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1 Journal of Architect ure and Civil Engineering Vol. 23 No. 1 Mar : (2006) ,2, 1 (1., ; 2., ) :,,, : ;, ;,,,, ; : ; ;; ; :U :A Experimental Research on Concrete2Filled Steel Tube Truss Girder Under Bending HUAN G Wen2jin 1,2, CH EN Bao2chun 1 (1. School of Civil Engineering and Architecture, Fuzhou University, Fuzhou , Fujian, China ; 2. School of Transportation, Fujian Agriculture and Forestry University, Fuzhou , Fujian, China) Abstract : In order to make f urt her investigation into t he global action of concrete2filled steel t ube ( CFS T) t russ girder, experiment of CFS T t russ girder specimen under symmet rically quarter loading was carried o ut. Specimen of CFS T t russ girder was fabricated according to dimensio ns of stiffening girder and t russ arch rib of several built bridges and co de for design of steel t ube st ruct ure. Based o n t he measured deflectio n and st rain of specimen during experiment, t he defo rmatio n, st rain increasing mode of steel t ube, failure mode and load2carrying capacit y of joint s as well as t he whole girder were analyzed. The test result shows t hat deflection of CFST truss girder is mainly attributed to deformation of shear2bending part s and much smaller t han t hat of solid web girder. The behaviors of joint s are complex and it s ultimate load capacity will control t hat of t he t russ girder. Filled co ncrete in t he chord t ubes can increase t he memberπs radial rigidit y and keep it f ro m plastic failure t hus st rengt hens t he joint s. U nder t he symmet rically quarter loading, axial forces in web members for CFST welding truss girder are commonly less t han t hat of hinged truss, and t he chord members are subjected to prominent bending moment. Before t he failure of joint s, o bvio us shear deformatio n amo ng web member s can be o bserved during shearing2bending part s. Key words : concrete2filled steel t ube ; truss girder ; experimental research ; ultimate load capacity ; t ubular joint : : ( ) : (19752),,,,,E2mail edu. cn

2 ,,,,,,,, [1 ],,,, [224 ],, : [526 ],,,, 1 N Pratt, ( GB ) mm, mm, 488 mm, 222 mm, 13, 55, 18 mm, 1 (a), 1, 180 mm, 1 (b) #, ; #, 32 ; ; #, 37. 5, 1 (c) , 1 (d), MPa, 428 MPa, 209 GPa, C40,,,,, 50, Fig. 1 1 ( :mm) Sizes of Truss Girder Specimen ( Unit :mm),, MPa,,,, l/ 4 l/ 2, 2 (a), 2, c, c bc, 2 (a) l/ 4 [ a( a ) c(c ) ],l/ 4 l/ 2 [ c ( c ) e (e ) ],, , 2 (b), IMP, : 1/ 10, 2

3 1, : 31 2 Fig. 2 Measuring Points Arrangement 1/ 20, 2 min , , , ( ),, de ee ,, 3 2 A C,,: 2 2 3, 0 A A B B C CD D E 3 F l/ 4,U m Fig Relation of Load and Deflection,,,,, A F 110 kn, ab a, ,,0A,,, B 130 kn, a,, C, kn, A C : kn,, 4 2 Fig. 4 Relation of Load and Strain for Steel Tubes of Middle Part,, 5,,,,, 5 Fig. 5 Deflection of Truss Girder Specimen ( 3 C ) mm, 1/ ;, kn kn, 7. 8 %, mm 1/

