85 □ Flexure of reinforced concrete beams钢筋混凝土梁的性能
The design moment strength of the section is obtained by taking moment about the centriod of the tension reinforcement and is given by
这段的弯矩值是对受拉钢筋形心取距而得到的，其值为：
?Mn??[cc(d?a/2)?Cs(d?d')]/12
?0.9[345.4(27?4.23/2)?215.8(27?2)]/12 ?103 k3ip fseet3.2.3 Flanged section with tension reinforcement only（仅配置受拉钢筋的T型截面梁） A flanged member, with a flange width b, may be designed as a rectangular beam when the depth of the equivalent stress block is less than the flange thickness. 当受压区高度小于翼缘的厚度时，翼缘宽度为b的T型截面梁的设计可当作矩形截面梁来设计。
The depth of the stress block given by 受压区高度为： a?Asfy/0.85fc'b?1.18?d where ? may be determined from Table 3-2 using the calculated value of Mu/fc'bd2. 式中?是由表3-2利用Mu/fc'bd2.来确定的
The required reinforcement ratio, corresponding toMu, is given by在Mu作用下，其所需的配筋率为：
???fc'/fy
and the required area of tension reinforcement is 和所需的受拉钢筋的截面面积为： As??bd
When the depth of the equivalent stress block equals the flange thickness, the design moment strength of the section is given by 当受压区高度等于翼缘的厚度时，其弯矩设计值为：，
?Mn?0.85?fc'bhf(d?hf/2)?0.765fbhf(d?hf/2)'c
and the corresponding area of tension reinforcement is和相应的受拉钢筋的截面面积为： As?0.85fc'bhf/fy
The conditions a ultimate load in a flanged member, when the depth of the equivalent rectangular stress block exceeds the flange thickness, are shown in Figure 3-7. The area of reinforcement required to balance the compressive force in the outstanding flanges is given by
当矩形截面受压区高度大于T型截面的翼缘厚度时，T型截面梁的最终荷载由图3-7所示。
86 □ Flexure of reinforced concrete beams钢筋混凝土梁的性能
为平衡翼缘超出的压力，其所需的钢筋截面面积为：
Asf?Cf/fy?0.85fc'hf(b?bw)/fy
The corresponding design moment strength of the outstanding flanges is超出翼缘部分的相应弯矩值为：
Mf??Asffy(d?hf/2)
The residual moment to be developed by the beam web is 由梁来承担的剩余弯矩为： Mf?Mu?Mf
The required reinforcement ratio to provide the residual moment is其所需的配筋率为： ?w?0.85fc'[1?(1?Kw0.383fc')0.5]/fy where 式中 Kw?Mr/bwd2
The corresponding reinforcement area required to developed the residual moment is 来抵抗剩余弯矩的相应的钢筋截面面积为： Asw?bwd?w
Figure 3-7 Flanged member with tension reinforcement
图3-7 在拉力作用下的T型截面梁
Alternatively, the value of ?wmay be determined from Table 3-2 using the calculated value of
Mr/fc'bwd2.The corresponding reinforcement area required to developed the residual moment is 其中?w是由表3-2利用式Mr/fc'bwd2来确定的，来抵抗剩余弯矩的相应的钢筋截面面积为： Asw??wbwdfc'/fy
The total reinforcement area required is 钢筋总面积为： As?Asf?Asw
The total reinforcement ratio is ??As/bd钢筋的总配筋率为： The maximum allowable reinforcement ratio is given by Section 10.3.3 as 由10.3.3小节可知，最大配筋率为：
' ?max?0.75bw(?b??f)/b
Where式中 ?f?Asf/bwd
87 □ Flexure of reinforced concrete beams钢筋混凝土梁的性能
and 和
0.75?b??max ?0.75?0.85?87,000?1fc'/fy(87,000?fy)
is the maximum allowable reinforcement ratio for a rectangular section which may be obtained from Table 3-3
.由表3-3可得，对矩形截面梁而言，配筋率已是最大值。