Space Truss Research Articles

Steel and glubam hybrid space truss

This paper introduces a new type of hybrid truss system composed of glue laminated bamboo (glubam) for web and upper chord members and steel pipes for lower chords. Several experiments of physical and mechanical properties were carried out on the glubam material for structural design and construction according to timber specifications and codes. A full-scale space truss model with different configurations was constructed and tested under gravity loads. Different failure modes, such as buckling of web chords, shear fracture of bolted connecting joints and yield of bottom steel pipes, were discussed. Analyses of the structural behavior under static load are compared with the experimental results, showing a good agreement. The experimental results validate that the space truss system is of excellent load carrying capacity. If yielding of the lower chord steel pipes can be realized, the system can also have a large plastic deformation under the ultimate loading condition. A prototype structure was successfully designed and constructed as a rain-shed canopy of an office building.

STRUCTURAL PERFORMANCE OF SPACE TRUSSES UNDER FIRE

An experimental program was designed in the current work to capture the structuralbehavior of two different space trusses under static loads and under increasing the temperature atthe truss nodes up to failure. The results of the two space trusses tested include the centraldeflection of the truss and the axial forces in truss members under the applied loads andtemperature. Also analytical studies based on finite element method for the two tested trusses areintroduced in this paper. A comparison between experimental work and analytical study ispresented and discussed. The finite element simulation gives good agreement with theexperimental results. Also the results of the current work indicate that increasing the temperaturecauses a local failure due to fusion of the node at which the temperature was applied.

STRUCTURAL PERFORMANCE OF SPACE TRUSSES UNDER FIRE

An experimental program was designed in the current work to capture the structuralbehavior of two different space trusses under static loads and under increasing the temperature atthe truss nodes up to failure. The results of the two space trusses tested include the centraldeflection of the truss and the axial forces in truss members under the applied loads andtemperature. Also analytical studies based on finite element method for the two tested trusses areintroduced in this paper. A comparison between experimental work and analytical study ispresented and discussed. The finite element simulation gives good agreement with theexperimental results. Also the results of the current work indicate that increasing the temperaturecauses a local failure due to fusion of the node at which the temperature was applied.

Experimental and Numerical Study on Complex Multi-planar Welded Tubular Joints in Umbrella-Type Space Trusses with Long Overhangs

A test rig with multi-functional purposes was specifically designed and manufactured to study the behavior of multi-planar welded tubular joints subjected to multi-planar concurrent axial loading. An experimental investigation was conducted on full-scale welded tubular joints with each consisting of one chord and eight braces under monotonic loading conditions. Two pairs or four representative specimens (two specimens for each joint type) were tested, in which each pair was reinforced with two kinds of different internal stiffeners at the intersections between the chords using welded rectangular hollow steel sections (RHSSs) and the braces using rolled circular hollow steel sections (CHSSs) and welded RHSSs. The effects of different internal stiffeners at the chord–brace intersection on the load capacity of joints under concurrent multi-planar axial compression/tension are discussed. The test results of joint strengths, failure modes, and load–stress curves are presented. Finite element analyses were performed to verify the experimental results. The study results show that the two different joint types with the internal stiffeners at the chord–brace intersection under axial compression/tension significantly increase the corresponding ultimate strength to far exceed the usual design strength. The load carrying capacity of welded tubular joints decreases with a higher degree of the manufacturing imperfection in individual braces at the tubular joints. Furthermore, the interaction effect of the concurrent axial loading applied at the welded tubular joint on member stress is apparent.

