Dissertations / Theses on the topic 'Lap-splices'

Non-contact lap splices placed within a single concrete placement are often used and have been studied in previous research projects. However, non-contact lap splices used with each bar in a different concrete placement such that there is a cold joint between the bars, have not been investigated. This situation is found in the repair of adjacent box beam bridges and in the construction of inverted T-beam systems, among others. It is vital to understand whether the same mechanisms are present across a cold joint with two different types of concrete as are present in traditional non-contact lap splices. In this research, eight T-beam specimens with non-contact lap splices were tested. The spacing between the bars, the splice bar blockout length, and presence of transverse bars were varied to study the effectiveness of the splices. The beams were tested in four point bending so that the splice region was under constant moment and the tension forces in the spliced bars were constant. End and midspan deflections were measured along with surface strain measurements at midspan and at the quarter span points, top and bottom. Gap openings were also measured at the ends of the blockouts. The main conclusions found from this research are that beams containing non-contact lap splices were able to develop nominal capacity with the bar spacing less than or equal to 4 in. and the blockout between 17 and 20 in. long. Extending the blockouts and adding transverse bars underneath the splices did not add to the capacity.
Master of Science

The results of an investigation into the performance of reinforced concrete beam-column subassemblages containing lap spliced reinforcement in the potential plastic hinge region of a beam are presented. Two specimens were tested with simulated seismic loading. One specimen complied with the New Zealand Concrete Design Code, NZS 3101:1982, except for the placement of the lap splices. The second specimen contained beam reinforcement details from a building constructed in the early 1960s. Current concrete design codes specify lap splices should not be placed in beam potential plastic hinge regions where inelastic reversing stresses are possible during seismic events. During testing the transverse steel specified for the confinement of the lap splices was unable to prevent bond deterioration between the spliced bars once inelastic bar strains had developed at one end of the splice. The failure of the lap splices led to a loss of lateral load capacity and a low level of ductility from the specimen. Reinforced concrete buildings designed to pre-1970s codes may be considered inadequate when viewed in light of the provisions in current codes for seismic design. The testing of beam details taken from one such building indicates insufficient anchorage existed for the plain longitudinal beam bars in the joint. The loss of bond for the plain bars began in the initial load cycles of the test and led to a lack of specimen stiffness and lateral load capacity. The presence of the lap splices is considered to have accelerated the loss of bond from the bars. Testing investigating the performance available from plain bar reinforced subassemblages should use anchorage for the bars that represent the conditions in the existing structure. The rapid loss of bond from the bars during cyclic loading can lead to the member end connections influencing the test results.

Thesis (M.S. in in civil engineering)--Washington State University, December 2009.
Title from PDF title page (viewed on Jan. 26, 2010). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 42).

assessed and strengthened. Performance evaluation of deficient buildings has become a major concern due to devastating earthquakes in the past. In order to justify new provisions in design and assessment codes, experiments and analyses are inherently necessary. In this thesis study, investigations into the behaviour of two deficient reinforced concrete frames built at Middle East Technical University&rsquo
s Structural and Earthquake Laboratory and tested via pseudo-dynamic tests were made. These frames were modelled on the OpenSees platform by following methods of analyses outlined in the Turkish Earthquake Code of 2007 (TEC 2007) and ASCE/SEI-41-06. Both deficient frames were essentially the same, with the only difference being the presence of insufficient lap splices, which was the focus of the study. Time history performance assessments were conducted in accordance to TEC 2007&rsquo
s damage state limits and ASCE/SEI 41-06&rsquo
s performance limits. The damages observed matched the performance levels estimated through the procedure outlined in TEC 2007 rather well. Specific to the specimen with lap splice deficiencies, ASCE/SEI 41-06 was overly conservative in its assessments. TEC 2007&rsquo
s requirements for lap splice lengths were found to be conservative in the laboratory and are able to tolerate deficiencies up to 25% of the required length. With respect to mathematical models, accounting for materials in deficient systems by using nominal but reduced strength properties is not very efficient and unless joint deformations are explicitly accounted for, local deformations cannot be captured.

The use of light-weight building materials in modern construction has resulted in efficient designs and considerable cost savings by reducing structural weight and supporting sections. This has only been possible because of many years of research to better understand the properties of the light-weight material, and its structural behaviors. However, light-weight grout is a relatively new building material in reinforced masonry construction and little is known about its structural properties. The main objective of this study was to determine if the use of light-weight grout would impact the performance of reinforcing steel, specifically development length, in masonry construction.The research included testing masonry wallettes made with normal and light-weight grout containing No. 4 (12 mm) bars with splice lengths as prescribed by the current design equation as well as splices with a modification factor. The modification factor was based on preliminary grout testing, using the procedure given in the concrete building code. The wallettes were tested in a tension test to determine if the splices were of sufficient length to fully develop the yield stress of the reinforcement.For small bar sizes, No. 4 or smaller, it is not necessary to include a modification factor when calculating development length. The minimum length of lap of 12 in. governs when No. 4 or smaller bars are used, and provides sufficient length to fully develop the yield stress of the reinforcement both for normal and light-weight grout types.

