huangyhg

monorail beam design
i have a exsiting monorail system ,we'er planning a special lift . i have used a recommended analysis in the past which adds 20% of the lift load as a horz. load . this lift is inside a enclosed structure ,under very controlled guidlines ,minimum speed no lateral movement.this lift is for construction related activites ,i assume the addition of the horz. component is to compensate for unknown loadings in normal use. since this is not the case i am inclined to overlook this horz, component ,the verticle lift load puts the stress levels at 1/2 that allowable ,any comments .

the horizontal component is in part from acceleration and braking while moving load along the monorail. if your plan is to move load along the rail i would not overlook the horizontal components.
make sure the load is lifted vertically and not dragged transversely from the side into position. make sure load is not "swinging".
longitundinally, you should have an allowance for accelerating and braking as indicated above.
comments & opinion: you may be mixing crane design requirements with crane use requirements - they are very different.
the 20% allowance for horizontal forces, that i am familiar with, is for sizing the supporting structural steel (see aisc manual of steel construction, section a3). this has little to do with the actual use of the crane.
crane "use" requirements are typically based on the crane manufacturer's stated lifting capacity (assuming the structural steel supports were correctly designed). in the usa, osha allows normal crane use up to rated capacity and even controlled condition test loads up to 125% of rated capacity.
since your calculations indicate that the structural steel supports are adequate, suggest that you base your decision to proceed, or not, on the rated capacity of the crane. if the load exceeds the rated capacity let us know the numbers, we may be able to provide additional comments.

agree with the above with an additional note:
check the deflection limitation of the equipment. sometimes it's l/450; sometimes it's higher. if the slope of the bottom flange due to deflection is too great, the hoist may not be able to move along the flange.
the horz. load i'm talking about is a lateral load placed at 90 degreees to the length of the monorail beam ,i have included a 10% of vertical lift load as a axial load to cover for acceleration and braking.
the reference that i find to the 20% horizontal load normal to the rail is for design of crane runway beams that have a trolley that travels normal to the rail. it states: "20% of the sum of the lifted load and the crane trolley (but exclusive of other parts of the crane)." as this is a monorail and the hoist doesn't travel perpendicular to the rail i would not think that this applies.
my only concern in eliminating this load case would be when someone tries to lift something that is not in line with the crane rail.
our inhouse standard is to use 10% for monorails. i believe 20% is excessive. as h57 mentioned above the trolley in a crane runway travels normal to the rail, so 20% makes sense for crane runways.
i agree, 20% sounds excessive. in fact the australian code specifies a figure as low as 4%.braking and inertia loads are considered separately to this of course.

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