Comparison of End Plate Connection Design Between AISC DG4 and GB Codes
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摘要: 端板节点是一种钢结构多层建筑中常用的节点,在美国应用较为普遍,在我国应用不多。针对此现象,将国标和美标规范进行了对比。通过对比发现,美国标准对端板节点的研究很完善,AISC DG4和DG16都是对端板节点的设计指导,DG4设计流程适用于风和地震作用下的端板外伸式梁柱节点(即刚接节点),梁柱节点域的计算参见DG13;DG16适用于非地震或风作用时的平端板和外伸端板计算(即半刚接节点)。相比之下,国标规范对端板节点的核算就较为简单,在JGJ 82—2011《钢结构高强度螺栓连接技术规程》(简称《螺栓规程》)和GB 51022—2015《门式刚架轻型房屋钢结构技术规范》(简称《门刚规范》)中均涉及到了端板节点的计算,但《螺栓规程》中未给出板厚计算方法,仅按构造要求板厚不小于16 mm且不小于螺栓直径;而《门刚规范》未给出螺栓计算方法,仅给出了板厚的计算。可见:两个规范对此类节点的计算都不够完整。
为了论证国标规范对螺栓及端板厚度的选取是否合理,也为了判断按照国标规范设计端板节点是否可以作为刚接节点,选取AISC DG4与国标规范进行对比,从基础理论开始,简单论述了美国对于端板节点的研究历史以及美标DG4 的计算原理、计算假定,然后以实例的形式按照DG4的设计流程对该实例进行了详细的解答,并与《螺栓规程》《门刚规范》的计算结果对比,分析两国规范的计算原理和结果的不同之处。
通过对比发现,两国规范对受拉翼缘受力的计算原理相同,受拉翼缘所承受的拉力由受拉区螺栓承担,对受拉区螺栓的受力计算,两国规范有所差异,但差异不大,不至于影响螺栓规格选取;只是对端板厚度的计算方法差异较大,美标采用屈服线理论,利用了板的塑性抗弯强度,国标规范仍在板的弹性范围内计算,国标计算方法偏于保守。
DG4中附录B是端板节点的初步设计表格,通过分析表格内的数据,发现绝大多数情况下,螺栓直径大于端板厚度,尤其是采用50 ksi强度(即345 MPa)板材时,板厚全部小于螺栓直径。国标规范中虽然没有给出一个明确的端板计算标准流程,但是通过构造措施,比如端板厚度不小于螺栓直径,柱翼缘厚度不小于端板厚度,端板外伸部位设置加劲等措施,也可以达到端板的承载力不小于螺栓承载力的要求,满足厚板的条件。
通过以上研究对比,美标DG4理论较为清晰,且有实际工程和试验数据支撑,在有抗震要求的情况下,当需要计算端板节点时,若工程师判定国标规范的理论不适用,可按照美标进行计算。如果是非抗震设计,国标中的构造措施已经足够安全。Abstract: End plate connection is commonly used in multi-story buildings, which is widely used in American Standard Design, but rarely in Chinese Standard Design. In response to that, the comparison between American and Chinese standard design is conducted, through which it's found that the American Standard has been deeply investigated, such as AISC DG4, DG16. The DG4 design procedure suits to extended end plates yielding to wind and seismic design (rigid joint). For the beam-column joint of extended end plate, refer to DG13. DG16 suits to flush end plate and extended end plates yielding to non-seismic or wind design (semi-rigid joint). In contrast, associated calculation procedure per Chinese Standard is quite preliminary. Both JGJ 82-2011 Technical Specification for High Strength Bolt Connections of Steel Structures ("Bolt Regulations" hereinafter) and GB 51022-2015 Technical Code for Steel Structure of Light-weight Building with Gabled Frames ("Gabled Frames Specifications" hereinafter) provide clauses dealing with end plate connection design, but the plate thickness calculation method is not given in the Bolt Regulations, only with a mandatory term of plate thickness no less than 16mm nor less than the bolt diameter being identified. Meanwhile, calculation method of bolt arrays is not given in Gabled Frames Specifications, but only providing the end plate thickness calculation. Neither of these standards integrates the end plate connection design procedure.
In order to rationalize the bolt and end plate design of the connection, also to valid the end plate connection as rigid joint in Chinese Standard Design, the article presents what distinctively different between AISC DG4 and GB/JGJ since the researching history, calculation theory, assumptions, case studies and analysis.
The connection tension member design concurs between AISC DG4 and GB/JGJ, the bolt sizing procedures are basically the same, but the calculation of the end plate thickness varies drastically in between, Yield Line Theory was adopted by American Standard considering the controllable plastic development, in contrary, the Chinese Standard proceeds extremely conservatively, all the calculations are limited within the elastic theory.
Looking into Appendix B of AISC DG4, the end plate thickness is less than the bolt diameter in majority of the cases, especially for end plate of 50 ksi (equals to 345 MPa) and above, this criteria prevails. Even though the Chinese Standard leads a safe end plate connection design via mandatory requirements of end plate thickness no less than bolt diameter, column flange thickness no less than end plate thickness, stiffening of the extended end plate, and so forth, but obviously the AISC DG4 leads to reasonable design, especially for cases yielding to seismic requirements.
By comparing above research, we find that the theory of AISC DG4 is relatively clear, and can be supported by engineering and test data. In seismic design, if the engineers determine that the theory of GB code is not applicable, they can design according to AISC DG4. In non-seismic condition, the construction measures required in GB code are safe enough.-
Key words:
- yield line theory /
- seismic /
- extended end plate connection /
- plastic hinge
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[1] AISC. Extended end-plate moment connections seismic and wind applications:DG4[S]. 2nd ed. Chicago:American Institute of Steel Construction, 2004. [2] 但泽义,柴昶,李国强,等.钢结构设计手册[M]. 4版. 北京:中国建筑工业出版社,2019. [3] AISC. Flush and extended multiple-row moment end-plate connections:DG16[S]. Chicago:American Institute of Steel Construction, 2003. [4] AISC. Seismic provisions for structural steel buildings:AISC 341-16[S]. Chicago:American Institute of Steel Construction, 2016. [5] AISC. Specification for structural steel buildings:AISC 360-16[S]. Chicago:American Institute of Steel Construction, 2016. [6] AISC. Stiffening of wide-flange columns at moment connections-wind and seismic applications:DG13[S]. Chicago:American Institute of Steel Construction, 2003.
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