Recent Construction Technology Innovations and Practices for Large-Span Arch Bridges in China

Arch bridges provide significant technical and economic benefits under suitable conditions.In particular,concrete-filled steel tubular(CFST)arch bridges and steel-reinforced concrete(SRC)arch bridges are two types of arch bridges that have gained great economic competitiveness and span growth potential due to advancements in construction technology,engineering materials,and construction equipment over the past 30 years.Under the leadership of the author,two record-breaking arch bridges—that is,the Pingnan Third Bridge(a CFST arch bridge),with a span of 560 m,and the Tian’e Longtan Bridge(an SRC arch bridge),with a span of 600 m—have been built in the past five years,embodying great technological breakthroughs in the construction of these two types of arch bridges.This paper takes these two arch bridges as examples to systematically summarize the latest technological innovations and practices in the construction of CFST arch bridges and SRC arch bridges in China.The technological innovations of CFST arch bridges include cable-stayed fastening-hanging cantilevered assembly methods,new in-tube concrete materials,in-tube concrete pouring techniques,a novel thrust abutment foundation for nonrocky terrain,and measures to reduce the quantity of temporary facilities.The technological innovations of SRC arch bridges involve arch skeleton stiffness selection,the development of encasing concrete materials,encasing concrete pouring,arch rib stress mitigation,and longitudinal reinforcement optimization.To conclude,future research focuses and development directions for these two types of arch bridges are proposed.

Experimental study on ultimate flexural capacity of steel encased concrete composite beams

Based on the experimental study and inelastic theory, the ultimate flexuralcapacity of steel encased concrete composite beams are derived. The difference between steel encasedconcrete composite beams with full shear connection and beams with partial shear connection,together with the relationship between the inelastic neutral axis of steel parts and concrete parts,are considered in the formulae. The calculation results of the eight specimens with full shearconnection and the three specimens with partial shear connection are in good agreement with theexperimental data, which validates the effectiveness and efficiency of the proposed calculationmethods. Furthermore, the nonlinear finite element analysis of the ultimate flexural capacity of thesteel encased concrete composite beams is performed. Nonlinear material properties and nonlinearcontact properties are considered in the finite element analysis. The finite element analyticalresults also correlate well with the experimental data.

计算机取证技术研究

本文首先介绍了计算机取证的基本概念、发展历史及国内外研究概况,然后给出了计算机取证的基本步骤和一个具体的计算机取证实例,最后说明了目前计算机取证尚存在的问题及发展趋势。

Experimental study on the compressive behaviors of CFRP tube-encased concrete columns

Nine square concrete columns including 6 CFRP/ECCs and 3 concrete columns are prepared,which have cross-section of 200 mm×200 mm and height of 600 mm.The CFRP tubes with fibers oriented at hoop direction were manufactured to have 3 or 5 layers of CFRP with 10 mm, 20 mm,or 40 mm rounding corner radii at vertical edges.A 100 mm overlap in the direction of fibers was provided to ensure proper bond.Uniaxial compression tests were conducted to investigate the compressive behavior.It is evident that the CFRP tube confinement can improve the behavior of concrete core,in terms of axial compressive strength or axial deformability.Test results show that the stress-strain behavior of CFRP/ECCs vary with different confinement parameters,such as the number of confinement layers and the rounding corner radius.

Experimental Study on the Compressive Behavior of CFRP/ECCs

In this study,nine square concrete columns,including six CFRP/ECCs and three plain concrete control specimen columns,were prepared. The CFRP tubes with fibers oriented in the hoop direction were manufactured with 10,20,or 40 mm rounded corner radii at vertical edges. A 100 mm overlap in the direction of fibers was provided to ensure a proper bond. Uniaxial compression tests were conducted to investigate the compressive behaviors including the axial strength,stress-strain response,and ductility. It is evident that the CFRP tube confinement can improve the compressive behavior of concrete core,in terms of axial compressive strength or axial deformability. Based on the experimental results and some existing test database attained by other researchers,a design-oriented model is developed. The predictions of the model for CFRP/ECCs show good agreement with test results.