Modeling the creep behavior of GRFP truss structures with Positional Finite Element Method

Abstract This paper presents the development of a formulation, based on Positional Finite Element Method, to describe the viscoelastic mechanical behavior of space trusses. The numerical method used was chosen due to its efficiency in the applications concerning nonlinear numerical analyses. The formulation describes the positional variation over time under constant stress state (creep). The objective is to provide a way to quantify the creep behavior for space truss structures and thus contribute to the encouragement of GFRP usage in such structural components. Time-dependent behavior of such materials is one the most important factors for their use in design of structures, demanding studies about the deformations expected within the operational life of the structural systems. To perform this study, the proposed methodology considers a standard solid rheological model to describe stress-strain time-dependent law. This model is implemented in the formulation for quantify the total strain energy. The effects of the model parameters in the mechanical response of the structure with accentuated geometric nonlinearity were presented. In this analysis, it was possible to identify the influence of the elastic and the viscous moduli on the creep response. Model calibration was performed using test data obtained from literature and a GFRP transmission line tower cross-arm was simulated to predict the evolution of displacements under real operational loads. From the results, it was possible to observe a fast evolution of displacements due to the creep effect in the first 7,500 h. This increase was close to 0.6% in relation to the displacement obtained in the elastic behavior. The presented methodology provided a simple and efficient way to quantify the creep phenomenon in viscoelastic GFRP composites truss structures, as can be seen in the developed analyses.

Finite Element Simulation of Space Trusses

AbstractThe purpose of this paper is introducing a simplified and computationally efficient finite element model to investigate the nonlinear behavior of composite and non-composite space trusses. Two models were employed using the Finite Element ANSYS program in order to analyze the space trusses. The first model simulates the non-composite space trusses while the second model simulates the composite space trusses. Also this research presents the comparisons between the results of the current finite element models and four previous published space trusses in order to verify the validity of the current models. Comparisons between the results of the two models and the results of the four previous published space trusses indicated that the numerical analysis created by the FE ANSYS program using the two employed models can predict the general collapse behavior of the space trusses.

Two-stage Optimization Based on Force Method for Damage Identification of Planar and Space Trusses

In this study, an efficient two-stage optimization procedure based on the force method is proposed to properly identify the sites and extents of multiple damages in the planar and space truss structures. In the first stage, the elements which have the higher probability of damages are selected by using the anti-optimization (AO) method and the weighed sum procedure. In the second stage, the genetic algorithm (GA) is performed to determine the actual damage sites and their extents based on the force method. The accuracy and effectiveness of the proposed method are proved through the planar and space truss structures. The results from the present study indicate that the combination of the first stage with the second one can provide a reliable tool to accurately and efficiently identify the multiple damages of truss structures.

Damage assessment in truss structures with limited sensors using a two-stage method and model reduction

The paper proposes a practical two-stage approach for damage assessment in truss structures using noisy modal data collected from a limited number of sensors. In the first stage, a newly developed damage indicator, named here as normalized modal strain energy based damage index (nMSEBI), is proposed to locate effectively potential damage elements. In the second stage, the teaching-learning-based optimization (TLBO) algorithm is utilized as a robust optimization solver to determine the damage severity of suspected damage sites and also to exclude false alarms (if any) obtained in the previous stage. In addition, a Neumann series expansion-based second-order model reduction method (NSEMR-II) is adopted to condense the structural physical properties due to a limited number of sensors placed on the structure. The robustness and effectiveness of the proposed two-stage damage identification method are verified through two specific structures including a 31-bar planar truss and a 52-bar space truss with various damage scenarios. The obtained results clearly indicate that the proposed method can work well in determining both damage location and damage severity in the truss structures.

A hierarchical Bayesian method for vibration-based time domain force reconstruction problems

Traditional force reconstruction techniques require prior knowledge on the force nature to determine the regularization term. When such information is unavailable, the inappropriate term is easily chosen and the reconstruction result becomes unsatisfactory. In this paper, we propose a novel method to automatically determine the appropriate q as in ℓq regularization and reconstruct the force history. The method incorporates all to-be-determined variables such as the force history, precision parameters and q into a hierarchical Bayesian formulation. The posterior distributions of variables are evaluated by a Metropolis-within-Gibbs sampler. The point estimates of variables and their uncertainties are given. Simulations of a cantilever beam and a space truss under various loading conditions validate the proposed method in providing adaptive determination of q and better reconstruction performance than existing Bayesian methods.

