Improvement of soft soils using geogrid encased stone columns

In recent years, geotextile encasement has been used to extend the use of stone columns to extremely soft soils. Although the technique is now well established, little research has been undertaken on the use of other encasement materials such as geogrid. This paper discusses the results of a series of small-scale model column tests that were undertaken to investigate the behaviour of geogrid encased columns. The tests focused on studying the effect of varying the length of encasement and investigating whether a column that was partially encased with geogrid would behave similarly to a fully-encased column. In addition, isolated column behaviour was compared to group column behaviour. The results of partially encased column tests indicated a steady reduction in vertical strain with increasing encased length for both isolated columns and group columns. Bulging of the column was observed to occur directly beneath the base of the encasement. A significant increase in column stiffness and further reduction in column strain was observed for fully-encased columns, with strain reductions in the order of 80%. This range of performance may lend the techniques of partial and full geogrid encasement to a series of potential site applications.     

“高真空击密法”在厦门船运基地软基加固中的应用

本文结合高真空击密法在厦门船运基地的成功应用,对该法施工参数及后评估进行研究,为该法在其他地区软基处理推广中提供指导性依据和借鉴。     

In vitro adsorption study of fluoxetine in activated carbons and activated carbon fibres

We study the in vitro adsorption of fluoxetine hydrochloride by different adsorbents in simulated gastric and intestinal fluid, pH 1.2 and 7.5, respectively. The tested materials were two commercial activated carbons, carbomix and maxsorb MSC30, one activated carbon fibre produced in our laboratory and also three MCM-41 samples, also produced by us. Selected samples were modified by liquid phase oxidation and thermal treatment in order to change the surface chemistry without significant modifications to the porous characteristics. The fluoxetine adsorption follows the Langmuir model. The calculated Q₀ values range from 54 to 1112 mg/g. A different adsorption mechanism was found for the adsorption of fluoxetine in activated carbon fibres and activated carbons. In the first case the most relevant factors are the molecular sieving effect and the dispersive interactions whereas in the activated carbons the mechanism seams to be based on the electrostatic interactions between the fluoxetine molecules and the charged carbon surface. Despite the different behaviours most of the materials tested have potential for treating potential fluoxetine intoxications.     

碳-环氧片材增强铝试件的疲劳响应

对各种类型的铝试件进行疲劳试验以研究组合片材对破损和未破损铝试件的增强效果,探讨加工过程和试件尺寸对疲劳性能的影响。对破损和未破损试件进行修补,比较了其疲劳强度与普通铝S-N曲线上相对应的值。研究显示:黏合剂的抗剪强度对试件的疲劳性能影响很大,尤其在最高荷载水平时。通过准静态试验和相应的数学模型可以获得黏合剂抗剪强度。当黏合剂最大剪应力与抗剪强度近似相等时,可观察到疲劳荷载下试件的早期破坏,很显然后者对修复结构疲劳响应有很大的影响。     

某教学楼基础工程的加固处理

首先通过工况分析,质量事故原因调查分析,对几种方案进行比较,确定了锚杆静压桩加固方案。其次详细论述了该工程锚杆静压桩的设计、施工过程,最后对加固结果进行了总结。     

Flexural Behavior of GFRP-Reinforced Concrete Masonry Beams

An experimental and analytical study is conducted in order to investigate the flexural behavior of masonry beams that are internally reinforced using glass fiber-reinforced polymers (GFRP) rebars. Seven reinforced masonry beams with 4.0- and 2.4-m spans were tested under four-point bending setup. The beams were loaded monotonically up to failure. One had two courses of hollow concrete masonry units and the remaining six beams had three courses. Two masonry beams were reinforced using conventional steel rebars and were considered as the control specimens. The remaining five beams were internally reinforced using GFRP rods with different reinforcement ratios. Beams were detailed to have sufficient shear reinforcement such that they do not fail in shear. Flexural capacity, deformation, curvature, and strains of the tested GFRP-reinforced and steel-reinforced masonry beams were compared and discussed. Using the acquired data from the experimental and analytical studies, effectiveness of GFRP rods as internal reinforcement for concrete masonry beams is demonstrated.     

