BIODETERIORATION AND STRUCTURAL ANALYSIS
OF TIMBER ROOFS OF AN HISTORICAL BUILDING IN
SÃO PAULO, BRAZIL
Maria Beatriz Bacellar Monteiro1, Takashi Yojo2
ABSTRACT: This paper presents the diagnosis of biodeterioration and structural analysis of the roof of a building given
‘heritage’ status by the DPH – Department of Cultural Heritage of the City of São Paulo, Brazil. The building is currently in
use as a rehabilitation and training unit for disabled people. The roof structure consists of wooden trusses with vertical metal
tension rods, supported by masonry walls. The diagnosis of the biodeterioration was made with a detailed evaluation of the
structural wood frame embedded in masonry walls. For structural analyzes the criteria based on the remaining residual
strength of the cross section of the wood components were adopted. The diagnosis included the identification of the wood
species and a survey of construction details of the wooden structure where distortions and specific problems of overload
were observed. The results of this study lead to a conclusion about the stability and structural safety of the roof in order to
support corrective and preventive measures for conservation of the building.
KEYWORDS: timber structure; inspection; decay fungi; termites, historical building; structural analysis
1 INTRODUCTION 12
This paper presents the results of an evaluation process
conducted in order to analyze the conservation status of the
timber roof structure of a building given ‘heritage’ status
by the DPH – Department of Cultural Heritage of the City
of São Paulo, Brazil. It describes the results of the process,
which included the definition of geometric and structural
characteristics, the intensity of biodeterioration of wooden
elements and the analysis carried out to evaluate the
structural safety condition of the roof timbers.
The building was constructed in 1923 as an establishment
for the processing, pressing and storing of cotton. At the
end of the 20th century it was adapted to accommodate a
rehabilitation and training unit for disabled people.
The roof structure consists of 93 wooden trusses with
vertical metal tension rods, supported by masonry walls.
The original roof was built with clay tiles of the Marseilles
type, more recently replaced by asbestos cement tiles
2 INSPECTION AND STRUCTURAL
ANALYSIS
At first, a diagnosis of the building was done in order to
evaluate the conservation status of the roof’s structure. A
1
Maria Beatriz Bacellar Monteiro, Brazil. Email:
[email protected]
2
Takashi Yojo, Institute for Technological Research – IPT, ZIP
05508-901, São Paulo, SP, Brazil. Email: [email protected]
multidisciplinary team composed of civil engineers,
biologists and architects, performed a detailed examination
of the building with the purpose of identifying the main
problems, and recognizing the types and degree of the
biodeterioration.
As part of the diagnosis, the types of wood used were
identified and this information was used to obtain data on
their physical and mechanical properties to be used on
structural analysis procedures.
2.1 VISUAL INSPECTION
The evaluation of the biodeterioration of the wooden
components was done by visual inspection.
The intensity of the biological attack was categorized into
five groups: sound wood (no reduction of the cross
section); initial attack (up to 15% of the cross section);
moderate attack (between 15% and 30% of cross section);
intense attack (between 30% and 80% of the cross section)
and heavy intense attack (over 80% of the cross
section) [1].
The identification of the organisms responsible for the
biodeterioration was done in the laboratory, based on the
analysis of samples collected during inspection.
2.2 MECHANICAL CHARACTHERISTICS
Aiming to gather data on the geometry and constructive
details of the wooden parts for the structural analysis, a
search was conducted of the characteristics of the main
structural elements of the building, observing the
connections, distortions around nodes and noting localized
problems of overload.
2.3 IDENTIFICATION OF WOOD SPECIES
A preliminary botanical identification took place at the
moment of the inspection. This identification was later
confirmed in the laboratory through the processes of
macroscopic and microscopic examination of wood
anatomy.
2.4 STRUCTURAL ANALYSIS
The analysis was carried out based on standards NBR
7190/97 – " Projeto de estruturas de madeira" [2], NBR
6120/80 – "Cargas para o cálculo de estruturas de
edificações" [3], NBR 8800: 2008 - “Projeto de estruturas
de aço e de estruturas mistas de aço e concreto de
edifícios” [4], NBR 6123/88 – “Forças devidas ao vento
em edificações” [5] of the Brazilian Association of
Technical standards – ABNT and CEN EN1995-1-1: 2004
"Eurocode 5: design of timber structures-part 1.1: general
– Common rules and rules for buildings" [6].
3 RESULTS
3.1 IDENTIFICATION OF WOOD SPECIES
The results of the botanical identification of wood samples
collected, led to the conclusion that the structure was
basically
constructed
with
peroba-rosa
wood,
Aspidosperma polyneuron, Apocynaceae.
3.2 BIODETERIORATION
Laboratory analysis of wood samples collected during
the inspection enabled the location, identification and
quantification of the attack of decay fungi and dry wood
termites.
3.3 STRUCTURAL ANALYSIS
Some members of trusses had been designed to work only
when subjected to the compressive forces. However, due to
the replacement of clay tiles by other lighter ones, the wind
effect can have a reverse action in these parts that will
function when tensioned
4 CONCLUSIONS
A generalized attack of fungi and dry wood termites on the
wooden structure of the roof was observed. This
contributed to a significantly reduced strength and stiffness
of the constructive elements. Of a total 93 wooden trusses,
84% had at least one of the supports deteriorated by these
organisms and 34% had moderate attack which
compromised their structural safety.
Based on the extent and intensity of the problems as
well as the particular features of the building, all the
trusses should be replaced. The portions of damaged wood
should not be considered for use in the design of
reinforcements.
To avoid risks arising from the effects of wind, the
central connections of trusses should be reinforced.
In addition, measures should be taken to control the
organisms responsible for the deterioration of the wood.
Sources of moisture such as spills, leaks and capillary
water must be eliminated in order to control the
development of decay fungi and stop the decay progress.
These leaks or spills may also compromise the efficiency
of procedures for controlling insects.
ACKNOWLEDGEMENT
The authors would like to express their gratitude to the
researchers and technicians of the “Centro de Tecnologia
de Recursos Florestais - IPT”, Raphael J.B. Pigozzo,
Ricardo G. F. N. B. Pereira, Aline Abacherly de Camargo,
Johnny Wing Moreira, Fabiola Margoth Zambrano
Figueroa and Paulo de Assis for their valuable support in
collecting field data.
REFERENCES
[1] T. Yojo, M.B.B. Monteiro, F. M. Z. Figueroa, G.A.C.
Lopez, M.J.A.C. Miranda, Models for evaluating
structural wood damaged by xylophagous, World
Conference on Timber Engineering, 2012, pp. 419423
[2] Associação Brasileira de Normas Técnicas, NBR 7190
- Projeto de estruturas de madeira “Design of wooden
structures”, 1997.
[3] Associação Brasileira de Normas Técnicas, NBR 6120
- Cargas para o cálculo de estruturas de edificações
“Loads for calculating of building structures”, 1980.
[4] Associação Brasileira de Normas Técnicas, NBR 8800
- Projeto de estruturas de aço e de estruturas mistas de
aço e concreto de edifícios “Design of steel structures
and mixed concrete and steel structures for the
buildings”, 2008.
[5] Associação Brasileira de Normas Técnicas, NBR 6123
- Forças Devidas ao Vento em Edificações “Wind
Forces on Buildings”, 1988.
[6] EN 1995-1. Eurocode 5 – Design of Timber
Structures – Part 1 – 1 : General –Common Rules and
Rules for the Buildings, 2004.