Papers by Keyword: Dynamic Testing

Abstract: In the paper, experimental analysis of dynamic plastic behaviour of different structural materials at high and very high strain rates up to 10⁵ s^-1 in various modes at lowered, room and elevated temperatures, is presented. The paper describes laboratory set ups for testing material specimens, based on various modifications of the Hopkinson bar technique. The paper focuses the attention on experimental tests and their interpretation. The results reported here will be useful for the designers working on the dynamic behaviour of building and mechanical protective structures made of different materials such as steels, aluminium alloys, ceramic and sand bricks, mortars, woods (pine, birch and aspen), ceramics and concrete fireproof and soils (sand, clay and sandy soil clay).

Abstract: This paper aims to demonstrate the feasibility of a recently proposed approach (termed VisCoDyn) to assess the viscoelastic behaviour of concrete from the earliest ages, by introducing a known dynamic excitation to a simply supported specimen. The method involves the continuous monitoring of the response of the tested sample in terms of amplitude (force and displacement), as well as the evaluation of the phase lag between the applied force and the response. The acquired data is then used to calculate the storage and loss moduli, according to procedures that are normally used in the context of material testing in polymer science. Indeed, the loss modulus is known to be relatable to the viscoelastic properties of materials.The paper presents the current state of development of the VisCoDyn test methodology together with several test results obtain in specimens that were tested during the first 24 hours of curing. Parallel testing with other techniques is also presented for reference.

Abstract: The structural use of wood has increased steadily in recent times, including a renewed interest in the use of timber as a bridge material. As the only environment-friendly and resource-saving building material, wood has been gradually uesd for short and medium span bridges in China. In 2014, The domestic largest single-span glued-laminated timber (glulam) deck arch bridge crossing a freeway was completed and put into operation in Zhangjiajie City, central China' Hunan province. In order to know the bearing capacity of superstructures and assess its working conditions, in-site static and dynamic testings has been carried out. Many measures including finite element simulation, field test and comparision between test results and calculated results have been employed to study responses of the bridge under static loads and dynamic loads as well. The researches indicate this glulam footbridge has performed well in service and appear to be cost effective when compared with the cost of installing traditional concrete and steel bridges.

Abstract: Microwave remote sensing is the most recent experimental methodology suitable to the non-contact measurement of deflections on large structures, in static or dynamic conditions. After a brief description of the radar measurement system, the paper addresses the application of microwave remote sensing in ambient vibration testing of two historic masonry towers.

Abstract: In case of laminated glass strips, the mechanical characteristics of the composite element are different from the values that are obtained for the same element from a homogeneous and isotropic material. The experimental tests presented in the paper aims to determine the mechanical characteristics of laminated glass strips used to make a staircase. For the experiment, quasi-static and dynamic tests were conducted on different glass stair steps, made from normal and tempered glass, with different number and thicknesses glass sheets. The paper presents the carrying out conditions for the experiments, the synthesis of data processing and comments on the experimental results. Experimental test results led to the constructive solution of the glass staircase steps. For staircase building up, tempered glass was chosen and the values obtained for the mechanical properties, strength and deformation capacity of the system were used in its design. Whole set of experimental tests led to a successful design and build-up of the glass staircase.

Abstract: This paper discusses three general automatic scoring algorithms including software quality metric algorithm, dynamic testing algorithm and static analysis algorithm based on program understanding, analyzes and designs their rationality, practicality and maneuverability. Therefore, a new automatic scoring strategy which combines dynamic testing and pattern matching based on program understanding is proposed. This method focuses on the accurate expressions on program algorithm and semantic points in student program, enhances the performance of the automatic scoring system and matches the idea of manual scoring better.

Abstract: The online test system of the vertical spindle motion error of the ultra-precision fly cutting machine tool was established. And then using the online test system established to test and analyze the state of the rotary motion of the spindle under the idling condition. The axial synchronous motion error value of the spindle under 390rpm is about 61 nm, and the asynchronous error motion is about 33nm. The radial error motion value is about 91nm, and the asynchronous error is about 35nm. Through the test, we found that the axial and radial spindle error motion accuracy under idling speed can been improved with the spindle speed increases.

Abstract: This paper makes a brief characterisation of some aspects related with the extensive research activity of the Laboratory of Vibrations and Structural Monitoring (ViBest) of the Faculty of Engineering of the University of Porto (FEUP) in the field of Continuous Dynamic Monitoring of Bridges and Special Structures, selecting four examples where large high quality databases have been created since 2007, namely Infante D. Henrique bridge, Pedro e Inês footbride, FEUP Campus stress-ribbon footbridge and Trezói railway bridge.

Abstract: Photogrammetric techniques have demonstrated their suitability for monitoring static structural tests. Advantages include scalability, reduced cost, and three dimensional monitoring of very high numbers of points without direct contact with the test element. Commercial measuring instruments now exist which use this approach. Dynamic testing is becoming a convenient approach for long-term structural health monitoring. If image based methods could be applied to the dynamic case, then the above advantages could prove beneficial. Past work has been successful where the vibration has either large amplitude or low frequency, as even specialist imaging sensors are limited by an inherent compromise between image resolution and imaging frequency. Judgement in sensor selection is therefore critical. Monitoring of structures in real-time is possible only at a reduced resolution, and although imaging and computer processing hardware continuously improves, so the accuracy demands of researchers and engineers increase. A new approach to measuring vibration is introduced here, whereby a long-exposure photograph is used to capture a blurred image of the vibrating structure. The high resolution blurred image showing the whole vibration interval is measured with no need for high-speed imaging. Results are presented for a series of small-scale laboratory models, as well as a larger scale test, which demonstrate the flexibility of the proposed technique. Different image processing strategies are presented and compared, as well as the effects of exposure, aperture and sensitivity selection. Image processing time appears much faster, increasing suitability for real-time monitoring.

Abstract: The evaluation of the safety and the estimation of the remaining service life of existing structures need a thorough knowledge of the effective operational conditions, achievable implementing a health monitoring system. The measured quantities, if opportunely chosen, allow to follow the evolution of the structural behavior in the lifetime and to recognize the occurrence of damages. Hence the collected data can be considered as symptoms and used to assess the reliability and the prognosis of the monitored structure. This paper presents the application of symptom-based reliability formulation to a real case study: a set of precast bonded post-tensioned concrete bridge beams, recently dismounted after a service life of 50 years. Both static and dynamic tests were carried out at the aim of evaluating the residual load-bearing capacity and investigating the effects of deterioration on their dynamic properties. The experimental results of test campaigns have been used as symptoms in order to estimate the reliability function of the beams and the evolution of their resistance in time.