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In many historical buildings lintel area is being damaged by time degradation, overload and uneven settlement of foundations. The effect occurs as visible cracks in the lintels and area near them. Some types of lintels are more vulnerable than others. All these factors are important in consideration of construction durability. This paper shows the results and analysis of experimental tests performed on lintels with different shapes at West Pomeranian University of Technology in Szczecin, Poland.
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Procedia Engineering 193 ( 2017 ) 345 352
Available online at www.sciencedirect.com
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the scientific committee of the International Conference on Analytical Models and New Concepts in Concrete and
Masonry Structures
doi: 10.1016/j.proeng.2017.06.223
ScienceDirect
International Conference on Analytical Models and New Concepts in Concrete and Masonry
Structures AMCM’2017
Comparison of brick lintels types for their durability effect
Rafaá Nowaka*
aWest Pomeranian University of Technology in Szczecin , Piastów 50 street 70-311 Szczecin, Poland
Abstract
In many historical buildings lintel area is being damaged by time degradation, overload and uneven settlement of foundations.
The effect occurs as visible cracks in the lintels and area near them. Some types of lintels are more vulnerable than others. All
these factors are important in consideration of construction durability. This paper shows the results and analysis of experimental
tests performed on lintels with different shapes at West Pomeranian University of Technology in Szczecin, Poland.
© 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the International Conference on Analytical Models and New
Concepts in Concrete and Masonry Structures.
Keywords: brick; lintel; zone; arch; durability
1. Introduction
Lintels are structural elements that allow to create the openings in masonry walls. In the past the width of wall
openings was limited to the length of available materials, as seen in the example of single-stone lintels. The
invention of masonry arch allowed to extend the span of used lintels. The properties of arch lintels were studied
mostly by the Romans. However, the invention was not made by them. The first arch lintels were created by ancient
Greeks around 1st century B.C. The longest lintels found in Greece were 6 m in span. Development of technique and
knowledge allowed Romans to extended the span up to 40 m. Invention of arch lintels allowed to introduce elements
that carry compressive stresses reducing the influence of tensile stresses. At first the shape of arch lintels was
* Corresponding author. Tel.: +48-605-642-800; fax: +48-605-642-800.
E-mail address: rnowak@zut.edu.pl
© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the scientific committee of the International Conference on Analytical Models and New Concepts in
Concrete and Masonry Structures
346 Rafał Nowak / Procedia Engineering 193 ( 2017 ) 345 – 352
obtained through trial and error. Later the builders used ropes and other elements to model the forces subjected to
lintels. This way they were able to achieve optimal shape. The compression-tension stresses relationship in lintel
depends on load to curvature ratio [1,2].
One of the most common lintel type in historical buildings is the arch lintel. Other used lintels include flat brick
lintels with bricks at an slight angle to each other. An interesting fact is that there is a lot of information on
calculation methods for load-bearing support steel beams for balconies, simple masonry and masonry stairs, yet the
brick arch lintels aren’t described at all. Even now there are not many known methods of calculating those lintels.
The technical standards also do not include any information on arch lintels. Simplified method of limit state analysis
can be found in the literature [3] however it is not precise enough and requires calibration through experimental test.
In many buildings lintel area is being damaged by time degradation [4], overload and uneven settlement of
foundations. It is especially visible in old buildings, some of which should be preserved due to their historical
importance. The damages appear as clearly visible cracks in the lintel area (Fig. 1).
Fig. 1. Example of crack in: (a, b) flat lintel zone; (c, d) segmental arch lintel zone.
Some lintel types are more susceptible to external forces than others. It is very important to look for any signs of
cracking near lintels as well as on them [5]. All these factors are an important part of considerations on structural
durability and capacity of lintels. This papers presents the results and analysis of experimental tests performed on
lintels with different shapes, conducted at West Pomeranian University of Technology in Szczecin, Poland.
2. Experimental tests
Main focus of the experimental tests was placed on brick arch lintels as the most prevalent lintel type in old
buildings. Flat brick lintel can be considered as an flat arch (lintel with curvature of 0). Four shapes of lintels were
a) b)
c) d)
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Rafał Nowak / Procedia Engineering 193 ( 2017 ) 345 352
analyzed during the experimental tests: flat lintel (Fig. 2 a, b), segmental arch lintel (Fig. 2 c, d), semicircular arch
lintel (Fig. 3 a, b) and gothic arch lintel (Fig. 3 c, d). Chosen lintels are the most prevalent arch shapes that can be
found in old buildings - especially in old German buildings located here in Poland. All models were tested with and
without additional wall fragment to investigate if the interaction of masonry influences the overall lintel capacity.
