Seismic Retrofit

It is well-known that the existing building stock is responsible for non-renewable resource depletion, energy and material consumption, and greenhouse gas (GHG) emissions. Life cycle analysis (LCA) procedures have thus been developed, in recent years, to assess the environmental impact of construction and operational phases through the entire building life cycle. Furthermore, the economic, environmental, and social consequences of recent natural disasters have encouraged the additional integration of hazard-induced impacts into common LCA procedures for buildings. Buildings are however expected to provide the population with safe living and working conditions, even when hit by different types of hazards during their service life, such as earthquakes. Hence, next-generation LCA procedures should include not only hazard-induced impacts, but also the contribution of potential retrofitting strategies that may alter the structural and energy performances of buildings throughout their rem...

The majority of existing buildings are in need of seismic retrofit. The main reasons are: the original design was not optimised with respect to the required safety level, poor construction quality, modifications or enlargements of buildings during their life and increase in the requirements of the seismic design. Even if steel solutions can often be more efficient and economic, their possibilities are practically unknown and their application has been limited to a few particular cases. The aim of the research proposal focused to set up steel solutions for the seismic retrofit of existing buildings, furnishing design and construction methodologies, tools for dimensioning of elements and connections.

The expected seismic losses of structures with Rotational Friction Dampers (RFDs) are assessed by the Endurance Time (ET) method considering the optimal frictional moment of the devices. A practical method is proposed to obtain the optimal frictional moment of the dampers in multi-story structures at multiple seismic hazard levels. The ET method is used as the analytical tool in this research due to its ability to reduce the number of required analyses and providing good estimations of structural responses at various hazard levels. In order to investigate the effectiveness of the dampers, the life cycle costs of a weak steel structure equipped with optimal RFDs are compared with a standard structure with optimal RFDs and without RFDs. To this end, a comprehensive performance evaluation is performed on the structures based on FEMA P-58 methodology. The ET method is also used as a tool to assess the structural responses in the framework of this methodology. The probability of collapse, fatalities, and expected damage costs are estimated utilizing a Monte Carlo procedure considering uncertainties. Also, a cost-benefit analysis is performed to determine the payback period of investment for the additional cost of the rotational friction damping systems.

There is a huge inventory of existing vulnerable buildings and only a little research has been done concerning the economic side of their retrofit. The study presented in this paper aims to show how further issues, for example costs, can be taken into account from the early stages of the rehabilitation project, like the building survey, through collecting and organising the data, to building a cost assessment. It describes a way from the building survey, identifying the loadbearing structure through to cost assessment for rehabilitation works. The core idea is that each structure can be divided into units called "retrofit elements", for which both seismic performance and costs are easier to assess. There is literature about typical performance curves for selected retrofit elements, like columns or frames. The conclusions of a study regarding the cost-effectiveness study are being used for the integration purposes.

