摘要
为了在变截面波形钢腹板悬臂梁的剪应力计算时考虑翼板、腹板以及组合箱梁截面转角差异,首先从翼板、腹板以及组合箱梁截面转角出发建立位移函数,采用能量变分法将翼板与腹板承剪进行剥离,利用弯矩等效分离顶、底板承剪;其次结合变截面波形钢腹板组合箱梁的梁段分析单元刚度矩阵及节点荷载列阵建立了剪应力求解程序;最后分析了悬臂梁在不同荷载工况下顶、底板及腹板剪应力与承剪比.结果表明:相较于有限元计算结果,考虑转角差异后顶板、腹板和底板承剪比计算结果较已有变截面剪应力计算结果精度最大可提高3.48%、3.43%和6.91%;悬臂梁各组件承剪比取决于荷载形式,梁端集中荷载作用下,顶、底板各自承剪比达到最大,分别为自由端的12.82%和固定端的60.81%;均布荷载作用下,腹板承剪比达到最大,为自由端的78.11%.
波形钢腹板组合箱梁因其有效地解决了混凝土腹板开裂问题而被广泛使
在波形钢腹板组合箱梁的发展过程中,国内外众多学者对波形钢腹板组合箱梁的抗剪性能展开了一系列的研究.抗剪强度方面Luo
本文从翼板、腹板以及组合箱梁截面转角出发建立位移函数,基于能量变分法及有限梁段法结合弯矩等效,将顶板、底板及腹板承剪进行剥离并求解,在此基础上,分析悬臂梁在不同荷载工况下顶板、底板、钢腹板剪应力及承剪比.
1 传统剪应力计算公式
1.1 等截面箱梁剪应力计算
假设剪力全部由腹板承担且剪应力沿高度方向均匀分布时:
(1) |
式中:τ为腹板竖向剪应力;Q为全截面竖向剪力;Aw为腹板承剪面积.
1.2 变截面箱梁剪应力计算
参考文献[
(2) |
式中:Q、N、M分别表示全截面剪力、轴力和弯矩;ϕ为截面形心连线的水平倾角;b3为剪应力计算点的截面宽度;Aa为剪应力计算点至梁顶的截面面积;A、I分别为横截面面积及对形心轴的惯性矩;Sa为Aa对全截面形心轴的静矩;τQ、τN、τM分别为由剪力、轴力、弯矩引起的剪应力分量.

图1 微段平衡示意图
Fig.1 Micro segment equilibrium diagram
2 顶板、底板、腹板剪力分离及计算
2.1 基本假定
1) 结构处于弹性工作阶段,材料受力符合胡克定律;
2) 弹性工作阶段拟平截面假定成立;
3) 考虑波形钢腹板的手风琴效应,忽略波形钢腹板上的法向应变,并认为混凝土顶、底板主要贡献抗弯强度,波形钢腹板仅提供抗剪强度;
4) 忽略钢腹板混凝土翼板连接界面处的剪切滑移;
5) 剪应力沿高度方向均匀分布,不考虑顶、底板的有效分布宽度及剪切变形.
2.2 组合箱梁位移函数
波形钢腹板组合箱梁截面示意如

图2 组合箱梁示意图
Fig .2 Composite box beam diagram
波形钢腹板组合箱梁承受任意荷载,考虑腹板手风琴效应,各组件变形如

图3 波形钢腹板变形模式示意图
Fig.3 Deformation mode diagram of corrugated steel web
由
(3) |
(4) |
由
(5) |
式中:.
由式(3)~
(6) |
式中:.
2.3 控制微分方程
由式(3)~
顶板正应变为:
(7) |
底板正应变为:
(8) |
腹板剪应变为:
(9) |
应变能为:
(10) |
其中:
(11) |
(12) |
(13) |
式中:As、Ax和Aw分别为组合箱梁顶板、底板和腹板的面积;Ec为翼板混凝土弹性模量;Gs为钢材的剪切模量;Gw表示组合箱梁钢腹板的换算剪切模量;a、b、c为波形参数,如

