Paper17-YILDIZ-Meltem Vatam-Risk Level Assessment of Monumental Historical Structures by Visual Inspection

8/4/2019 Paper17-YILDIZ-Meltem Vatam-Risk Level Assessment of Monumental Historical Structures by Visual Inspection

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Risk Level Assessment of Monumental HistoricalStructures by Visual Inspection

M. Vatan, G. Arun, Structural Systems Division of the Faculty of Architecture, YildizTechnical University, Istanbul, Turkey

1 Introduction

Monumental historical structures are symbols of the cultural identity and continuity andthey are the main part of the heritage and the human history. There is no fixed descriptionof the term historic structure, definition depends on the history and cultural context towhich it belongs and the place where it is located.In this paper, monuments are dealt with that have survived hazards for 100 - 1500 years.Along with the history and the new empires of this land the function of some of thosestructures had been changed and during these changes new structural elements wereadded. Minarets as well as some praying parts are the most distinctive and familiaradditional elements during conversion of churches to mosques. These structuraladditions affect the behavior of the existing structure and made it more complicated.The masonry structures constructed with bricks, stones, adobe and mortar have verycomplex structural and geometrical layout. Depending on the construction period;geometrical typology, construction and organization of the structure, element size andtype of construction material used are diverse (Figure 1). During their long life historicalstructures have experienced many actions occurred over long periods of time; enduredlong term deteriorating effects and earthquake loads.Safety is guaranteed by technical codes for new constructions. These codes are mostlynot applicable to the existing historical structures because these structures do not meetthe hypothesis assumed for new constructions. Since the value and authenticity ofhistorical structures can not be assessed by fixed criteria, preservation and protection ofhistorical monumental structures is a difficult task /1/.There are check lists for evaluating the risk level after any natural disaster for existingconcrete and vernacular masonry structures (e.g. FEMA - Federal EmergencyManagement Agency, part of the U.S. Department of Homeland Security) but pre-hazardrisk assessment of historical structures and monuments is not common. Beforehazardous events, identification of potential seismic hazard in existing historical buildingsfor hazard mitigation, disaster preparedness and prior knowledge of potential hazards isvery important because they are culturally valuable and are open to large assembles ofpeople.The aim of this paper is to present a method for assessing the risk level of monumentalhistorical structures. The proposed method is the main part of the ongoing PhD studywhich can be used also for identifying the pre hazard vulnerability of those structures inseismic zones. Due to the fact that the researches on this field are mostly on vernacularbuildings with regular geometry this study is focused on domed and vaulted historicalmonumental masonry structures in Turkey.



Figure 1: Examples of monumental structures in Istanbul (constructed in different periods)

Study on the structural safety of a historic building necessitates an interdisciplinary teamof specialists and requires specific techniques. Safety assessment based on qualitativeand quantitative data is necessary before making any intervention decision. The

qualitative data is visual inspection of structural damages, decays and deteriorations andthe quantitative data requires laboratory tests, structural analysis etc. Obtaining the



quantitative data requires detailed method which necessitates specialists and takes moretime and can only be performed on a limited number of buildings /2/.The fact that there are so many historical structures and few specialists on this field it isvery important to develop quick methods for assessing the safety condition of historic

structures.

2 A Method for Evaluating the Risk Level of Historical MonumentalStructures Based on Visual Inspections

Cultural heritage preservation is a complex phenomenon and to make precise andgenerally accepted decisions and get quantitative risk assessment is very difficult.Documentation, protection, and conservation of historical structures and monuments arethe most important parts of the cultural heritage preservation. The aim of this method is tofacilitate specialists’ works on the preservation and conservation of historical monumentalstructures. This method suggests using non-expert inspectors as students of architectureand civil engineering who are able to make a survey on historical structures, to fill ininspection forms developed for monumental structures in Turkey. Many rapid inspection

methods used data obtained from the street and the inspection is done in a short time.Acquisition of data in the proposed method of this paper, differently from many existingmethods, is made by inspection both from interior and exterior of the building. Since alldata is obtained by visual inspection it is possible to say that by this method manypotentially valuable and historical structures could be inspected in a relatively short time.There are some researches on this field, especially in the seismic zones. Mostly, theseresearches are on vernacular masonry buildings shaped of simple geometry. In thefollowing the existing researches and the necessity of the evaluation methods formasonry monumental historical structures with complex geometry will be discussed.D’Ayala and Speranza developed TOSQA99 (An Integrated Procedure for theAssessment of Seismic Vulnerability of Historic Buildings) for evaluating the seismicvulnerability of historic buildings /3/. This approach is based on a simplified analysis ofthe structural characteristics of the buildings. Surveying is made from the street and

