Prof. Ing. Carlo Andrea Castiglioni Seismic Behaviour of Steel ...

Seismic behaviour of steel storage pallet racking systems . 240.65 WEAKBig number of pieces stored on the pallet whose size is small incomparison to the pallet size0.5LOOSE ANDUNCONSTRAINED1.0 LIQUID Liquid in partially filled drumsTable 1.2 : Pallet weight modification factorsPallet sliding(1) The sliding of the pallets is expected to occur when the pallets are not restrainedon the beams, and the horizontal seismic action on the pallets at one of the loadlevels evaluated by using the design spectrum with modification factor E D1 =1 isgreater than the horizontal reaction generated by the friction between the palletand the beams:F i > γ µS × µ S × Q Pwhere:F i = seismic force on pallet at level iµ S = pallet-beam friction coefficientγ µS = partial safety coefficient for pallet-beam friction coefficient(usually assumed γ µS = 1)Q P = design weight of the palletThe above condition is equivalent to:a g,i / g > γ µS × µ Swhere:a g,i = seismic horizontal acceleration at level ig = gravity acceleration(2) The pallet-beam friction coefficient to be considered is the static one; in thefollowing Table 1.3 reference values are reported.Upper-bound values of the friction coefficient shall be used for assessment ofthe occurrence of sliding in the ULS analysis, while lower bound values shall beused for the assessment of the occurrence of sliding in the SLS analysis.(3) In case of sliding occurrence the pallets move and can reach improperequilibrium positions on the beam; therefore each single pallet beam must bedesigned considering the most severe possible position of the pallets inequilibrium in the load cell.(4) In any case the chance of falling down of the pallets must be limited by placingadditional components or devices, such as depth beams, additional centralbeams etc.