4 32 建筑科学与工程学报 2006 年腹梁 ( 圆形和哑铃形截面) 跨中变形超过梁跨的1/ 20 时,荷载2挠度关系曲线仍处于上升趋势 [ 728 ] 钢管混凝土桁梁变形明显小于实腹梁,其主要原因 : 一是桁式截面的抗弯刚度较实腹式截面的大 ; 二是桁梁试件节点破坏先于整体破坏发生, 各杆件尤其是弦杆远未达到构件的极限承载能力 ; 三是变形主要集中于边段而中段的变形很小在峰值荷载之后,荷载2挠度关系曲线并不像一般受弯构件一样出现平滑的下降段, 而是随着节点 a 裂缝的不断开展,曲线出现了一个急速下降段, 至 D 点时节点 a 的受拉接头完全失效, 此后荷载基本维持在 kn 左右,但变形迅速增大, 节点 a 的受压接头逐渐外鼓在跨中挠度迅速增加的同时, 另一个节点 b 的受拉接头也出现裂纹且不断发展, 至 E 点时,节点 b 的受拉接头完全破坏, 边段只由接头处局部屈曲的受压腹杆 aa 和 bb 及弦杆抵抗剪切变形, 桁梁试件迅速卸载, 试验终止此时, 桁梁左右半跨的边段都连续出现两个节点 ( 左半跨为节点 a 和 b,右半跨为节点 h 和 i ) 破坏由此可见 : 钢管混凝土桁梁受弯与钢管桁梁相似, 节点破坏仍是结构极限承载力的控制因素 3 节点破坏模式和节点承载力分析图6 Fig. 6 桁梁试件破坏模式 Failure Modes of Truss Girder Specimen 应变计算腹杆的换算轴力 F1,并以腹杆的换算轴力作为节点的支杆轴力当 l/ 4 截面荷载 F 增加到 110 kn 时,即荷载2挠度关系曲线到达 A 点时,受拉腹杆 ab 节点 a 处的应变最大,节点 a 处钢管开始屈服 ; 当 l/ 4 截面荷载 F 增加到 130 kn 时,即荷载2挠度关系曲线到达 B 点时, 受拉腹杆 ab 节点 a 处的弦杆钢管开始开裂若分别以实测的钢材屈服强度和极限抗拉强度分别计算荷载2挠度关系曲线上 A B 点的节点强度,并忽略腹杆面内弯矩的影响,则按当荷载2挠度关系曲线 ( 图 3) 进入 B 点时,节点 a 处弦杆钢管冠点开始出现裂缝, 裂缝沿受拉腹杆 ab ( 斜腹杆 ) 四周发展, 受压腹杆 aa ( 直腹杆 ) 在接头处也发生局部屈曲, 见图 6 ( a ) ; 至荷载2挠度关系文献 [ 9 ] 中计算的冲剪承载力 F2 和按文献 [ 10 ] 中计算的塑性失效承载力 F3,以及按铰接桁架模型计算的杆件轴力 F4 见表 1, 其中, 铰接桁架模型假定所有的节点均为铰接且节点偏心距为零如表 1 所曲线的 C 点时,节点 b 也发生受拉腹杆 bc 开裂, 边段可见较明显的腹杆剪切变形和弦杆弯曲, 见图 6 ( b) ; 剖开弦杆钢管后, 上下弦杆管内混凝土基本保持完好,见图 6 ( c) ( d) 对于间隙接头的空心管结构, 腹杆与弦杆管径比β小于中值时 (β< 0. 6 ), 接头失效模式一般为弦杆表面塑性失效 ( A 模式), 弦杆与受压腹杆连接处压陷而与受拉腹杆连接处鼓曲 ; 当管径比β 为中值示,桁梁试件实际节点破坏为弦杆钢管冲剪失效,塑性失效承载力 F3 仅为腹杆换算轴力 F1 的 1/ 4, 铰接桁架腹杆轴力 F4 比 F1 小约 1/ 3,而按文献 [ 9 ] 中计算的空钢管冲剪承载力 F2 与 F1 则非常接近考虑到桁梁试件腹杆除了承受轴力外还承受有弯矩,受拉接头的实际应力要比受拉腹杆中截面的时 (β= ), 弦杆表面经常出现冲剪失效 ( B 模式) 与空心管结构不同,钢管混凝土桁梁试件管径比β为小于中值, 由于弦杆钢管填充混凝土,试件边段的节点破坏为弦杆钢管冲剪失效,因此接头的失效模式为 B 模式而不是 A 模式由于受节点的影响, 腹杆接头与中截面的钢管应变变化有一定的差别, 同时在接头开裂至完全失效过程中,腹杆接头应变波动很大而腹杆中截面相对较稳定,因此本文中通过腹杆中截面的平均轴向平均轴向应力要大,因此,钢管混凝土桁梁试件受拉接头的节点强度远大于空钢管节点发生弦杆钢管表面塑性失效时的承载力按铰接桁架模型进行简化计算时,节点腹杆轴力计算值与受拉腹杆中截面的实际轴力值有较大的误差对于钢管混凝土桁梁, 节点冲剪承载力应采用空钢管的冲剪承载力进行验算,但同时还应考虑腹杆弯矩的影响由此可见 : 桁梁试件弦杆填充混凝土后既增加弦杆的抗压和抗弯刚度也增加了弦杆的径向刚度, 填充混凝土可以约束节点变形和增大节点强度, 弦杆本身还可以分担部分剪力,进而提高了桁梁试件的整体承载力 China Academic Journal Electronic Publishing House. All rights reserved.