图4 波形参数示意图
Fig.4 Schematic diagram of waveform parameters
总势能为:
(14) |
由最小势能原理δΠ=0,可得:
(15) |
控制微分方程为:
(16) |
(17) |
边界条件为:
(18) |
(19) |
(20) |
由边界条件可知,顶板和底板变形产生的弯矩为:
(21) |
顶板和底板绕自身中心的弯矩为:
(22) |
截面总剪力为:
(23) |
其中,波形钢腹板承担的剪力为:
(24) |
顶板和底板承担的剪力为:
(25) |
波形钢腹板剪应力为:
(26) |
求出w(x)、α(x)、θ(x),便可求解各剪力.
2.4 顶、底板承剪分离
如

图5 箱梁受剪示意图
Fig.5 Shear diagram of box beam
Qcs1、Qw1、Qcx1计算方法如下:
(27) |
(28) |
(29) |
式中:S为横截面上该点以外部分的面积对中性轴的静距;I为横截面对中性轴的惯性矩;b0为截面有效宽度.
参考文献[

图6 等效弯矩示意图
Fig.6 Diagram of equivalent bending moment
则:
(30) |
(31) |
(32) |
(33) |
式中:φ为底板形心轴与水平线的夹角;Qcx为底板所受剪力;Qcs为顶板所受剪力.
顶板剪应力为:
(34) |
底板剪应力为:
(35) |
2.5 承剪比
承剪比为:
(36) |
式中:Qi为各组件所受剪力.
3 转角位移求解
为求解w(x)、α(x)、θ(x),建立2节点6自由度的梁段单元,如

图7 有限梁段模型
Fig.7 Finite beam segment model
位移向量
(37) |
(38) |
式中:wi和wj分别表示梁段单元i端和j端的竖向位移;和分别表示单元i端和j端顶、底板截面形心的转角;αi和αj分别表示单元i端和j端顶、底板绕各板中心的转角;Qi和Qj分别表示单元i端和j端截面的全部剪力;Mwi和Mwj分别表示单元i端和j端顶、底板绕截面形心转动产生的弯矩;Mαi和Mαj分别表示单元i端和j端顶、底板绕各自板中心转动产生的弯矩.
由
(39) |
其中:
(40) |
(41) |
微分方程(39)的解为:
(42) |
式中:C0
由
(43) |
对无载梁段:
(44) |
由
(45) |
求解α(x)可得:
(46) |
其中:
(47) |
(48) |
由式(39)~
(49) |
(50) |
(51) |
将
(52) |
向量C及AE为:
(53) |
(54) |
将
(55) |
(56) |
将系数矩阵代入
(57) |
单元任一点处的位移为:
(58) |
位移形函数Ν 为:
(59) |
(60) |
根据虚功原理,可求得均布荷载作用时的等效节点荷载为:
(61) |
(62) |
式中:
(63) |
(64) |
转角位移的求解,采用计算软件编写程序进行.
4 算例分析
4.1 几何参数
参考文献[

(a) 纵向示意图

(b) 截面示意图
图8 变截面梁几何尺寸(单位:mm)
Fig.8 Geometric dimension of variable section beam (unit:mm)
4.2 有限元模型
根据模型尺寸,采用ANSYS软件建立三维有限元分析模型,如

图9 有限元模型示意图
Fig.9 Diagram of finite element model
4.3 转角位移求解
采用MATLAB计算软件编写对应的梁段分析程序,进行转角位移的求解.模型梁划分30个单元,单元尺寸1 m,计算流程如

图10 计算流程图
Fig.10 Calculation flowchart diagram
4.4 剪应力分析
4.4.1 均布荷载
在悬臂梁上施加均布荷载q=35 kN/m,采用对称加载,如

图11 均布荷载加载示意图
Fig.11 Diagram of uniformly load
将本文推导的计算结果与

图12 均布荷载作用下的顶板剪应力
Fig.12 Shear stress of top flange under uniform load

图13 均布荷载作用下的腹板剪应力
Fig.13 Shear stress of web under uniform load

图14 均布荷载作用下的底板剪应力
Fig.14 Shear stress of bottom flange under uniform load
由
由
由
4.4.2 集中荷载
在悬臂梁端部作用一竖向集中力P=500 kN,加载示意图如

