Analysis of Strengthening Variants of Existing Masonry Buildings for Seismic Resistance - Case Studies of Typical Residential Buildings in Niš (original) (raw)
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Seismic Evaluation and Strengthening of an Existing Masonry Building in Sarajevo, B&H
Buildings, 2019
A significant number of old unreinforced load-bearing masonry (URM) buildings exist in many countries worldwide, but especially in Europe. In particular, Bosnia and Herzegovina has an important stock of masonry buildings constructed from the 1920s until the 1960s without application of any seismic code, due to their nonexistence at that time. With the 1963 Skopje earthquake, this class of buildings were shown to be rather vulnerable to seismic actions, which exhibited serious damage. This article assesses the seismic vulnerability of a typical multi-storey residential unreinforced load-bearing masonry building located in the heart of Sarajevo, which may be exposed to an earthquake of magnitude up to 6 by Richter's scale. The buildings of this kind make up to 6% of the entire housing stock in the urban region of Sarajevo, while in Slovenia this percentage is much higher (around 30%). The analysis of a typical building located in Sarajevo revealed its drawbacks and the need for some kind of strengthening intervention to be implemented. Additionally, many structures of this type are overstressed by one to two additional floors (not the case of the analyzed structure) constructed from 1996 onwards. This was due to the massive population increase in the city center of Sarajevo and further increased the vulnerability of these buildings.
Buildings
The paper presents a study on the existing low-rise unreinforced masonry (URM) buildings constructed in the period from 1945 to 1980 in Serbia and neighbouring countries in the Balkans. Buildings of this typology experienced damage in a few earthquakes in the region, including the 2010 Kraljevo, Serbia earthquake and the 2020 Petrinja, Croatia earthquake. The focus of the study is a seismic design approach for Simple masonry buildings according to Eurocode 8, Part 1, which is based on the minimum requirements for the total wall area relative to the floor plan area, which is referred to as Wall Index (WI) in this paper. Although the intention of Eurocode 8 is to use WI for design of new buildings, the authors believe that it could be also used for seismic assessment of existing masonry buildings in pre- and post-earthquake situations. A study on 23 URM buildings damaged in the 2010 Kraljevo, Serbia earthquake has been presented to examine a relationship between the WI and the extent ...
Seismic resilience of existing masonry building
Croatia is located on seismically active grounds. Its built heritage is with a large percentage of the existing built environment consisting of masonry structures built prior the first earthquake regulations, which therefore pose a serious threat for the inhabitants and society itself. Knowing this, it is of essence to know the vulnerability of the buildings, which most of the old city cores are built of. But knowing the structural vulnerability is just a small percentage of the work needed to increase the resilience of the buildings and the society. The engineer role is to formulate the platform emphasizing the mitigation of disaster effects while participating in the decision system managing the disaster leading to the conclusion that a minor investment to prevention is better than the one addressed to a cure. The current state of the structure is evaluated with a method which combines experimental data and engineering knowledge for evaluation of the seismic safety factors and expected structural performance under strong events. This method is also used for the choice of strengthening methods. The strengthening methods are evaluated balancing the costs and the benefits on the building resilience. When the building owner is aware of the potential risk, and is willing to prepare the structure to cope the serious earthquake hazard the whole risk mitigation process is to begin, which is presented in this article. It is presented on a masonry structure dating from the beginning of the 20th century and it is of major social value, and therefore high resilience is of essence. The presented risk mitigation process consists of structural vulnerability estimation, comparison of the cost of retrofit to those of loss and recovery of functionality in a disaster. The methods of mitigation and decisions based on resilience of this example building are presented.
A review of the current status of seismic design and assessment of masonry buildings in Europe
Journal of Structural Engineering (Madras)
Masonry construction, especially the unreinforced and the non-engineered type, is the most prevalent construction technique in the world, even in zones of substantial seismic hazard. The bulk of historical and monumental structures in the world, that have stood the test of time, are in masonry. Under seismic load, masonry construction can be considered to be earthquake-resistant up to reasonable levels of intensity and even capable of energy dissipation. Research in the last few decades in Europe, which possesses an abundance of built stock in masonry, has focussed on understanding the behaviour of unreinforced masonry structures under seismic excitation, identification of the weak links in masonry construction for an acceptable seismic performance, development of recommendations for strengthening existing masonry structures and provisions and safety checks for masonry design of new structures. Research effort has also been dedicated to development of reliable and easily applicable seismic analysis and assessment procedures aspiring to bridge the wide variety, in materials and construction techniques, of masonry. The current paper puts into perspective the state-of-the-art of research and practice of seismic design and assessment of masonry buildings in Europe in the last few decades with specific reference to recent Eurocode and Italian national seismic code advances.
Buildings
After a long period of no excessive ground shaking in Croatia and the region of ex-Yugoslavia, an earthquake that woke up the entire region was the one that shook Croatia on 22 March 2020. More than 25,000 buildings were severely damaged. A process of reconstruction and strengthening of existing damaged buildings is underway. This paper presents proposed strengthening measures to be conducted on a cultural-historical building located in the city of Zagreb, which is under protection and located in zone A. After a detailed visual inspection and on-site experimental investigations, modeling of the existing and strengthened structure was performed in 3Muri. It is an old unreinforced masonry building typical not only for this region but for relevant parts of Europe (north, central, and east). The aim was to strengthen the building to Level 3 while respecting the ICOMOS recommendations and Venice Charter. Some non-completely conservative concessions had to be made, to fully retrofit the b...
