| Composite sheathing protection is a common fire protection measure for steel members,whose surface in the steel members by covering fire protection board and insulation wool to achieve the fire protection effect,which has many advantages,such as thermal insulation performance,durability and easy maintenance.It has been widely used in residential and office steel structure buildings.At the same time,in order to ensure that the steel structure building satisfies the fire safety requirements,it is necessary to carry out regular fire performance inspection of steel members.However,the current research on fire performance design for steel members with composite sheathing protection is still very limited and there is a lack of fire inspection methods for steel members with composite sheathing protection.In view of this,this thesis carried out experiments and theoretical research on steel columns,involving full-scale load-bearing experiments of square steel tube columns with composite sheathing protection under fire conditions,composite sheathing protective H-shaped steel columns & square steel tube columns fire performance simplified design method,small-scale test method for full-scale load-bearing experiment of square steel tube columns with composite sheathing protection,etc,and proposed a fire performance inspection method of steel columns with composite sheathing protection.The main contents and conclusions are as follows:1.Full-scale load-bearing experimental investigation of square steel tube columns with composite sheathing protection under fire conditionsThe composite protection form of "gypsum board + aluminum silicate wool" was adopted,and the full-scale load-bearing fire resistance experiment of 6 cold-formed square steel tube columns was carried out.The height of the specimens is 3500 mm.The ISO 834 curve was used for the fire environment of the fire resistance experiment,and the load ratio of the fire resistance experiment specimens is 0.6.The results showed that :(1)6 mm wall thickness steel columns specimens showed full-section buckling,and 12 mm wall thickness steel columns specimens showed overall bending;(2)The temperature rise of steel columns can be divided into 110℃ as the boundary of the early steel columns slow heating period and the late steel columns fast heating period.In the steel columns fast heating period,the average temperature rise rates of 6and 12 mm wall thickness steel columns specimens were between 5℃/min～6.5℃/min and 3.5℃/min～4℃/min respectively;the steel columns slow heating period will be extended by 20-35 min or 30 min-50 min for each add of 12 mm gypsum board or 30 mm aluminum silicate wool;(3)By changing the thickness of gypsum board and aluminum silicate wool,a cold-formed square steel tube columns with composite sheathing protection configuration was proposed to meet the requirements of the first fire performance class(corresponding to the fire performance limit of three hours)under 0.6 load ratio,corresponding to specimen Z6 and specimen Z8 of this thesis,which also has good integrity after fire and no obvious "thermal bridge" effect.2.Composite sheathing protective H-shaped steel columns & square steel tube columns fire performance simplified design methodTo carry out theoretical and FE on the fire performance of H-shaped steel columns & square steel tube columns with composite sheathing protection subjected to four-sided fire exposure:(1)The simplified method of equivalent one-dimensional heat transfer of the H-shaped steel columns and square steel tube columns with composite sheathing protection subjected to four-sided fire exposure was established respectively.The simplified method was proved to be applicable for finite element modeling(FEM),before having the complex two-dimensional heat transmission problem transformed into the equivalent one-dimensional counterpart;(2)Based on the simplified method of equivalent one-dimensional heat transfer,the simplified theoretical model of equivalent one-dimensional heat transfer for H-shaped steel columns and square steel tube columns with composite sheathing protection was proposed,and the control equations of the simplified theoretical model were derived,compared with the experimental and finite element extension results,the average error of temperature rise of steel columns for H-shaped and square steel tube columns is2.99% and 6.03% respectively,and the calculation efficiency is improved by 63.7times and 35.7 times,respectively;(3)Combined with the critical temperature method,a simplified design method for fire performance of H-shaped steel columns & square steel tube columns with composite sheathing protection was proposed.Compared with the results of more than 20 experiment and finite element expansion example,the average error of fire performance limit of square steel tube columns simplified design method is 4.46%.3.Small-scale test method for full-scale load-bearing experiment of square steel tube columns with composite sheathing protectionTo carry out small-scale test method and supporting device for full-scale load-bearing experiment of square steel tube columns with composite sheathing protection:(1)Based on the simplified method of equivalent one-dimensional heat transfer of the square steel tube columns with composite sheathing protection,a small-scale equivalent heat transfer entity experiments were proposed instead of the full-scale model of the composite sheathing protection square steel tube columns;(2)According to the characteristics of the equivalent heat transfer entity experimental of square steel tube columns,a set of small-scale standardized test furnace system was developed,the test results show that the test furnace system has the ISO 834 standard fire heating capacity;(3)Compared with the full-scale fire performance experiment results of square steel tube columns,the maximum positive error of the fire performance limit of the small-scale alternative experiment is 8%,and the maximum negative error is-18.5%,the average temperature difference of all tests is 36.7℃ and the average error is 8.4%.4.Fire performance inspection method of steel columns with composite sheathing protectionOn-site rapid inspection method and laboratory re-inspection method for fire performance of composite sheathing protective steel columns:(1)Based on the simplified design method of fire performance of composite sheathing protective steel columns in this thesis,the on-site rapid inspection method for fire performance of composite sheathing protective steel columns was proposed,and the corresponding inspection instruments were given;(2)Based on the small-scale test method and supporting device of full-scale load-bearing fire performance experiment of steel columns in this thesis,a laboratory re-examination method for the fire performance of steel columns with composite sheathing protection was proposed.The innovation points of this thesis are as follows:Focus on composite sheathing protection,a new configuration of square steel tube columns with convenient construction and high fire resistance is proposed.A simplified theoretical model of equivalent one-dimensional transient heat transfer of H-shaped steel columns & square steel tube columns under fire is proposed.A small-scale test method instead of full-scale load-bearing experiment of square steel tube columns is developed,and a rapid on-site inspection and laboratory re-inspection method for fire performance of steel columns is formed. |
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