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Abstract In Japan, many tunnels have been in service for several decades, which require effective inspection methods to assess their health conditions. The ambient vibration test has attracted more and more attentions in the recent studies for health management of concrete structures. In this study, the vibration characters of tunnel lining shells built with poling-board method was analyzed by application of the analytical solutions of the Love-Timoshenko shell theory and Donnell-Mushtari shell theory. The natural frequency estimated by Love theory is slight smaller than that of Donnell theory. The rock-concrete contacts, including the poling board and interfaces between rock mass and concrete lining, was represented by elastic boundaries with normal and shear stiffness. It was found that the stiffness of weak contacts has the great effect on the natural frequency of the lining. Numerical simulations were also carried out to compare with the results of the proposed method, even though the low natural frequency is difficult to distinguish. It is possible to conclude that the proposed approach is convenient, effective and accurate. 1. Instructions Japan is a country surrounded by sea and 70% of its land is covered by mountains. More and more tunnels through mountains have been constructed during the last 50 years, and those tunnels have become an indispensible part of the traffic networks. The persistent ageing of tunnels causes many problems on the lining of tunnel, such as corrosion, buckling, fracturing, the creation of internal voids and the seepage induced by flaws (Malmgren et al. 2005). Deteriorations and damages of lining concrete decrease the integrity of tunnel lining and subsequently affect the workability, serviceability and safety reliability of tunnels (Aktan et al. 2000, Bhalla et al. 2005). Therefore, appropriate inspection needs to be conducted at appropriate time to ensure the effective function of tunnel. To date, a number of inspection methods including destructive and nondestructive approaches have been proposed and used in practices to evaluate the tunnel integrity. However, these methods can only provide local information and require considerable time and cost to estimate overall tunnel integrity (Park & Choi 2008).With the development and application of high sensitivity accelerometer, the low-cost ambient vibration test has attracted much more attentions for evaluating the structural condition of the whole structure. Therefore, it is important to study the analytical solutions of tunnel lining vibrations with an appropriate model in order to better understand its dynamic behaviors.
- Health & Medicine > Consumer Health (0.87)
- Energy > Oil & Gas > Upstream (0.49)
The earthquake response of typical concrete gravity structures in 100 to 200 m of water was evaluated. Response spectrum and fast Fourier-trans-form solution techniques were used. Parametric studies showed that the analysis method markedly affects magnitude and distribution of computed foundation and structural forces and that correct modeling is essential. Introduction One specialty session at the 1975 Seventh Annual Offshore Technology Conference was about offshore earthquake engineering. Few state-of-the-art presentations then addressed the response of concrete gravity presentations then addressed the response of concrete gravity platforms to earthquake influences. This is not surprising platforms to earthquake influences. This is not surprising because the first production platforms of this kind were installed in the North Sea only in 1975 and to the author's knowledge, none have been ordered yet for an offshore region characterized by a high earthquake risk. Among the chief advantages of the concrete gravity platform are its potential for carrying payload to location platform are its potential for carrying payload to location and the limited offshore work required. In a short-installation weather window like that of the North Sea, these advantages only now are appreciated fully. The Gulf of Alaska has weather characteristics similar to the North Sea, but also has a high earthquake risk. This paper presents part of an over-all investigation into the presents part of an over-all investigation into the feasibility of constructing and installing concrete gravity platforms in the Gulf of Alaska. The investigation was platforms in the Gulf of Alaska. The investigation was conducted from Sept. 1974 through April 1975. When the study began, there were sound geological reasons for anticipating suitable foundation conditions at or close to the mud line; however, only limited numerical data existed. Objectives One can assume that the intensive nuclear power development program in the 1960's generated ample means to evaluate earthquake problems of massive concrete structures. While this is undoubtedly true with respect to understanding the basic phenomena and developing methodology, certain factors must be remembered. First, the mass and geometry of a typical gravity production platform are significantly larger than those of a nuclear platform are significantly larger than those of a nuclear reactor. Second, the superstructure of a platform is relatively flexible. Third, the inter-action with the surrounding water represents another complication in a submerged structure. Finally, the emphasis is on the detailed evaluation of a particular site in a typical nuclear-reactor design, whereas this Gulf of Alaska study was geared more to identifying sites that would be satisfactory from all viewpoints. For these reasons, this study was considered only preliminary and emphasis was placed on the following objectives:to assess the importance of foundation compliance, added mass effect from the water, damping behavior, and method of analysis, to quantify typical design forces in the structure and its foundation, and to assess the design implications for the major parts of the structure. These objectives were accomplished within 6 months. JPT P. 318
- North America > United States > Alaska (0.85)
- Europe > United Kingdom > North Sea (0.65)
- Europe > Norway > North Sea (0.65)
- (2 more...)
