Showing papers on "Embedment published in 2006"

Debonding Failures of RC Beams Strengthened with Near Surface Mounted CFRP Strips

Abstract: This paper presents the results of a series of tests conducted on reinforced concrete (RC) beams strengthened in flexure with near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. As the main focus of the research is on debonding failure mechanisms, the only test variable investigated was the embedment length of the NSM strip and the NSM strip was extensively strain-gauged to monitor its bond behavior. Load-deflection curves, failure modes, strain distributions in the CFRP strip, and local bond stresses at the CFRP–epoxy interface from the tests are all examined in detail and compared with the predictions of a simple analytical model where appropriate. Of the four embedment lengths investigated, all but the shortest one led to a notable increase in the load-carrying capacity and, to a lesser extent, in the postcracking stiffness of the beam. Debonding was found to be the primary failure mode in all cases except for the beam with the longest embedment length. Also reported in this paper are results from preliminary bond tests used to characterize the local bond-slip behavior of the NSM system. Apart from gaining a better understanding of debonding failures in RC beams with NSM FRP strips, the test results reported in the paper should be useful for future verification of numerical and analytical models.

Three-dimensional lower-bound solutions for the stability of plate anchors in sand

Abstract: Soil anchors are commonly used as foundation systems for structures that require uplift or lateral resistance. These types of structure include transmission towers, sheet pile walls and buried pipelines. Although anchors are typically complex in shape (e.g. drag or helical anchors), many previous analyses idealise the anchor as a continuous strip under plane strain conditions. This assumption provides numerical advantages, and the problem can be solved in two dimensions. In contrast to recent numerical studies, this paper applies three-dimensional numerical limit analysis and axisymmetrical displacement finite element analysis to evaluate the effect of anchor shape on the pullout capacity of horizontal anchors in sand. The anchor is idealised as either square or circular in shape. Results are presented in the familiar form of break-out factors based on various anchor shapes and embedment depths, and are also compared with existing numerical and empirical solutions.

Interpretation of Impact Penetration Measurements in Soft Clays

Abstract: The need for obtaining estimates of undrained shear strength of shallow seafloor sediments often arises in offshore engineering practice. Impact penetrometers offer a promising means of obtaining strength estimates in such sediments. However, variable conditions of embedment and velocity require careful consideration in the interpretation of impact penetration tests. This paper presents an analysis of the expendable bottom penetrometer (XBP), a device that measures acceleration during impact penetration. The analyses indicate that acceleration measurements can be reasonably related to undrained shear strength of soft clays. Further, acceleration measurements can be integrated to obtain velocity and embedment depth data at any point during the penetration analysis, thereby providing a basis for accounting for rate and embedment effects. Applying the proposed analysis to data from a series of test sites in the Gulf of Mexico indicate satisfactory agreement between XBP and reference strength profiles in soft clays.

Seismic Bearing Capacity of Shallow Strip Footings Embedded in Slope

Abstract: The seismic bearing capacity factors for shallow strip footings embedded in sloping ground with general c-ϕ soil are found out by using the limit equilibrium method. The seismic forces are considered as pseudostatic forces acting both on the footing and on the soil below the footing. A composite failure surface involving planar and logspiral is considered in the analysis. A new methodology to establish minimum bearing capacity factors has been adopted by numerical iteration technique to determine the critical focus of the logspiral. Three different types of failure surfaces are considered depending on the embedment depth and ground inclinations. The seismic bearing capacity factors with respect to cohesion, surcharge and unit weight components viz. Ncd , Nqd , and Nγd , respectively, are found out separately for various values of soil friction angles and seismic acceleration coefficients both in the horizontal and vertical directions, ground inclinations, and embedment depths. Results of the present study...

