Compressive Stress In Concrete Research Articles

Mechanical characteristics of dowel bar-concrete interaction: based on substructure experiment

ABSTRACT Loading tests were carried out on the dowel bar-concrete substructure of concrete pavement. Mechanical characteristics of dowel bar-concrete interaction were studied. In the elastic range of concrete, the bearing modulus, which is a crucial parameter but is usually determined by presumption, was calculated using classic Westergaard equations. Its influencing factors were evaluated such as concrete strength, dowel bar thickness, joint width, and anti-cohesive layer. Besides, a theoretical equation for tangential stress at the most dangerous point of concrete was deduced from Westergaard's and Timoshenko's equations. The equation reveals how the tangential stress of the most dangerous point at the dowel bar-concrete interface is affected by influencing factors. Lastly, the deterioration process of concrete around the dowel bar was revealed. The strain gauges’ data show that deterioration of concrete develops from the most dangerous point to far away from the dowel bar gradually. Two failure modes were found; one is circular spalling, the other is three main cracks. The initiation of the dowel-bar concrete structure's deterioration is circular spalling, attributed to high radial compressive stress in concrete. The deterioration starts around half the load capacity of the structure.

Compressive Behavior Characteristics of High-Performance Slurry-Infiltrated Fiber-Reinforced Cementitious Composites (SIFRCCs) under Uniaxial Compressive Stress.

The compressive stress of concrete is used as a design variable for reinforced concrete structures in design standards. However, as the performance-based design is being used with increasing varieties and strengths of concrete and reinforcement bars, mechanical properties other than the compressive stress of concrete are sometimes used as major design variables. In particular, the evaluation of the mechanical properties of concrete is crucial when using fiber-reinforced concrete. Studies of high volume fractions in established compressive behavior prediction equations are insufficient compared to studies of conventional fiber-reinforced concrete. Furthermore, existing prediction equations for the mechanical properties of high-performance fiber-reinforced cementitious composite and high-strength concrete have limitations in terms of the strength and characteristics of contained fibers (diameter, length, volume fraction) even though the stress-strain relationship is determined by these factors. Therefore, this study developed a high-performance slurry-infiltrated fiber-reinforced cementitious composite that could prevent the fiber ball phenomenon, a disadvantage of conventional fiber-reinforced concrete, and maximize the fiber volume fraction. Then, the behavior characteristics under compressive stress were analyzed for fiber volume fractions of 4%, 5%, and 6%.

Artificial neural network model using ultrasonic test results to predict compressive stress in concrete

This study focused on modeling the behavior of the compressive stress using the average strain and ultrasonic test results in concrete. Feed-forward backpropagation artificial neural network (ANN) models were used to compare four types of concrete mixtures with varying water cement ratio (WC), ordinary concrete (ORC) and concrete with short steel fiber-reinforcement (FRC). Sixteen (16) <TEX>$150mm{\times}150mm{\times}150mm$</TEX> concrete cubes were used; each contained eighteen (18) data sets. Ultrasonic test with pitch-catch configuration was conducted at each loading state to record linear and nonlinear test response with multiple step loads. Statistical Spearman's rank correlation was used to reduce the input parameters. Different types of concrete produced similar top five input parameters that had high correlation to compressive stress: average strain (<TEX>${\varepsilon}$</TEX>), fundamental harmonic amplitude (A1), <TEX>$2^{nd}$</TEX> harmonic amplitude (A2), <TEX>$3^{rd}$</TEX> harmonic amplitude (A3), and peak to peak amplitude (PPA). Twenty-eight ANN models were trained, validated and tested. A model was chosen for each WC with the highest Pearson correlation coefficient (R) in testing, and the soundness of the behavior for the input parameters in relation to the compressive stress. The ANN model showed increasing WC produced delayed response to stress at initial stages, abruptly responding after 40%. This was due to the presence of more voids for high water cement ratio that activated Contact Acoustic Nonlinearity (CAN) at the latter stage of the loading path. FRC showed slow response to stress than ORC, indicating the resistance of short steel fiber that delayed stress increase against the loading path.

Hydration and early-age expansion of calcium sulfoaluminate cement-based binders: experiments and thermodynamic modeling

Calcium sulfoaluminate (CSA) cements have been shown to have lower carbon footprint than that of Portland cement. In addition, the expansive nature of CSA-based cement can be utilized to enhance the resistance against shrinkage cracking by inducing compressive stress in concrete. The current paper reports the hydration and early-age volume changes of three OPC-CSA binary cement systems with varying CSA content. Hydration and phase development was monitored through calorimetry and quantitative X-ray diffraction. Expansion characteristics of OPC-CSA blends were monitored in saturated lime water. A geochemical modeling program (GEMS-PSI) was used to estimate the saturation levels of ettringite which had strong correlation with 1 day-expansion. The volume fraction of ettringite in a given pore volume was found to have a stronger correlation with expansion of OPC-CSA blends than the ettringite content. Furthermore, a poromechanical model was used for estimating the tensile stress in OPC-CSA blends.

