Bearing Capacity Of Concrete Columns Research Articles

Machine learning-based shear bearing capacity of concrete columns confined by transverse reinforcement subjected to lateral cyclic loading

Machine learning-based shear bearing capacity of concrete columns confined by transverse reinforcement subjected to lateral cyclic loading

Prediction of Ultimate Capacity of Concrete Columns Reinforced with FRP Bars.

FRP bars are used in concrete structures as an alternative to steel bars as they have many advantages such as high tensile strength, high strength-to-weight ratio, electromagnetic neutrality, lightweight and no corrosion. There is a perceived lack of standard regulations for the design of concrete columns with FRP reinforcement, e.g., in Eurocode 2. This paper describes a procedure for predicting the bearing capacity of concrete columns with FRP reinforcement based on the interaction of axial force and bending moment, which was developed on the basis of existing design recommendations and standards. It was shown that the bearing capacity of eccentrically loaded RC sections depends on two parameters, which are the mechanical reinforcement ratio ω and the location of the reinforcement in the cross-section expressed by the β factor. The analyses carried out showed the existence of a singularity in the n-m interaction curve indicating the fact that in a certain loaded range, the curve is concave, and more it was shown that the balance failure point for sections with FRP reinforcement takes place for eccentric tension. A simple procedure for calculating the required reinforcement from any FRP bars in concrete columns was also proposed. Nomograms developed from n-m interaction curves provide for the accurate and rational design of FRP reinforcement in columns.

STRENGTH MODEL FOR CALCULATING CENTRALLY COMPRESSED CONCRETE ELEMENTS WITH COMPOSITE REINFORCEMENT, TAKING INTO ACCOUNT THE SPACING OF STIRRUPS

The article discusses the relevance of developing techniques for confined elements with FRP reinforcement. The method for calculating centrally confined concrete columns with non-metallic GFRP reinforcement (without regard to its compression work) is proposed for the first time in the Russian Federation. The strength model was developed based on the well-known theoretical model of confined concrete. The article considers the effect of strengthening the concrete core of the columns, which is obtained due to the more frequent placement of both transverse and longitudinal reinforcement. The dependence of the bearing capacity of concrete columns on the strength of the transverse reinforcement material is shown. It was proved that with a decrease in the spacing of the longitudinal reinforcement, the area of ​​the effectively confined concrete core inside the reinforcement cage increases. It was shown that, due to the low compressive modulus of elasticity of the FRP reinforcement, the stress in it will be comparable to the concrete stress. Therefore, the compressive strength of the FRP reinforcement can be neglected in the case of determining the bearing capacity of centrally confined concrete elements. As a result, a strength model for calculating confined concrete elements with FRP reinforcement was proposed, considering the spacing of transverse reinforcement, the longitudinal and transverse reinforcement ratio, and the strength of the material of transverse reinforcement. The developed strength model can be applied not only for square, but also for columns of round and rectangular sections.

ДЕФОРМИРОВАНИЕ ЦЕНТРАЛЬНО СЖАТЫХ ЖЕЛЕЗОБЕТОННЫХ КОЛОНН ИЗ БЕТОНА С ДОБАВЛЕНИЕМ КРУПНОГО ЗАПОЛНИТЕЛЯ ИЗ БЕТОННОГО ЩЕБНЯ

The article presents results of experimental studies of centrally compressed reinforced concrete columns with the addition of concrete rubble as coarse aggregate. Previous studies shows that recycled concrete in the form of crushed concrete rubble obtained from construction waste is an environmentally friendly alternative to traditional coarse aggregate for the manufacture of load-bearing structures. Currently, the scientific literature has a limited amount of information about the calculation methods to be used for the design of reinforced concrete columns with the addition of concrete rubble as coarse aggregate. In this paper, the experimental data on the physicomechanical properties of concrete available in the foreign and domestic literature are summarized. In addition, the deformation features of reinforced concrete columns are highlighted to substantiate the initial premises, hypotheses and possible limitations when developing methods for calculating centrally and eccentrically compressed elements from the specified concrete. Researches are analyzed related to the effect of different content of recycled concrete aggregate in the concrete, the number of longitudinal steel reinforcement in the cross section of the element and its yield strength, pitch and yield strength of transverse reinforcement on the deformability and bearing capacity of concrete columns with the addition of coarse aggregate from concrete rubble. The use of such concrete for the manufacture of centrally and eccentrically compressed concrete columns leads to an insignificant decrease in their bearing capacity. This indicates the possibility of recycling a significant amount of concrete rubble resulting from the processing of reinforced concrete structures destroyed during the demolition of buildings; it allows to attribute this technology to “green building”.

