Column Jacketing Research Articles

변형경화형 시멘트 복합체를 사용한 프리캐스트 끼움벽의 내진성능

지진이 빈번하게 발생하는 지역에서는 비내진상세구조물은 지진 발생시 연약층을 형성하고 취성적 붕괴를 일으키게 된다. 그러나, 기존 구조물을 해체하고 내진상세 구조물을 신축하는 방법은 건설폐기물, 환경오염 및 민원 등 여러가지 문제들을 가지는 등 비경제적 방법이라 할 수 있다. 따라서 기존 구조물이 내진성능을 만족하도록 내진보강에 관한 많은 연구가 이루어졌으며, 이러한 내진보강방법에는 끼움벽, 철골브레이스, 연속벽, 부벽, 날개벽, 기둥/보의 자켓팅 등이 있다. 이 중 끼움벽 골조는 큰 변형과 접합부에서의 회전이 발생하는 골조와, 비교적 작은 변형에서도 전단파괴를 야기하는 끼움전단벽 등 복합적인 거동특성을 나타낸다. 따라서, 이러한 시스템의 거동특성은 개개의 골조나 벽에서 나타나는 거동특성과 매우 다르게 된다. 본 연구에서는 끼움벽의 내진성능을 평가하고자 하였으며, 손상에너지의 효과적 흡수를 위해 변형경화형 시멘트 복합체 (SHCC)를 사용하였다. 실험은 1/3 축소모형의 끼움벽을 반복가력하는 것으로 계획하였다. 실험 결과, SHCC 끼움벽에서는 섬유의 가교작용을 통해 시멘트 복합체 내 응력을 재분배함으로써 미세균열이 발생하였으며, 강도 및 에너지소산능력이 우수한 것으로 나타났다.

Temperature controllable hplc column for preparative fractionation of polymers

An HPLC column with a self-contained temperature control device was constructed for preparative temperature programmed interaction chromatography. Two Peltier plates were attached to a large bore column (120×22 mm i.d.) and the column temperature was controlled by PID mode feed back control. At a flow rate of 1.5 mL/min, the column temperature could be increased and decreased at a rate as high as 50 °C/min and 10 °C/min, respectively, which is much faster than using a column jacket and bath/circulator. The rapid heating and cooling rates allows a high repetition rate of chromatographic fractionation. The performance of the temperature controllable column was demonstrated successfully by the fractionation of homo-polymer precursors from diblock copolymers.

