Unreinforced Masonry Buildings Research Articles

Nested Buildings: An Innovative Strategy for the Integrated Seismic and Energy Retrofit of Existing Masonry Buildings with CLT Panels

The Italian building heritage is aged and inadequate to the high-performance levels required nowadays in terms of energy efficiency and seismic response. Innovative techniques are generating a strong interest, especially in terms of multi-level approaches and solution optimizations. Among these, Nested Buildings, an integrated intervention approach which preserves the external existing structure and provides a new structural system inside, aim at improving both energy and structural performances. The research presented hereinafter focuses on the strengthening of unreinforced masonry (URM) buildings with cross-laminated timber (CLT) panels, thanks to their lightweight, high stiffness, and good hygrothermal characteristics. The improvement of the hygrothermal performance was investigated through a 2D-model analyzed in the dynamic regime, which showed a general decreasing in the overall thermal transmittance for the retrofitted configurations. Then, to evaluate the seismic behavior of the coupled system, a parametric linear static analysis was implemented for both in-plane and out-of-plane directions, considering various masonry types and connector spacings. Results showed the efficiency of the intervention to improve the in-plane response of walls, thus validating possible applications to existing URM buildings, where local overturning mechanisms are prevented by either sufficient construction details or specific solutions.

Assessment of the seismic behaviour of heritage masonry buildings using numerical modelling: A study of Fernand Pouillon's Totem Tower in Algiers, Algeria

This paper deals with the seismic response evaluation of the Totem tower of Diar Es Saada, which is one of the taller unreinforced masonry (URM) building in Algeria with twenty floors and 62 m in height. The tower located in Algiers, a town exposed to important earthquakes, has survived so far without major damage or alteration. This high-rise building was designed by the French architect Fernand Pouillon in 1953 without considering regulations for earthquake-resistant construction. It was built in only fifty days by adopting an original structural system and an innovative construction processes developed by this architect: URM stone and brick load-bearing walls with reinforced concrete floors. The study carried out consists of a multidisciplinary approach. First, a detailed diagnosis was performed on site to assess the state of conservation of the building. Then, the seismic behaviour was modelled and analyzed by using both linear dynamic and non-linear static analysis in SAP2000 and TreMuri software. With regard to the current Algerian seismic design regulation, the results obtained in terms of time period, frequency, storey drifts and displacements showed that the tower can be considered as an earthquake-resistant building fulfilling the required structural safety conditions. In this respect, the Totem tower of Diar Es Saada deserves to be classified as a national heritage and its satisfactory overall structural behaviour confirms that the architect Pouillon has also excellent skills in engineering construction.

Seismic capacity of irregular unreinforced masonry buildings with timber floors

The in-plane stiffness of single straight-sheathed timber floors is normally supposed to be not sufficient to confer suitable seismic behaviour to the building. However, accurate evaluations of the in-plane behaviour of timber diaphragms and the effects of their deformability on the building response are difficult, especially for unreinforced masonry (URM) buildings. Various stiffening interventions of floors are possible; among them, the use of an additional layer of boards at 45° often demonstrates optimal behaviour as it combines the advantages of partial stiffening with minimum mass increase. This work was focused on the experimental characterisation of a stiff timber floor through cyclic loading testing of a three-dimensional full-scale specimen. The effects of in-plane flexibility and the non-linear behaviour of floors on the global response of URM buildings were evaluated by analysing the response of two buildings: a regular building and a building irregular in both plan and elevation. Analyses were conducted using a non-linear macro-element model to simulate the non-linear behaviour of masonry and the hysteretic behaviour of floors. The results showed that the seismic capacity of an URM building may be worsened by excessive stiffening of floors and/or mass increase.

Roles of timber tie-rods to reduce seismic vulnerability of historical buildings in Egypt

Historical un-reinforced masonry (URM) buildings in Egypt from the medieval period generally comprise timber tie-rods that link the arches of arcades at the top of the column heads and along the arcade plane (in-plane). Usually, additional tie-rods are found perpendicular to the arcades (out-of-plane). Timber ties can also be used between facing tall URM bearing walls to minimise their buckling vulnerability. They play a considerable role in resisting seismic forces and minimising the deficiencies of URM buildings. A limited experimental investigation and a wide analytical campaign were conducted on two model buildings with the prevailing dimensions and materials of historical medieval buildings in Cairo by employing finite-element three-dimensional modelling. The focus of the work was the roles timber tie-rods play in the seismic stability of parallel-arcaded and cross-arcaded URM historical buildings. A proposal for enhancement of the seismic resistance of parallel-arcaded systems using a steel bracing system is provided.

