Reduction of stress concentration after repair using of polymer flexible joint

Paper deals with the stress concentration problem in civil engineering structures, especially damaged and possibility of their reduction using of polymer flexible joints. This aspect was analyzed based on a numerical model, as well as a simple bar model of flexible joint of nonlinear characteristic, which was described by linear constitutive equations

CFRP strengthening of bent RC beams using stiff and flexible adhesives

W artykule przedstawiono badania belek żelbetowych wzmocnionych taśmami CFRP aplikowanymi na podatnych złączach. Metoda złączy podatnych, opracowana na Politechnice Krakowskiej, polega na stosowaniu polimerowych warstw adhezyjnych przy łączeniu materiałów CFRP z podłożem betonowym. W badaniach belki żelbetowe wzmocniono taśmami CFRP klejonymi na warstwie epoksydowej i pięciu warstwach polimerowych o różnych sztywnościach. W belce wzmocnionej taśmą CFRP na warstwie polimerowej o średniej sztywności wykazano najbardziej równomierny rozkład odkształceń taśmy na jej długości i równocześnie najmniejsze jej ugięcie spośród wszystkich badanych belek. Stosowanie omawianej technologii we wzmacnianiu konstrukcji z betonu może przynieść dodatkowe korzyści, ale obecnie konieczne są dalsze badania nad tym zagadnieniem

The synthesis and structural characterization of graft copolymers composed of γ-PGA backbone and oligoesters pendant chains

© 2017 The Authors. Published by American Chemical Society. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1021/jasms.8b05393The novel copolymers composed of poly-γ-glutamic acid (γ-PGA) and oligoesters have been developed. The structures of the obtained copolymers including variety of end groups were determined at the molecular level with the aid of electrospray ionization multistage mass spectrometry (ESI-MSn). The fragmentation experiment performed for the selected sodium adducts of the copolymers confirmed that the developed methods lead to the formation of graft copolymers composed of poly-γ-glutamic acid (γ-PGA) backbone and oligoesters pendant chains. Moreover, it was established that fragmentation of selected sodium adducts of graft copolymers proceeded via random breakage of amide bonds along the backbone and ester bonds of the oligoesters pendant chains. Considering potential applications of the synthesized copolymers in the area of biomaterials, the hydrolytic degradation under laboratory conditions and in vitro cytotoxicity tests were performed. The ESI-MSn technique applied in this study has been proven to be a useful tool in structural studies of novel graft copolymers as well as their degradation products.This work was supported by the Polish National Science Centre (Decision No DEC-2013/11/N/ST5/01364

Design of an innovative self-compacting material modified with recycled steel fibers and spent equilibrium catalyst for ultra-high performance applications

The main aim of the present study is to design an innovative self-compacting material modified with recycled steel fibers (RSF) from waste tires and spent equilibrium catalyst (Ecat) from the petrochemical industry for ultra-high performance application. For this purpose, 17 different mixtures were developed and analysed using different percentages of RSF (0%-3%) and replacement of cement by different percentages of Ecat (0%-15%). The developed mortars' self-compatibility was evaluated in a fresh stage using mini-cone tests. Regarding the hardened stage, the mortars were characterized at the ages of 7 days and 28 days using compression and unnotched flexural tests. The abilities of RSF to increase the post-cracking behavior of the specimens and to use Ecat to increase the bond performance between RSF and the cement matrix were assessed by performing notched three-point bending tests. The results of notched flexural tests were used to obtain the residual flexural strength in service limit state (SLS), ultimate limit state (ULS), and two equivalent flexural strengths. The experimental results for the fresh stage demonstrated that inclusion of RSF and Ecat significantly reduced the workability of mortars. The beneficial use of RSF and Ecat was observed to increase compressive strength and flexural strength for 7 days and 28 days of tested specimens. Notched flexural tested specimens showed that the addition of RSF and Ecat can significantly decrease the brittle behavior of cement-based materials by improving its toughness and post-cracking resistance. Middle-span deflection, crack initiation load, and ultimate flexural load were also increased with the addition of RSF and Ecat. In this sense, the results of this research showed that RSF and Ecat seem to have the potential to constitute a sustainable material for structural and nonstructural applications