The effectiveness of a new structural material, namely textilereinforced mortar (TRM), was investigated experimentally in this study as a means of confining old-type reinforced concrete columns with limited capacity due to bar buckling or due to bond failure at lap splice regions. Comparisons with equal stiffness and strength fiber-reinforced polymer (FRP) jackets allow for the evaluation of the effectiveness of TRM versus FRP. Tests were carried out on full scale non-seismically detailed RC columns subjected to cyclic uniaxial flexure under constant axial load. Thirteen cantilever-type specimens with either continuous longitudinal reinforcement (smooth or deformed) or lap splicing of longitudinal bars at the floor level were constructed and tested. Experimental results indicated that TRM jacketing is quite effective as a means of increasing the cyclic deformation capacity of old-type RC columns with poor detailing, by delaying bar buckling and by preventing splitting bond failures in columns with lap spliced bars. Compared with their FRP counterparts, TRM jackets used in this study were found to be equally effective in terms of increasing both the strength and deformation capacity of the retrofitted columns. From the response of specimens tested in this study, it can be concluded that TRM jacketing is an extremely promising solution for the confinement of reinforced concrete columns, including poorly detailed ones with or without lap splices in seismic regions.

Cantilevered reinforced concrete columns with a lap splice of the longitudinal reinforcement near the base can induce high moment demands on the splice region when lateral loads are present on the structure. Code design specifications typically require a conservative splice length to account for these high moment demands and their consequences of bond failure. The required splice length is calculated as a function of required development length, which is a function of the bond between the reinforcement and the surrounding concrete, and a factor depending on the section detailing. However, the effects of concrete deterioration due to alkali silica reaction (ASR) and/or delayed ettringite formation (DEF) may weaken the bond of the splice region enough to overcome the conservative splice length, potentially resulting in brittle failure of the column during lateral loading. This thesis presents the following results obtained from an experimental and analytical program. * Fabrication of large-scale specimens of typical column splice regions with concrete that is susceptible to ASR/DEF deterioration * Measurement of the large-scale specimen deterioration due to ASR/DEF accelerated deterioration * Analytical model of the column splice region based on flexure theory as a function of the development length of the reinforcement and a factor to account for deterioration of the bond due to ASR/DEF * Experimental behavior of two large-scale specimens that are not influenced by premature concrete deterioration due to ASR/DEF (control specimens). This experimental data is also used to calibrate the analytical model. The conclusions of the research are that the analytical model correlates well with the experimental behavior of the large-scale control specimens not influenced by ASR/DEF. The lap splice region behaved as expected and an over-strength in the splice region is evident. To account for ASR/DEF damage, the analytical model proposes a reduction factor to decrease the bond strength of the splice region to predict ultimate performance of the region with different levels of premature concrete deterioration.

Many existing bridges were built before modern seismic design guidelines were written. This means that particularly in countries with moderate seismicity where another type of loads such as gravity, wind or snow are more demanding, the seismic hazard may have been underestimated in the past years. Past experience shows that critical details, including lap-splices on the potential plastic hinge region above the foundation and low transverse reinforcements ratios, can lead to a small deformation capacity of the existing bridge piers and therefore to a possible major structural damage. The performance of RC members featuring lap splices was extensively studied in the past. However, a large number of authors focused on the force capacity of lap splices while their deformation capacity was rather neglected. This topic has become a target of interest only recently. This dissertation represents the first part of a research project developed at École Polytechnique Fédérale de Lausanne that has the final goal of presenting a constitutive law capable of predicting the lap splice behavior, in particular its deformation capacity. The dissertation presents an experimental campaign regarding the lap splice performance under cyclic loading. This experimental campaign gives continuity to the experimental campaigns presented by Bimschas (2010) and Hannewald et al. (2013), where three large-scale piers featuring lap splices near the foundation were tested. Three specimens representing a boundary region of the previously specimens are presented in this dissertation. The test specimens subjected to the same cyclic load history only differ regarding the transversal reinforcement. Particular attention is given to the slippage between the rebars and the steel strains in the lap splice zone. These tests along with the results of future specimens intend to create a database that will allow to validate the future expression mentioned above.

