Lattice Girder Research Articles

Pelvic Reconstruction for Massive Acetabular Insufficiency

Joint reconstruction for pelvic discontinuity because of massive acetabular insufficiency presents a significant surgical challenge. Using retrograde-inserted Steinmann pins to rebuild the dome may be associated with early implant failure because of insufficient mechanical stability and neurovascular injury resulting from pin misplacement. Retrograde pins cannot be placed completely across the pelvic defect. We hypothesized that large Steinmann pins placed anterograde under direct vision from the iliac crest completely across the acetabular column and floor defects would minimize the risk of early failure, and could be placed safely without the use of fluoroscopy in combination with a posterior hip approach. The purpose of our study was to review the mechanical failure and complication rates of nine patients (10 hips) treated between 1996 and 2002 for pelvic discontinuity using this pin placement technique to reinforce a cemented roof ring hip reconstruction done via a posterior approach. None of the patients had implant loosening or failure, there were no neurovascular complications, and no perioperative deaths. One patient required cup revision for recurrent dislocation. All patients were bedridden or wheelchair-bound before surgery, but regained independent household walking by 6 weeks postoperatively. Reinforcing the acetabulum with a lattice girder of anterograde pins provides safe and effective hip reconstruction.

Underground excavation in Xiaolangdi project in Yellow River

The paper summarizes the excavation methodology, based on analysis of the characteristics of the surrounding rock mass, which has been involved in Xiaolangdi multipurpose dam project. Some special support and excavation methods, such as twin side drift and lattice girder, moderate blasting and double-layer mesh to collapsed tunnel and fault zone, are presented.

Large-diameter tunnelling collapses: recovery design and execution

A number of large-diameter tunnels with completed excavation areas up to approximately 150 m2 were mined in weak sedimentary rock and soils using sequential excavation and support (SES) methods. The ground is weak to extremely weak. Tertiary sedimentary rock and soil, poorly cemented, locally folded and faulted, and has moderate to high groundwater tables. Excavation was carried out using hydraulic excavators and breakers. Owing to the low strength of the ground mass and the large excavation cross-section, the section was mined in three stages - a top heading with a height of about 5-7 m, followed by a bench with a height of about 3-4 m and an invert with a height of about 2 m. The total excavation height and span reaches maximums of approximately 12-13 and 14-15 m respectively. During or immediately after each excavation stage, initial support, termed the ''outer lining'', is installed to support and stabilize the excavated cross-section prior to installation of a cast concrete inner lining. The outer lining consists of steel ribs (lattice girders or H-profiles), shotcrete with welded wire fabric (WWF), rock dowels. Depending on the ground quality pre-support of the upper part of the tunnel (crown zone) ahead of the excavation face is required. This comprises forepoling with various combinations of steel bars, pipes, sheets and grouting. Six collapses of part or most of the tunnel crown occurred during the tunnel drives. Four occurred during the top heading stage and two during bench or invert excavation and support installation. The length of the collapsed sections varied from 20 to 277 m. Two of the collapses can be referred to as ''small'', one medium and three ''large''. Remedial measures were designed to allow re-mining through the collapsed lengths using the same excavation method (SES) and, thus, essentially the same tunnelling equipment and personnel. The re-design processes comprised post-collapse/schedule reviews and evaluations, site investigations, ground treatment and re-design of the outer lining. The processes required considerable time and careful management to avoid and mitigate potential delays to tunnel completion. The process of design management, design and execution of the recoveries is the subject of this paper. A tunnel cross-section with typical pre-support and outer lining required for the re-mining is shown in the underlying figure. At the time of preparing the paper the re-mining of the collapses were complete or well underway. Placement of the inner lining had been completed in two of the tunnels and final design of the inner linings in the other tunnels was underway. This process requires the evaluation of the performance of all the geological, geotechnical and monitoring data measured during the excavation of the top headings. The performance to date shows that SES soft ground tunnelling methods can be applied to the re-excavation of large span excavations through collapsed ground provided an extensive program of excavation pre-support is undertaken followed by careful excavation and tunnel monitoring. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Historic Timber Bridge System, Böheimkirchen, Austria

The new pedestrian and cyclist bridge in Böheimkirchen, Lower Austria, is the result of the development of a historic structural system, namely Howe’s lattice girder, with simple diamond panels. The variable inclination of the diagonals and the glued timber joints make it possible to create a modern version of a classic construction.

