Maximum longitudinal reinforcement ratio in the critical regions of beams

Clauses In beams the value of ^ specified via equations (D5.ll) for plastic hinge regions is provided, through an upper limit on the ratio of the tension longitudinal reinforcement in the critical, regions, p, max = Asl mJbd. The value of pL max is derived as follows., When the tension reinforcement is less than that in compression, A,, <As2, the ultimate deformation at the end of the beam will take place when the effective ultimate strain of the tension reinforcement, esu, is exhausted. With the restrictions on steel classes allowed in DCM or DCH buildings posed in Section 5 and the penalty on p0 when steel of Class B is used in DCM buildings as noted in Section (see p. 105), it is expected that this condition will not be reached before the end of the beam attains its ultimate deformation by failure of the compression zone, when the larger of the two reinforcements is in tcnsion: /4s[ >As2. The limit of jOj max refers to this latter situation. Therefore, with ^ taken as (¡>J4>y, <pu is given by the second term in parentheses in equation (D5.8). In that term, ¿cu is taken equal to the ultimate strain given in Eurocode 2 for unconfined concrete, ecu2 = 0.0035, because ductility of the beam critical regions does not rely on confinement of the compression zone; xcu is taken equal toxcu = £cud, with £cu given by equation (D5.3) with u,, = 0, v = 0 and with the conventional values ec2 = 0.002 and ecu2 = 0.0035 for ec and ecu, respectively. Using in = (pj(j)y the semi-empirical value <j> = 1.5ey/d derived from test results of beams at yielding, the outcome for the upper limit value of the beam tension reinforcement ratio, pv is

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