Twelve large-scale reinforced concrete (RC) specimens were tested at Purdue University’s Bowen Laboratory to evaluate the deformability of structural walls with longitudinal lap splices at their bases. Eight specimens were tested under four-point bending and four specimens were tested as cantilevers under constant axial force and cyclic reversals of lateral displacement. All specimens failed abruptly by disintegration of the lap splice, irrespective of what loading method was used or what splice details were chosen. Previous work on lap splices has focused mainly on splice strength. But, in consideration of demands requiring structural toughness (e.g. blast, earthquake, differential settlement), deformability is arguably more important than strength.

Approximations of wall drift-strain relationships are presented in combination with estimates of splice strength and deformability to provide lower-bound drift capacity estimates for RC walls with lap splices at their bases. Deformations in slender structural walls (with aspect ratios larger than 3) are controlled by flexure. Shear deformations must be considered for walls with smaller aspect ratios. For slender walls with lap splices comparable to those tested, the observations collected suggest that drift capacities can be as low as 0.5%. That is: splices with minimum concrete cover, minimum transverse reinforcement (0.25% transverse reinforcement ratio) terminating in hooks, and lap splice lengths selected to reach yielding in the spliced bars (approximately 60 bar diameters for splices of Grade-60 reinforcement) can fail as yield is reached or soon after. For splices of the same length, doubling the amount of hooked transverse reinforcement increases deformation capacity by nearly 50%. By maintaining the same transverse reinforcement ratio but confining splices with closed hoops (instead of hooks), deformation capacity nearly doubles. Increasing splice length increases the expected splice strength but also increases the strain required to reach the same drift ratio.

Evidence from this and similar experimental programs suggests that lap splices with minimum cover and confined only by minimum transverse reinforcement terminating in hooks should not be used in critical sections of structural walls when toughness is required. To prevent abrupt failure during events that demand structural toughness, it is recommended that lap splices be shifted away from locations where yielding in structural walls is expected.

The development of current design standards for reinforced concrete beams containing lap splices has been mainly aimed at preventing failures due to static (monotonic) loading, or low cycle, high intensity (seismic) loading. However, little consideration has been given in these standards or in previous research to the performance of lap splices when subjected to high cycle, low intensity (fatigue) loading. Also, recently proposed design equations for lap splices under static loading will permit shorter lap lengths. For these reasons, a study was initiated to investigate the fatigue resistance of reinforced concrete beams with lap splices. A principal variable in this research program was the degree of transverse reinforcement (stirrups) which was provided along the lap splice. The specimens used in this experimental program were seven meters in length, with a cross section 330 mm wide and 508 mm deep, and were reinforced with two No. 30 Grade 400 bars, top and bottom. A lap splice was provided in the bottom tension bars situated in a constant moment region created by a symmetrical two point loading system. The lap splice length and confinement were designed according to ACI Committee 408 recommendations for static loading. Two different lap splice configurations were provided for the test specimens. The first used the maximum number of stirrups that were deemed to be effective for static loading, permitting a shorter lap length. In the second configuration nominal stirrups were provided to the splice at a spacing of one half the effective beam depth, requiring a longer lap length. Failure of the specimens with the heavier stirrups occurred from fatigue of the tensile reinforcing steel and showed similar fatigue resistance to beams containing continuous reinforcement. The specimens with nominal stirrups usually resulted in a splice failure after fewer load cycles, after splitting and delamination of the concrete confining the lap had occurred. Both beams had a similar static bond resistance; however, the beams with the heavier stirrup confinement (shorter lap length) displayed a greater fatigue resistance than the beams with lighter stirrups (longer lap length). These results are in agreement with conclusions reached for seismic loading conditions, which found that splice confinement provided by a high degree of transverse reinforcement is required under cyclic loading to offset the rapid deterioration of the concrete cover confinement.

A previously completed study in the field of concrete block construction by Ahmed and Feldman (2012) indicated that, on average, the reinforcing bars in non-contact lap splices, where the lapped bars are located in adjacent cells, only develop 71% of the tensile resistance of spliced bars which are in contact. An experimental program was therefore initiated to design and evaluate remedial measures which can potentially increase the tensile resistance of non-contact lap splices to that of contact lap splice of the same lap length. Implementation of the proposed measures in various field situations was also analyzed. Six unique remedial splice details, along with standard contact and unaltered non-contact lap splices were evaluated and compared. The mitigative details included providing additional confinement, installing knock-out webs, placing splice reinforcement between the lapped bars, and combinations of these aforementioned details. Three replicates of each splice detail were constructed for a total of 24 wall splice specimens. Each wall splice specimen was reinforced with No. 15 Grade 400 deformed steel reinforcing bars with 200 mm lap splice lengths at located the midspan. The specimens were tested in a horizontal position under a monotonic, four-point loading geometry. Load and deflection data were collected throughout testing and were subsequently used in an iterative moment-curvature analysis to calculate the maximum tensile resistance of the spliced reinforcement. This was then used to compare the structural performance of each remedial splice detail to the standard contact and non-contact lap splices. The wall splice specimens which contained non-contact lap splices with knock-out webs, s-shaped, and transverse reinforcement in the splice region achieved similar tensile capacities as the wall splice specimens with standard contact lap splices. Industry professionals have indicated that the installation of the remedial measures evaluated in this study would not affect the constructability of masonry assemblages in field situations. The splice detail with knock-out webs confined within the lap splice length was determined to be the most viable procedure as it can be installed to increase the resistance of non-contact lap splices in almost all construction situations. This remedial procedure was able to improve the tensile resistance of the lapped reinforcement by 63% compared to the wall splice specimens with standard non-contact lap splices.

