Increase In Embedment Depth Research Articles

Horizontal Pullout Capacity of a Group of Two Vertical Square Anchors Embedded in Medium Dense Sand

In the present study an attempt is made to evaluate the ultimate horizontal pullout capacity of group of two square anchors embedded in medium dense sand by conducting laboratory model tests. The size of the model box used in the present study is 1.2m lengthx0.75m width and 1.5m height. A series of experiments were conducted on single and group of anchors subjected to horizontal pullout load on mild steel square plates of size 10 cm and 15 cm were used .Clean dry local river sand was used in the present study. All the tests were carried out on dry clean sand with a relative density of 55% corresponding to medium dense state. The raining technique was adopted to prepare the sample in the model box to achieve the desired density. In the present study the ratio of H/B is equal to 5 and 6; where H = depth of embedment from top of tank to bottom of lower anchor, B=width of anchor. The parameter S/B is equal to 0,1,2; where S = clear spacing between the anchor, and B= width of anchor. It was found from the present study as H/B ratio increases the pull out capacity increases and also for each H/B ratio as the S/B ratio increases pull out capacity decreases due to decrease in passive resistance. In the present study the group efficiency factor was found which is defined as the ratio pull out capacity of group of anchors to the pull out capacity of single anchor. It was found that the group efficiency factor was found to be greater than 1 and further as S/B ratio increases the group efficiency factor decreases for same H/B ratio. Also as H/B increases the efficiency factor also increases. The anchor breakout factor (Nγ) was also found which tends to increase with increase in depth of embedment and decreases with clear spacing between the anchors. The present data was compared with that of published literature on single anchors and it was found to compare well.

Critical setback distance for a footing resting on slopes under seismic loading

A footing located on slopes possess relatively lower bearing capacity as compared to the footing located on the level ground. The bearing capacity further reduces under seismic loading. The adverse effect of slope inclination and seismic loading on bearing capacity can be minimized by proving sufficient setback distance. Though few earlier studies considered setback distance in their analysis, the range of considered setback distance was very narrow. No study has explored the critical setback distance. An attempt has been made in the present study to comprehensively investigate the effect of setback distance on footing under seismic loading conditions. The pseudo-static method has been incorporated to study the influence of seismic loading. The rate of decrease in seismic bearing capacity with slope inclination become more evident with the increase in embedment depth of footing and angle of shearing resistance of soil. The increase in bearing capacity with setback distance relative to level ground reduces with slope inclination, soil density, embedment depth of footing and seismic acceleration. The critical value of setback distance is found to increase with slope inclination, embedment depth of footing and density of soil. The critical setback distance in seismic case is found to be more than those observed in the static case. The failure mechanisms of footing under seismic loading is presented in detail. The statistical analysis was also performed to develop three equations to predict the critical setback distance, seismic bearing capacity factor (Nrqs) and change in seismic bearing capacity (BCR) with slope geometry, footing depth and seismic loading.

Elastoplastic consolidation above and beneath strip anchors under uplift forces

ABSTRACTAlthough the uplift behavior of offshore plate anchors under undrained conditions has been investigated well in the past, studies on the behavior of anchors under long-term sustained loading are in relatively few numbers. The time required for consolidation under sustained load is important because the shear strength of soil changes after dissipation of excess pore pressure. In this paper, small strain finite-element analyses have been performed to investigate the consolidation time history above and beneath strip anchors. The modified cam clay plasticity constitutive model is used for modeling coupled pore fluid stress analysis. The effects of magnitude of preloading with embedment level have been studied. As expected, the FE results have shown that excess pore pressure dissipation time for soil above the anchor increased with the increase in embedment depth and the magnitude of preload. Rapid dissipation of negative excess pore pressure beneath the anchor was observed with increasing embedment depth, if the preload magnitude is equal to or more than 60% of the undrained capacity. Observed consolidation responses are presented as nondimensional design charts and simplified equations for ease of practice.

