Showing papers on "Embedment published in 1994"

Settlement of Shallow Foundations on Sand

Abstract: A new method for estimating the settlement of shallow foundations on sand is presented. The method is based on elastic stress-strain theory and is designed for use with soil data from the Standard Penetration Test (SPT). The elastic modulus is assumed to vary with mean effective normal stress and strain level. The variations of modulus with depth and the effects of footing size and shape, depth of embedment and groundwater level are introduced through their effects on the mean effective normal stress. The non-linear nature of the stress-strain relation is based on a normalized version of the Seed-Idriss curves, which relate shear modulus to strain level and relative density. SPT data are used to estimate relative density. In the general solution, the zone of influence beneath the footing is divided into sublayers and the foundation load is applied in increments. Then the incremental load solution is used to develop a simplified procedure in which the total load may be applied in one increment. The proposed method is applied to data from published case histories. The results of the proposed method are shown to compare favorably with those from other currently used methods.

Vertical Uplift Capacity of Horizontal Anchors

Abstract: The method of characteristics coupled with a log-spiral failure surface was used to develop a theory for vertical uplift capacity of shallow horizontal strip anchors in a general c-phi soil. Uplift-capacity factors F(c), F(q) and F(gamma), for the effects of cohesion, surcharge, and density, respectively, have been established as functions of embedment ratio lambda and angle of friction phi. The extent of the failure surface at the ground has also been determined. Comparisons made with existing test results support the predictive capability of the theory, and comparisons with the analysis proposed by Meyerhof and Adams show the proposed analysis provides slightly more conservative predictions of pullout capacity.

Suction force below plate anchors in soft clay

Abstract: The results of a number of laboratory model tests for the short‐term ultimate uplift capacity of a circular plate anchor embedded in saturated soft kaolinite and montmorillonite are presented. The tests were conducted with and without venting the bottom of the plate anchor in order to determine the variation of the suction force with embedment ratio. The variation of the suction force is presented in terms of the undrained shear strength of the clay and also the net ultimate uplift capacity.

Analysis of compressible axially loaded piles in rock

Abstract: Analytical solutions are developed for the prediction of the load–settlement response of a compressible axially loaded cast in situ pile in rock. The principal input parameters are derived from the τ–z curve which applies to the contact zone between the pile shaft and the embedment material. For larger diameter piles in rock, these τ–z curves can differ markedly from curves that apply to piles in clay and may include a significant strain hardening region prior to reaching peak strength. In addition to the complete analyses which would normally require the use of a computer, simplified solutions suitable for hand calculations have been derived for the peak load and the pile head displacement to peak. An example of the application of these simplified design calculations is presented.

Performance and Optimization of Induced Strain Actuated Structures Under External Loading

Abstract: This paper addresses the actuator/substrate thickness ratio that maximizes the static/dynamic response of a beam for a variety of actuator-structure integration configurations, actuator activation levels, and inertia/external loading conditions. The three different actuator-structure integration configurations considered are actuators embedded inside the substrate, actuators bonded to the surface of the substrate, and actuators discretely attached and offset from the surface of the substrate. In the category of embedded actuators, a shallow embedment just beneath the surface usually maximizes the moment/induced curvature, but for stiffer actuators, a deeper embedment results in a greater induced curvature

Effect of boundary conditions on buckling of friction piles

Abstract: In practice, evidence suggests that long, slender piles subjected to axial loads can fail under axial stresses below the yield point of the pile material. A general solution for critical buckling capacity of long, slender friction piles in clay is presented using the minimum potential energy method. The Rayleigh-Ritz method is adopted to select deflection functions satisfying six geometric boundary conditions encountered in practice. Parameter studies were performed to investigate the buckling response of fully and partially embedded piles and the effect of pile-top and tip conditions on buckling capacity. Results indicated that the boundary conditions at the pile tip have no effect on the critical buckling capacity in cases in which the nondimensional embedment length (\Ih\N’) exceeded a critical value. In addition, for fully embedded piles, the effect of embedment length was nearly negligible after \Ih\N’ exceeded a value of 6 for fixed-with-sway pile-top conditions.

Determining lengths of installed timber piles by dispersive wave propagation

Abstract: Timber piles are used as a primary means of support for many structures, such as bridges, throughout the continental United States and must periodically be inspected. Sometimes a pile's overall length is not known because pile records are incomplete or nonexistent ; so, calculating the effects of scour on its embedment length can present a problem. A new nondestructive testing method is described that employs dispersive stress-wave propagation and special signalprocessing techniques to find the lengths of installed timber piles. The method was studied and developed in the laboratory and then applied to installed piles in the field for which there were records. Some piles were pulled to verify the method directly. The computed pile lengths, compared with records or measurements after pulling, were within error bounds of approximately ±10 percent. The test method holds promise for calculating the depth and physical condition of deeply embedded piles as well as those embedded in shallow concrete footings, and it has been shown to be predictive for piles of varying physical conditions and ages.

