【導(dǎo)讀】繼續(xù)進(jìn)行，由于拉鋼筋到混凝土之間裂縫的轉(zhuǎn)換力量。這一種混凝土的拉力被稱為混凝土的張力。在開(kāi)裂后它會(huì)影響鋼筋混凝土的剛度，因此它的撓度和裂縫寬度必須根據(jù)屈服強(qiáng)度負(fù)載。對(duì)輕混凝土，例如樓板，全部裂縫的彎曲剛度比沒(méi)有裂縫部分的要小很多，張力加勁有助于剛度。最后，建議書(shū)包括建模系統(tǒng)緊張撓度控制的鋼筋混凝土樓板設(shè)計(jì)變硬。允許的最低含量。力加勁大大促進(jìn)了開(kāi)裂后剛度。在設(shè)計(jì)中，撓度和裂縫的控制通常是在屈服水平調(diào)整考慮的，并。撓度計(jì)算中最常用的方法包括確定為破解構(gòu)件平均慣性有效時(shí)刻。式可用于Ie，包括著名的方程開(kāi)發(fā)Branson和ACI318。代方程，這基本上是與Eurocode2方案兼容。在負(fù)載超過(guò)負(fù)荷少的開(kāi)裂，Pcr，該。有一個(gè)剛度突變，并立即出現(xiàn)裂紋。事實(shí)上，實(shí)際的響應(yīng)介于這兩個(gè)。的鋼產(chǎn)量和負(fù)荷接近極限地步。在每個(gè)板跨中撓度的預(yù)測(cè)結(jié)果與實(shí)測(cè)時(shí)，在跨中時(shí)刻等于，2。

　　

【正文】 derably greater in practice than that indicated by the laboratory tests reported here. Unlike the Eurocode 2 and BS 8110 approaches, the ACI 318 model does not recognize or account for the reduction in the cracking moment that will inevitably occur in practice due to tension induced in the concrete by drying shrinkage or thermal deformations. For many slabs, cracking will occur within weeks of casting due to early drying or temperature changes, often well before the slab is exposed to its full service loads. By limiting the concrete tensile stress at the level of the tensile reinforcement to just MPa, the BS 8110 approach overestimates the deflection of the test slabs both below and immediately above the cracking moment. This is not unreasonable and accounts for the loss of stiffness that occurs in practice due to restraint to early shrinkage and thermal deformations. Nevertheless, the BS 8110 approach provides a relatively poor model of the postcracking stiffness and incorrectly suggests that the average tensile force carried by the cracked concrete actually increases as M increases and the neutral axis rises. As a result, the slope of the BS 8110 postcracking momentdeflection plot is steeper than the measured slope for all slabs. The approach is also more tedious to use than either the ACI or Eurocode 2 approaches. In all cases, deflections calculated using Eurocode 2[ Eqs.(3)–(5)] are in much closer agreement with the measured deflection over the entire postcracking load range. As can be seen in Fig. 2, the shape of the loaddeflection curve obtained using Eurocode 2 is a far better representation of the actual curve than that obtained using Eq. (1). Considering the variability of the concrete material properties that affect the inservice behavior of slabs and the random nature of cracking, the agreement between the Eurocode 2 predictions and the test results over such a wide range of tensile reinforcement ratios is quite remarkable. With the ratio of ( predicted/ exp??) in Table 2 varying between and with a mean value of , the Eurocode 2 approach certainly provides a better estimate of shortterm behavior than either ACI 318 or BS8110. Conclusions Although tension stiffening has only a relatively minor effect on the deflection of heavily reinforced beams, it is very significant in lightly reinforced members where the ratio Iuncr / Icr is high, such as most practical reinforced concrete floor slabs. The models for tension stiffening incorporated in ACI （ 2021） , Eurocode 2 (CEN 1992), and BS 8110 （ 1985） have been presented and their applicability has been assessed for lightly reinforced concrete deflections calculated using the three code models have been pared with measured deflections from 11 laboratory tests on slabs containing varying quantities of steel reinforcement. The Eurocode 2 approach （ Eq.（ 5） has been shown to more accurately model the shape of the instantaneous loaddeformation response for lightly reinforced members and be far more reliable than the ACI 318 approach （ Eq.（ 1） . References American Concrete Institute （ ACI） .（ 2021） . ―Building code requirements for structural concrete.‖ ACI 31805, ACI Committee 318, Detroit. Bischoff, P. H. (2021). ―Reevaluation of deflection prediction for concrete beams reinforced with steel and fiberreinforce polymer bars.‖ . Eng., 131(5), 752–767. Branson, D. E. (1965). ―Instantaneous and timedependent deflections ofsimple and continuous reinforced concrete beams.‖ HPR Rep. No. 7,1, Alabama Highway Dept., Bureau of Public Roads, Ala. British Standards Institution (BS).（ 1985） . ―Structural use of concrete, Part 2, code of practice for special circumstances.‖ BS8100: Part2:1985, British Standard, London, England. European Committee for Standardization（ CEN） . （ 1992） . ―Eurocode 2:Design of concrete structures Part 11: General rules for buildings.‖DD ENV 199211, European Prestandard, Brussels, Belgium. Gilbert, R. I.（ 2021） . ―Deflection by simplified calculation in AS36002021—On the determination of fcs.‖ Australian J. Structural Engineering,5（ 1） , 61–71. Standards Australia（ AS） . （ 2021） . ―Australian standard for concrete structures.‖AS 36002021, Sydney,