Stiffness of restraint for steel struts with elastic end supports

The force induced in a restraint for steel struts is given by BS 5950, Part 1, 1990 as 1% of the applied axial load, and for struts forming the compression flange of lattice girders as 2·5%. These values are used in the ultimate strength design of restraints. The code also states that these restraints should have sufficient stiffness but it does not quantify this requirement. The available literature deals with the determination of restraint forces and their required stiffness for struts with pinned or fixed ends. In practice, it is rare to have such ideal end conditions, but somewhere in between. This is due to the fact that connections in structural steelwork possess resistance to moment ranging from nominal to full rigidity depending on the moment–rotation characteristics of the joint under consideration. This paper deals with the design of restraints considering strength as well as stiffness through a mathematical model based on the elastic behaviour of a strut elastically supported at its ends and restrained at a point located along its length by an elastic restraint. The results obtained show that, for a given induced restraint force, the restraint stiffness requirement decreases with the increase of rotational stiffness at the ends of the strut. Although this, to some extent, is expected from a qualitative point of view, it does deserve to be better known by designers, and the present work attempts to quantify the effect of the various parameters involved so that the results can be used in the relevant design cases.

Stiffness of restraint for steel struts with elastic end supports

The force induced in a restraint for steel struts is given by BS 5950, Part 1, 1990 as 1% of the applied axial load, and for struts forming the compression flange of lattice girders as 2·5%. These values are used in the ultimate strength design of restraints. The code also states that these restraints should have sufficient stiffness but it does not quantify this requirement. The available literature deals with the determination of restraint forces and their required stiffness for struts with pinned or fixed ends. In practice, it is rare to have such ideal end conditions, but somewhere in between. This is due to the fact that connections in structural steelwork possess resistance to moment ranging from nominal to full rigidity depending on the moment–rotation characteristics of the joint under consideration. This paper deals with the design of restraints considering strength as well as stiffness through a mathematical model based on the elastic behaviour of a strut elastically supported at its ends and restrained at a point located along its length by an elastic restraint. The results obtained show that, for a given induced restraint force, the restraint stiffness requirement decreases with the increase of rotational stiffness at the ends of the strut. Although this, to some extent, is expected from a qualitative point of view, it does deserve to be better known by designers, and the present work attempts to quantify the effect of the various parameters involved so that the results can be used in the relevant design cases.

A LUMPED-MASS MODEL FOR THE DYNAMIC ANALYSIS OF THE SPATIAL BEAM-LIKE LATTICE GIRDERS

A method is presented to replace the distributed mass of each bay of a spatial beam-like lattice girder by 24 lumped masses, half of the latter being located at the upper plane and the other half at the lower one of the bay respectively, where the correct magnitude and location of each lumped mass are determined according to the actual arrangement of all the members constituting the bay. Based on the locations of the 24 lumped masses, the coefficients associated with the “masses” translating in thex,yandzdirections and those associated with the “mass moment of inertias” rotating about thex-,y-, andz-axis for the effective mass matrix of a bay-equivalent (continuum) beam are calculated. Numerical results show that the presented lumped-mass model together with the effective stiffness matrix of the bay-equivalent beam derived on the assumption that the cross-sections at both ends of each bay remain plane after deformation will give more accurate natural frequencies for the multi-bay spatial X-braced, Pratt or Warren beam-like lattice girders. Besides, the presented lumped-mass model is available for various transverse side-length ratios Raband longitudinal side-length ratiosRaL .

