Rubble Stone Masonry Research Articles

Modal identification and dynamic analysis of a 1000 years old historic minaret of Kalaa Beni-Hammad

From structural and material point of view each historic monument is a textbook case, as it differs in shape, age, material characteristics and level of preservation. New means and approaches are used for geometric and shape survey, material and modal characterization, which helps restitute detailed information regarding the structural elements of the edifices. This paper investigates a 1000 years old historic minaret having a square base of 6.50 m of side and 24.70 m height. An ambient vibration survey has been carried out and the results were used to update a Finite Element (FE) model of the minaret in two stages. First, the elastic modulus of the rubble stone masonry has been determined by matching the experimental and numerical fundamental frequency. In a second phase, a frequency response function (FRF) correlation is carried out iteratively by adjusting the damping ratios to minimize the FRF error. The elastic modulus of the rubble stone masonry is found to be in the lowest range of values given in the literature, which confirms a deteriorated quality of the material. A seismic performance of the structure has been carried out using the updated FE model subjected to a set of acceleration time histories having the mean spectrum matching a compatible site spectrum. The stress concentration zones have been determined and a steel tie system to retrofit the structure is proposed. Beside the proposed investigation framework, the characterization results are valuable facts that can be added to the available database of historic monuments.

Structural Assessment of Ancient Masonry Structures: An Experimental Investigation on Rubble Stone Masonry

ABSTRACT Non-destructive investigation procedures are appropriate approaches for the qualitative mechanical assessment of heritage masonry structures. This study aims to contribute to the knowledge of one of the most common ancient masonry typologies, particularly in Roman archaeological sites, the rubble stone masonry, that is the ancient opus incertum, with an extensive experimental program carried out in the archaeological site of Pompeii. The research focused on archaeological masonry structures with different states of preservation and with or without modern interventions. A non-destructive investigation procedure was carried out including detailed geometrical and material surveys, visual inspections and an extensive program of sonic pulse velocity tests, with a total of 1965 acquired velocities. The paper describes the adopted investigation protocol and detailed analysis and discusses the experimental outcomes. Comparisons with available literature data concerning different masonry typologies at the Pompeii site are also presented. Furthermore, the results of the non-destructive investigation have been compared with available mechanical information from destructive and non-destructive tests performed by the authors on Pompeii-like masonry panels. The unique set of data collected may represent a sound tool for the estimation of the mechanical parameters of the ancient masonry structures, which is a crucial step for the definition of preservation actions.

Rubble Stone Masonry Buildings with Cement Mortar: Base Shear Seismic Demand Comparison for Selected Countries Worldwide

Full base shear seismic demand analyses with calculated examples for heavy stone masonry buildings are not present in the literature. To address this shortcoming, analyses and calculations are performed on nominally reinforced rubble stone masonry house and school designs, as typically built in Nepal. The seismic codes are literally applied for countries where the technique is still allowed (Nepal, India, China, Tajikistan, Iran, Croatia), or should be reintroduced based on current practices (Pakistan, Afghanistan, Turkey). First, this paper compares the base shear formulas and the inertia forces distributions of these codes, as well as material densities, seismic weights, seismic zoning, natural periods of vibration, response spectra, importance factors and seismic load combinations. Large differences between approaches and coefficients are observed. Then, by following Equivalent Lateral Force-principles for Ultimate Limit State verifications (10%PE50y), the base shear and story shears are calculated for a design peak ground acceleration of 0.20 g, as well as the effects of critical load combinations on the forces and moments acting on the lateral-resisting elements. It is concluded that Pakistan has the most tolerant code, Nepal represents an average value, whereas India and China are most conservative toward the case study buildings. Overall, it is observed that heavy-masonry-light-floor systems with negligible diaphragm action behave different under seismic motion than most other building typologies. Given the observations in this paper, the applicability of conventional ELF, S-ELF and S-Modal methods for heavy masonry buildings is questionable. The codes however do not introduce modified approaches that address these differences. Possible implications of the exclusion of plinth masonry and large portions of seismic weight need further assessment and validation, for which different (possibly more sophisticated) concepts must be considered, such as the equivalent frame method or distributed mass system. Since Nepal allows stone masonry in areas with higher seismic hazard levels >0.40 g (opposed to India <0.12 and China <0.15 g), their code is taken as the reference and starting point for follow-up research, which aims to verify the seismic demand by performing seismic capacity checks of the masonry piers and spandrels. The paper ends with an appeal for global collaboration under the research project SMARTnet.