collected data are those which can qualify the seismic performance of masonry buildings.Therefore site surveying is quick but includes only external features of the buildings. Theblock shape, the building position within it, number of free walls and floors, and so on, issurveyed. This post earthquake survey defines the damage level for each building. Thisprogram applied in seismic zones of Italy had satisfying results. After the TOSQA99 theProgramme FAMIVE is developed from it /4/. These methods are based on a failureanalysis of the structures through the identification of feasible collapse mechanisms andcalculation of their associated failure load factors (Figure 2).



Figure 2: Failure mechanisms in TOSQA99 /3/

The frequent occurrence of damaging earthquakes in urban areas in India hasdemonstrated to the researchers the need of a comprehensive earthquake disaster riskmanagement policy. Since detailed vulnerability evaluation is a technically complex and

expensive procedure, the scientists in India, highlighted the importance of using simplerprocedures that can help to rapidly evaluate the vulnerability of different types of buildingsand then to limited detailed evaluations to the most critical buildings. According to thesefacts, India’s national vulnerability assessment methodology includes three basicprocedures. Level 1: Rapid visual screening (RVS) which requires only visual evaluationand limited additional information; Level 2: Simplified vulnerability assessment (SVA)which requires limited engineering analysis based on visual observations’ information andstructural drawings; Level 3: Detailed vulnerability assessment (DVA) which requiresdetailed computer analysis. The simplified vulnerability assessment procedure hasproviding more reliable assessment of the seismic vulnerability of the building and isformed the basis for determining the necessity for more complex vulnerability assessment /5/.MDDS, the Monument Damage Diagnostic System is an expert system widely used inmany European countries. MDDS is originally developed within an EC – research projectfor the diagnosis of damage to masonry structures. This expert system is based on thevisual observations and contains an extensive damage atlas and also information ondecay processes /6, 7/. All damages are defined in the computer data system. Thisapproach is focused on decay and damage types. Inspection of the building can be doneat distinct levels e.g. a whole wall or a part of the wall or composing units. The system isuseful for regular geometric shapes (especially for rectangular walls or parts of the wall).Visual monitoring is performed by repeating MDDS survey over the years.All these researches indicate that there is no current method and general criteria forassessing the damage state of the monumental masonry structures as well as currentdefinition of the term monument. Depending on the structural typology, culture andeconomy of the country involved in heritage conservation; methods and researches aredifferent. It is very important to use simpler methods to evaluate the potential risk of manybuildings as a first step of heritage preservation. The common point of the researches on



this field mentioned above is that the first step of the damage assessment is visualobservation and check lists (inspection forms, damage atlas) are useful for this purpose.It is obvious that definition of the structural elements with complex geometry and takinginto consideration the building as a whole during the risk assessment still is a problem.

The focus of the proposed method in this paper is to define all structural elements in theirreal geometric shape, individually, then take into account building as a whole byinterrelation all structural elements during the risk assessment procedure. The hardestpart of this study is defining the structural elements with complex and irregular geometryin the inspection form. In this method, obtained data by visual inspection of the inspectedbuilding will be evaluated and classification of the risk level will be made through thedeveloped data base computer system. With reference to this classification, buildings thatnecessitate any further detailed inspection can be oriented to the team of specialists. Thisstudy will also provide a systematic data collection and photographs’ archive of surveyedstructures.The proposed method consist of two main parts: developing of the inspection form anddeveloping of the evaluation form of the inspection. Inspection form collects data ashistorical information, physical condition, geometrical typology, structural elements, and

construction material, damage type etc. of the inspected building. Historical informationcontains information as date of construction, past interventions and change of function.To gain information of the building as a whole, the first step of the building’s inspection isthe identification of structural elements and especially the relation between theseelements. Due to the complexity of the geometrical typology of monumental masonrystructures, identification of each element is very difficult. In this method representation ofthe structural system as well as each structural element is provided by using codes foreach structural element based on given axial system on the plan drawing. Through theseelements’ codes, the geometry of the structural element can be identified and damageson each structural element can be interrelated. By this way the building can beconsidered as a whole during the evaluation process.

