Suction Caisson Capacity in Anisotropic, Purely Cohesive Soil

This paper presents a plastic limit analysis of the lateral load capacity of suction caissons in an anisotropic, purely cohesive soil assuming conditions of rotational symmetry about the vertical or gravity axis. The formulation utilizes a form of the Hill yield criterion that is modified to allow for different soil strengths in triaxial compression and extension. Using this yield criterion, energy dissipation relationships are formulated for continuous and discontinuous deformation fields. These dissipation relationships are then applied to a postulated caisson failure mechanism comprising a wedge near the free soil surface (mudline), a two-dimensional flow-around failure at depth, and a hemispherical slip surface at the base of the rotating caisson. The plastic limit analysis predictions compared favorably to predictions obtained from finite-element simulations employing a Hill yield criterion. For the range of anisotropic undrained strength properties commonly reported for normally K0-consolidated clays, parametric studies indicate that suction caisson horizontal load capacities predicted using a conventional approach (a von Mises yield surface fitted to the soil simple shear strength) will differ from anisotropic predictions by less than 10%.     

Flexural Response of Reinforced Concrete Beams Strengthened with End-Anchored Partially Bonded Carbon Fiber-Reinforced Polymer Strips

This paper presents the results of experimental and analytical studies carried out to investigate the flexural behavior of reinforced concrete beams strengthened with end-anchored partially bonded carbon fiber-reinforced polymer (CFRP) strips. A total of six beams, each 2400 mm long, 150 mm wide, and 250 mm deep with a tension steel reinforcement ratio of 1.18%, were tested. One beam was left unstrengthened as the control, another beam was strengthened with a fully bonded CFRP strip, and the remaining four beams were strengthened with partially bonded CFRP strips placed on the tension face of the beam and fixed at both ends using a mechanical anchor. The influence of varying the CFRP unbonded length (250 mm, 750 mm, 2×500 mm, and 1,250 mm) on the beam flexural response was studied. The experimental results revealed that end-anchored partially bonded CFRP strips significantly enhanced the ultimate capacity of the control beam and performed better than the fully bonded strip with no end-anchorage. This observation stresses the importance of end-anchorage in such strengthening schemes, especially considering that the end-anchored partially bonded CFRP strengthened beams showed similar flexural behavior trends. Finally, an inelastic section analysis procedure that takes into consideration the incompatibility of strains was developed to verify the obtained test results. The analysis produced good predictions of the experimental results in terms of the moment-curvature response and showed the effect of CFRP unbonded length on the strain of the internal tension steel.     

Effects of Electrode Configuration on Electrokinetic Stabilization for Caisson Anchors in Calcareous Sand

The study is on the electrokinetic strengthening of caisson anchors embedded in offshore calcareous sand. The effects of electrode configuration on the effectiveness of electrokinetic treatment are investigated based on electric field analysis and are verified by results from a series of large scale laboratory tests on caisson models of 200?mm diam and 400?mm height, embedded in calcareous sand submerged under seawater. The electrokinetic treatment generates cementation of soil solids as well as bonding between soil and caisson shafts, which leads to increases in the side resistance and overall pullout resistance. The effectiveness of electrokinetic treatment is directly related to the electric field intensity. A linear relationship is observed between the increase in the side resistance and energy consumption. The study shows that the effectiveness of electrokinetic treatments can be maximized by the optimization of the electric field distribution through the electrode configuration.     

Uplift Behavior of Blade-Underreamed Anchors in Silty Sand

To evaluate the uplift behavior of anchors installed by the blade underreaming system, a numerical model for anchors in silty sand has been developed in this study and the calculated results are compared to the results of full scale anchor pullout tests. Although the blade-underreamed anchor tends to be irregular in shape due to possible collapse of the borehole, the excavated anchor showed an underreamed body of approximately multiple-stepped shape. Despite the difference in shape, the numerical results indicate that the difference between the load–displacement curve of the multiple-stepped anchor and that of the conical shaped anchor is small. In addition, the anchorage behavior of conical shaped anchors calculated from this numerical model was in good agreement with those of full scale anchor tests. No sign of progressive soil yielding along the underreamed body was found from the numerical analysis. So, the pull-out capacity of this underreamed anchor increases more than linearly with the length of the underream. Since only a small underream angle is needed to generate a substantial increase in anchor pull-out resistance, the ultimate pull-out capacity of the blade-underreamed anchor is found to be higher than that of straight shaft anchor in silty sand.     

