Paolo Negro

Performance of industrial buildings during the Emilia earthquakes in Northern Italy and recommendations for their strengthening

A series of earthquakes, the highest of magnitude

A performance based approach for the seismic assessment and rehabilitation of existing RC buildings

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A Critical Review of Current Assessment Procedures

Mw 5.9, hit a portion of the Po Valley in Northern Italy, which was only recently classified as seismic. The paper reports the findings and the lessons learnt from a preliminary field survey which was conducted immediately after the second event. As a result of the economic attitude of the affected area, and possibly of the characteristics of the event, an unprecedented number of industrial precast buildings were affected, resulting into most of the casualties as well as in large economic losses. Whereas most of the damaged and collapsed buildings were designed for gravity loads only, evidence of poor behavior of some precast buildings designed according to seismic provisions were discovered. The paper provides a description of the performance of precast buildings, highlighting the deficiencies that led to their poor behavior as well as some preliminary recommendations.

The Importance of Plan-Wise Irregularity

The experimental campaign carried out at the European Laboratory for Structural Assessment of the Joint Research Centre at Ispra in a two-storey steel frame is presented herein. The experimental activity is part of the Environmental and Climate SteelQuake Project, for the assessment of the low-cycle fatigue behaviour of steel beam-to-column welded connections of beams noncomposite with the slab in the location of the plastic hinges. The description of the mock-up, the testing apparatus and the relative instrumentation for measuring displacements, forces and deformations is presented. Pseudo-dynamic and cyclic tests were performed and the corresponding results are presented at the structure and connection levels in terms of the absolute and accumulated plastic ductilities in relation to the failure events of the welded connections. The importance of the panel zone in contributing towards the total rotation of the connection is highlighted.

The importance of connections in seismic regions: Full-scale testing of a 3-storey precast concrete building

Using the results of a past experimental project in which a non-ductile, seismically under-designed building was tested pseudo dynamically in its as-built configuration as well as in two conceptually different rehabilitated configurations, a method for a simplified seismic performance assessment, based on the standard Pacific Earthquake Engineering Research Centre (PEER) methodology, is discussed. The two retrofitting methods compared in the experimental activity were: Fiber Reinforced Polymer wrapping of all the vertical elements and r.c. jacketing of selected vertical elements. The experimental activity consisted in bi-directional pseudodynamic (PsD) tests at increasing Peak Ground Acceleration (PGA) levels on a full-scale specimen in the two configurations. For this specific study, the results of the tests were used to quantify the achieved improvements in terms of performance brought about by the two retrofitting strategies in the tested building. In order to do that, at first, the benchmark structure was converted into a real building of the same age, then the costs for rehabilitation and repair and the losses referred to the ‘realistic’ building were estimated with the advice of an Italian licensed practicing engineer, based on market values and current practice. Finally, the performance-based assessment exercise consisted into the evaluation of the costs associated to each rehabilitation measure and the expected losses during the remaining life-span of the building for all the defined limit states: these numbers represent a suitable performance indicator for a simple and straightforward comparison of the different retrofitting strategies.

Pseudodynamic tests on a full-scale 3-storey precast concrete building: Global response

A series of earthquakes, the highest of magnitude Mw 5.9, hit a portion of the Po Valley in Northern Italy, which was only recently classified as seismic. The paper reports the findings and the lessons learnt from a preliminary field survey which was conducted immedi- ately after the second event. As a result of the economic attitude of the affected area, and pos- sibly of the characteristics of the event, an unprecedented number of industrial precast buildings were affected, resulting into most of the casualties as well as in large economic losses. Whereas most of the damaged and collapsed buildings were designed for gravity loads only, evidence of poor behavior of some precast buildings designed according to seismic pro- visions were discovered. The paper provides a description of the performance of precast buildings, highlighting the deficiencies that led to their poor behavior as well as some prelim- inary recommendations.

Pseudodynamic tests on a full-scale 3-storey precast concrete building: Behavior of the mechanical connections and floor diaphragms

The correct evaluation of seismic vulnerability of the existing building stock is a key issue for every earthquake prone Country; the need for reliable decision making tools for the assessment and retrofitting of the existing building stock is widely recognized. Still, the applicability, effectiveness, accuracy of currently codified seismic assessment procedures strongly vary, depending on the features of the assessed structures, and often also on the engineering judgement and knowledge of the applicator. Moreover, time and costs constraints, to which the assessment procedures are necessarily bound, pose further issues as to the details and immediateness of the implementation of such analyses. In the paper, a critical review of the most widespread currently codified seismic assessment procedures is carried out, with reference to the case study of a plan-wise irregular reinforced concrete (RC) frame structure which underwent extensive pseudo-dynamic testing, both in the “as-built” and in retrofitted configurations, in the framework of the activity of the ELSA Laboratory of the JRC. Some conclusions on the relative performance of such assessment procedures and their possible improvements, with reference, in particular, to the issues posed by torsion, are finally presented.

Static and dynamic analysis of a reinforced concrete flat slab frame building for progressive collapse

In the framework of the experimental activity of the ELSA Laboratory of the JRC, an extensive PsD testing campaign was carried out on a doubly bi-eccentric plan-wise irregular R.C frame structure representative of non-seismically designed buildings widespread in Europe. In spite of the torsional irregularity being minor, the torsional response turned out to be quite significant, as a result of the choice of the seismic input. The opportunity was thus taken of experimentally assessing the effects of irregularity on the seismic behaviour and to compare it to the effects of poor structural detailing and lack of basic seismic design requirements. Also, the effectiveness was assessed of two different retrofitting strategies, a ductility-only intervention and a strength-only one, in providing a satisfying seismic response and tackling the structural weaknesses detected by the tests in the unretrofitted configuration. Conclusions are thus drawn on the basic criteria to be taken into account when devising a retrofitting strategy for existing irregular buildings under strict time and budget constraints. Also, it is discussed if whether a reduction of torsional effects is a basic aim to be pursued in retrofitting under above said constraints or if it can be neglected in the decision making process, even though the role of torsional effects in affecting the response is indisputably acknowledged.