Mechanical characterization of historical rubble stone masonry and its correlation with the masonry quality assessment

The paper presents a study on the mechanical characterization of eight rubble stone masonry walls from different structures of a Portuguese monument and on the assessment of their quality using the Masonry Quality Index (MQI) and the Italian Building Code Commentary (IBCC 2019). Rebound hammer tests were used to evaluate the quality of stone units and mortar joints, and flat-jack tests to assess the mechanical properties of masonry walls. The results allowed to propose new quantitative criteria to rate the quality of mortars and stones in MQI and to support the decision of applying the multiplication factor concerning the quality of mortars in IBCC 2019 methodology.Image processing was used to quantify several features of masonry walls and introduce new quantitative criteria on MQI. The results identified the amount of mortar, the mortar quality, the shape features of stone units and the horizontal alignment of joints as key parameters in the mechanical resistance of rubble masonry made of irregular hard stone and lime-based mortars. The mechanical properties obtained by IBCC 2019, MQI and double flat-jacks tests showed good correlations, highlighting the advantages that come from the quality assessment of masonry to estimate masonry mechanical properties.

Seismic retrofit of stone walls with timber panels and steel wire ropes

Historic constructions are common in Europe, but natural hazards can produce significant damage. Shear reinforcement of historic walls, especially in seismic areas, is often necessary and new retrofitting methods have recently been proposed to restore or increase the lateral capacity of shear walls. In this paper the combined use of cross-laminated timber panels and steel wire ropes is proposed to reinforce rubble stone masonry walls with the aim of increasing their lateral load capacity while improving the energy performance of the building envelope. An experimental programme was carried out in the laboratory to assess the mechanical effectiveness of this retrofitting method. The results from a series of quasi-static cyclic shear tests are presented. The test programmes are described and the analysis of test results is included. The potential benefits and limitations regarding the use of the proposed combined method for reinforcing masonry structures are discussed, with an emphasis on the in-plane behaviour.

In-plane behaviour of rubble stone masonry walls: Experimental, numerical and analytical approach

Unreinforced masonry construction is predominant in many urban areas world-wide.Many of these constructions are vulnerable to earthquakes, which are the main cause of damage and loss of cultural heritage. Understanding the in-plane behaviour of masonry walls when subjected to horizontal loadings will improve the society capacity to preserve and protect this cultural heritage. An experimental campaign on rubble stone masonry walls under different loading conditions is presented. This experimental campaign allows calibrating non-linear numerical models used to study these elements in a more comprehensive way, performing parametric studies regarding the geometry, pre-compression level, boundary conditions and mechanical properties. The capacity to estimate the shear strength using available analytical models is also reviewed, applied and compared.

Rubble Stone Masonry Buildings With Cement Mortar: Design Specifications in Seismic and Masonry Codes Worldwide

Nearly 325 seismic and masonry codes from all over the world have been analyzed, of countries where stone masonry was, or still is, abundantly practiced. This paper compares and summarizes design specifications and construction requirements, with a specific focus on “nominally reinforced rubble stone masonry (NRM) with cement mortar and wooden diaphragms in seismic areas”. Currently, the technique is only allowed and described in some detail in the codes of Nepal, India, China, Tajikistan, Georgia, Iran and Croatia. It is concluded that the design specifications vary greatly without any consensus on the main sizes, dimensions or details. This raises questions about the completeness and correctness, as well as the reliability and actual value of the knowledge in this field. It is further observed that types of stone masonry and stone properties are seldom clearly described in the codes. It is also noted that several countries where stone masonry is still broadly practiced, are currently not allowing the technique (or have no codes in place), such as Afghanistan, Pakistan, Bhutan, Azerbaijan, Kyrgyzstan, Morocco, Tunisia, Turkey, Yemen and Albania. This, however, does not serve the current engineering practices and construction needs in these countries. To address all shortcomings, the paper recommends clear descriptions and terminology; the international adaption of NRM as a fourth masonry category; and the development of a stand-alone code specifically for this technique. Therefore, the authors propose a full assessment, validation, optimization and complementation of the existing knowledge, by means of the current state-of-the-art for calculating, testing and modeling. This envisions a structured research approach with focus on vernacular and traditional construction techniques, called “Non-Engineered 2.0”, for which a research initiative is started under the name “SMARTnet”, meaning “Seismic Methodologies for Applied Research and Testing of non-engineered techniques”. The findings of this paper will serve as the starting point for the upcoming follow-up paper, which will complement the seismic demand with hand-made base shear calculations for countries that still allow the technique. The paper ends with an appeal to experts, academics and final-year students worldwide, to exchange their knowledge and to support the project with their time and expertise.

