Review of Innovative Rehabilitation Techniques for Reinforced Concrete Buildings

Building rehabilitation encompasses the act of repairing damaged structural elements, as well as the upgrading of older buildings to bring them up to modern standards. In recent years, due to the extreme economic and environmental cost of new construction, building rehabilitation is gaining ground as the most viable solution to the problem posed by damaged or substandard buildings. With the constant development of new materials with favorable properties and the improvement of our understanding of earthquakes, new rehabilitation techniques are being developed, improving on the efficiency and effectiveness of older ones. Reinforced Concrete (RC) buildings are a type of building that emerged in the late 19th century and are designed to sustain controlled damage during earthquakes of certain magnitudes. Since most of the world’s modern seismic design codes were developed in the 1980s or later, a large number of existing RC buildings are unable to handle design earthquake loads sufficiently and require seismic upgrading. Additionally, since RC buildings are designed to sustain damage under earthquakes of large magnitudes, they are also often in need of repair. Due to the above facts, the rehabilitation of RC buildings is a crucial part of their life cycle. In this problem report, innovative rehabilitation techniques for RC buildings developed in recent years are reviewed and presented, including methods for global (structural level) seismic rehabilitation and the element level rehabilitation of RC beams, RC columns, and RC beam-column joints

Tensile and Impact Behaviour of Shape Memory Alloy Fibre Reinforced Engineered Cementitious Composites

Extreme loading events such as impact, blast, and earthquakes have often led to partial or total collapse of structures, associated with economic and human life loss. Therefore, civil engineers have been seeking innovative materials and systems that would allow designing resilient and smart structures which can withstand such catastrophic events. Recently, engineered cementitious composites (ECC) and shape memory alloys (SMA) have emerged as strong contenders in the production of smart and resilient structural systems. The aims of this study are to explore the possible synergy between ECC and SMA for developing a novel hybrid fibre-reinforced ECC incorporating randomly dispersed SMA and polyvinyl-alcohol short fibres (HECC-SMAF) with possible strain recovery and superior impact resistance. The mechanical properties of the composite, including uniaxial tensile and strain recovery performance, were examined. Moreover, the behaviour of the composite under impact loading was explored using a drop weight impact test. Test specimens were also heat-treated to investigate possible pre-stressing effects of SMA fibres on the impact resistance of the ECC. A two-parameter Weibull distribution was used to analyze variations in experimental results in terms of reliability function. Furthermore, numerical simulation was developed to predict the behaviour of the composite under impact loading. Results indicate that SMA fibres significantly enhanced the performance of the composite both under static and dynamic loading. Adding fibres beyond a certain dosage led to fibre clustering, thus, no further gain in tensile and impact performance was measured. The impact resistance of HECC-SMAF specimens was further improved after exposure to heat treatment. This highlights the significant contribution imparted by the local pre-stressing effect of SMA fibres to the impact resistance of the composite. The Weibull distribution was adequate to predict the impact failure strength of the new composite, allowing to avert additional costly experiments. Also, numerical simulation predictions of the impact behaviour of the hybrid composite were in good agreement with experimental findings, thus offering a suitable predictive tool and allowing to preclude costly and time-consuming experiments. This research underscores the potential to engineer new cementitious composites with superior tensile properties and impact resistance for the protection of critical infrastructure in the event of explosive or impact loading

Finite Element Analysis of Beam – Column Joints Reinforced with GFRP Reinforcements

Glass Fibre Reinforcement Polymer (GFRP) reinforcements are currently used as internal reinforcements for all flexural members due to their resistance to corrosion, high strength to weight ratios, the ability to handle easily and better fatigue performance under repeated loading conditions. Further, these GFRP reinforcements prove to be the better alternative to conventional reinforcements. The design methodology for flexural components has already come in the form of codal specifications. But the design code has not been specified for beam-column joints reinforced internally with GFRP reinforcements. The present study is aimed to assess the behaviour of exterior beam-column joint reinforced internally with GFRP reinforcements numerically using the ABAQUS software for different properties of materials, loading and support conditions. The mechanical properties of these reinforcements are well documented and are utilized for modelling analysis. Although plenty of literature is available for predicting the joint shear strength of beam-column joints reinforced with conventional reinforcements numerically, but no such study is carried for GFRP reinforced beam-columns joints. As an attempt, modelling of beam-column joint with steel and with GFRP rebars is carried out using ABAQUS software. The behaviour of joints under monotonically increasing static and cyclic load conditions. Interpretation of all analytical findings with results obtained from experiments. The analysis and design of beam-column joints reinforced with GFRP reinforcements are carried out by strut and tie model. Strut and Tie models are based on the models for the steel reinforced beam-column joints.  The resulting strut and tie model developed for the GFRP reinforced beam-column joints predicts joint shear strength. Joint shear strength values obtained from the experiments are compared with the analytical results for both the beam-column joints reinforced with steel and GFRP reinforcements. The joint shear strength predicted by the analytical tool ABAQUS is also validated with experimental results.

