Cable Nets Research Articles

Field measurements of anchored flexible systems for slope stabilisation: Evidence of passive behaviour

Flexible systems anchored to the ground constitute a technique for slope surface stabilisation. They are formed by membranes (cable nets, wire mesh, ring net), reinforcement cables and bolts tightly anchored to the ground forming regular patterns. Most manufacturers and independent researchers assume active behaviour of these systems when they propose their design models, which means that the system avoids occurrence of instability. To consider active behaviour, two conditions have to be fulfilled: the membrane has to be initially prestressed and the slope must present a convex shape. Neither of these two conditions has been verified so far, therefore, there are no guarantees that current design methods are adequate. Review of the technical brochures of manufacturers shows that applied prestress force on membranes and reinforcement cables is nonexistent or very low.In this paper, three field systems in north Spain with cable nets anchored to the ground have been instrumented. Net cables, reinforcement cables and bolt heads have been instrumented by using sensors based on electrical extensometry. Tensile forces on cables and compression forces on bolt heads have been monitored for more than a year from the beginning of installation. Initial tensile forces in net and reinforcement cables induced an average value of 0.7% and 2.1%, respectively, of the ultimate strength of each component. In relation to bolts, average compression force on bolt heads was 5.3% of their ultimate strength.These measurements demonstrate that prestress force on flexible systems is very low, and nearly negligible. Therefore, flexible systems anchored to the ground cannot be considered as active, but passive, which means that most current design methods are not adequate.

"Landshape"--Modular Constructions of Wildlife Crossings

In 2010, the American organization ARC held an international competition to design a series of 25 wildlife crossings across highways to connect the southern and northern Rocky Mountains. Zwarts & Jansma Architects, in collaboration with OKRA landscape architects, Iv-Infra, and Sjef Jansen Plan Ecology, won 1 of the 5 finalists' places with their Landshape design. For the designers and ecologists, the main challenge was to create a series of wildlife crossings that would be buildable, affordable, and adaptable to context. To meet the set criteria, the team made an important technical invention. They designed a repeatable, modular structure. For its construction, the team developed a flexible formwork, which can be used to create variable shells. The formwork is made of cable nets, over which a fabric (textile membrane) is placed. Its unique property is that the cable nets can be re-used many times in varying forms. The ecological composition of an area is the decisive factor in the composition of a wildlife crossing. The most important organizational feature of the architecture is the extrapolation of existing curves in the landscape. With Landshape, the team produced a physical entity that connects culture and nature.

전산구조해석을 위한 기하학적 비선형 유한요소해석 예제 개발

An undergraduate course named computational structural analysis becomes more significant in recent years because of its important role in industries and the recent innovation in computer technology. Typically, the course consists of introduction to finite element method, utilization of general purpose finite element software, and examples focusing on static and linear analyses on various structural members such as a beam, truss, frame, arch, and cable. However, in addition to the static and linear analyses, current industries ask graduates to acquire basic knowledge on structural dynamics and nonlinear analysis, which are not listed in the conventional syllabus of the computational structural analysis. Therefore, this study develops geometrically nonlinear examples, which can help students to easily capture the fundamental nonlinear theory, software manipulation, and problem solving skills. For the purpose, five different examples are found, developed for the analyses of cables and cable nets, which naturally have strong geometrical non-linearity. In the paper, these examples are presented, discussed, and finally compared for a better subject development.

USAGE OF SOCIAL NETWORKING WEBSITES: LITHUANIAN UNIVERSITY STUDENTS’ POSITION

Over the latter decade a rapid development of information communication technologies has been going on in various directions. Technological possibilities have increased very significantly (Lamanauskas, 2011). The development of internet and technologies related with it has been extremely fast. A lot of internet service providers have appeared in the market, their number still continues to grow. The internet connection methods are changing - from the ordinary usage of phone line modems (dial - up) to broadband internet technology (DSL) and cable TV internet nets. It can be asserted, that over the mentioned period Web 1.0 internet (static, used for getting information) has been changed to Web 2.0 internet (social). The internet diaries, social portals, technologies allowing live communication on the internet (Internet Relay Chat, IRC), talk programme Windows Live Messenger (MSN), ICQ forums and other have occurred and are spreading. With the appearance of “Skype”, the internet telephony has acquired a qualitatively new characteristic and practically has become a daily routine. Thus, today a consumer can create his profile on the internet, can make friends, communicate in the interest groups and so on. It can be stated, that every human being contributes in his own way to the internet and at the same time to ICT development, in general. It is obvious, that together with technological problems also arise social internet problems. Social networking websites are closely related with economical, psychological, educational, paleological and other aspects. There is a shortage of researches grounding socio-educational social network aspects. It is important to know not only how much time the consumers spend surfing the net, but how much of this time is allotted for communicating in social networking websites, which of them are the most popular and why, how the respondents evaluate social networking website functions, what in general they know about them, what advantages, disadvantages and threats they discern. Finally, it is important to find out whether the usage of social networking websites improves information – communication abilities in some way. Key words: social networking websites, survey, university students.

