Impact loads appear to be inherently difficult to solve. The key to solving them is to understand that it's really an energy transfer and energy equations must be used. The difficulty comes in a) transferring the energy into force-stress equations via the stress-strain relationship; or b) approximating the force impacting the structure. The approximation method is usually the tried first because it appears to be the "easiest" to solve. The difficulty here is that there is no easy/accurate/comfortable way to convert and energy transfer into a direct force. In design, we use this method but understand that we are significantly overdesigning the structure. If you are doing this for forensic engineering, then the only accurate way that I have found is to use the energy equations. Otherwise, it can be easily shown that your equations contain way too many assumptions/rules-of-thumb to be accurate.

Imagineer

Most steel fabricators and errectors normally provide tempoary bracing to columns and other steelwork during errection such to  maintain the tempoary adequacy of the steel work. My question would therefore be why is it of concern?

As far as physically calculating the impact force the best I could come up with is the Asutralian Standard AS 1170.1 "Dead and Live Loads" which gives and energy type equation for the impact loads of vehicles onto barriers. Perhaps a bit of judgement could be used in applying this equation for your particular application.

From Clause 4.5

F=mV^2/(2d)

where

F = impact force in Newtons
m = gross mass in kilograms
V = velocity at impact in metres per second
d = deceleration length in metres

d is normally taken as the sum of the deflections of both the vehicle and the barrier. For example a car impacting a rigid barrier during parking operations has a d = 0.1 metres and a V=2m/s min.

Perhaps the above equations can be used for your aprticular application.

Regards

Tim
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Here is one way to determine the effective force. First calcualte the energy of the impact by   .5 x mass x Velocity**2. This would be the velocity and the mass of the object that is impacting the column. This energy would be absorbed by the column based on the equation  .5 x force x d, where d is the deflection of the column. The deflection of the column is (force x l**3)/(3 x E x I). Now, the impact energy would equal .5 x force**2 x l**3/(3 x E x I).
The only unknown would be the force. Once the force is calculated, the anchor bolt can then be evaluated. I hope this helps you.