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《第2章2 静定结构受力分析-桁架ppt课件.ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、2.3桁架受力分析桁架可分为:平面桁架和空间桁架只受结点荷载作用的直杆、铰结体系称为桁架结构(trussstructure),其受力特性是结构内力只有轴力,没有弯矩和剪力。2.3.1桁架结构(b)网架示意(a)屋架示意图2-7桁架结构实例根据结构几何组成方式,桁架可以分成三类:(1)简单桁架(simpletruss):由基础或基本三角形,通过依次加二元体所组成的桁架。2.3桁架受力分析(2)联合桁架(combinedtruss):由几个简单桁架按二、三刚片组成规则构造的静定结构。(3)复杂桁架(complicatedtruss):除这两类以外的其他桁架。2.3.2
2、结点法轴力FN及其分力X和Y关系方法:隔离体每次只包含一个结点。特点:平面汇交力系,两个平衡方程,一次能解两个轴力。顺序:与去掉二元体的顺序相同(简单桁架)。适用:简单桁架的全部轴力,某些其他桁架。2.3桁架受力分析3m×4=12mBEDC4mAFGH(a)40kN60kN80kNFByFAxFAy例题2-1试用结点法分析图2-10a所示桁架各杆件的内力。图2-10例题2-1图解法1:(1)由整体平衡条件求出支座反力=0=80kN=100kN2.3桁架受力分析FNCDCFNFC40kN60kN(c)F40kN(d)FNFGFNFD100kNFNGHG90kN(e)
3、FNGD(f)FNDE60kN50kN60kNFNDHD(g)90kN25kNHFFNHEFNHB(i)75kN125kN100kNBFNEBE80kN80kN75kN(h)图2-10例题2-1图3m×4=12mBEDC4mAFGH(a)40kN60kN80kNFByFAxFAyFNACFNAFA80kN(b)(2)截取各结点求解杆件内力按照“结构几何组成相反顺序”2.3桁架受力分析图2-10例题2-1图3m×4=12mBEDC4mAFGH(a)40kN60kN80kNFByFAxFAy=0=80kN=100kN(b)FNACFNAFA80kN-100kN60kN
4、结点A:隔离体如图2-10(b)所示,列再列2.3桁架受力分析结点C:隔离体如图2-10(c)所示,列再列FNCDCFNFC40kN60kN(c)60kN40kN3m×4=12mBEDC4mAFGH(a)40kN60kN80kNFByFAxFAy图2-10例题2-1图=0=80kN=100kN-100kN60kN图2-10例题2-1图=0=80kN=100kN-100kN60kN2.3桁架受力分析结点F:隔离体如图2-10(d)所示,列再列60kN40kN3m×4=12mBEDC4mAFGH(a)40kN60kN80kNFByFAxFAy图2-10例题2-1图=0
5、=80kN=100kN-100kN60kN图2-10例题2-1图=0=80kN=100kN-100kN60kNF40kN(d)FNFGFNFD100kN50kN-90kN2.3桁架受力分析结点G:隔离体如图2-10(e)所示,很明显60kN40kN3m×4=12mBEDC4mAFGH(a)40kN60kN80kNFByFAxFAy图2-10例题2-1图=0=80kN=100kN-100kN60kN图2-10例题2-1图=0=80kN=100kN-100kN60kN50kN-90kNFNGHG90kN(e)FNGD0-90kN2.3桁架受力分析60kN40kN3m×
6、4=12mBEDC4mAFGH40kN60kN80kNFByFAxFAy图2-10例题2-1图=0=80kN=100kN-100kN60kN图2-10例题2-1图=0=80kN=100kN-100kN60kN50kN-90kN0-90kN(f)FNDE60kN50kN60kNFNDHD结点D:隔离体如图2-10(f)所示,列再列25kN75kN2.3桁架受力分析结点H:隔离体如图2-10(g)所示,列再列60kN40kN3m×4=12mBEDC4mAFGH40kN60kN80kNFByFAxFAy=0=80kN=100kN-100kN60kN=0=80kN=100
7、kN-100kN60kN50kN-90kN0-90kN25kN75kN(g)90kN25kNHFFNHEFNHB-125kN80kN2.3桁架受力分析结点E:隔离体如图2-10(h)所示,列校核60kN40kN3m×4=12mBEDC4mAFGH40kN60kN80kNFByFAxFAy=0=80kN=100kN-100kN60kN=0=80kN=100kN-100kN60kN50kN-90kN0-90kN25kN75kN-125kN80kNFNEBE80kN80kN75kN(h)平衡条件满足,计算正确。75kN2.3桁架受力分析结点B:隔离体如图2-10(I)所
8、示,校核平
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