Analysis and seismic retrofitting of unreinforced masonry building: a case study

Analysis and seismic retrofitting of unreinforced masonry building: a case study

Seismic performance of existing low-rise URM buildingsconsidering the addition of new stories

In low-rise unreinforced masonry (URM) buildings, structural design is generally performed considering the load effects induced by seismic forces as well as the vertical loads. However, there might be cases where the additional or unforeseen loads may be encountered during the lifespan of these buildings. The loads that are induced from the addition of a new storey during the service life is a good example for these additional loads. Since the reconstruction licenses and building height limits specified by the local authorities may vary in life cycle of the structures, it is important to decide the addition of a storey to an existing building considering the structural safety concerns. In this study, an existing low-rise URM building is modelled with added stories (subsequently planned after its construction), and numerical analyses are carried out considering the extra loads of this additional stories. The aim of this study is to assess the earthquake performance of the structures considering this unforeseen situation which was not considered in the original structural design. The suitability of the initial structural design project to the existing building was examined by the site investigations. The results of the analytical analysis were compared with the seismic code requirements, and the seismic performance level of the building is estimated. The study is intended to be useful in determining the path to be followed for the determination of the seismic capacity if existing buildings are exposed to such additional loads. The findings of this study could be used to design local and global retrofitting works. Especially, for the typologies underwent such interventions, solutions that reduce earthquake demands by providing high lateral strength and rigidity could be considered. It is believed that the outcomes obtained with respect to the evaluation of this case study could be generalized to a wide variety of such template buildings and extrapolated for a wide masonry building type.

Seismic protection of unreinforced masonry buildings by means of low cost elastomeric isolation systems

Thousands of rural houses in developing countries with high seismicity were built without adequate seismic protection due to economical reason. This paper discusses a possibility to improve the seismic protection of typical unreinforced masonry in developing regions using low cost base isolation devices. The proposed isolation system involves fibre reinforced elastomeric isolators (FREIs) having small dimensions and few layers of rubber pads to reduce the fabrication cost. A series of 3D FE simulations are carried out to investigate the performances of the proposed FREIs utilised in the isolation of a one story masonry house prototype. The model is assumed subjected to several accelerograms to have an insight into the sensitivity of the isolation system against different earthquakes. The results reveal that the proposed low cost FREI system provides significant damage mitigation to the masonry house with good applicability of the FREI devices.

Methodology for an effective retrofitting strategy of existing masonry buildings: a case study near L'Aquila

The whole Mediterranean area historical heritage is mostly constituted by 'ancient' unreinforced masonry constructions which are particularly vulnerable to earthquakes. Due to the particular attitude to out-of-plane collapse mechanisms, 'ancient' constructions largely contribute to increase the seismic risk. In this paper, a methodology for retrofitting unreinforced masonry buildings, aimed to gradually transforms the 'ancient' masonry building into a 'modern' code-conforming building, is proposed. This approach has been applied to an existing masonry building located near L'Aquila (Italy) and damaged during the 2009 earthquake. The results demonstrate the usefulness of a methodological approach to implement retrofitting actions. Thus, appears more easily to calibrate the interventions as a function of the structural weakness and to quantify the role of each intervention in terms of capacity-to-demand ratio. Moreover, a gradual control of the seismic performance enhancement with respect to the original capacity can be achieved, avoiding high economic costs related to unnecessary interventions.

