THE MARKET FOR MURFOR REINFORCED MASONRY IN EUROPE

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1 Seminário sobre Paredes de Alvenaria, P.B. Lourenço & H. Sousa (Eds.), Porto, THE MARKET FOR MURFOR REINFORCED MASONRY IN EUROPE Pol TIMPERMAN Product manager building products Bekaert Belgium ABSTRACT The reinforced masonry technology has obtained a wide experience and acceptance in Europe. The system allows to realize two objectives for which often people are reluctant to apply it. First of all, bed joint reinforcement is the most adequate mean to prevent masonry from cracking. Cracking which is due mostly from shrinkage but also from a number of other causes as seismic events. Murfor bed joint reinforcement will control the crack width and bring this down to acceptable levels. The structural applications offer the designers, architects and contractors alternatives to the classical reinforced concrete construction method. The benefit of this technology is both economical and technical. 1. INTRODUCTION: REINFORCED MASONRY: THE PAST AND PRESENT The use of reinforcement in masonry structures is already more than 75 years old. The first recognised use of reinforced masonry was in 1813 when a British engineer Marc Brunel built a chimney for an industrial production plant near London. In 1825 that same technique was used by Brunel to construct a hydraulic tunnel under the Thames.

2 134 The market for Murfor Reinforced masonry in Europe The development of reinforced masonry was halted in 1867, when the French gardener Joseph Monier introduced the concept of reinforced concrete. After that time, the use of reinforced masonry was put aside until the end of the First World War, when it was reintroduced in Canada, UK, USA and Australia. The more recent architect, Eladio Dieste Argentina, built a lot of important structures in reinforced masonry (even churches) and as such motivated the architects to use the full benefits of this construction technology. Today, the use of reinforced masonry is well developed in most western and Far East countries. Both in the US and Europe the adopted building codes have greatly increased the potential use. As such the European Cen standards will regulate the use of reinforced masonry for all major application, even for the construction in seismic areas. The latter has been the result of different scientifically research programmes such as Brite Euram, Saferr, etc. At this time greater attention is being given to the potential of masonry structures, not only because of the growing knowledge of the material and its composition, but also because of the economic benefits of the technique. 2. THE USE OF BED JOINT REINFORCEMENT In Europe, reinforced masonry, in its widest sense, is mostly used for crack control. Several studies have been carried out to evaluate the benefits the benefits of using bed joint reinforcement. The results are conclusive; the use of bed joint reinforcement reduces considerably the level of damage in masonry construction. Based on this, a number of specialist insurance companies dealing with construction are encouraging the use of bed joint reinforcement to reduce their claims for the cost of crack repair.

3 P. Timperman Crack control Masonry cracks may be classified by: - Structure type - Masonry type - Location - Pattern - Width - Cause For a given type of structure and material, the location, pattern, and width often provide clues to the cause. Cracks result from strain, which induces stress in excess of strength in compression, tension, or shear. Strain may be induced by the imposition of loads or by restraint of volume changes in the masonry materials. Volume changes include those induced by change in temperature, moisture, water or salt crystallization, or corrosion. Movements of foundations, structural frames, shelf angles may impose loads, roof slabs, spreading of pitched roofs, wood expansion, or retaining wall deflection. Vibration, blasting, and fire may also cause cracks. Seismic events are even the best example of the creation of cracks. Types of masonry structures include: - Arches and shells - Fireplaces and chimneys - Floors and pavements - Revetments and channels - Beams and slabs - Bearing walls and columns - Non bearing walls The type of cracked masonry units include all masonry materials, such as clay bricks, concrete blocks, stone or terra cota Cracks are located in the masonry units, in the mortar joints, between units and mortar, and continuous through units and mortar. Crack pattern are: horizontal, vertical or diagonal (typical as a result of a seismic event). If vertical, they may be straight or cogged, and, if diagonal, they may be straight or stepped. Crack smaller in width than 0,1 mm are insignificant to water permeance because that is the least width through which wind-driven rain will enter. The maximum width of a crack that will neither impact appearance nor cause alarm is said to be 0,25 to 0,35 mm. The application of horizontal bed joint reinforcement will largely contribute to the reduction of crack widths and bring them down to acceptable levels. Typical application where bed joint reinforcement have proven evidence are: - Shrinkage - Around door and window openings