The role of aggregate and binder content in the physical and mechanical properties of mortars from historical rubble stone masonry walls of the National Palace of Sintra

The relevant role of mortars for the structural behavior of historical rubble stone masonry and the scarce information available justifies the research on these materials. Mortars collected from several masonry structures of the National Palace of Sintra (Portugal), built across different centuries, were examined in situ and in laboratory. The influence of b:a ratio, pore structure, aggregate and binder attributes on the mortars properties is discussed. The results led to purpose drilling resistance and modified Schmidt hammer to assess and distinguish the mortars quality from a mechanical point of view based on their hardness and drilling strength. Moreover, a contribution is provided to estimate a possible order of magnitude of rebound values and drilling resistance with respect to the binder content for similar mortars.

Response Reduction Factor for Mansory Buildings

Most of the seismic codes used today incorporate the nonlinear response of a structure by providing an appropriate response reduction factor so that a linear elastic force-based approach can be used in designs. This study focuses on evaluating the response reduction factor for masonry buildings with different mechanical properties, which are used in modern codes to scale down the elastic response of the structure. Using a similar frame-approach, a nonlinear static pushover analysis is carried out on the analytical models of masonry building in finite element analysis software SAP2000v20.0.0. The response reduction factor components, flexibility, and over strength were computed from the results obtained from the nonlinear static pushover analysis. Finally, the response reduction factor is evaluated for different masonry buildings. It is concluded that the R-value given in IS: 1893-2016 for unreinforced masonry is not recommended for random rubble stonemasonry buildings in mud mortar.

Failure analysis of a Portuguese cultural heritage masterpiece: Bonet building in Sintra

The paper addresses the failure analysis under horizontal loads of the most ancient body of the National Palace of Sintra, Portugal: the Bonet building. This is a URM construction built on top of Arabic foundations during the reign of King Denis of Portugal around 1281; since then, few alterations have been made to the building. Due to the exemplary conservation of the whole palace, a few crack patterns are identified only on the top floor of the Bonet building, an area that is not open to visitors and that will soon undergo restoration works. The seismic vulnerability assessment of this building is carried out following two different approaches, enacted in two distinct numerical models: the so-called Equivalent Frame Method (EFM) and the Finite Element Method (FEM) developed in 3Muri and ABAQUS software, respectively. Both approaches adopt a numerical procedure based on the use of nonlinear static analyses, introducing “equivalent” boundary conditions that are defined to consider, approximately and conventionally, the possible interaction effects among the different parts of the structure. To minimize the multiple uncertainties usually existing in complex masonry buildings, whether related to geometry or masonry mechanical properties, a detailed structural survey is conducted through the laser scanning technology as well as in situ experimental tests. Different types of experimental tests are carried out, both non- and semi-destructive, including a Ground Penetrating Radar test, ambient vibration tests, flat-jack tests, and the collection of masonry samples. All these tests are important to adequately characterize the building and to calibrate the numerical models. Moreover, these tests enable the extraction of values for the mechanical properties of the rubble stone masonry that are used in the later numerical simulations on the Bonet building and, most importantly, can be used as a reference for future works regarding historical Portuguese monuments of the same period. Afterwards, the results obtained from the nonlinear static analyses with the two different software 3Muri and ABAQUS are presented and discussed. Specifically, the differences in modelling strategies and characterization of materials between the two software are considered with special regard to their feasibility, required computational effort, data availability and applicability to large scale structures. Efforts to calibrate and obtain the same behavior of the building for the different software are made, involving geometry, boundary conditions and characterization of the material constitutive laws. Eventually, a nonlinear dynamic analysis is carried out in ABAQUS to further assess the seismic vulnerability of the Bonet building; a spectrum-compatible accelerogram is applied to the numerical model, and the time-history of displacements in relevant control points of the buildings are extracted and discussed.

