A steel beam weights 10 to 100 kg per meter, railway rail is 40 kg/meter, so I’ll take 50 kg. Four story building in Europe is approximately 12m.
In the drawing, beam+timber are almost as long as the building is tall, so for simplicity we can assume 11m, of which 5m is the beam and 6m is the timber, and we can assume the pendulum being suspended at 1m above ground in resting position. Beam’s centre of mass is located at half it’s length, so 8.5m is our effective length. Angle at which the beam-timber are standing looks like, dk, 35°? Then, the beam is suspended ~5m above ground. A 250 kg beam would have potential energy of 12.5 kJ (close to .50 cal). Alternatively, I can guestimate a 100° swing arc and 32 kJ energy, which is slightly more than muzzle energy of 14.5mm anti tank rifle. With panzers 3 or 4 we’re looking at something like 15-20mm side armour, 14.5mm B-32 bullet (steel core) could pen 32mm at range, probably closer to 40+? point-blank. Of course, a bullet concentrates this force on a small area, through an I beam could also hit with a corner, give or take bigger kinetic energy of the beam and the need to puncture (absolute best case scenario, ofc) 15mm instead of 40+, and the fact that the bullet doesn’t expend all energy purely during pen, so required energy for penetration is even lower. Another interesting moment in considering impact to and near hatches, welds, riveted joints, etc, is that unlike a bullet, which penetrates and carries a significant portion of it’s kinetic energy inside - even a steel beam which initially punctured the armour with it’s corner would still get stuck and transfer all its energy to whichever it hit.
In conclusion, with an older/lighter WW2 tank the beam under optimal conditions could maybe perforate the armour, break some welds, or at least dent it. And if we’re talking about a less armoured vehicle, like an APC or an armoured car- the beam can either go through or significantly bend the ppate, likely disabling the vehicle. Could even work against IFVs (BMPs are cardboard, there are areas on the side which can be penned with small arms), through it’s hard to imagine how it would be worth the hassle in modern context. And in any case crew would get disorientated by their whole world turning into a bell.