An Extended Force Density Method for the form finding of cable systems with new forms

The Force Density Method (FDM) is a well known and extremely versatile tool in form finding of cable nets. In its linear formulation such method makes it possible to find all the possible equilibrium configurations of a net of cables having a certain given connectivity and given boundary conditions on the nodes. Each singular configuration corresponds to an assumed force density distribution. Its improvement as Non-Linear Force Density Method (NLFDM) introduces the possibility of imposing assigned relative distances among the nodes, the tensile level in the elements and/or their initial undeformed length. In this paper an Extended Force Density Method (EFDM) is proposed, which makes it possible to set conditions in terms of given fixed nodal reactions or, in other words, to fix the positions of a certain number of nodes and, at the same time, to impose the intensity of the reaction force. Through such extension, the (EFDM) enables us to deal with form findings problems of cable nets subjected to given constraints and, in particular, with mixed structures, made of cables and struts. The efficiency and the robustness of method are assessed through comparisons with other form finding techniques in dealing with characteristic applications to the prestress design of cable systems. As a further extension, the EFDM is applied to structures having some parts not yet geometrically defined, as can happen in designing new creative forms.

On the force density method for slack cable nets

The design of cable nets and light tenso-structures requires a non conventional mechanical analysis, due either to the various sources of non linearity (large displacements, unilateral behaviour of the cables, non conservative loads) and to the fact that the initial configuration of the cable net is not known, depending on the prestress applied and, in general, on the dead load acting on it. As a consequence, the first problem that the engineer has to face is to determine the initial state of the structure under its own weight compatible with a set of fixed supports (the so called zero state). This problem is known as form finding.The paper examines the force density method for form finding, and it is presented a generalization that uses the exact expressions of the equilibrium derived from the equation of the catenary. The method allows to obtain an exact configuration that may be used as a starting point for subsequent incremental non linear analyses.In the paper it is shown that the use of the exact equilibrium conditions leads to a form finding method that is very similar to the FDM, but yields significant differences in the initial form when the weight of the cables is not negligible. A dimensionless parameter is introduced as degree of freedom of the form.

SOCIALINIAI TINKLAPIAI: NAUJA EDUKACINĖ ERDVĖ

Over the latter decade the spread of information communication technologies was going on in various directions. Technological possibilities grew up very significantly (Lamanauskas, 2011). Especially rapid was the development of the internet and technologies related with it. A lot of internet service providers occurred in the market, their number still continues to grow. The internet link methods change - from the ordinary usage of phone line modems (dial - up) to broadband internet technology (DSL) and cable TV internet nets. It can be asserted, that over the mentioned period Web 1.0 internet (static, used for getting information) was changed by Web 2.0 internet (social). The internet diaries, social portals, technologies allowing live communication on the internet (Internet Relay Chat, IRC), talk programme Windows Live Messenger (MSN), ICQ forums and other have occurred and are spreading. With the occurrence of “Skype”, internet telephony acquired a qualitatively new characteristic and practically became a daily routine. Thus, today a consumer can create his profile on the internet, can make friends, communicate in the interest groups and so on. It can be stated, that every human being in his own way contributes to the internet and at the same time to ICT development, in general. It is obvious, that together with technological problems arise social internet problems as well. Social networking websites (SNW) are closely related with economical, psychological, educational, valeological and other aspects. There is a lack of researches based on socio-educational social networking website aspects. It is important to know not only how much time the consumers spend surfing the net, but how much time is allotted for communicating in social networking websites, which of them are the most popular and why, how the respondents evaluate social networking website functions, what in general they know about them, what advantages, disadvantages and threats they discern. Finally, it is important to find out whether usage of social networking websites makes information – communication abilities better in any way. Key words: ICT, educational technologies, social networking websites