Use of deep learning models in street-level images to classify one-story unreinforced masonry buildings based on roof diaphragms

In this paper, we explore the potential of convolutional neural networks to classify street-level imagery of one-story unreinforced masonry buildings (MURs) according to the flexibility of the roof diaphragm (rigid or flexible). This information is critical for vulnerability studies, disaster risk assessments, disaster management strategies, etc., and is of great relevance in cities where unreinforced masonry is the most common building typology or where the majority of the population resides in such buildings. Our contribution could be useful for local governments of cities in developing countries seeking to significantly reduce the number of deaths caused by disasters. Our research results indicate that VGG19 is the convolutional neural network architecture with the best performance, with an accuracy of 0.80, a precision of 0.88, and a recall of 0.84. The results are encouraging and could be used to reduce the amount of resources (both human and economic) for the development of detailed exposure models for unreinforced masonry buildings.

Design Considerations for Retrofitting of Historic Masonry Structures with Externally Bonded FRP Systems

ABSTRACT Historic masonry buildings often require structural repair or retrofit to attain a satisfactory level of seismic resistance. This paper analyses the effect of externally bonded fibre-reinforced polymer (FRP) retrofitting systems on the global seismic response of such buildings in order to achieve the fundamental code-based requirements that refer to the structure’s state of damage for a specified limit state. As a case study, a three-storey historic unreinforced masonry (URM) building was selected. The first part of the paper presents an FRP design procedure for determining which vertical structural elements should be retrofitted and to what extent. As a result, six different FRP retrofitting layouts have been selected and analysed with the aid of non-linear static analyses in the second part of the paper. The paper concludes with a cost-feasibility study by introducing a cost-effectiveness index for FRP reinforcement that identifies the effectiveness of an FRP layout by accounting for the amount of retrofitting material used and comparing it with its effectiveness in improving the global seismic resistance.

Out-of-plane behavior of clay brick masonry walls retrofitted with flexible deep mounted CFRP strips

The installation of carbon fiber reinforced polymer (CFRP) strips to deep vertical slots in masonry using a flexible adhesive was developed as a minimally-invasive and cost-effective out-of-plane seismic retrofitting technique for clay brick unreinforced masonry (URM) buildings. The purpose of the current experimental campaign was primarily to investigate the out-of-plane performance of full-scale, flexible deep mounted (FDM) CFRP retrofitted masonry walls. An additional objective was to assess the validity of existing model for determining the out-of-plane capacity of FDM CFRP retrofitted walls. In the experimental testing program, nine full-scale masonry walls were tested, of which six walls were retrofitted using the FDM CFRP technique. A new six point-bending test setup was adopted for quasi-dynamic cyclic testing with loading rates up to 30 mm/s. Experimental results confirmed the significant increase for out-of-plane lateral resistance and displacement capacity for the FDM CFRP retrofitted specimens with respect to the URM specimens. By implementing multiple bed joint-crack formation and cyclic degradation of the masonry, the proposed engineering model provided a good approximation of the experimentally obtained moment – mid-span displacement relations.

Experimental Evaluation of Full-Scale URM Buildings Strengthened Using Surface-Mounted Steel Bands

AbstractConstruction of unreinforced masonry (URM) buildings has been a common practice in many countries. Strengthening of such buildings located in seismically active regions has become extremely...

A Multilevel Procedure at Urban Scale to Assess the Vulnerability and the Exposure of Residential Masonry Buildings: The Case Study of Pordenone, Northeast Italy

More than the 60% of the Italian residential building stock had already been built by 1974, when seismic codes were enforced on a minimal part of the country. Unreinforced masonry buildings represent most of that share, but they are typical for each region, in terms of both materials and structural configurations. The definition of ‘regional’, i.e., more specific, vulnerability and exposure models are required to improve existing forecast models. The research presents a new geographic information system (GIS)-based multilevel procedure for earthquake disaster prevention planning at urban scale; it includes multicriteria analysis, such as architectural types, structural vulnerability analysis, microzonation studies, and socio-economic aspects. The procedure has been applied to the municipality of Pordenone (PN), a district town of the Friuli–Venezia–Giulia region, in Northeast Italy. To assess the urban seismic risk, more than 5000 masonry residential buildings were investigated and common types within sub-municipal areas and exposure data were collected. Simplified mechanical analysis provided a ‘regional’ vulnerability model through typological fragility curves. The integration of results into GIS tool permitted the definition of cross-mapping among vulnerability, damage scenarios (conditional and unconditional) and exposure (seismic losses, casualties, impact), with respect to various earthquake intensities expected in the town. These results are presented at different scales: from the single building, to submunicipal area and to the entire town.

