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Research by ROSE Students

Below, the titles of MSc Dissertation and Individual Study projects carried out by our students are listed As expected, the range of themes under investigation is quite broad; a natural reflection of the multidisciplinary character of the ROSE School For further information on each one of these projects, click on the titles listed below

MSc dissertations & Individual Studies - Year 2004

Displacement-based design of continuous concrete bridges under transverse seismic excitation

Bidirectional modelling of high-damping rubber bearings Record selection for nonlinear seismic analysis of structures Seismic vulnerability of masonry arch bridges

Dynamic behaviour of reinforced concrete frames designed with direct displacement-based design

Rocking isolation of bridge piers resting on spread foundations

Displacement capacity of reinforced concrete columns with limited shear resistance Probabilistic implementation of a mechanics-based procedure for seismic risk assessment of classes of R.C buildings

Seismic analysis of the structure of an underground railway station including SSI Equivalent viscous damping equations for direct displacement-based design An Isogeometric Analysis Approach for the Study of Structural Vibrations Design of a dynamic and pseudo-dynamic testing facility

Effects of column base behaviour on the overall response of steel moment frames

Seismological criteria for selecting and scaling real accelerograms for use in engineering analysis and design

FRP seismic retrofit of square hollow seimic bridge piers 3D pushover of irregular reinforced concrete buildings

Shape-memory alloy devices in earthquake engineering: mechanical properties, constitutive modelling and numerical simulations

Periods of vibration for displacement-based assessment of RC buildings Comparative parametric study on normal and buckling restrained steel braces Seismic hazard assessment of the historical site of Jam and stability analysis of the minaret

Limitations and performances of different approaches for seismic assessment of existing buildings

A simplified mechanics-based procedure for the seismic risk assessment of unreinforced masonry buildings

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Explorative study of scatter in strong-motion attenuation relationships for application to seismic hazard assessment

Displacement-based seismic analysis for out-of-plane bending of unreinforced masonry walls

Dynamic amplification of bending moments and shear forces in cantilever walls A simplified deformation-based method for seismic vulnerability assessment Does liquefaction protect overlying structures from ground shaking?

Fragility analysis of reinforced concrete structures using a response surface approach

The current limitations of displacement based design Cyclic soil plasticity

Current Research Topics

The following list includes a succinct, and surely incomplete, sample of the topics of research currently offered to students It is noted that a strong experimental

component is present in a number of investigation areas and that the vast majority of the projects are carried out within the scope of National and International research networks Further details may be obtained by contacting the School Director:

Applied mechanics and advanced computer modelling

Development of non-isotropic and/or inelastic constitutive equations for innovative materials, in large deformation regime

Development of finite element technologies for nonlinear static and/or dynamic analysis of structures

Experimental and analytical work on reinforced concrete structures

Assessment and retrofitting of beam-column and flat slab-column joints Assessment, repair and strengthening of reinforced concrete buildings Assessment of existing pre-cast concrete buildings

Vulnerability evaluation, at urban scale, of existing reinforced concrete buildings (using mechanical or mechanical-empirical approaches)

Experimental and analytical work on reinforced concrete bridges

Assessment of frame and arch bridges

Assessment, repair and strengthening of hollow bridge piers Carbon fibre strengthening of bridge slabs

Isolation systems for bridges

Relevance of re-centering capacity of isolating devices

Experimental and analytical work on masonry arch bridges

Interaction between infill material and parapet walls in relation with a possible out-of-plane collapse

Influence of non-synchronous input or soil incoherency

Relevance of vertical acceleration in relation to arch-pier interaction, and its potential for damage to the arch structure

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Experimental and analytical work on masonry buildings

Performance-based assessment of existing masonry buildings (based on pushover analysis methods)

Out-of-plane response and collapse mechanisms of masonry walls Seismic assessment of historical structures

Engineering seismology

Regional estimation of macro-seismic attenuation in Italy

Estimation of local amplification effects using historical MCS intensities Estimation of earthquake recurrence laws for seismic hazard analysis Catalogue incompleteness and its effects on seismic hazard

Experimental and Numerical Facilities

Structural Laboratory

The School makes use of the structural laboratory of the University of Pavia, the largest University testing facility in Italy The total area inside the laboratory exceeds 1500 m2 Reaction structures include a strong floor of approximately 400 m2, with a capacity of approximately 500 kN/m2, and four reaction walls, with a reaction

capacity of approximately 600 kN each, at 8 m of height.