Thesis (M.S.)--University of Wisconsin--Madison, 1999.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 78-80).

Reinforced concrete bridge columns can deteriorate prematurely due to the alkali-silica reaction (ASR) and/or delayed ettringite formation (DEF), causing internal expansion and cracking on the surface of the concrete. The performance of the longitudinal reinforcement lap splice in deteriorated concrete columns is the focus in this research. This thesis presents the results from the deterioration of large-scale specimens constructed and placed in an environment susceptible to ASR/DEF deterioration, the experimental results from four-point and three-point structural load tests, and an analytical model based on bending theory characterizing the specimen behavior during the structural load tests. Fourteen large-scale specimens were constructed, placed in an environment to accelerate the ASR/DEF deterioration mechanisms, and instrumented both internally and externally to measure the internal concrete expansions, and surface expansions and crack widths. In addition, two control specimens were constructed and kept in a laboratory, preventing ASR/DEF deterioration. Post-tensioning was used to simulate axial load on a bridge column. Structural load tests were performed on eight specimens with no ASR/DEF damage to late stage ASR and minimal DEF damage. Comparing the specimen behaviors during the loading testing, it was found that the yield strength increased about 5-15%, and post-cracking stiffness up to first yielding of the deteriorated specimens was about 25-35% stiffer than the control specimens. The increased specimen strength and stiffness likely occurred from volumetric expansion due to ASR/DEF damage which engaged the reinforcement, further confining the concrete and causing a beneficial increase in the axial post-tensioning load. The analytical model matched the control specimens well and matched the non-control specimens when the axial load was increased.

碩士
國立中央大學
土木工程學系
86
The concept of Strong-Column-Weak-Beam is adopted by construction design code currently in which the plastic hinge occurs on the beam-column joint. This phenomenon will induce the decay of strength and stiffness, effect the whole earthquake resistant behavior of intersection. Decreasing the decay of the stiffness of intersection can be performed by the moving of the plastic hinge from the intersection of beam-column. The purpose of this paper is to apply the lap-splices of beam steel bars on the beam-column joint in order to remove the plastic hinge to decrease the damage of joint. Four full-scale beam-column joint specimens including three specimens produced by high strength concrete(HSC) and one by common concrete are prepared for the investigation of the effect of the lap-splices of steel bars on the behavior of HSC beam-column joint. From the observation of the result of experiment, the arrangement of the lap-splices of beam steel bars can remove the plastic hinge from the surface of column. The bonding force of steel bar is well developed in HSC and it decreases the slippage of steel bar either. If the specifications about lap-splices of code are taken, the steel bar with larger diameter would produce high shear stress on the joint and increase the damage of the joint due to the longer length of lap-splice. Therefore, the length of lap-splice is important to the behavior of whole joint. Well confining effect of concrete of the joint is fulfilled if the tie bar is produced by high tension steel. Furthermore, the adoption of HSC offers positive contribution to the joint.

The tensile resistance of No. 15 lap spliced reinforcing bars with varying transverse spacing and lap splice length was evaluated in full-scale concrete block wall splice specimens. The range of the transverse spacing between bars was limited to that which allowed the bars to remain within the same cell, and included the evaluation of tied spliced bars in contact. Two-and-a-half block wide by three course tall double pullout specimens reinforced with contact lap splices were initially used to determine the range of lap splice length values to be tested in the wall splice specimens such that bond failure of the reinforcement occurred. The double pullout specimens were tested in direct tension with six replicates per arrangement. Three values of lap splice length: 150, 200, and 250 mm, were selected from the testing of the double pullout specimens and tested in the wall splice specimens in combination with three values of transverse spacing: 0, 25, and 50 mm, with three replicates per configuration. A total of twenty-seven two-and-a-half block wide by thirteen course tall wall splice specimens reinforced with two lap splices were tested in four-point loading. Both the double pullout and the wall splice specimens were constructed in running bond with all cells fully grouted. The tensile resistance of the lap spliced bars in the double pullout specimens was measured directly. The contact lap splices with a 150, 200, and 250 mm lap splice length developed approximately 38, 35 and 29% of the theoretical yield load of the reinforcement, respectively. The difference between the mean tensile resistances of the three reinforcement configurations tested in the double pullout specimens was found to be statistically significant at the 95% confidence level. Different than expected, the tensile resistance of the lap spliced reinforcing bars in the double pullout specimens was inversely proportional to the lap splice length provided. For the short lap splice lengths used in this investigation, the linear but not proportional relationship between bond force and lap splice length known from reinforced concrete is believed to have caused this phenomenon. An iterative sectional analysis using moment-curvature response was used to calculate the tensile resistance of the lap spliced reinforcement in the wall splice specimens. The calculated mean tensile resistance of the reinforcement increased with increasing lap splice length, and was greater when the bars were in contact. Securing the bars in contact may have influenced the tensile capacity of the contact lap splices as higher stresses are likely to develop as a result of the bar ribs riding over each other with increasing slip. Results of the data analysis suggest that the tensile resistance of non-contact lap splices within the same cell is generally independent of the spacing between the bars. A comparison of the experimental results for the wall splice specimens with the development and splice length provisions in CSA S304.1-04 and TMS 402-11 indicate that both the Canadian and U.S. design standards are appropriate for both contact and non-contact lap splices located within the same cell given the limited test database included in this investigation.