Experimental investigation of strength, stiffness and drift capacity of rubble stone masonry walls

There is limited available research on rubble stone masonry walls, which are vulnerable under seismic loading. This paper presents an experimental campaign of cyclic shear compression tests on six large-scale walls of this topology. The effect of the axial load and shear span ratio on the wall behaviour, notably on the wall stiffness, strength, and drift capacity, was investigated. It was found that the drift at crack onset is only half of that in previous campaigns on stone masonry walls, likely because one face of each wall was plastered, making the damage more visible. Additionally, splitting cracks opening between the wall leaves appear to play a key role in the collapse mechanism. Finally, testing the walls up to the loss of their axial-load-bearing capacity provides new input for the collapse risk analysis of stone masonry buildings.

Mechanical performance of full-scale Pompeii-like masonry panels

Designing suitable structural interventions to preserve ancient masonry structures subjected to seismic activity requires a comprehensive and interdisciplinary knowledge of traditional building techniques. The mechanical properties of materials and the shear behaviour of masonry walls are essential parameters to design suitable interventions for the preservation of ancient assets from the seismic action. However, such information is still lacking for the ancient masonry structures at the archaeological site of Pompeii.This study investigated the shear strength of rubble stone masonry panels. The reproduced full-scale masonry complies with the ancient building technique “opus incertum” identified at the Pompeii site. Three panels were built based on a detailed survey of the ancient masonry structures involved in the 79 AD eruption that first emerged during the new excavation work conducted at Regio V. Original rock units from the ruins of the new excavation area and lime and pozzolana-based mortar produced according to the Vitruvius provisions were used to build the panels. In-situ sonic pulse velocity tests and diagonal compression tests were carried out on the panels in order to identify an appropriate correlation between the results of non-destructive and destructive tests.The realization of the panels is described herein and the results of sonic and diagonal compression tests are presented and discussed.

Triplet Test on Rubble Stone Masonry: Numerical Assessment of the Shear Mechanical Parameters

Rubble stone masonry walls are widely diffused in most of the cultural and architectural heritage of historical cities. The mechanical response of such material is rather complicated to predict due to its composite nature. Vertical compression tests, diagonal compression tests, and shear-compression tests are usually adopted to investigate experimentally the mechanical properties of stone masonries. However, further tests are needed for the safety assessment of these ancient structures. Since the relation between normal and shear stresses plays a major role in the shear behavior of masonry joints, governing the failure mode, a triplet test configuration is herein investigated. First, the experimental tests carried out at the laboratory of the University of L’Aquila on stone masonry specimens are presented. Then, the triplet test is simulated by using the total strain crack model, which reflects all the ultimate states of quasi-brittle material such as cracking, crushing, and shear failure. The goal of the numerical investigation is to evaluate the shear mechanical parameters of the masonry sample, including strength, dilatancy, normal, and shear deformations. Furthermore, the effect of (i) confinement pressure and (ii) bond behavior at the sample-plate interfaces are investigated, showing that they can strongly influence the mechanical response of the walls.

Uşak-Banaz-Yeşilyurt (Holuz) Köyü Camii ve Kalemişi Bezemeleri

The inner Aegean region is an area where mosques with depictions can be seen frequently. Yesilyurt (Holuz) village mosque in the Banaz district of Usak province is an important village mosque because it has rubble stone masonry, a wooden roof covering where the lath-and-plaster (bagdadi) dome is used, a writing program, rich painting works (kalemisi), and the name of the master who completed the painting works. The motif repertoire of the painting works consists of miniature trees placed in vases, symbolic religious lodge (tekke) tools, urban depictions, floral decorations placed on curved branches and various motifs that are under the plaster. The structure, which is owned by the village legal entity, is registered with the decision of the Izmir Cultural and Natural Heritage Protection Board No.1 dated 1988 and numbered 463. Although it is not known by whom and when the mosque was built since it does not have an inscription, when its decoration characteristics are evaluated, it can be dated to the end of the 19th century. In the study, the architectural characteristics and painting work decorations of the building have been examined in detail, and its place and importance within its period have been determined. The work, which provides important clues about its period, is significantly ruined and about to collapse. It should be repaired as soon as possible following its original form and passed onto future generations.