This paper assesses the seismic performance of typical reinforced concrete (RC) existing framed
structures designed for gravity loads only. The sample two-storey structural system exhibits high
vulnerability, i.e. low lateral resistance and limited translation ductility; hence an effective strategy
scheme for seismic retrofitting was deemed necessary. Such a scheme comprises buckling restrained
braces (BRBs) placed along the perimeter frames of the multi-storey building. The adopted design
approach assumes that the global response of the inelastic framed structure is the sum of the elastic
frame (primary system) and the system comprising perimeter diagonal braces (secondary system); the
latter braces absorb and dissipate a large amount of hysteretic energy under earthquake ground
motions. Comprehensive nonlinear static (pushover) and dynamic (response history) analyses were
carried out for both the as-built and retrofitted structures to investigate the efficiency of the adopted
intervention strategy. A set of seven code-compliant natural earthquake records was selected and
employed to perform inelastic response history analyses at serviceability (operational and damageability
limit states, OLS and DLS) and ultimate limit states (life safety and collapse prevention limit
states, LSLS and CPLS). Both global and local lateral displacements are notably reduced after the seismic
retrofit of the existing system. In the as-built structure, the damage is primarily concentrated at the
second floor (storey mechanism); the computed interstorey drifts are 2.43% at CPLS and 1.92% at LSLS
for modal distribution of lateral forces. Conversely, for the retrofitted system, the estimated values of
interstorey drifts (d/h) are halved; the maximum d/h are 0.84% at CPLS (along the Y-direction) and 0.65%
at LSLS (yet along the Y-direction). The values of the global overstrength O vary between 2.14 and 2.54
for the retrofitted structure; similarly, the translation ductility mD-values range between 2.07 and 2.36.
The response factor (R- or q-factor) is on average equal to 5.0. It is also found that, for the braced frame,
under moderate-to-high magnitude earthquakes, the average period elongation is about 30%, while for
the existing building the elongation is negligible (lower than 5%). The inelastic response of the existing
structure is extremely limited. Conversely, BRBs are effective to enhance the ductility and energy
dissipation of the sample as-built structural system. Extensive nonlinear dynamic analyses showed that
more than 60% of input seismic energy is dissipated by the BRBs at ultimate limit states. The estimated
maximum axial ductility of the braces is about 10; the latter value of translation ductility is compliant
with BRBs available on the market. At DLS, the latter devices exhibit an elastic behaviour. It can thus be
concluded that, under moderate and high magnitude earthquakes, the damage is concentrated in the
added dampers and the response of the existing RC framed structure (bare frame) is chiefly elastic

Moderate and severe earthquakes have struck different places in the world, causing severe damage to reinforced concrete structures. Retrofitting the existing structures is one of the major challenges to face. One of the retrofit techniques of RC structural members is confinement with a composite enclosure. This external confinement of concrete by high strength Carbon Fibre Reinforced Polymer composites can significantly enhance the strength and ductility and will result in large energy absorption capacity of structural members. Beam-column joints, being the lateral and vertical load resisting members in framed RC structures are more vulnerable to failures during earthquakes and hence strengthening of the joints is often, the key to achieve successful seismic retrofit strategy.This paper depicts experimental investigations carried on RC frames subjected to broad band excitation, which are conducted to study the performance of wrapping on retrofit effects on it & the influence of Carb...

Earthquakes can cause considerable fatalities, injuries and financial loss. The forces of nature cannot be blamed, as the problem lies with the structures in seismic regions that may not have been designed or constructed to a sufficient degree to resist earthquake actions or they may have design flaws. This Structural Engineering Document (SED) concerns reinforced concrete and masonry buildings together with geotechnical aspects and presents in a concise and practical way the state of the art of current understanding of building failures due to earthquakes. It classifies the different types of seismic failure, explains the reasons for each failure, describes good practices to avoid such failures and also describes seismic retrofitting/upgrading procedures for pre-earthquake strengthening and post-earthquake repair and/or strengthening techniques for deficient buildings. Carefully selected photographs and diagrams illustrate the different failure types. This document could be considered as quite unique, as this is the first time such material concerning characteristic seismic failures of buildings has been presented together in one single document. It is intended to be a valuable educational reference textbook aimed at all levels of experience of engineers. It provides background information, ideas, guidance and reassurance to engineers in earthquake regions faced with the task of building a safer future for the public and to protect lives.

https://www.iabse.org/IABSE/Publications/IABSE_Bulletins/SED_Books/Current/IABSE/publications/Bulletins/SED/Current.aspx

ASEIZMICKO PPROJEKTOVANJE I ARHITEKTURA je prva  knjiga kod nas, koja se bavi orginalnom temom uticaja arhitektonskih rešenja na seizmičko reagovanje objekata. Uloga arhitekture u seizmičkom regovanju objekata nikada nije ozbiljno tretirana u zemljotesnom inženjerstvu. Pažnja je uglavnom usmerena na metode analize i proračuna, zatvarajuči oči pred činjenicom da je objekat trodimenzionalna realnost, koji će tako i reagovati bez obzira na "dubinu" i sofisticiranost metode proračuna.

