Krzysztof Kamiński

Research on Compresive Strength and Strain of Expansive Concrete

This paper presents chosen results of extensive research conducted on strain and compressive strength of concrete with admixtures causing expansion. The efficiency was tested with use of two commercially available products: MC-Einpresshilfe and Expancrete, as well as self developed, according to own recipe. Own apparatus was designed and presented, which was used for the strain study of concrete. From the tested admixtures, only Expancrete MAPEI allowed to obtain expansive concrete. Other used admixtures - MC-Einpresshilfe and composition of gypsum, lime and kaolin cannot be used to obtain expansive concrete. However, they can reduce concretes shrinkage.

Research on the Phenomenon of Relaxation of Compressed Concrete Elements

This article presents results of research aimed at identifying the phenomenon of stress relaxation in compressed concrete elements. The study used a special test stand, designed and constructed by Dr.Eng. Krzysztof Kaminski which allows permanent strain of cylindrical concrete sample by adjusting force. Cylindrical samples with a diameter of 15 cm and 10.5 cm and a height of 30 cm for the study were used. The samples were made of different classes of concrete. There was also defined the influence of applied tensile stress and the age of the sample on the relaxation phenomenon. The expected result of the research was to obtain relaxation curves of concrete samples with different compressive strength and age. Relaxation of concrete is important for the analysis of bending elements sections, which behavior during the operational phase of the concrete can significantly deviate from the assumed one, causing other than triangular or parabolic distribution of compressive stresses.

Designing Compressed Reinforcement Cross-Sections by Curvature and Nominal Stiffness Methods

The paper attempts to discuss the still significant issue of methods of design of the reinforced concrete columns according to PN-EN 1992-1-1:2008/A1:2015-03. Two algorithms of the dimensioning sections were developed according to two standard methods of dimensioning eccentrically compressed sections: the method of nominal stiffness (NS) and the method of nominal curvature (NC). Using both algorithms, computer programs in Excel were created. A comparative analysis of several examples of calculation were performed to compare the results of dimensioning of sections eccentrically compressed. The results obtained by the NC method give about 10% less surface reinforcement when loaded with big eccentricity and over 50% less when small eccentricity is applied.

Generating Interaction Curve Graph Based on the Rotation Angle of Strain Diagram, According to EN 1992

The most comfortable way to present capacity is M-N interaction curve diagram (bending moment and longitudinal force). Graph of M-N most commonly appears as a function, where an axial force is the argument and the bending moment is the value. This work introduce a formation of the curve way, where the the rotation angle of the strain diagram is the argument, and the full strain diagram is the value. Using the complete state of the strain of the cross section, enables easy calculation the M-N forces using stress-strain diagram for a given material. Interaction graph is based on parabola-rectangle diagram for concrete and the graph with inclined top branch with strain limit for reinforcing steel. The method has no restrictions due to the concrete class.

Computational Analysis of Biaxial Bending in Reinforced Concrete Columns

The aim of this paper is to provide a solution for easy calculations of reinforced concrete with biaxial bending cross-section. The paper presents in an orderly manner basic definitions related to the discussed topics, to the extent necessary to understand the discussed issues. As a result of the computational analysis dozens of sections with biaxial bending, there was developed a table and a chart containing the correction factor for bending moments, allowing to obtain the correct bearing capacity of cross-section, subjected to biaxial bending. This work presents proposition for a new, own calculation method of such cross-section. Calculations were made according to PN-EN 1992-1-1:2008, Eurocode 2, Design of concrete structures. Part 1-1: General rules and rules for buildings, using algorithms based on simplified methods. According to carried out calculations, cross-section dimensioning compressed with biaxial eccentricities separately on each side and values of bending moments should be increased to maintain cross-sections bearing capacity. The coefficient K scaling moments was determined as a function of eccentricity ey. With the increase of eccentricity, the coefficient K decreases.

Calculation of Reinforced Concrete Beam Cross Sections According to General Method Included in EC2

The aim of this paper is to determine values of strains, while using the assumptions required in calculation of reinforced concrete beam cross sections according to general method included in EN-1992-1-1. It is related to application of the parabolic rectangular diagram of stresses in concrete. Various types of strain analysis were carried out using derived formulas and script written by K. Kamiński in MS Excel. A high sensitivity to changes of reinforcement area has been noticed while carrying out the analysis with the same assumptions as in the calculation of cross sections according to general requirements included in EC2. It has been found out, that the reason of this sensitivity is related to the applied design values in strain-stress relations. Other approach to the strain analysis has been suggested. The main assumption of this approach is related to using characteristic values of material parameters. Finally, both: the calculations of necessary reinforcement area and strain analysis assuming characteristic values of concrete compressive strength and yield strength of steel gained in satisfactory results conformity for area of reinforcement calculated in simplified and non‑simplified method according to EN-1992-1-1.