huangyhg

construction load factors - concrete
we've been hired by a contractor to look at how much shoring will be required in order to drive a crane onto raised concrete slab. its a series of one way slabs spanning between beams that are in some cases conventionally reinforced and in other cases post-tensioned. i have the outrigger loads from the crane manufacturer - but how much should i factor this load up by to compare it to the strength level capacities i calculate with aci. any thoughts on construction load factors in general . . . didn't asce come out with a book on construction design loads similar to asce 7-02?
thanks for any help you can provide.
i would take a careful look at dynamic loads. suppose you have a hook load dropping and it is jerked to an abrupt halt while the jib is at maximum extension. i suspect the dynamic reactions would be substantial. a 1.7 live load factor may not approximate this effect.
i would also ask the crane manufacturer for their design load limits.
yes, sei/asce 37-02 "design loads on structures during construction." it deals with construction loads due to equipment and personnel, and appropriate load combinations. note that you will probably need to alter these load combinations if you are using the aci code prior to the '02 code. it also has info on temporary wind loads for temporary structures like curtain walls. it's not very expensive fortunately, not like the 7-02.
thinking about it, the loads provided by the crane manufacturer should be including the dynamic effects.
that consideration is the description of load case aci 9.2.6. the dynamic live load is further factored.
u = 1.7 ( l = l dynamic ) + whatever else.
it might be informative to see what the factors of safety are for the crane itself. typically, they are fairly low- may be stated in the crane load charts.
remember that when the crane is making a pick off the corner and is at its max, either from an angle or load, the diagonnally opposite outrigger has almost no load. if they overload the pick, the crane may lift on the opposite corner. the pressure on that one outrigger will be about 75% of the load and 75% of the crane weight. you may have to put the crane up onpads that double and even triple the bearing surface.

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