ANALYTICAL AND EXPERIMENTAL BEHAVIOR OF UNSTRENGTHENED MASONRY ARCHES

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 4, April 2017, pp , Article ID: IJCIET_08_04_105 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed ANALYTICAL AND EXPERIMENTAL BEHAVIOR OF UNSTRENGTHENED MASONRY ARCHES Zaid Bin Nissar Student M.Tech Structural Engineering, SRM University, Kattankulathur, Tamilnadu, India M. Prakash Assistant Professor, Department of Civil Engineering, SRM University, Kattankulathur, Tamilnadu, India ABSTRACT Among different structural systems arches are the most efficient forms which are mainly used in buildings and bridges. The behavior of arches usually depends on characteristics based on geometry of the structures, viz. span, thickness, rise and width, types of loading, materials used for the construction, and support conditions. This paper deals with the experimental and analytical behavior of unstrengthened brick masonry arch having dimensions of span of 1m, rise of 0.4m,1.2m and 1.5m, rise of 0.5m respectively. Scaled modeled of masonry arch were subjected to point load and is tested under displacement control upto failure and then arches were analyzed by using ANSYS. Key words: Masonry Arch; Fibre reinforced; local failure; intrados; extrados; Vaults. Cite this Article: Zaid Bin Nissar and M. Prakash, Analytical and Experimental Behavior of Unstrengthened Masonry Arches. International Journal of Civil Engineering and Technology, 8(4), 2017, pp INTRODUCTION An arch is a mechanical arrangement of wedge shaped blocks of bricks or stones supporting each other and supported at the end by abutments.[1] It is actually an arciform which is not really known for their load bearing capability but has an aesthetic, historic, cultural and architectural importance. On synonymous terms arches are often referred to as vaults but a vault is different from an arch as it is a continuous arch which resembles a roof. The history and appearance of arches dates back to 2 nd millennium (B.C) Mesopotamia as brick architecture and their efficient and methodic adoption started in Ancient Rome where they applied the technique to a wider range of architectural masterpieces. Arches are known to have lesser tensile strengths and to eliminate the stress it spans over a large area and resolves the forces in such a way that the tensile stress is relieved. This is often called as arch-action editor@iaeme.com

2 Analytical and Experimental Behavior of Unstrengthened Masonry Arches As the force is applied on the arch towards the ground, there is a resultant outward push at the base by the arch referred to as thrust. As the height of the arch decreases, the thrust increases outwards[2]. To prevent the collapse of the arch we need to arrest the thrust action either by internal ties else external bracing, for example by using abutments. Such a structure (arch) is said to be in the form of pure compression and the building materials of an arch like stone and concrete (unreinforced) are able to resist the compression but not tensile stress. The weight of all the constituents is responsible to hold the arch in place, making it problematic to construct an arch. One of the solutions is to construct a frame prior to the construction of an arch resembling exactly the underside of the arch, commonly known as the centering. Until the structure is self-supporting and accomplished Voussoirs are used on it and scaffolding is done for the arches that are higher than the head-height in combination with the structure support. At times the arch would fall down if the frame was dislodged or if the construction be been faulty, as it happened to the A85 Bridge at Scotland in 1940 s on its very first attempt. The interior curve of an arch is called as intrados. The old arches often need reinforcements because of the decay of keystones, forming bald arches[3]. The main principle used in the construction of reinforced concrete arches is the strength and stability of the concrete, resisting stress of compression. If the tensile stress or any other kind of stress is increased, the resistance is to be increased by placing reinforcement-rods or reinforcement fibers. With the advancement of the world new methods have been developed to increase the stability and strength of the arches or vaults. The most common and efficient method being the one using fiber-reinforced polymer (FRP) which makes use of various polymers like glass, polyvinyl alcohol, carbon etc. fixed in a polymeric matrix. The wide range use of FRPs owes to the fact that their specific weight is negligible, immunity towards corrosion, higher tensile strength, convenient to use and their flexibility[4]. Nowadays research is being done to understand the masonry vaults strengthened by CFRPs (carbon FRPs) and GFRPs (glass FRPs) used on the interior or outer surfaces of the arch. Epoxy adhesives are being used for multilayer adhesions that provide homogenous support for the fibers. Ferit Cakir et al (2014)[5] they worked on the strengthening of arches by using Prepreg composites(which consists of a matrix and the reinforcement material ) which was impregnated with a polymer. Graphene nanoplatelets were mixed with epoxy to get a modified matrix. They concluded that the tensile strength of GRP composites is higher than the tensile strength of unreinforced prepreg composites. Daniel V. Oliveira et al (2010)[6] they concluded that strengthening applied at the intrados is the best way of strengthening the masonry arches and strengthening the extrados provides the higher deformation capacity of the arches. They also concluded that continuous strengthening methods are able to prevent the typical local failure mechanisms of unstrengthened arches. S. Briccoli Bati et al (2007)[7] a comparison was made between two different composite material (CFRP and GFRP) and the arches were strengthened with these composite materials and the two kinds of strengthening showed different collapse mechanism. GFRCM model showed a fracture pattern that affected the wall, while CFRP model arch showed changed behavior of the original structure. 2. BEHAVIOR AND FAILURE OF UNSTRENGTHENED MASONRY ARCHES The durability and invulnerability of masonry arches depends on its geometry and on the standardized constituents used to build them. The tensile strength of the masonry structures is known to be negligible. Thus the condition for the safety of the arches can be achieved by inducing compression on it until the thrust-line coincides with polygon made by joining the editor@iaeme.com