Performance Comparison of Metaheuristic Algorithms for the Optimal Design of Space Trusses

In this study, eight population-based metaheuristic algorithms were employed for the design of truss structures with continuous design variables. The selected algorithms were genetic, ant colony, particle swarm, artificial bee colony, gravitational search, firefly, gray wolf optimization and Jaya. The purpose was to objectively evaluate the performance of these algorithms under the same conditions and select the best efficient algorithm by assessing three example truss structures. The results obtained from the examples showed that the algorithms were both computationally efficient and robust when the number of design variables was approximately 10 and a significant number of iterations were performed. When the number of design variables was increased to 53, artificial bee colony, Jaya and gray wolf optimization were found to be computationally more effective than the remaining algorithms.

Size and Shape Optimization of Space Trusses Considering Geometrical Imperfection-Sensitivity in Buckling Constraints

Optimal design considering buckling of compressive members is an important subject in structural engineering. The strength of compressive members can be compensated by initial geometrical imperfection due to the manufacturing process; therefore, geometrical imperfection can affect the optimal design of structures. In this study, the metaheuristic teaching-learning-based-optimization (TLBO) algorithm is applied to study the geometrical imperfection-sensitivity of members’ buckling in the optimal design of space trusses. Three benchmark trusses and a real-life bridge with continuous and discrete design variables are considered, and the results of optimization are compared for different degrees of imperfection, namely 0.001, 0.002, and 0.003. The design variables are the cross-sectional areas, and the objective is to minimize the total weight of the structures under the following constraints: tensile and compressive yielding stress, Euler buckling stress considering imperfection, nodal displacement, and available cross-sectional areas. The results reveal that higher geometrical imperfection degrees significantly change the critical buckling load of compressive members, and consequently, increase the weight of the optimal design. This increase varies from 0.4 to 119% for different degrees of imperfection in the studied trusses.

Strength of steel fiber reinforced concrete beams in pure torsion

This paper presents a simple yet accurate technique for determining the strength of steel fiber reinforced concrete beams loaded in pure torsion. The results of the model are compared with 21 beams found in the literature as well as two new beams tested by the authors and reported herein. The model considers the beneficial effect of the fibers in resisting tension after the concrete matrix has cracked, and it is implemented into the widely accepted space truss analogy for reinforced concrete members subjected to pure torsion. The proposed model provides good correlations to the collected test data with a test to predicted ratio of 1.10 and COV of 0.19. A simplified method of the aforementioned model, suitable for design, is also presented and is shown to provide good predictions to the test data.

Axial load detection in compressed steel beams using FBG-DSM sensors

Nondestructive testing methods are required to assess the condition of civil structures and formulate their maintenance programs. Axial force identification is required for several structural members of truss bridges, pipe racks, and space roof trusses. An accurate evaluation of in situ axial forces supports the safety assessment of the entire truss. A considerable redistribution of internal forces may indicate structural damage. In this paper, a novel compressive force identification method for prismatic members implemented using static deflections is applied to steel beams. The procedure uses the Euler–Bernoulli beam model and estimates the compressive load by using the measured displacement along the beam\'s length. Knowledge of flexural rigidity of the member under investigation is required. In this study, the deflected shape of a compressed steel beam is subjected to an additional vertical load that was short-term measured in several laboratory tests by using fiber Bragg grating–differential settlement measurement (FBG–DSM) sensors at specific cross sections along the beam\'s length. The accuracy of midspan deflections offered by the FBG–DSM sensors provided excellent force estimations. Compressive load detection accuracy can be improved if substantial second-order effects are induced in the tests. In conclusion, the proposed method can be successfully applied to steel beams with low slenderness under real conditions.