ABSTRACT The earthquake response of typical concrete gravity structures in a 100 to 200m water depth range was evaluated using response spectrum and Fast Fourier Transform solution techniques. A series of parametric studies showed:The analysis method has a marked effect on magnitude and distribution of computed foundation and structural forces. Correct modeling of the foundation compliance, especially radiation damping, is essential. At the lower end of the soil stiffness range, foundation instability governs and at the upper, structural strength. INTRODUCTION One of the specialty sessions at the 1975 OTC was dedicated to the subject of earthquake engineering offshore. It was evident from the state of the art presentations at that time, that few if any investigations had addressed the question of the response of concrete gravity type platforms to earthquake influences. This is hardly surprising since the first production platforms of this kind were installed in the North Sea in the summer of 1975 and to the authors' knowledge, none has yet been ordered for an offshore region characterized by high earthquake risk. One of the chief advantages of the concrete gravity platform is its potential for carrying payload to location and the very limited amount of offshore work required. The advantage of this in a short installation weather window, like that of the North Sea, is only now becoming fully appreciated. The Gulf of Alaska has similar weather characteristics to the North Sea but also is associated with a high earthquake risk. This paper presents a part of an overall investigation into the feasibility of constructing and installing concrete gravity platforms in the Gulf of Alaska. This was conducted from September 1974 through April 1975. At the time the study commenced, there were sound geological reasons for anticipating the presence of suitable founding conditions at or close to the mudline but only limited numerical data existed. OBJECTIVES It would be logical to assume that the intensive nuclear power development programme in the 1960's would have generated ample means for evaluating earthquake problems experienced by massive concrete structures. While this is undoubtedly true with respect to an understanding of the basic phenomena and the provision of some of the methodology, certain factors must be remembered. In the first instance, the size in terms of both mass and geometry of a typical gravity production platform is significantly greater than that of a nuclear reactor installation. Secondly, the superstructure of the former is relatively flexible. Thirdly, the interaction with the surrounding water represents a further level of complication in the case of a submerged structure. Finally, in a typical nuclear reactor design situation the emphasis is on the detailed evaluation of a particular site whereas the type of investigation undertaken in this Gulf of Alaska study was geared more to the identification of which type of site would be satisfactory from all view points.
- Europe > United Kingdom > North Sea (0.65)
- Europe > Norway > North Sea (0.65)
- Europe > Netherlands > North Sea (0.65)
- (3 more...)
ABSTRACT: A laboratory study has been made of the direct shearing of concrete-sandstone interfaces under conditions of constant normal stiffness. The results demonstrate that the peak and residual strength envelopes (stress ratio versus normal stress) are independent of the test path. RESUME: Une etude de laboratoire a ete faître sur le cisaillement direct de la surface separante beton-grès sous la condition de rigidite normale constante. Les resultats montrent que les enveloppes de la resistance maximale et de la resistance residuelle (rapport des contraintes vs la contrainte normale) sont independentes du chemin d'essai. ZUSAMMENFASSUNG: Eine Laboruntersuchung der direkten Scherung von Beton-Sandstein Zwischenflachen unter konstant normalen Steifheitbedingungen wurde durchgefuehrt. Die Resultate zeigen, dass die maximalen und die residuellen Widerstande (Spannungsverhaltnis verglichen mit der Normalspannung) unabhangig sind von der Spannungstestrichtung. 1 INTRODUCTION The mechanical behaviour of interfaces between concrete and rock can have an important influence on the response of certain foundations systems to applied loading. A particular example occurs when a concrete pile, formed in a rock socket, is used to support structural loads. Resistance to the loading will be provided by the development of shear stresses at the cylindrical interface along the length of the shaft. Some resistance will also be provided in end bearing at the base of the pile, but, unless the pile is extremely short or the magnitude of the loading is extremely high, most of the applied loading will be carried in side shear. Laboratory studies of the shear behaviour of concrete-rock interfaces are important, not only because they provide basic data essential in the design of rock-socketed piles, but also because they provide insight into the fundamental behaviour. Conventionally, the testing of interfaces has been carried out in the direct shear apparatus with constant normal stress applied across the shear interface. This type of testing provides a reasonable model for cases in practice where no constraint is placed upon the normal displacements accompanying the shearing, e.g. when rock blocks slide freely under gravity. However, in cases such as a concrete pile contained within a rock socket, the stress normal to the plane of shearing can be far from constant. When this type of pile is loaded axially, the pile shaft will displace vertically and at large enough loads (often within the working load range for the