1、 Flexure of reinforced concrete beams 钢筋混凝土梁的性能 75 Example 3-10 (Design of a reinforced concrete beam with tension reinforcement only)=A reinforced concrete beam , with an effective depth of 16 inches and a width of 12 inches ,is reinforced with Grade 60 bars and has a concrete cylinder strength of
2、4000 pounds per square inch. The beam carries a superimposed dead load ,including its self weight, of 2.5 kips per foot run and superimposed live load of 2.7 kips per foot run over on effective span of 15 feet .Determine the area of tension reinforcement required. 例 3-10 （在拉力作用下钢筋混凝土梁的设计）一个钢筋混凝土梁，其有
3、效高度为 16 英寸，宽度为 12 英寸，钢筋的强度等级为 60，混凝土的强度等级为 4000 磅每平方英寸，计算跨度为 15 英尺，该梁承受的恒载为 2.5 千磅每英尺，活载为 2.7 千磅每英尺，求受拉钢筋的截面面积。 Solution 解 ： The applied dead load moment is given by 恒载作用下的弯矩为： fe e t ki p 13.708/155.28/22 DD wM The applied live load moment is given by 活载作用下的弯矩为： fe e t ki p 94.758/157.28/22 DD wM T
4、he factored moment at mid span is obtained from ACI Equation (9-1) as 由 ACI 方程式得到的在跨中的弯矩为： f e e t ki p 53.22795.757.131.704.17.14.1 LDu MMM The maximum allowable factored moment for a singly reinforced beam is obtained from Table 3.3 as 由表 3.3 得出，单筋混凝土梁的最大允许弯矩为： u22( m a x )M f e e t k i p 62.2 390
5、 00,12/16129 36 dbKM wuu Hence the section is adequate.从而这个弯矩是满足的。 Flexure of reinforced concrete beams 钢筋混凝土梁的性能 76 The design moment factor is 弯矩设计系数为 i n c h s qu a r epe r pou n ds 79.888)1612/(000,1253.227/22 dbMK Wuu and 和 2222.0 4000/79.888/Cu fK From Table 3-2, the corresponding tension rein
6、forced index is 从表 3-2 可知，相应的张拉系数是 0.299 The required tension reinforcement ratio is given by 所需受拉钢筋的配筋率是： 0 2 0.00 0 0,60/4 0 0 02 9 9.0f/f yc The required area of tension reinforcement is 受拉钢筋 的截面面积为 i n c h e s s qu a r e 3.8316120.020db A ws Provide three No. 10 bars which, from Table 1-7, given
7、 an area of 3.81 square inches. = 由表 1-7 查得 3 根 10 元钢筋的面积是 3.81 平方英寸。 Examples 3-11 (Analysis of a reinforced concrete slab) = A one-way, reinforced concrete slab is continuous over four, equal, clear spans of 15 feet. The slab has an overall depth of 7 inches with concrete cylinder strength of 3000
8、 pounds per square inch. The reinforcement at the top of the slab at the first interior support consists of No. 4,Grade 60,bars at 11 inches on center. In addition to its own weight, the slab carries a superimposed dead load of 26 pounds per square foot. Determine the maximum uniformly distributed s
9、uperimposed live load which the slab can support. 例 3-11（钢筋混凝土板的分析） 一个四边连续，相等的混凝土单向板，其净跨为 15 英尺，板的全高为 7 英寸，其混凝土强度等级为 3000 磅每平方英寸，板的上部配筋为间距 11 英寸4 根强度等级 60 的钢筋，包括板的自重，板上的恒载为 26 磅每平方英尺。求板所能承受的最大均布活载。 Solution 解 : The minimum allowable concrete cover to the reinforcement in the slab, in accordance with
10、 ACI section 7.7.1, is 根据 ACI 7.7.1 小节知，混凝土最小保护层厚度为： Flexure of reinforced concrete beams 钢筋混凝土梁的性能 77 in c h e s 0 . 7 5 cc The effective depth provides is 有效高度为 i n c h es 62/5.075.072/dc-h d bc The area of tension reinforcement in a 12 inches width of slab with No. 4 bars at 11inches on center is
11、 obtained form Table 1-8 as 由表 1-8 可得，宽 12 英寸配置元 4 间距为 11 英寸的受拉钢筋截面面积为： i n c h e s s q u a r e 0 . 2 2 A s The tension reinforcement ratios provide is given by 受拉钢筋的配筋率为： )10.3.3S e c t i on A C I f r om 0160.0()7.12 .2S e c t i on A C I f r om 0018.0(0.00 3066)0.22 / ( 12db/A m a xm i nws Hence th
12、e reinforcement provide is satisfactory.因此配置的钢筋是满足要求的。 The tension reinforcement index is 受拉钢筋系数为： 0612.03000/000,6000306.0f/f cy From Table 3-2, the corresponding value of 由表 3-2 可得，其相应的值为： 0531.0f/K cu The allowable factored moment is given by 允许弯矩设计值为： f e e t ki p 73.5000,12/61230000531.0dbK M22wuu + The self weight of the slab is 板的自重为： f o o tp e r k i p 0875.0144/15.0127W SD The total dead load is given by 恒载的总值为： f ootpe r ki p 1135.0026.00875.0www ADSDD
