Alkali silica reaction (ASR) and delayed ettringite formation (DEF) are two causes of concrete deterioration. Both mechanisms cause expansion of concrete and thus extensive cracking. Most previous research on ASR and DEF focused on understanding the material science of the mechanisms. This dissertation adds to the smaller body of knowledge about ASR/DEF’s effect on the structural behavior of reinforced concrete columns. It compares the structural performance of ASR/DEF affected concrete columns to mechanically cracked columns, evaluates the relative performance of four different concrete repair methods for strengthening damaged columns, and describes how to model pre-existing cracks in the finite element program ATENA. Previous research on scaled columns used mechanically cracked concrete as an approximation of ASR/DEF cracking damage. These earlier column tests, by Kapitan, were compared to two columns affected by ASR/DEF. Due to a deficiency in original design of the actual columns modeled, all of these scaled column specimens failed in bearing during testing under biaxial bending. The ASR/DEF affected columns exhibited nearly identical performance (including bearing capacity) as Kapitan’s control specimen. Thus, with over one percent expansion due to ASR/DEF, there was no reduction in bearing capacity for these columns. Based on the bearing failure observed in these scaled column specimens, concrete repairs were designed to increase confinement of the column capital to address the bearing capacity deficiency. A series of bearing specimens was constructed, externally reinforced using four different strengthening schemes, and load tested. From this bearing specimen series, both an external post-tensioned repair and a concrete jacketing repair performed well beyond their designed capacities and are recommended for bearing zone confinement repair of similar ASR/DEF affected concrete columns. Further, this dissertation presents how Kapitan’s scaled column results were modeled using ATENA (a reinforced concrete finite element program). A technique for modeling the mechanical cracking was developed for ATENA. Once calibrated, a parametric study used the model to find that a 0.17-inch wide through-section crack in the scaled columnd (5/8 inches in the field) was the threshold that reduced capacity of the scaled column to the factored design load. / text

Reinforced concrete deep beams are vital structural members serving as load transferring elements. The behavior of reinforced concrete deep beams is complex. Nonlinear distribution of strain and stress must be considered. Prior to 1999, ACI 318 Codes included an empirical design equation for reinforced concrete deep beams. Since 2002, the strut and tie model and nonlinear analysis have been required. However, both methods have disadvantages of complexity or lack of transparency. The objective of this study is to produce a simple, reliable design equation for reinforced concrete deep beams. A nonlinear finite element program, ATENA, was used for analyzing and predicting the behavior of concrete and reinforced concrete structures. First, applicability of ATENA was verified by developing the computer models of simply supported and two span continuous deep beams based on Birrcher’s tests of simply supported deep beams. Tests by Rogowsky and Macgregor and by Ashour are the basis for the models of continuous two span deep beams. Those tests were selected because the researchers reported adequate details of the experimental program and on specimen behavior. Then a series of simply supported and two span continuous deep beam models were developed based on the details and geometry of Birrcher's beams. The computer models were used to investigate the following parameters: the compressive strength of concrete, shear span to depth ratios, longitudinal reinforcement ratios, web reinforcement, effect of member depth, and loading conditions. Finally, a proposed design equation for shear strength of reinforced concrete deep beams was derived based on the observed the behavior of reinforced concrete deep beam tests, the results of the analytical study, and a plastic truss model. The proposed equations were in good agreement with test values and provide an alternate approach to current design procedures for deep beams. / text