Columns for gas chromatography: performance and selection

Preface. Acknowledgments. 1 Introduction. 1.1 Evolution of Gas Chromatographic Columns. 1.2 Central Role Played by the Column. 1.3 Justification for Column Selection and Care. 1.4 Literature on Gas Chromatographic Columns. 1.5 Gas Chromatographic Resources on the Internet. References. 2 Packed Column Gas Chromatography. 2.1 Introduction. 2.2 Solid Supports and Adsorbents. Supports for Gas-Liquid Chromatography. Adsorbents for Gas-Solid Chromatography. 2.3 Stationary Phases. Requirements of a Stationary Phase. USP Designation of Stationary Phases. Kovats Retention Index. McReynolds and Rohrschneider Classifications of Stationary Phases. Evaluation of Column Operation. Optimization of Packed Column Separations. 2.4 Column Preparation. Coating Methods. Tubing Materials and Dimensions. Glass Wool Plugs and Column Fittings. Filling the Column. Conditioning the Column and Column Care. 2.5 United States Pharmacopeia and National Formulary Chromatographic Methods. References. 3 Capillary Column Gas Chromatography. 3.1 Introduction. Significance and Impact of Capillary Gas Chromatography. Chronology of Achievements in Capillary Gas Chromatography. Comparison of Packed and Capillary Columns. 3.2 Capillary Column Technology. Capillary Column Materials. Fused Silica and Other Glasses. Extrusion of a Fused-Silica Capillary Column. Aluminum-Clad Fused-Silica Capillary Columns. Fused-Silica-Lined Stainless Steel Capillary Columns. 3.3 Preparation of Fused-Silica Capillary Columns. Silanol Deactivation Procedures. Static Coating of Capillary Columns. Capillary Cages. Test Mixtures for Monitoring Column Performance. Diagnostic Role Played by Components of Test Mixtures. 3.4 Chromatographic Performance of Capillary Columns. Golay Equation Versus the van Deemter Expression. Choice of Carrier Gas. Measurement of Linear Velocity and Flow Rate. Effect of Carrier Gas Viscosity on Linear Velocity. Phase Ratio. Coating Efficiency. 3.5 Stationary-Phase Selection for Capillary Gas Chromatography. Requirements. History. Comparison of Columns from Manufacturers. Polysiloxane Phases. Polyethylene Glycol Phases. Cross-Linked Versus Chemically Bonded Phase. Chemical Bonding. MS-Grade Phases Versus Polysilarylene or Polysilphenylene Phases. Sol-Gel Stationary Phases. Phenylpolycarborane-Siloxane Phases. 3.6 Specialty Columns. EPA Methods. Chiral Stationary Phases. Gas-Solid Adsorption Capillary Columns: PLOT Columns. 3.7 Capillary Column Selection. Practical Considerations of Column Diameter, Film Thickness, and Column Length. Capillary Columns of 0.53mm i.d.: Megabore Columns. Correlation of Column Dimensions and Film Thickness with Parameters in the Fundamental Resolution Equation. Column Selection for Gas Chromatography by Specifications. 3.8 Column Installation and Care. Carrier Gas Purifiers. Ferrule Materials and Fittings. Column Installation. Column Conditioning. Column Bleed. Retention Gap and Guard Columns. Column Fatigue and Regeneration. 3.9 Special Gas Chromatographic Techniques. Simulated Distillation. Multidimensional Gas Chromatography. Computer Modeling of Stationary Phases. References. 4 Column Oven Temperature Control. 4.1 Thermal Performance Variables and Electronic Considerations. 4.2 Advantages of Temperature Programming over Isothermal Operation. 4.3 Oven Temperature Profiles for Programmed-Temperature Gas Chromatography. 4.4 Role of Computer Assistance in Optimizing Separations in Gas Chromatography. DryLab (LC Resources). ProezGC (Restek Corporation). GC-SOS (Chem SW). 4.5 Fast or High-Speed Gas Chromatography. Selectivity Tuning. Resistively Heated Columns and Column Jackets. 4.6 Subambient Oven Temperature Control. References. Selected References. Appendix A: Guide to Selection of Packed Columns. Appendix B: Column Selection. Index.

Seismic retrofit of a reinforced concrete flat-slab structure: Part I — seismic performance evaluation

An evaluation of seismic performance was conducted for a reinforced concrete (RC) frame structure representative of 1980s construction in the Central United States. The case study building is a five-story RC flat-slab office building designed for the code requirements used in this region. The structural response was predicted using nonlinear static analysis and nonlinear dynamic analysis with synthetic ground motion records. The FEMA 356 criteria were used to evaluate the seismic performance of the case study structure. Because the case study building does not meet the FEMA 356 basic safety objectives for the Memphis motions, three seismic retrofit techniques were applied to enhance the seismic performance including the addition of shear walls, the addition of RC column jackets, and confinement of the column plastic hinge regions using externally bonded steel plates. Finally, the predicted seismic performance for the three retrofitted structures was compared to that for the unretrofitted structure. Varying levels of improvement in the seismic performance were demonstrated through the use of the selected seismic retrofits. Based on the seismic evaluation with the FEMA 356 criteria, the addition of shear walls provided the greatest improvement in the seismic performance of the case study building.

Fundamental Principles That Govern Retrofitting of Reinforced Concrete Columns by Steel and FRP Jacketing

Extensive investigations on seismic retrofitting of reinforced concrete columns have been undertaken in recent years and many retrofitting methods have been developed and reported in the literature. However contradictory results and conclusions are not rare especially for jacketing of rectilinear columns, and there is not a clear picture on the current state-of-the-art in the literature. This work is based on the review and assessment of more than 120 papers, and collection and analysis of more than 700 column tests. In combination with the authors' original theoretical studies and experimental testing, this work identifies the key factors that affect the effectiveness and deficiencies of different retrofitting techniques and provides engineers with a clearer picture on the capabilities of different retrofitting techniques, in particular how to improve the effectiveness of a jacketing system. From the theoretical studies, this work also provides researchers with fundamental insight and principles that govern the retrofitting of RC columns, which shed light on the development of new models and identification of further research subjects.

