mjhjmtu

I'm trying to add the > and >> on the two sets of parallel lines and having no luck.

documentclassscrreprt
usepackagetikz

begindocument


begintikzpicture[scale=1,xscale=2]
 coordinate (A) at (0,0);
 coordinate (B) at (2,2.5);
 coordinate (C) at (4,2.5);
 coordinate (D) at (2,0);
 draw[<->,thick,shorten >=-60pt,shorten <=-60pt] (A) -- (B)node[midway]SINGLE;
 draw[<->,thick,shorten >=-60pt,shorten <=-60pt] (C) -- (D)node[midway]SINGLE;
 draw[<->,thick,shorten >=-60pt,shorten <=-60pt] (A) -- (D)node[midway]DOUBLE;
 draw[<->,thick,shorten >=-60pt,shorten <=-60pt] (B) -- (C)node[midway]DOUBLE;
endtikzpicture

enddocument

You can use a decoration to do this. The code below defines two new arrow types ->- and ->>- that do what you want

Presumably the arrows stack because these are decorations.

Here is the code:

documentclassscrreprt
usepackagetikz
usetikzlibrarydecorations.markings
tikzset%
 ->-/.style=decoration=markings, mark=at position 0.5 with arrow>,
 postaction=decorate,
 ->>-/.style=decoration=markings, mark=at position 0.5 with arrow>>,
 postaction=decorate,


begindocument


begintikzpicture[scale=1,xscale=2]
 coordinate (A) at (0,0);
 coordinate (B) at (2,2.5);
 coordinate (C) at (4,2.5);
 coordinate (D) at (2,0);
 draw[<->,thick,shorten >=-60pt,shorten <=-60pt,->-] (A) -- (B);
 draw[<->,thick,shorten >=-60pt,shorten <=-60pt,->-] (D) -- (C);
 draw[<->,thick,shorten >=-60pt,shorten <=-60pt,->>-] (A) -- (D);
 draw[<->,thick,shorten >=-60pt,shorten <=-60pt,->>-] (B) -- (C);
endtikzpicture

enddocument

Notice that I had to reverse the code for the D-C line. Alternatively, you could use -<- if you add the definition:

tikzset%
 -<-/.style=decoration=markings, mark=at position 0.5 with arrow<,
 postaction=decorate,

Just a complement, an option in tikz Euclide, that has some ad hoc mark statements, decorations also available using scope for the desired marks.

RESULT:

MWE:

documentclass[tikz,border=20pt]standalone
usepackagetkz-euclide
usetikzlibraryarrows.meta
usetkzobjall

begindocument
 begintikzpicture
 %Definindo os vertices
 %%The best way to define Axis is using polar notation:
 tkzDefPoint(0,0)A %The reference point
 tkzDefShiftPoint[A](0:5)B% POINT B 
 tkzDefShiftPoint[A](40:4)D %POIN D

 %%Find point C colinear at D from AB
 tkzDefPointWith[colinear= at D](A,B) tkzGetPointC 

 %%Find point E colinear at C from DB
 tkzDefPointWith[colinear= at C](D,B) tkzGetPointE 

 %Drawing modified style lines
 %style only afects commands inside 
 tikzsetline style/.append style=<->,>=Stealth[scale=2.2,inset=0pt,angle'=20] 
 tkzDrawLine[add=40pt and 40pt](A,B)
 tkzDrawLine[add=40pt and 40pt](D,C)
 tkzDrawLine[add=40pt and 40pt](A,D)
 tkzDrawLine[add=40pt and 40pt](B,C)
 
 beginscope[decoration=markings,mark=at position .6 with arrow[scale=2]>>;]
 tkzDrawSegments[postaction=decorate,dashed](D,B C,E)
 endscope


 %Drawing and label Points
 tkzDrawPoints[color=blue,fill=blue,size=6pt](A,B,C,D)
 tkzLabelPoints[color=blue,below=5pt,inner sep=0](A,B,C,D)

 %Mark Segments
 tkzMarkSegments[mark=||](A,B D,C)
 tkzMarkSegments[mark=|](B,C A,D)
 endtikzpicture

enddocument