Abstract not available

This report details the design and construction of an AASHTO Type IV prestressed girder and a PCI BT-56 prestressed girder. It also details the shear testing and shear performance of the BT-56 girder. The results are compared with results from previous research dating back to 1986. Finally, all research was compared with the AASHTO Standard (2002), AASHTO LRFD (1998) and AASHTO LRFD (2004) Specifications to examine thier overall accuracy in predicting shear strengths.

Aging bridges in the United States demand effective, efficient, and economical strengthening techniques to meet future traffic requirements. One such technique is to bond steel or fiber reinforced polymer (FRP) plates to the tension faces of reinforced concrete bridge beams with adhesives to strengthen them in flexure. However, beams that have been flexurally strengthened in this manner often fail prematurely, in particular by plate end peeling. The benefits of flexural strengthening by externally bonded reinforcement can only be fully realized by preventing premature failure modes so as to allow the development of composite action between the beam and the external reinforcement. With this goal in mind, several critical limit states of externally reinforced beams are examined in this thesis. Models developed by Roberts (1989) and by Colotti, Spadea, and Swamy (2004) that predict premature plate end debonding are examined in depth using data from previously conducted experimental programs that employed both steel and FRP external reinforcement. In addition, various parameters of the concrete beam, adhesive, and external reinforcement are analyzed in each model to determine the role of each parameter in failure prediction. A critical appraisal of the performance of the models using existing experimental data leads to the selection of the Roberts (1989) model. This model is used to develop recommended design guidelines for flexurally strengthening reinforced concrete bridge beams with externally bonded FRP plates and for preventing premature plate peeling.

Ultra-High Performance Concrete (UHPC) is a new class of concrete characterized by no coarse aggregate, steel fiber reinforcement, low w/c, low permeability, compressive strength exceeding 29,000 psi (200 MPa), tensile strength ranging from 1,200 to 2,500 psi (8 to 17 MPa), and very high toughness. These properties make prestressed precast UHPC bridge girders a very attractive replacement material for steel bridge girders, particularly when site demands require a comparable beam depth to steel and a 100+ year life span is desired. In order to efficiently utilize UHPC in bridge construction, it is necessary to create new design recommendations for its use. The interface between precast UHPC girder and cast-in-place concrete decks must be characterized in order to safely use composite design methods with this new material. Due to the lack of reinforcing bars, all shear forces in UHPC girders have to be carried by the concrete and steel fibers. Current U.S. codes do not consider fiber reinforcement in calculating shear capacity. Fiber contribution must be accurately accounted for in shear equations in order to use UHPC. Casting of UHPC may cause fibers to orient in the direction of casting. If fibers are preferentially oriented, physical properties of the concrete may also become anisotropic, which must be considered in design. The current research provides new understanding of shear and shear friction phenomena in UHPC including: *Current AASHTO codes provide a non-conservative estimate of interface shear performance of smooth UHPC interfaces with and without interface steel. *Fluted interfaces can be created by impressing formliners into the surface of plastic UHPC. AASHTO and ACI codes for roughened interfaces are conservative for design of fluted UHPC interfaces. *A new equation for the calculation of shear capacity of UHPC girders is presented which takes into account the contribution of steel fiber reinforcement. *Fibers are shown to preferentially align in the direction of casting, which significantly affects compressive behavior of the UHPC.

Condition assessment of existing concrete bridge pier caps using the general shear provisions of the AASHTO LRFD Bridge Design Specification has caused the Georgia Department of Transportation (GDOT) to post a large number of bridges in the State of Georgia. Posting of bridges disrupts the free flow of goods within the region served by the bridge and has a negative economic impact. To prevent structural deterioration, diagonal cracking or failure of concrete pier caps in shear, the GDOT employs an in-situ strengthening technique that utilizes an external vertical post-tensioning system. However, the fundamental mechanics of this system and its effectiveness under service load have not been examined previously. This research examines the behavior of reinforced concrete pier caps that utilize the above strengthening system in a combined analytical and experimental program. In the experimental part of the study, two groups of full-scale reinforced concrete deep beam specimens were tested. The first group consisted of six deep beams with shear span/depth ratios of approximately 1.0, which is typical of bridge pier caps; of these six, two included the external post-tensioning system. In the second group, nine deep beam specimens that included a segment of the column representing the pier were tested; four of those tests included the external post-tensioning system. The tests revealed that the shear capacity computed using the AASHTO LRFD Bridge Design Specifications provided a conservative estimate of the specimen capacity in all but one case when compared to the experimental results. However, the AASHTO strut and tie provisions were found to provide a much closer assessment of the load carrying mechanism in the pier cap than the general shear provisions, in that they were able to predict the load at which yielding of the tension reinforcement occurred as well as the angle of the compression strut. The presence of the column segment in the second group had a significant impact on the failure mechanism developed in the specimen near ultimate load. The stress concentration at the reentrant corner between the pier cap and column interface served as an attractor for the formation of diagonal shear cracks, a mechanism not observed in previous deep beam tests in shear. The research has led to recommendations for improving the design of pier caps and the external post-tensioning system, where required, based on mechanics which are consistent with the results of the experimental program.