Étude du comportement de colonnes en béton armé d’armature en PRFV soumises à des charges cycliques quasi-statiques

Abstract: Corrosion of the steel reinforcement in the conventional concrete structure is a serious and expensive problem which adversely affect the service life of the structure. The use of fiber-reinforced polymer (FRP) as internal reinforcing bar offers structurally safe alternative in concrete members such as beams, and slabs; due to its corrosion resistance, durability, and high strength-to-weight ratio when to compared to traditional steel bars. However, there is a lack of information concerning the performance of the reinforced-concrete columns confined with FRP bars under simulated seismic load. Study of reinforced concrete columns is useful for the construction of building, highway, and railway bridge columns. Currently, several highway and railway bridge columns and buildings need rehabilitation work due to deterioration of internal steel reinforcement (mainly transverse reinforcement) due to corrosion which affects the economy of the country. Thus, the experimental work is needed to verify the confinement effect of FRP bars on concrete columns subjected to quasi-static cyclic load to be use in new construction. The present study investigates the experimental performance of reinforced-concrete columns confined with glass fiber-reinforced polymers (GFRP) spiral and cross tie. Eight full-scale columns were constructed with entirely GFRP reinforcement. Four other columns were constructed with hybrid reinforcement consisting of longitudinal steel rebars and confined with GFRP spirals and cross ties. The columns had a cross section of 400 × 400 mm with an overall height of 1850 mm. The columns were tested to failure under combined constant axial compression and quasi-static reversed cyclic loading. Parameters under study were longitudinal bar type (GFRP and steel), longitudinal reinforcement ratio (1.48% and 2.14%), transverse reinforcement size (#3, #4, and #5) and spacing of transverse reinforcement (100, 120 and 150 mm). Overall performance of each specimen was examined in terms of cracking patterns, hysteresis response, strain developed in reinforcing bars, energy dissipation capacity, drift capacity, and strength capacity. Based on the test results, well-confined concrete columns showed a stable performance attending acceptable drift capacity which meets the recommendation of most design codes. The longitudinal reinforcement type significantly affected the column performance in terms of important seismic parameters. The hybrid-reinforced columns consisting of longitudinal steel and transverse GFRP reinforcement (spiral and cross tie) exhibited higher ductility and dissipated more energy than the GFRP-reinforced concrete columns. Failure progression of GFRP-reinforced column was more gradual with no strength degradation contrary to columns reinforced with longitudinal steel bars. The column behavior was patently influenced by longitudinal and transverse reinforcement ratio. The strain developed in transverse GFRP spirals and cross ties showed its effectiveness in confining the column core irrespective of the longitudinal bar type. Proposed displacement deformability index based on experiment showed reasonably good prediction for GFRP-reinforced concrete columns. The test results achieved comparable strength compared to North American design codes for columns reinforced with hybrid longitudinal steel and transverse GFRP reinforcement while the low elastic modulus of the GFRP longitudinal bar had a significant impact on the theoretical capacity of the concrete columns.La corrosion de l'armature d’acier dans les structures en béton est un problème sérieux et coûteux et qui réduit la durée de vie de l’ouvrage. L'utilisation des barres d’armature composites en polymère renforcé de fibres (PRF) offre une très bonne alternative pour les éléments en béton