Footing Load Tests on Sand

Abstract: Four full size footings were load tested at a site in Texas. The embedded footings were situated on a thin layer of stiff clay underlain by a thick deposit of medium dense to dense sand. A comprehensive in situ and laboratory testing program was performed to evaluate the engineering properties of the subsoils. Finite element analysis was performed to evaluate the effect of embedment and subsoil layering. The load/settlement response of the footings was compared with 20 procedures for predicting bearing pressure at a settlement of 25 mm (1 in.).

Strengthening of prestressed concrete composite beams using external prestressed stirrups

Abstract: Strengthening of older bridges designed for relatively light loading and traffic is necessary in many places around the world. This paper presents experimental results on the use of external prestressed stirrups to improve the shear strength and concrete-to-strand bond strength of pretensioned composite beams. 5 beams were tested under stationary static loads until failure. The basic unstrengthened beam showed a very dramatic shear failure. The strengthened beams with external prestressed stirrups, however, performed well, even with very short strand embedment lengths. External prestressed stirrups considerably increased the shear capacity of the strengthened beams. Also, when prestressed to adequate levels the stirrups allowed the development of the flexural capacity of the beams with strand embedment lengths as short as 100 times the strand diameter.

Buckling of friction piles supporting bridge foundations

Abstract: In practice, evidence suggests that long, slender piles subjected to axial loads can fail under axial stresses below the yield point of the pile material. However, using the minimum potential-energy method, it is possible to quantify a general solution for the critical buckling capacity of long, slender friction piles in clay. The Rayleigh-Ritz method is used to select deflection functions satisfying nine geometric boundary conditions. The equivalent buckling length and the critical axial load of the piles are determined from eigenvalues estimated by the Jacobi Rotation Transformation method. Parameter studies performed to investigate the buckling response of fully and partially embedded piles indicated that the boundary conditions of pile tip have no effect on the critical buckling loads when nondimensional embedment length exceeds a critical value. The critical value depends on the pile-top condition and embedment ratio (defined as embedded length divided by total pile length). Side friction's contribution to buckling stability results in less than a 7% variation in critical buckling length. The model's applicability is illustrated using a design example and load-test data reported in the literature.

Mechanical and microstructural investigation of the aggregate and cement interface

Abstract: The understanding of the interface between aggregate and cement is crucial in determining the properties of concrete. Recently, a pushout experimental technique and a theoretical model have been developed to determine the stiffness, strength and surface energy of the interface layer. The validity of these material parameters was verified in the present study by examining the effect of diameter and embedment length of aggregate. In addition, the effect of the pretreatment of aggregate surface and various admixtures was investigated. All pushout tests were performed in a closed-loop manner to obtain the load vs. displacement relationship. The interfacial zone was further investigated by using backscattered electron imaging and energy dispersive analysis of x-rays (EDAX) to characterize the microstructure of the interface. The relationship between mechanical properties and microstructure of interfacialzone was studied. It was shown that the microstructure of the interface plays a substantial role in the mechanical behavior of the aggregate/cement bond.

Uplift capacity of strip plate anchors in clay with sloping surface

Abstract: Laboratory model test results to determine the ultimate uplift capacity of strip anchors embedded in a saturated clayey soil are reported. The slope of the ground surface with respect to the horizontal was varied from zero degrees to 25 degrees. Based on the model test results, the variation of the critical embedment ratio and the breakout factor for shallow and deep anchors with the slope of the ground surface are discussed.

Torch-on roofing degranulator system

Abstract: A torch is mounted on the central portion of a frame having a near end portion and a far end portion The torch directs heat toward the far end portion of the frame, adjacent to a rotatable embedment roller A handle is formed on the near end portion of the frame The torch melts the granules of torch-on roofing, and the embedment roller follows behind to smoothen the surface of the roofing in the area of a lap joint

Development of a Plasticity Bond Model for Reinforced Concrete - Preliminary Calibration and Cyclic Applications.

Abstract: : A bond model is developed to describe the inelastic behavior of the bond between reinforcing bars and concrete. The bond model is applicable to both monotonic and cyclic loading conditions. It is based on classical non-associative, elasticity-plasticity theory. The model is calibrated by considering available experimental bond studies for short embedment length bond tests. There is good quantitative agreement between the predictions of the bond model and the results of several published bond pull-out tests with steel bars. The tests vary significantly in specimen configuration, concrete strength, and bar rib geometry. (MM)

Vertical Loads on Drag Embedment Anchors

Abstract: This paper shows that current high holding power anchors can withstand significant vertical loads. By introducing a mooring line angle at the seabed, the vertical load at the anchor only increases slightly. The technical feasibility and economic benefits of this concept are described. New types of drag embedment anchors specifically designed to withstand vertical loads are also discussed.