图15 集中荷载加载示意图
Fig.15 Diagram of concentrated load

图16 集中荷载作用下的顶板剪应力
Fig.16 Shear stress of top flange under concentrated load

图17 集中荷载作用下的腹板剪应力
Fig.17 Shear stress of web under concentrated load

图18 集中荷载作用下的底板剪应力
Fig.18 Shear stress of bottom flange under concentrated load
由
由
由
4.5 承剪比分析
为了更直观地表达各组件的承剪情况,用承剪比来进一步说明各组件对抗剪的贡献,选取4种荷载工况(工况Ⅰ q=35 kN/m,工况Ⅱ P=500 kN,工况Ⅲ q=17 kN/m,工况Ⅳ P=300 kN),其中工况Ⅰ与工况Ⅱ在截面1处弯矩近似相等;工况Ⅱ与工况Ⅲ在截面1处剪力近似相等;工况Ⅰ与工况Ⅲ荷载形式相同,大小不同;工况Ⅱ与工况Ⅳ荷载形式相同,大小不同.利用

图19 顶板承剪比
Fig.19 Shear capacity ratio of top flange

图20 腹板承剪比
Fig.20 Shear capacity ratio of web

图21 底板承剪比
Fig.21 Shear capacity ratio of bottom flange
工况 | 承剪比/% | ||||||||
---|---|---|---|---|---|---|---|---|---|
式(1) | 式(2) | ANSYS | 式(33)/(24)/(32) | ||||||
截面1 | 截面2 | 截面1 | 截面2 | 截面1 | 截面2 | 截面1 | 截面2 | ||
顶板 | Ⅰ | 0 | 0 | 5.16 | 14.63 | 1.41 | 10.95 | 1.90 | 11.15 |
Ⅱ | 0 | 0 | 1.39 | 14.25 | 0.16 | 10.19 | 0.12 | 12.82 | |
Ⅲ | 0 | 0 | 5.16 | 14.63 | 1.41 | 10.95 | 1.90 | 11.15 | |
Ⅳ | 0 | 0 | 1.39 | 14.25 | 0.16 | 10.19 | 0.12 | 12.82 | |
腹板 | Ⅰ | 100 | 100 | 65.49 | 81.54 | 60.53 | 76.12 | 62.53 | 78.11 |
Ⅱ | 100 | 100 | 41.94 | 80.10 | 39.06 | 74.12 | 39.07 | 76.71 | |
Ⅲ | 100 | 100 | 65.49 | 81.54 | 60.53 | 76.12 | 62.53 | 78.11 | |
Ⅳ | 100 | 100 | 41.94 | 80.10 | 39.06 | 74.12 | 39.07 | 76.71 | |
底板 | Ⅰ | 0 | 0 | 29.35 | 3.83 | 38.06 | 12.93 | 35.57 | 10.74 |
Ⅱ | 0 | 0 | 56.67 | 5.65 | 60.78 | 15.69 | 60.81 | 10.47 | |
Ⅲ | 0 | 0 | 29.35 | 3.83 | 38.06 | 12.93 | 35.57 | 10.74 | |
Ⅳ | 0 | 0 | 56.67 | 5.65 | 60.78 | 15.69 | 60.81 | 10.47 |
由
1) 工况Ⅰ、Ⅲ各截面承剪比相同,工况Ⅱ、Ⅳ各截面承剪比相同,但工况Ⅰ、Ⅲ与Ⅱ、Ⅳ不同,由此说明组合悬臂梁承剪比取决于荷载形式.
2) 随着跨度增加,顶板和腹板的承剪比逐渐增大而底板的承剪比逐渐减小.梁端集中荷载作用下,顶、底板各自承剪比达到最大,分别为自由端的12.82%和固定端的60.81%;均布荷载作用下,腹板承剪比达到最大,为自由端的78.11%.
3) 荷载作用下,顶板承剪比与
5 结 论
本文从翼板、腹板以及组合箱梁截面转角差异出发,求解变截面波形钢腹板悬臂梁顶板、底板、腹板剪应力及承剪比,结合算例分析得出如下结论:
1) 采用等截面剪应力计算公式高估腹板承剪的最大误差达到2.44倍.
2) 变截面波形钢腹板悬臂梁由固定端到自由端,顶板、腹板承剪比逐渐增大,底板承剪比逐步减小.
3) 变截面波形钢腹板悬臂梁顶板、底板及腹板承剪比取决于荷载形式;梁端集中荷载作用下,顶、底板各自承剪比达到最大,分别为自由端的12.82%和固定端的60.81%;均布荷载作用下,腹板承剪比达到最大,为自由端的78.11%.
4) 从截面转角出发可使均布荷载下顶板、腹板和底板承剪比的计算精度最多提高3.48%、3.43%和6.91%.
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