Provenance and characterization of stones used in the rubble stone masonry of the National Palace of Sintra (Portugal)

Investigations on materials used in historical monuments are of great importance to support studies on archaeology, history and conservation sciences. Most of these investigations focus the characterization, evaluation of the state of conservation and provenance of ornamental stones and mortars but little attention is given to stones in rubble stone masonry. Nevertheless, the determination of their provenance can predictably contribute to expand the knowledge about the site/monument history and eventually provide some clues for the comprehension of constructive processes, as well.This investigation aimed at ascertaining the provenance of the stone blocks of the masonry walls of National Palace of Sintra through their mineralogical and petrographic characterization and by deepening the available information about the local geology. Besides, it aimed at ascertaining if the spatial distribution of the lithotypes across the monument walls can contribute for increasing the historical information about its constructive evolution.Four outcropping “units” comprising metamorphized carbonate rocks were identified beneath the monument. Petrographic and mineralogical correspondence between these outcropping rocks and the stone blocks from masonry walls indicate that the local bedrock was exploited to build the Palace masonry walls.The grouping of different masonry walls according to their stone diversity showed interesting correspondences with the thought constructive periods and/or with the relative position of the walls to the ground. Although this information does not validate construction periods per se, it will further contribute to better comprehend the constructive evolution of the monument when gathered with other information from the masonry analysis to be addressed in future works.

Distinct Element Modelling of Masonry Walls under Out-Of-Plane Seismic Loading

ABSTRACTThe out-of-plane vulnerability of masonry walls plays a crucial role in the seismic response of existing structures. Depending upon mechanical properties and section morphology, collapse may occur by the onset of a mechanism or, as historic constructions often exhibit, leaf separation, disaggregation or sliding. In these latter cases, structural analyses based on rigid-body mechanics may overestimate the seismic capacity, thus resulting unconservative. The distinct element method (DEM), which represents masonry as an assembly of discrete blocks and nonlinear interfaces, could instead be used. Nevertheless, it is more complex and requires more input parameters, so it is still barely applied in engineering practice. In this paper, the seismic out-of-plane response of masonry walls was modelled with DEM. A shake table test on a two-leaf rubble stone masonry wall and a single-leaf wall in tuff blocks was simulated through nonlinear dynamic analyses. The mechanical properties of joints were calibrated on the basis of dynamic identification under low-intensity white noise input, leading to a good prediction of the seismic response. Then, they were further tuned based on the surveyed crack pattern for an improved matching between experimental results and numerical postdictions. Finally, the results provided by the limit analysis were discussed in the light of DEM simulations.

Cost Analysis of Mountain Schools in Nepal: Comparison of Earthquake Resistant Features in Rubble Stone Masonry vs. Concrete Block Masonry

This paper analyzes the cost breakdown of earthquake resistant schools in Kaski District of Nepal, as built by Smart Shelter Foundation. Three types of designs are compared, which are rubble stone masonry with a wooden roof structure, and concrete block masonry with either a wooden roof or with a steel trussed roof. An in-depth cost analysis and cost comparison was carried out, based on a unique collection of local building prices from 19 different villages, as well as generally applicable District Rates, all spanning a period of 10 years between 2007 and 2017. Master Estimates were divided into the 5 main building phases of foundation, walls, roof, floor and finishing, and then further broken down into local costs for materials, labor and transportation. These cost comparisons give a detailed insight in the distribution of the costs, the pricing of individual materials and construction elements, the effect of price fluctuation on the total costs, and the cost implications of different solutions for seismic measures. It is concluded that the market prices, especially of locally sourced materials, fluctuate too much, making it impossible to detect useful patterns for general application or future predictions. Also, no similarities were found between the local village rates versus the general District Rates, which insufficiently reflect variations at the micro level, such as availability of materials, site accessibility, or local preferences. To address these issues, the paper introduces a helpful tool for rapid cost estimation of different school designs. The last chapter analyzes the price implications of adding or removing certain seismic features. It concludes that improving masonry with cement mortar has the highest cost impact, but that inclusion of important seismic features such as horizontal bands, buttresses and steel bars is not that expensive, meaning there is basically no financial obstacle to incorporate these in new constructions of schools and houses. However, all interventions require in-depth technical and scientific validation, for which the authors have started an initiative named SMARTnet. The paper ends with an appeal to experts and academics worldwide, to exchange their knowledge and to support the project with their time and expertise.

