Słowa kluczowe

concrete |reinforced concrete structures |bond |pull-out test |steel deformed bar

Streszczenie

This article deals with the issue of the bond between concrete and reinforcement. The bond is crucial for reinforced concrete elements because it is possible to transfer forces (stresses) from concrete to the reinforcement. Basic information related to the cooperation of concrete and rebars was recalled in the article. Selected issues concerning theoretical and numerical analysis as well as experiments of the bond phenomenon were presented. The article also proposes its own concept of experimental studies on the bond on two types of specimens: so-called short specimen and large specimen that will be subjected to pull-out tests. The described concept is ultimately to form the basis for creating a numerical model, enabling the simulation of bond in various reinforced concrete elements, calibrated based on the results of experimental studies.

Słowa kluczowe

compressive strength |AAC blocks |FRCM system |superficial strengthening

Streszczenie

This paper describes results from studies on the effects of superficial strengthening with FRCM system on compressive strength of autoclaved aerated concrete (AAC) masonry. Tests were carried out on models without any strengthening, strengthened at one or both sides. Two-side strengthened masonry demonstrated an increased compressive strength and deformability. Increased deformability was observed for one-side strengthened masonry when compared to tests on masonry without any strengthening.

Słowa kluczowe

parametric design |digital fabrication |concrete fencing |prefabrication |Rhinoceros |Grasshopper |CNC |detail

Streszczenie

This paper is a summary of the research on parametric design methods and digital fabrication in architecture and industrial design. Through the author’s projects, he presents how effective parametric designing process can be in contemporary architecture. This publication is a testimony of a long and full production process of a set of concrete fencings – from design part, through prototyping, digital fabrication, post-production, concreate fabrication and selling process. The design part of this research pertains to algorithmic design methods in Grasshopper software as well as presents a broad range of various technological aspects involved in the fabrication process. In the conclusion part of this paper, the author discloses his expectations towards the future of concrete fencing in Poland and describes a set of appropriate rules that foster a further development of this technology.

Słowa kluczowe

punching shear |column-slab connections |lateral expansion |membrane action |normal stress

Streszczenie

The problem related to the effect of the corner column load on the punching shear resistance of the slab was presented. Existing experimental studies on internal columns demonstrated that the column pressure could lead to an increase in the punching shear resistance. Because of different confinement conditions of corner column-slab connection joints, it is unclear if such an effect exists for corner columns. New experimental investigations were initiated to clarify this issue. They covered a total of three corner column-slab connection specimens – slabs with a thickness of 140 mm and a longitudinal reinforcement ratio ρl = 1.09% connected with columns of a cross-section of 200×200 mm. The only variable parameter was the column load equal to 500, 1000 and 1500 kN.

A reduction of the slab load-carrying capacity of about 9% due to a three-fold increase in the column load was noted. Therefore, the effect of the column load turned out to be opposite to that observed for most previous tests on internal column-slab connections, which could have a result of a limited capacity of the slab reinforcement due to additional tensile forces from the lateral expansion of joint concrete.

Comparison in the light of test results demonstrated, that EN 1992-1-1 procedure allowed for safe, yet conservative estimation of the punching shear resistance. An average ratio of experimental to theoretical load of 1.82 was obtained.

Słowa kluczowe

SEN-beam |X-FEM |fracture mechanics |Abaqus user subroutine

Streszczenie

This article presents the results of the computer simulations of a four-point bending test of a concrete single-edge notched beam. In this publication, the authors compared the X-FEM method of simulating the crack in the Abaqus FEA system. The paper also contains the results obtained with the Abaqus subroutine recently developed by the authors, used for defining the direction of the crack and the failure criterion. The publication explains the way of working of this algorithm. The described calculations show that computer analysis gives unrealistic results in terms of the destructive force. SEN-beam is an interesting laboratory test in which a lot of factors influence the results. It is especially important to study what phenomena occur in the final phase of the study, when the crack tip is near the opposite side.

This research was financed by the Lublin University of Technology Science Financing Subsidy FN16/ILT/2020.

Słowa kluczowe

concrete composite beam |interface reinforcement |T-shaped beams

Streszczenie

The tests results of composite reinforced concrete T-shaped beams with an interface between the web and the flange are presented. The interface in the beams differed in the degree of the adhesion activity and the joining reinforcement ratio. Five series of beams were tested for deflection, displacement of composite parts in relation to each other, strain of main and transverse reinforcement, and crack pattern. The results were compared with the theoretical forces at which interface cracks and achieves the bearing capacity, calculated in accordance with fib Model Code 2010.

