The ELSA Database and What Can Be Done Regarding SERIES Networking Activities

This document critically presents the ELSA database for experimental results and compares its data structure with the one of the NEEScentral repository established in the US for storing the experimental results of 15 laboratories. This comparison leads to some proposed modifications of the ELSA data format that could be further used as a template for the SERIES/NA1 network activities. Some implementation directions are also given.JRC.G.5-European laboratory for structural assessmen

Two stress update algorithms for large strains: accuracy analysis and numerical implementation

Two algorithms for the stress update (i.e., time integration of the constitutive equation) in large-strain solid mechanics are compared from an analytical point of view. The order of the truncation error associated to the numerical integration is deduced for each algorithm a priori, using standard numerical analysis. This accuracy analysis has been performed by means of a convected frame formalism, which also allows a unified derivation of both algorithms in spite of their inherent differences. Then the two algorithms are adapted from convected frames to a fixed Cartesian frame and implemented in a small-strain finite element code. The implementation is validated by means of a set of simple deformation paths (simple shear, extension, extension and compression, extension and rotation) and two benchmark tests in non-linear mechanics (the necking of a circular bar and a shell under ring loads). In these numerical tests, the observed order of convergence is in very good agreement with the theoretical order of convergence, thus corroborating the accuracy analysis

Non-linear shear model for R/C piers

The work presented has been developed within the Prenormative Research in support of EuroCode 8 (PREC8) programme of the European Commission. The EuroCode 8 (EC8) are the provisional European standards for the design of civil engineering structures in seismic prone areas. This programme included experimental test on a series of bridge structures that have been tested under Pseudo-Dynamic conditions. Experimental tests were carried out to study the behaviour of bridge piers under cyclic loading. The results from these tests underlined the need to improve an existing fiber model to represent the non-linear behaviour of structures where the influence of the shear forces is not negligible. Thus, a strut-and-tie formulation coupled with the classic fibre model for flexural forces was developed. This formulation is based on the analogy of a R/C structure damaged with diagonal cracking with a truss made of concrete diagonals and steel ties. The model is applied to a set of bridge piers tested at the ELSA laboratory and the results are compared with the experimental response.JRC.DG.G.5-European laboratory for structural assessmen

Stiffness-Displacement Correlation from the RC Shear Wall Tests of the SAFE Program: Derivation of a Capacity Line Model

The response of 13 reinforced concrete shear walls submitted to successive seismic tests has been postprocessed to produce time histories of secant stiffness and displacement oscillation amplitude. For every wall an envelope curve of displacement amplitude versus stiffness is identified which is fairly modelled by a straight line in double logarithmic scale. This relatively simple model, when used as a capacity line in combination with the demand response spectrum, is able to predict in an approximate manner the maximum response to the applied earthquakes. Moreover, the graphic representation of the demand spectrum and a unique model capacity line for a group of equal walls with different assumed design frequencies on them gives a visual interpretation of the different safety margins observed in the experiments for the respective walls. The same method allows as well constructing vulnerability curves for any design frequency or spectrum. Finally, the comparison of the different identified line models for the different walls allows us to assess the qualitative effect on the behaviour of parameters such as the reinforcement density or the added normal load

Calibration procedure for force and displacement measurements at the HOPLAB

The report explains the calibration procedure of the HOPLAB facility. A short description of the facility is first included concerning the mechanical structure and its equipment in terms of sensors, transducers and relevant electronic instruments. A detailed explanation of the calibration procedure is next presented, which is principally centered at calibrating the force measurements along the input and output bars with a certified load cell. The main issues and problems connected to this particular testing rig are discussed. Finally an example of a typical elaboration, starting from raw experimental data to obtain the force-displacement curve of a specimen in tension, is provided.JRC.G.5-European laboratory for structural assessmen