Description and Regulation of Drilling Completion Fluid Cake Structure

In the process of oil and gas well drilling and completion, under the action of positive pressure gradient or self-absorption, drilling and completion fluid solid phase particles block the reservoir pore and form the filter cake. The filter cake plays a vital role in reservoir protection, and is closely related to the oil and gas well productivity from cake formation to remove. The filter cake is always expected to be thin, tough, with low permeability and easy to remove. Many scholars made a lot of research from the filter cake layer structure, space truss structure, pore structure and the structure of fractal structure of filter cake. However, the researches on the structure of the filter cake are mainly conducted qualitatively at home and abroad, while the quantitative research progress is slow. At the same time, the research on the relationship between the filter cake structure and its performance is also relatively weak. In recent years, with the wide application of horizontal wells, it has called widespread attention on how to effectively remove filter cake in order to improve the oil and gas well production capacity at home and abroad. The widely-used filter cake removal technology mainly includes natural clear, mechanical removal, chemical removal and biological removal technology currently. Among them, the biological removal technology is developed in recent years as a new type of filter cake removal technology. With the further development of mud cake removal technology and downhole filter cake removing circumstance with increasing complexity, a single filter cake removal technology cannot completely meet the requirements. The filter cake removal technology is developing in the direction of the composite to clear, in order to obtain ideal filter cake removal effect.

Static stability and load capacity of pyramidal trusses

The analysis of pyramidal trusses has an immediate practical interest since these structures are currently used in many present-day civil constructions, either as main parts or a constitutive element. They can be used to represent tripod-like structures, cap of masts, tower cranes, big span roofs, and even a portion of a single-layer geodesic dome or of a generic-shaped reticulated shell. This paper examines the nonlinear static stability and load capacity for a simple class of space trusses in the shape of a regular pyramid. Joints located at the vertices of the base polygon are fixed while the joint at the apex is subjected to static loads acting in either the vertical direction, in the horizontal plane, or along a generic oblique direction. Despite their apparent simplicity, these structural systems exhibit a wide variety of post-critical responses, not exhausted by the classical snapping and bifurcation phenomena. In addition to regular primary and secondary branches, the equilibrium paths may include neutral branches, namely branches entirely composed of bifurcation or limit points. The analysis is conducted using the Finite Element Method together with a corotational formulation for the bars. The numerical results are validated in the elastic domain using the closed-form solutions found in literature.

Field Measurements of Wind Pressure on an Open Roof during Typhoons HaiKui and SuLi

Full-scale measurements of wind action on the open roof structure of the WuXi grand theater, which is composed of eight large-span free-form leaf-shaped space trusses with the largest span of 76.79 m, were conducted during the passage of Typhoons HaiKui and SuLi. The wind pressure field data were continuously and simultaneously monitored using a wind pressure monitoring system installed on the roof structure during the typhoons. A detailed analysis of the field data was performed to investigate the characteristics of the fluctuating wind pressure on the open roof, such as the wind pressure spectrum, spatial correlation coefficients, peak wind pressures and non-Gaussian wind pressure characteristics, under typhoon conditions. Three classical methods were used to calculate the peak factors of the wind pressure on the open roof, and the suggested design method and peak factors were given. The non-Gaussianity of the wind pressure was discussed in terms of the third and fourth statistical moments of the measured wind pressure, and the corresponding indication of the non-Gaussianity on the open roof was proposed. The result shows that there were large pulses in the time-histories of the measured wind pressure on Roof A2 in the field. The spatial correlation of the wind pressures on roof A2 between the upper surface and lower surface is very weak.When the skewness is larger than 0.3 and the kurtosis is larger than 3.7, the wind pressure time series on roof A2 can be taken as a non-Gaussian distribution, and the other series can be taken as a Gaussian distribution.

Torsional behavior of a hybrid FRP-aluminum space truss bridge: Experimental and numerical study

A novel lightweight hybrid fiber-reinforced polymer (FRP) – aluminum space truss structure that consists of two triangular deck-truss beams has been designed for rapid emergency bridging system. This paper reports a large-scale pure torsion test on a cantilever full-scale specimen to evaluate the detailed linear-elastic torsional behavior and the load-carrying mechanism of the hybrid twin-trackway spatial structure. Additionally, a structural computational finite element model (FEM) was constructed and validated against the experiments. To fully understand the load-carrying mechanism obtained from the experiments, numerical analyses were performed by equivalently converting the torsion reaction of the hybrid twin-trackway structure to the bending and torsion of its twin triangular deck-truss beams. The results indicate that the experimental structure exhibits a good and specific torsional response, which can be well described by FEM. The unidirectional pultruded FRP profiles are mainly subjected to axial forces and are thus appropriate for application to this unique twin-trackway space truss, unlike in the case of the alone single-trackway triangular beam under torsion. The vertical bending of the twin triangular deck-truss beams play a key role in the behavior of load-carrying of the entire bridge, unlike in the case of the conventional torsional calculation method for the separated box beam. In the initial design, the torsional calculation of such a novel bridge can be carried out using the flexural analytical and numerical models of the triangular deck-truss beam.

