International Journal of Steel Structures
September 2012, Vol 12, No 3, 381-389
DOI 10.1007/s13296-012-3007-5
www.springer.com/journal/13296
Study on Failure modes of Steel Truss Bridge Gusset Plates Related to Tension and Shear Block Failure
Hideyuki Kasano1*, Teruhiko Yoda1, Kuniei Nogami2, Jun Murakoshi3,
Naoki Toyama3, Mamoru Sawada3, Kentaro Arimura3, and Lu Guo3
1Department of Civil and Environmental Engineering, Waseda University,
3-4-1 Shin-okubo, Shinjuku-ku, Tokyo, 169-8555, Japan
2Department of Civil and Environmental Engineering, Tokyo Metropolitan University,
1-1, Minami-osawa, Hachioji-shi, Tokyo, 192-0397, Japan
3Bridge and Structural Engineering Research Group CAESAR, Public Works Research Institute,
1-6, Minamihara, Tsukuba, Ibaraki, 305-8516, Japan
Abstract
Tension and shear block failure is a limit state which occurs in the connection of tension steel members. The failure mechanism is a combination of tensile failure on one plane and shear failure on the perpendicular plane. The design strength equations for the tension and shear block failure are described in the well known design codes. However, they provide inconsistent levels of safety when they are used in different types of connections. In this paper, the authors survey the design strength equations in the various codes. Then, the pertinent strength equations for the gusset plates of steel truss bridges are selected. Moreover, the authors propose a pair of strength equations for compression and shear block failure for gusset plates subjected to compressive force. And to examine the applicability of proposed equations and to investigate the mechanical behavior of compression gusset plates, parametric analyses on the various thicknesses of gusset plates were conducted.
Keywords: tension and shear block failure, strength equation, FEM analysis, gusset plates, steel truss bridges
1. Introduction
Generally truss bridges are less of redundancy, than other types of bridges. The reason is that their structure is based on the statically determinate triangular members. In the case of I-35W steel truss bridge collapse in Minneapolis, U.S.A. in 2007, the cause of collapse was primarily due to the inadequate design thickness of gusset plates. Generally, gusset plates are so designed that they have enough adequacy, and they are unlikely to fail. Therefore, detailed verification of gusset plates is not put into practice in designing either in U.S.A. or in Japan. However, the fact that the collapse of I-35W steel truss bridge was originally caused by the failure of inadequate gusset plates indicates that failure of gusset plates connecting several truss members is more likely to lead to collapse of
Note.-Discussion open until February 1, 2013. This manuscript for this paper was submitted for review and possible publication on Sep-tember 21, 2011; approved on August 10, 2012.
copy; KSSC and Springer 2012
*Corresponding author
Tel: ; Fax: 81-3-5286-3399 E-mail: kasano@aoni.waseda.jp
entire bridge than failure of one of truss members. Therefore, it is significant to investigate mechanical behavior of gusset plates in ultimate states and to take the outcomes into the design of gusset plates. In this study, the authors focus on one of the failure mode of connection part which is called “tension and shear block failure”.
Tension and shear block failure is a fracture mode which occurs in the connection of tension steel members. A typical fracture mode of tension and shear block failure is shown in Fig. 1. And as illustrated in Fig. 1, the failure mechanism is a combination of tensile failure on one plane and shear failure on the perpendicular planes.
Early studies on tension and block shear failure started in Canada in the 1980s (Agarwal and Shan, 2009; Orbison et al., 1999; Huns et al., 2002; Yam et al., 2007). Main targets of the studies have been bolted or riveted ends of tension members or coped beam connections of architectural structures. And now, the design strength equations for tension and block shear failure are developed in many famous steel structure standards in the advanced countries. However, the design strength equations in respective codes are slightly different for each other, and each equation provides inconsistent level of safety over a wide variety of connection types (Driver et al., 2006).
382 Hideyuki Kasano et al. / International Journal of Steel Structures, 12(3), 381-389, 2012
Figure 1. Mechanism of tension and shear block failure.
In this paper, the authors begin with overviewing the strength equations for tension and block shear failure in respective codes, Then, applicability of the strength equations for tension and block shear failure to gusset plates of steel truss bridges is examined by FEM analysis. Furthermore, the authors newly propose strength equations for “compression” and shear block failure, which is applied to gusset plates subjected to compressive force. And FEM analysis reveals mechanical behavior of gusset plates subjected to compressive force. Then the applicability of the proposed equations is examined.