Performance of Anchors in Concrete Controlled by Splitting Failure under Dynamic Push-In Loadings

Anchors in concrete are widely used to transfer any given load combination into a concrete member. The dynamic behavior of post-installed rebar anchors has been experimentally investigated in this study. The attention was focused on anchors controlled by concrete splitting failure, the case that may occur with anchors and fastenings located close to an edge or to a corner. In this regard, Split Hopkinson Pressure Bar (SHPB) technique has been employed to test the anchorage systems under dynamic push-in loads. The effect of loading rates, concrete compressive strengths, and embedment depths on ultimate splitting load has been studied. The results showed the loading rates had a pronounced effect on the anchor ultimate loads and total absorbed energy by the anchors. Whereas the variation of concrete compressive strength influenced the ultimate load, the increase in embedment depth had no noticeable effect on ultimate load.

Induced Settlement Reduction of Adjacent Masonry Building in Residential Constructions

Many buildings and heritages are yearly damaged due to new construction plans in vicinity of them. Current engineering practice in Iran lacks unfortunately regulations to enforce the designers of new buildings to re-evaluate the structural integrity of adjacent old buildings which are prone to unacceptable induced settlement and distortions. To damage assessment of old building, deflection ratio was used for unreinforced load-bearing wall (masonry) building. In this paper some practical methods like story limits for the new buildings according to the specification of old structure, improvement of shallow foundations and increasing the embedment depth of new foundations have been studied in order to decrease the settlement and undesirable effects of adjacent constructions. Parametric studies using numerical analysis, Flac3D, have paved the way how above mentioned methods can remedy the problem. So induced consolidation settlements due to new construction in adjacent building were studied. In conclusion, increase of admissible story of new building up to one floor by increase of embedment depth as much as one meter and three floors by using of mat foundation instead of single footing were highlighted these methods.

Effects of insulation types on in-plane shear behavior of insulated concrete sandwich wall panels with GFRP shear connector

This paper describes the in-plane shear behavior of insulated concrete sandwich wall panels (CSWP) reinforced with corrugated glass fiber-reinforced polymer (GFRP) shear connector. The study included testing 8 insulated CSWP specimens with different types of insulation and corrugated shear connector. All specimens were loaded in direct shear. The test variables were embedment depth of shear connector and removal of adhesive stress between insulation and concrete. Test results indicated that the reinforcement of corrugated GFRP shear connector significantly increased in-plane shear strength. And dispersion reinforcement will be more effective in the case of expanded polystyrene (EPS) insulation. Meanwhile, reinforcement at a degree close to 45° will be more effective in the case of extruded polystyrene with surface treatment (XPSS) insulation. Increase of embedment depth of shear connectors was able to restrain pull-out phenomenon of shear connectors. And removal of adhesive force of insulation tended to decrease in-plane shear strength.

Numerical study of pull-out capacities of dynamically embedded plate anchors

Dynamically embedded plate anchors (DEPLAs) are a type of offshore anchor that combine the capacity advantages of vertically loaded plate anchors with the installation benefits of dynamically installed anchors. DEPLA capacity under monotonic loading conditions in clay has been investigated through centrifuge and field tests. In this paper, the monotonic capacity of DEPLAs in normally consolidated clay was studied using a three-dimensional large deformation finite element approach based on frequent mesh regeneration. Results from the numerical simulations were validated by comparison with centrifuge test data and existing numerical and analytical solutions for circular and rectangular plates. The effect of anchor embedment depth, anchor roughness, fluke (or plate) thickness, plate inclination, and DEPLA geometry were investigated in a parametric study where soil was prescribed to remain attached to the DEPLA base. The findings indicate that for a horizontal anchor subjected to vertical loading, most DEPLA geometries exhibit deep behaviour at an embedment ratio of 2.5, but that this embedment ratio is dependent upon the plate inclination, with vertical plates requiring the highest embedment depth for a deep localized failure mechanism. At a shallow embedment depth equal to one plate diameter, the reduction in capacity factor as the plate inclination changes from horizontal to vertical is 23.4%, compared with 1.3% at an embedment depth equal to four plate diameters. Plate roughness and fluke thickness are shown to have a minimal effect on the anchor capacity factor for vertical loading. Analyses that considered the breakaway (no tension) at the DEPLA base demonstrated that the anchor capacity factor approaches the no breakaway value as the embedment depth increases and as the soil strength (relative to the effective unit weight of the soil) decreases. The paper proposes a simple means of approximating the anchor capacity factor for breakaway conditions, by summing the capacity factor in weightless soil (which is unique for a given DEPLA geometry) and the normalized overburden pressure.