Međuzavisnost arhitekture i konstrukcije čini neophodnim da se arhitekte više informišu o sizmičkoj problematici i konstrukciji uopšte, dok sa druge strane konstuktori moraju biti više osetljivi na arhitektonske zahteve i spoznati seizmički značaj arhitektonskih rešenja.

Cilj knjige je da opremi studente postimplomskih studija arhitekture, a naročito profesionalne arhitekte i konstruktore, onsovnim znanjima iz oblasti aseizmičkog proejktovanja.

Konceptualni pristup problematici će bez sumnje poslužiti i inženjerima koji se profesionalno bave projektovanjem konstrukcija a koji preferraju praktičniji prilaz problematici.

Ima 356 strana, oko 400 crteža i fotografija, veći broj primera

This paper represents the overall review about the change in structural behavior and strength of Reinforced concrete short columns when strengthened with ferrocement jackets. The installation of reinforcement in RC short columns using closely spaced lateral ties not only creates a problem of much increased honeycombing, but also adds to it a plane of
weakness between core and the concrete cover. In order to overcome this failure of RC short columns even before its service period is over an immediate attention is required in and it can be done by replacing the damaged part of reinforced concrete by Ferrocement jackets. In the past few decades, ferrocement come out as a long lasting strengthening
material because of its superior mechanical properties and high in-plane strength. This paper also focuses on the effect of increased no. of wire mesh layers at different orientations and it was found that ferrocement jackets increases the overall load carrying capacity, first crack load, and the total stiffness of column, but the deflection decreases to a large extent.

ARKITEKTURA SIZMIKE a book (in albanian) published  in August 2012.
Book explores the role of architecture and architects  in seismic response of building structures.It has 362 pages in color and more than 400 photographs and drawings.

Libri eksploron rolin e arkitekturës në REAGIMIN sizmik të strukturave dhe është e para e këtij lloji në gjuhën shqipe. Ka 362 faqe, me ngjyra dhe më shumë se 400 fotografi dhe vizatime.

This work is an elementary but comprehensive textbook which provides the latest updates in the fields of Earthquake Engineering, Dynamics of Structures, Seismology and Seismic Design, introducing relevant new topics to the fields such as the Neodeterministic method. Its main purpose is to illustrate the application of energy methods and the analysis in the frequency domain with the corresponding visualization in the Gauss-Argant plan. However, emphasis is also given to the applications of numerical methods for the solution of the equation of motion and to the ground motion selection to be used in time history analysis of structures. As supplementary materials, this book provides “OPENSIGNAL", a rare and unique software for ground motion selection and processing that can be used by professionals to select the correct earthquake records that would run in the nonlinear analysis.

The book contains clear illustrations and figures to describe the subject in an intuitive way. It uses simple language and terminology and the math is limited only to cases where it is essential to understand the physical meaning of the system.
Therefore, it is suitable also for those readers who approach these subjects for the first time and who only have a basic understanding of mathematics (linear algebra) and static analysis of structures.

Structures constructed in developing world are typically RC frames with masonry infill. These structures
have little resistance for lateral loads caused by earthquake and wind. Even for adequately designed structures
also, due to permissible deformation beyond elastic limits, failure of masonry causes severe loss of life and
property. In the case of structures designed to sustain excessive deformation such as of defence establishments,
functioning and serviceability of machines and equipment installed therein are adversely affected. This co-lateral
damage may be reduced by adopting another design philosophy of structure response control. In this methodology,
a supplementary damping device is incorporated in the primary structure, which absorbs most of the seismic
energy imparted to it, restricting the structural response within serviceable limits. These devices may be passive,
active, semi-active or hybrid types. Other than passive all options are technology-intensive and dependent on
external energy source, not a favourable proposition for developing nations. Among all the passive devices, tuned
liquid dampers (TLDs) promise to be most suitable. Here, existing overhead water tanks (OHWT) may be used
as TLD with slight adjustment and modification. This method will be able to control the structural response
without putting any extra load on the existing or newly-designed buildings. This paper reviews various types of
dampers and discusses evolution of tuned liquid dampers. A method has also been proposed for incorporating
TLDs in existing and new structures. This methodology may be very useful for structures of defence establishment
which are scattered and remotely placed by location, housing important equipments sensitive to vibrations, as it
is free from external power dependence and regular maintenance.