The failure modes of gusset plates are various, however, this study focuses on the tension or compression and shear block failure mode.
Figure 2. Failure sections.
Eventually, maximum strength for tension and shear block is reached when the failure on one section occurs in conjunction with the yielding of the other section. This is confirmed by the past experimental data.
2.2. Strength equations in various codes
Here, strength equations for tension and shear block in some of the world famous codes are introduced for comparison.
2. Strength E
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有关钢桁架桥节点板的破坏模式和剪切块失效研究
摘要
拉伸和剪切块破坏是一种在拉力型钢构件连接中发生的极限状态。破坏机制是一个平面上的拉伸破坏和垂直平面上的剪切破坏的组合。在已知的设计规范中有关于张力和剪切破坏描述的设计强度方程式。然而，当它们被用于不同类型的连接时，它们提供的安全性不一致。在本文中，作者从各个方面调查设计强度方程式。然后，选择钢桁架桥节点板的相关强度方程式。此外，作者提出了一种关于节点板受压的抗压强度方程。并探讨了方程的适用性，探讨压缩节点板的力学性能，对节点板厚度不同参数进行了分析。桥的部分失效可能不会导致进一步损坏甚至导致整个桥的倒塌。不同的区别来自于桥梁的冗余，这一问题在最近几年吸引了许多研究人员和工程师们。本文对钢桁梁桥的后件失效分析方法进行了研究。对于冗余的调查，简单的分析是首选，因为通常有一定数量分析要求。然而，目前的研究表明，静态分析产生相当不同的结果，由于动态分析。然后提出了一种故障分析方法。实例问题证实了所提出的方法的有效性，而它需要计算时间，只有尽可能多的静态分析。
关键词：张力和剪切块失效，强度方程、有限元分析、节点板、钢桁架桥
1、简介
与其他类型的桥梁相比，一般桁架桥的冗余度较少.其原因是，它们的结构是基于静态确定的三角形构件。比如2007年美国明尼阿波利斯的I-35W钢桁架桥由于节点板设计厚度不足坍塌。一般来说，节点板设计的安全系数很高，足够安全，所以他们也不太可能发生破坏。因此，无论是在美国还是在日本，节点板的详细验证不付诸实践。然而，事实上，I-35W钢桁梁桥的倒塌是由不足的节点板故障引起的，这表明节点板连接的桁架构件的失效是更可能导致整座桥的崩塌而不仅仅是一杆失效。因此，极限情况下节点板的力学分析是十分有意义的，并将此结果作为节点板设计。在这项研究中，作者专注于一个连接部分的故障模式被称为“张力和剪切块故障”。 2007，在美国，明尼苏达I-35W桁架桥，完全崩溃了，司机都死了。一个节点板断裂导致整个结构的崩溃。在同一年，在日本的一个桁架桥由于腐蚀作用，被发现有一个被切断的成员。幸运的是这座桥完全倒塌了。在2010，日本的混凝土桥由于冲刷作用失去了一个桥墩，但仍没有倒塌。
这些经历意味着调查当结构一部分构件失效时，结构整体的表现的重要性。尤其重要的是要调查关键构件部分的断裂（FCM），其故障会导致桥梁的进一步损害。尽管如此，这并不是一个明朗的工作，后期的失效分析，也可以被称为冗余分析，吸引了众多研究人员。
构件破坏会导致桁架桥的动力特性，并且在动力特性上的位移能超过静力性能。因此，动态分析将是桁架桥构件故障后的相关评估分析。然而，动态分析，需要大量的计算时间，并且冗余的调查通常需要大量的分析，分析每一个损坏的构件，并且每一个构件都不能被单独挑出来的，应当整体考虑。因此，一个简单的后失效分析方法将是首选的实际冗余分析。这就是静态分析通常用来预测后构件的破坏行为的原因2008）。
在本问研究内容中中，静态分析是为了从冗余的角度调查研究钢桁架桥的失效构件的情况。本研究的主要目的是调查钢桁架桥失效后的研究方法，而不是一个特定的桁架桥的冗余。为此，还进行了动态分析，并通过比较两组数值结果，讨论了静态分析的有效性。