tels que les poutres et les dalles notamment en raison de leur résistance à la corrosion, de durabilité et de son rapport résistance / poids élevé par rapport aux barres d'acier traditionnelles. Cependant, il y a un manque d'information technique sur le comportement des colonnes en béton armé avec des barres en PRF sous charges sismiques. L'étude des colonnes en béton armé est utile pour la construction de nombreux ouvrages dont les bâtiments et les ponts. Actuellement, plusieurs colonnes d’ouvrages nécessitent des travaux de réhabilitation en raison de la détérioration des armatures d’acier (principalement des armatures transversales) due à la corrosion. Ainsi, des travaux expérimentaux sont nécessaires pour vérifier l’utilisation de barres en PRF comme armature longitudinale et transversale dans des colonnes en béton armé soumises à des charges latérales cycliques. La présente étude examine les performances expérimentales de colonnes en béton armé avec armature transversale en composite de polymère renforcé de fibres de verre (PRFV) de forme spirale en spirale et en épingle. Huit colonnes à pleine échelle ont été construites avec un renforcement entièrement en PRFV (armature longitudinale et transversale). Quatre autres colonnes ont été construites avec une armature hybride constituée d’armature d’acier longitudinale et d’armature transversale constituée de spirales et d’épingles en PRFV. Les colonnes ont une section transversale de 400 mm x 400 mm avec une hauteur totale de 1850 mm. Les colonnes ont été testées jusqu'à la rupture sous une charge axiale constante combinée à un chargement cyclique latéral. Les paramètres d’étude considérés sont : le type de barre longitudinale (PRFV et acier), le taux de renforcement longitudinal (1,48% et 2,14%), la grosseur des armatures transversales (#3-10 mm, #4-13 mm et #5-15 mm) et l'espacement des armatures transversales (100, 120 et 150 mm). Les performances globales de chaque colonne ont été examinées en termes de réseaux de fissuration, de la courbe d'hystérésis, de déformation dans les barres d'armature, de capacité de dissipation d'énergie, de taux de déplacement latéral et de résistance. Sur la base des résultats des essais, les colonnes en béton bien confinées avec de l’armature transversale en PRFV ont montré une performance stable correspondant à une capacité de déplacement latéral acceptable qui répond aux recommandations de la plupart des codes de conception. Le type de renforcement longitudinal (acier ou PRFV) a eu un impact significatif sur les performances des colonnes en termes de paramètres sismiques. La colonne renforcée avec de l’armature hybride constituée d’acier (armature longitudinale) et de PRFV (armature transversale) présentait une ductilité plus élevée et dissipait plus d'énergie que la colonne en béton armé entièrement en PRFV. La progression de la rupture dans les colonnes en béton armé d’armature en PRFV (armature longitudinale et transversale) était plus progressive et sans dégradation de la résistance contrairement aux colonnes en béton armé avec des barres d'acier longitudinales. Aussi, le comportement des colonnes a été clairement influencé par le taux d’armature longitudinale et transversale. La déformation développée dans les spirales transversales et les épingles en PRFV a montré l'efficacité de la spirale et des épingles en PRFV quel que soit le type de barre longitudinale de la colonne (acier ou PRFV). L'indice de déformabilité proposé en se basant sur les résultats expérimentaux obtenus a montré une bonne prédiction pour les colonnes en béton armé de PRFV. Les résistances des colonnes testées concordent très bien avec les prédictions des normes de conception nord-américains aussi bien pour les colonnes avec armature hybride ou entièrement en PRFV. Le module d'élasticité réduit de la barre longitudinale de GFRP a eu un impact significatif sur la capacité des colonnes de béton armé de PRFV