A state-of-art of traditional and modern retrofitting techniques emphasizing the advantage of the use of metallic materials. General issues of structural intervention starting from the mechanical causes of damage, the logical phases of intervention, the technical and administrative steps and different levels of consolidation are shortly over viewed. The main characteristics of the new strategies for anti-seismic protection of buildings are presented.

Ujjayanta Palace, standing in the heart of Agartala city, in Tripura, a famous royal house, covering an area of 1 sq. km. and styled in Greek sculpture, was built by Maharaja Radhakishore Manikaya in 1901. The two-storeyed palace has a mixed architecture with three high domes (the center one being 26 m high). Ujjayanta Palace, a declared heritage building, has been in existence for the past 110 years and the environmental effects have taken their toll. A detailed survey of the existing structure and the surrounding soil strata was made. The properties of the building materials were assessed using modern techniques. The soil was found to be prone to liquefaction in the event of an earthquake. It was decided to carry out extensive retrofitting of the palace without in any way altering its architectural features. The criteria adopted for undertaking the retrofitting was to permit the structure to undergo deformation without brittle failure or loss of life during design basis earthquake and to limit the damage to minor repairable cracks when the structure was subjected to maximum considered earthquake. In this paper, details of the assessment of the palace structure and the environment are presented. Further, a comprehensive description of the retrofitting techniques adopted and their efficacy are explained.

Sustainability has become a fundamental requirement for the future of our cities.
This requirement is mostly associated with environmental issues, and a great effort has been made in the past years to build a low-carbon society. However, sustainability must also be associated with safety.
As a consequence, in seismic countries, sustainable cities must be not only low-carbon-emitting bust also earthquake-safe.
This concept represents the basic premise of this book.
According to this premise, in earthquake-prone nations like Italy—where most of the building stock is both highly earthquake-vulnerable and energy-consuming—energy renovation actions should be combined with seismic upgrades. Nevertheless, many barriers significantly limit the real possibility of undertaking combined retrofit measures, especially in the case of multi-owner housing and high-rise buildings. These barriers are of different kinds: economic/financial (high renovation costs, insufficient incentives and subsidies, landlord-tenant dilemmas, etc.), technical (ineffectiveness of conventional upgrade solutions, need of regulatory simplification, etc.), organizational (occupants’ dislocation and disruption, consensus to the retrofit expenditure by condominium ownerships, excessive time for getting construction permits, etc.), and cultural/social (insufficient information and skills, lack of adequate policy measures for promoting renovation actions).
This book aims to overcome these barriers and to bridge the gap between sustainability and safety, so to conserve both human and environmental resources. It brings together 11 contributions on different seismic and energy renovation measures, proposing technical solutions at district, building, and component level, for both historic and modern case studies.
Finally, I would like to thank the editorial team of Sustainability for inviting me to guest-edit the Special Issue on “Energy and Seismic Renovation Strategies for Sustainable Cities” which has been transformed into this book. I also thank all the authors and reviewers for their fundamental contributions.

