پديد آورندگان :
كماني، فاطمه دانشگاه آزاد اسلامي اراك - گرايش سازه , بختياري، سعيد مركز تحقيقات راه، مسكن و شهرسازي تهران , مزروعي، علي دانشگاه آزاد اسلامي واحد تهران مركز - دانشكده مهندسي - گروه عمران , ميرحسيني، محمد دانشگاه آزاد اسلامي اراك - دانشكده مهندسي - گروه عمران
كليدواژه :
ستون لوله اي فولادي پرشده با بتن (CFST) , ظرفيت باقي مانده , پس از آتش , پيش بيني , و خروج از مركزيت
چكيده فارسي :
ﭘﻴﺶﺑﻴﻨﻲ ﻇﺮﻓﻴﺖ ﺑﺎرﺑﺮي ﺑﺎﻗﻲﻣﺎﻧﺪه ﺳﺘﻮنﻫﺎي ﻟﻮﻟﻪاي ﻓﻮﻻدي ﭘﺮﺷﺪه ﺑﺎ ﺑﺘﻦ (CFST) آﺳﻴﺐدﻳﺪه در اﺛﺮ آﺗﺶﺳﻮزي، ﺑﺎ ﺗﻮﺟﻪ ﺑﻪ آﺛﺎر ﺧﺮوج از ﻣﺮﻛﺰﻳﺖ ﺑﺰرگ ﺑﺎر، ازﺟﻤﻠﻪ ﻣﻮﺿﻮﻋﺎﺗﻲ اﺳﺖ ﻛﻪ ﻛﺎرﻫﺎي ﭘﮋوﻫﺸﻲ ﻛﻤﻲ اﻧﺠﺎمﮔﺮﻓﺘﻪ اﺳﺖ. در اﻳﻦ ﭘﮋوﻫﺶ، ﻧﺘﺎﻳﺞ ﻳﻚ ﺳﺮي از آزﻣﺎﻳﺶﻫﺎ ﻇﺮﻓﻴﺖ ﺑﺎﻗﻲﻣﺎﻧﺪه ﭘﺲ از آﺗﺶ، ﺑﺮاي ﺳﺘﻮنﻫﺎي CFST ﺑﺎ ﺳﻄﺢ ﻣﻘﻄﻊ ﻣﺨﺘﻠﻒ داﻳﺮهاي و ﻣﺮﺑﻌﻲ(، ﺗﺤﺖ ﺑﺎرﻣﺤﻮري و ﺑﺎ ﺧﺮوج از ﻣﺮﻛﺰﻳﺖﻫﺎي ﺑﺰرگ ﺗﺎ ﻣﺮﺣﻠﻪ ﺷﻜﺴﺖ، اراﺋﻪﺷﺪه اﺳﺖ. در اﻳﻦ ﺑﺮﻧﺎﻣﻪ آزﻣﺎﻳﺸﮕﺎﻫﻲ ﺗﺄﺛﻴﺮ ﭘﺎراﻣﺘﺮﻫﺎي ازﺟﻤﻠﻪ: ﻧﻮع ﻣﻘﻄﻊ ﻋﺮﺿﻲ، ﻧﺴﺒﺖ ﻻﻏﺮي، ﺧﺮوج از ﻣﺮﻛﺰﻳﺖ ﺑﺎر،ﭘﻮﺷﺶ ﻣﺤﺎﻓﻈﺘﻲ در ﺑﺮاﺑﺮ آﺗﺶ ﺑﺮرﺳﻲ ﻗﺮارﮔﺮﻓﺘﻪ اﺳﺖ. ﺑﺮرﺳﻲﻫﺎ ﻧﺸﺎن ﻣﻲدﻫﺪ ﻛﻪ ﻇﺮﻓﻴﺖ ﺑﺎﻗﻲﻣﺎﻧﺪه ﺑﺎ اﻓﺰاﻳﺶ ﺧﺮوج از ﻣﺮﻛﺰﻳﺖ ﻛﺎﻫﺶ ﻣﻲﻳﺎﺑﺪ در اﻳﻦ ﭘﮋوﻫﺶ، ﺿﺮاﻳﺐ ﻛﺎﻫﺸﻲ ﺑﺮاي ﺑﺮآورد ﻇﺮﻓﻴﺖ ﺑﺎﻗﻲﻣﺎﻧﺪه ﺳﺘﻮنﻫﺎي CFST ﺑﺎ ﺧﺮوج از ﻣﺮﻛﺰﻳﺖ ﺑﺎر، ﺑﺮاﺳﺎس ﻧﺘﺎﻳﺞ آزﻣﺎﻳﺶﻫﺎي ﻗﺒلي ﭘﻴﺸﻨﻬﺎد ﺷﺪه اﺳﺖ. ﺑﺎ اﻓﺰاﻳﺶ دﻣﺎ ﺳﻄﺢ ﻣﻘﻄﻊ ﺳﺘﻮنﻫﺎي CFST ﺑﻪﻃﻮر وﻳﮋه ﺳﺨﺘﻲ ﻣﺤﻮري و ﻇﺮﻓﻴﺖ ﺑﺎرﻣﺤﻮري ﻛﺎﻫﺶ ﻣﻲﻳﺎﺑﺪ. درﻧﻬﺎﻳﺖ، ﺑﺮ اﺳﺎس ﻧﺘﺎﻳﺞ آزﻣﺎﻳﺶﻫﺎي ﺻﻮرت ﮔﺮﻓﺘﻪ، ﻗﺎﺑﻠﻴﺖ روشﻫﺎي ﭘﻴﺶﺑﻴﻨﻲ ﻇﺮﻓﻴﺖ ﺑﺎرﺑﺮي ﺑﺎﻗﻲﻣﺎﻧﺪه ﺳﺘﻮنﻫﺎي ﺗﻮﺧﺎﻟﻲ ﭘﺮﺷﺪه ﺑﺎ ﺑﺘﻦ ﭘﺲ از ﻗﺮار ﮔﺮﻓﺘﻦ در ﻣﻌﺮض آﺗﺶ اﺳﺘﺎﻧﺪارد اﻳﺰو 834، ﺑﺮ اﺳﺎس روشﻫﺎي اﺻﻼحﺷﺪه ﻃﺮاﺣﻲ ﻣﻮﺟﻮد در ﻳﻮرو ﻛﺪ 4 در وﺿﻌﻴﺖ آﺗﺶ و دﻣﺎي ﻣﺤﻴﻂ ارزﻳﺎﺑﻲﺷﺪه اﺳﺖ. ﺑﺮرﺳﻲﻫﺎ ﻧﺸﺎن داد ﻛﻪ روش ﭘﻴﺸﻨﻬﺎدي اﺻﻼحﺷﺪه ﻳﻮرو ﻛﺪ 4، ﺑﺮاي ﭘﻴﺶﺑﻴﻨﻲ ﻣﻘﺎوﻣﺖ ﺑﺎﻗﻲﻣﺎﻧﺪه ﺳﺘﻮنﻫﺎ CFST ﭘﺲ از ﻗﺮار ﮔﺮﻓﺘﻦ در ﻣﻌﺮض آﺗﺶ، ﺗﺤﺖ ﺑﺎرﮔﺬاري ﺑﺎ ﺧﺮوج از ﻣﺮﻛﺰ و ﻣﺮﻛﺰي ﺑﻬﺘﺮﻳﻦ روش ﭘﻴﺶﺑﻴﻨﻲ را اراﺋﻪ ﻣﻲﻧﻤﺎﻳﺪ. ﺑﺮ اﺳﺎس اﻳﻦ روش ﻣﻴﺎﻧﮕﻴﻦ درﺻﺪ ﺧﻄﺎ ﭘﻴﺶﺑﻴﻨﻲ ﻣﻘﺎوﻣﺖ ﺑﺎﻗﻲﻣﺎﻧﺪه ﺳﺘﻮنﻫﺎ CFST ﺑﺮاي ﺑﺎرﮔﺬاري ﺑﻪﺻﻮرت ﺑﺪون ﺧﺮوج از ﻣﺮﻛﺰ و ﺑﺎ ﺧﺮوج از ﻣﺮﻛﺰ ﺑﻪ ﺗﺮﺗﻴﺐ ﺑﻪﻃﻮر ﻣﻴﺎﻧﮕﻴﻦ%5/51 ﻛﻤﺘﺮ از ﺣﺪ ﭘﻴﺶﺑﻴﻨﻲ، ﺑﻪﻃﻮر ﻣﺤﺎﻓﻈﻪﻛﺎراﻧﻪ اﺳﺖ. ﺑﻪ ﻋﺒﺎرﺗﻲ، ﺧﻄﺎي ﻣﻴﺎﻧﮕﻴﻦ روﻳﻜﺮد ﭘﻴﺶﺑﻴﻨﻲ ﺑﻪ ﺗﺮﺗﻴﺐ 0/25 و 0/17 اﻧﺤﺮاف ﻣﻌﻴﺎر، ﭘﺎﻳﻴﻦ ﺗﺮاز ﺧﻂ 1:1 اﺳﺖ.
چكيده لاتين :
Predicting the residual load-bearing capacity of damaged concrete-filled steel tube (CFST) columns exposed to fire, based on the effects of eccentricities, is a subject on which relatively little research has been done. This paper aims to present the results of a series of post-fire residual capacity tests for CFST columns with different cross sections (circular and square), under axial load, and different eccentricities in the event of a failure. In this experimental study, the influence of parameters such as cross-sectional shape, load eccentricity, slenderness