Embedded piezoelectric ceramic transducers in sandwiched beams

Abstract: Surface bonded piezoelectric ceramic (PZT) transducers are currently the most prominent area of research in structural health monitoring using electromechanical impedance methods. This paper presents a new embedded PZT patch and its interaction with the host sandwiched beam. Durability and protection from surface finish, vandalism and the environment are important features of the embedment. The paper also demonstrates the use of thickness vibration of the PZT patch in electromechanical admittance formulations. This embedded PZT–structure interaction model is based on the new concept of 'average sum impedance'. The formulations used for this model can be conveniently employed to extract the mechanical impedance of any 'unknown' PZT patch embeddable plane structure. The mechanical impedance of the structure is obtained from the admittance signatures of the embedded PZT patch. The proposed model is experimentally verified on sandwiched beams.

Fiber-optic laser speckle-intensity crack sensor for embedment in concrete

Abstract: The development of a fiber-optic displacement/strain sensor using the intensity variation of laser speckle pattern has been demonstrated. This sensor can be embedded in concrete for the detection and measurement of crack opening displacements. The transduction mechanism is based on the correlation between the external axial perturbation to the optical fiber and the integrated light intensity variation of speckle patterns due to mode redistribution in a multimode fiber. Calibration tests indicated that the sensor possesses sufficient sensitivity and dynamic range for application in cementitious composite. Application of the sensor has been demonstrated by embedment of the sensor in concrete beams for measurement of the crack tip opening displacements. Experimental results have been validated with analytical formulations. The proposed sensor is simplistic in design and offers a method for the measurement of internal strains and displacements in concrete.

Effectiveness near boundaries of fibre reinforcement in concrete

Abstract: Materials testing of relatively small specimens can lead to biases due to disturbances in fibre reinforcement near external surfaces. This paper presents a complete methodological framework for investigating reinforcement characteristics in bulk and in boundary zones. The developed model assumes actual fibre dispersion a mixture of 3D, 2D and 1D portions. Mostly, the 1D component is small, so that a partially planar fibre composite is resulting. Separate expressions for 2D and 3D portions are obtained for the average projected fibre length (tangent height) that governs fibre characteristics in sections (for image analysis purposes), and for the average embedment characteristics that are at the basis of the stress transfer capability. Crack opening in concrete is assumed counteracted by friction between fibres and matrix pockets. However, additional mechanisms can easily be incorporated. Plain cylindrical steel fibres, eventually curved, were envisaged, but anchoring facilities and arbitrary cross sections could be dealt with, as well. Expressions are given for stress transfer capability (strength) in bulk and in boundary zones. Most of the boundary effects are restricted to a zone half the fibre length in width. Magnitude of strength reduction in this zone is of the order of 10%.

FE modelling of bond interaction of FRP bars to concrete

Abstract: In this paper a computational modelling approach is used to investigate the bond behaviour of fibre-reinforced plastic (FRP) bars in concrete. Two finite element packages (ANSYS and ABAQUS) are used to model the bond interaction of FRP reinforcing bars in cubes and beams. The main purpose of this work is to develop additional understanding of how FRP bars ‘cooperate’ with concrete to sustain the pullout load. Two modelling approaches are presented. In the first approach, a spring describing the behaviour of short embedment lengths in pullout tests was used for predicting the behaviour of longer embedment lengths. In the second approach, spring characteristics obtained from an experimentally determined bond stress against anchorage length envelope are used in FE modelling of beams. Both approaches showed good agreement between analytical and experimental results. However, further development on the analytical modelling of the bond interaction is required, in order to consider the effect of all parameters t...

Concrete formwork wall serving also as reinforcement

Abstract: The invention concerns wall made of concrete or the like produced from an unfolded formwork integrated in the wall and comprising two boxing panels (8. 8', 10) facing each other and connected by linking elements ( 1 ) articulated to the casing panels via stiffeners (2) integral with the casing panels The space between said casing panels after they have been unfolded is filled with a filler material (7) such as concrete. At least one of the casing panels comprises an embedement made of concrete, mortar or the like ,in added thickness relative to the stiffeners ( (2) and articulated linking elements (1). Said embedment (11, 12) is arranged outside and/or inside the casing panel, the stiffeners ((2) and the articulated linking elements (1) and the casing panel (8) when it is embedded form an inner reinforcement of the wall encased in the wall and covered by said embedment. The use of seperate stiffeners, which must be inserted before casting concrete, is thus avoided or highly reduced.

