it also facilitates removal and replacement of the beam if it is severely damaged the enlarged holes in the beam 11 are shown by the dotted lines 21 in fig3 consequently as illustrated in fig3 the beam 11 may deflect upon impact by a forklift truck shown schematically as element 22 such impact will cause a deflection of the beam 11 and thus a shifting in the bolts relative to the elongated oversize holes 21 in the beam 11 as can be appreciated then the beam 11 is clamped by means of the plates 18 and 19 to allow it to be raised but the beam 11 can shift in the horizontal plane as a consequence of the oversize holes 21 which allow the beam 11 to move relative to the bolts 20 the result is deflection of the beam without damage to the pivot structure because the force is totally resisted then by the barrier posts this is shown in fig3 by the contact of the beam 11 against the posts 6 and 8 while the barrier may be easily moved by hand given the counterweight structure fig4 illustrates a second modification those items which are identical to the embodiment of.