Słowa kluczowe

lightweight aggregate concrete |columns |second-order effects

Streszczenie

The paper presents a numerical analysis of deformability and load-bearing capacity of lightweight aggregate concrete (LWAC) elements subjected to bending with axial force. The nonlinear material model of LWAC presented in Eurocode 2 (EC2) was assumed. Several different densities and compressive strengths of concrete were taken into account. The investigations included the comparison of the sectional capacity and the behaviour of slender elements made with normal and lightweight aggregate concrete. It was observed that density-dependent mechanical properties of concrete affect the obtained values of the maximum axial force and the bending moment despite the same mean compressive strength. In every case, the capacity of the RLWAC section was lower than the one of normal weight, which was caused by a linear characteristic of the LWAC. Other important factors were the modulus of elasticity and the ultimate strain of concrete. LWAC with the higher density and the lower ultimate strain gave greater stiffness to slender columns but reduced the cross-sectional capacity. It was concluded that the elastic modulus and the peak strain of LWAC which are applied in columns calculations should be verified experimentally.

Słowa kluczowe

autoclaved aerated concrete (AAC) |precast lintels |Digital Image Correlation (DIC) |confined wall |lightweight concrete

Streszczenie

This paper presents the test results of reinforced precast lintels made of autoclaved aerated concrete (AAC) used to cover window openings in walls made of AAC masonry units. Walls were confined with reinforced lightweight concrete. The two variants of wall confinement with different way of lintel support and the static diagram of a simply supported beam and a constrained beam were tested. Cracks and deformations of test models around window openings were recorded with the Aramis software for non-contact measurements of displacements. Failure of lintels caused the loss of load capacity of test models. Lintels were cracked in the same way, but the sequence of crack formation and their location were different. The test results were compared with the test made for similar walls confined with ordinary concrete. Additional tie-columns did not significantly affected the load capacity of the test models contrary to the walls confined with ordinary concrete.

Słowa kluczowe

design point |design formula |prestressed concrete girders |resistance factor |reliability index |bridge live load |safety margin

Streszczenie

There has been a considerable progress in the reliability-based code development procedures. The load and resistance factors in the AASHTO bridge design code were determined using the statistical parameters from the 1970’s and early 1980’s. Load and resistance factors were determined by first fixing the load factors and then calculating resistance factors. Load factors were selected so that the factored load corresponds to two standard deviations from the mean value and the resistance factors were calculated so that the reliability index is close to the target value. However, from the theoretical point of view, the load and resistance factors are to be determined as coordinates of the so-called “design point” that corresponds to less than two standard deviations from the mean. Therefore, the optimum load and resistance factors are about 10% lower than what is in the AASHTO LRFD Code. The objective of this paper is to revisit the original calibration and recalculate the load and resistance factors as coordinates of the “design point” for prestressed concrete girder bridges. The recommended new load and resistance factors provide a consistent reliability and a rational safety margin.

This work was supported by the Highway Research Center at Auburn University.

Słowa kluczowe

recycled fibres |flexure |hybrid fibres |self-compacting concrete

Streszczenie

In the present study the steel fibres coming from the end-of-life tires were applied as a reinforcement of self-compacting concrete. The influence of the recycled fibres and their mixture with glass or polypropylene fibres (hybrid mixes) on the flexural behaviour of SCC was tested. The research revealed that the dosage of 1.5% of recycled fibres is highly effective in the SCC matrix. The values of the residual flexural tensile strengths obtained in the tests classified the R-SCC to be used as a partial replacement of the conventional reinforcement. The addition of other types of fibres to R-SCC caused the further enhancement of flexural parameters with no negative effect on the distribution of the fibres in the mix.

This work was supported by the Higher Education and National Science Centre for funding the grant no. DEC-2017/01/X/ST8/01864.

Słowa kluczowe

AAC blocks masonry |floors deflections |damages of masonry walls |transversal deformations of masonry

Streszczenie

The paper presents selected results of tests of full-scale masonry walls linearly supported on a deflecting beam. The walls with thin bed joints and unfilled head joints were 4.55 m long and 2.45 m high, and were made of group 1 calcium silicate masonry units. The tests included walls with and without openings.

The tests were carried out in a specially designated and constructed test stand, which allowed simultaneous vertical load on the upper edge of the wall and vertical deflection of the beam supporting this wall. During the test, measurements of mutual displacements of six points on the wall surface were carried out. On both faces of masonry specimens, the changes of the length of the measuring bases connecting these six points were recorded.

Walls without openings were detached from the central part of the supporting beam at a deflection not exceeding 2 mm. Walls with one door opening also cracked at an early stage of tests. In this case, a detachment from the supporting beam and cracking at the ends of the lintel occurred because of the rotation of the pillars connected by the lintel above the opening. In walls with two door openings, first cracks were formed at the ends of lintels due to the rotation of pillars with a small deflection of the supporting beam, less than 3 mm. Whereas, in walls with door and window openings, first cracks occurred under the window and at the end of the lintel in the outer pillar of the wall.