中美混凝土规范.doc

中国和美国混凝土规范的几点比较一、符号的差别a = 等效矩形应力区的高度，中国的为h0av = 剪跨，作用在连续梁或悬臂梁上的集中荷载到任意支座表面的距离，而中国的为：（人）Ao = 剪力流包围的总面积，中国的为：Acor二、 钢筋细节1中国的规范是配筋率不超过Pb（界限配筋率），而美国的包括配筋率不得超过0.75b，强度折减系数的确定，和弯矩重分配这些在多年的规范中都有的规定，其中包括1999 年的规范。这些规定适用于钢筋混凝土和预应力混凝土构件。2中国的钢筋的弯钩或弯折应符合下列规定：级钢筋末端需要作180弯钩，其圆弧变曲直径(D)不应小于钢筋直径(d0)的2.5倍，平直部分长度不宜小于钢筋直径(d0)的3倍；用于轻骨料混凝土结构时，其弯曲直径(D)不应小于钢筋直径(d0)的3.5倍；、级钢筋末端需作90或135弯折时，级钢筋的弯曲直径(d)不宜小于钢筋直径(d0)的4倍；级钢筋不宜小于钢筋直径(d0)的5倍(见图3.3.3.2)。平直部分长度应按设计要求确定。而美国的：在钢筋的自由端弯曲180且再伸长其值取为4db与65mm 的最大值。在钢筋的自由端弯曲90且再伸长12db 的长度。美国的：对于箍筋和拉筋的弯钩：（a）16 号钢筋和更细的钢筋，在钢筋的自由端弯曲90且再伸长6db 的长度；或（b）19 号、22 号和25 号钢筋，在钢筋的自由端弯曲90且再伸长12db 的长度；（c）25 号和更细的钢筋，在钢筋的自由端弯曲135后。再伸长6db 的长度。那些10 号到16 号箍筋和拉筋的除外，3中国的钢筋加工的形状、尺寸必须符合设计要求。钢筋的表面应洁净、无损伤，油渍、漆污和铁锈等应在使用前清除干净。带有颗粒状或片状老锈的钢筋不得使用。而美国的预应力钢筋应该干净和表面无油渍、脏物、蚀斑和过量的铁锈。在铁锈上进行涂层应该是允许。三、模板工程的差异。中国的具有足够的强度、刚度和稳定性，能可靠地承受新浇筑混凝土的重量和侧压力，以及在施工过程中所产生的荷载。而美国的是当与模板和支撑系统一致的结构部分有足够的强度来承受它的重量和上面的荷载除外，结构的任何部分在施工期间不能承受结构荷载，同时任何支撑也不能从中拆除。足够的强度被说明通过被考虑的推荐的荷载的结构分析、模板和支撑系统的强度和混凝土强度数据的结构分析。混凝土强度数据应以在现场养护的（混凝土）圆柱体的试验或，当得到建设方允许时，根据其它的措施去评估混凝土强度。四、钢筋的连接中国的是钢筋的连接可分为两类：绑扎搭接、机械连接或焊接。轴心受拉及小偏心受拉构件，例如桁架和拱的拉杆的纵向钢筋不得采用绑扎搭接接头。当受拉钢筋直径d28mm及受压钢筋直径d32mm时，不宜采用绑扎搭接接头。（1） 绑扎搭接当接头用搭接而不加焊时，其搭接长度l规定如下：1）受拉钢筋的搭接长度应根据位于同一连接范围内的搭接钢筋面积百分率按下使计算，且不得小于300mm，l=l1*x式中：l为受拉钢筋的搭接长度，l1为受拉钢筋的锚固长度，x为受拉钢筋的搭接长度的修正系数，按规定取用。搭接接头面积百分率，是指在同一连接范围内，有搭接接头的受力钢筋与全部受力钢筋面积之比。对梁类、板类及墙类构件，不宜大于25%；对于柱类构件，不宜大于50%。当工程中确有必要增大这个百分率时，梁类则不应大于50%，而板类柱类及墙类，可根据实际情况放宽。另外，同一构件中相邻纵向受力钢筋的绑扎搭接接头以互相错开。2）受压钢筋的搭接长度取受拉钢筋的搭接长度的0.7倍，但在任何情况下都不应小于200mm3）机械连接或焊接，形式较多，目前我国用得较多的是冷轧直螺纹套筒连接。纵向受力钢筋的焊接接头应相互错开，且其连接区段的长度为35d，且不小于500mm，凡接头中点位于该立案区段内的焊接接头均属于同一区段。位于与同一连接区段纵向受力钢筋的焊接接头面积百分率，对纵向受拉钢筋接头，不应大于50%,纵向受压钢筋的接头面积百分率可不受限制。美国的：螺旋筋使用时可能要拼接，拼接长度可由以下方法确定：搭接长度不得小于300mm 和下面(1)-(5)中长度的较大值：(1)光面的变形钢筋或钢丝为48db(2)光面的普通钢筋或钢丝为72db(3)涂有环氧树脂的钢筋或钢丝为72db(4)配有普通箍筋和吊钩的光面的普通钢筋或钢丝，这种吊钩要满足本规范螺旋筋的搭接要求并要埋入螺旋筋的内部48db(5)配有普通箍筋和吊钩的涂有环氧树脂的钢筋或钢丝,这种吊钩要满足螺旋筋的7.1.3 搭接要求并要埋入螺旋筋的内部48db五、中美轴压构件可靠度比较对于轴心受压构件,ACI318299 规范轴压构件的可靠度在4. 75. 1 之间变化。GBJ10 -89 规范一级构件的可靠度在4. 24. 5 之间变化,二级构件在3. 74. 0 之间变化。与美国ACI318299 规范相比, GBJ 10289 规范的可靠度水平的偏低幅度比轴心受拉构件要大一些,其中二级构件平均偏低约22 % 左右;而一级构件平均偏低约10 % 左右。造成我国轴心受压构件的可靠度水平比美国规范偏低的原因,主要是我国规范荷载分项系数和材料强度分项系数的取值偏低,且美国规范考虑附加偏心距等因素的影响,对轴心受压构件的抗力还分别考虑了0. 80. 9 的折减系数,而我国规范没有考虑此项折减系数。 总结，中国和美国有关混凝土规范的区别远不止这些，还有待于我们去认真学习，虽然这些差异有它的自然因素影响，但也不能忽视社会因素对他的影响，其中人们对事物的看法不一样也会导致产生不同的设计准则。这一点是具有地域性和历史性的。总而言之我们对不同地区的建筑的设计就要遵照不同的规范，所谓具体问题具体分析，不能太死板！3.Bar sizes are designated by numbers with Nos. two to eight representing the number of eighths of an inch in the bar diameter. 4.Bar Nos. 9, 10, 11, 14, and 18 have areas equivalent to that of square bars with a side dimension of 1, 1 , 1 , 1 , and 2 inches. pounds per square inch6.ACI requires that specified yield strengths exceeding 60,000 pounds per square inch shall be the stress corresponding to a strain of 0.35 percent. This is to ensure that adequate plasticity is available to develop the ultimate strength required.