Steel-based applications in earthquake-prone areas

Steel-Earth project aims at distributing among technicians, engineers, design companies and standardization bodies the results of three past RFCS projects (Steel-Retro [3], Opus [2] and PrecaSteel [1]), providing useful tools for the design and for the retrofit of existing buildings. Technical documents and practical applications to case studies, regarding design of steel and composite steel/concrete buildings and innovative steel-based techniques for the retrofit of existing r.c. and masonry constructions, have been elaborated and collected into a volume distributed during the final workshop of the dissemination project. Pre-normative and background documents concerning the design of steel and composite structures and the rehabilitation of existing constructions have been prepared. A lot of attention has been paid to the analysis of the influence of overstrength factors on the seismic design of steel and composite structures. The prepared documents have been distributed to the attending people and to the members of WG 2 (CEN/TC 250/SC 8/WG 2 “Steel and Composite Structures”) during the final workshop of the project. Technical sheets, working examples and background documents have been translated into several languages (German, French, Italian, Romanian and Greek) and are free available on the website of the project (https://www.steelconstruct.com/site/), where information regarding Steel-Earth are also presented.11 Workshops in Italy, Greece, Germany, Belgium, Portugal, Spain and Romania and 5 conferences in Emilia-Romagna have been organized, as well as 2 practical courses for engineers and academic people in Pavia (Italy). Flash-drives with the technical documents and applications elaborated in Steel-Earth have been distributed to the attending people

Corroded TempCore® vs dual-phase steel reinforcing bars

The paper summarizes the results of an experimental test campaign on enhanced reinforcing grades provided by Dual-Phase (DP) microstructure, compared to TempCore®. The DP improvement mainly concerns durability: due to their ‘mixed’ microstructure, DP steels are less affected by corrosion. Accelerated corrosion tests and mechanical tests on corroded samples were performed, using two different techniques (salt-spray chamber and impressed current density). Results highlight how different corrosion procedures can affect results, even if conclusions remain the same: DP steel bars result to be less sensitive to corrosion, showing a smaller decrease in ductility compared to TempCore bars. No relevant influence is revealed on strength performance and cyclic behaviour

Cyclic bar model with bond slip for nonlinear analysis of existing RC structures

The maximum displacement demand..

Experimental and numerical assessment of a steel frame equipped with Dissipative Replaceable Bracing Connections

In the last decades, high priority has been given by the research community to the development of low-damage structures, and reparability has become fundamental for minimizing the environmental and economic impact of reconstruction. In this context, the European Research Fund for Coal and Steel (RFCS) project DISSIPABLE was carried out, with the aim to test large-scale structures where the dissipation is concentrated on replaceable components introduced in the structure. In this paper, the performance of a six storey braced steel frame with dissipative systems is analysed. The capacity of withstanding seismic actions relies on Dissipative Replaceable Bracing Connections (DRBrC), used for the brace-column joints. The energy dissipation is ensured by wide hysteresis loops experienced by DRBrC, whose configuration enables an easy replacement after a medium-high intensity earthquake. Results of a wide experimental test campaign on full-scale structures and numerical analyses on refined models are presented and compared. In particular, experimental data were used to validate and to calibrate the simplified numerical laws used to represent the cyclic performance of the dissipative components and it was proved the effectiveness of using a simplified formulation from both a theoretical and a practical point of view

Seismic demand on steel reinforcing bars in reinforced concrete frame structures

Modern design standards for reinforced concrete (r.c.) buildings allow the achievement of ductile structures, able to globally dissipate seismic energy through the development of plastic deformations located in the dissipative regions (i.e. plastic hinges). The hysteretic capacity of r.c. structures is related to the ability of reinforcing steel bars to sustain many cycles of high plastic deformations without the exhibition significant decrease of strength and stiffness; this condition, typically due to cyclic/seismic action, shall be widely investigated in order to obtain a full and detailed knowledge of the structural behaviour of modern r.c. buildings. In the present paper, elaborated inside the European research project “Rusteel”, the evaluation of the seismic ductile demand on steel reinforcing bars due to real earthquake events was carried out. Representative r.c. case study buildings were designed following the actual European and Italian prescriptions and analyzed using the Incremental Dynamic Analysis technique for the assessment of the behaviour under real seismic events. The elaboration of a simplified mechanical model for the steel reinforcing bars, calibrated on the basis of experimental monotonic and cyclic tests, allowed the evaluation of the effective level of deformation and energy dissipation required by earthquakes and the assessment of the ability of the actual European production to satisfy the effective seismic ductile requirements. © 2014, Springer Science+Business Media Dordrecht

