تفضل اخي
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CDAQFjAA&url=http%3A%2F%2Fosp.mans.edu.eg%2Fimam%2FBooks%2FBook1%2FCh10.pdf&ei=_QTbUKf_HbOO4gSdg4CoCw&usg=AFQjCNFTIUNHAuQeJpvQUSz2nAeFJTo5BQ&sig2=sSUm1VjmNrNV9xkkueficw&bvm=bv.1355534169,d.Yms
و
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=2&cad=rja&ved=0CDoQFjAB&url=http%3A%2F%2Flebeton.free.fr%2Favenir.html&ei=lQbbULbzBaz04QSQ1IDADA&usg=AFQjCNHVzcKm_hT_nCwkc2ShuHy6Cd2ybg&sig2=JIx6yxh7OKEwRRJ0_jJUkQ&bvm=bv.1355534169,d.Yms