Engineers often ignore the influence of wall while considering arch lintels. This could result in incorrect judgement
and improper choice of repairs methods. The calculations of brick arch lintels are only conducted for the lintel itself,
regarding its compressive capacity and pressure line that depends on its shape and applied loads. The study was
conducted on two types of models for each lintel shape – one consisting of lintel alone, the second made as lintel
with additional brick layers on top of it. Models (Fig. 2 d, Fig. 3 b, d) were used to investigate the differences in
capacity.
The models were made using solid bricks with nominal compressive strength of 25 MPa and M5 class mortar.
The mortar layer was approx. 1 cm thick for parallel layers. Arch’s joints thickness varied because of geometrical
requirements. The guidelines for constructing brick arches can be found in archive materials [6]. To simulate the
extension of the wall in models with wall fragment steel blockades were used to limit the horizontal deflection.
Fig. 2. Examples of experimental models of lintels: (a) flat lintel without constrained supports; (b) flat lintel with constrained supports;
(c) segmental arch lintel, (d) wall fragment containing segmental arch lintel.
Flat lintels were fit on a steel frame that simulated the supporting wall. Two steel plates were added to the frame
at an angle to simulate the wall edge so crucial for this type of lintel. To be able to compare the results additional
freely supported flat lintel was prepared. There aren’t many known methods of calculating brick flat lintels.
Generally they are similar to freely supported beams, differing mainly with wedge-shaped edges at supports. The
results of bearing capacity achieved in the experimental tests for this type of lintel exceeded the expectations.
Similar results were not found in any other piece of literature.
Tested models had span of 1 m. The mortar layer were not completely adherent to the brick to simulate the
existing bond found in old buildings. The models were subjected to concentrated load.
a) b)
c) d)
348 Rafał Nowak / Procedia Engineering 193 ( 2017 ) 345 – 352
Fig. 3. Example of experimental models of lintels: (a) semicircular arch lintel; (b) wall fragment containing semicircular arch lintel; (c) gothic
arch lintel, (d) wall fragment containing gothic arch lintel.
The tests investigated and compared capacity, deflections and horizontal forces in models. Results also provided
very important information on the destruction process of lintels and their susceptibility to other factors. Even though
other factors are dominant in the destruction process of lintels often the load applied by higher layers causes the
destruction of wall fragment containing lintel.
The progressing crack pattern was recorded by a camera during the experimental tests. In addition, the horizontal
tie force and vertical force applied by an hydraulic actuator were recorded for all arch models of the lintels.
Deflections were measured with displacement transducer and for some models the strain gauges were used to record
strains. Everything was connected into one data acquisition amplifier. Main results of experimental tests are
presented below.
3. Results
The most important results from experimental tests are presented in Table 1 - 4. For brick lintels with arch shape
(Table 2 - 4) there were a visible influence of brick layers over the lintel on its capacity limit. For segmental arch the
model with wall fragment with symmetrical imposed load in the middle of span was 176 % stronger than the one
without, but 665 % stronger in case of non-symmetrical load. Comparing segmental arches with symmetrical load in
the middle of span and non-symmetrical imposed load the difference in bearing capacity reached 402 %, however
was only 106 % for model with wall fragment. The impact of non-symmetrical load is less noticeable in case of
models with additional layers of bricks (three layers over the lintel). Similar comparison can be done for
semicircular lintel, because models had similar points of force application. Semicircular lintel with wall fragment
was 6000 % stronger than the lintel itself under symmetrical load in the middle of span. Under non-symmetrical load
the difference was 10000 %. Comparison between lintels under different types of load showed 200 % difference in
favor of symmetrical loaded lintel without wall fragment, but only 120 % difference in favor of symmetrical loaded
a) b)
c) d)
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Rafał Nowak / Procedia Engineering 193 ( 2017 ) 345 352
lintels with wall fragments. Gothic arches were tested only using symmetrical load in the middle of span to compare
the influence of wall fragment. The model with wall fragment was 732 % stronger than the lintel itself. The biggest
influence of additional wall layers over lintels on overall capacity was registered for gothic arches.