4 136 The market for Murfor Reinforced masonry in Europe - Areas of differential settlements - Excessive deflection in the support - In long wall construction - Seismic constructions Problem Solution Problem Solution Problem Solution Problem Solution

5 P. Timperman 137 The amount of reinforcement required, largely depend on the materials used and type of construction type The structural applications Reinforced masonry = reinforced concrete More and more acceptance is obtained for the application of the structural use of reinforced masonry. In recent time more analysis, research and development is carried out at different universities in Europe. The main argument is the need to prove these constructions have a similar or equivalent behaviour to standard reinforced concrete or other traditional methods. The results are positive and this for a number of reasons: - Prevention of cold bridging by the use of indepently reinforced cavity leaves - Homogenous masonry work - Architectural benefits - Acceptance of the technology. - Optimal cost /performance Lintels in reinforced masonry are maybe the best example and currently represent the widest use. But also the suppression of the intermediate beams (in horizontal or vertical direction) is in some countries excellent alternatives to the standard building practice.

6 138 The market for Murfor Reinforced masonry in Europe 3. MURFOR BED JOINT REINFORCEMENT Murfor is a prefabricated reinforcement to be embedded in the horizontal joints of the masonry. Its unique shape and quality increase the tensile strength of the masonry. Murfor masonry reinforcement was first introduced into the European Market more than 35 years ago. Over this period, Murfor was developed in Belgium at a time of prolific building and changing construction methods. After de destruction as a result of the Second World War, there was an urgent need for new buildings and new industries. Priority was given to the number of buildings erected rather than n to the quality of the construction. After some years, a great number of complaints and disasters resulted from this hectic period and people became more conscious about quality. The problems caused by cracks in masonry have had a serious impact on insurance claims. 4 construction examples show the benefits of the use of Murfor: - Masonry walls subjected to excessive deformation of their supports - Masonry wall subjected to variations in moisture content and temperature - Use of Murfor in infilled masonry wall of seismic constructions - The use of Murfor as an alternative to RC beams in large walls 3.1. Murfor reinforced walls subjected to deformation of its support In 1968 the Belgian Building Research Centre, carried out a research programme in order to investigate the problem of cracking in masonry. The conclusion was that approx. 40 % of all cracks where found to have resulted from excessive deflection of slabs or beams. When the survey was repeated in the late 80 s, the proportion has dropped to less than 10 %. Excessive deformations were noticed most frequently in the case of the slabs or beams of reinforced concrete. In these cases, creep is believed to be the main cause of the deformation. Masonry walls placed on a support are rigid structures and do not easily follow the shape of a deforming support without cracking. Although important deflections can be permitted in steel structures or reinforced concrete structures from a stability point of view, these deflections may be incompatible with what is placed on them, especially if masonry is used.

7 P. Timperman 139 The likely deformation of steel or concrete structures is well known; the problem has been described in many publications. During the deformation of floors, e.g., a partition wall of masonry can only follow the deflected shaped of the floor to its limit elasticity. If the length of the wall is longer than the height of the wall, an arch can be created within the wall; As the deflection increases, cracking can occur unless the tensile strength of the masonry is improved so as to be able to resist the cracking stresses. This can be achieved by using bed joint reinforcement in the bottom layers of the masonry. The wall will act like a beam supported on two points, vertically loaded by its dead weight. If the deformation of the floor increases, the section of the wall under this arch will separate from the upper part and will follow the deflection. A horizontal crack will occur in the lower part of the wall (Fig 3), due to the tensile strength in the lower part of the wall exceeding the bond strength between the mortar and the masonry units, so that the crack will be concentrated in the mortar joint. Cracks at the top of the masonry wall may also appear due to the differentia stresses between the centre and the corners of the walls. Cracks forming in this way can be wide and very difficult to repair. Creep of the concrete may continue for a number of years and, only after this time, does the situation stabilise. Repairs carried out before the creep has stopped are likely to have little effect.

