Tipping Hazard
Tipping Hazard
(OP)
I am starting work on the design of an optical fixture that is going to be around 5m high, with a mass of hundreds of kilograms, perhaps in the low thousands. I have a requirement for part of this to be 300mm thick, although I can mess with the configuration of the base. Probably, I can put anchor studs in the floor.
My ideal case is that this thing will sit on the floor of the lab, held in place by gravity.
Is there a formal standard somewhere on tipping hazards, specifying the base configuration, and/or tie-downs?
My ideal case is that this thing will sit on the floor of the lab, held in place by gravity.
Is there a formal standard somewhere on tipping hazards, specifying the base configuration, and/or tie-downs?
JHG






RE: Tipping Hazard
Anyway, selfweight plus stiffness of some structural support would lead to some deformation, some of which migh come out of required tolerance.
By including sensors for temperatures and distances, and pressure or mehcanical/electrical jacks in your support structure you can monitorize your structure is keeping the mirror as wanted. Furthermore, it could even correct somewhat some fabrication geometrical imperfection of the mirror in the weak deformation ranges since applied to the combined stiffnesses of part of the structure and the mirror.
RE: Tipping Hazard
RE: Tipping Hazard
A stand-alone, static, not-being-moved, protected "thing" will rarely fall over - unless your region is subject to periodic earthquakes. Even a two meter long, 150 mm diaa pipe could stand n end forever on the lab floor if nothing ever touched it,
Problem is, you can't prevent all these hazards in the real world and so can't pretend to just "leave it alone" and "nothing will run into it" as a adequate solution.
Have you seen the photo of a multi-hundred million dollar JPL satellite tipped over inside the lab? That's what I mean be by this kind of "moving" hazard even in a "safe" lab enviroment with highly-trained people.
You need a risk assessment and hazard analysis document to present to your boss (the design team): What things at what weight (what energy) could hit this platform at what elevtion above grade? What is the probability of impact, and how can I design things to prevent/mitigate that impact? What is the most severe "routine" movement or impact (a broken brake could jar the mirror when it hits the stops, or a sudden startup of the mirror motor will create dynamic forces each time an adjustment is made, what if four people are standing on the same side of the platform when they are installing the mirror -> this will create an unbalanced load up high on the platform) that is expected? Then, assign a safety factor on that load, and design the bottom of the mirror platform (size of baseplate, legs, and max width of the legs away from the CG, and size and number of anchor bolts) to resist that maximum expected dynamic force.
you can't protect against everything: But you must make reasonable assumptions about reasonably-expected hazards, chose a reasonable safety margin, then design against that. Not all things are in the OSHA and design books. A guard rail around the base might be cheaper than an elaborate foundation and leg assembly.
But, if a tornado tears the roof off of the building, or a semi-truck runs through the parking lot and hits the building, that mirror will fall down. 8<)
RE: Tipping Hazard
RE: Tipping Hazard
This device will sit in an optical lab where high powered lasers will be firing. Access is restricted accordingly. Outside of lasers, I am not sure of the safety discipline in the lab. I am strongly tempted to install bollards around the structure just in case somebody does go in there with a cart. A small impact that does not tip it could still mess up the optical alignment. Earthquakes are rare up here, but not unheard of.
The structure will have to be accessed for assembly and alignment, and then for optical testing. If I separate the access platform from the structure, I eliminate a source of disturbance that might cause misalignment or tipping. If I integrate the platform, I wind up with a fatter, more stable base.
I just want to make sure I understand overturning factor.
Structure mass m=1000kg. Structure breadth b=300mm. Structure height h=5m. I assume centre of gravity is in the middle. An assembler might exert f=200lb at the top.
Gravity moment Mg = wb/2 = mgb/2 = (1000kg × 9.81m/s2 × 300mm × .001m/mm) / 2 = 1470(kg.m/s2).m = 1470N.m
Overturning moment MO = fh = 200lb × 4.45N/lb × 5m = 4400N.m
Overturning factor: Mg/MO = 1470N.m / 4400N.m = .33 (it is tipping over)
Is this correct? (the .33, not the tipping over)
I am just punching in numbers here. The 300mm is an optical requirement. It does not have to control the base breadth.
RE: Tipping Hazard
RE: Tipping Hazard
RE: Tipping Hazard
I have to fatten the base to the point that I have an acceptable overturning factor. I am just trying to verify that I understand overturning factor.
I have considered tying the top of this to structure overhead, but I am not sure of where I can attach. Also, it has to be stable while we erect it.
RE: Tipping Hazard
Safety factor against overturning=W·(B/2)/(F·5m)
This was once considered for ***walls*** be better around 3, then later reduced to 2, and now 1.5 safety factors start to seem acceptable. If the forces atop can vary wildly because the use I would take a high value; otherwise, in a lab environment 1.5 might be fine.