ﺑﺮرﺳﯽ ﻋﺪدي رﻓﺘﺎر اﺗﺼﺎل ﻧﺒﺸﯽ ﺑﺎﻻ و ﭘﺎﯾﯿﻦ ﭘﯿﭽﯽ و ﺟﻮﺷﯽ در ﺧﺮاﺑﯽ ﭘﯿﺸﺮوﻧﺪهي ﺳﺎزهﻫﺎي ﻓﻮﻻدي

Numerical Investigation of the Behaviour of Bolted and Welded Top and Seat Angle Connection in Progressive Collapse of Steel Structures

ﭘﺲ از ﺧﺮاﺑﯽ ﯾﮏ ﺳﺘﻮن در ﺳﺎزه ﺑﺪﻟﯿﻞ ﺑﺎرﻫﺎي ﻏﯿﺮ ﻋﺎدي، ﻋﻤﻠﮑﺮد ﻧﺎﻣﻄﻠﻮب و ﺧﺮاﺑﯽ در اﺗﺼﺎﻻت ﺗﯿﺮﻫﺎي ﻣﺘﺼﻞ ﺑﻪ ﺑﺎﻻي اﯾﻦ ﺳﺘﻮن، ﻣﯽﺗﻮاﻧﺪ ﺑﺎﻋﺚ ﺧﺮاﺑﯽ ﻣﻮﺿﻌﯽ ﺳﻘﻒ و ﻣﺘﻌﺎﻗﺒﺎ ﺑﺮوز ﺧﺮاﺑﯽ ﭘﯿﺸﺮوﻧﺪه در ﺳﺎزه ﮔﺮدد .ﺑﻬﺘﺮﯾﻦ اﯾﺪه ﺑﺮاي ﻣﻘﺎومﺳﺎزي ﺳﺎزه در ﺑﺮاﺑﺮ اﯾﻦ ﭘﺪﯾﺪه ﻣﻘﺎوم ﮐﺮدن اﺗﺼﺎﻻت ﻣﯽﺑﺎﺷﺪ. ﻣﻘﺎوﻣﺖ و اﻧﻌﻄﺎفﭘﺬﯾﺮي اﺗﺼﺎﻻت در دورانﻫﺎي زﯾﺎد ﻣﻮﺟﺐ ﮔﺴﺘﺮش ﻧﯿﺮوﻫﺎي ﻣﺤﻮري در ﺗﯿﺮ و ﺗﺸﮑﯿﻞ ﻋﻤﻠﮑﺮد زﻧﺠﯿﺮي ﻣﯽﺷﻮد. اﯾﻦ ﻋﻤﻠﮑﺮد ﻣﯽ ﺗﻮاﻧﺪ ﺗﺎ ﺣﺪود زﯾﺎدي ﻣﺎﻧﻊ ﺧﺮاﺑﯽ ﺳﺎزه در اﺛﺮ ﺣﺬف ﺳﺘﻮن ﮔﺮدد. در اﯾﻦ ﻣﻘﺎﻟﻪ ﻋﻤﻠﮑﺮد اﺗﺼﺎل ﻣﺘﺪاول ﻧﺒﺸﯽ ﺑﺎﻻ و ﭘﺎﯾﯿﻦ ﭘﯿﭽﯽ و ﺟﻮﺷﯽ ﻓﻮﻻدي ﺑﻪ ﺻﻮرت ﻋﺪدي ﺑﺮرﺳﯽ ﺷﺪه اﺳﺖ. ﮐﻠﯿﻪ اﺟﺰاي اﺗﺼﺎﻻت در ﻧﺮم اﻓﺰار اﺟﺰاي ﻣﺤﺪود ﻣﺪل ﺷﺪه اﺳﺖ. ﺳﺎزه ﻣﺪل ﺷﺪه ﺗﺤﺖ ﺟﺎﺑﺠﺎﺋﯽ ﻗﺎﺋﻢ در ﻣﺤﻞ ﺳﺘﻮن ﺣﺬف ﺷﺪه، ﻣﻮرد ﺗﺤﻠﯿﻞ ﻏﯿﺮﺧﻄﯽ ﻗﺮار ﮔﺮﻓﺘﻪ اﺳﺖ و ﻧﺘﺎﯾﺞ آن ﺑﺎ ﻧﺘﺎﯾﺞ آزﻣﺎﯾﺸﮕﺎﻫﯽ ﺻﺤﺖ ﺳﻨﺠﯽ ﺷﺪه اﺳﺖ. ﻫﻤﭽﻨﯿﻦ، رﻓﺘﺎر، ﻣﻮدﻫﺎي ﺷﮑﺴﺖ، ﻧﺤﻮه ﺗﻮﺳﻌﻪ ﻋﻤﻠﮑﺮد زﻧﺠﯿﺮي و اﺛﺮ ﭘﺎراﻣﺘﺮﻫﺎي ﻣﺨﺘﻠﻒ ﺑﺮ رﻓﺘﺎر اﺗﺼﺎل ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﻗﺮار ﮔﺮﻓﺘﻪ اﺳﺖ. ﻧﺘﺎﯾﺞ ﺣﺎﮐﯽ از آن اﺳﺖ ﮐﻪ اﺗﺼﺎل ﻫﺎي ﭘﯿﭽﯽ از ﻋﻤﻠﮑﺮد ﺑﻬﺘﺮي ﻧﺴﺒﺖ ﺑﻪ اﺗﺼﺎل ﻫﺎي ﺟﻮﺷﯽ ﺑﺮﺧﻮردار ﻣﯽ ﺑﺎﺷﻨﺪ. ﻫﻤﭽﻨﯿﻦ در اﺗﺼﺎﻻت ﺟﻮﺷﯽ ﺑﺎ اﻓﺰاﯾﺶ ﺿﺨﺎﻣﺖ ﻧﺒﺸﯽ ﻫﺎ و اﻓﺰاﯾﺶ ﻃﻮل ﺑﺎل ﻧﺒﺸﯽ در ﻣﺤﻞ اﺗﺼﺎل ﺑﻪ ﺳﺘﻮن، ﻋﻤﻠﮑﺮد زﻧﺠﯿﺮي و ﻣﻘﺎوﻣﺖ اﺗﺼﺎل در ﻣﻘﺎﺑﻞ ﺧﺮاﺑﯽ ﭘﯿﺸﺮوﻧﺪه ﺑﻬﺒﻮد ﻣﯽﯾﺎﺑﺪ، اﻣﺎ اﺿﺎﻓﻪ ﮐﺮدن ورق ﺳﺨﺖ ﮐﻨﻨﺪه در وﺳﻂ ﻧﺒﺸﯽ ﻧﺸﯿﻤﻦ در ﺗﻤﺎم ﺣﺎﻻت ﺑﺎﻋﺚ اﻓﺰاﯾﺶ ﻇﺮﻓﯿﺖ اﺗﺼﺎل ﻧﻤﯽ ﮔﺮدد.

After failure of a column in structure by an abnormal loading, undesirable performance and damage of connections of the beams connected to the top of this column, can lead to the local failure of floor and in turn result in progressive collapse in the structure. Accordingly, the best method for rehabilitation of the structure against this incident is the strengthening of the connections. The strength and flexibility of the connections during the large rotations result in spreading the axial forces in beams and forming the catenary action. This action can greatly prevent structural failure due to the column removal. In this paper, the performance of prevalent bolted and welded top and seat angle steel connections is evaluated numerically. All parts of the connections are modeled in finite element software. The modeled structure is analyzed nonlinearly under the vertical displacement in the location of removed column, and its results have been verified with experimental results. In addition, the behavior, failure modes, how the catenary action develops and the effects of different parameters on connection behavior are investigated. The results indicated that bolted connections have better performance than welded connections. Also, in welded connections, increasing the thickness of the angles and increasing the length of the connected angle leg to column, improve the catenary action and the resistance of the connections against progressive collapse. But adding the stiffener plate in the middle of the seat angle does not increase the connection capacity in all cases.