Parametric study on performance of bridge retrofitted by unseating prevention devices

Over the past decade, seismically induced damage to bridges has been widely reported following major earthquakes such as the 1994 Northridge, 1995 Kobe and 1999 Chi-Chi events. Since these earthquakes, restrainers and stoppers have been installed on bridges to prevent unseating and excessive displacements, respectively. Alternatively, column jacketing has also been proven to be effective. However, the enhanced shear strength may result in extra retrofitting works on the footing. For bridges damaged in the Chi-Chi earthquake, investigations revealed that most bridge columns experienced none-to-minor damage in the longitudinal direction. The reason for this unexpected performance was the construction practice of using a rubber bearing, which is an unbolted design that may slide under large lateral forces. In this paper, parametric studies on simply-supported bridges retrofitted by a restrainer or concrete shear key along the longitudinal and transverse axes were carried out. The research focuses on finding suitable combinations of the design force and gap spacing so the restrainer and concrete shear key can be used as an unseating prevention device, with respect to the allowable column damage in terms of displacement ductility under near-facult type earthquakes. A two-lane PCI-girder bridge was selected as the benchmark model. In the longitudinal direction, a total of nine combinations considering yielding strength and gap spacing for the restrainer were analyzed; while parameters for the concrete shear key were divided into three shear force levels and three gap spacings. In the transverse direction, a similar approach was adapted, except smaller gap spacing was used. For each of the above mentioned earthquakes, seven input ground motions were selected and their PGAs were adjusted to 0.36g and 0.45g as the Design earthquake and Maximum Considerable Earthquake, respectively. Based on the results of nonlinear time history analyses, proper parameters to design the restrainers and concrete shear keys are obtained. Responses obtained from numerical simulations under the Chi-Chi earthquake leaded to new implications to design those devices. Restrainer should not exceed its breaking strain and sufficient unseating length will be needed always. Concrete Shear key was determined by considering both displacement demand of the superstructure and displacement ductility of the column at the same time. Further study is needed to provide optimal design parameters for use in performance based bridge design.

Seismic Upgrading Of Square And RectangularRC Columns Using FRP Wrapping

This paper presents the results of an experimental study to evaluate the effectiveness of using FRP wrapping for repair and seismic upgrading of square and rectangular RC columns in buildings. The factors affecting the performance of FRP wrapping in rectangular columns under the action of both axial and combined axial and lateral loads are considered in this paper. These factors include the rectangularity ratio of the column cross section, the thickness of the FRP jacket, and the use of carbon verses glass FRP for column jacketing. Techniques to improve the performance of strengthening rectangular columns were also proposed and evaluated in the paper. Such techniques include rounding the sharp edges of the columns, and transferring square into circular columns using mortar. A total of fourteen half-scale reinforced concrete columns, divided into two groups, are tested in this research. The first group of columns consists of three square columns and three rectangular columns which are tested under axial loads. The second group consists of four square columns and four rectangular columns tested under combined axial and lateral loads.

Concrete or FRP Jacketing of Columns with Lap Splices for Seismic Rehabilitation

Seismic rehabilitation of rectangular columns with corner deformed bars lap-spliced at floor level through RC jacketing or CFRP wrapping, is experimentally studied. In three unretrofitted columns, deformation capacity and energy dissipation drop fast with lap length below 45-bar diameter. Three columns were cyclically tested after concrete jacketing of their full length and another nine after CFRP wrapping of the lap splice and plastic hinge region. Five CFRP layers were found to be more effective than two, but the improvement was not major. The positive effect of FRP wrapping on flexural resistance, ultimate deformation and energy dissipation declined with decreasing lap length. There is a limit to the improvement that can be obtained through FRP wrapping: if lapping is as short as 15-bar diameter, its adverse effects on force capacity and energy dissipation cannot be sufficiently removed by FRP wrapping. Overall, RC jacketing is more effective than FRP wrapping for the improvement of the deformation capacity of columns with 15-bar diameter lapping.