School Buildings in Rubble Stone Masonry With Cement Mortar in Seismic Areas: Literature Review of Seismic Codes, Technical Norms and Practical Manuals

A literature review was carried out with the aim to determine the current state-of-the-art with regards to non-engineered stone masonry in seismic areas. Specific search criteria and definitions were determined for school buildings with loadbearing walls of rubble stone masonry in cement mortar, nominally tied with horizontal reinforcements. A total of 47 relevant field manuals between 1972 and 2017 were analyzed for eligibility and checked for compatibility with the national building codes. An overview was created of similarities, contradictions, gaps and differences between the publications. As the majority of the practical manuals target the Himalayan context, the most relevant codes for the comparison were the Indian and Nepali seismic and building codes. Only 9 manuals describe design and construction processes for schools, even though this conflicts with the codes which specifically prohibit the use of stone masonry for buildings with importance factor 1.5 or higher. It was noticed that 7 out of 9 manuals are (co-)written by the same author, and that the available knowledge, which is largely based on empirical evidence, can be traced back to just a few main sources. However, no consistency nor consensus was found on almost all key topics, such as main dimensions, openings and reinforcing elements. Also, the same illustrations and tables are copied over and over again, including apparent conflicts between the details. The fact that this has never been rectified, as well as the fact that the Indian and Nepali seismic codes have not been properly updated since 1994, are indications that the knowledge has not evolved much since the 1980's. It is concluded that the available information contains many contradictions and has become ambiguous. This raises questions about the correctness and actual value of the knowledge. The paper suggest that the existing knowledge must be fully assessed, validated, optimized and complemented by means of the current state-of-the-art for calculating, testing and modeling. To address this, the authors have started an initiative named SMARTnet, and make an appeal to experts and academics worldwide, to exchange their knowledge and to support the project with their time and expertise.

Parametrical study of rubble stone masonry panels through numerical modelling of the in-plane behaviour

This paper focus on the investigation of the behaviour of rubble stone masonry piers, with air lime mortar, loaded in their plane using nonlinear static parametric analysis. This investigation is crucial for the seismic assessment of existing old unreinforced masonry buildings in Lisbon, since there is a clear lack of data for the nonlinear characterization of this kind of masonry. Numerical analyses are performed by adopting the macro-modelling approach implemented in the DIANA software. The adopted procedure for model calibration consists on fitting its behaviour with the results of the performed experimental tests on rubble stone masonry piers with air lime mortar. The parametric analyses are carried out by varying the slenderness and thickness of the piers, as well as the axial load in order to evaluate the influence of such parameters on shear strength, displacement capacity and stiffness. A sensitivity analysis is executed to define the most appropriate size of the elements’ mesh. A good agreement is obtained between the piers tested experimentally and its numerical counterpart models in terms of the force–displacement diagram, damage pattern, failure mode and dissipated energy. In addition, the comparison in what concerns both ductility and energy dissipation is also presented for different cases. The results attained by numerical parametric analyses are presented and discussed along with the main conclusions.

Experimental characterization of in-plane behaviour of old masonry walls strengthened through the addition of CFRP reinforced render

Abstract This article presents the results of an extensive experimental programme investigating the structural performance for in-plane loads of old masonry walls strengthened using a specific technique that consisted of applying a CFRP mesh embedded within a shotcreted render. In this article the expression old masonry refers to rubble stone masonry with lime-based mortar but it is believed that the strengthening technique can also be applied to other types of old masonry (e.g. solid or almost solid clay or concrete brick masonry). The reinforcing composite material, called CFRP reinforced render (CFRP-RR), is characterized by the use of a CFRP mesh and the shotcreted pre-mixed mortar, lime-based, specific for the rehabilitation of old masonry load bearing walls. This material is applied to one or both faces of the masonry walls, thus improving both the in-plane and out-of-plane behaviour for horizontal loads (the latter benefits are described in Ref. [ 1 ]). The experimental programme consisted of the in-plane testing of full-scale physical models of walls, herewith called specimens. These were subjected to reversed cyclic horizontal loads (simulating earthquake loads) with constant vertical loads (simulating gravity loads). The comparison between the experimental results of the non-reinforced with the reinforced (strengthened) specimens allowed the quantification of the inherent benefits in terms of structural performance under earthquake actions.