Simple Strengths of Mat Question

[toastedhead]

Ive got a plate - 1/4" thick carbon steel. It holds a hydraulic motor and is mounted by 4 3/8" bolts to a rigid body. I want to know what it would take to permanently bend the bend plate.

Its been aboout 10 years since Ive done a strengths problem - so dont taze me.

The plate is drawn in AutoCAD. Please let me know what info Im leaving out.

Thanks for your help.

 

[SNORGY]

It will bend over time but for a 40 pound motor, assuming it's reasonably balanced during operation, I am inclined not to worry too much *on first inspection*. Consider vertical L-channel stitch welded near each plate edge as a potential plate stiffener.

Roark's does a pretty good job of presenting equations on plate deflection.

Regards,

SNORGY.

 

[Ron]

Couldn't open your sketch...you might post a pdf file.

A small, supported 1/4-inch steel plate with a 40 lb load? Stress would be miniscule, whether you consider bending, contact, Von Mises, shear, torsion or any other imaginable stress orientation.

 

[rb1957]

ron,

the arrangement is abit unusual ... the plate is vertical, the motor off-set, looks as though it's fitted thru the plate.

statically, not a problem, the plate will bend about an line thru the upper supports ... these bolts will react tension, so tighten them up good 'n' tight.

like snorgy, i'd worry about vibration, impulse loads as the hydraulics cycle.

conventionally the web would be stiffened with an angle, welded, fastened, or bent from the web. alternatively, add an angle between your web and the top of the "rigid body", these fasteners would then react the moment in shear (as fasteners are meant to).

 

[toastedhead]

Ive already redesigned this plate. I know the higher the motor is mounted, the worse the condition.

What force would it take to bend the plate at the fasteners if indeed there was TOO much force and the plate bent past the limit? See pic attached.

 

[rb1957]

i'll assume that the plate bent when the pump was working.

statically, the plate should be fine. 40 lbs motor, off-set say 10" from the "rigid body" interface (higher doesn't matter for weight) ... the plate is resisting a moment of 400 in.lbs. assume 10" wide plate, 0.25" thick, peak bending stress is 6*400/(10*0.25^2) = 240*16 < 4ksi (yawn)

so something is happening when the motor is running ... assume 10x the static moment is being added to the dead weight moment ... that'd be enough to yield annealled (36ksi) steel. a moment of 4000 in.lbs, assume a 20" moment arm (this is where the hieght of the motor comes in), implies a force at the motor (normal to the plate) of 200 lbs ...

 

[toastedhead]

I agree. The plate looks torqued (sp?), not bent from weight.

 

[Ron]

Geez! I thought you were talking about an electric motor, not a hydraulic motor. Sorry.

Have you considered cavitation stresses and line surge that could produce torque on the plate? Also, those hoses on the far side of the motor add a significant weight(moment) to the plate.