In terms of organizing the data, the simplest approach is to create two matricies for stiffness and deflection that have two dimensions, time and temperature. Assuming these vectors are constant and known in advance, they can be defined as:
time_series(:,1) = [8,15,30,60,120,420]; % along dimension 1
temp_series(1,:) = -36:6:-18; % along dimension 2
Note: It is generally good practice to have the dimensions of these vectors correspond to the matrix you construct. Here, time is chosen to be a column vector, defined along dimension 1, and temperature is a row vector, defined along dimension 2.
It is also useful to have the length or number of elements along each dimension:
Ntime = numel( time_series );
Ntemp = numel( temp_series );
Next, assuming your spreadsheet is loaded into a matrix M, we can construct stiffness and deflection matricies that match these dimensions. This is done by reshaping the 2D matrix M:
stiffness(1:Ntime,1:Ntemp) = reshape( M(:,2) , [Ntime, Ntemp] );
% Read as: All rows in col. 2 of M are reshaped to matrix "stiffness" of size Ntime x NTemp
deflection(1:Ntime,1:Ntemp) = reshape( M(:,3) , [Ntime, Ntemp] );
% Read as: All rows in col. 3 of M are reshaped to matrix "deflection" of size Ntime x NTemp
Then, if you want to plot time-series of stiffness and deflection for each temperature, excluding the first temperature:
subplot(2,1,1); hold on; grid on; title('Stiffness over Time');
plot( time_series, stiffness(:,2:end), '-x')
subplot(2,1,2); hold on; grid on; title('Deflection over Time'); xlabel('Time (sec)')
plot( time_series, deflection(:,2:end), '-x')
% optional legend
legend( sprintfc('%d',temp_series(2:end)) )
This assumes the first temperature is always zero, another approach is needed if the location of zeros is at some other time or temperature. I get the following figure:
