Support reinforcement

Although the beams are designed as simply supported structures, it is advisable to place additional reinforcement over the support to prevent excessive cracking when the beams rotate at the support under service load. The additional steel may be calculated as follows : DL (imposed) =1.75×8 =14.0kN/m LL = 3.0 X 8 = 24.0 kN/m

Ultimate loading = 1.4 x 14.0 + 1.6 x 24.0 = 58.0 kN/m

= 0.08ql2

= 0.08 X 58.0 x7.32 = 247.3 kNm

As = M / (0.87fy z) z = 0.8h

A, = 247.3 x 106/(0.87 x 460 x 0.8 x 600) = 1287 mm2

Provide 4T20 (As = 1257 mm2) over the support as shown in Figure 4.2.

c. Deflection

At mid-span, M* = 786.2 kNm

MVbd2 = 786.2 X 106/ (500 x 4602) = 7.43

fs =(5/8)fyx(Asreq/AsprJ = (5 / 8) x 460 x (5486/5629) = 280 N/mm2

From Part 1, Table 3.11, CP65 the modification factor for tension reinforcement = 0.75 and for compression reinforcement = 1.08

Minimum d =7300/(20 x 0.75×1.08)

233

End bearing

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