The Influence of Reinforcement Ratio to the Mechanical Behavior of Reinforced Concrete Column

Abstract

Steel and concrete were the most important building materials, reinforced concrete was widely used in building structures. For the study of the influence of steel bar content in reinforced concrete columns, three specimens were designed for pseudo static test. The test shows that: the stirrup ratio does not significantly affect the bearing capacity and stiffness degradation of column, but when the stirrup ratio is too low will reduce the ductility and energy dissipation capacity of column. To improve the ratio of longitudinal reinforcement can significantly improve the bearing capacity of the column, but will decrease the energy dissipation and ductility, stiffness degradation becomes more serious. Introduction In building structure, reinforced concrete structure was a form of the most widely used, steel and concrete could work together was determined by the material properties of its own. First of all, steel and concrete had approximately the same linear expansion coefficient, and will not produce excessive stress due to different environment. Secondly, there was good adhesion between steel and concrete, reinforced rib could improve the mechanical engagement between concrete and steel. The stirrup was used to meet the shear strength of the inclined section, and connected reinforcement and compressive region concrete. Therefore, reinforcement ratio had an important effect on mechanical properties of the mechanical behavior of reinforced concrete column. Specimen Design and Test Methods Specimen Design. Three reinforced concrete frame column specimens were designed. The stirrup ratio was different between Z1 and Z2, while the stirrup ratio was different between Z1 and Z3.The specific parameters were shown in tab.1. Tab.1 The design parameters of reinforced concrete frame column No. axial compression ratio stirrup ratio the ratio of longitudinal reinforcement shear span ratio Z1 0.9 Ф 8@85/150 (4) (1.8%) 12Ф 14 (2.05%) 2.92 Z2 0.9 Ф 6@150 (2) (0.29%) 12Ф 14 (2.05%) 2.92 Z3 0.9 Ф 8@85/150 (4) (1.8%) 12Ф 20 (4.19%) 2.92 Material Characteristic Test and Results. Steel tensile strength was tested by five 6, two 8, four 14, two 22, the average results were shown in Tab.2. The grade of concrete strength was C30, three concrete test cube by 150mm×150mm×150mm in one-time-concreting were taken through axial compressive strength test, the results were shown in Tab.3. International Conference on Material Science and Application (ICMSA 2015) © 2015. The authors Published by Atlantis Press 571 Pseudo-static Test. The test method was the quasi-static test [1] , by applying multiple reciprocating cyclic loading on the component, the structure repeated the process of loading and unloading in the pros and cons direction, to simulate the deformation characteristics and force characteristics of the structure in reciprocating vibration during earthquake. The purpose was to establish the restoring force characteristics of structure under earthquake, and determine the calculation model of restoring force of structural members, which could judge the seismic performance of structure in the strength, deformation and energy dissipation. Tab.2 Material characteristic results of steel bar Steel bar Diamete r[mm] Yield strength[MPa] Ultimate strength [MPa] Yield strain Stirrup (HPB235) 6 447 638 0.002235 Stirrup (HPB235) 8 417.5 527.5 0.002088 Longitudinal reinforcement (HRB335) 14 493.8 657.8 0.002469 Longitudinal reinforcement (HRB335) 20 480 597.5 0.0024 Tab.3 Material characteristic results of concrete test cube No. Axial compressive strength [MPa] 1 47.93 2 46.01 3 45.73 Average 46.5 Loading Equipment. The reinforced concrete column end was anchored and horizontal cyclic loading was applied on the top. A vertical concentrated load was applicated on the top of the column, though and upper roller device between the hoisting jack and reaction beam to ensure the top of the column could produce free horizontal displacement[2]. The test equipment was shown in Fig.1. The horizontal load is loaded by the method of deformation control: When the specimen cracked, according to multiple cracking displacement to load step by step, two cycles per level, until the first cycle load of the structure was lower than 85% maximum load , and it was considered that structure had already destroyed. The test loading program was shown in Fig. 2. Fig.1 Test equipment Fig.2 Test loading program Experimental Phenomena. Specimen Z1 was taken as an example to explain the phenomenon in the process of test. When 2Δ, mortar and concrete were peeled on the upper column at the height of 1-1.5 section, vertical cracks appeared, the compression zone of mortar layer appeared obvious signs of crushing. When 5Δ, the crushing of concrete significantly increased, cracking phenomenon