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2018 | Book

Strengthening and Retrofitting of Existing Structures

Editors: Prof. Aníbal  Costa, Prof. António  Arêde, Prof. Humberto  Varum

Publisher: Springer Singapore

Book Series : Building Pathology and Rehabilitation


About this book

This book presents the fundamentals of strengthening and retrofitting approaches, solutions and technologies for existing structures. It addresses in detail specific techniques for the strengthening of traditional constructions, reinforced concrete buildings, bridges and their foundations. Finally, it discusses issues related to standards and economic decision support tools for retrofitting.

Table of Contents

Structural Strengthening and Retrofit; Motivations, Concepts and Approaches
Various scenarios may entail the need for the retrofit of an existing structure, which will be exposed to a variety of loading conditions and degrading environmental actions during its life time. In most cases, the objective of structural strengthening will be to reduce the risk of loss of life, whilst recognizing the importance of buildings and monuments to our societies’ heritage. However, the general criterion that should guide any decision related to structural strengthening should be to optimize the resources to be invested compared with the benefits to be obtained. In this chapter a range of important motives, concepts and approaches for strengthening and retrofitting are introduced. The various phases of a modern seismic assessment are described, since earthquakes have been seen to cost society dearly around the world. However, it is also explained that similar assessment and retrofit considerations and procedures are applicable for other hazards too. It is demonstrated that a variety of interventions will be possible and means of gauging their impact on response is conceptually explained. Later chapters in this book will build on this introduction to provide the detail required to finalise a retrofit design.
Giorgio Macchi, Gian Michele Calvi, Timothy John Sullivan
Cultural Heritage Monuments and Historical Buildings: Conservation Works and Structural Retrofitting
The preservation and strengthening of historical constructions over time is highly to be supported due to their cultural and heritage value and the potential economic exploitation related to tourism. Old masonry buildings are subjected to slow aging processes, which must be monitored in order to prevent irreversible deterioration of materials and structural damage, as well as reduce vulnerability to natural hazards, in particular earthquakes. Conservation requirements may be summarized with the principle of “minimum intervention”, which is based on the idea of maintaining, as much as possible, the original characteristics of the buildings, avoiding the use of invasive strengthening techniques that would compromise their authenticity. However, the daily use of this building stock, which is very important to avoid abandonment, raises the problem of complying not only building conservation but also safety principles. Within this scope, the selection and use of correct structural modelling tools to assess the present state and to support the design of the necessary strengthening interventions is a challenging issue. Thus, this chapter presents, by means of case studies, examples of methodological approaches for the diagnosis and seismic assessment of historical structures, as well as for the design of retrofitting and strengthening works.
Romeu Vicente, Sergio Lagomarsino, Tiago Miguel Ferreira, Serena Cattari, J. A. R. Mendes da Silva
Strengthening of Stone and Brick Masonry Buildings
Today, the scientific community has recognised that the structural safety aspects of existing masonry buildings cannot be treated according to standard procedures that are fit for new constructions. Hence, new approaches for assessing the actual structural performance of existing masonry buildings and developing more appropriate methods and criteria for their repair and strengthening are in progress. The basic idea is that the usual design approaches naturally imply a certain level of “over-design”, and this can lead to unacceptable solutions, under the point of view of costs and conservation, when dealing with existing structures. For these reasons, attention must be paid to the appropriate selection and design of materials and technologies for intervention, taking into account the possibilities offered by traditional solutions and their possible combinations with innovative ones. As existing buildings are usually designed for vertical actions, the “seismic conditions” have the most awkward implications. Indeed, the earthquake actions refer to the very extreme structural resources, i.e. those connected with resistant mechanisms that are normally neglected, and are very difficult to be implemented into structural models. In this chapter, after a general introduction on the characteristics and peculiarities of existing buildings made of stone and clay brick masonry, where we will take into account mainly ordinary buildings, and after some general considerations on the more suitable approaches and criteria for the design of interventions, the most relevant techniques used to strengthen this kind of buildings will be presented.
Francesca da Porto, Maria Rosa Valluzzi, Marco Munari, Claudio Modena, António Arêde, Alexandre A. Costa
Seismic Retrofit of Adobe Constructions