Efficiently installable and durable embedment tile for producing tactilely-detectable surfaces

Abstract: Disclosed is an embedment tile for producing a tactilely detectable surface in a moldable material and method for using same The tile comprises a tile member substantially planar in form, having a pattern of upwardly extending projections on its upper surface forming a tactilely detectable pattern and two or more cross beams on the lower surface of the tile member, the cross beams having hollow chambers defined by a sidewall, end openings and optional apertures to allow for the release of air and moldable material from the exterior into the hollow chambers of the cross beams as the tile is embedded in the material, thus easing and speeding installation of the tile in the moldable material The embedment tile may further consist of support members that function to support and further interlock the embedment tile to the moldable material once set

Behavior of Axially Loaded Pile Groups Subjected to Lateral Soil Movement

Abstract: Response of a pile due to lateral soil movement and axial load has been investigated extensively by the authors. Typical results deduced from single pile tests in sand are presented previously in terms of effect of pile diameter, soil movement profile, sliding depth and magnitude of axial load. In this paper, a brief description of the apparatus was presented. Results from two model tests were reported, which were conducted on two instrumented pile groups embedded in sand subjected to a uniform lateral soil movement at a sliding depth of 0.57 L ( L = pile embedment length). Analysis revealed the effect of the direction and depth of soil movement, together with the magnitude of axial load, which are illustrated via profiles of bending moment, shear force, soil reaction, and pile deflection along instrumented piles in groups at various stages.

Test of Headed Reinforcement in Pullout II: Deep Embedment

Abstract: A total of 32 pullout tests were performed for the multiple headed bars relatively deeply embedded in reinforced concrete column-like members. The objective was to determine the minimum embedment depth that was necessary to safely design exterior beam-column joints using headed bars. The variables for the experiment were embedment depth of headed bar, center-to-center distance between adjacent heads, and amount of supplementary reinforcement. Regular strength concrete and grade SD420 reinforcing steel were used. The results of the test the indicated that a headed bar embedment depth of was not sufficient to have relatively closely installed headed bars develop the pullout strength corresponding to the yield strength. All the experimental variables, influenced the pullout strength. The pullout strength increased with increasing embedment depth and head-to-head distance. It also increased with increasing amount of supplementary reinforcement. For a group of closely-spaced headed bars installed in a beam-column joint, it is recommended to use column ties at least 0.6% by volume, 1% or greater amount of column main bars, and an embedment depth of or greater simultaneously, to guarantee the pullout strength of individual headed bars over 125% of and ductile load-displacement behavior.

Pipe-Soil Interaction Behaviour during Lateral Buckling

Abstract: This paper addresses lateral pipe/soil interaction behavior at the large displacements that occur with lateral buckling of a pipeline. Force-displacement-response models were developed by the Safebuck joint-industry project (JIP) to replace the use of simple friction- coefficient approximations. Such simplistic models are unrealistic for modeling large lateral displacements or the building of soil berms that occurs with cyclic lateral loading. The models are based on large- and small-scale tests carried out by the Safebuck JIP on deepwater soils from the Gulf of Mexico and west Africa, as well as on kaolin clay. To this database was added project-specific test data donated by JIP participants. Four stages of pipe/soil interaction are considered: Embedment of the pipe at installation. Breakout during buckle formation on the basis of different levels of initial pipe embedment. Large-amplitude lateral displacement as the buckle forms. Cyclic lateral displacement influenced by the building of soil berms. While breakout loads have been the subject of much research and published papers on pipeline stability, there is little guidance on modeling lateral resistance at the large displacements experienced in lateral buckling. There is also little guidance on modeling subsequent large-amplitude cyclic behavior, which occurs with each shutdown and restart of the pipeline. New equations were proposed where appropriate, and recommended models for each part of the characteristic response were developed. These models provide a valuable basis for lateralbuckling design guidance. They currently are being applied by JIP participants on a number of projects in which pipelines are being designed for lateral buckling.