Equipment includes two small shaking tables (100 kN capacity), two MTS dynamic actuators (500 kN capacity), four screw jacks (500 kN capacity), more than two hundred displacement transducers, twenty digital accelerometers and two laser velocity interferometers The data acquisition system is fully consistent with the available instruments thanks to the continuous use of the most advanced hardware/software test processing tools The laboratory is fully equipped with standard material testing machines and with a workshop for in-house preparation of all necessary test-rig components.

Computer Labs

The School has its own numerical facility, in addition to the large University system The School system includes a network of 15 workstations, fully interacting with a local server connected through optical fibres to the University system Available software includes a number of commercial structural computer codes, such as Adina and SAP2000, in addition to programmes developed or modified locally, such as Feap, Ruaumoko or Drain2D.

FRP seismic retrofit of square hollow seimic bridge piers

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Student: S Peloso

Supervisor: Dr A PaveseAbstract

Over the past 20 years, fibre reinforced polymers (FRP) have been increasingly employed in the upgrade and repair of concrete and masonry structures in seismic prone countries, with extensive research programmes being carried out worldwide, focusing primarily on the improvement of the seismic capacity of bridge piers.

However, the majority of such research has not considered the case of square hollow section bridge piers These are very common in Europe, featuring also a construction date between the ‘50s and ‘70s, when seismic zones were often not recognized, resulting thus in piers designed for gravity loads alone As a consequence, these bridge piers call now for large strength and ductility enhancements in order to meet the prerequisites of modern earthquake resistant regulations.

In addition, a number of such bridges have been subjected to earthquakes resulting, in some instances, in failure mechanisms due to: shear, combined flexure/shear and insufficient lap splice It is thus clear that the development of efficient structural intervention methods to be applied in the repair and strengthening of square hollow bridge piers is of great importance and relevance, in particular within the framework of European transport infrastructures.

Within the scope of the current research, quasi-static cyclic tests were performed with increasing levels of drift applied to scaled specimens of FRP retrofitted piers, taking trace of the force-displacement diagram and flexural and shear deformations Further, the effect of FRP intervention in the level of section confinement, the

efficiency of the anchorage, the energy dissipation, the achieved ductility and horizontal strength of the retrofitted piers were all thoroughly scrutinised, through comparison with the response of previously tested specimens without FRP

application Finally, the experimental results were also employed to assess the adequacy of currently available design formulae, calibrated through experiments on solid section piers, in the prediction of the capacity of retrofitted hollow bridge piers You may download (4700 kB) a digital version of this MSc dissertation here.

Shape-memory alloy devices in earthquake engineering: mechanical properties, constitutive modelling and numerical simulations

Student: Davide Fugazza

Supervisors: Prof F Auricchio, Dr A Pavese, Dr L PetriniAbstract

Shape-memory alloys (SMAs) are a class of solids showing mechanical properties not

present in materials usually employed in engineering SMAs have the ability to undergo reversible micromechanical phase transition processess changing their

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cristallographic structure This capacity results in two major features at the macroscopic level which are the superelasticity and the shape-memory effect Due to these unusual characteristics, materials made of SMAs lend themselves to innovative applications in many scientific fields ranging from biomedical devices, such as stents or orthodontic archwires, to apparatus for the deployment and control of space structures, such as antennas and satellites.

Experimental and numerical investigations have also shown the possibility of using such smart new materials in vibration control devices In particular, they seem to be an effective mean of improving the response of buildings and bridges subjected to seismic loads

Despite the availability of a large number of mechanical tests conducted by many authors, few works deal with their constitutive modelling for earthquake engineering applications Also, their dynamic response under high-frequency loading conditions would need further studies As a consequence, the main aim of the present work is to cover this lack of information

The main objectives of the present dissertation are the following:

- To present and comment the mechanical properties of SMA materials with emphasis on their response under dynamic loading conditions.

- To study the constitutive modelling of SMAs for seismic applications - To implement a robust uniaxial constitutive model for superelastic SMAs.

- To understand the influence of the SMA's mechanical properties on their dynamic behavior through parametric analyses

You may download (1600 kB) a digital version of this MSc dissertation here.

Periods of Vibration for Displacement-based Assessment of RC Buildings

Student: Helen CrowleySupervisors: Dr R PinhoAbstract

Simple empirical relationships are available in many design codes to relate the height of a building to its fundamental period of vibration These relationships have been realized for force-based design and so produce conservative estimates of period such that the lateral shear force will be conservatively predicted from an acceleration spectrum Where assessment of a structure is concerned, it is the displacement demand that gives an indication of the damage that can be expected, this

displacement would be underestimated with the use of the aforementioned period – height formulae Furthermore, the period of vibration of interest in assessment is the yield period, which is calculated using the yield stiffness, also often referred to as the cracked or elastic stiffness The derivation of a yield period – height formula for use in displacement-based assessment of European buildings is thus the focus of this dissertation Analytical fibre element models of RC frames of varying height have been developed and the yield period has been sought using eigenvalue, pushover and dynamic analyses

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Comparative parametric study on normal and buckling restrained steel braces

Student: Edison Ochoa EscuderoSupervisors: Prof M NakashimaAbstract

This study presents the results of parametric analyses performed on various frame models, characterizing the behavior and response of steel frames with braces under seismic action.