Seismic Retrofit of State Street Bridge on Interstate 80

The State Street Bridge, in Salt Lake City, was designed and built in 1965 according to the 1961 AASHO specifications; the design did not include earthquake-induced forces or displacements since only wind loads were considered. The bridge consists of four reinforced concrete (RC) bents supporting composite welded steel girders; the bents are supported on cast-in-place concrete piles and pile caps. A vulnerability analysis of the bridge was conducted that determined deficiencies in (1) confinement of column lap splice regions, (2) anchorage of longitudinal column bars in the bent cap, (3) confinement of column plastic hinge zones, and (4) shear capacity of columns and bent cap.column joints. Seismic retrofit designs using carbon-fiber-reinforced-polymer (CFRP) composites and steel jackets were performed and compared for three design spectra, including the 10% probability of exceedance in 250 years earthquake. The CFRP composite design was selected for implementation and application of the composite was carried out in the summer of 2000 and 2001, while the bridge was in service. The paper describes the CFRP composite design, which, in addition to column jackets, implemented an ”ankle wrap” for improving joint shear strength and a ”U-strap” for improving anchorage of column bars in the bent cap; other retrofit measures were implemented, such as bumper brackets and a deck slab retrofit. A capacity versus demand evaluation of the as-built and retrofitted bents is presented.

Jacketing of reinforced concrete columns subjected to axial load

This paper investigates the suitability of two existing confined concrete models, based on the concept of an effectively confined concrete core, to predict the behaviour of jacketed reinforced concrete columns when subjected to axial loads. Two types of jacketing with reinforced concrete (RC) were studied: full-length and partial jacketing. Consideration is also given to variations in the properties of the different concretes used in the jacket and the original column. Existing experimental data show that jacketing of RC columns using reinforced concrete enhances the axial load-carrying capacity, strain at peak axial load and post-peak ductility. However, conventional methods of analysis underestimate both the peak axial load and the corresponding strain. The two models were used to predict the entire load–strain relation of jacketed RC columns subjected to axial loading. The predictions agree well with available test results. For columns subjected to patch jacketing with only one set of stirrups, the predicted peak loads showed good agreement with experimental results. However, the corresponding strains were overestimated by as much as 20%.

Development of a Specification for Bridge Seismic Retrofit with Carbon Fiber Reinforced Polymer Composites

The U.S. Interstate 80 bridge over State Street in Salt Lake City is very near the Wasatch fault, which is active and capable of producing large earthquakes. The bridge was designed and built in 1965 according to the 1961 American Association of State Highway Officials specifications, which did not consider earthquake-induced forces or displacements. The bridge consists of reinforced concrete bents supporting steel plate welded girders. The bents are supported on cast-in-place concrete piles and pile caps. A seismic retrofit design was developed using carbon fiber reinforced polymer (CFRP) composites, which was implemented in the summer of 2000 and the summer of 2001, to improve the displacement ductility of the bridge. The seismic retrofit included column jacketing, as well as wrapping of the bent cap and bent cap-column joints for confinement, flexural, and shear strength increase. This paper describes the specifications developed for the CFRP composite column jackets and composite bent wrap. The specifications included provisions for materials, constructed thickness based on strength capacity, and an environmental durability reduction factor. Surface preparation, finish coat requirements, quality assurance provisions, which included sampling and testing, and constructability issues regarding the application of fiber composite materials in the retrofit of concrete bridges are also described.

Development of fragility curves of bridges retrofitted by column jacketing

This study represents results of fragility curve development for two (2) sample bridges typical in southern California, strengthened for seismic retrofit by means of steel jacketing of bridge columns. Monte Carlo simulation is performed to study nonlinear dynamic responses of the bridges before and after retrofit. Fragility curves in this study are represented by lognormal distribution functions with two parameters and developed as a function of PGA. The improvement in the fragility due to the retrofit is quantified by comparing fragility curves of the bridge before and after retrofit. In order to formulate the problem of fragility enhancement, the quantification is made by comparing the median values of the fragility curves before and after the retrofit. Under the hypothesis that this quantification also applies to empirical fragility curves developed on the basis of Northridge earthquake damage, the enhanced version of the empirical curves is developed.