Post-earthquake examinations of reinforced concrete structures often show structural damage resulting from bond and shear failures. Such failures typically occur in reinforced concrete elements with details known to cause problems, such as widely spaced transverse reinforcement and/or lap splices located in regions of flexural yielding. These details are common in older reinforced concrete buildings (built before 1970) that have reinforced concrete columns with longitudinal reinforcement spliced just above the floor level, and transverse reinforcement spaced at a distance of d/2 or longer. This investigation focused on means to increase the deformability of existing reinforced concrete elements susceptible to bond and shear failures during a seismic event or other applications requiring toughness. The effects of confinement provided by epoxied anchors, spiral transverse reinforcement, and post-tensioned external clamps were investigated. Emphasis was placed on producing a strengthening device that can be sized, fabricated, and installed with ease because most of the existing strengthening techniques require specialized labor, tools, and materials. The observations collected support the idea that active confinement provided by post-installed and post-tensioned transverse reinforcement was the most effective method to improve structural deformability among the methods studied and within the ranges considered.

Past earthquake damage assessments have shown the seismic vulnerability of older non-ductile reinforced concrete buildings. The life safety-risk these buildings pose has motivated researchers to study, develop, and improve modeling techniques to better simulate their behavior with the aim to prioritize retrofits.

This study focuses on the lap splice detailing at the base of the building in columns, shorter than those recommended by modern codes which consider seismic effects. Current modeling efforts in non-ductile reinforced concrete frame structures have considered the connection at the foundation fixed. This study models the influence of the performance of short lap splices on the simulation of response of an instrumented perimeter-frame-non-ductile building located in Van Nuys, California, and to compare results with those of previous studies of the same building.

The methodology consisted of evaluating the response of a non-ductile concrete building subjected to a suite of ground motions through the comparison of three base connections: fixed, pinned, and a rotational spring modeling the short lap splice. Comparison and performance evaluation are done on the basis of drift as the main performance metric. In the building response evaluation flexure and shear forces in frame elements were also compared using the different base conditions.

The models consist of two-dimensional frames in orthogonal direction, including interior and exterior frames, totaling into 4 frames. The dynamic analysis was performed using SAP2000 analysis software. The proposed rotational spring at the base was defined using the Harajli & Mabsout (2002) bond stress – slip relationship and moment – curvature sectional analysis, applied to 24d_b and 36d_b lap splices. Deformation considered flexure and slip. Adequacy of shear strength was checked prior to the analysis to verify that shear failure did not occur prior to either reaching first yield of the column reinforcement or splice capacity.

In this study, the response of the frames using the proposed rotational spring model was found to be between the fixed and pinned base conditions with regard to roof displacement and interstory drift ratio, also termed as story drift ratio. The behavior of the frames changed depending on the yielding of the longitudinal reinforcement, as depicted by the interstory drift ratio and displacement. The performance of the building frames also depended on the ground motion. The N-S and E-W direction frame computational models considered three and four earthquakes, respectively, totaling to 14 computational models per base condition. Three computational models out of the 14 with the proposed rotational spring base condition simulated recorded roof displacement results with accuracy. In the frame simulations where yielding of most of the column longitudinal bars was not calculated, the maximum interstory drift occurred in the upper stories, matching column damage observations during the event. The findings of the study showed that short lap splice increases the drift and displacement compared to the fixed base supporting its effect, i.e. the behavior of a non-ductile reinforced concrete case study building to an earthquake.

