The main point in favour of partial or limited prestressing is that required in cross section of a prestressed member for various reactions such as to resist differential shrinkage temperature effects and handling stresses.

Generally, self weight may be assumed on basis of previous experience and use of design chart containing dimensions of beams for various spans and applied loads as recommended by magnel is very useful in regard.

In case of small span prestressed members, thinner webs of about 40 to 60mm may be used however in case of long span, heavily loaded girders when large, curved cables have to pass through webs a minimum thickness of 120 to 150mm is mandatory to accommodate cables with adequate cover.

P = 182×10³ e = 10⁵, L = 1000, elastic modulus of concrete = 34×10³, I = 3200×10⁵
PeL²/8E_cI = (182×10³x10⁵x6²x1000²/8x34x10³x3200x10⁵) = 6.8mm.

The thickness of web is generally determined on basis of shear strength considerations discussed according to british code recommendations shear reinforcements are not required where V is less than 0.5v_c and in members of minor imporatance when shear for V exceeds (V_c to 0.4b_wd), shear reinforcement are designed at spacing S_v = A_sv0.8f_y/0.4b_w.

f_cu = 50n/mm²,f_ck = 35n/mm² according to BS: 8110 recommendations for f_cu = 50n/mm² and f_ci = 35n/mm², f_ct = 0.5f_ci = 17.5n/mm²For class 1 structure f_u = h_tw = 0, f_br = (?f_ct-ftw) = (0.85×17.5) = 15n/mm², f_cw = 0.33f_cu = (0.33×50) = 16.5n/mm², f_cu = (fcw-?fu) = 16.5n/mm².

A_ps = 3000mm², d = 1150mm, f_cu = 50n/mm², b_w = 150mm, f_pu = 1500n/mm², b = 600mm, h_t = 250mm, design ultimate moment m_ud = 3400knm, according to BS: 8110-1985, _Aps = (A_pw+A_pf) = A_pf = 0.45×50(600-150)(250/1500) = 0.45xf_cu(b-b_w)(h_f/f_pu) = 1680mm², A_pw = (1300-1680) = 1320mm², ratio(f_puA_pw/f_cub_wd) = (1500×1320/50x150x1150) = 0.23.

Several empirical relations have been developed to estimate width of cracks but it is considered that a calculation based on stress in reinforcement obtained by convential ory of cracked reinforcement concrete section is inherently more accurate than a computation based on fictitious tensile stress in an uncracked section.

b = 0.5d, d = 270mm, d/h = 0.85, h = 315mm, adopt effective depth, d = 275mm overall depth , h is 320mm, width of flange of 160mm and Average thickness of flange is 70mm since sloping flanges are used, increases flange thickness by 20 percent:
Thickness of flange = (0.2×275) =55mm Approximate thickness of web = (0.85v_u/f_th) = (0.85×27.75×10³/1.7×320) = 43mm.

E_ce = E_c/1+?, ? = 1.6, E_e = 2.6E_ce
Deflection due to self weight g = (5gL⁴/384E_cI) = (5×0.76×6⁴x1000⁴/384x34x10³x3700x10⁵) = 1.02mm.