SOCIAL NETWORKING WEBSITES: NEW EDUCATIONAL SPACE

Over the latter decade the spread of information communication technologies was going on in various directions. Technological possibilities grew up very significantly (Lamanauskas, 2011). Especially rapid was the development of the internet and technologies related with it. A lot of internet service providers occurred in the market, their number still continues to grow. The internet link methods change - from the ordinary usage of phone line modems (dial - up) to broadband internet technology (DSL) and cable TV internet nets. It can be asserted, that over the mentioned period Web 1.0 internet (static, used for getting information) was changed by Web 2.0 internet (social). The internet diaries, social portals, technologies allowing live communication on the internet (Internet Relay Chat, IRC), talk programme Windows Live Messenger (MSN), ICQ forums and other have occurred and are spreading. With the occurrence of “Skype”, internet telephony acquired a qualitatively new characteristic and practically became a daily routine. Thus, today a consumer can create his profile on the internet, can make friends, communicate in the interest groups and so on. It can be stated, that every human being in his own way contributes to the internet and at the same time to ICT development, in general. It is obvious, that together with technological problems arise social internet problems as well. Social networking websites (SNW) are closely related with economical, psychological, educational, valeological and other aspects. There is a lack of researches based on socio-educational social networking website aspects. It is important to know not only how much time the consumers spend surfing the net, but how much time is allotted for communicating in social networking websites, which of them are the most popular and why, how the respondents evaluate social networking website functions, what in general they know about them, what advantages, disadvantages and threats they discern. Finally, it is important to find out whether usage of social networking websites makes information – communication abilities better in any way.

Characterisation of pressure coefficients on hyperbolic paraboloid roofs

The necessity of covering large areas without intermediate supports requires the design of medium to large span roofs. Tensile structures made of cable nets represent, among other structural solutions, one of the technologies available to do this. They owe their appeal to lightness, cost-effectiveness and aesthetics. For these structures, however there is a lack of clear regulations concerning structural design, especially regarding assessment of environmental loads. This paper is part of an extensive research project on the behaviour of tensile hyperbolic paraboloid roofs. The first stage of the project developed a procedure for optimisation of their shapes during preliminary design. The second stage, the results of which are presented here, focused on characterisation of wind pressure distributions. The results of wind tunnel tests are discussed and synthesised in pressure coefficient maps. These can be used for design applications and lend themselves to implementation in Codes.

Form-finding of a mixed structure with cable nets and tubular trusses

This paper presents the main results of the form finding analysis, model testing and on-site investigation on a mixed structure consisting on a system of steel tubular trusses coupled with a spatial cable net. Firstly, the combining method of force density and finite element is proposed for the form finding analysis of the mixed structure. Then, experimental tests are carried out on a scaled model in order to assess the different levels of pretension to be introduced in the cable system. Finally, the result of the on-site assessment activity carried out to monitor the real force level acting on different cables is presented and the comparison between the inspection results and the design target is made. The construction of the mixed structure has been successfully carried out and completed on the basis of the work presented in this paper.

Nonlinear dynamic behavior of saddle-form cable nets under uniform harmonic load

The dynamic response of saddle-form cable nets is investigated in this paper. Even though they consist of cables, which are well known for their geometric nonlinearity, such systems could be characterized as weakly nonlinear due to the high levels of pretensioning of their cables and to their hyperbolic paraboloid surface, having opposite curvatures at all points and thus increased stiffness. Nevertheless, resonance phenomena that are typical of highly nonlinear systems are detected here, for common geometries and levels of pretension, even for low levels of load amplitude. First, a single-degree-of-freedom (SDOF) cable net is studied analytically and numerically, and nonlinear resonances are confirmed. Then, the response of multi-degree-of-freedom (MDOF) cable nets, subjected to harmonic dynamic excitation, is investigated. Although the static response is proved to be almost linear, the dynamic nonlinearity is intense, as verified by jump phenomena, bending of the response curve, superharmonic resonances, and dependence on the initial conditions.