Provision of Reinforcement in Concrete Solids Using the Generalized Genetic Algorithm

A generalized genetic algorithm has been developed to find the global optimal reinforcement contents for a concrete solid structure subjected to a general three-dimensional (3D) stress field. Feasible solutions were examined based on the genetic algorithm, and the heterogeneous strategy used ensures that all of the local optimal regions are searched and the most optimal reinforcement content found. The effectiveness of the proposed approach has been validated by comparing the steel contents evaluated using the present method with those obtained from other available methods. A more economic design is achieved by the proposed algorithm. The method developed provides the designer with a valuable tool for the determination of reinforcements in complicated solid concrete structures.     

Mechanism of material removal during three-body abrasion of FRP composite

The low-stress abrasive wear behaviour of chopped-glass-fibre-reinforced polyester composites has been studied by using a rubber wheel abrasion test (RWAT) apparatus. Silica sand particles of two different size ranges were used in the current study as dry and loose abrasives. Weight loss of the composites during three-body abrasion has been examined as a function of the sliding distance. Abrasive wear of the composites shows dependence both on abrasive particle sizes and applied load, as well as the weight fraction of glass fibre reinforcement. It has also been observed that the wear rate becomes constant with the increasing sliding distance. Scanning electron microscopy was used to observe the worn surfaces and to understand the mechanism involved in material removal. This revised version was published online in June 2006 with corrections to the Cover Date.     

Realistic Bond Strength of FRP Rebars in NSC from Beam Specimens

The bond strength of reinforcing bars in concrete is a prerequisite for the evaluation of the development length in reinforced concrete structures. This study concerns these phenomena for fiber reinforced polymer (FRP) rebars in normal strength concrete (NSC). Three different types of rebars were tested using the beam specimen: Carbon, glass, and steel. This involved a total of 26 beam specimens containing 10, 16, and 19?mm rebars. The test embedment lengths were 10, 15, and 20 times the rebar diameter (db). For each rebar tested, the results concern load deflection curves, bond stress-slip responses, and the mode of failure. The results showed that the bond strength of a FRP rebar is, generally, lower than that of steel rebar. Based on this and previous research, proposals for the average bond strength and for the development length of straight FRP rebars under tension in NSC are made.     

Influence of Reinforcement on the Behavior of Concrete Bridge Deck Slabs Reinforced with FRP Bars

This paper presents the results of an experimental study to investigate the role of each layer of reinforcement on the behavior of concrete bridge deck slabs reinforced with fiber-reinforced polymer (FRP) bars. Four full-scale concrete deck slabs of 3,000?mm length by 2,500?mm width and 200?mm depth were constructed and tested in the laboratory. One deck slab was reinforced with top and bottom mats of glass FRP bars. Two deck slabs had only a bottom reinforcement mat with different reinforcement ratios in the longitudinal direction, while the remaining deck slab was constructed with plain concrete without any reinforcement. The deck slabs were supported on two steel girders spaced at 2,000?mm center to center and were tested to failure under a central concentrated load. The three reinforced concrete slabs had very similar behavior and failed in punching shear mode at relatively high load levels, whereas the unreinforced slab behaved differently and failed at a very low load level. The experimental punching capacities of the reinforced slabs were compared to the theoretical predictions provided by ACI 318-05, ACI 440.1R-06, and a model proposed by the writers. The tests on the four deck slabs showed that the bottom transverse reinforcement layer has the major influence on the behavior and capacity of the tested slabs. In addition, the ACI 318-05 design method slightly overestimated the punching shear strength of the tested slabs. The ACI 440.1R-06 design method yielded very conservative predictions whereas the proposed method provided reasonable yet conservative predictions.