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Fatigue Capacity of Plain Concrete Under Biaxial Fatigue Stresses With One Constant
Song, Yu-pu (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China) | Wang, Huai-liang (Civil and Architectural Engineering College, Dalian University, Dalian, China)
The fatigue tests of concrete have been conducted with constant confined stress, including biaxial compression ㉣biaxial tension compression and alternate tension-compression fatigue loading. The experimental results show that an increase of the horizontal stress leads to a change of the maximum vertical load-carrying capacity. Empirical relationships are proposed for predicting the maximum stress ratio as a function of lateral stress and fatigue life. Also, the observation of the failure modes indicates that concrete possesses similar failure patterns under monotonic and fatigue loadings. The investigation of this paper can provide for the design of concrete structures such as reinforced concrete bridge ㉣ crane beams ㉣ offshore platforms ㉣ concrete sleepers㉣ nuclear power plants and pressure vessels. It can also give some suggestions for the revision of existing Design Code. INTRODUCTION Many structures are often subject to repetitive cyclic loads. Examples of such cyclic loads include machine vibration, sea waves, wind action and automobile traffic. The exposure to repeated loading results in a steady decrease in the stiffness of the structure, which may eventually lead to fatigue failure. The earliest research on fatigue properties of concrete materials is traced back to the end of the 19th century (Joly, 1898), the compressive fatigue tests so far have been most investigated (ACI Committee 215; Hsu, 1981; Oh, 1991).In recent years, many investigations concerning plain concrete under uniaxial cyclic tension ㉣uniaxial alternate tension-compression and biaxial fatigue loads have also been carried out. Very few experimental results on the response of concrete subjected to repeated biaxial loading are available in the literature. Fatigue behavior of plain concrete under biaxial compression (Su and Hsu, 1988), high-strength concrete subjected to proportional biaxial-cyclic compression (Nelson et al., 1988) and steel fiber reinforced concrete subjected to biaxial compressive fatigue loading (Yin et. al., 1995) were investigated. (2002).
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.34)
- Data Science & Engineering Analytics (0.47)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.34)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.34)
Abstract An important aspect of the behavior of joints in rock masses is damage and degradation of mechanical properties due to progressive fracturing of the rock bridges or cemented materials existing in the joint. The damage can occur in both normal and shear modes. In this work a coupled normal-shear damage model is developed based on the mechanism mentioned here above. The joint parameters decrease as a function of a damage scalar variable "D" which increases from zero for non-damaged state to one for a totally damaged joint. This results to a coupled evolution of stiffness in normal and shear directions as well as equivalent cohesion and tensile strength of the joint. The damage variable D is a function of relative displacement in the joint. The damage criterion delimits a domain in stress space whose size decreases with the damage parameter increase. The model is implemented in CESAR-LCPC which is a general Finite Element code for civil engineering and geotechnical applications. The numerical applications carried out show that the model is capable to represent principle aspects of geotechnical damageable joint's behavior. Introduction Existence of joints and discontinuities in geological structures modify dramatically the stress and deformation fields. This is the case also for engineering structures particularly for concrete joints and rock-concrete interfaces. Rock joints in underground constructions, mining, rock slope stability, geothermic sites and faults, concrete joints in massive structures like concrete dams and interface of concrete structures founded on or constructed in rocks are examples of this problem. These types of quasi-brittle materials reveal in general a damage behavior by stiffness softening which is recognizable especially under cyclic loading. Consequently the joints existing in these materials could show similar behavior. Damage may occur in the joints containing some continuous segments as rock bridges or cemented material as well as in the partially cemented rock-concrete interfaces. Some authors as Cervenka et al. [1], Carol et al. [2] and Puntel et al. [3] have proposed the joint models based on fracture mechanic concept and cohesive crack model (cf. Galvez et al. [4] and Bazant [5] for cohesive crack models). These models however do not take into account the stiffness reduction of joint and focus on the resistance deterioration due to fracture development in connected segments of the joints. Jefferson [6] proposes a plastic-damage model for cementitious interfaces. Jefferson [7] proposes also a "tripartite cohesive crack model" for concrete. These two models developed by Jefferson take into account many physical aspects of quasi-brittle joints behavior, they are however relatively complex on mathematical formulation. In the present paper a relatively simple model is proposed for quasi-brittle joints and interfaces. In this model damage may occur under normal, shear or mixed loading condition and results to lose of resistance parameters as well as stiffness of the joint. Deterioration of joint parameters in each direction (normal/shear) affects the parameters in the other direction. This model is applicable to a variety of rock and concrete joints and rock-concrete interfaces. The application of this model is particularly interesting in the case of cyclic loading; for example fluctuation of water pressure in concrete 1008 joints or bed joints of a dam so as in adjacent rock joints, and dynamic loading in all type of aforementioned joints. Another example is thermal and hydraulic oscillations affecting the stability of a fractured rock slope.