Wiring board and method of manufacturing the same, and ceramic chip for embedment

Abstract: PROBLEM TO BE SOLVED: To provide a wiring board having an excellent adhesion strength between an interlayer insulation layer constituting a build-up layer and a ceramic chip for embedment. SOLUTION: A wiring board 10 comprises a board core 11, a ceramic chip 101 for embedment, and a build-up layer 31. The board core 11 has an accommodation hole 91 that opens on a core main surface 12. The ceramic chip 101 for embedment has a plurality of terminal electrodes 111 and 112 consisting of metalized layers 116 projected on a chip main surface 102, and a dummy metallized layer 118 projected on the chip main surface 102. The ceramic chip 101 for embedment is accommodated in the accommodation hole 91, with the core main surface 12 and the chip main surface 102 directed to the same side. The build-up layer 31 has a structure that interlayer insulation layers 33 and 35 and a conductive layer 42 are alternately laminated on the core main surface 12 and the chip main surface 102. COPYRIGHT: (C)2007,JPO&INPIT

Bond decay at bar–concrete interface under variable fatigue loads

Abstract: The bond decay at the bar–concrete interface under variable fatigue loads is investigated in this paper. Two kinds of loading paths are considered: low- and high-amplitude cycles. Based on the shear-lag model, the governing equations of the problem are established and solved with reference to three different interfacial degradation models. By the aid of Paris formula, the interfacial debonding rate, the debonded length, and the pull-out force are studied. The effect of the amplitude of the middle applied load and of several material parameters on bond decay is discussed. It is found that the power-degradation model is suitable for short embedment lengths, while both the linear-degradation model and the modified power-degradation model are advantageous in study of bond in long embedment length. It is also found that interfacial friction plays an important role in resisting interfacial debonding, in spite of the effects of Poisson's contraction.

The determination of the embedment strength of Malaysian hardwood.

Abstract: Research on determining the embedment strength of Malaysia timber species is currently being conducted. Prior to this, there is no data on the embedment strength of Malaysian timber available as there are no study been conducted locally which emphasize in this area. The experimental works on determining this fundamental parameter of a connection are being carried out on selected species of local hardwood timber. The species selected represents various joints groups. Data and results were analysed and using the embedment strength values approaches which are similar to those adopted in Europe, the basic load of timber joints to be used in the limit state design method will be forwarded for consideration to be incorporated in the Malaysian code of practice.

Uplift response of strip anchors in sand using fem

Abstract: The load displacement relationship of shallow rigid strip anchors embedded in sands and subjected to uplift pressures has been examined by using the finite element method. The soil medium is modeled as a linear elastic-perfect plastic material following Mohr-Coulomb failure criterion and an associated flow rule. The computed load displacement response is presented in non-dimensional form. The ultimate failure load is expressed in the form of non-dimensional uplift factor F, the variation of which is plotted as a function of soil friction angle (phi) and the embedment ratio (lambda) of the anchor. The magnitudes of F-gamma, as well as the displacements of anchor at failure are found to increase with the increases in the values of the anchor embedment ratio and the angle of shearing resistance of soils. In all the cases, it was seen that even at complete collapse, the soil mass lying just vertically above the anchor remains more or less non plastic. The failure of the anchor occurs on account of the development of a thin curved plastic shear zone emerging from the bottom of the anchor and then extending up to the ground surface.

Dem analysis of soil-pipeline interaction in sand under lateral and upward movements at deep embedment

Abstract: The soil-pipeline interactions under lateral and upward pipe movements in sand are investigated using DEM analysis. The simulations are performed for both medium and dense sand conditions at different embedment ratios of up to 60. The comparison of peak dimensionless forces from the DEM and earlier FEM analyses shows that, for medium sand, both methods show similar peak dimensionless forces. For dense sand, the DEM analysis gives more gradual transition of shallow to deep failure mechanisms than the FEM analysis and the peak dimensionless forces at very deep depth are higher in the DEM analysis than in the FEM analysis. Comparison of the deformation mechanism suggests that this is due to the differences in soil movements around the pipe associated with its particulate nature. The DEM analysis provides supplementary data of the soil-pipeline interaction in sand at deep embedment condition.