Stress distribution in masonry infills connected with stiff and flexible interface

Masonry infills are largely used in RC structures for various purposes, and in seismic zones, they are also preferred for providing earthquake resistant systems. However, due to the rigid connection between infills and RC frames, these systems are vulnerable when large deformations are demanded. Cyclic loads that are occurring during seismic excitations cause stress concentration level to increase, particularly in frame-infill contact zones. As a result of stress increment, infill panels get weaker in terms of both in-plane and out-of-plane resistance. These drawbacks cause loss of lives and properties, thus affecting governments and societies adversely. In order to overcome this obstacle, an innovative solution is proposed which uses flexible polymers (Polyurethane PM) as joint elements for protecting the structural elements. The research is focused on numerical analyses of three types of frames with masonry infills, which are excited through both in-plane and out-of-plane directions by different earthquake records. Infill walls are connected to the frames in three manners: stiffly (classical approach), with flexible joints at 3-boundaries and with flexible joints at 4-boundaries. Differences in calculated stress distribution as well as some other linear and non-linear results are presented and discussed. The primary results give promising outcomes that this new method might be used in seismic zones for protecting structures

Repair of composite-to-masonry bond using flexible matrix

The paper presents an experimental investigation on an innovative repair method, in which composite reinforcements, after debonding, are re-bonded to the substrate using a highly deformable polymer. In order to assess the effectiveness of this solution, shear bond tests were carried out on brick and masonry substrates within two Round Robin Test series organized within the RILEM TC 250-CSM: Composites for Sustainable strengthening of Masonry. Five laboratories from Italy, Poland and Portugal were involved. The shear bond performance of the reinforcement systems before and after repair were compared in terms of ultimate loads, load-displacement curves and strain distributions. The results showed that the proposed repair method may provide higher strength and ductility than stiff epoxy resins, making it an effective and cost efficient technique for several perspective structural applications

Highly Deformable Polymers for Repair and Strengthening of Cracked Masonry Structures

Damages existing in masonry engineeringstructures are caused by various loads and has to be repairbecause of structural and architectural requirements. Repair ofcracked masonries using materials of high stiffness and lowdeformability, like lime and cement mortars or epoxy resins, doesnot increase significantly the tensile strength of the repair joint.This is because of the stress concentration occurrence. The use ofhighly deformable bonding materials allows reducing peaks ofstress concentration, causing (after repair) increase of strength ofcracked masonry elements. Proposed repair materials of highdeformability can be easily covered with original masonrymaterial to ensure protection of architectural value.In the paper, there were tested masonry units (bricks),investigated in two kinds of loading. One of them was the fourpoint bending test on Polish Bonarka bricks and the second onewas the Single Lap Shear Test on Italian Rosso Vivo - A6R55Wbricks, strengthened using CFRP and SRP strips bonded onepoxy resin. In both cases, the primary failure appeared in formof cracks (or detachment) going through the brick materials. Thefailure surfaces of both tests were repaired using materials of lowand high deformability. More significant strength increase of thetested masonry elements (after repair) was obtained in the caseof the use of highly deformable interface materials than of barelydeformable bonding materials.Efficiency of highly deformable repair materials was alsoexamined as repair on cracked masonry walls in laboratory usingpolymer injection and externally bonded composite mats made ofglass fibers bonded on highly deformable polymer. Additionally,the highly deformable polymer joints were tested dynamically insitu on a masonry building, up to failure also

The animal cemeteries as sites of cultural performance

Using the tools and definitions provided by performance studies (Richard Schechner, Jon McKenzie, Erika Fischer-Lichte, Małgorzata Sugiera, Dariusz Kosiński and others) as well as by newer post-human turn (Ewa Domańska) the author analyses the phenomenon of burying domestic animals on sites located on the outskirts of populated areas (resembling the old cholera graveyards). Animal burial sites are denied the term ‘cemetery’ by official legislation which reserves the notion only for human necropolises. Almost every suggestion of establishing an animal cemetery in Poland is met with highly emotional reactions and protests. Itself being acts of social performance, the protests evoke burial as a social performance art, where the community participates in an event based on a standard Christian funeral ceremony. The unstandardized character of the animal’s funeral challenges this view. In the act of animal burial an oppressive gaze of a society is juxtaposed with an intimate one. The confrontation becomes a chance for the society for a self-reflection and transformation. Hence one may prove that the animal burials have a significant performative power and can have social and cultural impact