Design of autoclaved aerated concrete (AAC) masonry in the United States is currently based on Appendix A of the 2008 Masonry Standards Joint Committee (MSJC) Code. Those provisions include the design of lap splices, and equations for the nominal capacity in interface shear transfer between grout and AAC. The provisions for lap splices are an extension of the provisions for concrete or clay masonry, modified to neglect the contribution of AAC to splice capacity. This thesis describes a testing program aimed at verifying the current provisions using tests of lap splices in grouted AAC masonry. Based on the results of those tests, the provisions are shown to be appropriate. The provisions on interface shear transfer between grout and AAC require that the transferred shear be checked against a nominal capacity based on limited test results. This thesis describes a testing program aimed at verifying and refining this nominal capacity using pullout tests of grout cores in AAC masonry units. Based on the results of those tests, the currently used nominal capacity is shown to be conservative, and a recommendation is made to increase it.
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Ένα από τα κύρια προβλήματα που συναντώνται σε κτίρια ή γέφυρες που έχουν κατασκευασθεί πριν από το 1980, είναι η μειωμένη καμπτική αντοχή και πλαστιμότητα, το οποίο αρκετά συχνά οφείλεται στην έλλειψη περίσφιξης και στη παρουσία κοντών αναμονών που είχαν οι κατασκευές αυτές. Ο κύριος σκοπός της παρούσας διατριβής είναι να παρουσιάσει και να αξιολογήσει πέντε από τα διαθέσιμα στη βιβλιογραφία αναλυτικά μοντέλα προσδιορισμού του απαιτούμενου πάχους του εξωτερικά εφαρμοζόμενου μανδύα για την αποφυγή της αστοχίας των ματιζομένων οπλισμών των υποστυλωμάτων συμπεριλαμβανομένου και του αντίστοιχου μοντέλου το οποίο δίνεται στο Σχέδιο 1 και Σχέδιο 2 του ΚΑΝΕΠΕ. Τα αναλυτικά μοντέλα αξιολογούνται μέσω πειραματικών αποτελεσμάτων από τη βιβλιογραφία. Η αξιολόγηση γίνεται σε δύο επίπεδα. Στο πρώτο επίπεδο αξιολογείται η αξιοπιστία πρόβλεψης του απαιτούμενου πάχους του υλικού ενίσχυσης –χρησιμοποιώντας τις μέσες τιμές των υλικών- ενώ στο δεύτερο επίπεδο εξετάζεται η αντίστοιχη καταλληλότητα κάθε προσομοιώματος για το σχεδιασμό –χρησιμοποιώντας τις αντίστοιχες τιμές σχεδιασμού των υλικών-. Τροποποιημένες εξισώσεις βασιζόμενες στο προσομοίωμα του ΚΑΝΕΠΕ παρουσιάζονται. Η χρήση των τροποποιημένων εξισώσεων ελέγχεται μέσω διαθέσιμων πειραματικών αποτελεσμάτων και προκύπτει ικανοποιητική σύγκλιση με αυτά.
Reinforced concrete frames or bridges constructed in the early 80s or before, were usually designed and detailed to resist lower lateral forces than those required today. Building columns were commonly designed for compression only and as a result they do not have the adequate lateral strength to resist the imposed earthquake loads. One of the main deficiencies in these older structures is the limited flexural strength and ductility often due to short and lightly confined lap splices. The main aim of this thesis is to present and evaluate five of the proposed analytical models in order to rehabilitate reinforced concrete columns with short lap splices by external confinement, including and the confinement model given by the draft version of the Greek Retrofitting Code (GRECO). The above analytical models are validated against experimental results. The validation is performed in two levels. In the first level, the reliability of the prediction for the required jacket thickness given by the models, is examined, by using the average values of the materials. In the second level, the propriety for the design of each model is examined by using the design values of the materials. A modified equation based on the model given by GRECO is presented as well. By using the proposed modified equation a satisfactory agreement with the experimental results was accomplished.