Influence of fastener size on lateral strength of steel-to-wood screw joints

Abstract: Single shear steel plate to wood screw joints were tested to study the influence of screw diameter on lateral strength for load parallel to grain or perpendicular to grain. Joint tests encompassed use of steel wood screws with shank diameters of 4.2 mm (by 51 mm long) and 5.5 mm (by 76.4 mm long); steel self tapping screws of 6.1 mm diameter (by 76.4 mm long); and steel lag screws of 6.4 mm diameter (by 76.4 mm long). In addition, embedment tests were conducted using these fasteners and two other screw sizes (2.86-mm wood screw and 7.8-mm lag screw). Although in general the failure mode and strength depended on both the direction of loading and the screw diameter, differences between strengths parallel to grain and perpendicular to grain increased in proportion to screw diameter. There was only a small effect of loading direction for joints with 4.2-mm-diameter wood screws and less, although subsidiary embedment tests revealed that convergence of the strengths in the two loading directions occurred at shank diameters of about 3 mm and less. Existence for steel screws of a threshold fastener diameter below which the direction of loading has no influence on joint strengths is consistent with prior findings for nails or bolts. Based on the new data and synthesis of earlier data, it is concluded that structural design practices need only account for the influence of loading direction on lateral strengths of screws when fastener diameter is greater than 4.2 mm.

Two-dimensional large deformation finite element analysis for pulling-up of plate anchor

Abstract: Based on mesh regeneration and stress interpolation from an old mesh to a new one, a large deformation finite element model is developed for the study of the behaviour of circular plate anchors subjected to uplift loading. For the determination of the distributions of stress components across a clay foundation, the Recovery by Equilibrium in Patches is extended to plastic analyses. ABAQUS, a commercial finite element package, is customized and linked into our program so as to keep automatic and efficient running of large deformation calculation. The quality of stress interpolation is testified by evaluations of Tresca stress and nodal reaction forces. The complete pulling-up processes of plate anchors buried in homogeneous clay are simulated, and typical pulling force-displacement responses of a deep anchor and a shallow anchor are compared. Different from the results of previous studies, large deformation analysis is of the capability of estimating the breakaway between the anchor bottom and soils. For deep anchors, the variation of mobilized uplift resistance with anchor settlement is composed of three stages, and the initial buried depths of anchors affect the separation embedment slightly. The uplift bearing capacity of deep anchors is usually higher than that of shallow anchors.

Influence of Soil Strength on Optimal Embedment Depth of Geosynthetic Reinforcement Layer in Granular-Reinforced Foundations

Abstract: The effect of soil friction angle value on the optimal embedment depth of a single geosynthetic reinforcement layer in granular foundations was investigated with a numeric simulation approach. The numeric model was validated against the measured results of reduced-scale plane strain model foundations tested with two footing width sizes. The model foundations were constructed with gravel-sized round aggregates and were subjected to the concentrated vertical load of shallow footings analogous to a track-ballast system. After the validation of the numeric model, a series of parametric analyses was carried out with an idealized, full-scale foundation model to investigate the dependency of the optimal reinforcement embedment depth on the soil friction angle value. The optimal reinforcement depth in field-scale reinforced foundations under strip footings is between 10% and 15% of footing width, depending on the site soil friction angle value. The optimal reinforcement depth is found to be slightly closer to the...