Evaluation of embedded concrete-filled tube (CFT) column-to-foundation connections

Concrete-filled tubes (CFTs) are effective structural components. Relative to conventional reinforced concrete components, they have higher strength-to-size efficiency and facilitate rapid construction. Yet they are not used frequently in US construction. The component response is well understood from extensive experimental and analytical studies that have been conducted on CFT components themselves. There remains a fundamental challenge of implementing these components in structural systems, which is caused by the uncertainty of the connection design and performance. Relative to component research, limited research has focused on the connections of CFT columns. A recent research effort has resulted in a new embedded connection for a CFT column anchored into a reinforced concrete foundation. The connection is fully capable of transferring combined bending and axial loads and has sufficient deformability to sustain multiple inelastic deformation cycles under extreme loading. In addition, the connection has unique features that facilitate constructability and rapid construction. However, the connection design to date is solely based on experimental study, which evaluated a very limited range of design parameters. A coordinated analytical study, using high-resolution continuum models, was undertaken to investigate the unstudied parameters and develop appropriate design expressions, which is the subject of this paper. An analytical model was developed and verified using the test results. The verified model was then used to conduct a parametric study to enhance the understanding of the experimental behavior and extend the test databases. Parameters studied included the embedment depth, diameter-to-thickness (D/t) ratio, shear reinforcement ratio, strength ratio of the concrete in the footing and concrete infill, and the axial load ratio. From the analysis results, the failure mechanisms were evaluated with respect to the individual parameters. The results showed that an increase in embedment depth, D/t ratio, shear reinforcement ratio, the axial load ratio, or the ratio of the concrete strength in the footing relative to the concrete infill of CFT column increased the connection strength and could result in ductile yielding of the CFT column, which is the desired response mode. Finally, the analysis and test results were combined to develop a refined design equation for the required embedment depth.

Numerical simulation of a partially buried pipeline in a permeable seabed subject to combined oscillatory flow and steady current

Hydrodynamic forces exerting on a pipeline partially buried in a permeable seabed subjected to combined oscillatory flow and steady current are investigated numerically. Two-dimensional Reynolds-Averaged Navier–Stokes equations with a k− ω turbulent model closure are solved to simulate the flow around the pipeline. The Laplace equation is solved to calculate the pore pressure below the seabed with the simulated seabed hydrodynamic pressure as boundary conditions. The numerical model is validated against the experimental data of a fully exposed pipeline resting on a plane boundary under various flow conditions. Then the flow with different embedment depths, steady current ratios and KC numbers is simulated. The amplitude of seepage velocity is much smaller than the amplitude of free stream velocity as expected. The normalized Morison inertia, drag and lift coefficients based on the corresponding force coefficients of a fully exposed pipeline are investigated. The normalized Morison force coefficients reduce almost linearly with the increase of embedment depth and that the KC only has minor effect on the normalized Morison coefficients. It is also found that the permeable seabed condition causes a slight increase on the inline force and has a little effect on the lift force, compared with corresponding conditions in an impermeable bed.