- Europe (0.46)
- North America > United States (0.28)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (0.88)
ABSTRACT: Plastic composites made of fiber reinforcements are being increasingly used for structural applications. The widespread use is motivated primarily by their light weight and corrosion resistance. Low-cost, mass-produced pultruded sections are becoming increasingly competitive with conventional materials like steel and reinforced concrete. However, the conventional design approach and analysis as applied to steel and concrete have serious limitations if directly applied in the design and construction of structures with the fiber-reinforced plastics (FRP). These difficulties are rooted primarily in the microstructural characteristics of these materials. This paper summarizes the results of a study and analysis of the effects of severe temperature (cold) on the FRP materials. INTRODUCTION A constantly growing need for improved materials, processes, and products for the cost-effective manufacture and design of engineering structures and systems has been a driving force in the development of composite materials for structural applications. The favorable strength-to-weight ratios and the versatility in design and fabrication that permits material tailoring to a particular need make composites attractive design materials. Parts designed from composite materials not only offer weight savings and improved corrosion resistance, but can also give greater resistance to impact and fatigue, lower maintenance costs, and greater opportunities for parts integration during the manufacturing process than their counterparts made from conventional metals (Lubin, 1982). However, conventional design approach and analysis as applied to steel and concrete have serious limitations in direct applications in the design and construction of structures with the fiber-reinforced plastics (FRP). These difficulties are rooted primarily in the micro- structural characteristics of these materials. The fiber reinforcement imparts significant anisotropy in stiffness, induces complex modes of failure and allows accumulation of severe residual stresses under extreme temperature environments. Due to the viscoelastic nature of the matrix, the rate of loading also significantly affects the performance of these materials.
- Construction & Engineering (1.00)
- Materials > Construction Materials (0.84)
- Energy > Oil & Gas > Upstream (0.69)
SUMMARY: The phenomena which occur in swelling rock are described. With the aid of a Finite Element program for.the evaluation of stresses and displacements caused by swelling [6], the results of a large scale test in the Wagenburgtunnel in the city of Stuttgart [1] are interpreted. On the basis of corresponding calculations on idealized examples general statements on the relationship between the displacements caused by swelling and the shape of the cross-section of a tunnel as well as the in situ stresses are made and criteria for the design and construction of tunnels in swelling rock are worked out. In connection with the design and construction of the underground turning loop of the Stuttgart Subway the above mentioned criteria and calculatory method were successfully applied. An extensive field measurement program for the evaluation of the rock mechanical parameters and for monitoring of the completed structure was performed. RESUME: On decrit les phenomènes surgissants dans le rocher expansif. Les mesurages de l'essai en grand au Wagenburgtunnel à Stuttgart [1] sont interpretes à l'aide d'un programme de calcul des elements finis pour la recherche de contraintes et de deformations dues à l'expansion [6]. A l'aide d'exemples de calcul on conclut sur la dependence des deformations d'expansion de la section du tunnel et de l'etat de contraintes primaires et on etablit des critères pour la projection et l'execution de tunnels dans le rocher expansif. Les dits critères et le procede da calcul en liaison avec un grand programme de mesurage sont verifies à la projection et à la construction du tunnel de la boucle de virage du metro de Stuttgart. ZUSAMMENFASSUNG: Es werden die in quellendem Gebirge auftretenden Phanomene beschrieben. Anschlieβend werden mit Hilfe eines FE-Rechenprogramms zur Ermittlung quellbedingter Spannungen und Verformungen [6] die Meβergebnisse des Groβversuchs Wagenburgtunnel (Stuttgart) [1] interpretiert. Anhand von Berechnungsbeispielen werden dann hieraus Aussagen ueber die Abhangigkeit der Quellverformungen von der Querschnittsform eines Tunnels und dem Primarspannungszustand im Gebirge gemacht, und es werden Kriterien fuer Entwurf und Ausfuehrung von Tunnels in quellendem Gebirge erarbeitet. Beim Entwurf und Bau des Tunnels der Wendeanlage der S-Bahn Stuttgart wurden die o.g. Kriterien und das Rechenverfahren in Verbindung mit einem umfangreichen Meβprogramm erfolgreich erprobt. INTRODUCTION The swelling behavior of certain types of rock masses has often led to large heavings of tunnel inverts and has even caused the destruction of concrete linings at the invert [1 - 4]. As a consequence of these cases of damage and the thereby required repair measures a series of mineralogical and rock mechanical investigations were carried out in recent years which led to an expansion of the knowledge of the chemical and physical causes of swelling phenomena. In addtion to this, general criteria for the design and construction of tunnels in swelling rock were evaluated. The senior author and his previous coworker, Dr.-Ing. Riβler, reported in 1976 on the development of a stress-strain law and a corresponding calculatory method [5], with the aid of which the stresses and displacements in the rock mass and tunnel lining caused by swelling can be evaluated. This paper, however, represented only a small step towards the solution of the problem because the applied stress-strain law was neither verified in laboratory experiments nor was the method applied to a project. In the meantime the results of the research work were applied in connection with the design and construction of the turning loop of the Hasenbergtunnel of the Stuttgart Subway, which is located in gypsum keuper, a swelling rock. The following paper attempts to summarize the state of knowledge in this field and to report on the experiences gained during construction of the turning loop. SWELLING PHENOMENA The Transformation or Anhydrite into Gypsum Calcium sulfate occurs in two modifications in nature: as anhydrite (CaS04) and as gypsum (CaS04.2H20). During the transformation of anhydrite into gypsum according to equation (1a) two molecules of water per molecule of CaS04 are transformed into crystal water and bound to the CaS04 molecule. This is accompanied by an increase in volume of theoretically approximately 51 % (equation 1b). Since at temperatures < 3Sc gypsum is the more stable modification of the calcium sulfate in comparison to anhydrite, rock which contains anhydrite increases its volume in this manner, that means, that it swells when water is introduced from the outside through cracks, joints or other openings within the rock mass. Swelling of Corrensite Corrensite is a clay mineral with a flaked structure and consists of numerous aluminum silicate layers. Water can penetrate between these layers and thus causes the crystal to swell. In unleached rock corrensite usually has, according to present knowledge, a base interval of 29 Å which can increase, by means of incorporation of water molecules in the crystal lattice, to 33 Å This corresponds to an increase in volume of approximately 14 % [1]
- Well Drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)