Στην παρούσα διδακτορική διατριβή αναπτύσσεται μια νέα τεχνική ενίσχυσης υποστυλωμάτων οπλισμένου σκυροδέματος με βάση τη χρήση συνθέτων υλικών, τα οποία αποτελούνται από πλέγματα ινών σε ανόργανη μήτρα (π.χ. κονίαµα µε βάση το τσιμέντο), αποσκοπώντας στην επίλυση προβλημάτων που χαρακτηρίζουν τα Ινοπλισμένα Πολυμερή (ΙΟΠ) σχετικά µε τη χρήση εποξειδικών ρητινών. Τα Ινοπλέγματα σε Ανόργανη Μήτρα (ΙΑΜ) δοκιμάζονται στη μορφή μανδύα µε στόχο την περίσφιγξη και την αύξηση της πλαστιμότητας υποστυλωμάτων παλαιού τύπου, σχεδιασμένων δηλαδή χωρίς τις νέες αντισεισμικές λεπτομέρειες όπλισης. Εξετάζονται διάφορες παράμετροι, που περιλαμβάνουν τη χρήση ράβδων λείων ή με νευρώσεις, την πιθανή ένωση των ράβδων με υπερκάλυψη στον πόδα των υποστυλωμάτων και το μήκος υπερκάλυψης. Έτσι προσδιορίζεται η αποτελεσματικότητα των μανδυών ΙΑΜ και συγκρίνεται με αυτή τον ΙΟΠ ως μέσου περίσφιγξης στις κρίσιμες περιοχές υφισταμένων υποστυλωμάτων για όλες τις περιπτώσεις καμπτικών αστοχιών στην περιοχή της πλαστικής άρθρωσης. Το πειραματικό πρόγραμμα που ακολουθείται για την απόκτηση δεδομένων γύρω από τη συμπεριφορά υποστυλωμάτων οπλισμένου σκυροδέματος, ενισχυμένων με μανδύες ανόργανης (ΙΑΜ) ή οργανικής (ΙΟΠ) μήτρας, περιλαμβάνει συνολικά 28 δοκιμές επί δοκιμίων υποστυλωμάτων δύο τύπων: (α) 15 πρισματικά δοκίμια οπλισμένου σκυροδέματος που δοκιμάζονται σε κεντρική θλίψη και (β) 13 δοκίμια υποστυλωμάτων πλήρους κλίμακας, τα οποία δοκιμάζονται σε ανακυκλιζόμενη κάμψη με σταθερό αξονικό φορτίο. Καταδεικνύεται ότι η αποτελεσµατικότητα των µανδυών ΙΑΜ είναι υψηλή και γενικώς παρόµοια µε αυτή των µανδυών ΙΟΠ για όλες τις περιπτώσεις που εξετάστηκαν. Επιπροσθέτως, τα πειραματικά αποτελέσματα των 13 υποστυλωμάτων πλήρους κλίμακας που υποβλήθηκαν σε ανακυκλιζόμενη κάμψη (με σταθερό αξονικό φορτίο), συμβάλλουν στη διερεύνηση δύο ακόμα “θολών” μέχρι σήμερα πεδίων, όπως: (α) Ο λυγισμός των διαμήκων ράβδων σε περισφιγμένο με μανδύες ΙΑΜ ή ΙΟΠ σκυρόδεμα. Ιδιαίτερη έμφαση δίνεται στη μελέτη της αλληλεπίδρασης μεταξύ του μανδύα ΙΑΜ ή ΙΟΠ και των διαμήκων ράβδων, κατά την έναρξη και εξέλιξη του λυγισμού των τελευταίων. (β) Η αντοχή σε συνάφεια μεταξύ των ενωμένων με παράθεση ράβδων και του περισφιγμένου με μανδύες ΙΑΜ ή ΙΟΠ σκυροδέματος. Ιδιαίτερη έμφαση δίνεται στην πειραματική και αναλυτική μελέτη του μηχανισμού με τον οποίο η περίσφιγξη με μανδύες ΙΟΠ και ΙΑΜ συνεισφέρει στη βελτίωση των συνθηκών συνάφειας μεταξύ ράβδων οπλισμού και σκυροδέματος. Ακόμα στην παρούσα διδακτορική διατριβή διεξάγεται η πρώτη συστηματική μελέτη καμπτικής ενίσχυσης υποστυλωμάτων υπό ανακυκλιζόμενη κάμψη (και σταθερό αξονικό φορτίο) με Πρόσθετους Οπλισμούς νέου τύπου σε Εγκοπές (ΠΟΕ). Εξετάζονται υποστυλώματα που έχουν ενισχυθεί με πρόσθετο οπλισμό ινοπλισμένων πολυμερών (ελάσματα άνθρακα ή ράβδους γυαλιού) καθώς και με ράβδους ανοξείδωτου χάλυβα τοποθετημένων σε εγκοπές. Άλλη μια καινοτομία που εισαγάγει η παρούσα διατριβή είναι ο συνδυασμός του ΠΟΕ με τοπικούς μανδύες ινοπλεγμάτων σε ανόργανη μήτρα (IAM), οι οποίοι αποτελούν ένα εξαιρετικά αποτελεσματικό και πολλά υποσχόμενο σύστημα περίσφιγξης, όπως αναπτύσσεται και περιγράφεται λεπτομερώς στην παρούσα διδακτορική διατριβή. Η έρευνα που υλοποιείται για την απόκτηση δεδομένων γύρω από τη συμπεριφορά υποστυλωμάτων οπλισμένου σκυροδέματος ενισχυμένων σε κάμψη με ΠΟΕ, περιλαμβάνει τη διεξαγωγή 11 δοκιμών επί υποστυλωμάτων πλήρους κλίμακας, τα οποία υποβάλλονται σε ανακυκλιζόμενη κάμψη υπό σταθερό αξονικό φορτίο. . Καταδεικνύεται ότι μέσω ενός κατάλληλου σχεδιασμού, στα πλαίσια του οποίου ο ΠΟΕ συνδυάζεται με τοπικό μανδύα στα άκρα του υποστυλώματος (κορυφή και πόδα), είναι εφικτό η αύξηση της καμπτικής αντίστασης των υποστυλωμάτων να μην συνοδεύεται από μείωση της διαθέσιμης ικανότητας παραμόρφωσης. Τα χρήσιμα πειραματικά ευρήματα από τα ενισχυμένα