Steel Jacket으로 보강된 콘크리트 교량에 대한 지진취약도 개발

본 연구의 궁극적인 목표는 콘크리트 교량의 교각을 Steel Jacket으로 보강한 효과를 정량적으로 산정함으로써, 지진 발생시 도로/교통 시스템의 역할을 평가할 수 있는 자료를 제공하는 데에 있다. Steel Jacket으로 보강 시, 교각의 연성능력이 어느 정도 증가되는지, 또 그로 인해 교량의 취약 상태가 어느 정도 개선되는지를 취약도 곡선을 통하여 나타내었다. 본 연구에서 해석적으로 구한 취약도 곡선이, 과거 지진 발생시 수집된 손상 자료를 이용하여 작성된 보강이 안된 교량의 취약도 곡선을 보정하는데 사용하였다. 그 보정은 Steel Jacket 보강 전과 후의 취약도 곡선상의 중간 값들을 비교해 그 증가분 만큼을 반영하는 방식으로 수행되었다. The ultimate goal of this research is to improve highway system performance in earthquakes by evaluating the effectiveness of retrofitting bridges with column jacketing. The objective of the study is to determine if steel jacketing increases the ductility capacity of bridge columns and hence improves the fragility characteristics of the bridge. Analytical fragility curves are used to adjust the empirical fragility curves obtained for the unretrofitted bridges using seismic damage data collected following past earthquakes. The adjustment was carried out by increasing the median values of the empirical curves through comparison with the median values of the corresponding fragility curves obtained analytically, both before and after being retrofit.

Structural rehabilitation of columns with reinforced concrete jacketing

AbstractStrengthening and rehabilitation by reinforced concrete jacketing of columns is assessed, considering different practical aspects: anchoring and slab crossing of the added longitudinal reinforcement, interface surface preparation, spacing of added stirrups, temporary shoring of the structure and addition of new concrete. Recent research on these topics and the main recommendations to achieve good RC jacketing are presented. Copyright © 2003 John Wiley & Sons, Ltd.

Fragility curves of concrete bridges retrofitted by column jacketing

The Northridge earthquake inflicted various levels of damage upon a large number of Caltrans’ bridges not retrofitted by column jacketing. In this respect, this study represents results of fragility curve development for two (2) sample bridges typical in southern California, strengthened for seismic retrofit by means of steel jacketing of bridge columns. Monte Carlo simulation is performed to study nonlinear dynamic responses of the bridges before and after column retrofit. Fragility curves in this study are represented by lognormal distribution functions with two parameters and developed as a function of PGA. The sixty (60) ground acceleration time histories for the Los Angeles area developed for the Federal Emergency Management Agcncy (FEMA) SAC (SEAOC-ATC-CUREe) steel project are used for the dynamic analysis of the bridges. The improvement in the fragility with steel jacketing is quantified by comparing fragility curves of the bridge before and after column retrofit. In this first attempt to formulate the problem of fragility enhancement, the quantification is made by comparing the median values of the fragility curves before and after the retrofit. Under the hypothesis that this quantification also applies to empirical fragility curves developed on the basis of Northridge earthquake damage, the enhanced version of the empirical curves is developed for the ensuing analysis to determine the enhancement of transportation network performance due to the retrofit.