Ascending and descending device of window curtains

Abstract: This invention is related to an ascending and descending device of window curtains. The device is provided with an axle center apparatus having a base. The axle center apparatus is externally covered with a transmission apparatus which is peripherally provided with a gear plate and is nested with an embedment apparatus. The embedding body of the embedment apparatus is mutually fitting with the peripheral positioning embedding trough of the axle center apparatus. And the embedment apparatus is internally provided with a recovery component. Another end of the recovery component is resistantly pressing inside a shell body. When using it, insert the reel of the window curtains into the shell body and make the window curtains be rolled up on the shell body. By using the rope of the gear plate to pull the gear plate to rotate, and the embedment apparatus is rotated therewith, which makes the embedment apparatus no longer be limited by a blocking body and makes the embedding body thereof depart from the embedding trough of the axle center apparatus to move the embedment apparatus toward the shell body and drive the shell body to rotate, thus the window curtains and the reel thereof are rotated therewith. Further by the oppression of the elastic member, the embedment apparatus is recovered to a mutual fitting state with the axle center apparatus, which makes the window curtains and the reel thereof stop on a located position after rotating. Therefore, by continuously persisting the movements mentioned above, the window curtains can be ascended or descended. And by the mutual embedment of such embedding members, the force of the buckle positioning can be increased whereby the window curtains rod will not slide when rolling window curtains with large surface are heavier. And taking advantage of the mutually driving between the axle center apparatus with different surface area, the transmission apparatus and the embedment apparatus, the window curtains can be rolled up easily just like the effect of gear-change.

Three-dimensional nonlinear finite element static calculation of complete bearing spiral case

Abstract: Complete bearing spiral case is a kind of preponderant spiral case,which has not been applied to large power stations in our country so far.If this embedment method is applied to No.15 turbine unit in Three Gorges Hydropower Station,the reliability of spiral case structure and the security of units under working condition must be verified by both numerical calculation and model test.Therefore,a three-dimensional nonlinear finite element analysis has been carried out by using a damaged plasticity model for concrete.Accordingly,the stress distribution of spiral case and rebar,the range of damages in surrounding concrete,the width of concrete cracks,and the displacement of structure are obtained.The result shows that the embedment method ensures the structure's safety in strength.The application of this embedment method to No.15 turbine unit of Three Gorges Hydropower Station is feasible if some appropriate engineering measures are adopted for limiting the width of concrete cracks satistying the(code's) requirement.

Steel column having rustproof property of embedment land side part

Abstract: PROBLEM TO BE SOLVED: To provide a steel column having excellent rustproof protective property of an embedment land side part even when marking by dogs or the like is carried out. SOLUTION: The steel column having rustproof property of the embedment land side part has an anti-corrosive coating and has a coating layer comprising an anticorrosion material excellent in durability to water solution containing ammonium ions in an outer part of at least 50 mm of the steel column on the atmosphere side and on the filling material side of an upper end part of an interface where the steel column contacts with the filling material for embedment. COPYRIGHT: (C)2006,JPO&NCIPI

Numerical simulation of cracking using embedded surfaces in a three dimensional constitutive model for concrete

Abstract: This thesis presents three new three-dimensional constitutive models for cementitious materials. All three models use embedded damage planes and adopt the theory of contact mechanics to describe the characteristic behaviour of cracks formed in concrete and other cementitious materials. The first of these is a smooth frictional contact model which incorporates a simplified Mohr-Coulomb yield surface to capture plastic slip planes in concrete. The aim of the model is to accurately represent the behaviour of smooth construction joints in large concrete structures. The second proposed model is the dual-surface contact model. The model employs two contact surfaces, each of which nominally represents a different component of concrete composite, i.e. coarse aggregate particles and mortar. The third model is the 'embedded planes with local plasticity contact' model (EPLPC). The model adopts a yield surface, which is similar to the damage surface in strain space, to capture plastic embedment on crack surfaces. This model, as with the dual-surface contact model, is developed to simulate crack opening-closing, as well as the behaviour of aggregate interlock. The models are integrated with a hardening/softening frictional plasticity component that uses a smoothed triaxial plastic yield surface developed from that used by Lubliner et al. (1989). Each of the proposed models is implemented with a consistent tangent stiffness operator and return mapping algorithm, similar to that of the Closest Point Projection algorithm. The models are coded in Fortran77 and implemented in a constitutive driver program, and also a finite element software package LUSAS. The models are assessed using a series of stress/strain paths at the constitutive level, and also validated against a range of experimental data. These include data from uniaxial and multiaxial compressive tests, uniaxial tensile tests with and without unloading-reloading cycles, and also tests in which shear load is applied on open cracks.