Seismic performance of a Low-Cost base isolation system for unreinforced brick Masonry buildings in developing countries

Unreinforced masonry (URM) buildings are one of the most common type of constructions in developing countries, due to their reduced cost and ease of fabrication. However, the traditional non-engineered nature of these buildings combined with the poor mechanical performance of their structural materials pose a major threat to their earthquake performance, often resulting in heavy damage and losses. This study investigates the possibility of improving the response of typical URM buildings in developing countries, using a novel low-cost fibre reinforced elastomeric isolators (FREIs) developed with recycled rubber (RR). Detailed three-dimensional finite element analyses were carried out on the fixed-base (FB) and base-isolated (BI) configurations of the prototype building subjected to a set of strong recorded ground motions, considering both the design basis earthquake (DBE) and maximum considered earthquake (MCE). The numerical model of the URM building was developed using non-linear shell elements and bilinear springs that respectively simulated the hysteretic behavior of masonry walls and RR-FREIs. Numerical results show a significant reduction in both the accelerations and inter-story drifts of the BI configuration when compared to the response of the FB building. The global elastic response and corresponding enhanced seismic performance of the BI building under DBE confirm the effectiveness of the proposed base isolation system in protecting non-engineered URM buildings from seismic events with medium-to-high intensity.

Dynamic Characterization of High Plinths of Temples in the Kathmandu Valley Using Microtremors

ABSTRACT The 2015 Gorkha earthquake damaged many unreinforced masonry buildings in the UNESCO World Heritage Sites of Kathmandu Valley, such as Kathmandu, Patan, and Bhaktapur. But there were a few multi-tiered temples, with high plinths, that survived the recent earthquake. The temples with a massive high plinth have shown better seismic performance both in past historical earthquakes as well as in the recent 2015 earthquake. In this paper, the results of a reconnaissance survey conducted to assess the seismic effect on the high plinth caused by the 2015 Gorkha earthquake is presented first. Extensive field investigation of excavation works indicates the bulky volume of the traditional construction materials were used to build the high plinth with distinct construction techniques. Second, the dynamic properties of high plinths of nine Nepalese temples measured from microtremor data are presented. The damage assessment shows that the 2015 Gorkha earthquake had minor effects on the plinths. The predominant frequencies obtained at the ground points nearby the temples vary from 0.44–1.32 Hz and predominant frequencies obtained from the H/V spectral ratio ranged 2.88–12.70 Hz. Damping ratios obtained vary from 2.01–8.50%. 1-D wave propagation shows that the plinth act as damping agent.

Seismic Capacity Assessment of Unreinforced Brick Masonry Building Performed According To Eurocode

Brick Masonry Building with cement sand mortar is a common type of building typology in Nepal. Regardless of being one of the eldest construction technology, the behavior of masonry building is still a matter of study. The uncertainty in the behavior of masonry structures is due to material heterogeneity, complex behavior under different loading conditions and may be due to less research in this arena. Different modeling strategies are used and proposed worldwide to design and to identify the seismic performance of Masonry Building. The analysis strategy ranges from the simple linear method, equivalent frame method, static nonlinear method to dynamic nonlinear, which may be chosen according to engineering design aims and research purpose. In this attempt, authors choose two degrees of freedom 3D model of Unreinforced Brick Masonry Structures which catches both overturning and hysteresis mechanisms due to the shear response implemented by the TREMURI program with static nonlinear procedures. This verified method of modeling and analysis is applied to assess the performance of three different Unreinforced Brick Masonry buildings of the same plans with different numbers of storey.