Improper Detailing Results in Delayed Commissioning

A 144 m × 60 m factory building (which is the largest span in India using cold-formed steel sections) was constructed at Cochin, India. The building is made up of portal frames spanning 60 m and placed at 6 m intervals. The portal frames are supported alternately on columns and on a lattice girder that was placed longitudinally at the midspan. The portals and columns were made up of four angles, which are laced to form a box section. The lattice girder and the central column were made of 4 channels, laced to form a compound section. The building was covered with asbestos cement (AC) sheets, which are supported by cold-rolled sigma sections. The sides of the building were also covered by cladding from 1.5 m above ground level. Due to improper detailing, all the purlins and side cladding girts twisted after the AC sheets were laid, resulting in cracking of some AC sheets. In addition, diagonal sag rods were not provided in the girts and this resulted in sagging of these members. The design, detailing, and other particulars of this factory building are discussed in this paper. The solution adopted for rectifying the problems is also discussed.

The effect of joint eccentricity on the distribution of forces in RHS lattice girders

This paper is concerned with investigating the effect of joint eccentricity on the local and overall behaviour of truss girders made from rectangular hollow section members. Three typical truss girders with identical general layout and comprising different joint eccentricities are analysed. Different numerical models of analysis are presented and the implications for design are discussed.

DETERMINATION OF RESTRAINT FORCES FOR STEEL STRUTS.

In design, it is generally assumed that the restraint force for struts has a constant value, regardless of the end conditions of the strut and the stiffness and location of the restraint Furthermore, BS 5950: Part 1 (Clause 4.7.1.2) recommends that the force in a restraint for struts (other than those forming the flanges of lattice girders), is equal to 1% of the compressive force in the strut. It is also recommended in Eurocode 3: Part 1.1 (Clause 5.2.4.4) that the restraint force is equivalent to a uniformly distributed load of q (- compressive force / (50 x length of strut)). And for a single restraint anywhere along the strut this will give a restraint force of 1% of the compressive force in the strut This paper deals with the determination of the force induced in the restraint for struts subjected to an axial load and having various end conditions. The restraint which is located at various points along the strut is assumed to act as a spring having a specified stiffness. The mathematical model of the strut, which incorporates the equivalent out of straightness imperfection, was solved and the results obtained show that the restraint force can exceed the 1% value depending on the location and stiffness of the restraint and the end conditions of the strut.

NORTHAM RAILWAY BRIDGE:AN UNUSUAL BRIDGE IN SOUTHAMPTON.

Northam Bridge in Southampton dates from 1908. It has an unusual layout, with one main girder on one side and two on the other. Its structure is also unusual, consisting of twin lattice girder webs with members of varying size. The history of the bridge in the context of the London and South Western Railway is presented together with a detailed breakdown of its structure. A finite element analysis of the structure was carried out to examine the load path through the highly redundant web. The structural response was compared with the behaviour of a simple truss and a plate girder. It was shown that the bridge is generally sound even for 40 t vehicle loading, although the deck supports give some cause for concern.

Railway Lattice Girders in Japan, an Historical Survey

Railway Lattice Girders in Japan, an Historical Survey

Dynamic analysis of spatial beam-like lattice girders

A structural simplification method that can save computer time and space and achieve reasonable accuracy for solving the dynamic problem of spatial beam-like lattice girders was studied. Incorporated with the simplification method, a lumped-mass model for arriving at better accuracy in natural frequencies was presented. The recovery expressions for determining the nodal displacements and nodal forces of each member of the original spatial lattice girder from the simplified equivalent beam were derived. Numerical results show that the simplification method is suitable for the dynamic analysis of the X-braced, Warren or Pratt spatial (or planar) beam-like lattice girders. For a 20-bay spatial X-braced lattice girder with rigid joints, the simplification method needs computer time less than 0.2% of that required by the conventional finite element method and achieves an average accuracy higher than 95% in natural frequencies. To demonstrate the application of the present method in structural design, the dynamic responses of a 10-bay X-braced lattice girder subjected to 1940 El Centre NS earthquake acceleration were solved and the maximum nodal displacements and forces of each constituent member in the lowermost and topmost bays were determined.