Procedure for load cell calibration at ELSA Reaction Wall

This report describes the procedure currently applied for the calibration of the load cells used for the mechanical experiments in the ELSA laboratory. The procedure is based on the international norm ISO 7500-1 and the definitions there proposed. The calibration experiment consists of applying a number of load cycles simultaneously on the object load cell in series with a traceable measuring proving instrument externally calibrated (reference load cell). The accuracy of the measures of the object load cell is the most important result of the test delimiting the maximum difference between both instruments. Other important results of the test are the resolution, repeatability and reversibility of the object load cell. All these error parameters determine the quality of the object instrument at the state of the calibration test. In order to extend the validity of the calibration test to the experiments performed with that load cell when connected to amplifiers different from the one of the calibration test, an additional gain test of the signal conditioning chain is also undertaken at ELSA after the calibration test.JRC.G.5-European laboratory for structural assessmen

Error study of a hybrid testing system of structures through a state-space model

Experimental methods such as hybrid or pseudo-dynamic tests are always subjected to experimental errors which effect on the obtained response is important to assess. An analytical linear model formulated on state-space equations has been developed for a multi DoF hybrid testing system including the components of the control and the specimen. For an example of a single DoF steel frame, the parameters of the model have been calibrated through comparison with experimental data of the control system. The model has been used to predict in pseudo-dynamic tests on such specimen the control errors and their consequences in terms of eigenfrequency and damping distortion in the test response. These predictions match with the observed experimental data and allow understanding, for example, the effects on the response of performing the test at different testing speeds or for different parameter configurations of the control algorithm.JRC.G.5-European laboratory for structural assessmen

Electrical Blast simulator (e-BLAST): design, development and first operational tests

The Electrical Blast Simulator (e-BLAST) activity involves the development of an apparatus capable of reproducing the effects of a blast pressure wave on large-scale structural components (such as columns, walls, etc.) with the objective of improving their strength in such severe loading situations. The work relates to the BUILT-CIP project which deals with the protection and resilience of the built environment (critical buildings, transportation and energy infrastructure etc.) under catastrophic events such as blast and impacts. The e-BLAST facility has been conceived and designed with the expertise acquired in the previous project “Blast Simulation Technology Development”, supported through an Administrative Arrangement by DG HOME. Differently from the prototype developed in that project, the e-BLAST exploits a recent technology that appears to be very promising in this particular research field. Specifically, three synchronous electrical linear motors have been adopted for accelerating the impacting masses. This choice has led to develop a more effective, versatile and low-cost facility. The report presents in detail the facility design, its components and their assembly, and a series of preliminary tests carried out in the ELSA laboratory in order to assess the performance of the e-BLAST. Finally, a brief description of further developments and feasible large-scale structural tests, planned to be performed with the new facility, are discussed.JRC.G.4-European laboratory for structural assessmen

Hybrid simulation of complex structural systems based on partitioned time integration schemes

In the last two decades, the increasing complexity of engineering systems boosted the development of very efficient simulation methods based on partitioning. In view of coupling dynamic parts of hybrid systems, the finite element tearing and interconnecting approach emerged as the most promising technique. Nonetheless, there is still a lack of a comprehensive study of algorithmic performances from the experimental perspective. In this view, the present paper sheds light on the application of two well-known parallel partitioning methods for the purpose of the simulation of hybrid models. Thus, an existent reinforced concrete bridge is chosen as a benchmark case study. In order to perform hybrid simulations, a novel coupling software was devised. It allowed for combining two physical piers to the numerical model of the remaining part of the bridge. As a result, successful tests were conducted at the ELSA laboratory of the Joint Research Centre of Ispra (Italy)

Blast Simulator project: First tests on reinforced concrete beams

The Blast Simulator project involves the development of an apparatus able to reproduce the effects of a blast pressure wave on large scale structural components (such as columns, walls, etc.) with the objective to improve their strength in these severe loading situations. After a series of preliminary tests to assess the performance of the blast actuator for what concerns the energy capability, this technical report presents some results related to a test campaign on two full scale structural components, specifically tworeinforced concrete beams.. With appropriate improvements made to the impactor, it has been possible to successfully bring the components to failure. A full suite of test parameters has also been recorded, valuable for guiding the numerical modelling. These experiments validate the potentiality of this kind of equipment to reproduce in a laboratory the effects of a blast explosion on full scale structural elements without using explosives. Further tests with the same experimental setup and with a new testing rig based on a more innovative technology (electrical linear motor) will be conducted in 2015 in the context of BUILTCIP project.JRC.G.4-European laboratory for structural assessmen