1、4.4 Reinforced Concrete Column,4.4 鋼筋混凝土柱,Axial Compression,軸向受壓,承受壓力的構(gòu)件被稱作柱子,Columns are defined as members that carry loads chiefly in compression.,In addition to the common type of compression member, i.e. vertical elements in structures, compression members include arch ribs, rigid frame members

2、 inclined or otherwise, compression elements in trusses or shell.,除了一般的受壓構(gòu)件，即結(jié)構(gòu)中的豎向構(gòu)件，受壓構(gòu)件還包括拱肋，斜的剛架構(gòu)件，桁架或殼結(jié)構(gòu)中的受壓構(gòu)件。,Composite compression members reinforced longitudinally with structural steel shapes, pipe, or tubing, with or without additional longitudinal bars, and various types of lateral reinf

3、orcement.,配置縱向結(jié)構(gòu)型鋼、鋼管或管形材料并配有各種類型橫向鋼筋的復(fù)合受壓構(gòu)件，無論是否配置附加的縱向鋼筋。,steel shapes 型鋼,The main reinforcement in columns is longitudinal, parallel to the direction of the load, and consists of bars arranged in a square, rectangular, or circular pattern.,柱中的主要受力筋為縱向鋼筋，與荷載作用方向平行，沿正方形、矩形或環(huán)形布置。,Lateral reinforceme

4、nt, in the form of individual relatively widely spaced ties or a continuous closely spaced spiral, serves several functions.,橫向鋼筋為具有較大間距單個(gè)箍筋或連續(xù)的近間距的螺旋箍，它具有若干功能。,for one 作為其中一個(gè); 舉例來說,For this purpose, longitudinal and transverse steel is wired together to form cages, which are then moved into the for

5、ms and properly positioned before placing the concrete.,因此，將縱向鋼筋和箍筋綁扎在一起，形成鋼筋骨架，然后將其移入模板中，在澆筑混凝土前正確擺放。,For another, transverse reinforcement is needed to prevent the highly stressed, slender longitudinal bars from buckling outward by bursting the thin concrete cover.,另外，箍筋能夠防止應(yīng)力較大的、細(xì)長縱筋向外彎曲，崩裂單薄的混凝土

6、保護(hù)層。,Behavior of Axially Loaded Short Column,軸心受壓短柱的特性,When an axial load is applied to a reinforced concrete short column, the concrete can be considered to behave elastically up to a low stress of about (1/3),.,當(dāng)荷載作用在鋼筋混凝土短柱形心時(shí)，應(yīng)力低于,混凝土被認(rèn)為具有彈性特性。,At this load the concrete fails by crushing or shea

7、ring outward along inclined planes, and the longitudinal steel bars fail by buckling outward between ties, as shown in Figure 4.26(a).,普通箍筋柱在荷載Na作用下破壞。在此荷載下，由于混凝土壓碎或向外沿斜面受剪破壞，縱筋由于在箍筋之間向外彎曲而破壞，如圖（4.26a）所示。,It is at this stage that the confining action of the spiral has a significant effect, and if si

8、zable spiral steel is provided, the load will ultimately fail the column by causing the spiral steel to yield .,正是在這個(gè)階段，螺旋箍發(fā)揮著重要的約束作用。如果配置大量的螺旋箍，當(dāng)荷載使螺旋筋屈服時(shí)，柱子發(fā)生破壞。,Na,load,(a) Unsupported bars buckle (b) Concrete shell spalls off Failure of tied and spirally reinforced concrete column,Short Columns

9、under Combined Axial Force and Moment,軸力及彎矩共同作用下的短柱,When a member is subjected to combined axial compression N and moment M, such as in Figure 4.28(a), it is usually convenient to replace the axial load and moment with an equal load N applied at eccentricity, as in Figure 4.28 (b).,當(dāng)柱子承受軸力N以及彎距M的共同作

10、用時(shí)，如圖4.28a，通常用軸力N作用在距離軸心e=M/N處取代構(gòu)件承受的軸力和彎矩，如圖4.28b所示，是一種很簡便的方法。,Balanced failure,界限破壞,Under this mode of failure, yielding of the tensile steel on the far side of the loading point occurs simultaneously with the attainment of limit compressive strain of 0.0033 in concrete.,在這種破壞方式下，遠(yuǎn)離軸向力作用點(diǎn)一側(cè)的受拉鋼筋屈服