论计算机取证

随着信息技术的发展,计算机犯罪活动越来越多。如何利用计算机取证技术搜集电子证据、惩治犯罪,已成为人们关注的焦点。该文主要介绍了计算机取证的概念、原则、过程以及一些常用的计算机取证工具,并详细介绍了Encase软件的使用。

Mechanical Behavior of a Partially Encased Composite Girder with Corrugated Steel Web： Interaction of Shear and Bending

The synergistic use of partially encased concrete and composite girders with corrugated steel webs （CGCSWs） has been proposed to avoid the buckling of corrugated steel webs and compression steel flanges under large combined shear force and bending moment in the hogging area. First, model tests were carried out on two specimens with different shear spans to investigate the mechanical behavior, including the load-carrying capacity, failure modes, flexural and shear stress distribution, and development of concrete cracking. Experimental results show that the interaction of shear force and bending moment causes the failure of specimens. The bending-to-shear ratio does not affect the shear stiffness of a composite girder in the elastic stage when concrete cracking does not exist, but significantly influ- ences the shear stiffness after concrete cracking. In addition, composite sections in the elastic stage sat- isfy the assumption of the plane section under combined shear force and bending moment. However, after concrete cracking in the tension field, the normal stresses of a corrugated web in the tension area become small due to the ＂accordion effect,＂ with almost zero stress at the flat panels but recognizable stress at the inclined panels. Second, three-dimensional finite-element （FE） models considering material and geometric nonlinearity were built and validated by experiments, and parametric analyses were conducted on composite girders with different lengths and heights to determine their load-carrying capacity when subjected to combined loads. Finally, an interaction formula with respect to shear and flexural strength is offered on the basis of experimental and numerical results in order to evaluate the load- carrying capacity of such composite structures, thereby providing a reference for the design of partially encased composite girders with corrugated steel webs （PECGCSWs） under combined flexural and shear loads.

A comparative study for the performance of encased granular columns

This paper describes a three-dimensional(3D) numerical analysis of a test embankment on geotextileencased columns(GECs), in comparison with two-dimensional(2D) axisymmetric and plane strain analyses. The 3D numerical analysis was performed considering a rectangular strip under the embankment centerline. The 2D analysis was also carried out using axisymmetric unit cell and plane strain approaches.Numerical results indicated that the adopted 3D strip model represented well the measured deformations and pore pressure evolution during embankment construction and post-contraction periods.Unlike the unit cell model, both plane strain and 3D analyses could properly determine the settlement profile along the embankment base as well as the profile of the horizontal soil deformation beneath the embankment toes. The plane strain analysis, however, was not able to compute the geotextile ring force which might be simply calculated using the axisymmetric unit cell approach. The paper also showed that, due to horizontal boundary fixities applied to the embankment borders, the unit cell model clearly underestimated the tension developed in the basal geogrid.

Research on Algorithm for Generating Min-Area Rectangle Encasing Box for Closed Contour

In many engineering applications, it is necessary to calculate the min-area encasing box of a circumscription. In this paper, an algorithm for generating the min-area rectangle encasing box, based on revolving angle, is investigated and hence put forward. The algorithm computes the areas of the outer rectangular bounds of a closed contour in different revolving angles θ by dispersing approach where 0< θ < π/2 because of the axial symmetry. It is very simple, straight forward and highly efficient. The complexity of its computing time reaches O(n·k ). Practical applications suggest its usefulness and efficiency.

Experimental research on mechanical properties of prestressed truss concrete composite beam encased with circular steel tube

Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.

Linux系统取证实践研究

IDC服务器调查取证过程中经常会涉及到Linux操作系统,调查人员较为关注Linux操作系统的查看、密码绕过、逻辑卷的查看、Linux分区只读设置、Linux下Web服务器的调查和数据库调查等内容。本文在研究Linux常用取证技术的基础上,介绍了Linux系统取证的实践操作步骤,为取证调查一线的工作与研究人员提供参考。

基于EnCase的计算机取证技术研究

本文首先介绍了计算机取证的概念、电子证据的特点、计算机取证的步骤,然后探讨了如何利用EnCase来进行计算机取证。

Evaluation of Current Design Practices on Estimation of Axial Capacity of Concrete Encased Steel Composite Stub Columns： A Review

This paper presents the design assessment of concrete encased I-sections composite column based approaches given in Eurocode, ACI Code, BS Code and AISC-LRFD. This study includes comparison of various design parameters and evaluation of design strength based on the procedures predicted in the various codes of practices. A practical example has been assumed and calculation has been shown to evaluate their potentiality in understanding in predicting the potentiality of various procedures. The obtained results based on the methods varies widely, because of the different design considerations adopted by the different codes. As such, they have hardly considered the effect of confinement of the concrete due to the presence of longitudinal reinforcements as well as lateral ties. The study has attempted to throw light on critical review and their potentiality in assessing the strength of such concrete encased composite column under purely axial loads.

