Experimental Analysis of Guardrail Structures for Occupational Safety in Construction

Background: Guardrails are structures that protect workers from falling from heights at construction sites. Objective: The objective is to evaluate experimental models by applying static and impact loads to wood and steel guardrails. Methods: Brazilian and international standards were consulted to define the actions applied to guardrails, which were tested experimentally in three models of each material in a full-size prototype. Results: The experimental results indicate that the models studied could support the applied loads, and no local or global system rupture occurred. However, the displacements for the static load of 1500 N/m required by Brazilian RTP 01 for both models did not comply with Brazilian standard NBR 14718 because they had displacements above 20 mm, despite meeting other international standards for static testing and impact testing. Conclusion: From the results obtained in the experimental tests, it was possible to verify that the structures withstood the applied loads and could be used safely in civil construction works. However, the load requirements of RTP 01 are excessive, and NBR 14718 is not suitable for checking temporary guardrail structures. This demonstrates the need for the Brazilian standard to be revised to guide the dimensioning and verification of structures in order to adapt to international standards.

Repositional-fixation ring for surgical treatment of acetabular fractures (preliminary results of static tests)

BACKGROUND: Currently, several types of designs of support rings of M. Muller, Burch-Schneider, rings of the company Protek (Switzerland), implanted in the BB are widely used, which are used in the surgical treatment of long-standing fractures of the BB, as a rule, as a device that strengthens the walls of the BB. AIM: Study of the deformation properties of the repositional-fixing ring. MATERIALS AND METHODS: For carrying out mechanical tests, a ring with an external diameter of 52 mm was made by the method of sequential sintering using additive technologies by the company Konmet LLC, Moscow. Laboratory mechanical tests were carried out by the Testing Laboratory of Medical Devices and Materials of the N.N. Priorov National Medical Research Center of Traumatology and Orthopedics. RESULTS: As a result of static testing of the ring for compression, tension, torsion, and joint stretching and twisting of the edges of the ring connector, its deformation properties are studied. Load corresponding to the deformation of 2 mm, kN: compression 0.180; tension 0.061; torsion (torque corresponding to the angle of rotation of 5 degrees, Nm) 2.653; joint tension with twisting of the edges of the ring connector (load corresponding to the deformation of 10 mm, kN) 0.048. CONCLUSION: The results of the initial study of the deformation behavior of the ring structure show that it is necessary to refine the ring design and further study the deformation and strength characteristics of the ring.

Foot Function Determination: Agreement Between Tests?

Background: Foot pronation is generally linked to musculoskeletal injuries, especially in relation to joint deviation caused by pronation during dynamic activities. However, no consensus appeared in the methodological way to determine foot function, and several tests propose to identify foot pronation under different conditions, from static testing to running. The aim of this study was to determine the level of agreement between different foot function classification measures. Methods: One hundred and six subjects completed 5-foot function tests at standing position, walking and running. Foot Posture Index (FPI) was undertaken to determine foot function during static posture. The Center of Pressure Excursion Index (CPEI) and 3 Foot Balance tests (FBs) were realized during walking and running trials to assess pronation during dynamic activities. Agreement between the measures was determined using the Cohen’s Kappa coefficient (K) between 2 measures and the Fleiss Kappa (FK) between 3 or more measures. Results: Overall agreement between the measures reported a fair agreement (Kf = 0.2). Static and walking foot tests determination agreement was moderate (K = 0.5), while agreement between FPI and FBs tests were fair (K < 0.4). Fair results were also reported between walking and running tests (K < 0.4). The concordance between running tests classification was fair (Kf = 0.2). Conclusions: The lack of agreement between tests confirms the need for a consensus on an appropriate measurement of the foot function. Static foot tests are mainly used to determine foot function during dynamic activities. However, the lack of agreement between tests could question the relevance of the static foot function assessments. The FPI reported a moderate agreement with the walking classification test, but it should be accompanied by a dynamic test in order to limit the risk of misinterpretation.

Calibration of DEM for Cohesive Particles in the SLS Powder Spreading Process

In this paper, a new DEM calibration procedure based on two different types of procedures to compare simulation with experiments is proposed. The aim is to find the values of the interfacial adhesive surface energy and the coefficient of rolling friction between the particles to be used in the simulation. The approach adopted is the so-called Bulk Calibration method. The experimental values of the angle of repose and unconfined yield strength, found with a static testing method and by shear testing, respectively, are compared, respectively, with the angle of repose, found in a simulation reproducing the experimental procedure, and the unconfined yield strength, obtained from an idealized uniaxial testing procedure. The simulated DEM particles are spheres equipped with the Hertz Mindlin with JKR contact model. The results suggest that a bulk calibration approach is not able to provide results that are consistent with two simple bulk property evaluations and, therefore, direct ways to estimate the surface energy based on the evaluation of interparticle forces, for example, should preferably be adopted.

A New Test Method for in vitro Evaluation of Pedicle Screw Loosening Potential

This paper proposes a new testing method based on the toggle effect under transverse loads (cranial-caudal) to investigate the loosening potential of pedicular screw designs. A three-step in vitro testing procedure was developed to mimic the loosening mechanism of pedicular screws. Firstly, the pedicular screw of a certain design is inserted into a bone substitute model specifically designed for the test. Secondly, a controlled cyclic cranial-caudal loading is applied transversally to the longitudinal axis of the screw for three ascendent load levels (staircase) by a pre-determined number of load cycles. Lastly, each pedicular screw is adjusted and submitted to axial pull-out quasi-static testing. The results are used to calculate a loosening index that, together with statistical analysis, indicates the potential for loosening of the specific design evaluated. The proposed testing method effectively provides a simulated environment to evaluate the loosening potential of pedicular screw designs. The proposed loosening index calculation may be used to compare different pedicular screw designs. The proposed methodology was verified as a valuable tool to investigate the influence of the cranial-caudal loads on pedicular screw behavior. It offers a new alternative for use in pre-clinical studies on the loosening potential of pedicular screw designs.