Bronius Jonaitis

A model for strength and strain analysis of steel fiber reinforced concrete

Abstract The article proposes a model for strength and stain analysis of steel fiber reinforced concrete (SFRC). The model is based on general principles for creating and modelling structural composites and on reinforced concrete code. Differently from other examples, the elastic and plastic properties of the components (concrete and steel) of the introduced model are directly taken into account. The model gives an opportunity to determine tension and compression strength, the elasticity modulus of fiber concrete and the main parameters of its elasticity and plasticity. A good agreement between the obtained results and those of experiments performed by other investigators was confirmed. Differences between the ratios of theoretical and experimental values are insignificant and vary within the limits of 1.06–1.10. This model may be used for the analysis of reinforced concrete members reinforced by steel fibers (SFRC) in a dispersible way assuming stress distribution diagrams.

Effect of long‐term loading and fire temperatures on mechanical properties of concrete

Abstract During a fire, reinforced concrete structures are exposed to high temperatures and subjected to long‐term action of variable and permanent loads. This paper deals with analysis of influence of fire temperatures and long‐term action of loads on compression strength and deformability of normal weight concrete. Results of experimental investigations of compression strength and deformability of normal‐weight concrete subjected to long‐term load and exposed to high temperature are presented. Specimens in the shape of prisms of normal‐weight concrete were subjected to long‐term compression of intensity η(t) = σc/fc (τ) = 0,3. The long‐term compression was sustained for 400 days. Some of the specimens were heated (at 250 °C and 450 °C) before application of long‐term load; other specimens were heated after application of long‐term load. The paper presents coefficient of service conditions for concrete subjected to long‐term load and exposed to high temperature that gives opportunity to evaluate compress...

Flexural capacity and stiffness of monolithic biaxial hollow slabs

The article presents a research on flexural behaviour of hollow monolithic reinforced concrete slabs. It focuses on the results of experimental investigation into full-size hollow reinforced concrete slabs and analyses their flexural capacity and stiffness. The self-weight of the slabs directly depends on the shape and number of hollows. An increase in the hollowness of a slab significantly reduces the load caused by self-weight. This allows increasing the estimated length of the slab under the same payload. An increase in the amount of hollows of the slab changes the stiffness of the slab cross-section that has a direct impact on slab deflection. Considering the shape of the slab cross-section, theoretical calculations of the flexural capacity and deflection of experimental slabs were made. The design of a new type of slabs and variations in different parameters of the slab experience difficulties in conducting a large amount of experimental tests. Therefore, the initial analysis may apply to numerical simulation. The paper describes the principles of designing a numerical model. The calculations were made using DIANA software. The stiffness and flexural capacity of the hollow slabs were established employing numerical simulation compared to the results of experimental investigations. The findings indicate that numerical simulation can be applied for analysing the stress state of the examined structures.

Numerical and experimental analysis of grouted hollow block masonry under compression

Abstract Highly hollow masonry units, which allow reducing the weight of masonry constructions and improving heat and sound insulation qualities, are commonly used in masonry construction. Filling the hollows with concrete, or concrete with light additives, results in complex masonry. Overall performance of such masonry is affected by initial stresses, which are caused by shrinkage deformations of different infill concrete and masonry units. Behaviour of infill concrete and concrete blocks is analysed by applying numerical detailed micro modelling. Experiments revealed that masonry deformations of blocks with concrete filled hollows are similar to those of longitudinal deformations of infill concrete samples. σ-e relations were received through numerical micro modelling and compressive strength of masonry match values were estimated during experiments.

PECULIARITIES OF STRUCTURAL PROPERTIES OF MASONRY FROM HOLLOW BLOCK UNITS AND THEIR ESTIMATION

Summary Performed analyses of investigations have shown that properties of masonry from hollow blocks depend on many factors, and on material type and shape of the blocks including. But there is no unified method for determining the main structural properties-the compressive strength and modulus of elasticity. Theoretical investigations into masonry from hollow blocks and analysis of character of failure have shown that horizontal stress due to vertical loads has great influence on the strength of such masonry. The failure is initiated by vertical cracks crossing transverse webs. Values of strengths of concentrically compressed masonry calculated according to codes [2, 3] lead to different deviations from experimental results. Lower deviations for masonry of blocks are obtained according to [2] than according to [3]. Strength of masonry of calcium silicate blocks calculated by [3] is greater than that determined by experiments. Modulus of elasticity of such type masonry is lower than that of the same stre...

Assessment of bed joints behavior of calcium silicate brick masonry during execution

AbstractThis article examines masonry as the composite material. Factors affecting the mechanical deformation characteristics of masonry bed joints are reviewed. The strength and deformation characteristics of bed joints under the influence of changing mortar strength and variable compressive load are analysed Compressive strength, shrinkage and plastic deformation of masonry fragments and bed joints under variable compressive strength are also examined.

New European Union method for the design of reinforced concrete structures exposed to fire temperatures

Abstract The analysis of a method for the design of reinforced concrete structures exposed to fire temperatures is presented in the article. The main essential factors which must be evaluated in the design of structures and their parts to provide their adequate carrying capacity and ability to prevent fire spread are analyzed. In fire design it is necessary to take into account the behaviour of structural system exposed to fire temperatures, the possible effect of heat and positive effects of active and passive protection systems against fire and the consequences of collapse of the structure. The method is intended for buildings, fire load is associated with the building and its use. At the same time thermal and mechanical actions for structures exposed to fire are considered.

Investigation of the Behavior of Hardening Masonry Exposed to Variable Stresses

This paper analyzes the behavior of masonry under variable loads during execution (construction stage). It specifies the creep coefficient for calcium silicate brick masonry, presenting the research data of masonry deformation under variable and constant long-term loads. The interaction of separate layers of composite material in masonry is introduced and the formulae for determining long-term deformations are offered. The research results of masonry’s compressive strength and deformation properties under variable and constant long-term loads are presented. These are then compared to calculated ones. According to the presented comparison, the calculated long-term deformations coincide quite well with those determined experimentally.