Dynamic modelling and analysis of space webs

Future space missions demand operations on large flexible structures, for example, space webs, the lightweight cable nets deployable in space, which can serve as platforms for very large structures or be used to capture orbital objects. The interest in research on space webs is likely to increase in the future with the development of promising applications such as Furoshiki sat-ellite of JAXA, Robotic Geostationary Orbit Restorer (ROGER) of ESA and Grapple, Retrieve And Secure Payload (GRASP) of NASA. Unlike high-tensioned nets in civil engineering, space webs may be low-tensioned or tensionless, and extremely flexible, owing to the microgravity in the orbit and the lack of support components, which may cause computational difficulties. Mathematical models are necessary in the analysis of space webs, especially in the conceptual design and evaluation for prototypes. A full three-dimensional finite element (FE) model was developed in this work. Trivial truss elements were adopted to reduce the computational complexity. Considering cable is a compression-free material and its tensile stiffness is also variable, we introduced the cable material constitutive relationship to work out an accurate and feasible model for prototype analysis and design. In the static analysis, the stress distribution and global deformation of the webs were discussed to get access to the knowledge of strength of webs with different types of meshes. In the dynamic analysis, special attention was paid to the impact problem. The max stress and global deformation were investigated. The simulation results indicate the interesting phenomenon which may be worth further research.

Analysis of masonry structures by funicular networks

A numerical approach for the ultimate analysis of large masonry structures composed of multiple linear members is presented. The approach is based on the use of computer-simulated cable nets representing the equilibrium lines (or load paths) that describe the equilibrium condition of structures. Based on this description, limit analysis is applied according to the static approach. Cable net solutions complying with the limit theorems of plasticity – in particular the safe (or lower-bound) and the uniqueness theorems – are generated by means of convenient optimisation techniques. An efficient cable element is adopted with explicit analytical expressions available for the description of the deformed shape in equilibrium and the tangent stiffness matrix. This type of cable element enables the computation of very large cable nets, including a large number of individual cables, with high computational efficiency. The calculation procedure is applied to complex spatial structures and the ability of the technique to deal with such systems is illustrated by an example involving a practical assessment of a real three-dimensional masonry structure.

Basics in Tension Structures

Tensioned structures are made of cable nets, fabrics or foils, the surfaces are plane, singe curved or double curved and are mechanically tensioned or inflated. Depending on the material the design process is different Designers and manufacturer have to know the common properties and differences creating optimized structures for each material and avoiding mistakes and failures. In the following the typical design procedure is pointed out of the different materials, the capability and features of the different materials are shown in examples.

Simulation Evaluation of BER Characteristics for M-PSK and M-QAM Modulations used in the Reverse Channel of Cable TV Nets

A profile is drawn for the various types of square modulations, which are used in transmitting digital signals in the reverse channel of cable TV networks (CATV). The latter are attacked by disturbances, which deteriorate the quality of transmitted signals and cause errors in the digital flow. 32, 64, 128-QAM are also analyzed. Signal to noise ratio is calculated as a function of error probability. Based on the obtained results, it is possible to establish the dependence of the cable length sector on the transmission speed featured by different types of cables provided we have an allowable error coefficient. Simulation and experimental results are compared. Ill. 6, bibl. 12 (in English; summaries in English, Russian and Lithuanian).

Vibration modes and natural frequencies of saddle form cable nets

The objective of this paper is to investigate the dynamic behaviour of cable networks, in terms of their natural frequencies and the corresponding vibration modes. A multi-degree-of-freedom cable net model is assumed, having circular plan view and the shape of a hyperbolic paraboloid surface. The cable supports are considered either rigid or flexible, thus accounting for the deformability of the edge ring. On the basis of numerical analyses, empirical formulae are proposed for the estimation of the linear natural frequencies, taking into account the mechanical and geometrical characteristics of the cable net and the ring, expressed in the form of appropriate non-dimensional parameters. The sequence of the symmetric and antisymmetric modes of the network and the occurrence of modal transition can be predicted in relation to one of these parameters, in analogy to single cables. The differences between a network with rigid cable supports and one with boundary ring, concerning the eigenmodes and the corresponding eigenfrequencies are identified.