5 1, : 33 Tab. 1 1 Calculation Values Comparison of Joint Strength Under Tension for CFST Truss Girder l/ 4 F/ kn F1/ kn [9 ] F2/ kn [10 ] F3/ kn F4/ kn ( F2 F ) / % ( F3 F ) / % ( F4 F ) / % (1),, (2), (3),, (4),, (5), : References : [ 1 ] J. [ M ]. :,2004. WARDEN IER J. Construction Application of Steel Tubular Section [ M ]. Shanghai : Tongji University Press,2004. [ 2 ],. [J ].,2002,32 (7) : CH EN Yi2yi, CH EN Yang2ji. Research Actuality of Steel Tubular Structure Joint s[j ]. Building Construc2 tion,2002,32 (7) : [ 3 ],,. [J ].,2005, 22 (1) : NIE Jian2guo, Q IN Kai, ZHAN G Gui2biao. Experi2 mental Research and Theoretical Analysis on Flexural Capacity of Connections for Concrete2Filled Steel Square Tubular Columns with Inner Diaphragms[J ]. Journal of Architecture and Civil Engineering, 2005, 22 (1) : [ 4 ],,. [J ].,2005,22 (1) : ZHAO J un2hai, GUO Hong2xiang,WEI Xue2ying. Re2 search on Bearing Capacity of Concrete Filled Double Skin Steel Tubes Column[J ]. Journal of Architecture and Civil Engineering,2005,22 (1) : [ 5 ] YOSHINA GA S. Experiments on Concrete Filled and Reinforced Tubular K2Joint s of Truss Girder [ J ]. Journal of Constructional Steel Research, 2004, 60 (5) : [ 6 ]. [J ].,1997,14 (3) :8212. PAN G Shou2xian. Fatigue Experiment and Analysis of Concrete Filled Steel Tubular Model [ J ]. Railway Construction Technology,1997,14 (3) :8212. [ 7 ]. [J ].,1985,15 (3) : CA I Shao2huai. Experimental Research on Bending Strength of Concrete Filled Steel Tubular[J ]. Building Construction,1985,15 (3) : [ 8 ],,. [J ].,2005,22 (4) : CH EN Bao2chun, SH EN G Ye, WEI Jian2gang. Ex2 perimental Study of Concrete Filled Steel Tubular Dumbbell2Shaped Beam Under Bending[J ]. Engineer2 ing Mechanics,2005,22 (4) : [ 9 ] PACKER J A, H ENDERSON J E,CAO J J. [ M ]. :,1997. PACKER J A, H ENDERSON J E,CAO J J. Hollow Tubular Structure Joint Design Guide [ M ]. Beijing : Science Press,1997. [10 ] GB , [ S]. GB ,Steel Structure Design Code[ S].

33 4-67 Fig. 1 1 Plan of typical floor 2 Fig. 2 Analysis model - 1 0. 85 4 1 Table 1 Period results s SATWE ETABS SAP2000 ABAQUS T 1 4. 681 4. 679 4.

33 4-67 Fig. 1 1 Plan of typical floor 2 Fig. 2 Analysis model - 1 0. 85 4 1 Table 1 Period results s SATWE ETABS SAP2000 ABAQUS T 1 4. 681 4. 679 4. 33 4 2011 8 Earthquake Resistant Engineering and Retrofitting Vol. 33 No. 4 Aug. 2011 1002-8412 2011 04-0066-07-1 2 2 2 3 1. 100084 2. 518029 3 523808-215m 11. 2 - TU973 +. 17 A Summarization of Structural