The correct equations (15), (16) and (17) are:  
C11=12/Ebt3{l2r+2r[t4r+t6r2+4rt+t2+6r2r+t2t1/24r+t1/2atan1+4r/t1/2]2r+t14r+t3}
(15)
 
C12=6l/[Ebt32r+t4r+t2]{4r+t[l2r+t4r+t24r216r2+13rt+3t2]+12r22r+t2t1/24r+t1/2atan1+4r/t1/2}
(16)
 
C22=3/Eb{4l2rl2lr+r23t31+1/2{{t1/24r+t1/2[80r4+24r3t+83+2πr2t2+41+2πrt3+πt4]+42r+t36r24rtt2atan1+4r/t1/2}2t5/24r+t5/21+[40r4+8lr22rt+12r3t+43+2πr2t2+21+2πrt3+πt4/2]t24r+t2+8l2r6r2+4rt+t22r+t1t24r+t2{22r+t[24lr2r28r3t+14r2t2+8rt3+t4]atan1+4r/t1/2}t5/24r+t5/2}}.
(17)