- The design strength, or capacity, of a member consists of the theoretical ultimate, or nominal, strength of the member Rn multiplied by the appropriate strength reduction factor . The design strength must exceed the effect of the factored loads on the member. The value of the load factor is selected to compensate for the following factors:l The unfavorable deviation of the loading from the nominal value.lUncertainties in methods of analysis.lUnexpected deviations in structural behavior.lThe reduced probability of the full nominal loads, in a combination of loads, being present simultaneously. The value of the strength reduction factor is selected to compensate for the following factors:lThe possibility of adverse variations in material strength.lInadequate workmanship.lDimensional inaccuracies.lThe strength of the material in the structure being less than that of the control specimens.lThe degree of importance of the member to the integrity of the structure.China and the U.S. Some relatively concrete norms First, the symbol of the difference a = height of equivalent rectangular stress region, China is h0av = shear span, the role of a continuous beam or cantilever to any concentrated loads on the bearing surfaces of the distance, while Chinas is: (people) Ao = shear flow The total area surrounded by the Chinese for: Acor Second, the reinforcement details A reinforcement ratio of Chinas specification is no more than Pb (Reinforcement rate), while the United States, including reinforcement ratio should not exceed 0.75b, the determination of strength reduction factor , and the bending moment re-distribution of these specifications in both years Some provisions, including the 1999 specification. These provisions apply to reinforced concrete and prestressed concrete components. 2 Chinas steel hook or bend shall meet the following requirements: grade steel needed for the 180 end hooks, bending the arc diameter (D) should not be less than the bar diameter (d0) of 2.5 times the straight Part of not less than the length of the bar diameter (d0) 3 times; for lightweight aggregate concrete structures, the bending diameter (D) should not be less than the bar diameter (d0) of 3.5 times; , grade steel needed for the end of 90 or 135 bend when, grade steel bending diameter (d) not less than the bar diameter (d0) 4 times; grade steel should not be less than the bar diameter (d0) 5 times (see Figure 3.3.3.2 .) Length of straight part of the design requirements should be determined. United States: in the free end of bent steel 180 and then its value is taken as 4db elongation and 65mm maximum. The free end of the bar 90 and then bending the length of elongation 12db. United States: For the stirrups and the reinforcement of the hook: (a) 16 号 reinforced steel and a more detailed, the free end of the bar 90 bend And then stretch the length of 6db; or (b) 19 and 22 and 25 bar, bending the free end of the bar 90 , and then stretch the length of 12db; (c) 25 bar number and finer in The free end of the bar after bending 135 . Then stretch the length of 6db. Those 10 to 16, except stirrups and reinforcement, 3 Chinas steel processing the shape, size must meet the design requirements. Steel surface should be clean, no damage, grease, dirt and rust paint, etc. should be cleaned before use. Granular or flaky rust with steel and not use the old. Reinforcing Steel in the United States and the surface should be clean and no oil stains, dirt, and excessive rust plaque. Coating on the rust should be allowed.Fourth, the connection steel bar China is the reinforcement of the connection can be divided into two categories: lap banding, mechanical connection