pile) relative displacements (slip) will occur between the shaft and the surrounding rock. If the socket containing the pile has a rough surface, then the relative displacement will be accompanied by some dilation at the interface. Because the surrounding rock mass tends to restrain this dilation, the normal compressive stresses acting on the side of the pile will not remain constant but will increase. This phenomenon has been measured and described previously, e.g. by Johnston (1977) and Williams (1980), and it has been shown that, to sufficient accuracy, the normal stiffness of the surrounding rock mass is approximately constant. Hence, it is reasonable to expect that direct shearing under conditions of constant normal stiffness will provide a more realistic laboratory model of the shaft behaviour of concrete piles socketed into rock, than would direct shear testing under conditions of constant normal stress. Several direct shear devices, capable of applying a variety of constraints on the normal mode of deformation, have already been described in the literature, e.g. Lam and Johnston (1982), Desai et al (1985), Natau et al (1979), and some data are available for interfaces of concrete and artificial mudstone (Johnston and Lam, 1984). This paper describes a new constant normal stiffness, direct shear device capable of applying static and cyclic shear loading to a sample containing one of a variety of possible interfaces. The sample may contain a specially prepared interface such as a concrete-sandstone interface of arbitrary roughness and bonding, it may be formed of two blocks from either side of an artificially prepared or a natural discontinuity (e.g. a joint or a bedding plane), or it may be an intact specimen of rock or cohesive soil which does not contain a pre-existing discontinuity plane. When used in a servo-controlled testing machine the device is capable of applying either load or displacement controlled static or cyclic shear loading. The cyclic shear loading may be either one-way or two-way in nature. The device has been used to study the behaviour of concrete-sandstone interfaces with reference to pile sockets, and a comprehensive set of results is presented in this paper. 2 CONSTANT NORMAL STIFFNESS CONDITION As suggested above, if dilation accompanies shearing at the interface between a pile and the surrounding rock formation, then to a first approximation the stiffness of the formation with respect to the normal displacement can be regarded as constant.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
ABSTRACT: Prediction of rock socket shaft resistance is a complex problem, but seldom could rock socket piles be loaded to failure in field load tests due to their high ultimate load capacity. The laboratory study of resistance behavior of rock socket is usually based on shear box test, however, the rock concrete interface prepared in shear box test is planar but the actual surface of rock socket is circular. To achieve a more reasonable simulation, two rock socket shaft models were constructed and tested in this research. In these tests, two concrete shafts models with diameter of 160mm were constructed in rock blocks, and vertical load tests were performed on them. The axial forces at different depth were recorded during the tests. The test results are evaluated by numerical calculation, and the failure process and mechanism at rock concrete interface are studied in this paper. The measured data and calculated results indicated that the shaft resistance was greatly influenced by the normal stress generated at concrete rock interface. INTRODUCTION Rock socket piles are widely adopted in Hong Kong area, as they can provide high load capacity at a very low displacement. The shaft resistance at rock socket length is usually considered as the major or the only one resistance in load capacity calculation. The resistance behavior of the rock socket dominates the working performance of the piles. The resistance characteristic of rock socket is influenced by many factors, such as the strength and deformation properties of rock and concrete, the roughness of the interface, the original lateral stress existing in rock mass, and the construction method used to build the pile. The prediction of rock socket shaft resistance is a complex problem, but seldom could rock socket piles be loaded to failure in field tests due to their high ultimate capacity. Laboratory tests were widely employed as a practical way for this purpose. Many researchers had used the original and some derivative shear box tests to evaluate the shear resistance behavior at rock concrete interface. Artificial rock materials were adopted in shear box tests by Lam and Johnston in theoretical study for the rock concrete interface with varied roughness profiles [1]. In direct shear tests, CNL (constant normal load) and CNS (constant normal stiffness methods were both employed to simulate the different boundary stress conditions. The effects of interface profiles were often focused in study, and the rock concrete interface is usually prepared as a planar interface with some prefabricated profiles [4][5]. However, different from those prepared surfaces, the actual rock concrete interface of rock socket piles is circular. Under an actual working situation, the mobilized resistance is distributed on a circular shaft but not planar surface. The working characteristics of these two kinds of surfaces should be different due to their geometric difference. A shear test with geometric characteristics more close to the actual situation will give us more reasonable information about the resistance behavior of rock socket piles under working conditions.