με ΠΟΕ υποστυλώματα, συμπληρώνονται με την ανάπτυξη ενός αναλυτικού και υπολογιστικού προσομοιώματος, το οποίο έχει διττή συμβολή, καθώς επιτρέπει: (α) την εκτέλεση παραμετρικών αναλύσεων ώστε να μελετηθεί σε βάθος και χωρίς κόπο (πειραματικές δοκιμές) η επίδραση όλων σχεδόν των παραμέτρων, στην καμπτική αντίσταση των ενισχυμένων με ΠΟΕ υποστυλωμάτων. (β) Τη χρήση του ως πολύτιμου υπολογιστικού εργαλείου από το Μηχανικό για το σχεδιασμό καμπτικών ενισχύσεων υποστυλωμάτων με ΠΟΕ και / ή μανδύες συνθέτων υλικών. Η αξία της συμβολής του εν λόγω προσομοιώματος μεγιστοποιείται αν ληφθούν υπόψη ορισμένα χαρακτηριστικά του όπως: (1) Η μείωση των ροπών αντοχής ως προς τους δύο κύριους άξονες (ισχυρός και ασθενής), η οποία οφείλεται στην έντονη σύζευξή τους, για τα ενισχυμένα σε κάμψη υποστυλώματα που υποβάλλονται σε διαξονική κάμψη. (2) Η εφαρμογή ενός τραπεζοειδούς στερεού τάσεων για το σκυρόδεμα σε θλίψη, το οποίο σε σύγκριση με το κλασικό ορθογωνικό στερεό, προσομοιώνει με αρκετά μεγαλύτερη ακρίβεια τον όγκο του σκυροδέματος της θλιβόμενης ζώνης, ιδιαίτερα για τις ενισχυμένες διατομές. (3) Η ταυτόχρονη δράση της εξωτερικής περίσφιγξης με μανδύες συνθέτων υλικών στις ενισχυμένες σε κάμψη διατομές.
The effectiveness of a new structural material, namely Textile-Reinforced Mortar (TRM), was investigated experimentally in this PhD Thesis as a means of confining old-type reinforced concrete (RC) columns with limited capacity due to bar buckling or due to bond failure at lap splice regions. Comparisons with equal stiffness and strength fiber-reinforced polymer (FRP) jackets allow for the evaluation of the effectiveness of TRM versus FRP. Tests were carried out on nearly full scale non-seismically detailed RC columns subjected to cyclic uniaxial flexure under constant axial load. Thirteen cantilever-type specimens with either continuous or lap-spliced deformed longitudinal reinforcement at the floor level were constructed and tested. Experimental results indicated that TRM jacketing is quite effective as a means of increasing the cyclic deformation capacity of old-type RC columns with poor detailing, by delaying bar buckling and by preventing splitting bond failures in columns with lap-spliced bars. Compared with their FRP counterparts, the TRM jackets used in this study were found to be equally effective in terms of increasing both the strength and deformation capacity of the retrofitted columns. From the response of specimens tested in this study, it can be concluded that TRM jacketing is an extremely promising solution for the confinement of RC columns, including poorly detailed ones with or without lap splices in seismic regions. Moreover this PhD Thesis presents the results of a large-scale experimental program aiming to study the behavior of RC columns under simulated seismic loading, strengthened in flexure (of crucial importance in capacity design) with different types and configurations of near-surface mounted (NSM) reinforcing materials. The role of different parameters is examined, by comparison of the lateral load versus displacement response characteristics (peak force, drift ratios, energy dissipation, stiffness). Those parameters were as follows: carbon or glass fiber-reinforced polymers (FRP) versus stainless steel; configuration and amount of NSM reinforcement; confinement via local jacketing; and type of bonding agent (epoxy resin or mortar). The results demonstrate that NSM FRP or stainless steel reinforcement is a viable solution towards enhancing the flexural resistance of reinforced concrete columns subjected to seismic loads. With proper design, which should combine compulsory NSM reinforcement with local jacketing at column ends, it seems that column strength enhancement does not develop at the expense of low deformation capacity.