Fire resistance (hrs)	Minimum beam width (mm)	Minimum thickness of floors (mm)	Minimum wall thickness (p<0.4%)	Min wall thickness (0.4%	Min wall thickness (p>1%)
0.5	200	75	150	100	75
1	200	95	150	120	75
1.5	200	110	175	140	100
2	200	125	–	160	100
3	240	150	–	200	150
4	280	170	–	240	180

Source: Concrete Centre

Reinforcement for beams

●     Spacing

The minimum spacing of steel reinforcement bars is

1.    Maximum size of coarse aggregate plus 5mm

     Or

     2.   Bar size(whichever is greater)

●     Number of bars

Max bars per layer for beams = (beam width – 2 x cover – 2 x link diameter)/(2 x bar diameter)

●     Size of bars

Beam width (mm)	Bar diameter (assuming 35mm cover)
	25	32	40
300	3	3	2
350	4	3	3
400	5	4	3
450	6	5	4
500	7	5	4
550	8	6	5
600	9	7	6
650	10	8	6
700	11	9	7
750	12	10	8
800	13	10	8
900	15	12	9
1000	17	13	11

Source: Concrete Centre

●     Areas of reinforcement

Max of tension or compression reinforcement is 6% of cross sectional area of concrete

Min percentages are shown in the table below, which is Table 3.25 of BS 8110

​

●     Shear Links

Shear links should be spaced no more than 0.75d. No longitudinal bars should be spaced more than 150mm or d from a vertical leg. Shear links should follow the following requirements:

Bar diameter (mm)	16	20	25	32	40
Max spacing (mm)	192	249240	300	384	480
Min link diameter (mm)	6	6	8	8	10