Reliability of ultrasonic tomography in detecting grouting defects in post-tensioned structures by PoD curves

The present research aims to assess the reliability of Ultrasonic Tomography (UT) of void detection in post-tensioning ducts due to inappropriate execution of grouting. The methodology is based on the construction of the Probability of Detection (PoD) curves for this specific non-destructive technique, by relating the probability of success to identify a specified ungrouted region. The PoD curves are built on data collected during a testing campaign in the laboratory, under fully known grouting conditions. Six walls containing prestressing strands and bars in metallic and plastic ducts with simulated voids of different sizes were designed and executed. Both water-filled (infiltration) and empty voids (ungrouted region) were simulated. The classical frequentist and Bayesian approaches are used to derive the PoD curves. Since the available experimental data are limited, the Bayesian approach provides more reliable data and is, thus, proposed as the best alternative. It is finally concluded that the minimum size of the voids in metallic ducts that UT can detect with 95% confidence and 90% probability, is around 30 cm and this value will be used in future inspection campaigns in posttensioned bridges

Ductility demand on steel reinforcing bars in concrete buildings

According to actual Italian and European standards for constructions, reinforced concrete buildings in seismic areas should be designed following the capacity design approach, in order to dissipate seismic energy through the development of plasticisations located in particular areas, providing global collapse mechanisms and avoiding premature failures of non-ductile elements (for example mechanisms of soft storeys). The areas in which plastic hinges are located, generally coinciding with the ends of beam elements, are known as dissipative zones. In common practice, the seismic design of new buildings is developed through the elaboration of simplified linear models that, in spite of their simplicity, do not take into account all the problems related to the non-linear response of materials and consequently are not really calibrated on the base of the effective ductility demand imposed by earthquakes. For this reason, in a European research project funded by the Research Fund for Coal and Steel (RFCS) named Rusteel "Effects of Corrosion on Low-Cycle Fatigue (Seismic) Behaviour of High Strength Steel Reinforcing Bars", a detailed investigation of the effective behaviour of reinforced concrete buildings under seismic action was executed through the consideration of accurate non-linear models and the execution of non-linear analyses. The main aim of the research project consists in the correlation between the ductility demand imposed by earthquakes and the ductility capacity of dissipative elements such as beams, whose hysteretic behaviour is strictly related to the ability of steel reinforcing bars (rebars) of sustaining a relative large number of high plastic deformations without showing evident losses of ductility and strength (low-cycle fatigue (LCF) condition). The evaluation of the ductility capacity of steel reinforcements shall consider the consequences, both in terms of strength and ductility, of corrosion phenomena resulting from aggressive environmental conditions. A detailed experimental test programme, including monotonic and LCF tests on uncorroded and corroded rebars, was executed in the framework of Rusteel and preliminary results are showed in thispaper. As regards the investigation of the ductility demand, different case studies were designed following the prescriptions imposed by actual standards and using dynamic modal analysis; refined non linear models implemented in OpenSees were then developed including the effects of the interaction between steel and concrete (bond-slip phenomena), through the development of a simplified constitutive stress-slip law. In this paper, preliminary results about both the mechanical capacity of corroded and uncorroded steel rebars under monotonic and cyclic loads and the ductility demand under seismic action are presented

Ductility Demand on Steel Reinforcing Bars in Concrete Buildings

In the present paper, developed inside the framework of the European Research project Rusteel, the behaviour of steel reinforcing bars under the combined effects of low-cycle fatigue action and corrosion phenomena is studied. The project aims at the definition of the effective ductility capacity of reinforcements, to be compared with the ductility demand imposed by earthquakes, investigated through the execution of non-linear dynamic analyses on numerical models of representative modern reinforced concrete buildings. The comparison between demand and capacity will enable understanding of the effective relationship between the requirements of earthquakes and the capacity of rebars (strength and ductility), providing indications for the design and structural details of new building in seismic areas

Inspection and assessment of PT structures: results from application to an existing bridge

Pre-stressed concrete with post-tensioned (PT) cables historically represented an attractive alternative to ordinary reinforced concrete (RC). A wide portion of the worldwide existing concrete bridges was PT. As the nominal service life of those structures expires, several collapses occurred, highlighting the problem of the inspection. The main issue is that PT cables may be affected by relevant corrosion phenomena related to the presence of air or water inside the ducts: such ‘hidden’ defects need to be determined through reliable testing methodologies. This paper presents the in-progress research aiming to quantify the influence of the damage of the single cable on the entire structure. The case study is an Italian viaduct composed of simply supported beams connected by an upper slab. An extensive investigation campaign was carried out to locate and quantify the damage. Starting from the data collected on-site a series of damage conditions of cables can be simulated