Evaluation on the axial compression mechanical properties of short BFRP laminated bamboo lumber columns

To investigate the effect of BFRP (basalt fiber) reinforced short laminated bamboo lumber (LBL) columns on axial compressive static performance, axial compression tests of twelve BFRP reinforced short LBL columns and three normal short LBL columns were conducted, and tensile tests of 13 BFRP were carried out. The test results show that the failure mode of BFRP reinforced short LBL columns was consistent with that of normal short LBL columns, buckling failure and adhesive layer failure. With the increase of BFRP cloth ratio, the bearing capacity of the columns increased. However, when the cloth ratio exceeded 2.3% (4 layers of BFRP), the average improvement of the load-bearing capacity was not obvious, and the reasonable cloth ratio was reached at 2.3%. The short LBL columns wrapped BFRP showed good compressive ductility, and the higher the cloth ratio of BFRP, the better the compressive ductility. Based on the suitable analysis of test data and referring to the relevant methods of fiber reinforced wood columns, the calculation model of axial compressive bearing capacity and stress-strain relationship model of BFRP reinforced short LBL columns were established. The comparison between theoretical calculation and experimental results verified the reliability and accuracy of the proposed bearing capacity calculation model and stress-strain model

Seismic Performance of Superelastic Shape Memory Alloy Reinforced Concrete Shear Wall Systems

A major sustainability issue for reinforced concrete (RC) structures is the residual deformations caused by the yielding of the steel bars during extreme seismic events. Numerous efforts have been made to develop self-centering structures, which minimize these deformations and the associated seismic damage. Superelastic shape memory alloys (SE-SMA) can be utilized in concrete elements to achieve such behaviour. This thesis focuses on the use of SE-SMA bars in RC walls. First, the thesis starts by conducting a fragility analysis to assess the seismic performance and vulnerability of ten and twenty-story SE-SMA RC walls. SE-SMA bars are used within the plastic hinge length of the walls and are assumed to replace all longitudinal steel bars or those reinforcing the boundary elements. The considered walls were found to possess an adequate margin of safety against collapse as compared to steel RC walls. Due to the unique properties of SE-SMA material, the ductility and overstrength factors for SE-SMA RC walls are then evaluated. Nine-hundred and seventy-two walls were analyzed to investigate the effects of different design parameters on the ductility and overstrength factors. Suggested values for the design factors were then evaluated by conducting nonlinear time history analyses for three, six, and nine-story buildings. The seismic performance of SE-SMA RC dual systems is evaluated. Incremental dynamic analysis is carried out under considering different seismic load events. Results allowed choosing a suitable SE-SMA layout for dual systems to achieve good seismic performance. The seismic performance of RC core walls is significantly different from rectangular RC walls because of their ability to resist bidirectional and torsional loading. The seismic performance of reinforced concrete core walls under unidirectional and bidirectional seismic excitations, while accounting for variations in the torsional eccentricity, was examined. SE-SMA bars reduced not only the mean lateral displacements but also the floor rotations. Finally, and to mitigate the seismic residual deformations and corrosion problems associated with steel RC walls, the seismic performance of walls reinforced with SE-SMA bars or hybrid (SMA-FRP) bars over the plastic hinge length and fiber-reinforced polymers (FRP) elsewhere is examined. The SMA-FRP bars resulted in a significant improvement in the wall capacity as compared to SE-SMA bars. Also, they resulted in lower seismic damage

Experimental Study on the Effect of Fibers on Engineered Cementitious Composite Short Square Columns

Recent earthquakes severely damaged short columns due to high lateral stiffness and low ductility. Some conditions, such as reductions in the heights of some columns compared to others on the same floor, deep beams, partially buried basements, and non-structural walls, cause short column effects. The prominent characteristics of engineered cementitious composites (ECCs) reinforced with polyvinyl alcohol (PVA) fibers – including their high tensile strength, micro and multiple cracks, energy dissipation, high ductility, and strain hardening – lead to improved seismic performance and economic efficiency in structure elements. In this study, 11 ECC columns with different fiber fractions (0–1.5%) and aspect ratios (3–7), as well as one conventional concrete column, were tested and evaluated. The results showed that increasing fiber friction and shear aspect ratio increased the length of the plastic hinge zone and ductility by at least 50% and 100%, respectively. Furthermore, the failure mode changed from brittle shear to ductile shear

Multi-objective optimal seismic design of buildings using advanced engineering materials

Although seismic safety remains a major concern of society--and unfortunately this observation has been underpinned by recent earthquakes--economy and sustainability in seismic design are growing issues that the engineering community must face due to increasing human population and excessive use of the earth???s nonrenewable resources. Previous studies have addressed the design and assessment of buildings under seismic loading considering a single objective, namely, safety. Seismic design codes and regulations also center on this objective. The goal of this study is to develop a framework that concurrently addresses the societal-level objectives of safety, economy and sustainability using consistent tools at every component of the analysis. To this end, a high-performance material; namely, engineered cementitious composites (ECC) is utilized. ECC is classified under the general class of fiber-reinforced concrete (FRC); however, ECC is superior to conventional FRC in many aspects, but most importantly in its properties of energy absorption, shear resistance and damage tolerance, all of which are utilized in the proposed procedure. The behavior of ECC is characterized through an experimental program at the small-scale (scale factor equal to 1/8). Numerical modeling of ECC is also performed to carry out structural level simulations to complement the experimental data. A constitutive model is developed for ECC and validated at the material, component and system levels. Additionally, a parametric study of ECC columns is performed to investigate the effect of material tensile properties on the structural level response metrics. Reducing the LCC of buildings (through reductions in material usage and seismic damage cost) is required to achieve the objectives of economy and sustainability. A rigorous LCC formulation that uses advanced analysis for structural assessment, and that takes into account all sources of uncertainty, is used along with an efficient search algorithm to compare the optimal design solutions. A novel aspect of this work is that three different structural frames are considered, RC, ECC and a multi-material frame in which ECC is deployed only at the critical locations (e.g. plastic hinges) to improve seismic performance. By considering the inelastic behavior of structures and incorporating all the required components, the proposed framework is generic and applicable to other types of construction such as bridges, to other innovative materials such as high performance steels, and to other extreme loading scenarios such as wind and blast.unpublishednot peer reviewe