The shear capacity of reinforced concrete pier caps in existing bridge support systems can be a factor which limits the capacity of an existing bridge. In their usual configuration, pier caps behave as deep beams and have the ability to carry load through tied arch action after the formation of diagonal cracks. Externally bonded fiber reinforced polymer (FRP) reinforcement has been shown to increase the shear capacity of reinforced concrete members which carry load through beam action. However, there is an insufficient amount of research to make it a viable strengthening system for beams which carry load through arch action, such as pier caps. Accordingly, this research was aimed at investigating the behavior of reinforced concrete pier caps through a coordinated experimental and analytical program and to recommend an external strengthening method for pier caps with perceived deficiencies in shear strength. The experimental study was performed on laboratory specimens based on an existing bridge in Georgia. A number of factors were examined, including size, percentage longitudinal reinforcement and crack control reinforcement. The results showed that increasing the longitudinal tension reinforcement increased the beam capacity by changing the shape of the tied arch. In contrast, the presence of crack control reinforcement did not change the point at which diagonal cracking occurred, but it did increase the ultimate capacity by reinforcing the concrete against splitting. The results of the experimental study were used in conjunction with a larger database to examine different analytical methods for estimating the ultimate capacity of deep beams, and a new method was developed for the design of external strengthening. Two specimens were tested with externally bonded FRP reinforcement applied longitudinally to increase the strength of the tension tie. The test results correlated well with the proposed method of analysis and showed that increasing the strength of the longitudinal tension tie is an effective way to increase the strength of a reinforced concrete deep beam.

A special problem in many reinforced concrete structures built in the 1970s and earlier is the lack of continuity between elements. Continuity is a characteristic of structures essential to preventing collapse. Therefore, in extreme loading conditions such as loss of a column support due to terrorist attack or if earthquake or other extreme actions occur, the structures could be vulnerable to collapse. The study reported here focused on two structural discontinuities in existing reinforced concrete structures, discontinuity in bottom reinforcement in beams (horizontal discontinuity) and poorly detailed lap splices in columns (vertical discontinuity). The objective of this study was to develop rehabilitation methods using CFRP to provide continuity of reinforcement in existing structures. To develop the rehabilitation methods, two separate experimental studies were conducted using beam and column specimens. CFRP materials were applied to the bottom or side face of a beam and anchored using CFRP anchors or U-wraps to provide horizontal continuity in bottom reinforcement and tested under dynamic loading. After CFRP rehabilitation, the ductility of the bottom reinforcement and large rotational capacity of the beam were realized. CFRP materials were also applied to the lap splice region in square and rectangular columns which exhibited a brittle splice failure as-built. After rehabilitating the columns using CFRP jackets and anchors, the failure mode changed from a brittle splice failure to yield of column reinforcement, and the strength and deformation capacity were improved under both monotonic and cyclic loading. Based on the results of beam and column tests, design guidelines for CFRP rehabilitation were proposed. Horizontal and vertical continuities can be provided through the use of CFRP for rehabilitating existing reinforced concrete structures that were designed prior to the introduction of codes that require continuous reinforcement along members and between adjacent members. The vulnerability of such structures to collapse can be reduced through rehabilitation. / text

Modelling behaviour of cracked tensile concrete is a complicated issue. Due to bond with reinforcement, the cracked concrete between cracks carries a certain amount of tensile force normal to the cracked plane. Concrete adheres to rein-forcement bars and contributes to overall stiffness of the structure. The phe-nomenon, called tension-stiffening, has significant influence on the results of short-term deformational analysis. Assumption of a tension-stiffening law has great influence on numerical results of load – deflection behaviour of reinforced concrete members subjected to short – term loading. Under wrong assumption of this law, errors in calculated deflections, particularly for lightly members, may exceed 100 %. Most known tension-stiffening relationships relate average stresses to average strains. However, some experimental and theoretical investi-gations have shown that tension-stiffening may be affected by other parameters. The scientific supervisor of the thesis has proposed a tension-stiffening model depending on reinforcement ratio. This model has been developed using experi-mental data reported in the literature. Besides, concrete shrinkage effect was not taken into account. The main objective of this PhD dissertation is to propose a tension-stiffening law for bending RC members subjected to short-term loading with eliminated concrete shrinkage effect. / Gelžbetonis yra kompozitinė medžiaga, kurios komponentai yra betonas ir plieninė armatūra. Kaip žinoma, betono stipris tempiant yra 10-20 kartų mažesnis nei stipris gniuždant. Atrodytų, kad tempiamojo betono įtaka, atlaikant įrąžas skerspjūvyje, yra nereikšminga. Iš tiesų, nustatant lenkiamųjų elementų stiprumą normaliniame pjūvyje, tempiamo betono įtempių galima nevertinti. Kita vertus, skaičiuojant įlinkius, neįvertinus tempiamojo betono įtakos, gali būti daroma didesnė nei 100 % paklaida. Adekvatus supleišėjusio tempiamojo betono įtakos įvertinimas, nustatant trumpalaike apkrova veikiamų gelžbetoninių elementų deformacijas, yra bene svarbiausia ir sudėtingiausia problema. Plyšio vietoje betonas negali atlaikyti tempimo įtempių, todėl visą įrąžą atlaiko armatūra. Kadangi plyšyje ir gretimuose pjūviuose armatūra praslysta betono atžvilgiu, kontakto zonoje atsiranda tangentiniai įtempiai. Šie įtempiai perduodami betonui, todėl jis atlaiko tempimo įtempius. Armatūros ir betono sąveika ruožuose tarp plyšių standina gelžbetoninį elementą. Supleišėjusio betono gebėjimas atlaikyti tempimo įtempius vadinama tempimo sustandėjimu (angl. tension stiffening). Šis efektas dažniausiai modeliuojamas supleišėjusio betono įtempių ir deformacijų diagrama, taikant vidutinių plyšių koncepciją. Tuomet neatsižvelgiama į diskrečius plyšius, o supleišėjęs betonas traktuojamas kaip ortotropinė medžiaga su pakitusiomis savybėmis. Dauguma tempimo sustandėjimo modelių įvertina betono įtempių... [toliau žr. visą tekstą]

