the 2% value will typically govern for falsework heights less than 30 feet, wind MAY control for falsework heights between 30 and 40 feet, and wind will govern most designs where falsework height exceeds about 40 feet.

Please keep in mind:

This is not the current version of the manual. The current one is probably available as a download from the Caltrans website.

This is applicable to construction types and wind conditions typical of California. Your situation may vary.