Earthen construction has been widely used since ancient times. Currently, this type of construction is used by approximately one third of the world population. In comparison to other, more modern building materials, such as brick masonry, reinforced concrete, and steel, earth is costless and primarily accessible. For these reasons, it is massively used by no-income or low-income families, in developing countries and in communities where the mentioned industrial materials were never incorporated, frequently without adequate attention being paid to structural safety and reinforcement issues. Moreover, buildings are generally constructed and rehabilitated by non-specialized staff, with empirical knowledge passed through generations, lacking information and understanding of their structural behaviour. The seismic behaviour of earthen structures is typically characterized by fragile and sudden failure, because earth is a brittle material with very low tensile strength. Thus, earthen constructions and, in particular, adobe constructions, if not adequately designed and strengthened may perform very poorly when subjected to seismic loads. There are, in fact, various examples of recent earthquakes that caused severe damage to earthen buildings. The study of the structural behaviour of earthen constructions and the development of effective strengthening solutions are fundamental. In the present chapter, an introduction to earthen construction, including a brief description of its use throughout the world and main vulnerabilities, is presented. The structural behaviour of adobe construction is explained, in particular when subjected to seismic demands. Different repair and strengthening solutions are presented, together with various experimental studies conducted by different authors. A short review of the existing standards and codes that address the seismic design of earthen buildings is also presented. Finally, a brief reference is made to the numerical modelling of adobe construction.
Julio Vargas-Neumann, Cristina Oliveira, Dora Silveira, Humberto Varum
Repair and Strengthening of Traditional Timber Roof and Floor Structures
In many countries, traditional buildings comprise timber roof and floor structures. Most of these structures are degraded from different causes and need to be repaired or strengthened to ensure current and/or to fulfil the requirements of a new use of the building. Current knowledge assumes the need to preserve and to protect existing timber structural systems as a cultural value, with important advantages to the overall behaviour of the building. This growing sensibility towards the preservation and maintenance of heritage buildings has led researchers to study different repair and strengthening solutions. In the case of timber roof structures, this strengthening in many cases involves the connections between the roof structural members. Joint strengthening can be done with different methods, traditional or modern ones, using well-chosen materials, simple techniques or more sophisticated ones: from simple replacement or addition of new fasteners, to the use of timber or metal elements, glued composites, or even full injection with fluid adhesives. Each solution has advantages and disadvantages concerning conservation philosophy, architecture, aesthetics, construction issues and moreover unique consequences in engineering terms for the joint final strength, stiffness and ductility. All the above have to be evaluated in order the proper intervention to be chosen for each case. The main problem of existing timber floors is their low stiffness, which results in high bending deformations and vibrations under service loads. Permanent deflection due to creep can also reach critical values. Moreover, in earthquake prone areas, if seismic resistance has to be assured in existing masonry buildings, both roof and floor diaphragm behaviour must be achieved. This chapter aims to present a state-of-the-art review mainly on strengthening solutions for timber roof and floor structures, focusing on the most promising techniques taken into account the level of intrusion and reversibility. “Dry” interventions, based on timber or timber based elements will be highlighted.
Jorge M. Branco, Thierry Descamps, Eleftheria Tsakanika
Strengthening of RC Buildings with Steel Elements
Existing reinforced concrete (RC) buildings often need some strengthening interventions due to different reasons, such as change in usage, repair of visible damage or seismic strengthening. Nowadays, few guidelines and codes that specifically addressing this issue are available in Europe, even though a wide range of research activities and scientific literature is available. As a result, the lack of clarity and guidance from current codes leads most practitioners to rely on their engineering judgment and to resort to assessment procedures that are conceptually suitable to the design of new structures, rather than to the assessment of existing ones. Hence, this chapter aims at providing a brief discussion on the assessment procedures most commonly adopted by practitioners and at clarifying the adequacy of such approaches. Moreover, building on the manifold applications and versatility of steel, the use of steel elements in the strengthening of existing RC buildings is herein addressed. A number of strengthening techniques, from traditional to more innovative solutions, are presented alongside with a brief discussion on the relevant issues characterizing their design and performance.
J. M. Castro, M. Araújo, M. D’Aniello, R. Landolfo
Strengthening of RC Buildings with Composites