3 Zaid Bin Nissar and M. Prakash points of thrust inside the structure[8]. When excess thrust is applied on the arch the resultant forces start to move outside the arch. As long as the line of thrust is kept inside the core of the arch the safety of the structure is maintained. After certain point when the load is increased on the arch, the resultant moves outwards and the structure develops a crack near the crosssection and hinge formation takes place at the interior or the exterior boundary of the arch. Formation of consecutive number of hinges eventually leads to the failure of the arch due to the augmentation of hinge based mechanism. The following Fig 1 shows the collapse mechanism of unstrengthened arches when applied to point load. Figure 1 Line of Thrust and Collapse Mechanism of Unstrengthened Arch Subjected to Point Load 3. OBJECTIVE The main objective of this research is - To study Experimental Behavior of circular arch subjected to monotonic loading. To study Analytical Behavior of circular arches using ANSYS workbench. To compare the results between experimental and analytical results. 4. MATERIALS AND METHODS 4.1. Preparation of Masonry Arches Arches which have spans in excess of 6 feet or whose rise to span ratio is greater than 0.15 are called Major arches. A wooden mould for the arches was prepared of different dimensions circular arches of three models were created having dimension of span 1000mm, rise 400mm, thickness of 500mm. Second arch having span of 1200mm, rise 500mm, thickness 500mm. Third arch having span of 1500mm, rise of 500mm, thickness of 500mm were build from bricks and mortars. In this study, solid clayey first class bricks of dimension (22.5 x11x 7.5 cm 3 ) and mortar of mix ratio of 1:3 was used throughout the arches. 5. MECHANICAL CHARACTERIZATION OF THE MATERIALS The mechanical characteristics of the brick and cement mortar used in the arch models were determined. The masonry bricks and mortar (at 28 days) were subjected to compression tests in order to determine the mechanical properties. The mortar mixture consisted of one part of cement and three parts of sand. The compressive strengths for the bricks were obtained from UTM (Universal testing machine) as well as on cube specimens of cement mortar. The cube specimens (70.6 x 70.6 x 70.6 mm 3 ) of 3 were casted and tested after 28 days of curing. An average compressive strength of brick was found out to be 105 kg/cm 2 and for cement mortar editor@iaeme.com

