很簡單的一段翻譯,太懶了:( 感覺我.
keli1987好像不是土木工程專業(yè)的吧
Concrete is characterized by strong compressive strength,but is relatively weak in tension and shear.It can support large axial loads,and is used extensively in the foundations of large structures such as bridges and tall buildings.but it breaks easily under bending without reinforcing steel.Concrete with compressive strength of 3,000 6,000 pounds per square inch (psi) is common.
混凝土材料特點是抗壓能力強,抗拉和抗剪切能力差.能夠承受很大的軸向壓力,能夠廣泛的應用與橋梁和高層建筑的基礎.但是如果不加鋼筋,其很容易破壞.混凝土一般具有3,000 6,000psi抗壓強度.（1psi=0.069公斤=6900Pa）
The American Concrete Institute defines any concrete over 6,000 psi as high-strength concrete.
For structures that require flexural strength for resistance to bending moments,reinforcing steel--rebar--is embedded in the concrete.In some cases,tensioned cables are placed in the concrete to make prestressed or post-tensioned concrete.The tension to resist the bending moment comes from the reinforcing steel or the stressed cables.
美國混凝土協(xié)會定義超過6,000 psi抗壓強度的混凝土為高強混凝土.
對于結(jié)構(gòu)來說,需要彎曲應力去抵抗彎矩,因此鋼筋被嵌入到混凝土材料中.有些情況,拉索（預應力筋）埋入混凝土構(gòu)成預應力混凝土,可以采用先張法或者后張法.鋼筋或者預應力索的拉力用于抵抗彎矩.
For a concrete mix to reach its ultimate strength,a long period of time is needed.The ultimate strength of concrete and its 28-day strength are not the same.For design purposes,engineers use the 28-day strength,and the concrete should be subjected to only minimum loads until the 28 days have passed.That rule is very rigidly enforced in heavy construction.It is not at all uncommon for work in residential and medium-rise commercial building construction to be processed on a 3-day floor cycle.Place concrete one day,form and shore the next floor over the next two days,this puts minimum load on the new slab,and then place concrete on the third day.This placement increases the load on the previously placed floor,but the load is carried primarily by the shoring,which passes continually down for several floors,thereby shifting the load to concrete that has had time to reach its ultimate strength.
Note the shoring and reshoring in Fig.6.5 is in place to a depth of four floors below the slab that is currently being placed.
混凝土達到極限承載力齡期需要很長時間.極限承載力和28天強度還有點區(qū)別.對于設計,工程師通常使用28天強度,混凝土未達到28天強度前僅能承受很小的荷載.這個規(guī)定在特殊建筑中需要強制執(zhí)行.不同于一般的住宅和多層商業(yè)建筑可以3天作一個樓層.澆注混凝土1天,接下來2天給下一層支模,給新澆注的樓板最小的荷載,然后第三天再澆混凝土.這種澆注方法給前一層澆注的樓層施加荷載,但是這部分荷載主要給支撐模板,模板能把這部分荷載分散到先前的若干層上,因此這部分荷載能夠分散到以前達到極限強度的樓層上.注意,圖6.5的板下面4層樓高的支架已替換.
（ultimate strength of concrete
The compressive strength of concrete continues to increase slowly for many months.The ultimate strength may be higher than the 28-day strength,which is used for design calculations.）
（混凝土極限強度：混凝土抗壓強度災數(shù)月內(nèi)緩慢增加,混凝土極限強度可能高于28天強度,其用于設計計算）