Improved group theoretic method using graph products for the analysis of symmetric-regular structures

In this paper, a new combined graph-group method is proposed for eigensolution of special graphs. Symmetric regular graphs are the subject of this study. Many structural models can be viewed as the product of two or three simple graphs. Such models are called regular, and usually have symmetric configurations. The proposed method of this paper performs the symmetry analysis of the entire structure via symmetric properties of its simple generators. Here, a graph is considered as the general model of an arbitrary structure. The Laplacian matrix, as one of the most important matrices associated with a graph, is studied in this paper. The characteristic problem of this matrix is investigated using symmetry analysis via group theory enriched by graph theory. The method is developed and decomposition of the Laplacian matrix of such graphs is studied in a step-by-step manner, based on the proposed method. This method focuses on simple paths which generate large networks, and finds the eigenvalues of the network via analysis of the simple generators. Group theory is the main tool, which is improved using the concept of graph products. As a mechanical application of the method, a benchmark problem of group theory in structural mechanics is studied in this paper. Vibration of cable nets is analyzed and the frequencies of the networks are calculated using the combined graph-group method.

Design and Evaluation of Two Laboratory Tests for the Nets of a Flexible Anchored Slope Stabilization System

Abstract This paper evaluates two new tests to characterize cable nets used in slope stabilization; a concentrated load test (CLT) and a distributed load test (DLT). These tests enable engineers to obtain the stress versus displacement graph and the maximum resistance. Both test devices and test methodology have been designed by the Construction Technology Research Group (GITECO) at the University of Cantabria. These two tests have enabled the certification of two different manufacturers of cable nets, Geobrugg and Malla Talud Cantabria (MTC). The results showed that these tests provide representative results of the net resistance. To verify the effectiveness of these new tests, they have been performed with various cable nets, from which homogeneous, logical results have been obtained, which are representative of the real working conditions. When performing the distributed load test, the force was applied to a pyramid of fine gravel sacks that enabled the forces to be distributed throughout the net. With this configuration, the net was deformed, acquiring an elliptical form in the lower free area. In the concentrated load test, the force was applied through a metallic plate of 600 mm diameter that deformed the net locally. The result always showed homogeneous behavior of the different samples tested. This allowed the test to be repeated in the same conditions several times. With the results of both tests an analysis was carried out relating the net grid, the load applied, and the displacement obtained. This enabled the generation of regression functions that provided information about the resistance value and the net displacement according to the chosen grid.

Non-linear analysis of cable networks by FEM and experimental validation

This work studies the analysis of the resistant capacity of cable nets for the stabilization of slopes. Two tests have been carried out, one with a distributed longitudinal load and the other with distributed transversal load, in order to simulate in situ the working conditions of these systems. Tensile tests were also carried out on the cable elements of the network in order to obtain the non-linear mechanical properties. On the one hand, the proposed numerical procedure uses the finite element method (FEM) and it takes into account the material and geometrical non-linearities due to the geometrical change in the cable net substructure. On the other hand, the contour (boundary) beam is modelled by linear beam elements with contact between them. The numerical results of the longitudinal and cross tests were simulated for different geometrical configurations, generating convergent results with respect to strain and resistance, which permit the extrapolation from tested cable nets to untested simulated cable nets, maintaining a basic configuration of constant parameters. The laboratory tests only provide information about the strain and maximum resistance, but they do not establish a relationship between the values of stresses of each net element. These data have been obtained through the computational simulation by FEM. A reliable model of the interaction of the flexible contour beam with the cable network enables the achievement of more efficient solutions in the design analysis. Finally, we compare the structural behaviour of the numerical and experimental results by means of the equivalent elastic modulus and the equivalent Poisson ratio. Excellent agreement between the predicted results by FEM and test observations was found. Besides, conclusions and suggested procedures of calculation applied on the cable networks are given and numerical models to evaluate the stability of the slope protection systems are presented.

Redesign of the Velodrome in Abuja, Job Report

The original roof, finalized in 2003 did fail shortly after the installation process during a thunderstorm. The complete membrane was destroyed but the main masts were still in place and not damaged. It was then decided to replace this roof by a more redundant system, but with the same appearance. Main goal for the redesign was to avoid any modification on the main masts, and ideally no replacement of the main suspension cables. The design was started with the evaluation of different types of large scale cable nets, to achieve a system with a comparable load bearing behaviour. It ended up with a pentagon and hexagon pattern, forming a similar shape like the previous membrane roof, and so with a comparable geometric stiffness.