Elastic Anisotropic Viscoplastic Modeling of the Strain-Rate-Dependent Stress–Strain Behavior of K0-Consolidated Natural Marine Clays in Triaxial Shear Tests

This paper presents a new three-dimensional (3D) anisotropic elastic viscoplastic (EVP) model for the time-dependent stress–strain behavior of K0-consolidated marine clays. A nonlinear creep function with a limit for the creep volumetric strain under an isotropic or odometer K0-consolidated stressing condition and a nonsymmetrical elliptical loading locus are incorporated in the 3D anisotropic EVP model. An α-line defines the inclination of the nonsymmetrical elliptical loading locus in the p′-q plane and is commonly used for natural soils. All model parameters are determined from the results of one set of consolidated undrained compression tests and an isotropic consolidation/creep test. With the parameters determined, the 3D anisotropic EVP model is used to simulate the behavior of K0-consolidation tests and the strain-rate-dependent stress–strain behaviors of the K0-consolidated triaxial compression and extension tests on natural Hong Kong marine deposit clay specimens. These triaxial K0-consolidated specimens were sheared at step-changed axial strain rates from +2?to?+0.2, +20, ?2 (unloading) and +2%/h (reloading) for compression tests; or from ?2?to??0.2, ?20, +2 (unloading), and ?2%/h (reloading) for extension tests, all in an undrained condition. The simulation results of all these tests are compared with the test results. The validation and limitations of the model are then evaluated and discussed.     

Relationship between the Undrained Shear Strength, Water Content, and Mineralogical Properties of Fine-Grained Soils

The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soils; these relationships, however, have not yet been investigated. The findings described in this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals, their quantity in soil composition, and the interlayer water quantity in the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.     

Shear Stress in Smooth Rectangular Open-Channel Flows

The average bed and sidewall shear stresses in smooth rectangular open-channel flows are determined after solving the continuity and momentum equations. The analysis shows that the shear stresses are function of three components: (1) gravitational; (2) secondary flows; and (3) interfacial shear stress. An analytical solution in terms of series expansion is obtained for the case of constant eddy viscosity without secondary currents. In comparison with laboratory measurements, it slightly overestimates the average bed shear stress measurements but underestimates the average sidewall shear stress by 17% when the width–depth ratio becomes large. A second approximation is formulated after introducing two empirical correction factors. The second approximation agrees very well (R2>0.99 and average relative error less than 6%) with experimental measurements over a wide range of width–depth ratios.     

Behavior of Composite Unreinforced Masonry–Fiber-Reinforced Polymer Wall Assemblages Under In-Plane Loading

An experimental investigation was conducted to study the in-plane behavior of face shell mortar bedded unreinforced masonry (URM) wall assemblages retrofitted with fiber-reinforced polymer (FRP) laminates. Forty-two URM assemblages were tested under different stress conditions present in masonry shear and infill walls. Tests included prisms loaded in compression with different bed joint orientation (on/off-axis compression), diagonal tension specimens, and specimens loaded under joint shear. The behavior of each specimen type is discussed with emphasis on modes of failure, strength and deformation characteristics. Results showed that the application of FRP laminates on URM has a great influence on strength, postpeak behavior, as well as altering failure modes and maintaining the specimen integrity. The retrofitted specimens reached compressive strength of 1.62–5.64 times that of their unretrofitted counterparts, depending on the bed joint orientation, and joint shear strength increased by eightfold.     

Shear Strengthening of Reinforced Concrete Beams Using Carbon-Fiber-Reinforced Polymer Laminates

Shear failure is catastrophic and occurs usually without advance warning; thus it is desirable that the beam fails in flexure rather than in shear. Many existing reinforced concrete (RC) members are found to be deficient in shear strength and need to be repaired. Externally bonded reinforcement such as carbon-fiber-reinforced polymer (CFRP) provides an excellent solution in these situations. To investigate the shear behavior of RC beams with externally bonded CFRP shear reinforcement, 11 RC beams without steel shear reinforcement were cast at the concrete laboratory of the New Jersey Institute of Technology. After the beams were kept in the curing room for 28?days, carbon-fiber strips and fabrics made by Sika Corp. were applied on both sides of the beams at various orientations with respect to the axis of the beam. All beams were tested on a 979?kN (220?kips) MTS testing machine. Results of the test demonstrate the feasibility of using an externally applied, epoxy-bonded CFRP system to restore or increase the shear capacity of RC beams. The CFRP system can significantly increase the serviceability, ductility, and ultimate shear strength of a concrete beam; thus, restoring beam shear strength by using CFRP is a highly effective technique. An analysis and design method for shear strengthening of externally bonded CFRP has been proposed.     