Post-occurrence consequences of catastrophic natural phenomena produced by a diversity of factors have a negative impact on the quality of life of the general population. Immediate recovery measures are needed to be taken in order to re-establish the minimum living conditions necessary in the least possible time. In this context, modular units for living supply suited to the affected area conditions constitutes an urgent action, this choice must be based on technical and economic criteria, allowing transparent processes for procurement and distribution. Current methods use a country process of soliciting submissions for modular units for living after each major emergency, slowing down the implementation of most of the action plans established in these cases due to a lack of general standards to select the most appropriate alternative, both technical and economic, because of the limited dissemination of information existing in the domestic market about modular construction, its mechanical behavior, and their properties and benefits. This work analyses the structural behavior and thermal comfort levels of two modular systems taken as alternatives for emergency modular units for living, to determine which one has the greatest comparative benefits for implementing it in Piura, the main Peru department concerned by El Niño Costero 2017 climate phenomenon. The study focuses in structural analysis, assessing the effects of static and dynamic loads, vertically and horizontally applied, thermal comfort levels provided by each construction system, and a project cost estimation for each system element. The findings and outcomes of this study allow to conclude which option presents the most favorable indicators for each assessment criteria, based on the project location.

Probabilistic methods to evaluate the seismic vulnerability of reinforced concrete (RC)frames are largely used in the context of performance based design and assessment, often de-scribing the structural response using global engineering demand parameters (EDPs) such as theinterstory drift. While such EDPs are able to synthetically describe the structural behavior, theuse of intermediate or local parameters of RC frames without seismic detailing can enable a morerealistic and thorough description of failure mechanisms for structural vulnerability. This study proposes an optimized methodology for the probabilistic evaluation of seismic demand of low ductility RC frames by exploring a range of intermediate, local and global EDPs, identifying ap-propriate regression models and comparing performances of different ground motion intensity measures used in the probabilistic analysis. Moreover, a probabilistic methodology for assessing the vulnerability of buildings retrofitted by means of dissipative braces is proposed. The method-ology use local EDP in order to develop single component and system fragility curves before andafter the retrofit. The proposed approach allows to highlight the possible changes in the mostsignificant collapse modalities before and after the retrofit and to evaluate the effectiveness of theretrofit by taking into account the probabilistic properties of the seismic behavior of the consid-ered systems. A benchmark 2-dimensional reinforced concrete frame with low ductility capacity isconsidered as case study. The frame is designed for gravity-loads only and does not comply with modern anti-seismic code requirements. It is retrofitted by introducing elasto-plastic dissipativebraces designed for different levels of their target base-shear capacity, following a design methodinvolving the pushover analysis of the bare frame. The obtained results show the effectiveness of the use of component level vulnerability evaluation of low ductility frames, and the effectivenessof the methodology in describing the changes in the performance due to retrofit. The proposedmethodology also allows testing the effectiveness of this simplified criterion employed for the de-sign of braces.

LUCRĂRILE SEMINARULUI
Overview of the STEEL-EARTH project (Steel-based applications in earthquake-prone areas) - acad. Dan Dubina
Performance based evaluation of structures in view of their consolidation - Adrian Dogariu
Strengthening of existing reinforced concrete frames with buckling-restrained braces: general presentation and study case - Aurel Stratan

Structural response control, with tuned sloshing water dampers (TSWD) may be adopted as seismic
retrofitting measure for the existing structures (ES).The water tanks of designed geometry rigidly attached with the
ES at strategic locations behave as TSWD. Response reduction during earthquake is affected by energy dissipated
through sloshing of water mass.
The energy dissipation is dependent on mutual tuning of ES and TSWD, mass ratio, damping ratio of
TSWD and damping ratio of ES. Larger the mass ratio more will be the response reduction. Mutual dependency and
uncertainties involved with the assessment of dynamic properties of ES make the design process of retrofitting
system iterative and cumbersome.
Multiple dampers, with their frequencies distributed around the first mode frequency of ES, shall perform
more robustly. The desired mass ratio may be accommodated in multiple tanks. The geometry of these tanks may be
moderated in such a way that it behaves as multiple dampers. The multiple TSWD system will overcome the errors
due to assessment approximations of dynamic properties of ES and TSWD.
The performance of the retrofitting system is assessed by reduction in maximum structural displacement
affected. Design charts in the form of effectiveness ratio, depicting the performance of TSWDs, have been presented
which reduces iterative computational effort. The retrofitting methodology is explained by example of an existing
four story structure. The effectiveness and robust performance of multiple TSWD has been demonstrated. The
method ensures all time preparedness of the ES, without occupancy and structural interference, against earthquake.