Fatigue tests on a welded RHS lattice girder joint

Abstract Fatigue tests have been carried out on rectangular hollow section K- and KT-joints with a brace to chord width ratio of 1·0, as this point design was believed to behave quite favourably with respect to its fatigue resistance. The investigation also comprised tests on joints with improved weld profiles and on joints subject to sea water environment. Only the effects of constant amplitude axial compressive and tensile brace loading were investigated. The test results have been statistically evaluated, thus establishing regression lines of mean values by the method of least squares. The investigation shows that the particular K-gap joint has a considerably better fatigue resistance than similar joints with a brace to chord width ratio of less than 1·0, and that the K-joint behaves better than the KT-joint. Improved weld profiles are favourable and the presence of sea water environment is disadvantageous, but none of these effects is significant.

The Dynamic Analysis Of An X-braced Lattice Girder Subjected To A Support Excitation

Based on the assumption that cross-sections at both ends of each bay remain plane after deformation, each bay of a X-braced lattice girder is replaced by an equivalent beam segment. By considering the requirement that the kinetic energy and strain energy of each bay should be equal to its equivalent beam segment, the mass matrix and stiffness matrix of the equivalent beam segment are derived. The assembly of mass matrices and stiffness matrices of all the equivalent beam segments defines the overall mass matrix and stiffness matrix of an equivalent beam corresponding to the entire X-braced lattice girder. The free vibration analysis of a 10-bay X-braced lattice girder and forced vibration analysis of a 12-bay one due to a support excitation are then made based on the simplified equivalent beams. It is found that the first five natural frequencies of the equivalent beam are in good agreement with those of the original 10-bay X-braced lattice girder obtained from the conventional finite element method or micropolar continuum theory.

Restauración de la Iglesia de San Pedro, en Ávila

The work have been carried out in two consecutive phases. Firstly the four wooden nave forms were sustituted by overdimensioned iron lattice girders that entered the aisles and ended in a capping hoop thus allowing the absorption of the pushes from the vaults that were ruining the church fabric. Besides a careful impermeabilization of both nave and aisles roof was undertaken. The second phase included the restoration of pases and sacristies roofs to their original configurations, both with a re-pointing of the tower's ashlers and a reopening of blinded windows in his intermediate volume. The ruined capping body made of bricks was substituted by another made of ashlers. New windows were designed according to the existent buttress and following the double arch configuration of the reopened ones.

Investigation of the performance of lattice girders in tunnelling

Investigation of the performance of lattice girders in tunnelling

Investigation of the performance of lattice girders in tunnelling

In order to investigate the structural and technological aspects of this relatively new constructional element a series of laboratory and field tests were carried out and the results compared with theoretical values. This article is concerned with a description of the lattice girder elements together with the results of the investigations and their practical application in the Munich Underground.

Lattice girders offer economy and performance for tunnel support : Braun, W M Tunn Tunnlg, V15, N5, May 1983, P19–21

Tunnel support systems based on lattice girders comprise assemblies of lattice girder rings, wire mesh and fixing devices designed to provide temporary support and also reinforcement for a sprayed concrete lining. The construction forms a cylindrical shell lining attached to the rock thus combining the strength of reinforced concrete with the strength of the formation. In addition, the lining system prevents air and moisture penetration to the tunnel face. In applications of the lining system in German tunnelling construction, it was confirmed that improved tunnel stability resulted from penetration of the lining material into voids between the lattice girders and surrounding rock. It is concluded that further research may be justified to evaluate claims that such a tunnel support and lining system can reduce construction costs. (TRRL)

Analysis of spatial beamlike lattices with rigid joints

Abstract Micropolar beam models are developed for the static, free vibration and buckling analysis of repetitive spatial beamlike lattices with rigid joints. The micropolar beam models have independent microrotation and displacement fields and are characterized by their strain energy, potential energy due to initial stresses and kinetic energy from which the governing differential equations and boundary conditions can be derived. The procedure for developing the expression for the strain energy of the micropolar beam involves introducing basic assumptions regarding the variation of the displacement and microrotation components in the plane of the cross-section, and obtaining effective elastic coefficients of the continuum in terms of the material properties and geometry of the original lattice structure. The high accuracy of the solutions obtained by the micropolar beam models is demonstrated by means of numerical examples for vierendeel and double-laced lattice girders with triangular cross-sections.