2.1 Identification of the Structural Elements of the Existing MonumentalMasonry Structures

Load bearing scheme and formation of the structure of historical monuments is verycomplex. In order to collect data of its damage state each element should be representedwith its true geometry on the inspection form. This representation is very difficult forinspecting each element one by one and then interrelate all of them to can evaluatebuilding as a whole. Typology of the existing monumental structures is diverse, thereforeload carrying system and transitional elements and relation between those elements isdifferent for each structure. To be able to define each structural element with their realgeometrical shape as circular, semi circular, curvilinear or irregular and position asorthogonal or non-orthogonal giving axial system to the existing structure is decided. Inrisk assessment, the geometry and position of the structural element in the buildingsystem is very important and this is lacking partly in this field.

The main idea of setting an axial system in plan drawing is to identify existing structuralelements. Hence it is not important to draw axis lines precisely like in an application plan



drawing and it is not necessary to draw each axis in the center of gravity of the element.The emphasis is to identify all structural elements in simple and understandable way asmuch as possible by using minimum axis lines to avoid confusions. Vertical, horizontaland diagonal axis lines are drawn along the structural elements and just vertical and

horizontal lines are entitled, in one direction by letters in the other direction by numbers.In case of the wall placed diagonally, the axis line is drawn along the wall in diagonal wayand the intersection point of the diagonal wall axis to the other element’s axis is identifiedwith vertical and horizontal axis lines. In case of curved walls, vertical and horizontal axesare drawn at both ends of the curved element and at the point where curvature is tangentto horizontal. Consequently, it is possible to differentiate wall types, pillars and columnsaccording to their codes represented by the intersection points of given vertical andhorizontal axes. Examples are given below:Pillar or column: intersection points of the vertical and horizontal axes; one letter and onenumber (Figure 3: G6; I6)Linear wall: intersection points of the vertical and horizontal axes at both ends of the wall;two letters and two numbers, two of them the same (Figure 3: A3C3)Diagonal wall: intersection points of the vertical and horizontal axes at both ends of the

wall; two letters and two numbers, all different (Figure 3: C2D1)Curvilinear wall: intersection points of the vertical and horizontal axes at both ends and attangent point of the wall; three letters and three numbers, two of them may be the sameor all may be different (Figure 3: G4H3I4)

Figure 3: Giving the axial system to the existing building

Codes of the structural elements are keys of the structure and useful to define elementsand their damages. By this way, it is possible to understand the location and position ofthe element, to inspect both interior and exterior part of it separately and then makerelation between exterior and interior damages. Especially when the crack pattern is

inspected, it is very important to understand if cracks pass through the element and arepresent on both sides of the element. Elements’ codes make possible to use this data as



an input for the evaluation data base system. Owing to the fact that evaluation will bedone automatically, interrelation between structural elements is made by codes and thebuilding can be evaluated as a whole.After giving axes to the whole building, before the inspection, the adjacent sections of the

building that is different in height and length as seen from the exterior has to beseparated so that each of these building sections can be inspected separately, one byone (Figure 4).

Figure 4: Division of the building into parts

2.2 Development of the Inspection Form

Processing the inspection forms to obtain data of damage state of the surveyed buildingsis a widely used method in visual inspections as mentioned in the previous paragraphs.According to the structural types, the questionnaire is changed. Common parts of manyinspection forms are geometrical data of the building, physical conditions, material typesand damage state. To avoid subjective interpretations of users during the survey aquestionnaire set is arranged and scoring system is used for the evaluation.According to the existing researches in this study it is decided to develop the inspectionform set for site survey. In order to collect data of the structures’ geometry and visibledamages as cracks, material decay and deteriorations, defects, interventions, man madedamages etc., the inspection form is developed. The main idea of this inspection form isto classify the risk level of monumental heritage, to minimize the data collection tasks ofspecialists if the building necessitates detailed investigation for the preservation and

protection of the cultural heritage buildings’ studies and intervention decisions. Datacollection and inspection of the structures can be done by non-expert inspectors as



students of architecture and civil engineering, but decision making process necessitatesthe team of specialists. Because non-expert inspectors tend to overestimate or tounderestimate the real level of damage, the inspection forms needed to be developed sothat no judgment is left to the inspectors.