The use of composite materials for reinforced concrete (RC) structures strengthening has become a well-established practice in the last decades, especially in seismic zones, either for retrofitting RC buildings not designed to resist seismic loads or for post-event structural rehabilitations. The most common composite materials used in structural engineering applications are Fibre Reinforced Polymers (FRPs). A large number of guidelines and codes have been developed, collecting the most advanced concepts in FRP-strengthening: this chapter makes reference to one such document, the Italian CNR DT-200 R1/2013 (Instructions for design, execution and control of strengthening interventions through fibre-reinforced composites. Consiglio Nazionale delle Ricerche (CNR), Roma, 1), and deals with all the aspects relevant to a correct design process, which should start with a proper structural safety assessment and then move to the definition of material properties, main strengthening schemes and design equations. The concepts discussed herein can also be found in EN 1998-3 (Eurocode 8: design of structures for earthquake resistance. European Committee for Standardization, Brussel, 2) and in a recent State-of-the-Art book by RILEM (3).
Giorgio Monti, Floriana Petrone
Structural Repair and Strengthening of RC Elements with Concrete Jacketing
Extensive investigations on repair and retrofitting of reinforced concrete elements have been undertaken in recent years and many methods have been developed, tested and reported in the literature. The reinforced concrete jacketing has been considered as one of the important and used methods to correct design errors, deficient concrete production and execution processes, repair damage after earthquake, accidents or in the cases where it is needed to proceed with the change in the functionality of the structure etc. In this chapter is performed a brief review of the literature concerning the numerical and experimental research performed as well as the detailing recommendation and general criteria and procedures used in the concrete jacketing. In the end it is presented an example of an application of RC jacketing to correct a soft-storey mechanism in an existent RC building and it is presented the recent experience in the use of reinforced concrete jacketing in the Kathmandu University after the 2015 Gorkha Earthquake.
H. Rodrigues, P. M. Pradhan, A. Furtado, P. Rocha, N. Vila-Pouca
Strengthening of RC Bridges
During past seismic events several cases of concrete bridges with poor structural behaviour and severe damage were reported. In this chapter, common damage patterns in RC bridges are illustrated, with reference to several previous studies about the seismic performance of bridge components. The focus of the chapter is on pier behaviour, wherein damage is usually more significant and quite often there is a need to retrofit these elements. In this context, the main objective of this chapter is to present the most common retrofitting strategies for RC bridges and the resulting benefits to their structural behaviour. Several types of piers are considered, where the cross section ranges from solid to hollow and from circular to rectangular. One of the most common retrofit measures for RC bridge piers is the full or partial jacket, which can be made in FRP, steel or RC. Experimental and numerical tests were carried out to assess the benefits to bridge pier behaviour, resulting from shear strengthening of piers with hollow cross section. Moreover, analytical studies are presented on the performance of bridges retrofitted using different techniques, aiming at strengthening and/or confinement, and a method for assessing the seismic fragility of retrofitted bridges is described, along with an application to a bridge with circular piers.
Pedro Delgado, Andreas Kappos
Strengthening of Masonry Bridges
The mechanical characteristics of materials and the interaction between the different elements of masonry bridges, typically arched ones, determine their behaviour, performance, structural deficiencies and failure modes. Therefore, it is particularly important to identify relationships between the main structural issues of this bridges’ type and the structural defects most commonly found, in order to allow defining appropriately sustained repair and/or reinforcement intervention programs for existing masonry bridges. This chapter presents a brief systematization of the structural behaviour of masonry arch bridges, with more emphasis on stone made ones, their relation with frequent structural damages and the identification of suitable rehabilitation and strengthening solutions. The structural behaviour of both the bridges and their structural elements is first addressed, focusing on mechanisms of load transmission across the bridge system, deficiencies and possible failure modes which are characteristic of bridges in operating conditions. A brief overview on damage and degradation present in masonry arch bridges is given in this chapter, concerning possible interventions deemed sufficient to ensure or restore the regular operation of these constructions. The main interventions on arch bridges, herein addressed, aim at correcting material and structural deterioration effects, to prevent further deterioration or to restore the existing system without changing bridge genuineness and construction authenticity.
Cristina Costa, António Arêde, Aníbal Costa
Strengthening and Retrofitting of Steel Bridges
