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<h2 class="rich_media_title" id="activity-name" style="margin: 0px 0px 14px; padding: 0px 0px 10px; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(231, 231, 235);"><span style="font-size:small;">一文学会钢桁架设计与选型</span></h2><p class="rich_media_content " id="js_content" style="margin: 0px; padding: 0px; overflow: hidden; min-height: 350px; position: relative;"><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;">一、钢桁架受力特点</span></span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;">钢桁架一般由上弦、下弦和腹杆组成。其受力与普通梁是有区别的:上弦受压、下弦受拉,形成力偶来平衡外荷载产生的弯矩;斜腹杆轴力的竖向分量来平衡外荷载产生的剪力。各杆单元均为轴向受拉或轴向受压构件,而没有弯矩和剪力,这一特点可以使材料的强度得到充分发挥。但在实际结构中,由于节点的非理想铰结等原因,还同时存在较小的弯矩和剪力,对轴力有很小的影响(因节点刚性和桁架杆横截面积与惯性矩比值的大小而不同,一般减小5%-0.1%),称为次内力。</span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;"><br style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;" /></span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;">二、钢桁架受力分析</span></span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;">1</span><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;">.计算假定</span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;">各杆的轴线在同一平面内,节点均为铰结,所有外荷载作用在桁架平面内,并集中作用于节点上。如果作用在节间杆件上,上、下弦的内力将成为压弯或拉弯构件。解决方法:使节点间距等分一致,或再分,尽量将外荷载作用于桁架节点上。</span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;">2</span><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;">.结构计算</span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;">根据平衡理论,节点承受汇交力系作用,逐次建立各节点的投影平衡方程:ΣX=0、ΣY=0,可求出所有的未知杆件内力,这种方法称节点法,最适用于简单桁架。求解时,可根据平衡理论先判定零杆,并尽可能避免解联立方程,有时只需求少数杆件内力。对于联合桁架和复杂桁架,节点法无法奏效时,需用截面法,有选择地截断杆件(一般不超过三根)以桁架的局部为平衡对象,由平衡方程即可求得所需杆件轴力。对于某些桁架(如K式桁架),联合应用节点法和截面法更有效。对于杆件很多的复杂桁架或空间桁架,最好选择电算法。</span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;">桁架结构的内力以轴力为主,各杆件内力分布不均匀。上弦杆件的内力为轴向压力,下弦杆件的内力为轴向受拉,形成力偶抵抗弯矩作用。竖腹杆和斜腹杆的内力可能为轴向拉力或轴向压力(由杆件布置决定),抵抗剪力作用。常见桁架如三角形桁架、矩形桁架、抛物线桁架、梯形桁架的斜腹杆布置方向对腹杆受力是有影响的,根据内力分布情况得到以下结论:</span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;">(1)</span><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;">三角形桁架:内力分布不均匀,弦杆要改变截面,施工困难,否则浪费材料,端点角度小,制作困难,一般应用于跨度小,跨度一般在18-24m以下,坡度大的屋架。</span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both; min-height: 1em; box-sizing: border-box !important; word-wrap: break-word !important;"><span style="font-size:small;"><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;">(2)</span><span style="margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; word-wrap: break-word !important;">矩形桁架:内力分布不均匀,如按内力选杆件,类型多,美观性欠佳,施工困难,材料浪费多,但如采用标准杆件,相同截面的弦杆可以使得结构整齐,而且采购方便,不至造成浪费。</span></span></p><p style="margin: 0px; padding: 0px; max-width: 100%; clear: both