This study aims at evaluating, by means of a probabilistic approach, the effectiveness of dissipative braces based on elasto-plastic devices in reducing the vulnerability of existing reinforced concrete buildings designed before the introduction of modern anti-seismic codes. A benchmark 2-dimensional reinforced concrete frame whit low ductility capacity is considered as case study. The dissipative braces are designed for different levels of the target shear capacity assigned to the bracing system, following a design method involving the pushover analysis of the bare frame. The probabilistic seismic response and vulnerability of the structure are investigated by building fragility curves of the system and of its most vulnerable components.

This paper reviews briefly traditional
rehabilitation methods and provides a detailed
discussion of design issues along with the
advantages and the disadvantages of innovative
strategies for seismic retrofitting of steel and
composite structures. Special emphasis is placed
on base isolation and supplemental damping
devices. The viability and cost-effectiveness of
these strategies are assessed on the basis of
multiple limit states within the framework of
performance-based design. A number of
parameters which govern the selection of the
intervention devices are investigated

This paper presents research on a conventional but practical retrofitting method for masonry walls along with the numerical modelling of it under in-plane lateral shear-compression loading. The latter is capable of predicting the experimental collapse load and overall behaviour quite accurately. The retrofitting approach is based on building a wall parallel to an existing single-leaf wall and bonding the two leaves together using a mortar (collar) joint, merging the two individual panels into a unified double-leaf wall. Experiments on this retrofitting approach for both undamaged and damaged masonry walls have been introduced in the present paper. The tests revealed that the pre-damage application can increase the strength by 50% while the post-damage one can restore the initial strength. A micro-scale numerical model has been devised by considering the bricks as rigid elements and the mortar joint as a nonlinear failure surface. The model was implemented in the commercial
Finite Element (FE) software MIDAS FEA and the numerical results were verified against the available experimental data.

The use of seismic isolation for the seismic rehabilitation of existing buildings is very attractive but often very tricky due to several aspects related to its implementation. In this paper, a case study of seismic rehabilitation of a high-rise residential building with seismic isolation is presented. The building under consideration is located in southern Italy and it is
placed next to another building from which it is separated by a gap of 400 mm. In the paper, all the steps of the seismic rehabilitation process are described. First, the target objective of the seismic rehabilitation and the choice of isolation system type and location are discussed.
The design of the isolation system, carried out following a direct displacement-based approach, is then examined. Finally, the main phases followed in the installation of the
isolation system are described. Some comments on costs and time needed to complete the intervention are also reported.

All around the world, a huge amount of buildings have been built before the enforcement of specific codes for seismic resistance and energy efficiency. Particularly in Italy, over 74% of residential buildings were constructed before 1980, when only 25% of the territory was classified as seismic, and nearly 86% were built before 1991, when the first restrictive regulation on energy efficiency was issued. This means that most buildings need both seismic and energy renovation actions to improve their sustainability level. The proposed combined retrofit strategy for reinforced concrete framed buildings is based on the replacement of the external layer of double-leaf infill walls, made of hollow bricks, with high-performing AAC blocks: this solution can be implemented by operating mainly from the outside of the building, thus reducing occupants' disruption during retrofitting. The generally neglected structural contribution of masonry infill panels is here considered using a recently developed macro-element modeling approach. The results suggest that, from a structural viewpoint, the proposed intervention involves the highest improvement at the damage limitation limit state, while lower upgrades are recorded at life safety limit state and near-collapse limit state. In regards to the energy issues, the energy demand can be reduced by 10% and 4% for heating and cooling, respectively, just by replacing the outer layer of blocks; further savings can be achieved through the application of a supplementary insulation layer.