and fire protective coating on the post-fire residual capacity of CFST sections was investigated. Based on the results of this study, the following conclusions were obtained in the scope of this research work:The results showed that eccentricity could be effective in reducing the residual capacity of the column, but the change in the amount of eccentricity cannot be as effective as reducing the residual capacity of the columns. The studies indicate that the residual capacity is significantly reduced by increasing the slenderness ratio. Therefore, in order to determine the residual capacity of the CFST columns under load eccentricity, a simplified equation for predicting the reduction factor was proposed, a comparison between the predicted and experimental results shows that there is a reasonably good agreement. The tests show that by increasing the temperature over a cross-section of CFST columns, the residual axial load capacity and the axial stiffness of the unprotected columns decreased significantly compared to the unheated columns. Comparison of the axial compressive capacity of CFST columns with square and circular have shown that for columns having the same concrete material, the circular column has slightly better structural post-fire behavior than the square column. To fire-protected sections, the effect of the cross-sectional shape on the residual strength is significant, relative to the unprotected sections is more. In fact, by comparing the temperature distribution on the surface of the circular and square sections, one can find that the maximum temperature distribution at the circular cross sections is less than the square cross sections. Therefore, with less degradation of the properties of the cross-sectional materials, the more residual load-bearing capacity is expected. Finally, based on the experimental results, the ability to predict the residual load-bearing capacity of the concrete-filled hollow tube columns after exposure to the ISO-834 standard fire as per the modified design method in Eurocode 4 for the fire and ambient conditions were evaluated. The investigation’s results showed that the simplified method of Eurocode 4, in the ambient temperature produced safe results for predicting residual resistance of CFST columns after fire exposure, under both concentric and eccentric loading conditions. This approach was considered as a conservative method, with the MPEs for concentric loads, as well as both concentric and eccentric loads as -5.51% and -3.06% lower than the prediction, respectively.