Seismic jacketing of RC columns for enhanced axial load carrying performance

Axial compression test results for square RC columns incorporating Taiwanese construction practice in the placement of stirrups and various kinds of jacketing schemes are presented. The jacketing schemes include circular, octagonal and square shapes. The jacketing materials vary from steel plate to carbon fiber reinforced polymer (CFRP) composites. It is found from the monotonic axial load test results that the failure mode of the benchmark non‐retrofitted specimen is identical to that observed in real damage cases subsequent to the 1999 Chi‐Chi Taiwan earthquake. The benchmark specimen developed its design strength but a non‐ductile failure mode occurred soon after the peak load was reached. Among the retrofitted specimens, the steel jacketed specimens exhibit not only greatly enhanced load carry capacity but also excellent ductility performance. Test results show that CFRP sheets are effective in increasing the column axial strength, but the sheets could fracture suddenly in high strain conditions due to their brittle material characteristics. Test results indicate that CFRP sheet wrapping in general is not as effective as steel jacketing in improving the axial ductility capacity of RC columns. However, the proposed octagon‐shaped CFRP wrapping scheme exhibits an improved performance compared to rectangular‐wrapped columns using the same layers of CFRP sheets. Tests confirm that all octagonal steel or CFRP jacketed specimens have axial loading capacities more than 2 times the nominal capacity.

Seismic Behavior and Retrofit of Outrigger Beam-Column Frames

A one-fourth scale outrigger beam-column frame with as-built details was tested to assess its performance under reversed cyclic loading and to develop a retrofit procedure suitable for moderate seismic regions. The ductility of the as-built frame was limited due to pullout of poorly embedded positive moment reinforcement in the joint and shear inadequacy in the joint and beam. Strut-and-tie truss idealizations were developed to aid in predicting the failure mechanism and failure loads. Sectional and nonlinear finite-element analyses were used to predict the performance of the as-built outrigger frames. The retrofit procedure involved fiber-reinforced concrete sleeving of the beam and the joint, together with column jacketing, to enable plastic hinging and energy dissipation to occur in the column. This retrofit solution increased the strength, ductility, and energy absorption of the system. The provision of high-performance fiber-reinforced concrete in the beam sleeve was very effective in controlling the cracks and hence would improve durability.

Prefabricated Composite Jacketing of RC Columns for Enhanced Shear Strength

The effectiveness of prefabricated composite jacketing to retrofit existing circular reinforced concrete (RC) bridge columns for enhanced seismic shear strength is described in this paper. The jackets consist of multilayer prefabricated glass fiber reinforced composite shells adhered together. Three half-scale circular columns were tested under cyclic shear in double curvature and constant axial load. One column was tested in the condition to investigate the shear failure mode of columns designed based on pre-1971 codes. Two other columns were tested after being retrofitted using prefabricated composite jackets. The as-built column suffered shear failure at low displacement ductility. The retrofitted columns developed significantly improved hysteretic responses with stable hysteresis loops even at displacement ductility levels as high as 10.0 corresponding to drift ratios exceeding 5.2%. Method for retrofit design using prefabricated composite jacketing is also provided and validated by the test results.

Upgrading of Nonductile Reinforced Concrete Frame Connections

An innovative seismic upgrading technique for existing reinforced concrete frame connections constructed prior to the 1970s using corrugated steel jacketing is proposed and evaluated. Six, one-third scale, reinforced concrete beam-to-column connections were tested under quasi-static cyclic loading to study their seismic performance. The investigated test parameters include the amount of joint and column transverse reinforcement, corrugated steel sheet thicknesses, and jacketing of column only or of both column and beam. Test results demonstrated that existing reinforced concrete frame connections upgraded using corrugated steel jackets performed satisfactorily when subjected to high cyclic load levels. The corrugated steel jacket was found to be an effective system of upgrading as it increases the joint shear strength and the energy dissipation capacity. A method for the design of the corrugated steel jacket thickness and depth of corrugation is formulated.

Seismic Retrofit of RC Columns with Continuous Carbon Fiber Jackets

The development, the validation, and the implementation of a new seismic retrofit system for reinforced concrete columns are described. The column jacketing system consists of continuous carbon fiber prepreg tows wound in an automated fashion onto existing circular or rectangular concrete columns, with variable jacket thickness along the column height based on experimentally validated design models. Jacket design criteria for various seismic column failure modes are described and detailed examples show their application to retrofits of columns with circular and rectangular column geometry, different reinforcement ratios, and detailing. The carbon jacket designs are validated through large-scale bridge column model tests and are found to be just as effective as steel shell jacketing in providing desired inelastic design deformation capacity levels. Furthermore, it is shown that the retrofit criteria and guidelines are also applicable to other advanced composite jacketing systems with appropriate considerat...