Interface Characteristics and Laboratory Constructability Tests of Novel Fiber-Reinforced Polymer/Concrete Piles

Conventional pile materials such as steel, concrete, and timber are prone to deterioration for many reasons. Fiber-reinforced polymer (FRP) concrete composites represent an alternative construction material for deep foundations that can eliminate many of the performance disadvantages of traditional piling materials. However, FRP composites present several difficulties related to constructability, and the lack of design tools for their implementation as a foundation element. This paper describes the results of an experimental study on frictional FRP/dense sand interface characteristics and the constructability of FRP–concrete composite piles. An innovative toe driving technique is developed to install the empty FRP shells in the soil and self-consolidating concrete is subsequently cast in them. The experimental program involves interface shear tests on small FRP samples and uplift load tests on large-scale model piles. Two different FRP pile materials with different roughness and a reference steel pile are examined. Static uplift load tests are conducted on different piles installed in soil samples subjected to different confining pressures in the pressure chamber. The results showed that the interface friction for FRP materials compared favorably with conventional steel material. It was shown that toe driving is suitable for installation of FRP piles in dense soils.     

An exact high order beam element

This work gives the exact stiffness coefficients for an high order isotropic beam element. The terms are found directly from the solutions of the differential equations that describe the deformations of the cross-section according to the high order theory, which include cubic variation of the axial displacements over the cross-section of the beam. The model has six degrees of freedom at the two ends, one transverse displacement and two rotations, and the end forces are a shear force and two end moments. Also given are the equivalent end forces and moments for several cases of loading along the member. The components of the end moments are investigated, and are found for exact results. Comparison is made with the Bernoulli-Euler and Timoshenko beam models.     

塔北隆起张性构造带形成机制与油气关系

塔北隆起张性构造带分布于隆起轴部的轮台断隆上,主要为早期断裂受喜马拉雅运动早期的左旋扭动在浅层派生的北西-南东向张性构造.断裂在平面上呈左行雁列展布,在剖面上为小型地堑组合,部分断裂向深部与先存断裂联合形成负反转构造.与断裂相伴的褶皱构造沿断裂走向分布,且受断裂活动控制.塔北隆起张性构造带位于极有利的构造部位,具有良好的油气远景.     

Design optimization of 3D reinforced concrete structures having shear walls

This paper presents a computer-based method for the optimal design of three-dimensional Reinforced Concrete (RC) structures having beams subjected to shear force and bending moment, columns subjected to biaxial moments, biaxial shears and axial loads, and shear walls subjected to pure shear. Regarding the beams and columns, the design variables are the width, depth and area of longitudinal reinforcement of member sections. The design variables for the shear walls are the thickness of the wall, the area of vertical reinforcement, horizontal distance between the vertical stirrups, the area of horizontal reinforcement, vertical space between the horizontal stirrups, and the area of vertical flexural reinforcement. The Optimality Criteria (OC) method is applied to minimize the cost of the concrete, steel and formwork for the structure. ACI code [1] provisions concerning the strength and ductility of beams, columns and shear walls are taken as constraints. The constraints also impose upper and lower bounds on the dimensions of beams and columns, and on shear wall thickness, reinforcement area and the maximum and minimum vertical and horizontal spaces between the stirrups of the shear walls. Sensitivity analysis is conducted for both internal forces and the capacities of the sections of the beams, columns and shear walls. The features of the design method are illustrated by a solved example.     

Objective Oriented Multistage Ring Shear Test for Shear Strength of Landslide Soil

Ring shear tests were conducted on five samples of different nature with a modified Imperial College type ring shear machine. The three different testing methods used, (1) individual sample testing for each normal stress, (2) increasing load multistage ring shear test, and (3) reducing load multistage ring shear test, all showed similar effective residual internal friction angle for the samples, irrespective of testing method. However, effective residual shear intercept was different according to the testing methodology. The internal friction angle did not vary, particularly after the first minimum point in the stress displacement curve, although the residual shear intercept decreased with increase in the displacement. The thickness of the shearing zone increased along with the displacement. The remolded peak shear strength for saturated conditions at field dry density varied with the consolidation history. Measurement of remolded peak shear strength was possible in a single sample using the increasing load multistage ring shear test at normal consolidation. The equilibrium water content of the sample after the ring shear test was nearly equal to the plastic limit.