Strengthening of masonry using natural fibers bonding with highly deformable adhesives

Strengthening of cracked masonries of poor construction using composite materials of high strength and stiff adhesives of low deformability, like lime and cement mortars or epoxy resins, does not increase significantly the capacity of masonries in seismic areas. This is because of the stress concentration occurrence. The use of highly deformable materials as adhesive and matrix allows reducing peaks of stress concentration in weak brittle substrates, causing increase of composite strengthening efficiency. In the paper, there were tested masonry units (bricks Rosso Vivo - A6R55W) strengthened by GFRP, BFRP, CFRP and BBFRP fibers bonded on epoxy resin and highly deformable polymer PS. The Single Lap Shear Test was used for comparison of stiff and deformable matrix and adhesive materials, bonding various fibers to the brittle substrate. The significant strength increase of the tested masonry specimens was obtained in the case of the use of highly deformable interface materials than of barely deformable bonding materials. Lower level of the shear stress in the substrate results in increasing of load capacity of masonries, thus applying of the highly deformable polymer PS as a matrix and an adhesive to the weak masonry substrate is more advantageous than classically using stiff epoxy adhesives. It was confirmed by other laboratory and insitu tests, in which GFRP and BFRP grids bonded on the polymer PS adhesive were applied for strengthening of masonry and concrete structural elements

Ochrona przed trzęsieniami ziemi konstrukcji żelbetowych ze ścianami wypełniającymi przy użyciu systemów PUFJ i FRPU

Advancements in technology and material sciences lead new solutions to be used in civil engineering. PolyUrethane Flexible Joints (PUFJ) and Fiber Reinforced PolyUrethanes (FRPU) are among those innovative solutions. PUFJ implemented systems comprise of seismic preventive buffer material between masonry infill walls and reinforced concrete (RC) frames, whereas FRPU solution is designed for covering the wall surfaces with thin composite strips. Both methods are primarily developed for increasing the ductility capacities of buildings while sustaining the overall structural strength without compromising on the safety of these systems against earthquakes. In this article, test results of the quasi-static cyclic experiments as well as dynamic tests on the shake tables including harmonic forces operating in resonance are presented. Moreover, numerical analyses are performed in order to comprehend the behavior of PUFJ implemented frames constituted with different masonry materials than above which are under various loading conditions. The outcomes confirmed the high efficiency of the proposed solutions, which at the same time meet the strict requirements of the modern seismic standards.Postępy w technologii i materiałoznawstwie prowadzą do nowych rozwiązań wprowadzanych w inżynierii lądowej. Wśród tych innowacyjnych rozwiązań znajdują się podatne złącza poliuretanowe (PUFJ) i poliuretany wzmocnione włóknami (FRPU). Systemy PUFJ instalowane są pomiędzy murowanymi ścianami wypełniającymi a ramami żelbetowymi jako anty-sejsmiczny element buforowy, natomiast systemy FRPU są przeznaczone do wzmacniania powierzchni ścian cienkimi pasami kompozytowymi. Obie metody zostały opracowane w celu zwiększenia ciągliwości budynków, przy jednoczesnym utrzymaniu ich ogólnej nośności, a tym samym w celu zwiększenia bezpieczeństwa użytkowania tych budynków w trakcie trzęsień ziemi. W artykule przedstawiono wyniki badań elementów w skali naturalnej pod quasi-statycznymi obciążeniami cyklicznymi oraz obciążeniami dynamicznymi na stole sejsmicznym i pod działaniem sił harmonicznych w rezonansie. Ponadto zostały przeprowadzone analizy numeryczne, mające na celu poznanie zachowania się podobnych konstrukcji z innymi materiałami murowymi współpracującymi z PUFJ, które poddane zostały różnym warunkom obciążenia. Wyniki potwierdziły wysoką skuteczność proponowanych rozwiązań, które jednocześnie spełniają surowe wymagania współczesnych norm sejsmicznych