8 140 The market for Murfor Reinforced masonry in Europe The preventative solution is to use Murfor as follows: Separate the masonry wall from the bearing slab or beam with a damp proof course - Install Murfor in the horizontal joints o the masonry. The wall can as such behave like a beam, which no longer follows the movement of the floor or supporting beam, but is able to span a reinforced masonry beam. The Murfor reinforcement elements are placed in the joints of the lower part of the wall (A in fig) and reinforce the arch to prevent or redistribute the cracks Murfor reinforced masonry wall to span as a beam In practice it is advisable to reinforce the remaining part of the wall (B in figure) in order to resist the small tensile stresses that might occur. If a masonry wall is built over intermediate supports, tensile stresses will also occur in the upper part of the wall, and so Murfor reinforcement is needed both top and bottom. The area of the tensile reinforcement in the lower part of a wall can be calculated by using the formula below: As. Ys. Yf. Mk Fy.0,8 h Where: A s = Area of Murfor Y s = Partial safety factor for the tensile strength of the steel Y f = Partial safety factor for loads F y = Characteristic tensile strength of the steel M k = Characteristic value of the bending moment resulting from the self-weight of the wall spanning between its supports

9 P. Timperman Murfor reinforced walls subject to variations in moisture content and temperature All constructions materials are subject to variations in volume when their moisture content changes. For cement-based units, an increase in water content normally creates an expansion while a decrease in water content produces shrinkage of the masonry element. The resulting stresses from expansions and contractions lead to dangerous cracking. The water content in material may arise from: - The residual water content from the production process - The exterior humidity - The interior humidity in the buildings As the deformation of a wall is proportional to its length and the shrinkage coefficient, in many cases long wall lengths can produce dangerous elongations. The deformation is generally restrained at the base and sides of the wall, and so, especially at the upper side of the wall, large tensile stresses are produced. When these stresses exceed the tensile strength of the wall, cracks will occur. These cracks are normally vertical, or inclined if there are openings in the walls. In the last case, when a high strength mortar is used, the cracks may pass through the masonry units. In other cases, they will follow the mortar joints. Experience shows that these cracks are small, not generally exceeding 1 mm in width. Movement joints are a way of preventing cracking, dividing the wall into separate sections, each behaving individually. Movement joints may affect the physical qualities of the masonry, and cost money. The use of murfor-reinforced masonry is a solution. Murfor will control the tensile stresses produced by the shrinkage of the walls. The murfor will redistribute these stresses over the total wall section. The spacing of the reinforcement depends on: - The type of bricks or blocks - The wall dimension Bekaert, showing the spacing of movement joints, they are the result of research and practical experience in Europe, has produced design tables. The table below considers three different materials: - Clay bricks - Concrete blocks - Aerated concrete blocks The table contents 2 parts; wall thickness of less than 140 mm and the wall thickness over 140 mm. Additionally the amount of Murfor used in the wall is taken into account. Generally the spacing of the movement joints may be increased by 50 % to 100 % for murfor-reinforced masonry compared to non-reinforced masonry.

10 142 The market for Murfor Reinforced masonry in Europe The spacing of movement joints and amount of reinforcement to be used can be calculated by a theoretical approach from the formula s. h. t. E. ε As = 2. fy Where: As =required murfor reinforcement E = modulus of elasticity of the masonry h = wall height t = wall thickness s = reduction coefficient estimated at 0.9 ε = shrinkage factor of the masonry fy = characteristic tensile strength of the steel 3.3. Murfor reinforced infill walls for seismic constructions Recent research at the University of Pavia (Italy) has compared Murfor reinforced masonry infill walls and non-reinforced masonry walls. The objective of the research can be summarised in following points: - To compare the in plane response of unreinforced and murfor reinforced masonry infills, for different intensity level earthquakes, in order to assess the potentially different damage level attained; - To asses the potential for out of plane expulsion of unreinforced and murfor reinforced masonry infill panels, at different level of damage induced by in plane action;

11 P. Timperman To evaluate the effects of different properties of the infill on the response of buildings with different geometrical configuration and different distribution of the infill panels, in terms of PGA required to induce given level of damage In plane test results: - Unreinforced infill Murfor reinforced infill F [kn] F [kn] displacement [mm] Displacement [mm] - Out of plane results (results after in plane tests) unreinforced murfor reinforced The use of murfor reinforcement, significantly improves the response of a single infilled frame, particularly for what concern the damage limit state. The crack pattern showed clearly the benefits of the bed joint reinforcement, where more and smaller cracks appear and which as such does not influence the serviceability of the wall. After