A RELIABLE METHOD FOR THE STABILITY ANALYSIS OF STRUCTURES

A space truss is in an unstable configuration if it can displace incrementally without an incremental change in its loading and its supports. The load path which follows after an unstable configuration can be unique (snap-through), or there can be several possible load paths (bifurcation). This paper presents a method to detect nearly unstable configurations of a truss, a method to determine the loading, displacements and reactions of the unstable configuration and a method to traverse the load path which follows after the unstable configuration. The detection of structural configurations with singular tangent stiffness matrix is essential because they can be unstable. The secondary paths, especially in unstable buckling, can play the most important role in the loss of stability and collapse of the structure. A new method for reliable detection and accurate computation of singular points on load paths is presented and applied to a space truss subjected to symmetric and asymmetric snow loads.

Analysis of the progressive collapse of space truss structures during earthquakes based on a physical theory hysteretic model

This study develops a force–displacement hysteresis model (computer program) for a bar element based on a physical theory model. The model is capable of capturing complex physical phenomena of member, such as yielding under tension, non-elastic buckling under compression, growth effect and degradation of buckling capacity due to the Bauschinger effect. The proposed element model is validated by comparing the simulation results with previous experimental results and is applied to the dynamic analysis of space truss structures. The explicit dynamic analysis method is adopted for solving the nonlinear equations of motion. Furthermore, a case study of a three-layer space truss structure is conducted. The reliability of the proposed algorithm and the need to develop the bar element are verified by comparing the results obtained using the proposed method and the ANSYS finite element analysis software package. Moreover, several fracture criteria for bar elements are defined and are used to analyse the progressive collapse of a space truss structure under seismic loading. The analytical results demonstrate that the selection of the fracture criterion for the bar members significantly affects the calculation of the collapse of the space truss structure under seismic loading. The strut buckling/softening-based fracture criterion can be used to relatively accurately evaluate the collapse resistance of a space truss structure under seismic loading. Finally, the collapse mode of a power transmission tower model under seismic loading is simulated. The simulation results are then compared with the collapse mode of a power transmission tower with a similar structure that collapsed during the Wenchuan earthquake. The simulation results agree closely with the observations, thereby verifying the reliability of the proposed algorithm.

Size, shape, and topology optimization of planar and space trusses using mutation-based improved metaheuristics

Abstract In this study, simultaneous size, shape, and topology optimization of planar and space trusses are investigated. Moreover, the trusses are subjected to constraints for element stresses, nodal displacements, and kinematic stability conditions. Truss Topology Optimization (TTO) removes the superfluous elements and nodes from the ground structure. In this method, the difficulties arise due to unacceptable and singular topologies; therefore, the Grubler's criterion and the positive definiteness are used to handle such issue. Moreover, the TTO is challenging due to its search space, which is implicit, non-convex, non-linear, and often leading to divergence. Therefore, mutation-based metaheuristics are proposed to investigate them. This study compares the performance of four improved metaheuristics (viz. Improved Teaching–Learning-Based Optimization (ITLBO), Improved Heat Transfer Search (IHTS), Improved Water Wave Optimization (IWWO), and Improved Passing Vehicle Search (IPVS)) and four basic metaheuristics (viz. TLBO, HTS, WWO, and PVS) in order to solve structural optimization problems. Highlights Improvements in four recently designed metaheuristics. Use of random mutation-based search technique. Applications on challenging/benchmark problems of simultaneous size, shape, and topology optimization of truss structures. Improvements effective over basic metaheuristics.