The inspection form is created in the MS Office – Excel software and includes sevenmain sections:A – General information,B – Description of the building,C – Physical information,D – Roof system and geometry,E – Facades,F – Inspected floor information andG – Interior places.Sections A, B, C, D and E collect data from the exterior and F and G from the interior ofthe building (Figure 5). Inspection forms shown in figure 5 are not written in English, thereason for which their readability is of less importance in this contribution. Figure 5demonstrates the overall layout of the inspection form.



Figure 5: Example of some pages of the inspection form

In case of the building being separated into parts with different in height and length, eachpart has to be inspected individually by the inspection form set. The first page of theinspection form which includes general information of the building (Section A - GeneralInformation and Section B - Description of the building) is a common page for allseparated parts of it. Separated parts of the building will be inspected by using sections C(Physical information), D (Roof system and geometry), E (Facades), F (Inspected floorinformation) and G (Interior places) and will be collected under the first page for the final

evaluation of the building as a whole.



The first page of the inspection form includes information about the person who inspectsthe building, date of inspection, name of the building, construction date or century,function of the building, information if there is change of the function of the building, axiscodes of the building’s parts, information if seismic joint can be observed between the

separated building parts, earthquake zone of the building. In this first page there is also asection showing the risk level to be filled out by experts after the building is evaluated.In the second page there is the section C – Physical information which includes typology,topographic information and relation with the adjacent parts (both in plan and in section)of the inspected part of the building.In the next page there is section D – Roof system and geometry which includesinformation about configuration of the roof system, how many roof levels are there in theroof system, which supporting elements are used, how many roof elements are there andif there are damages on those elements.In the next page there is section E – Facades which includes information about theelements of the facade, construction materials, damages and interventions and alsocrack pattern of the façade. Each façade is inspected separately and is drawnschematically on the space left at the left side of the inspection form. The axial code of

the plan has to be written above the sketch before starting the inspection. In order toidentify the place of the damage on each element of the facade, a similar axial system ofthe plan has to be given on each façade as shown in Figure 5. For this, vertical axes aregiven at the edges of the façade wall and at the midpoints of the openings and horizontalaxes are given at the bottom and top of the wall and at the midpoints of the openings.When the damage type is questioned in the form, the place of the damage is asked to beidentified by codes represented by the axes. For example in Figure 6, the cracks from leftto right have to be identified as AB23; F23; GH34 and IH34. If the code constitutes threeelements it means that the crack is between the edges of the wall or between twoopenings laid horizontally or vertically. And similarly if the code constitutes four elementsit means that the crack is in the area between the openings or the edge.



Figure 6: Giving axes to the façade

In the sixth page there are sections F – Inspected floor information and G – Interiorplaces. The section F includes information of the inspected floor. In the section G, theinspected building is divided into interior places and each place is inspected one by one.The inspection of interior places includes plan shape of the place, floor system and itsmaterial and supporting system and damages on each element. G.1 floor system, G.2structural elements of floor system, G.2.1 supporting elements of floor system anddamages on them, G.2.2 walls of the inspected interior place, dimensions, construction

material, damages and cracks, G.2.3 pillars, dimensions, material type and damages,G.2.4 columns, dimensions, material type, damages and G.2.5 arches, dimensions,construction material type and damages. During the inspection of the walls of eachinterior place, axial system similar to the facades is given on the wall to identify thelocation of cracks.

2.3 Processing of the Inspection Form

The user guide of the inspection form is prepared for the surveyors. Before any study orinspections on the field, the surveyor will read the instructions and explanations given inthe guide. This user guide explains the inspection form, types of damages, and aglossary of used terms. Survey of monumental masonry structures by processing thedeveloped inspection form consists of three parts:

Arrangement of site works in the office,

Inspection on site and



Writing the data collected to computer program in the office.The first step of the work is to make a research on the building such as history of thebuilding, earthquake zone and drawings. If there is an architectural drawing of thebuilding, it has to be controlled on the field to see if there are any changes. Afterwards

the axial system is set on the building’s plan. Depending on the size of the building, aninspection on site might require more than one day.The capability of processing of the inspection form is discussed and improved byapplications on the group of buildings in the Historic Peninsula in Istanbul. Students of theFaculty of Architecture made inspection by using this form and gave idea for itsimprovement. According to the discussions with them definition and categorization of thedamages made simpler, explanations in the user guide were changed, the time of work isobserved, the questionnaire was improved.

