function z = prob_grooteman_10_series_x2z_test(varargin)
%% settings

OPT = struct(...
    'U1', [],...
    'U2', [],...
    'U3', []...
    );

OPT = setproperty(OPT, varargin{:});

%% limit state function

z1  = -OPT.U1-OPT.U2-OPT.U3+3*sqrt(3);
z2  = -OPT.U3+3;
z   = min([z1, z2], [], 2);