Proceedings of IWAMISSE 2018 the International Workshop on Advanced Materials and Innovative Systems in Structural Engineering: Seismic Practices

The International Workshop on Advanced Materials and Innovative Systems in Structural Engineering: Seismic Practices, IWAMISSE 2018, is co-organised by The International Federation for Structural Concrete Turkey Branch, fib-Turkey, and Istanbul Technical University, ITU, on November 16, 2018 at ITU. The International Federation for Structural Concrete, fib, is a not-for-profit association formed by 45 national member groups and approximately 1000 corporate and individual members. The fib’s mission is to develop at an international level the study of scientific and practical matters capable of advancing the technical, economic, aesthetic and environmental performance of concrete construction. Istanbul Technical University (ITU) was established in 1773 and is a state university which defined and continues to update methods of engineering and architecture in Turkey. It provides its students with innovative educational facilities while retaining traditional values, as well as using its strong international contacts to mould young, talented individuals who can compete not only within their country borders but also in the global arena. With its educational facilities, social life and strong institutional contacts, ITU has always been preferred by Turkey’s most distinguished students since its foundation and has achieved justified respect. The workshop covers the topics of advanced materials and innovative systems in structural engineering with a focus on seismic practices as well as other issues related with steel fiber reinforced concrete, anchors/fasteners, precast structures, and recent advances on different types of structural systems such as reinforced concrete, steel, and reinforced masonry structures. This proceeding book contain sixteen papers from ten countries worldwide. We have no doubt that the up-to-date subjects covered during the workshop will be extremely beneficial for the workshop participants both from academia and industry. We would like to thank all authors for their contributions to the workshop as well as the members of the International Scientific Committee for their rigorous work for reviewing the papers. We also gratefully acknowledge the support of the sponsoring companies and we express our sincere thanks to organization committee for their tireless efforts in the overall organization of the workshop. Many thanks go as well to undergraduate and graduate students from ITU for their assistance during all stages of the workshop

Seismic Assessment, Repair and Retrofit of Existing Corroded Structures Using UHPC Jacketing

The bulk of our developed environment was constructed in the mid to late 20th century, when design codes did not address the importance of ductility and confinement, placing most of today’s concrete infrastructure in danger in case of a seismic event. Current assessment guidelines such as Eurocode 8-III or ASCE 41-17 take the lack of detailing into consideration in the assessment procedure however, they do not address a major concern, reinforcement corrosion. In this dissertation, modifications to current assessment guidelines were proposed and validated in order to take corrosion damage into consideration. Expressions for residual material properties as well as residual mechanical properties of columns were proposed with reinforcement mass loss being the only variable. The viability of using UHPC as both a strengthening and protective material against corrosion was studied in this dissertation. It was found that UHPC fully mitigates corrosion in case no service cracks were present and significantly reduces the corrosion rate in case of cracks between 0.5mm and 2mm were present. The final portion of the dissertation deals with repair and strengthening of corroded lap-spliced columns. Six lap-spliced columns designed based on pre-1970s design standards were constructed and subjected to artificial corrosion. Some of the specimens were tested without any prior strengthening intervention to simulate an earthquake damaging an existing column. They were then repaired using UHPC jacketing and re-tested under cyclic displacement reversals while other columns were strengthened after corrosion and then tested. This was done in order to study the increase in strength and ductility in case the strengthening was done prior to or after seismic activity. The results show a significant increase in strength and ductility of the columns, imparted by thin UHPC jackets replacing the conventional concrete cover