Study On The Mechanical Properties Of Carbonized Reinforced Concrete Beams

In the field of civil engineering,reinforced concrete structures,were used widely,have always been as an important structural system.Although the concrete material were titled having fire-resistant ability,the fire resistance of reinforced concrete beams have still been studied and have achieved fruitful results.However,most of them are still limited to focus on fresh concrete specimens with high moisture content and high porosity.There are still insufficient studies on mechanical properties of reinforced concrete beams in fire considering carbonation.In actual engineering,honestly,the reinforced concrete structures are in the state of long-term service,suffering the effects of carbonation.Therefore,in view of the shortcomings of the current research,this paper will mainly studied the mechanical properties of reinforced concrete beams under multi-factor coupling,and fulfilled the following work:(1)Fire experiments were carried out on the completely carbonized reinforced concrete beams to study the failure modes,temperature field,strain field and displacement in fire.The results showed that the completely carbonized beams experienced brittle failure in fire,and developed the cracks along the increased strain on the concrete surface,which was accompanied by a large change of temperature and displacement.(2)In order to study the factors affecting the fire mechanical properties of reinforced concrete beams,a group of non-carbonized reinforced concrete beams were made and pore pressure measuring rods were designed.The characteristic values of temperature,strain,displacement and pore water pressure are measured.After sorting out the measurement results,it is found that the non-carbonated reinforced concrete beams spalled in fire,and the concrete moisture content had a more serious effect on the high temperature concrete spalling.The pore water pressure of reinforced concrete beams was undulating and staggered at different depths.(3)Reinforced concrete beams with different carbonization;duration were prepared to study the effect of carbonization on the mechanical properties of reinforced concrete beams in fire.The fire tests were carried out on the reinforced concrete beams after carbonized 7 days and 14 days,and data samples such as temperature,strain,displacement and pore pressure were collected for comparative analysis.The results showed that the carbonation makes the concrete surface to form a dense carbonized layer and accompanied by a large number of free water,which enhances the compressive strength of the concrete.This lead to a temperature descend and displacement increment of specimens in fire,a more prominent rule of strain mutation,and a sudden drop in pore water pressure near the surface of the carbonized layer after the peak value.(4)By using ABAQUS finite element analysis software,the numerical simulation analysis of reinforced concrete beams under the coupling action of carbonization,high temperature and loads were conduct.The results showed that with the increase of carbonization depth,the strain on the surface of reinforced concrete beams decreased but the flexural deformation became larger.And the displacement of carbonized reinforced concrete beams increased with the increase of load ratio that had little effect on strain.The above research results of this paper have a certain reference value for the mechanical properties of reinforced concrete beams with different degrees of carbonization in fire,and it is of great significance to improve the fire resistance of reinforced concrete beams under normal service conditions.