Impact of ground floor openings percentage on the dynamic response of typical Dutch URM cavity wall structures

Unreinforced masonry (URM) buildings with cavity walls, typically constituted by the assembly of a loadbearing inner leaf weakly coupled to an outer veneer with no structural functions, are widely present in a number of regions exposed to tectonic or induced seismicity, including the Groningen province (The Netherlands), which has lately experienced low-intensity ground shaking due to natural gas extraction. Recently, experimental evidence has shown that the lack of seismic details, and, above all, the presence of large ground floor openings, makes these structures particularly vulnerable towards horizontal actions. In this endeavour, advanced discrete element models, developed within the framework of the Applied Element Method (AEM), are employed to investigate numerically the impact of ground floor openings percentage on the dynamic behaviour of cavity wall systems representative of the typical Dutch terraced houses construction, namely low-rise residential URM buildings with rigid floor diaphragms and timber roof. Firstly, the model is validated through comparison with a shake-table test of a full-scale building specimen, tested up to near-collapse. Then, a comprehensive numerical study, which featured several combinations of ground-floor openings and the application of various acceleration time-histories up to complete collapse, is undertaken. The ensuing results allowed a comparison of the fragility associated with each of the considered openings layouts, showing how the presence of large ground floor openings may significantly increase the seismic vulnerability of typical URM Dutch terraced houses.

Seismic out-of-plane retrofit of URM walls using timber strong-backs

Inadequate seismic performance of unreinforced masonry (URM) buildings is frequently encountered in earthquake prone countries such as Italy and New Zealand and consequently, effective and economical retrofit strategies need to be adopted in order to guarantee safety and the preservation of the URM building stock. The retrofit technique studied herein consisted of connecting vertical timber elements (strong-backs), to the interior surface of the walls of a building using mechanical screws or bolts. The vertical timber framing is typically a non-structural support for the inner wall lining of URM buildings and its use, as a part of the retrofits, resulted in being a cost effective and low impact solution. The out-of-plane behaviour of as-built and retrofitted masonry walls was investigated by conducting full scale static airbag tests. The walls were subjected to semi-cyclic out-of-plane loading through the application of uniformly distributed loads, using inflated airbags in order to simulate the self-weight inertia force induced by an earthquake. Five different wall specimens were tested in the as-built and retrofitted conditions, the improvement of out-of-plane seismic capacity was recorded and the performances of different retrofit configurations were investigated. A simplified numerical model to predict the response of the masonry wall retrofitted using timber strong-backs was developed using the finite element software SAP2000. Its effectiveness was validated by means of a comparison between the experimental and the numerical results as well as a sensitivity analysis of the model on parameter variations, and further considerations on the retrofit solution were drawn.

SEISMIC PERFORMANCE EVALUATION OF A MASONRY BUILDING SUBJECTED TO NEAR AND FAR FIELD GROUND MOTIONS

On October 23, 2011 an earthquake occurred approximately 20 km north of the province of Van,Turkey with a magnitude of Mw 7.2. Following the main earthquake, 111 aftershocks withmagnitudes of 4.0 and above occurred. The state of damage was very severe and considerableamount of unreinforced masonry buildings were affected highlighting the need for investigating theseismic design of unreinforced masonry buildings in the affected area. In this paper, seismicbehaviour of a two story masonry building designed according to the Turkish Building Seismic Code2018 is presented. The main objective of this activity was to study the near field and far field syntheticground motions, artificial ground motions and evaluating the responses to get reliable information onthe seismic response of masonry buildings.

Risk assessment of confined unreinforced masonry buildings based on FEMA P-58 methodology: a case study—school buildings in Tehran

Seismic performance of a representative single-story confined unreinforced masonry school building in Tehran, Iran is evaluated by means of incremental dynamic analyses according to FEMA P-58 framework. For this purpose, fragility curves are derived for each of the constituent walls of the building. The in-plane behavior of the walls is considered only. Both flexible and rigid diaphragm conditions are investigated. For comparison purposes, the corresponding unconfined building exactly duplicating the considered confined unreinforced masonry building is also studied. In order to analyze the effects of near-source seismic actions on the performance of masonry buildings, two separate far-field and near-field ground motion sets containing 326 records are used. By utilizing the results of the incremental dynamic analyses and the available data of unreinforced masonry school buildings in Tehran, a scenario-based risk assessment of this type of school buildings is performed considering all three adjacent faults for three different earthquake magnitudes. Considerable performance improvement is achieved by providing confinement to the walls which leads to over $100 million reduction in the damage costs for masonry school buildings in Tehran. Also, significant reduction in seismic vulnerability, especially for unconfined masonry buildings, is observed by providing the roof with more rigidity. The findings in this study can be of direct use for disaster management of masonry school buildings in Tehran and similar cities.