Experimental Study On Seismic Performance Of RC Frame Beams Corroded By General Atmospheric Acid Rain

Acid rain has become a vital factor in causing structural performance degradation of reinforced concrete structure since China became the third acid rain affected area.It can penetrate inside the structures,which would lead to the surface of concrete shedding,interior steel bars rusting and mechanics properties deteriorating finally.However,the state of research is primarily focused on the damage mechanics and the law of concrete performance degradation since the investigation was almost empty in the domain of seismic performance deterioration.Consequently,it is of the paramount importance to estimate seismic behavior degradation of caustic RC frame beams in the acid rain environment,which can provide the theory evidence for whole-life seismic research of RC frame structures.The main research contents and results are as follows:(1)9 RC frame beams with shear span ratio of 2.5 were designed in order to study the seismic behavior of RC frame beams corroded by acid rain.Then quasi-static tests were carried out to obtain the hysteric curves,skeleton curves,strength attenuation and stiffness degradation of RC frame beams after they were corroded by simulated acid rain environment.(2)The influence of acid rain erosion on the seismic behaviors of RC frame beams was analyzed.With the increase of the acid rain erosion cycles,the degree of acid rain erosion aggravated gradually,the acidification depth of concrete increased gradually as well.The reinforcement in the concrete was still not corroded when the acidification depth was smaller than the thickness of concrete protective cover.On the contrary,the bars began to rust when acid rain permeated throughout concrete cover and came closely to reinforcement.Then some seismic parameters,such as the bearing capacity,stiffness and energy dissipation,declined gradually along with the increase of reinforcement rust ratio.In addition,the effect of the stirrup ratio on the seismic performance of RC frame beams was also studied.(3)The restoring force model of RC frame beams was established under acid rain erosion environment.The skeleton curve formula of corroded RC frame beams was obtained via regression analysis of experimental results with trilinear skeleton curve with negative stiffness.According to the hysteretic energy cycle degradation index and the hysteretic rules,restoring force model of RC frame beams corroded by acid rain was established with the consideration of the pinch effect,hardening strength and stiffness deterioration,softening strength and stiffness degradation,unloading stiffness degradation and reloading stiffness degradation.(4)Restoring force model of frame beams corroded by acid rain was established based on OPENSEES.The cantilever beam is simplified as two parts of elastic element and plastic hinge at the end.And the plastic hinge adopts the uniaxial material model with "Modified Ibarra-Medina-Krawinkler deterioration Model with pinched hysteretic response rules(Mod IMKPinching Material)".Besides,it shows that the finite element numerical modeling method of RC frame beams has a certain range of applicability through the comparison of experiment and numerical simulation results.