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Polymers 2021, 13(10)
Seismic Protection of RC Buildings by Polymeric Infill Wall-Frame Interface
Ahmet Tugrul Akyildiz, Alicja Kowalska-Koczwara, Łukasz Hojdys

This paper is aimed at investigating the usage of flexible joints in masonry infilled walls surrounded by reinforced concrete (RC) frames. For this purpose, a real-size specimen was numerically created and exposed to the seismic loads. In order to evaluate both in-plane and out-of-plane performances of the infill walls, the system was chosen as a box shaped three-dimensional structure. In total, three different one-story constructions, which have single bays in two perpendicular directions, were modeled. The first type is the bare-frame without the infill walls, which was determined as a reference system. The second and third types of buildings are conventional mortar joint and PolyUrethane Flexible Joint (PUFJ) implemented ones, respectively. The influence of these joints on the material level are investigated in detail. Furthermore, general building dynamic characteristics were extracted by means of acceleration and displacement results as well as frequency domain mode shapes. Analyses revealed that PUFJ implementation on such buildings has promising outcomes and helps to sustain structural stability against the detrimental effects of earthquakes.

Keywords polyurethane; flexible joint; RC building; brick infill; concrete damaged plasticity (CDP); earthquake

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Materials 2020, 13(24)
Polymer Flexible Joint as a Repair Method of Concrete Elements: Flexural Testing and Numerical Analysis
Łukasz Zdanowicz, Szymon Seręga, Marcin Tekieli, Arkadiusz Kwiecień

Polymer Flexible Joint (PFJ) is a method for repairs of concrete elements, which enables carrying loads and large deformations effectively. This article presents the possibility of applying PFJ on beams subjected to bending and describes the influence of such joints on concrete elements. An experimental investigation was conducted to determine the behavior of concrete in a four-point bending test. The research program included flexural tests of plain concrete elements with a notch, as well as tests of elements which were repaired with PFJ after failure. Based on the experimental results, the numerical characteristics of analyzed polymer and concrete were calibrated. A nonlinear numerical model is developed, which describes the behavior of concrete elements and polymer in the experiments. The model is used to numerically analyze deformations and stresses under increasing load. The influence of flexible joint on concrete elements is described and behavior of elements repaired with PFJ is compared to original elements. Particular attention was paid to the stress redistribution in concrete. The application of flexible joint positively influences load capacity of the connected concrete elements. Furthermore, because of stress redistribution, connected elements can bear larger deformations than original ones. PFJ can therefore be considered an efficient repair method for connecting concrete elements.

Keywords polyurethane; flexible joint; concrete repair; stress redistribution

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Polymers 2020, 12(12)
Durability of PS-Polyurethane Dedicated for Composite Strengthening Applications in Masonry and Concrete Structures
Konrad Kwiecień, Arkadiusz Kwiecień, Teresa Stryszewska, Magdalena Szumera, Marta Dudek

Polyurethane flexible joints (PUFJ) and fiber reinforced polyurethanes (FRPU) have shown great potential in the repair and protection of masonry and concrete structures. However, some questions have been raised about the durability of such solutions. The accelerated weathering and thermal stability tests carried out so far have shown the mechanical stability of PS-polyurethane in temperatures up to 100 °C and some UV-induced surface degradation. The paper reports the results from tensile tests of PS-polyurethane, used in the technologies mentioned above after being subjected to aging in different corrosive factors, a thermal analysis of unaged polymer which consists of DSC-TGA and dilatometry studies, and SEM-microscopy observation of the specimens with the indication of the elemental composition (EDS). PS-polyurethane showed low sensitivity to weathering with exposition to UV-radiation, some reactiveness to aqueous environments of a different chemical nature, and resistivity to soil and freezing in both air and water. SEM observations indicated changes in the composition of mineral fillers as the main effect of immersion in different water solutions. DSC-TGA studies showed the thermal stability of PS-polyurethane up to 200 °C and degradation proceeding in five stages. Dilatometry studies revealed that the first-degree thermal degradation over 200 °C causes a serious loss of mechanical properties.

Keywords polyurethane; flexible-joints; durability; degradation; thermal analysis

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Composites Part B: Engineering 2020, Vol. 195
Flexural behaviour of NSM CFRP laminate strip systems in concrete using stiff and flexible adhesives
José Ricardo Cruza, Szymon Seręga, José Sena-Cruza, Eduardo Pereira, ArkadiuszKwiecieńb, Bogusław Zając