3 Evaluation of the Obtained Data

The evaluation of the data will be done automatically by a computer based system underthe supervision of the specialist. Evaluation part is based on scoring system. Similar to

the inspection form developed using MS Office – Excel software, a formulation and ascoring system will be made using the same software.Representing each structural element by the axial system code will help to set up relationbetween structural elements and will facilitate the risk evaluation of the building as awhole. Even though the development of the evaluation form, formulation of data anddevelopment of the data base system is not finished yet; the frame of the evaluation canbe listed as follows:In plane area ratio /8/;Area to weight ratio /8/;Effective shear ratio /8/;Slenderness of the walls;Ratio of the openings on the walls.

Beside these criteria, structural factors as geometry of the building, load bearingelements, supporting system of the structure, damages on the structural elements andearthquake zone will be considered.

4 Conclusions

Protection and preservation of historical monumental heritage is very important. Riskassessment is the fundamental institutional process and requires team work. Dependingon the scope and requirements, there are simple and detailed methods for assessing theexisting condition and potential risks of historical structures. Detailed risk assessment is atechnically complex and expensive procedure and can only be performed on a limitednumber of buildings. The professionals who can carry out detailed risk assessmentprocedures are few and it is necessary to involve inexperienced architects or civilengineers for risk assessment of the monumental heritage stock. It is therefore veryimportant to use simpler procedures that can help to evaluate the risk level of such



buildings, so that the more complex evaluation procedures can be limited to the mostcritical ones.The method proposed in this study is pre-hazard risk assessment of historicalmonumental structures where inspection forms are developed to be used by

inexperienced students of architecture and civil engineering. In cultural heritagepreservation, pre-hazard risk assessment of historical structures will help to identify thepotential seismic hazard in existing historical buildings for hazard mitigation, disasterpreparedness and prior knowledge of potential hazards.

5 References

/1/ L. Binda, A. Saisi: Research on Historic Structures in Seismic Areas in Italy, Prog.Struct. Engng Mater. 7:71–85, Wiley Interscience (www.intersciencewiley.com), 2005 /2/ P. Roca, P.: Recommendations for The Analysis, Conservation and StructuralRestoration of Architectural Heritage, International Symposium on Studies on HistoricalHeritage, Antalya, Turkey, September 17 – 21, 2007 /3/D. D’Ayala, E. Speranza: A Procedure for Evaluating the Seismic Vulnerability of

Historic Buildings At Urban Scale Based on Mechanical Parameters, 2nd

InternationalCongress on Studies in Ancient Structures, Istanbul, July 9 -13, 2001 /4/ D. D’Ayala, E. Speranza: An Integrated Procedure for the Assessment of SeismicVulnerability of Historic Buildings, 12th European Conference on EarthquakeEngineering, Elsevier Science Ltd., London, UK., 2002 (Paper Reference 561) /5/ R. Sinha, A. Goyal: A National Policy for Seismic Vulnerability Assessment ofBuildings and Procedure for Rapid Visual Screening of Buildings for Potential SeismicVulnerability, Report to Disaster Management Division, Ministry of Home Affairs,Government of India, 2004 /6/ K. Van Balen: Learning from Damage of Masonry Structures, Expert Systems CanHelp!, Historical Constructions, P. B. Lourenço, P. Roca (Eds.), Guimaraes, 2001 /7/ R. P. J. Van Hees, S. Naldini, L. Binda, K. Van Balen: The Use of MDDS in the VisualAssessment of Masonry and Stone Structures, SACoMaTiS 2008, International Rilem

Conference, Varenna, Italy, 2008 /8/ P.B. Lourenco, J.A. Roque: Simplified Indexes for the Seismic Vulnerability of AncientMasonry Buildings, Construction and Building Materials (200), 2006

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Paper17-YILDIZ-Meltem Vatam-Risk Level Assessment of Monumental Historical Structures by Visual Inspection