Design and Validation of an Accurate Low-Cost Data Acquisition System for Structural Health Monitoring of a Pedestrian Bridge

Structural health monitoring (SHM) is an effective operating technique devoted to enhance the robustness of an infrastructure, and to validate its safety requirements. The aim of SHM is to determine a structure’s reaction when subjected to any type of excitation, by means of identifying modifications in basic vibration measurements and modal parameters such as natural frequencies, damping and mode shapes. Consequently, sensors are mounted on a structure intending to record data on equal time intervals basis prior to, during and after an induced stimulation. Therefore, the necessity to adopt a computer-based data acquisition (DAQ) technique is required in this analytical approach in order to evaluate vibrational signals collected by sensors placed on a structure. In this work an accurate microcontroller-based DAQ system is proposed to monitor a pedestrian bridge located in Athens Greece for the purpose of characterizing the system state and evaluate the modal properties of the investigated structure. Four low-cost yet accurate triaxial accelerometers were systematically placed along the bridge intending to report the system response toward different generated perturbations. The proposed monitoring and computational system was tested in laboratory conditions prior to the bridge assessment. Three triaxial accelerometer were installed on a steel cantilever beam. A comparative analysis between the results of the suggested DAQ system and that of the standard laboratory DAQ system National Instrument DAQ was performed to test the accuracy of the suggested framework

Regression of atherosclerotic lesions by high density lipoprotein plasma fraction in the cholesterol-fed rabbit

PMCID: PMC296557The effects of homologous plasma HDL and VHDL fractions on established atherosclerotic lesions were studied in cholesterol-fed rabbits. Atherosclerosis was induced by feeding the animals a 0.5% cholesterol-rich diet for 60 d (group 1). Another group of animals were maintained on the same diet for 90 d (group 2). A third group was also fed the same diet for 90 d but received 50 mg HDL-VHDL protein per wk (isolated from normolipemic rabbit plasma) during the last 30 d (group 3). Aortic atherosclerotic involvement at the completion of the study was 34 ± 4% in group 1, 38.8 ± 5% in group 2, and 17.8 ± 4% in group 3 (P < 0.005). Aortic lipid deposition was also significantly reduced in group 3 compared with group 1 (studied at only 60 d) and group 2. This is the first in vivo, prospective evidence of the antiatherogenic effect of HDLVHDL against preexisting atherosclerosis. Our results showed that HDL plasma fractions were able to induce regression of established aortic fatty streaks and lipid deposits. Our results suggest that it may be possible not only to inhibit progression but even to reduce established atherosclerotic lesions by HDL administration.This work was supported by National Institutes of Health grant HL-39840 and by funds from a Heart Research Foundation grant.Peer reviewe

New Consistent Set of Design Equations for Equal‐leg Angle Sections and Members

peer reviewedAngles profiles have been used since the very beginning of the steel construction due to their easy production, transportation, and ability to be connected. However, they exhibit some specific features that clearly distinguish them from other types of common sections, as they are monosymmetric sections with very small constants in both torsion and warping, their bending capacity and radius of gyration around the weak axis are substantially lower compared to the strong axis ones, their legs are possibly susceptible to local buckling, their plastic resistances are significantly higher than their elastic ones and finally, due to the eccentric connection in one leg, they are also subjected to bending when used as single members. The above-listed features confirm that existing common design rules for other mostly doubly symmetric type of sections cannot safely cover angle sections, what inevitably leads to the need for development of specific design provisions for angles. Therefore, extensive experimental, analytical, and numerical studies have been conducted to propose a complete and duly validated set of design rules covering all aspects of their design (classification, cross-section and member resistance). The proposed rules will be included in the forthcoming version of EN1993-3

EFFECTS OF JOINTS ON THE BUCKLING RESISTANCE OF ANGLE MEMBERS MADE OF S460 STEEL -EXPERIMENTAL INVESTIGATIONS

Energy production is undergoing radical changes in Europe, with the development of more sustainable production means. These changes require a complete overhaul of the power transmission network, with the construction of new lines and, in particular, new transmission towers with higher load-bearing capacities than in the past. To meet this demand, the design of new towers, typically made of steel angles, requires increasingly the use of high-strength S460 steel. In the literature several studies provide experimental evidence regarding the buckling resistance of pin-ended angle members made of high strength steel, allowing the validation of the relevant design procedures. However, this is not the case for high strength steel angles with bolted connections on one leg at their extremities, like those used for bracing members in lattice towers. To fill this gap, a research project called "New Steel" has been recently launched. This project involves investigations aiming to study the influence of the structural joints at the extremities of S460 angle members on their buckling resistance through experimental, numerical, and analytical studies. The present paper firstly describes an experimental campaign conducted in the framework of this project and summarises the obtained results. A critical discussion of the findings follows and finally, an assessment of the accuracy of the design methods as recommended in the existing normative documents (such as EN 50341-1 and prEN 1993-3) is presented through comparisons to the experimental results.New Stee