This work presents the results of an experimental and numerical investigation on the flexural behaviour of reinforced concrete (RC) slabs strengthened by carbon fibre reinforced polymers (CFRP) laminates applied according to the near surface mounted (NSM) technique, using stiff and flexible adhesives. Two study variables were analysed: i) the adhesive type and ii) the existence or not of pre-cracking on the slabs. The results show a clear dependence of slab's flexural performance on the adhesive type: the use of flexible adhesive yields to 80% of the maximum load achieved with stiff adhesives. The existence of pre-damage did not affect the structural behaviour of the slabs. CFRP rupture was observed with the use of stiff adhesives while CFRP debonding has occurred with the flexible one. Finally, a higher ductility was observed when using flexible adhesive. A numerical model was worked out and calibrated to simulate the flexural behaviour of the tested slabs. The numerical simulations showed a very good agreement with the experiments. Besides the very good predictive performance in terms of load-displacement behaviour, the numerical model also correctly reproduced the failure modes obtained in the experiments and the differences in the bonding mechanisms of slabs strengthened with the stiff and flexible adhesives. It was demonstrated that the proposed numerical model can be used in engineering practice for the analysis and design of NSM CFPR strengthening systems for existing RC structures.

Keywords NSMStiff and flexible adhesivesCFRPSlabsFlexural testsNumerical modelling

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Polymers 2020, 12(12)
Deformable Polyurethane Joints and Fibre Grids for Resilient Seismic Performance of Reinforced Concrete Frames with Orthoblock Brick Infills
Arkadiusz Kwiecień, Bogusław Zając, Łukasz Hojdys, Piotr Krajewski et al.

The behaviour of reinforced concrete frames with masonry wall infills is influenced a lot by the stiffness and strength difference between the frame and the infill, causing early detrimental damage to the infill or to the critical concrete columns. The paper reports the results from shake table seismic tests on a full-scale reinforced concrete (RC) frame building with modified hollow clay block (orthoblock brick) infill walls, within INMASPOL SERA Horizon 2020 project. The building received innovative resilient protection using Polyurethane Flexible Joints (PUFJs) made of polyurethane resin (PU), applied at the frame-infill interface in different schemes. Further, PUs were used for bonding of glass fibre grids to the weak masonry substrate to form Fibre Reinforced Polyurethanes (FRPUs) as an emergency repair intervention. The test results showed enhancement in the in-plane and out-of-plane infill performance under seismic excitations. The results confirmed remarkable delay of significant infill damages at very high RC frame inter-story drifts as a consequence of the use of PUFJs. Further, the PUFJ protection enabled the resilient repair of the infill even after very high inter-story drift of the structure up to 3.7%. The applied glass FRPU system efficiently protected the damaged infills against collapse under out-of-plane excitation while they restored large part of their in-plane stiffness.

Keywords polyurethane; flexible joint; RC column; brick infill; shake table; resilience

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Polymers 2018, 10(4)
Flexible Adhesive in Composite-to-Brick Strengthening - Experimental and Numerical Study
Arkadiusz Kwiecień, Piotr Krajewski, Łukasz Hojdys, Marcin Tekieli, Marek Słoński

This paper investigates composite-to-brick strengthening systems with flexible adhesive made of polyurethane (Carbon Fibre Reinforced Polyurethane (CFRPU) and Steel Reinforced Polyurethane (SRPU)) and epoxy resin (Carbon Fibre Reinforced Polymer (CFRP) and Steel Reinforced Polymer (SRP). The specimens were tested in a single lap shear test (SLST). LVDT displacement transducers (LVDT – Linear Variable Differential Transformer) and digital image correlation method (DIC) based measurement systems were used to measure displacements and strains. The obtained results were applied in a numerical analysis of the 3D model of the SLST specimen, with flexible adhesives modeled as a hyper-elastic model. The DIC and LVDT based systems demonstrated a good correlation. Experimental and numerical analysis confirmed that composite-to-brick strengthening systems with flexible adhesives are more effective on brittle substrates than stiff ones, as they are able to reduce stress concentrations and more evenly distribute stress along the entire bonded length, thus having a higher load carrying capacity.

Keywords strengthening; masonry; CFRP; CFRPU; SRP; SRPU; flexible adhesives; experimental tests; DIC measurements; shear bond tests; numerical analysis

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Engineering Transactions, 65, 1, pp. 113–121, 2017
Validation of a New Hyperviscoelastic Model for Deformable Polymers Used for Joints between RC Frames and Masonry Infills
Arkadiusz Kwiecień, Matija Gams, Theodoros C. Rousakis, Alberto Viskovic, Jozef Korelc

In the paper, an attempt to alleviate the problem of premature damage to infills by using flexible polymers between the infill and the r.c. frame is presented. The flexibility of the polymer could serve to reduce the stress concentrations and thereby reduce damage to infills on one hand, and provide a high amount of damping and ductility on the other. Its efficiency is tested by cyclic shear tests carried out on a large-scale model. In the numerical part, the material is modelled using for the purpose developed finite element. The finite element with the new hyperviscoelastic constitutive model was coded in the AceGen/AceFEM program.

Keywords deformable polymers; hyperviscoelastic model; masonry infills

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