Self-monitoring of smart concrete column incorporating CNT/NCB composite fillers modified cementitious sensors

In this paper, cementitious sensors were fabricated with electrostatic self-assembled carbon nanotubes (CNT)/nano carbon black (NCB) composite fillers, and embedded into concrete columns to develop smart structural components. Self-sensing properties of the sensor/smart column were evaluated under cyclic loading and monotonic loading through measuring the fractional change in resistivity (FCR) of sensor. The effect of sensor on the mechanical strength of column was also studied. Experimental results showed that whether the sensor is embedded in concrete column or not, its piezoresistivity presents high stability and repeatability under cyclic loading within the elastic regime. The relationship between stress/strain and FCR of the sensor under monotonic loading obeys polynomial formulas. As the sensor is embedded into column, regardless of the concrete strength grade is C30 or C50, the piezoresistive behavior of the embedded sensor undergoes two phases, which is different from that of the sensor before embedded. This difference between the output signal characteristics results from the Poisson’s ratio and elastic modulus differences of sensor and concrete. In addition, the presence of sensor does not impact the bearing capacity of concrete column. The developed sensor is therefore suitable to be embedded into prefabricated components to make smart building products which can be calibrated for structural monitoring in real applications.

CFRP加固混凝土短柱轴压性能研究

通过对6个混凝土柱的静力加载试验，本文研究了碳纤维布加固对不同截面混凝土柱的力学性能的影响，分析了碳纤维布粘贴层数及短柱截面类型对碳纤维布加固效果的具体影响。结果表明：碳纤维布可明显提高混凝土柱的刚度和极限承载力，减小柱的竖向位移，减小柱的横向应变和纵向应变；当碳纤维布粘贴层数为两层时，其影响程度比粘贴一层时更为显著，但其提高程度不与加固面积成正比；碳纤维布加固对混凝土圆柱极限承载力和刚度的提高优于对混凝土方柱的提高。 Through the static load test of six CFRP reinforced concrete columns, the paper studies the CFRP reinforced concrete columns with different cross section of the influence of mechanical properties, and analyzes the specific influence of the carbon fiber cloth paste layer and column’s section type to carbon fiber cloth reinforcement effect. The results show that: Carbon fiber cloth can obviously increase the stiffness and ultimate bearing capacity of concrete columns, reduce the vertical dis-placement of column and reduce the lateral strain and the axial strain of the columns. When the paste layer of carbon fiber cloth is two, the impact is more obvious. But the increase degree is not proportional to the reinforced area; the improvement of carbon fiber cloth reinforcement to con-crete columns’ ultimate bearing capacity and stiffness is superior to the improvement of concrete square column.

Experimental Research on Bearing Capacity of Concrete Columns with High Strength Concrete Core under Axial Compression Loading

Based on experimental research on plain concrete columns with high strength concrete core, the formula to predict the bearing capacity of concrete columns with high strength concrete core under axial compression loading was brought forward in previous paper, in order to verify the formula whether right, axial compression test including 3 concrete columns with high strength concrete core and 1 ordinary reinforced concrete column were completed, and the failure characteristic was analyzed additionally. According to experimental results, it can be shown that the failure modes of concrete columns with high strength concrete core are similar to that of ordinary reinforced concrete columns, however, the bearing capacity of concrete columns with high strength concrete core is significant higher compared with that of ordinary reinforced concrete column; the results of the bearing capacity obtained by the formula (2) was in good agreement with the experimental results.