Resistance of Commercial Bed Covers against Faecal Pellets of House Dust Mites:Behaviour of Seams and Zippers

This study evaluated the allergen impermeability against airborne allergens of dust mite droppings through all parts of commercial bed covers, including surface seams and zippers. Specimens were taken from places with and without seams and zipper. A novel penetration cell was developed to expose the specimens to an inoculum of purified mite droppings that was assessed for its allergen content Der p1 prior to the penetration tests. Using covers of different construction and material, the penetration level increased significantly in the presence of seams and zippers and could reach up to 6% depending on the seam’s/zipper’s characteristics and quality. Therefore, zippers and seams have to be considered as access points for the penetration of mite droppings. As for the penetration of airborne mite particles through the zipper, the penetration level was greatly attenuated by the presence of a cover strip. Depending on the respective quality and the construction type, the mite allergen Der p1 penetrated most likely through the zipper and seams of the specimens, already after a single laundry cycle. Hence, laundry may compromise the barrier performance and proves to be an important quality feature. In all samples, the textile surface showed sufficient allergen impermeability. Our conclusions provide recommendations to both manufacturers and users.

电子证据的数据恢复及实践

在司法实践中,有大量的案件需要电子文件、图形图像、影音视频等信息作为证据使用,于是经常遇到犯罪嫌疑人使用的存储设备出现损坏或被故意删除犯罪证据,造成关键证据无法读取、甚至丢失。公安机关侦查部门就需要采用特殊手段设法将其恢复或将其转化为正常状态的文件,从而形成有法律效力的电子证据。本文介绍了运用几种有效的数据恢复工具,通过数据恢复的方式,提取由于各种因素导致的电子证据被删除情况,这为对电子证据的来源提供增加了一个渠道。

基于EnCase系统的计算机取证分析

随着信息技术的发展,计算机犯罪活动越来越多.如何利用计算机取证技术搜集电子证据、惩治犯罪,已成为人们关注的焦点.文章首先介绍了计算机取证的概念、原则和方法,并通过一个具体案例详细介绍了Encase系统的功能和使用方法,展示了计算机取证的过程和EnCase简单易用的特点.

Experimental,analytical and numerical studies on concrete encased trapezoidally web profiled cold-formed steel beams by varying depth-thickness ratio

Concrete encased with trapezoidally corrugated web profiled cold-formed steel beams are used worldwide to improve resistance toward fire and corrosion,higher load carrying capacity as well as significant increase in the bending stiffness by encasing concrete on the beam portion.The present work gives a detailed description on the experimental,analytical and numerical investigation on the flexural behavior of concrete encased trapezoidally corrugated web profiled cold-formed steel beams which were simply supported at both ends and subjected to two point symmetric loading.The flexural behavior of such structure has been experimentally tested to failure under pure bending.To find the effct of concrete encasement in the web,12 experiments were conducted by two different series.Beams having three different web corrugation angles of 0°,30°,and 45°with two different web depth-thickness(dw/tw)ratios of 60 and 80 were tested.Experimental results such as load-deflection relationship,ultimate capacity,load-strain relationship,moment-curvature curves,ductility and failure mode indices of the specimens are presented.From the static bending tests the concrete encased trapezoidally corugated web beam showed improved moment carrying capacity,ductility bchavior and the resistance to transverse deflections in comparison to concrete encased with plain web beam.Especially for the beams with concrete encased 30°trapezoidally corrugated web having(dw/tw)ratio 60 and 80,the loading capacity was improved about 54%and 67.3%and the ductility also increased about l.6 and 3.6 times,when compared to concrete encased beams with plain web.This research should contribute to the future engineering applications on seismic resistant structures and efficient usage of concrete encased with cold-formed steel beams by exhibiting its super elasto-plastic property.The analytical and numerical results showed good agreement with the experimental results at yield load,which indicates that the proposed analytical equations can be applied in predicting flexural strength accurately for such concrete encased trapezoidally corrugated web profiled cold-formed steel beams.