FRP-RC Beam in Shear: Mechanical Model and Assessment Procedure for Pseudo-Ductile Behavior

This work deals with the development of a mechanics-based shear model for reinforced concrete (RC) elements strengthened in shear with fiber-reinforced polymer (FRP) and a design/assessment procedure capable of predicting the failure sequence of resisting elements: the yielding of existing transverse steel ties and the debonding of FRP sheets/strips, while checking the corresponding compressive stress in concrete. The research aims at the definition of an accurate capacity equation, consistent with the requirement of the pseudo-ductile shear behavior of structural elements, that is, transverse steel ties yield before FRP debonding and concrete crushing. For the purpose of validating the proposed model, an extended parametric study and a comparison against experimental results have been conducted: it is proven that the common accepted rule of assuming the shear capacity of RC members strengthened in shear with FRP as the sum of the maximum contribution of both FRP and stirrups can lead to an unsafe overestimation of the shear capacity. This issue has been pointed out by some authors, when comparing experimental shear capacity values with the theoretical ones, but without giving a convincing explanation of that. In this sense, the proposed model represents also a valid instrument to better understand the mechanical behavior of FRP-RC beams in shear and to calculate their actual shear capacity.

Softening Effects in Design of R C Planar Members

It has been a well known phenomenon that the principal compressive stress in concrete is a function not only of the compressive strain but also of the co-existing principal tensile strain. Thus concrete subjected to high tensile strains in the direction normal to the compression is softer and weaker than concrete in a standard cube or cylinder test. Such ‘softening’ effect has been confirmed by experiments by various researchers for in-plane structures. In this paper, the phenomenon is extended to the study of a plate bending structure having bending moments of opposite signs (one hogging and the other sagging) in two mutually perpendicular directions at the same point. As concrete will be having compression and tension in two perpendicular directions above and below the neutral axis, it is believed that the same softening effect will exist in the plate bending structure. However, the effects have been commonly ignored by most local engineers. In the paper, the authors propose simplified equations to account for the effects.

Structural Design of 80-Story RC High-Rise Building Using 200 Mpa Ultra-High-Strength Concrete

This paper presents the design of an 80-story reinforced concrete (RC) high-rise building using 200 MPa ultra-high-strength concrete. Static nonlinear push over analyses, Level-1 and Level-2 nonlinear earthquake response analyses and nonlinear wind response analyses were carried out. Based on the three-dimensional static nonlinear analyses of the building subjected to design earthquake loading in two principal directions, the obtained maximum axial load ratio for the first story columns of 200 MPa compressive strength concrete were 0.53 and 0.48, respectively, at the ultimate limit state, which meets the design criterion based on the allowable compressive stress of concrete. The maximum story drift angle obtained under the synthetic wave motion at the construction site was smaller than the design limiting value of 1/100. While yield hinges developed only in some of the short beams, no yield hinge in columns was observed. The maximum ductility of 1.28 obtained in the beams is lower than the design limiting value of 4.0. The maximum story shear force for the level-2 wind load was almost half that of the level-2 earthquake load when using the lumped-mass model. The analyses confirmed that the use of 200 MPa concrete enables structural designers to provide the member sections with adequate sizes comparable to that of ordinary high-rise RC buildings. The analytical results showed that the performance of the building satisfies the design criteria for serviceability limits, design limits and ultimate limits.

プレキャストコンクリートに残存する圧縮応力の影響を受けるコンクリート合成梁の断面算定法の研究

Generally, Stresses caused by loading on the precast concrete members due to their self-weights under construction are permanently preserved in the concrete composite beams. The preserved compressive stress in concrete has an effect on the equilibrium condition with respect to stresses at the composite beam section. The preserved compressive stresses decreased by loading on the beams behave themselves as the same tension ones as of its reinforcements, steel bars and PC tendons. By using this calculation method, the simulation results show that the rational continuity and the clear relationship of the stresses in the composite beams on various conditions among RC, PRC and PC are confirmed.

RC部材の危険断面近傍でのトラス機構

The uniform truss model is now getting wider acceptance in Japan for calculating shear strengths of reinforced concrete members. The model, however, has two theoretical weak points : (1) compressive stress of concrete is assumed to distribute uniformly even in critical sections of member, and (2) longitudinal reinforcement is assumed to be strong enoueh beyond its yield strength, both of which contradict flexural analysis. This paper presents truss models which yield realistic stress distribution harmonious with flexural analysis. The models vary slightly in accordance with the amount of axial load, but they give almost same shear strength as the prevailing uniform truss model.