or welding. Axial tension and Eccentric tension members, such as lever arch truss, and the longitudinal lap joints reinforced banding shall not be adopted. When the tension bar diameter d 28mm and pressure bar diameter d 32mm, the inappropriate use of banding lap joint. (1) lap banding When the joints with lap without adding welding, the overlapping length l as follows: 1) by the pull of the lap length of reinforcement should be based on the same lap steel connections within the area to calculate the percentage of press, and not less than 300mm, l = l1 * x Where: l is the length of tension lap steel, l1 is the anchorage length of the tension steel, x steel tension lap for the length of the correction factor required access. Percentage of lap joint area, is within the same connection, there is the lap joint force with all the reinforced steel ratio of the area. On the beam type, plate type and wall type structures, not more than 25%; for the column class members, not more than 50%. When the project is really necessary to increase this percentage, the beam should not be greater than 50% of the class, while the column type of board and wall type, according to the actual situation relaxed. In addition, the same longitudinal force component in the adjacent steel banding lap joints staggered to each other. 2) compression lap length of reinforcement steel in tension lap to take the length of 0.7 times, but in no case be less than 200mm 3) mechanical connection or welding, the form of more, our country is more used cold-rolled straight screw sleeve connection. The reinforced longitudinal welded joints should be staggered, and the length of the connecting section 35d, and not less than 500mm, where the joints at the midpoint of the segment of the filing of welded joints belong to the same section. In connection with the same longitudinal section of the welded joint area of the reinforced percentage of longitudinal reinforcement on couplings, should not exceed 50% of the joint area of longitudinal compression reinforcement percentage can be unlimited. United States: spiral reinforcement stitching may be used, by splicing the length of the following methods: Lap length not less than 300mm and below (1) - (5) the length of the larger value: (1) the deformation of steel or glossy wire to 48db (2) Smooth as ordinary steel or wire 72db (3) epoxy coated steel or wire to 72db (4) with a smooth hook ordinary hoops and ordinary steel or steel wire, which hung hook to meet the specification requirements of spiral reinforcement of the lap and to be buried in the internal spiral ribs 48db (5) with normal stirrups and hooks of steel or epoxy coated steel wire helix reinforcement to meet this hook 7.1 .3 Bonding Requirements and to spiral reinforcement embedded within 48db Fifth, the reliability of Sino-US Comparison axial loads For the axial compression component, ACI318299 axial component reliability specifications in the 4.7 5.1 between the changes. GBJ10 -89 normative level the reliability of components in the 4.2 4.5 between the changes in the secondary component in the 3.7 4.0 between the changes. Compared with the United States ACI318299 specifications, GBJ 10289 standard level of reliability than the low rate of axial tension to a large number o