Response Spectrum of a Cantilever Plate

[Settler]

Hi all,

I'm trying to do a response spectrum for a cantilever plate. The commands I'm using are the following:

/TITLE, Plate
/PREP7

!Wall Geometry Definition
K,1,0,0
K,2,0,100
K,3,24,100
K,4,24,0
A,1,2,3,4

!Material Definition
!E=1200ksi
MP,EX,1,1200
!ρ=3.14513E-07 kips/in.^3
MP,DENS,1,3.14513E-07
!ν=0.25
MP,NUXY,1,0.25

!Define Element Type and Properties
ET,1,SHELL281
SECTYPE,1,SHELL,,2-IN-Plate
SECDATA,2,1,0,5

!Associate Area With Element Attributes, Mesh Options, and Mesh
AATT,1,,1,0,1
AESIZE, 1, 2
AMESH,1

!Apply Boundary Conditions
DL,4,,ALL,0

FINISH

!Obtain Modal Solution
/SOLU
ANTYPE,MODAL
MODOPT,LANB,25
NSEL,ALL
MXPAND,25,,,YES
SOLVE
SAVE
FINISH

!Obtain Spectrum Solution
/SOLU
ANTYPE,SPECTR
SPOPT,SPRS
SED,0,0,1
SVTYP,2,1,1
FREQ,0.1,100
SV,0.05,386.4,386.4
SOLVE
SAVE
FINISH

!Expand the Modes
/SOLU
ANTYPE,MODAL
EXPASS,ON
MXPAND,25,,,YES,0.00
SOLVE
SAVE
FINISH

!Combine the Modes
/SOLU
ANTYPE,SPECTR
MMASS,1,386.4
SRSS,0.005,DISP
SOLVE
SAVE
FINISH

!Review the Results
/POST1
SET,LIST
/INP,,mcom
PRNSOL,DOF
PRESOL,ELEM
PRRSOL,F
FINISH

I have put a simple response spectrum (1g at all frequencies) to validate the results. However, I don't get a reaction in the Z direction equal to the weight of the slab as would be expected.

Anyone had an idea of why is that happening?