Experimental and Numerical Study of Uplift Behavior of Shallow Circular Anchor in Two-Layered Sand

In this study, the behavior and scale effect of shallow circular anchors in two-layered sand is evaluated by comparing the results of a conventional 1?g model test with the results of finite-element analysis. The finite-element analysis is performed using an elastoplastic model in which progressive failure with shear band effect is introduced into the constitutive equation. The model is able to successfully predict the anchor behavior in two-layered sand. The direction of shear band propagation, within a sand layer, was observed to be a function of the density alone, regardless of the position of the layer. When the thickness of the lower layer was increased, maximum uplift resistance was found to increase with increasing thickness of a dense layer above a medium bed, and to decrease with increasing thickness of a medium layer above a dense bed. The scale effect was remarkable in the lower layer of dense sand.     

Novel Anchor System for CFRP Rod: Finite-Element and Mathematical Models

An innovative wedge-anchor system with a longitudinal circular profile has been designed for gripping carbon-fiber-reinforced-polymer rods. The anchor system, consisting of a barrel, a number of wedges, and a sleeve, is capable of carrying the ultimate tensile strength of the rod. Three-dimensional (3D) and axisymmetric finite-element models have been developed and applied in order to determine the stresses inside the anchor system. Using the 3D model, the overall performance of the anchor represented by the tensile load-displacement relationship compared favorably with the experimental results. A comparison study between the 3D and axisymmetric models revealed that the axisymmetric model underestimated the contact pressure on the rod surface. Using the force-fitting principle of thick cylinders, a mathematical model was also developed, and under specific assumptions, the mathematical solution compared favorably with finite-element model results.     

Design Considerations of Carbon Fiber Anchors

Carbon fiber-reinforced polymer (CFRP) sheets can be used to strengthen existing reinforced concrete members. However, debonding (separation of the CFRP sheet from the concrete surface) may occur at less than 50% of CFRP sheet’s tensile capacity, implying that half of the CFRP material is ineffective in increasing the strength of a concrete member. The use of carbon fiber anchors can increase the amount of tension carried in the CFRP sheets. Forty specimens were tested to develop initial design parameters of carbon fiber anchors. Tests showed that by providing anchors with a total cross-sectional area at least two times greater than that of the longitudinal sheet, it was possible to fracture the CFRP sheets. The best results were obtained using a greater number of smaller anchors. Further, surface preparation is unimportant when the CFRP sheets were well anchored and a 1:4 transition slope can manage any offsets in surface level. The general anchor design was then implemented on a series of long beams and demonstrated that the full CFRP sheet tensile capacity can be realized without incurring limitations due to debonding.     

自钻式锚管在软土层基坑支护中的应用实例

本文结合工程实例介绍了自钻式锚管在淤泥质土及砂层中的设计分析、抗拔试验以及基坑支护中的成功应用,为自钻式锚管在软土层中的应用积累了宝贵的经验。     

Experimental Behavior of Bridge Beams Retrofitted with Postinstalled Shear Connectors

A number of older bridges were constructed with floor systems consisting of a noncomposite concrete slab over steel girders. A potentially economical means of strengthening these floor systems is to connect the existing concrete slab and steel girders with postinstalled shear connectors to permit the development of composite action. This paper presents the results of an experimental investigation of this concept. Five large-scale noncomposite beams were constructed, and four of these were retrofitted with postinstalled shear connectors and tested under static load. The retrofitted composite beams were designed as partially composite with a 30% shear connection ratio. A noncomposite beam was also tested as a baseline specimen. Test results showed that the strength and stiffness of existing noncomposite bridge girders can be increased significantly. Further, excellent ductility of the strengthened partially composite girders was achieved by placing the postinstalled shear connectors near zero-moment regions to reduce slip demand on the connectors. The test results also showed that current simplified design approaches commonly used for partially composite beams in buildings provide good predictions of the strength and stiffness of partially composite bridge girders strengthened using postinstalled shear connectors.     

预应力锚拉桩在滑坡治理中的应用

介绍了预应力锚拉桩原理及特点,结合滑坡防治工程实例重点对其在滑坡治理设计中的应用进行了阐述。通过工程实例应用,验证了锚拉抗滑桩在受力特征、设计原则、施工方案等方面的优势,对滑坡的治理效果进行了监测验证。