11、，同時(shí)受壓區(qū)混凝土達(dá)到0.0033的極限壓應(yīng)變。,Compression failure of the column occurs when (a) the relative eccentricity,is small, or (b) although the relative eccentricity,is large, but the tension reinforcement ratio is large.,當(dāng)相對(duì)偏心距e0/h0較小時(shí)，或盡管相對(duì)偏心距e0/h0較大，但受拉鋼筋配置較多時(shí)，柱子會(huì)發(fā)生受壓破壞。,Columns of this type fail by crushing

12、of the concrete and compressive yielding of the steel on the side near the load, while the reinforcement on the side farthest from the load does not yield.,這種破壞表現(xiàn)為離荷載作用點(diǎn)近的一側(cè)混凝土壓碎鋼筋受壓屈服，而另一側(cè)鋼筋沒有屈服，如圖4.29b所示。,Capacity of short columns under combined axial force and moment,短柱抵抗彎壓共同作用的能力,The strength in

13、teraction diagram defines the failure load and failure moment for a given column for the full ranges of eccentricity from zero to infinity.,強(qiáng)度相關(guān)圖給出了某一柱子偏心距從零到無窮大時(shí)的破壞荷載與彎距。,The extreme concrete fiber strain reaches ultimate strain (0.003) simultaneously with yielding of the extreme layer of steel on

14、the opposite side (fy/Es=0.002).,混凝土的最大應(yīng)變達(dá)到極限應(yīng)變（0.0033），另一側(cè)的最外層鋼筋同時(shí)達(dá)到屈服應(yīng)變（fy/Es=0.002）。,The interaction diagram further reveals that as the axial force Nu becomes larger the section can carry smaller Mu before failing in the compression zone.,相關(guān)曲線進(jìn)一步顯示，在受壓破壞區(qū)，構(gòu)件破壞前，隨著軸力增大，截面所承受的彎距越來越小。,The large axi

15、al force produces high compressive strain of concrete keeping smaller margin available for additional compressive strain due to bending.,軸力大，混凝土產(chǎn)生壓應(yīng)變就大，從而無法承受更多的由彎曲引起的附加壓應(yīng)變。,This tensile yield stress reduces with the additional compressive stress due to additional axial load.,隨著附加軸力引起附加的壓應(yīng)力增大，這種受拉鋼筋

16、拉應(yīng)力降低。,Just as for simple bending, the actual concrete compressive stress distribution is replaced by an equivalent rectangular distribution having depth x.,僅對(duì)單純的受彎而言, 采用受壓區(qū)截面高度為x的等效矩形應(yīng)力分布圖替代實(shí)際混凝土壓應(yīng)力分布。,Actual and equivalent rectangular stress distribution of eccentrically loaded column at ultimate

17、strength,另外，混凝土壓應(yīng)力、鋼筋作用力以及外力N關(guān)于受拉鋼筋合力中心線的彎距和必須等于0。,In addition, sum of the moments of the concrete compressive stress, reinforcement force and the external force N about the centerline of the resultant force in the tension reinforcement must equal zero,Additional eccentricity,附加偏心距,Slender Columns,長

18、柱,On the other hand, the slender or long columns may fail at a much lower value of the load when sudden lateral displacement of the member takes place between the ends.,另一方面，當(dāng)構(gòu)件在兩支承端之間突然發(fā)生橫向側(cè)移，長柱會(huì)在非常低的荷載作用下破壞。,Capacity of Axially Loaded Slender Column,軸心受壓長柱承載力,stability reduction coefficient,穩(wěn)定系數(shù),T

19、he lower ratio limit is necessary to ensure resistance to bending moment not accounted in the analysis and to reduce the effects of creep and shrinkage of the concrete under sustained compression.,為了確保抵抗分析中沒有考慮的彎矩以及減少混凝土在持續(xù)荷載壓力作用下混凝土徐變和收縮的影響，必須設(shè)置配筋下限。,Spacing between longitudinal bars measured along

20、 the centroid should not exceed 300mm.,縱筋凈間距不超過300mm。,When the depth of the eccentrically loaded column is greater than 600mm, additional longitudinal bars with a diameter of 1016mm should be placed on the lateral sides.,當(dāng)偏心受壓柱的截面高度大于600mm時(shí)，沿兩側(cè)向應(yīng)該各增加一根直徑10-16的附加縱筋。,The ties shall be so arranged that every corner and alternate longitudinal bar shall have lateral support provided by the corner of a tie having an included angle of not more than, and no longitudinal bar shall be farther than 300mm on either side from such a laterally supported bar.,箍