Canadian journal of civil engineering, 2007
The results of lateral resistance tests of masonry walls and shaking table tests of a number of models of masonry buildings of various structural configurations, built with various materials in different construction systems, have been analyzed to find a correlation between the occurrence of different grades of damage to structural elements, characteristic limit states, and lateral displacement capacity. On the basis of correlation between acceptable level of damage and displacement capacity, it has been shown that the range of elastic force reduction factor values used to determine the design seismic loads for different masonry construction systems proposed by the recently adopted European standard Eurocode 8 EN-1998-1 for earthquake resistant design are adequate. By using the recommended design values, satisfactory performance of the masonry buildings that have been analyzed may be expected when subjected to design intensity earthquakes with respect to both the no-collapse and damage-limitation requirements.
Seismic Performance Assessment of Masonry Buildings, Albanian Context
IJSRCE22632 ISSN : 2456-6667, 2022
In Albania, as a country with high seismic risk, seismic design and assessment of structures is very important. In most cases, the seismic design situation is crucial in structural solution and in the dimensions of elements. In addition to designing new structures seismic assessment of existing structures is an ever-increasing need due to the existence of old structures built with design codes that reflect knowledge and accumulated experiences up to the time of their design and construction. It can be said that in compared to 30-40 years ago, the changes in design codes are significant. The building that will be used as a case study for analyses purpose is named as type 77/11 according to the previous institute of construction. This can serve as a reference for the social masonry buildings built in the communism era before the year 1980. Before this year, the design code used was the KTP-63. The analysis will be performed with ETABS software, and for the seismic performance will be used the KTP-89 spectre and EC-8 spectre (since Albania is trying to implement this code as a national standard). For strengthening technique will be used TRM.
Efficiency of strengthening techniques assessed for existing masonry buildings
Engineering Structures, 2015
The Azores archipelago is a zone with a vast cultural heritage, presenting a building stock mainly constructed in traditional stone masonry. It is known that this type of construction exhibits poor behaviour under seismic excitations; however it is extensively used in seismic prone areas, such as this case. The 9th of July of 1998 earthquake was the last seismic event in the islands, leaving many traditional stone constructions severely damaged or totally destroyed. This scenario led to an effort by the local government of improving the seismic resistance of these constructions, with the application of several reinforcement techniques. This work aims to study some of the most used reinforcement schemes after the 1998 earthquake, and to assess their effectiveness in the mitigation of the construction's seismic vulnerability. A brief evaluation of the cost versus benefit of these retrofitting techniques is also made, seeking to identify those that are most suitable for each building typology. Thus, it was sought to analyze the case of real structures with different geometrical and physical characteristics, by establishing a comparison between the seismic performance of reinforced and non-reinforced structures. The first section contains the analysis of a total of six reinforcement scenarios for each building chosen. Using the recorded 1998 earthquake accelerograms, a linear time-history analysis was performed for each reinforcement scenario. A comparison was then established between the maximum displacements, inter-storey drift and maximum stress obtained, in order to evaluate the global seismic response of each reinforced structure. In the second part of the work, the examination of the performance obtained in the previous section, in relation to the cost of implementing each reinforcement technique, allowed to draw conclusions concerning the viability of implementing each reinforcement method, based on the book value of the buildings in study.
Aspects of Seismic Assessment and Redesign of Traditional Masonry Buildings
Most of the traditional greek buildings (new-classic ones or not, small or large), with an age of more than 75 up to 250 yrs, are made of rubble stone masonry with a large volume of low strength lime mortars, while their floors/roofs are mainly made of timber. Their seismic assessment and redesign, based on recent conceptions and normative or informative code principles and criteria, is a challenging problem for the Structural Engineer, not to mention restrictions imposed due to the monumental character of almost all of these old buildings. To this end, the new “frame” of Euro-Codes, and especially of EC 6 and EC 8, is applied in general, as recently completed by the new Greek Codes on (Structural) Assessment and Interventions (nGCSI, 2012), fully harmonized with this “frame” of ECs but far beyond them and more detailed, with a lot of relative application rules. Several aspects are involved in structural assessment and redesign of such old buildings, as covered by the Codes and shortly presented/discussed in this paper, such as : Investigation and documentation of the geometrical and the mechanical data of the existing building, together with their reliability levels (DRLs), i.e. the so-called “knowledge levels”, influencing almost all phases and steps of the design; Quantitative assessment and documentation of any wear, deterioration or damage, of any kind, together with a practical but reliable and safe assessment of the residual mechanical characteristics, based on damage levels (DLs); Decision regarding the performance level (PL), i.e. the foreseen or expected degree of damage during the earthquake itself, probably different for the assessment or the redesign of the structural interventions; Aspects of mechanical behaviour of the masonry (and other) elements, out-of-plane and in-plane response, macro-models etc., before and after repair or/and strengthening, as well as Methods of analysis and dimensioning or redimensioning, linear and non-linear, checks in terms of force or of displacement, depending on PLs and based on skeleton curves. In this paper, most of the related issues are shortly covered, as faced during the structural design, while certain characteristic examples and applications are presented.
Seismic Assessment of Masonry Buildings According to Eurocode 6 and 8
2014
It is clear from several analyses that the existing building stock has a lower seismic capacity, in comparison with the buildings designed according to new codes. The problem is more serious for masonry buildings, especially those that have been constructed in earlier years. Despite the fact that the design code framework is clear through Eurocode 6 (2005) and Eurocode 8 (2005), the method of assessment of existing masonry structures is not obvious. It is worth to mention that Eurocode 6 (2005) is provided only for design of new masonry buildings not considering seismic actions. This paper deals with a comparison of seismic assessment methods of masonry buildings according to either the framework of Eurocode 6 (2005) or Eurocode 8 Part 3 (2005b) and an approximate method proposed by the Greek Earthquake Planning and Protection Organizations (EPPO, 2012). These methods are applied to selected buildings with particular characteristics, through a parametric study aiming to emphasise po...