This chapter begins with a brief description of the most common typologies of steel bridges. Typical structural deficiencies and damages of steel bridges are outlined to identify the basic needs of rehabilitation actions. It includes the damage produced by corrosion, fatigue, increasing of live loads, seismic actions, poor detailing and vehicle collision. Initially, a description of the characteristics and performance of traditional rehabilitation techniques is outlined. Later, the superstructure rehabilitation techniques based on the use of composite materials as carbon, aramid or glass fibre plates, as bonded external reinforcement, and aramid or glass fibre rods for prestressing are considered. The experience about the behaviour of strengthened beams under overloading and fatigue conditions are also outlined and the heat strengthening of steel girders after a collision is commented as well. The use of steel jacketing of columns is also described and the benefit of using link beams to improve the transverse seismic response of multicolumn bents. Base isolation as an appealing strategy for reducing the seismic demand in piers and foundations and the advantages of its application is discussed and the use of cable restrainers added for limiting the longitudinal displacement is also analysed. In the end, the methodologies more employed to assess the seismic vulnerability of bridges to select the best retrofit technique, and the parameters to be considered for a better selection of the bridge intervention are described.
José M. Jara, Manuel Jara, Bertha A. Olmos, Jamie E. Padgett
Ground Reinforcement and Rehabilitation of Foundations Systems for Their Reuse
The reuse of foundations for a second superstructure is technically feasible and is increasingly becoming part of standard practice. For refurbishment projects, reuse of old foundations and structures is the norm. For foundation reuse to be viable, the following conditions need to be satisfied: (i) there should be compatibility between the locations of the applied loads and the existing foundations, which should have sufficient bearing capacity to carry the new loads; (ii) sufficient verification should be carried out so that the old foundations are shown to be as reliable as new ones; (iii) there should be an expectation that the foundation performance over the range of expected loads will be acceptable, and that they will fulfil those functions reliably over the planned design life of the building; (iv) the project team needs to agree that all parties accept the risks associated with foundation reuse; (v) adequate insurance cover is available for the design team and client; (vi) regulatory approval is possible from the necessary authorities. Currently old foundations tend only be reused in a redevelopment, if there is a particular constraint that acts as a driver: (i) the ground beneath the building has already been filled; (ii) there are archaeological remains that can be preserved by foundation reuse. One of the main inhibitors to foundation reuse is uncertainty: unless records have been kept that indicate the foundation locations, sizes and capacities with a high degree of reliability, it can be difficult to reuse them reliably or efficiently. Therefore one important issue to maximize the future ability to reuse foundations is the collection and safe preservation of construction and maintenance records. When the risk to full trust on the original foundations is high, ground improvement techniques are advisable, mainly versatile and small diameter drilling techniques as jet grouting and micropiles.
A. Viana da Fonseca, A. Pinto
Code-Based Procedures for Seismic Safety Assessment and Retrofit
Earthquake engineering experts, public authorities and general public agree on the idea that the seismic safety and performance of the built environment is a matter of high priority. Moreover, the widespread interest in methodologies which address the assessment and the retrofit of existing constructions reflects the global perception that such constructions are exposed to disproportionate levels of seismic risk. Rational and cost effective interventions on the built environment are therefore needed in order to mitigate such risk and reduce the expected level of losses in future earthquakes. Hence, over the past few years, several standards and guidelines addressing the problem of structural assessment and upgrading have been emerging for the specific case of earthquake loading. In this context, the current chapter presents a review of existing international structural standards and codes that provide specific methodologies for the seismic safety assessment and the strengthening of existing constructions.
X. Romão, A. Penna
Evaluation of Strengthening Techniques Using Enhanced Data Envelopment Analysis Models
This research intends to develop a model to support the selection of the best strengthening technique to be adopted in rehabilitation projects. This methodology is particularly useful for project teams that need to select the most suitable strengthening technique among several solutions. The model proposed includes the typical variables that capture the main technical characteristics of the strengthening solution and also economic variables associated to the costs of the intervention. The model proposed is based on Data Envelopment Analysis specified with a directional distance function. It has the ability of calculating an overall performance score for each solution showing it in the best possible light. To demonstrate the advantages of the methodology developed, it were used the results of a study conducted in Portugal. From the empirical application, it was possible to conclude that the best strengthening solution may vary depending on whether the costs of the interventions are or not included in the model.
Isabel M. Horta, Celeste Varum
Strengthening and Retrofitting of Existing Structures
Prof. Aníbal Costa
Prof. António Arêde
Prof. Humberto Varum
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Springer Singapore
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Print ISBN