The results showed that the impact of non-symmetrical loading is less noticeable for arched lintels with wall
fragment. However, there are situations in existing buildings where the lintel is carrying non-symmetrical loads as
shown in Fig. 1 d. In this particular situation the lintel was in good shape, however the inhabitant of the building
raised a masonry wall on a slab supported by the lintel. This overloaded it which resulted in a visible bad condition.
Inhabitant raised the wall on his own, without consulting the idea with civil structural engineer. In this case it was
necessary to remove the additional wall from overloaded lintel and repair damaged masonry.
Destruction of the lintels without additional brick layers was sudden without being preceded by visible cracks.
The cracks shown in table 2-4 were caught by high-speed camera. The only visible signs of lintel destruction could
be read from deflection measurement. This type of destruction is dangerous, excluding the use of those lintels in
buildings.
For the same type of lintels but with wall fragments the destruction process was much more visible. The process
was not sudden and started with early visible cracks in wall layers over the lintel. With increasing load new cracks
appeared and the existing ones started to widen. Near the limit of model bearing capacity the cracks appeared on the
lintel itself. The process of destruction was similar in all models regardless of lintel’s shape. The end of destruction
process was also less sudden than in previous models. Despite reaching its maximum capacity, the model was still in
a good condition. While measured displacement continued to increase and force measurement from force sensor
decreased, the model still did not collapse. This progression of the destruction process is safer for buildings.
Noticeable cracks and slower process of destruction allow the inhabitants to realize the danger. Sudden collapse of
the lintel would also surely damage the slab supported by the lintel. This could result in heavy damage to building’s
structure.
Table 1. Main results from experimental tests – flat lintels
Shape of lintel: Geometry
f/l [-] Limit P Force
[kN]
-
-
0.1
0.15
-
-
59
77
The brick layers above the lintel increase lintels capacity. Regardless of the cause, cracks mostly start to occur in
the wall near the lintel. The cracks in experimental tests started to appear in layers over the lintel and slowly
progressed to lintel itself. The models with only lintels had lesser capacity than the models with additional layers of
bricks. As the destruction of lintel happened suddenly, the cracks were only registered a moment before the collapse
of the element. The cracks visible in the near-lintel area are the first sign of progressing destruction of the element.
That is why analyses of current state of lintels should also consider the wall near it.
350 Rafał Nowak / Procedia Engineering 193 ( 2017 ) 345 – 352
Table 2. Main results from experimental tests – segmental arch lintels
Shape of lintel: Geometry f/l Limit P Force
[kN]
0.2
0.2
173
43
0.2
0.2
304
286
Table 3. Main results from experimental tests – semicircular lintels
Shape of lintel: Geometry f/l Limit P Force
[kN]
0.5
0.5
4
2
0.5
0.5
240
200
Cracks not always are a result of lintel overload. Sometimes they appear because of mortar degradation due to
environmental effects or differential settlement of foundations. Most often cracks start to appear in layers over the
lintels. While lintel itself is not cracked it is safe to assume that it still has bearing reserves. The lintels with brick
layers on top will have better durability than a lintel on its own as seen in Fig. 1 d.
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Rafał Nowak / Procedia Engineering 193 ( 2017 ) 345 352
Degradation of the mortar sometimes causes the cracks to appear in the lintel itself, not as in case of overloading
in the near-lintel area. The cracks however aren’t dangerous because the capacity of the element is covered by the
brick layers over the lintel. Until they are in a good condition the capacity of the element is assured.
Flat lintels are also very interesting, their capacity mostly depends on the constraint effects at the supports. The
tests showed that the difference in capacity between a lintel with constrained and unconstrained supports is about
590 % - for symmetrical load in the middle of span and 513 % for non-symmetrical. The destruction of
unconstrained lintels occurred suddenly. The destruction of constrained lintels was not sudden, and occurred with
visible development of early cracks. The constrain at supports stopped the collapse of the element allowing for
further application of load. The horizontal displacement of the supports is very important here. It is vital to limit the
horizontal displacement, so the bricks will not fall off the lintel. These lintels are a good solution for the problem of
mortar destruction due to environmental effects. Capacity of flat lintels was not as good as capacity of segmental
gothic arches.