Effect of Geotextile Ties on Uplift Capacity of Anchors Embedded in Sand

This paper presents the results of experimental investigation on the effect of geotextile ties on uplift capacity of anchors embedded in sand. Uplift capacity of anchor increases with increase in embedment depth to base diameter (H/D) ratio irrespective of type of anchor. With the introduction of tie to anchors, uplift capacity of anchors increases and optimum number of layers of ties is found to be 2. A non linear power model has been developed to predict the uplift capacity at any settlement (QR) of anchors with tie in terms of uplift capacity at any settlement (QURs) of anchor without tie, H/D ratio, number of layers of tie and displacement to base diameter ratio (Δ/D). The model is applicable for predicting QR having the values of QRS, H/D, N and Δ/D in the range of 0.257 ≤ QURs ≤ 1.420, 1.5 ≤ H/D ≤ 3.0, 1 ≤ N ≤ 4, 0.8 ≤ Δ/D ≤ 8.

End Bearing Capacity of Drilled Shafts in Sand: A Numerical Approach

In this paper, a modeling procedure is carried out to numerically analyze the end bearing capacity of drilled shafts in sand. The Mohr–Coulomb elastic plastic constitutive law with stress dependent elastic parameters is used for all numerical analyses performed in this study. The numerical results are compared with the available experimental equations. It is seen that numerical results are in good agreement with experimental equations. The variation of the end bearing capacity of drilled shafts versus embedment depth is also studied. Numerical results show that with increase in pile embedment depth, the end bearing capacity increases. However, the rate of increase becomes smaller as the pile embedment depth increases. Also, numerical analyses show that, for equal settlement, the end bearing decreases with increase in the pile diameter. Finally, a sensitivity analysis is performed to obtain the separate effect of each sand parameter on the end bearing capacity of drilled shafts, and the parameters that are most influential are identified.

Three-Dimensional Response of Buried Pipes under Circular Surface Loading

Three-dimensional response of buried pipes under circular surface loading is investigated using the finite-element method. Previous work by Poulos in 1974 is reexamined, considering the longitudinal behavior of pipes under surface loading. Analyses are performed for pipes of varying stiffnesses and embedment depths. When stiff pipes are located close to the ground surface, the burial depth has little impact on the peak deflection. However flexible pipe deflections decrease significantly as embedment depth increases. Not surprisingly, peak moments increase with pipe stiffness and decrease as the pipes become more remote from the ground surface. The comparison of the new results with those of Poulos indicates that his Mindlin solution calculations are somewhat conservative relative to the finite-element solutions for deeply buried pipes, but unconservative at shallow burial.

An experimental investigation of vertical vibration of model footings on sand

Many free and forced vertical vibrations tests were conducted on surface and embedded models for footings on dry and moist poorly graded sand that has the following properties: D 10 = 0·21 mm, D 30 = 0·305 mm, D 60 = 0·423 mm, C u = 2, C c = 1·05, G s = 2·66, γ max = 1·74 cm −3 and γ min = 1·4 g cm −3. The tests were conducted at relative density Dr = 82%. The effect of mass, area, geometry, embedment, saturation, load amplitude and frequency were studied. For this purpose square, rectangular and circular models of concrete footings were chosen. Swieleh sand was chosen as the foundation soil. Results have been obtained for models having different mass, same base shape and area; models of different base area and equal base shape and mass; and models of different base shape geometry and about equal masses and base areas. Forced vertical vibration tests results showed an increase in natural frequency and a reduction in amplitude with the increase in embedment depth, degree of saturation and footing base area. Increasing the mass of model footing resulted in a decrease in the natural frequency while the dynamic response increased. Also, results showed that the circular model footing gives low values of dynamic response in comparison to other models. Free vertical vibration test results showed an increase in damping ratio with increase in the base area of the model footing, depth of embedment and saturation of sand. On the other hand, the results showed a decrease in damping ratio with increase in the footing mass. Circular footing gives the highest value of damping ratio among other footings. Results showed that the best method for evaluating the dynamic stiffness for vertical vibration is using Dobry and Gazetas 1 ( J. Geotech. Engng, ASCE, 1986, 112, 109–133) equations together with the formula proposed by Ronald and Bojan 2 ( J. Geotech. Engng, ASCE, 1995, 121, 274–286) for evaluating the equivalent shear modulus.