Ductile plastic hinge zones in beams of reinforced concrete frames are known to incur extensive damage and elongate. This ‘beam elongation’ can inflict serious damage to adjacent floor diaphragms, raising concerns of life safety. In light of this, the slotted reinforced concrete beam was investigated as a promising non-tearing floor substitute for conventional design. It consists of a conventional reinforced concrete beam, modified with a narrow vertical slot adjacent to the column face, running approximately three-quarters of the beam depth. Seismic rotations occur about the remaining concrete “top-hinge”, such that deformations are concentrated in the bottom bars of the beam, away from the floor slab, and beam elongation is minimised. The inclusion of the slot raised several design issues which needed to be addressed. These were the shear transfer across the top-hinge, buckling of bottom longitudinal reinforcement, low cycle fatigue, bond anchorage of reinforcement in interior joints, interior joint design, detailing with floor units and beam torsion resulting from eccentric floor gravity loads. These issues were conceptually investigated in this project. It was found that most issues could be resolved by providing additional reinforcement and/or specifying alternative detailing. As part of the experimental investigation, quasi-static cyclic tests were performed on in-plane beam-column joint subassemblies. Specimens tested included exterior and interior joint subassemblies with slotted-beams and a conventional exterior joint as a benchmark. This was followed by a test on a slotted-beam interior joint subassembly with precast floor units and imposed gravity load. Experimental tests revealed significant reductions in damage to both the beam and floor when compared to conventional beams. Issues of bar buckling, bond-slip and altered joint behaviour were also highlighted, but were resolved in the final test. A simple analytical procedure to predict the moment-rotation response of slotted-beams was developed and verified with experimental results. This was used to perform sensitivity studies to determine appropriate limits for the concrete top-hinge depth, top-to-bottom reinforcement ratio and depth of diagonal shear reinforcement. For the numerical investigation, a multi-spring model was developed to represent the flexural response of slotted-beams. This was verified with experimental tests and implemented into a five-storey, three-bay frame for earthquake time history analyses. To provide a benchmark, a conventional frame was also setup using the plastic hinge element developed by Peng (2009). Time history analyses showed that the slotted-beam frame response was very similar to the response of a conventional frame. Due to greater hysteretic damping, there was a slight reduction in the average interstorey drift and lateral displacement envelopes. The slotted-beam frame also exhibited 40% smaller residual drifts than the conventional frame. The research carried out in this thesis showed slotted reinforced concrete beams to be an effective non-tearing floor solution, which could provide a simple and practical substitute for conventional reinforced concrete design.

The recent earthquakes in Christchurch have made it clear that issues exist with current RC frame design in New Zealand. In particular, beam elongation in RC frame buildings was widespread and resulted in numerous buildings being rendered irreparable. Design solutions to overcome this problem are clearly needed, and the slotted beam is one such solution. This system has a distinct advantage over other damage avoidance design systems in that it can be constructed using current industry techniques and conventional reinforcing steel. As the name suggests, the slotted beam incorporates a vertical slot along part of the beam depth at the beam-column interface. Geometric beam elongation is accommodated via opening and closing of these slots during seismically induced rotations, while the top concrete hinge is heavily reinforced to prevent material inelastic elongation. Past research on slotted beams has shown that the bond demand on the bottom longitudinal reinforcement is increased compared with equivalent monolithic systems. Satisfying this increased bond demand through conventional means may yield impractical and economically less viable column dimensions. The same research also indicated that the joint shear mechanism was different to that observed within monolithic joints and that additional horizontal reinforcement was required as a result. Through a combination of theoretical investigation, forensic analysis, and database study, this research addresses the above issues and develops design guidelines. The use of supplementary vertical joint stirrups was investigated as a means of improving bond performance without the need for non-standard reinforcing steel or other hardware. These design guidelines were then validated experimentally with the testing of two 80% scale beam-column sub-assemblies. The revised provisions for bond within the bottom longitudinal reinforcement were found to be adequate while the top longitudinal reinforcement remained nominally elastic throughout both tests. An alternate mechanism was found to govern joint shear behaviour, removing the need for additional horizontal joint reinforcement. Current NZS3101:2006 joint shear reinforcement provisions were found to be more than adequate given the typically larger column depths required rendering the strut mechanism more effective. The test results were then used to further refine design recommendations for practicing engineers. Finally, conclusions and future research requirements were outlined.