张力和剪切块破坏是一种发生在张钢构件连接的断裂模式。一种典型的拉伸和剪切破坏模式的断裂模式如图1所示。如图1所示，这种破坏机构是一种拉伸破坏和垂直平面上的剪切破坏的组合。
早期的研究对拉剪破坏在加拿大开始于上世纪80年代（Agarwal和山，2009；奥比森et al.，1999；匈奴et al.，2002；山药et al.，2007）。本研究的主要目标是螺栓或铆接两端张力成员或应对建筑结构梁的连接。目前，在先进国家的许多著名的钢结构中，设计了拉剪破坏的设计强度方程。然而，设计强度方程在各自的代码是稍微不同的彼此，和每个方程提供了不一致的安全性，在各种各样的连接类型（驱动程序等，2006）。
图 1. 拉剪破坏机理。
图 2. 故障区段
在本文中，作者首先研究强度公式的张力和剪切块在各自的模式，然后，做有关于适用性的强度公式的张力和块剪切破坏的钢桁架桥梁节点板的有限元分析研究。此外，作者新提出的强度公式的“压缩”和剪切块失效，这是适用于节点板的受力。与有限元分析揭示板受力的力学行为。然后检查所提出的方程的适用性。
然而，节点板的失效模式是多种多样的，，本文的研究重点是拉伸或压缩和剪切块的失效模式。
2、强度方程
2.1、理论强度方程
从理论上讲，拉伸强度和剪切块失效方程如下
|
1 |
|
|
Rb1 = fyAgt ------fuAnv |
(1) |
|
3 |
|
|
or |
|
|
1 |
|
|
Rb2 = fuAnt ------fyAgv |
(2) |
|
3 |
FY是钢的屈服应力，fu是拉伸钢的强度，ant是净截面面积张力，AGT是毛截面面积进拉伸，ANV是的净截面受剪，和AGV是总截面积。
2.2。各种规范中的强度方程
在这里，与一些世界著名的模式的拉伸和剪切块的强度方程进行了比较。
|
R =fuAnt 0.6fyAgv le; fuAnt 0.6fuAnv |
(3) |
Eurocode 3 (ENV1993-1-1, 1992)
|
(3) CSA-S1 (Canadian Standards Association, 2001) |
|
|
R = fuAnt 0.6fuAnv |
(5) |
|
R = fuAnt 0.6fyAgv |
(6) |
3、钢桁架桥节点板的适用性
3.1。分析方法和条件
为了有针对性的强度方程，节点板在钢桁梁桥的有限元分析进行选择，采用图3所示的模型。这个有限元模型是建立在一个通用的基础上，通过桁架桥面板的点如图4所示。节点板和低线的侧壁是连续的。
在建模过程中，节点板，较低的线，和对角线与4节点壳单元建立，和铆钉采用线性弹簧单元模拟。加载点和边界点的创建具有非常硬的光束元素。的平移位移和旋转的边界点被限制。材料和物理性能，弹簧常数分别列于表2、表3和表1。模型所用的钢的应力-塑性应变关系如图5所示。
模拟拉在扣板指出图3的剪切破坏，拉伸力施加在斜拉结束。首先，负荷逐渐增大（100千牛每一步）。由于荷载位移曲线的峰值不能从分析模拟的节点板拉伸行为得到的极限荷载为负载
图3 图4
Table 1. Material properties
|
Steel |
Youngrsquo;s |
Poissonrsquo;s |
Yield |
|
Modulus |
Ratio |
Stress |
|
|
SS400 |
210000 |
0.3 |
235 |
|
(N/mm2) |
(N/mm2) |
||
|
Table 2. Thickness of members |
|||
|
Thickness (mm) |
|||
|
Gusset plate |
9 |
||
|
web (mm) |
flanges (mm) |
||
|
Diagonal (tension) |
20 |
20 |
|
|
Diagonal (compression) |
9 |
9 |
|
|
Lower cords |
9 |
15 |
|
|
Table 3. Spring constant |
|||
|
Axial |
Shear |
Rotetion |
|
|
Spring |
4.43times;106 |
1.71times;106 |
1.34times;108 |
|
constant |
(N/mm) |
(N/mm) |
(N/mm/rad) |
图5
在塑性模型的建模中，采用米塞斯屈服准则、关联流动法则和各向同性硬化规律。然而，不考虑有效应变效应。在本文的分析中，有限元软件，使用戴安娜版本。
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