如圖所示單元體中,ab斜面上的正應(yīng)力σa應(yīng)為()
A.(50-20)/2+[(50+20)/2]cos(-60°)-30sin(-60°) B.(50+20)/2+[(50-20)/2]sin(60°)-30cos(60°) C.(50+20)/2+[(50-20)/2]cos(-60°)+30sin(-60°) D.(50-20)/2+[(50+20)/2]cos(-60°)+30sin(-60°)
A.鋼材 B.木材 C.鑄鐵 D.鋁材
有一簡(jiǎn)支梁,中點(diǎn)受集中力P作用。梁端轉(zhuǎn)角θ=Pl2/16EI,當(dāng)梁的長(zhǎng)度l、橫截面尺寸、荷載P均增大一倍時(shí),梁端轉(zhuǎn)角等于原轉(zhuǎn)角的多少倍?()
A.1/2 B.1 C.2 D.4