The focus of this study is the analysis of the deformation response of two different frames, using conventional braces with various slenderness ratios, and buckling restrained braces The response of the frames is obtained by numerical simulation under the action of six strong ground motions, normalized to have the same levels of peak ground velocity P-delta effects are taken into account during the simulation Statistical analyses are performed to characterize the responses, obtaining

comparable results that allow the determination of the incidence of the various brace types and the additional parameters in the global behavior of the frame and its elements.

In the study, a review of the research conducted in Japan during the last 30 years is presented Analytical and experimental results regarding the most significant papers on buckling restrained braces are exposed in the study The analytical formulation corresponding to normal and buckling restrained braces is described in an simple manner, with a set of equations used for analysis and design Conclusions on the frame response are presented in the final chapter of this study.

Limitations and performances of different approaches for seismic assessment of existing buildings

Student: Giorgio Lupoi

Supervisors: Prof P.E Pinto, Prof G.M Calvi Abstract

The present study consists of a commented application of the three major guidance documents on the assessment of existing buildings currently available: the New Zealand Recommendations, the U.S ASCE-FEMA356, and the Japanese Standard, to three structures (two 2D and one 3D frames) which have been constructed at a large scale and tested The main purpose of the study is that of checking the practical applicability of the methods, the relative ease of use, and of course the degree of agreement on the results.

The theoretical framework on which each document is based as well as the proposed methods are outlined and commented Differences of conceptual nature existing

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between the various approaches are noted.

From the small number of cases examined is not possible to systematically trace the differences in the results produced by the different approaches The large difference in the way the shear capacities of members and joints are evaluated has been a decisive factor in some cases for the determination of the ultimate capacity of the entire building However, even if this source of discrepancy of the results from the various approaches was eliminated, the present exploration indicates that significant differences would remain, linked to the criteria used to relate the capacity curve to the response spectrum, or to the use of elastic analysis combined with local ductility factors, as in the U.S FEMA356, instead of the global mechanism analysis of New Zealand

Explorative study of scatter in strong-motion attenuation relationships for application to seismic hazard assessment

Student: Luis Fernando Restrepo Velez Supervisor: Dr J.J Bommer

Attenuation relationships for the estimation of strong-motion parameters for a particular earthquake scenario are fundamental to seismic hazard assessment These relationships are obtained from regression analysis on recorded values of the

parameter of interest and they generally have a relatively large degree of scatter that is usually characterized by the standard deviation of a lognormal distribution of the residuals The scatter in the attenuation relationship exerts a pronounced influence on the results obtained from seismic hazard assessments.

In disaggregation of PSHA to determine hazard-consistent design earthquake

scenarios, the scatter, defined by a certain number of standard deviations above the median, becomes part of the scenario together with the magnitude and distance In current disaggregation practice the number of standard deviations in the design scenario is added to the median values of all of the ground-motion parameters that are required without consideration of how likely it is that the ground motion will yield such high values of all the parameters simultaneously.

This project explores the nature of the scatter in attenuation relationships and shows that the scatter is not genuinely represented by the lognormal distribution of the residuals, particularly for the most extreme outliers The covariance of the scatter is discussed, along with the existence of physical upper

bounds for strong-motion parameters.

Displacement-based seismic analysis for out-of-plane bending of unreinforced masonry walls

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Student: Giammichele Melis

Supervisors: Dr G Magenes, Dr M.C GriffithAbstract

The importance of assessing the seismic resistance of existing masonry structures has drawn strong and growing interest in the recent years While conservative rules may be acceptable for the design of new masonry structures implying only a minor and negligible economic penalty, on the other hand in the case of existing buildings the same degree of conservatism may hold the balance between the necessity of strengthening or not the

structure under investigation, with hence a huge difference in the economic balance This study has investigated on the applicability of a displacement-based procedure to predict the response of unreinforced masonry walls when dynamically loaded, taking into account their reserve capacity due to rocking.

It has been found that the procedure proposed is reasonably accurate and at the same time fairly conservative, with a more acceptable degree of conservatism with respect to traditional methods of assessing seismic performance of unreinforced masonry walls based on elastic stress calculations which lead to excessively conservative results.