Baigiamajame magistro darbe nagrinėjami sijų, paveiktų gaisro temperatūros, stiprinimo būdai. Darbą sudaro septyni skyriai ir priedai. Pirmame skyriuje nagrinėjama gaisro temperatūrų įtaka gelžbetonio komponentams (armatūrai ir betonui). Antrame skyriuje apžvelgiama sijų elgsena ir suirimo priežastys gaisro metu. Trečiajame skyriuje aptariami galimi gelžbetoninių sijų stiprinimo būdai. Ketvirtajame atliekamas temperatūrinių laukų kompiuterinis modeliavimas sijos skerspjūvyje. Penktame ir šeštame skyriuose skaičiuojami gaisro temperatūrų paveikti ir sustiprinti elementai. Septintame skyriuje apibendrinami darbo rezultatai ir suformuluojamos darbo išvados bei pasiūlymai. Darbo apimtis - 106 psl. teksto be priedų, 79 iliustr., 5 lent., 21 bibliografiniai šaltiniai. Atskirai pridedami darbo priedai. / The final paper deals with beams, exposed fire-temperature strengthening mechanisms. The work consists of seven chapters and annexes. The first section examines fire temperature on reinforced concrete components (concrete and reinforcement). The second chapter discusses behavior of reinforced concrete beams and possible collapse reasons. The third section discusses possible ways of strengthening reinforced concrete beams. The fourth chapter consist of computer based temperature analysis of reinforced concrete beam cross-section. In the fifth and sixth chapters fire temperatures are calculated to affect and enhance elements. The seventh chapter summarizes the findings and formulating working conclusions. Working volume – 106 pages. text without appendixes, 79 pictures., 5 tables., 21 bibliographic sources. Appendixes.

Damage to reinforced concrete bridges due to carbonation and chloride induced corrosion is widespread in South Africa and prone in environments where carbon dioxide is at high levels as well as in marine environments where chlorides are present. Performance specifications are therefore essential in order that structural concrete can be designed and constructed to the required standards ensuring that the long term durability can be maintained. This dissertation includes a review of SANRAL‘s current durability specifications. The specifications are critiqued in terms of the testing methodology followed as well as strength and environmental exposure considerations, and recommendations are made for improving the specifications. The literature review, outlines the background to both carbonation and chloride induced corrosion to reinforced concrete bridges , considering the fundamental causes of deterioration of concrete caused by carbonation and chloride ingress and repair costs during their service life. The South African Durability Index tests are presented and reviewed, in particular the laboratory testing apparatus and procedures. In addition, the index tests are compared with durability test methods currently being used internationally. The background and previous durability specifications used in South Africa on road bridges as well as details of research into specifications to ensure durable concrete with specific emphasis on curing of concrete is summarised. The indications are that performance based specifications for concrete on bridge structures internationally follow similar criteria to the specifications currently being adopted by SANRAL. Both performance and prescriptive specifications used usually depend on the risk that a constructor needs to carry. Importantly both cement extenders to ensure long term durability and penalties are applied in performance based durability. SANRAL‘s current durability specifications are reviewed and both the negatives and positives are presented for the various sections. Amendments to the Committee of Land Transport Officials (COLTO) standard specifications are recommended address shortcomings. The latest project specifications used on SANRAL contracts incorporating target requirements for cover and oxygen permeability are evaluated. These impose penalties if targets are not achieved, while limits are placed on chloride conductivity values for various blended binders. Data is also included for the sorptivity index values on the five projects which may analysed and target values can be set and implemented in future. Descriptions of the five projects with regard to durability specifications, their environmental exposure condition and concrete mix designs are presented. Five projects in KwaZulu-Natal, are used as case studies for durability tests and specifications. The only distinct difference in the specifications is that the three projects commencing in 2006 and early in 2007 had the target values for water sorptivity whereas for the project, sorptivity values are only reported on. Durability index testing results at each of the sites from the trial panels, additional test cubes (cast for coring and testing of durability indexes) as well as coring and testing from the bridge structures are presented. A major change is coring and testing of samples from trial panels and additional test cubes on the site instead of coring of the structure. The information is drawn together and relationships are determined between the various durability indexes as well as to strength. It is evident that the quality of concrete as constructed in the structure which is reflected by the durability index results is different to that produced in the test cubes and trial panels. It is deduced that while more care is being taken to produce quality concrete on the sites, certain aspects of the specifications need revision in order to remove confusion as well as to ensure that the concrete in the structure meets the target requirements. Finally it is noted that climate change is having an impact on design of bridge infrastructure, and while the surveys undertaken at Ethekwini and Msunduzi Municipalities shows that carbon dioxide levels being recorded are still average levels, worldwide there has been an increase in CO2 levels and further modifications to specifications in future may be required. