Vibration investigation for telecom structures with smartphone camera: case studies

Telecom structures such as high guyed masts are tall and flexible, so that not only the main structure but also the components (i.e., guy cable and antenna) suffer from vibrations induced by wind or earthquakes. The installation of contact inertial accelerometers for high guyed mast cables or antenna can be logistically challenging and the original vibration state may be influenced by these sensors. With convenient implementation and acceptable accuracy, computer vision technologies have been applied for vibration tests both in labs and field. In this paper, videos taken with smartphone cameras are processed to extract guy cable and antenna vibration information for telecom structures and, as a result, providing an efficient cost-effective method for vibration investigation of this type of structure. The video processing method can also be used in similar cases for other structures.

Modeling and Analysis of a Large-Scale Double-Level Guyed Mast for Membrane Antennas

This paper proposes a double-level guyed membrane antenna for stiffness improvement of a large-scale tri-prism deployable mast using the collapsible tubular mast (CTM). Initially, the construction of the antenna and the modeling of the CTM boom are illustrated. Afterwards, the central mast with isosceles triangular cross section is mathematically equivalent to a continuum beam, in which the equations of motion and the constitutive relations are derived. Based on the equivalent central beam, the double-level guyed mast for the membrane antenna is modeled as a 2(3-SPS-S) mechanism, and then velocity Jacobian matrices and stiffness matrices of SPS branches are constructed. Additionally, the total stiffness matrix of the equivalent mechanism is derived with the principle of virtual work and then evaluated as an accurate approach. Finally, with the aim to improve the static stiffness of the double-level guyed mast, the numerical analysis using the Genetic Algorithm (GA) is carried out for optimizing the distribution of guys in terms of anchor positions and attachment heights.

Effect of Welding Residual Stress on Along-Wind Fatigue Life of Welded Joints in Guyed Mast

On the premise of only considering along-wind effect on guyed mast, the influence of welding residual stress on the fatigue life of welded joints is evaluated in this paper. Since the sum of residual stress and along-wind-induced dynamic stress exceeds the yield strength of structural steel, the effect of residual stress relaxation is included in the numerical analysis. The multiscale finite element analysis of guyed mast is developed in order to capture accurately stress field distribution of welded joint for the “welding-wind-induced” case in which both residual stress and along-wind-induced stress are taken into consideration, and the stress response characteristics at fatigue critical point of welded joints are pointed out. It is found that the “welding-wind-induced” stress field of welded joint can be approximately considered as multiaxial proportional loading state and hence the stress-based von Mises criterion can be adopted to evaluate the fatigue life of welded joints. Based on the S-N curve of stress fatigue life for welded specimens with structural steel commonly used in guyed masts, the fatigue damage of key welded joints is predicted, and as a consequence, the influence of welding residual stress on the fatigue life of welded joints is discussed.

Comparison of Dynamic Analysis Methods in a Cable-Stayed Tower Under Extreme Wind Loads in Cuba

Several methods and investigations have been conducted in order to dynamically analyze the behavior of guyed mast telecommunication towers subject to wind loading, due to the importance of such structures in current society. Due to their slenderness, flexibility and lightweight, these structures are particularly susceptible to wind loads, being strong hurricane winds the cause of several tower failures in Cuba. This works conducts the study of a 120 meters tall guyed mast, model MAR 2008, facing extreme wind loads in two different locations. The structure is modeled using the computational assisted software SAP2000 and a dynamic analysis is undertaken using two methods: the equivalent static method "Patch Load" and the full dynamic method "Time History" using Direct Integration. The basic wind speeds are determined according to the Method of Independent Storms (MIS) and standard turbulence intensities for cyclonés regions. Synthetic functions are generated for different heights of the tower in order to apply the "Time History" dynamic method. Finally, a comparison is established between the results in terms of axial loads, joint reactions and displacements. The main conclusion of the study is that as the basic speed decreases, there is a higher resemblance in inner forces and displacements between the results obtained for the two studied methods.

ANALYSIS OF BUCKLING AND BENDING FAILURE OF ALUMINIUM COLUMN SECTIONS USED IN EMERGENCY RESTORATION TOWERS

This paper presents an experimental analysis of buckling and bending failure modes of a 2.58 m long, 460×460 mm2 6061-T6 Aluminum alloy column section used in emergency restoration towers. The main objective is to determine the bending and buckling load capacities of the column section through experiments, as these values are critical in an emergency tower (guyed mast) design. Within the context of this overarching goal, a secondary objective is to ascertain whether the presence of certain manufacturing non-conformance affects the loading capacity of the section significantly. Finally, finite-element analysis (FEA) simulations are conducted in order to compare the experimental data with numerical results. The results show that the ultimate bending and buckling load capacities of the column section are 383 kN and 3,868 kN respectively. Furthermore, the results indicate that the presence of manufacturing non-conformances such as air bubbles and delamination do not have a detrimental effect on the load capacity of the column. Of the two non-conformances studied, the specimen with bubbles had a 1% difference from the good specimen, and the delaminated specimen had a 10% deviation. Comparison of experimental data with FEA simulation results shows that the numerical solution tends to overestimate the stiffness of the column, and that the FEA approach may require further calibration.

Blast Demolition Study of Guyed Masts

Demolition of guyed masts is usually carried out by cutting down some of the supporting guy cables using an explosive in such a way that the mast can fall into the desired direction. Without the cable supports, guyed tubular masts are very slender structures which are susceptible to local buckling based on the internal force distribution. If this local buckling occurs at the early stage of the demolition processes, it can cause uncertainty in the failure mechanism. The risk of undesirable demolition outcome due to this uncertainty can be mitigated by using controlled detonation setups. In this paper, a sensitivity analysis is presented using a case study to determine the influence of the explosive detonation time on the collapse development and pattern of the guyed mast. Then, the results of the sensitivity analysis are systematically categorized using cluster analysis to show possible types of collapse regimes which can be used to setup a controlled demolition scheme.

Instabilities of Elastic and Spinning Systems: Concepts and Phenomena

Bifurcational instabilities of increasing complexity are described, with instructive and intriguing applications. Multiple folds in the gravitational collapse of a star triggers a discussion about possible sequencing of folds. Columns, rings and a quirky floating log illustrate safe and dangerous pitchforks, with self-weight models as lecture demonstrations. Localized buckling is employed by biologists using magnetic tweezers to twist a DNA molecule and evaluate a cutting and de-knotting enzyme. Unfolding of complex bifurcations into “structurally-stable” forms by a number (codimension) of perturbations illuminates the imperfection-sensitivity of shells, and the interactive buckling of a guyed mast at a hyperbolic-umbilic catastrophe. Spinning of primitive planets introduces secondary bifurcations, while Kirchhoff’s analogy is displayed for rods and spinning tops. Examples of gyroscopic stabilization and levitation mimic the “traps” that are used in modern experimental physics to hold in place individual electrons and neutrons.