The wedge–shaped edges of lintels are an important factor in overall capacity of flat lintels. The wedge-shaped
edges of the lintel compress the lintel under load by interacting with side supports. This is an significant observation
and needs to be included in durability analysis of these lintels. Other lintel types are not as durable and are very
susceptible to horizontal displacements of the supports. Flat lintel constrained at supports will bear the load until it
gets overloaded by vertical forces or after the wedge-shaped wall support will exceed its limits.
Table 4. Main results from experimental tests – gothic arch lintels
Shape of lintel: Geometry f/l Limit P Force
[kN]
1.5
41
1.5
300
4. Conclusions
Analysis performed on different types of lintel showed that there is no clear choice that resists all the factors
influencing durability. The choice depends on major factors impacting on the lintel. The destruction process was
least sudden for gothic arches. However, all presented lintels with wall fragments, had very good bearing capacity
and overall good resistance to environmental effects. Many buildings with studied types of lintels have visible cracks
and are still standing. In the past, choice of the lintel depended on their aesthetics, not their durability or capacity.
Even nowadays there is not enough knowledge on the actual capacity of brick arch lintels and their real bearing
capacity. There is no information about calculating brick arch lintels in technical standards.
Study showed that brick layers over the lintel in all tested models had significant influence on their durability.
They increase overall bearing capacity and resistance to cracking. This is especially important for arches under non-
symmetrical load which is more dangerous for them. Lintels with brick layers over them much better handle the non-
symmetrical loading than lintels alone. Typical cracks/damages appear in brick layers over the lintel. The cracks are
352 Rafał Nowak / Procedia Engineering 193 ( 2017 ) 345 – 352
visible in early stage of destruction process way before reaching maximum bearing capacity of the wall fragment.
The limit state is reached when the lintel itself becomes cracked.
The flat lintel was taken as arch with curvature of 0. These lintels proved to have good capacity. The capacity of
the lintel depends on the shape of wall supports. When flat lintel loosens up the vertical load causes it to translate
downwards while wedge-shaped edges at the end compress it together. This effect allows for some deflections or
mortar degradation from environmental effects to appear in the lintel. However it is crucial to prevent bricks from
falling out of the lintel.
Analysis of the state of lintel for their environmental devastation cannot be limited only to lintel itself but should
consider also the wall fragment near it, because as proven in the study it is a vital component for its capacity.
Performed repairs must also include the wall area next to lintel. However, they should be performed when it is really
needed.
All of the existing brick lintel structures should be analyzed individually with respect to their actual shape and
repair needs. Performed repairs should preserve the original shape and look of the lintels. Very often cracked lintels
still have capacities reserves and could be left unrepaired, which would preserve their originals state. Every repair
changes the historical value of the structure. This is why it is important to repair only lintels that really require it.
Engineers have to remember that not all cracks in the lintels are dangerous, some of them can be left unrepaired.
References
[1] W. Wierzbicki, Mechanika Budowli, PaĔstwowe Wydawnictwo Naukowe, Warszawa, 1955.
[2] S.M. Holzer, Numerical arch and vault analysis, Journal of Heritage Conservation, DOI (2013).
[3] W.A. Baádin, I.I. Goldenblat, W.M. Koczenow, M.J. Pildisz, K.E. Tal, Obliczenia konstrukcji budowlanych metodą stanów granicznych.,
Warszawa, 1955.
[4] R. Nowak, Analiza noĞnoĞci i mechanizmów uszkodzeĔ odcinkowych ceglanych nadproĪy áukowych., Faculty of Civil Engineering and
Architecture, West Pomeranian University of Technology, Szczecin, 2014, pp. 112.
[5] R. Nowak, The problem of maintenance of historical arched lintels, Structural Analysis of Historical Structures (SAHC 2016), KU Leuven,
2016.
[6] R. Ahnert, K.H. Krause, Typische Baukonstruktionen von 1860 bis 1960, Beuth Verlag GmbH, Berlin, 2014.