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Corrosion of reinforcing bars is the major cause of deterioration of reinforced concrete (RC) structures in North America, Europe, the Middle East, and many coastal regions around the world. This deterioration leads to a loss of serviceability and functionality and ultimately affects the structural safety. The objective of this research is to formulate and implement a general stochastic finite element analysis (SFEA) framework for the time-dependent reliability analysis of RC beams with corroding flexural reinforcement. The framework is based on the integration of nonlinear finite element and reliability analyses through an iterative response surface methodology (RSM). Corrosion-induced damage is modelled through the combined effects of gradual loss of the cross-sectional area of the steel reinforcement and the reduction bond between steel and concrete for increasing levels of corrosion. Uncertainties in corrosion rate, material properties, and imposed actions are modelled as random variables. Effective implementation of the framework is achieved by the coupling of commercial finite element and reliability software. Application of the software is demonstrated through a case study of a simply-supported RC girder with tension reinforcement subjected to the effects of uniform (general) corrosion, in which two limit states are considered: (i) a deflection serviceability limit state and (ii) flexural strength ultimate limit state. The results of the case study show that general corrosion leads to a very significant decrease in the reliability of the RC beam both in terms of flexural strength and maximum deflections. The loss of strength and serviceability was shown to be predominantly caused by the loss of bond strength, whereas the gradual reduction of the cross-sectional area of tension reinforcement was found to be insignificant. The load-deflection response is also significantly affected by the deterioration of bond strength (flexural strength and stiffness). The probability of failure at the end of service life, due to the effects of uniform corrosion-induced degradation, is observed to be approximately an order of magnitude higher than in the absence of corrosion. Furthermore, the results suggest that flexural resistance of corroded RC beams is controlled by the anchorage (bond) of the bars and not by the yielding of fully bonded tensile reinforcement at failure. This is significant since the end regions can be severely corroded due to chloride, moisture, and oxygen access at connections and expansion joints. The research strongly suggests that bond damage must be considered in the assessment of the time-dependent reliability of RC beams subjected to general corrosion.

No description available.

Les propriétés généralement demandées aux armatures pour béton armé doivent répondre à des exigences particulières précisées dans des normes nationales, européennes et internationales. Actuellement, dans la pratique de la production de l'acier à béton, on tend à substituer différentes nuances d'armature par une armature unifiée ayant une valeur de limite d'élasticité minimale de 500 MPa. Le remplacement des ronds à béton de nuance 400MPa par cette armature conduit à une économie de métal de l'ordre de 10-20 % d'après les estimations de différents spécialistes.Il existe, généralement, plusieurs techniques de fabrication des armatures, dont la déformation à chaud suivie d'un refroidissement accéléré sous flux d'eau (traitement thermomécanique ou Thermomechanical Control Process - TMCP), ainsi que la déformation à froid (tréfilage â travers une filière conique et une filière à rouleaux, microlaminage...), qui se heurte cependant â l'impossibilité de satisfaire aux exigences des Normes vis-à-vis des propriétés de résistance (Re > 500MPa) et de plasticité.Le présent travail a pour but le développement d'un procédé combiné de production d'acier à béton profitant des aspects positifs de deux types de déformation à chaud ainsi qu'à froid, sous forme du traitement combiné mécano-thermomécanique (post déformations à froid après le TMCP). et d'étudier la possibilité de production d'aciers à béton de qualité 500 MPa (B(A)500), de petits diamètres, en couronne, répondant aux exigences des Normes modernes. L'objectif scientifique de ce travail est d'étudier les mécanismes microstructuraux qui se produisent lors de la déformation à froid de l'acier préalablement traité thermomécaniquement et leurs conséquences sur l'évolution des propriétés mécaniques.Plusieurs nuances d'acier bas carbone de différents diamètres ont été étudiées. De nombreuses techniques de caractérisation macroscopique et microscopique de la structure de l'acier ont été utilisées: traction monotone, essais de microdureté, microscopie optique, microscopie électronique â balayage (MEB) et en transmission (MET), diffraction des rayons X. spectrométrie mécanique..Les résultats des essais montrent qu'il est possible d'obtenir avec assurance l’armature de qualité B(A)500, possédant des propriétés mécaniques qui dépassent les exigences des nonnes, à l'aide d’une déformation par torsion avec un cisaillement maximal de 22%, pour des aciers à 0.15 -0.2 % C(en poids), faiblement alliés en Mn et Si et traités