EC3-Compatible Methods for Analysis and Design of Steel Framed Structures

The behaviour of steel structures is affected by two nonlinearities—the geometric and material nonlinearity—and by the unavoidable presence of imperfections. To evaluate the ultimate capacity of a structure, these effects should be taken into consideration during the design process, either explicitly in the analysis or implicitly through the verification checks. In this context, Eurocode 3 provides several design approaches of different complexity and accuracy. The advantages and disadvantages of these approaches are discussed. Five different methods in conformity with the Eurocode provisions are applied for the design of four moment resisting steel frames of varying slenderness. The influence of nonlinearities and imperfections in respect to the slenderness of the structure is illustrated. The examined methods are compared in terms of the predicted ultimate capacity and their efficiency is assessed against the most accurate between them, i.e., an advanced geometrically and materially nonlinear analysis. It is shown that considerable differences arise between the methods. Nevertheless, except for the commonly used 2nd order analysis followed by cross-section verifications, the remaining methods are mostly on the safe side

EC3-Compatible Methods for Analysis and Design of Steel Framed Structures

The behaviour of steel structures is affected by two nonlinearities—the geometric and material nonlinearity—and by the unavoidable presence of imperfections. To evaluate the ultimate capacity of a structure, these effects should be taken into consideration during the design process, either explicitly in the analysis or implicitly through the verification checks. In this context, Eurocode 3 provides several design approaches of different complexity and accuracy. The advantages and disadvantages of these approaches are discussed. Five different methods in conformity with the Eurocode provisions are applied for the design of four moment resisting steel frames of varying slenderness. The influence of nonlinearities and imperfections in respect to the slenderness of the structure is illustrated. The examined methods are compared in terms of the predicted ultimate capacity and their efficiency is assessed against the most accurate between them, i.e., an advanced geometrically and materially nonlinear analysis. It is shown that considerable differences arise between the methods. Nevertheless, except for the commonly used 2nd order analysis followed by cross-section verifications, the remaining methods are mostly on the safe side

Säulen griechischer Tempel unter Erdbebenbeanspruchung

olumns of Greek Temples under seismic loading:Columns of ancient Greek Temples consist of accurately dressed individual blocks in total absence on binding mortars. The seismic response of such multi-drum structures is completely different than the corresponding one of modern continuous structures. Their stability is governed by independent sliding and rocking of drums, which creates an external energy absorption mechanism. This paper presents numerical studies on the dynamic behaviour of ancient columns which exhibits a highly non-linear response. Alternative modeling methods are used and calibrated to experimental results. It is concluded that ancient columns may be less vulnerable to seismic events compared to modern structures. The perfection of the form unified esthetical, architectural and structural requirements

EXPERIMENTAL INVESTIGATIONS ON STEEL ANGLE BEAMS AND COLUMNS STRENGTHENED WITH CFRP PLATES

The results of a testing campaign are presented for rolled steel equal angle sections strengthened with Carbon Fiber Reinforced Polymers (CFRP) plates, targeting the strengthening of existing steel lattice towers. Three-point bending and compression tests have been carried out in order to determine the mechanical properties of members, specifically the bending capacity to principal and geometric axis loading and the buckling strength in the absence or presence of loading eccentricity arising from the connection in one leg. The experimental data include actual material properties, geometrical imperfections, the recorded response to loading in terms of displacements, end-rotations, twist of section, strains in steel or CFRP material, and photos. Also, the experimental set-up, the instrumentation, as well as simple experimental results to indicate the strengthening effect and utility of them to further analyses are provided.Funding was provided by the European Commission through the Research Fund for Coal and Steel (RFCS) project "ANGELHY – Innovative solutions for design and strengthening of telecommunication and transmission lattice towers using large angles from high strength steel and hybrid techniques of angles with FRP strips" (Grant Agreement No. 753993). Provision of the test specimens, consumables and application instructions by ArcelorMittal and Sika France is gratefully acknowledged