12 144 The market for Murfor Reinforced masonry in Europe the seismic event, renovation of the wall is still possible. For the unreinforced walls, rebuilding the wall is the only solution as the cracks are too big (> 2 mm). unreinforced panel Murfor reinforced Damage representation The use of Murfor, with a geometrical percentage lower than 1 %, results in an increase of the peak ground acceleration level to g depending on the damage level Murfor reinforced large walls as alternative to the use of RC ring beams In many cases Murfor reinforced walls have been preferred against walls in which normally at regular intervals rc beams and columns are used. The main advantages are the cost and time saving (no concrete, only masonry) and homogeneity of the structure. Murfor reinforced walls acts in an identical way as walls reinforced with RC beams. Such walls can absorb important horizontal loads. (wind) The section of reinforcement needed, will depend on the type of wall, the bricks or block size and the loads to resist. The design of such wall follows strictly the recommendations of the EC 6 Masonry codes.

13 P. Timperman 145 Recently the new Auditorium in Rome (Italy) designed by Arch. Renzo Piano was fully constructed in reinforced masonry, skipping the RC beams and increasing the span between columns to 24 m. Arch Renzo PIANO Auditorio di ROMA Italy Music center - 3 theatres Walls dimensions = 24 m x 7m

14 146 The market for Murfor Reinforced masonry in Europe 4. MURFOR PRODUCT APPROVALS AND SPECIFICATIONS 4.1. Approvals Murfor bed joint reinforcement is in accordance with the EN Ancillary components for masonry structures. As such it is in line for design and calculations as specified in EC-6: design of masonry structures. Murfor has been approved in different markets: e.g. Belgium ATG 1973 The Netherlands KOMO 28018/98 France Socotec BX 1030 Socotec BX 1438 Germany Z Norway NBI-2046 Sweden TG Demand for approbation has been introduced for Portugal at LNEC : 06/ Specifications Murfor reinforcement is a flat wire meshwork consisting of two parallel longitudinal wires which are welded together by means of a continuous diagonal wire, in such a way that the overall thickness of the wire meshwork does not exceed the diameter of the longitudinal wires. The quality of the steel used complies with the requirements according EN This means that the wire has a tensile strength of at least 550 N/mm² and yield strength of min 500 N/mm 2. The shear resistance of the welds is min 2500 N. Both longitudinal wires are indented so as to ensure a good bond with the mortar The product is available in different shapes, coatings and dimensions, depending the application with mortar or thin bed joints.

15 P. Timperman 147 Mortar joints: Murfor with round wires of dia 4 or 5 mm, available in widths ranging from 30 mm till 280 mm. The standard length is 3050 mm Available in galvanized, galvanized + epoxy and stainless steel Thin bed joints Murfor with flat wires, which allows an overall bed joint thickness of < 3 mm The products are available in widths 40, 90, 140, 190 mm and a standard length of 3050 mm Available in galvanized and stainless steel 5. CONCLUSIONS Reinforced masonry is already a widely used and experienced construction technique applied in many countries in Europe. Experience over the last 35 years show that masonry structures with Murfor offers an economical and technical benefit for the construction market. Over the years it has been proven that the damage levels, especially as far as cracking is concerned, are considerably reduced. The reinforced masonry technology offers the architect and designers more possibilities, which in many cases is equivalent to reinforced concrete structures. 6. BIBLIOGRAPHY [1] G. Vandeloock : Test on reinforced brick masonry in Belgium 1979 [2] P. Timperman : Murfor Reinforcement for Masonry 1996 [3] P. Timperman, T. Rice : Bed joint reinforcement in Masonry 1999 [4] P. Timperman : Murfor : La maçonnerie armee 1999 [5] St. Schaerlaekens, La maçonnerie armee CSTC 2001 [6] O. Pfeffermann, B. Haseltine, P. Timperman: The use of Murfor reinforced masonry to prevent cracking problems: 25 Years of experience [7] G.M. Calvi, D. Bolognini : Seismic response of reinforced concrete frames infilled with murfor masonry panels Pavia 1999 [8] G.M. Calvi: Reinforcement in seismic design of masonry structures Pavia 1999

16 148 The market for Murfor Reinforced masonry in Europe [9] EN : ancillary components [10] Pr EN : Eurocode 8 Design provisions for earthquake resistance of structures part 1-3 : General rules Specific rules for various materials and elements [11] Pr EN : Eurcode 6 : Design of Masonry structures [12] Part 1-1: Common rules for reinforced and unreinforced masonry structures