themomécaniquement. La déformation par torsion provoque une augmentation de dureté en surface mais aussi au cœur de l'armature. Cette augmentation de dureté à cœur peut être amplifiée par le traitement thermique de vieillissement à 100°C correspondant à l'utilisation en Génie Civil. Cet effet, lié aux interactions dislocation-impuretés interstitielles, a été expliqué grâce â la MET et à l'étude du frottement intérieur. / Properties which are required from an armature for the reinforced concrete should satisfy the requirements of National, European and International standards. At the present time, in practice of armature production, there is a tendency of replacement of various classes of reinforcing steels by the unified armature with the minimum value of yield strength of 500 MPa. Replacement of the armature of the 400 MPa class by such reinforcing steel brings the economy of metal of an order of 10-20 % according to the estimations of various experts.In general, a set of production technologies of the armature exists, including hot deformation with the subsequent accelerated cooling in water - Thermomechanical Control Process (TMCP), and also cold deformation (drawing in conic die block, drawing in roller die block, microrolling) which nevertheless face the impossibility to provide the required strength (yield strength > 500MPa) and plastic properties.The technological purpose of the given work is:- development of the combined mechano-thermomechanical processing of armature's production which would combine positive aspects of hot and cold deformations (post deformation processing after TMCP);- examination of possibilty to manufacture the reinforcing steel of the class of 500MPa (B(A)500) of the small diameter, in coils, meeting the requirements of modem standards.The scientific objective of the work is the analysis of change of the microstructure of reinforcing steels after the cold deformation which is preliminary subjected to thermomechanical processing, and, also, the examination of the influence of microstructural effect on change of mechanical properties of steels.In the present study, a significant quantity of grades of low-carbon steels of various diameters has been investigated. Also, different techniques for macroscopical and microscopical characterization of the steel structures have been applied: tensile tests, micro-hardness test, optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray analysis and mechanical spectroscopy.Results of tests show that it is possible to obtain, with assurance, the reinforcing steel of the strength class B(A)500, with a complex of the mechanical properties surpassing the requirements of standards. For this purpose it is proposed to use the deformation by cold torsion with the maximum relative shear of 22 %, after thermomechanical processing, for steels with carbon content of 0,15...0,25% and alloyed with Mn and Si. Deformation by torsion provides an increase of hardness not only on the surface, but also in the core of armature. The effect of hardness increase can be strengthened by means of thermal ageing at 100°C corresponding to the use in Civil Engineering. This effect, related to the dislocations- interstitial impurities interactions, was explained thanks to MET and internal friction effect.

The high cost of repairing reinforced or prestressed concrete structures due to steel corrosion has driven engineers to look for solutions. Much research has been conducted over the last two decades to evaluate the use of Fiber Reinforced Polymers (FRPs) in concrete structures. Structural engineering researchers have been testing FRP to determine their usability instead of steel for strengthening existing reinforced concrete structures, reinforcing new concrete members, and for prestressed concrete applications. The high strength-to-weight ratio of FRP materials, especially Carbon FRP (CFRP), and their non-corrosive nature are probably the most attractive features of FRPs. In this study, an experimental program was conducted to investigate the flexural behavior of prestressed concrete beams pre-tensioned with CFRP strands. The bond characteristics were examined by means of experimentally measuring transfer length, flexural bond length, and bond stress profiles. A total of four rectangular beams pre-tensioned with one 0.5-in. diameter CFRP strand were fabricated and tested under cyclic loading for five cycles, followed by a monotonically increasing load until failure. In investigating bond properties, the experimental results were compared to the equations available in the literature. The results from the four flexural tests showed that the main problem of CFRP strands, in addition to their liner-elastic tensile behavior, was lack of adequate bonding between FRP and concrete. Poor bonding resulted in early failure due to slippage between FRPs and concrete. As a result, a new technique was developed in order to solve the bonding issues and improve the flexural response of CFRP prestressed concrete beams. The new technique involved anchoring the CFRP strands at the ends of the concrete beams using a new "steel tube" anchorage system. It was concluded that the new technique solved the bond problem and improved the flexural capacity by about 46%. A computer model was created to predict the behavior of prestressed beams pre-tensioned with CFRP. The predicted behavior was compared to the experimental results. Finally, the experimental results were compared to the behavior of prestressed concrete beams pre-tensioned with steel strands as generated by the computer model. The CFRP beams showed higher strength but lower ductility.