You may download (870 kB) a digital version of this MSc dissertation here

Dynamic Amplification of Bending Moments and Shear Forces inCantilever Walls

Student: Alejandro Amaris

Supervisor: Prof M.J.N PriestleyAbstract

In recent years, Displacement based design procedure has been used to achieve a specified acceptable level of damage under the design earthquake The

inappropriateness of the Force based design assumptions of initial stiffness and ductility capacity suggests that results of base moments and shear reached in a structure when inelastic response had occurred are not valid For that reason, it is proposed in this analysis determine appropriate dynamic amplification factor for flexure and shear for a wide range of cantilever wall buildings of 2, 4, 8, 12, 16 and 20 stories which were design using the fundamental of displacement based design principles and compare the results with Force Based Design analysis and time history dynamic analyses.

In addition, the relationship between ductility demand and the dynamic amplification factor in each wall system was investigated This was carried out using time history analyses for five different earthquakes intensities for each wall, and analysing the bending moment and shear force envelopes.

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The effects of some of the issues discussed above were analysed through the use of the inelastic dynamic analysis program, Ruaumoko and the results were compared with existing code requirements.

It was found that dynamic amplification of both shear and moment envelopes became more severe as the initial elastic period of the structure increased, and also as the ductility increased (effected by increasing the seismic intensity) Since all the walls were designed to the same drift limit of 0.02, the level of ductility

corresponding to the design seismic intensity decreased as the number of stories increased.

It was further found that most of the dynamic amplification resulted from second mode response, and that existing design equations for dynamic amplification for walls were grossly non-conservative.

A simplified deformation-based method for seismic vulnerability assessment

Student: Simon GlaisterSupervisors: Dr R PinhoAbstract

The state-of-the-art earthquake loss estimation techniques make use of pushover analysis to define the performance of structures under earthquake loading, which is represented by a demand spectrum whose ordinates reflect the inelastic response The performance point defined in this way is then used as input to the fragility or loss curves This is a rigorous approach that both represents the earthquake actions by a parameter that is known to have a good correlation with damage and also to take into account the dynamic characteristics of different buildings However, for applications to large areas, including major cities, the available data on key input parameters such as soil conditions and the type and distribution of the exposed building stock, is often of sufficiently poor resolution to make the rigorous capacity spectrum approach disproportionately complex and time-consuming It is for such case scenarios that a much simpler displacement-based assessment methodology, presented herein, has been developed The proposed method possesses all the inherent accuracy advantages of a displacement-based approach, whilst reducing the required calculations by one or more orders of magnitude, when compared to

conventionally vulnerability assessment procedures.

Does liquefaction protect overlying structures from ground shaking?

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Student: Francisco LopezSupervisor: Dr J.B BerrillAbstract

When recordings have been obtained at sites that have been liquefied, it is clear that high-frequency components of motion are absorbed as the soil softens after the triggering of pore-pressure increase However, it is also clear, for example from the 1987 Superstition Hills, Calif., that significant acceleration peaks can be trasmitted before triggering of liquefaction effects Also, as is now well estblished, liquefied soil retains some shear strength, and long-period motions continue to propagate through the the liquefied layer The aim of this project is to examine a number of

instrumented sites where liquefaction has been seen and to compare estimates of the motion that would have been occurred in the absence of liquefaction with actual recorded motions If the results permit it, generalizations will be drawn and design rules formulated.

Fragility analysis of reinforced concrete structures using a response surface approach

Student: M.IJ Schotanus Supervisor: Prof P.E PintoAbstract

A general and sophisticated method for seismic fragility analysis of systems,

originally proposed by Veneziano et al (1983), is further developed in this work and applied to a reinforced concrete frame The method is not limited to a specific class of structures or systems, or to a particular representation of the random input Sophistication lies in the incorporation of state-of-the-art mechanical models; use of realistic models for the seismic action; assignment of probabilistic models for

mechanical parameters and capacity; and in accounting for multiple failure modes and their correlation

The basic proposal is to use a response surface to represent the capacity part in an analytical limit state function (g-function) as input for SORM analysis Response surface techniques are used to replace the algorithmic g-function, or the capacity part of it, with an explicit functional relationship, fitting a second order polynomial Such an explicit format highly reduces the number of expensive numerical analyses needed compared to classical methods that determine the failure domain In order to keep the method competitive, only a small number (with a maximum of about 6) of parameters are chosen to enter in the function as explicit variables, whose effect is denominated fixed The response surface methodology is then used as an iterative and evolutive procedure, to help distinguishing the important variables from the less important and to support the choices made Those random variables that are not explicitly incorporated are accumulated in an error term together with errors originating from the lack-of-fit of the model This error term is itself random and transfers the uncertainty to the output quantity More specifically, the effect of a

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