The ability to adjust structural response to external loading and ensure structural safety and serviceability is a characteristic of Smart Systems. The key to achieving this is through the development and implementation of smart materials. An example of a smart material is a Shape Memory Alloy (SMA). Reinforced concrete structures are designed to sustain severe damage and permanent displacement during strong earthquakes, while maintaining their integrity, and safeguarding against loss of life. The design philosophy of dissipating the energy of major earthquakes leads to significant strains in the steel reinforcement and, consequently, damage in the plastic hinge zones. Most of the steel strain is permanent, thus leading to large residual deformations that can render the structure unserviceable after the earthquake. Alternative reinforcing materials such as superelastic SMAs offer strain recovery upon unloading, which may result in improved post-earthquake recovery. Shape Memory Alloys have the ability to dissipate energy through repeated cycling without significant degradation or permanent deformation. Superelastic SMAs possess stable hysteretic behavior over a certain range of temperature, where its shape is recoverable upon removal of load. Alternatively, Martensite SMAs also possess the ability to recover its shape through heating. Both types of SMA demonstrate promise in civil infrastructure applications, specifically in seismic-resistant design and retrofit of structures. The primary objective of this research is to investigate experimentally the performance of concrete beams and shear walls reinforced with superelastic SMAs in plastic hinge regions. Furthermore, this research program involves complementary numerical studies and the development of a proposed hysteretic constitutive model for superelastic SMAs applicable for nonlinear finite element analysis. The model considers the unique characteristics of the cyclic response of superelastic materials.

Conselho Nacional do Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A utilização de diferentes tipos de lajes na execução de prédios altos vem crescendo muito nos últimos anos no mercado brasileiro. A têndência dos edifícios terem uma arquitetura arrojada e esbelta, trazem para a engenharia o desafio de executar uma estrutura com diferentes modelos e métodos executivos, e como consequencia surgem as dificuldades em garantir a estabilidade global das edificações. A escolha do tipo de laje e a inclusão de um núcleo rígido em estruturas de um edifício de múltiplos pavimentos é uma escolha importante, sendo que análise de estabilidade global de edificações são, diretamente, influenciadas por essa escolha. A avaliação da estabilidade global de estruturas de concreto armado, normatizada pela norma brasileira ABNT NBR 6118:2014, é realizada através dos parâmetros de estabilidade global parâmetro α (alfa) e coefiente γz (Gama Z), além do processo iterativo P-Delta. Nesta pesquisa buscou-se estudar a estabilidade global em edificações de múltiplos pavimentos com diferentes tipos de lajes e inclusão de núcleos rigidos, para a modelagem foi utilizado o programa comercial CAD/TQS. Os resultados evidenciaram que a estrutura com laje maciça se mostrou mais rígida comparada a estruturas com laje pré-fabricada e laje nervurada, obtendo menores valores de coefiente Gama Z e a inclusão do núcleo rígido aumentou, consideravelmente, a rigidez de todas as estruturas analisadas. / The use of different types of slabs in the execution of high buildings has been increasing a lot in recent years in the Brazilian market. The buildings have a bold and slender architecture, they bring to the engineering the challenge of executing a structure with different models and executive methods, and as a consequence arise the difficulties in guaranteeing the overall stability of the buildings. The choice of slab type and the inclusion of a rigid core in multi-floor building structures is an important choice, and global stability analysis of buildings are directly influenced by this choice. The evaluation of the global stability of reinforced concrete structures, normalized by the Brazilian standard ABNT NBR 6118: 2014, is performed through the global stability parameters parameter α (alpha) and coefficient γz (Range Z), in addition to the iterative P-Delta process. In this research, we tried to study the global stability in multi-floor buildings with different types of slabs and inclusion of rigid cores. For the modeling, the commercial CAD / TQS program was used. The results showed that the structure with solid slab was more rigid compared to structures with prefabricated slab and ribbed slab, obtaining lower values of Coefiente Gama Z and the inclusion of the rigid core considerably increased the rigidity of all structures analyzed.