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+R=0.15//rise, in m
+t=0.3//tread, in m
+sigma_cbc=5//in MPa
+sigma_st=230//in MPa
+l1=1.8+1.5//span for flight AB, in m
+l2=1.2+1.5+1.5//span for flight BC, in m
+l3=1.8+1.5//span for flight CD, in m
+//assuming 50 mm slab thickness per 1 m of span
+D=50*l2//slab thickness, in mm
+W1=D/10^3*25*1.5*sqrt(R^2+t^2)/t//slab load on plan, in kN/m
+W2=1/2*R*t*1.5*25/t//load of step per metre, in kN/m
+W3=1.5*5//live load, in kN/m
+W=W1+W2+W3//in kN/m
+//bending moment
+//(a) flight AB and CD, refer Fig. 10.9
+Rb=(W/2*1.5*(1.8+1.5/2)+W*1.8^2/2)/(1.5+1.8)//in kN
+Ra=W/2*1.5+W*1.8-Rb//in kN
+x=Ra/Rb//point of zero shear force from Ra, in m
+M1=Ra*x-W*x^2/2//maximum bending moment, in kN-m
+//(b) flight BC, refer Fig. 10.10
+Rb=(W/2*1.5^2/2+W*1.2*(1.2/2+1.5)+W/2*1.5*(1.5+1.2+1.5/2))/(1.5+1.2+1.5)//in kN
+Rc=Rb//in kN
+//maximum bending moment will be at centre
+M2=Rb*(1.5+1.2/2)-W/2*1.5*(1.5/2+1.2/2)-W*(1.2/2)^2/2//maximum bending moment, in kN-m
+M=max(M1,M2)//in kN/m
+d=sqrt(M*10^6/0.65/1.5/10^3)//in mm
+//assume 10 mm dia bars
+dia=10//in mm
+D=d+dia/2+25//< 210 mm (assumed value)
+D=210//in mm
+d=D-dia/2-25//in mm
+//steel
+//flight AB and CD
+z=0.9*d//in mm
+Ast=M1*10^6/sigma_st/z//in sq mm
+s1=1500*0.785*dia^2/Ast//spacing of 10 mm dia bars, in mm
+s1=210//round-off, in mm
+Ads=0.12/100*D*1.5*10^3//distribution steel, in sq mm
+//provide 6 mm dia bars
+s2=1000*0.785*6^2/Ads//in mm
+s2=70//round-off, in mm
+//flight BC
+Ast=M2*10^6/sigma_st/z//in sq mm
+s3=1500*0.785*dia^2/Ast//spacing of 10 mm dia bars, in mm
+s3=130//round-off, in mm
+//distribution steel is same as flights AB and CD
+//let span-to-depth ratio be 'a'
+a=l2*10^3/D
+//for Fe415 grade steel and pt=.32
+MF=1.2//modification factor
+b=20*MF//permissible span-to-depth ratio
+//as a < b, hence OK
+mprintf("Summary of design\nSlab thickness=%d mm\nCover = 25 mm\n(a)Flight AB and CD\nMain steel = 10 mm dia bars @ %d mm c/c\nDistribution steel = 6 mm dia @ %d mm c/c\n(b)Flight BC\nMain steel = 10 mm dia bars @ %d mm c/c\nDistribution steel = 6 mm dia @ %d mm c/c",D,s1,s2,s3,s2)
+//answer in textbook is incorrect