... The evaluation of the strength of masonry (Jasiński, Drobiec, and Mazur 2019;Łątka and Matysek 2017;Łątka, Seręga, and Matysek 2018;Matysek and Witkowski 2015;Tkacz 2015) component from which lintels are already made is useful in order to assess their strength parameters. A small number of researchers raised the problem of evaluation of the strength of existing lintels (Nowak 2016(Nowak , 2017 or the problem of their possible strengthening (Magnusson and Hervall 1984;Nowak 2016Nowak , 2017. For brick arches both in lintels or vaults significantly more studies can be found (Albuerne, Williams, and Lawson 2012;Alecci et al. 2017;Bednarz, Jasieńko, and Angelo 2009;Boothby 2001;Borri et al. 2007Borri et al. , 2009Bosnjak-Klecina and Lozancic 2010;Bovo, Mazzotti, and Savoia 2012;Briccoli Bati, Rovero, and Tonietti 2009;Castori et al. 2006;Cecchi 2012;Chen 2016;Corradi et al. 2015;Egidio et al. 2012;Ferretti and Pascale 2019;Foraboschi 2004;Gago, Alfaiate, and Lamas 2011;Holzer 2013;Hojdys and Krajewski 2013;Jasieńko, Bednarz, and Nowak 2009;Jasieńko, Di Tommaso, and Bednarz 2009;Maria Auciello 2019;Nowak and Romuald 2009;Oliveira, Basílio, and Lourenco 2006;Pulatsu, Erdogmus, and Lourenco 2019;Reccia, Cecchi, and Milani 2016;Ricci, Sacco, and Piccioni 2016;Sacco 2012;Uranjek, Lorenci, and Skrinar 2019). ...
... The evaluation of the strength of masonry (Jasiński, Drobiec, and Mazur 2019;Łątka and Matysek 2017;Łątka, Seręga, and Matysek 2018;Matysek and Witkowski 2015;Tkacz 2015) component from which lintels are already made is useful in order to assess their strength parameters. A small number of researchers raised the problem of evaluation of the strength of existing lintels (Nowak 2016(Nowak , 2017 or the problem of their possible strengthening (Magnusson and Hervall 1984;Nowak 2016Nowak , 2017. For brick arches both in lintels or vaults significantly more studies can be found (Albuerne, Williams, and Lawson 2012;Alecci et al. 2017;Bednarz, Jasieńko, and Angelo 2009;Boothby 2001;Borri et al. 2007Borri et al. , 2009Bosnjak-Klecina and Lozancic 2010;Bovo, Mazzotti, and Savoia 2012;Briccoli Bati, Rovero, and Tonietti 2009;Castori et al. 2006;Cecchi 2012;Chen 2016;Corradi et al. 2015;Egidio et al. 2012;Ferretti and Pascale 2019;Foraboschi 2004;Gago, Alfaiate, and Lamas 2011;Holzer 2013;Hojdys and Krajewski 2013;Jasieńko, Bednarz, and Nowak 2009;Jasieńko, Di Tommaso, and Bednarz 2009;Maria Auciello 2019;Nowak and Romuald 2009;Oliveira, Basílio, and Lourenco 2006;Pulatsu, Erdogmus, and Lourenco 2019;Reccia, Cecchi, and Milani 2016;Ricci, Sacco, and Piccioni 2016;Sacco 2012;Uranjek, Lorenci, and Skrinar 2019). ...
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Arched lintels are quite common structures in historical buildings. Most of them were made of brick or stones due to the available technology that days. There is no precise knowledge about the real strength of such lintels. Studies conducted in previous years and also nowadays aren’t comprehensive enough. The knowledge upon the proper calculation for lintels, due to technical standards (Eurocodes etc.), is only accurate for masonry without mortar or when the mortar is fresh, not yet bound. The overall strength of masonry wall near lintels can have much greater strength than we assumed, because of the secondary arch effect under the point force. The crack of such lintels not necessarily have to be the limit state of the construction. The article provides the analysis of real strength of such constructions mainly based on segmental brick arched lintels.
  • W Wierzbicki
  • Mechanika Budowli
W. Wierzbicki, Mechanika Budowli, Pastwowe Wydawnictwo Naukowe, Warszawa, 1955.
Numerical arch and vault analysis
  • S M Holzer
S.M. Holzer, Numerical arch and vault analysis, Journal of Heritage Conservation, DOI (2013).
Analiza no no ci i mechanizmów uszkodze odcinkowych ceglanych nadpro y ukowych., Faculty of Civil Engineering and Architecture
  • R Nowak
R. Nowak, Analiza no no ci i mechanizmów uszkodze odcinkowych ceglanych nadpro y ukowych., Faculty of Civil Engineering and Architecture, West Pomeranian University of Technology, Szczecin, 2014, pp. 112.