Interfacial Debonding and Sliding in Brittle Cementmatrix Composites from Steel Fiber Pullout Tests

Abstract: A specially designed single fiber pullout apparatus was used to provide simultaneous results on total fiber displacement versus load in addition to monitoring the fiber displacement at the free end. In this apparatus the fiber was going through the entire specimen, which made it possible to determine the point of complete debonding. To control the embedment length a plastic tube was inserted around the fiber. The described fiber pullout test method coupled with an appropriate analysis provides a quantitative determination of interfacial properties which are relevant to toughening of brittle materials through fiber-reinforcement. The technique was used on a high strength cement-based matrix called the Densified Small Particle system (DSP), and on an ordinary strength matrix. Other parameters investigated included fiber embedment length and fiber volume fraction in the cement matrix. The results indicate that: (1) the dense DSP matrix has significantly improved interfacial properties as compared to the ordinary strength matrix; (2) the major energy of pullout in both systems is due to sliding; and (3) both the debonding energy and sliding energy increase with fiber embedment length. These results are important in the understanding of the role of steel fibers in improving the tensile properties of high performance fiber reinforced composites.

Pull-out of short rods and fibres

Abstract: An experimental study has been carried out of the mechanics of pull-out of short nylon rods embedded in a rubber block, considered as a model of fibres embedded in an elastic resin. Two stages of pull-out were observed. First, rubber became detached from the base of the rod creating a large internal cavity. This process was apparently initiated by internal rupture of rubber under the rod, and occurred when the local triaxial tension reached a value similar to the tensile (Young's) modulus of the rubber. After cavitation, a cylindrical debond propagated up the rod, starting at the embedded end and ending in complete pull-out. Pull-out forces were found to be consistent with a simple fracture mechanics treatment based on the elastic compliance of partially debonded specimens, both measured and calculated by finite element analysis. The fracture energy for debonding is deduced to be about 300 J m−2. The effects of varying rod diameter and depth of embedment are shown to be in satisfactory agreement with theory.

Vertical Displacement Induced in Soil by Conical Shell Foundations

Abstract: Shells can hold prospect for adoption in foundation engineering only if they can be projected as economical alternatives to conventional flat foundations. Therefore, the initial enthusiasm for shell foundations, generated by the saving in construction materials, their structural integrity, and the anticipated improvement in their geotechnical behavior, should be tempered by the fact that they need extra expenditure for construction due to the complexity of their geometry. However, with new innovations in construction industry such as robotics and the progress in fabrication process of precast concrete units, the use of shell foundations becomes more competitive and feasible. This paper is part of an extensive experimental and numerical investigations conducted on different types of shell foundations to examine their performance with respect to: settlement, ultimate bearing capacity, contact pressure, stress distribution, and soil displacement. The work presented in this paper was limited to study vertical displacement induced in the soil by conical shell foundations under axial loading condition at working loads level. Parametric study using finite elements technique was performed on four foundation models (one circular flat and three different conical models). The soil behavior was modelled by a perfectly elastic model and soil parameters were defined by modulus of elasticity (E) and Poisson's ratio (ν). The effect of shell configuration, depth of embedment, soil parameters (ν and E) on the distribution of vertical displacement under the models were investigated and the results were presented in graphical format.

Measuring device for horizontal force acting on building foundation part

Abstract: PURPOSE:To directly measure the fluctuating soil pressure acting on the respective surfaces of the embedment part of a foundation part, the magnitude of the friction of the side surface or bottom surface of the foundation part with an underground surface and a horizontal force allotment ratio at the time of vibration. CONSTITUTION:An underground wall 20 is embedded in a model ground 12 at a predetermined depth of embedment. When this model ground 12 is vibrated, vibrating soil pressure, side surface friction force and bottom surface friction force act on the underground wall 20 crossing the vibration direction of the ground 12 at a right angle and the side surface and bottom plate 18 of the underground wall 12 positioned in parallel to the vibration direction. By the soil pressure and the friction forces, axial tension or shearing force acts on the acrylic rod materials 24, 52, 54 supporting the side surface and bottom plate of the wall 20 to generate distortion. By measuring this distortion by a load cell 30, the horizontal force acting on the respective surfaces of a foundation part can be calculated. When the horizontal force is divided by the inertial force generated in a structure model 12 and a foundation part model 14, the horizontal force allotment ratio of the embedded foundation part can be calculated.

Substructure deletion method: a boundary element approach for elastodynamic problems

Abstract: A Boundary Element formulation of the Substructure Deletion Method for the dynamic analysis of three-dimensional inclusions of arbitrary shape, subjected to external forces and embedded in a homogeneous viscoelastic half-space, is presented in this study. The analysis relies on the BEM for solving both the problem regarding the finite inclusion and the problem of the flat half-space. Such a method has been tested in the computation of the impedance matrix of square embedded foundations, with different values of the embedment ratio. The results are consistent with those obtained in previous studies.