4 Analytical and Experimental Behavior of Unstrengthened Masonry Arches an average compressive strength of 35 N/mm 2 was found. Elastic modulus of mortar and brick was found to be 3750MPa and 2289MPa and Water absorption of bricks was found out to be 9%. As per IS if bricks are submerged in water for 24 hours its weight should not be more than 20% of its own dry weight. 6. EXPERIMENTAL INVESTIGATION 6.1. Tests on Arches The Geometry for the arch is shown in fig.the arch of 1m span was fabricated with 22 bricks courses and characterized by a 513mm internal radius, rise 400mm, width 500mm and 110mm thickness. All arches were built over a rigid wooden mould and using two brick blocks fixed to the strong floor as supports. In this way the arch resulted in segmental arch of o and similarly the second arch of 1.2m arch was fabricated with 42 bricks, characterized by a 610mm internal radius, 500mm rise and width and thickness of 110mm which resulted in the segmental arch of and third arch of 1.5m span was fabricated with 50 bricks and characterized by 812.5mm internal radius, rise 500mm, width 500mm and 110mm thickness. The wooden mould was removed after 1 week of casting. The Load was applied in the centre of the arch and the parameters for the arch were checked. Figure 2 Adopted arch Geomerty and load arrangements (Font view) (A) editor@iaeme.com

5 Zaid Bin Nissar and M. Prakash (B) Figure 3 Two of the phases involved in the construction of the arches Laying of bricks; (b) removal of the wooden mould 7. TEST SETUP All specimens were loaded in the frame as shown in the fig 4. A proving ring was used to measure the load applied to the arch and the dial gauge was used to measure the deflection which was placed under the arch in the centre. The load was applied gradually by rotating the rod which transferred the pressure on the proving ring and then to the arch. (A) (B) Figure 4 (A) Frame for the Arch; (B) Experimental set up 8. ANALYTICAL INVESTIGATION With the help of ANSYS WORKBENCH 3D models of three different dimensions were created[9]. According to [10] Young s modulus for the composite material (Brick + Mortar) could be obtained by using homogenization procedures as follow [10]: editor@iaeme.com

6 Analytical and Experimental Behavior of Unstrengthened Masonry Arches In this formula t m and t b are the thickness of mortar and brick, E m and E b are the Young s modulus of mortar and brick respectively. p represent the efficiency factor. In addition Poisson ratio was also included. In this study t m =10mm, t b =110mm, Em=3750Mpa, E b =2289Mpa and p=0.5. According to formula Young s Modulus was calculated as 1183Mpa. In addition Poisson ratio was OBSERVATION AND TABULATION 9.1. Experimental Analysis All the specimens were tested which presented a similar structural behavior, essentially characterized by the development of a three hinge mechanism. Fig 1 illustrates the location of the three hinges. The Parameters for the arches were checked. The major areas of interest are load deflection characteristics of the specimen and the mode of failure Load Deflection Behavior Fig 5 shows the combined load-deflection results for all the arches tested. An ultimate load of 10kN was achieved for 1m span of arch and for 2 nd arch of dimension 1.2m an ultimate load of 8kN was achieved with max deflection of 0.42mm and for 3rd arch of dimension 1.5m an ultimate load of 6.6kN was achieved with max deflection of 0.41mm. Load v/s Deflection Load kn Deflection mm 1 meter arch 1.2m arch 1.5 arch ultimate Figure 5 Combined Load Deflection curve for the arches Mode of Failure Failure is defined as the point when the specimen can no longer bear the load and the specimen collapses. The arches failed at three points which is shown in the fig 6. The arches showed a similar failure pattern for other arches editor@iaeme.com

7 Zaid Bin Nissar and M. Prakash Figure 6 Mode of failure of arch 9.2. Analytical Work With the help of ANSYS WORKBENCH 3D models of three different dimensions were created. Load v/s deflection was found out. Below fig s show the finite element modeling for 1m, 1.2m, 1.5m arch span and their corresponding deformation. Figure 7 Ultimate Deflection for 1m Arch span using ANSYS (a) (b) Figure 8 (a) Ultimate Deflection for 1.2 m Arch (b) 1.5m Arch span using ANSYS editor@iaeme.com

8 Analytical and Experimental Behavior of Unstrengthened Masonry Arches Load v/s deflection Load kn M ARCH 1.5 M ARCH 1M ARCH Deflection mm Figure 9 Combined Load Deflection curve 10. COMPARISON BETWEEN EXPERIMENTAL AND ANALYTICAL A comparison was made between experimental and analytical values and the graphs were plotted between load v/s deflections. 12 Load v/s deflection for 1m Arch 10 Load kn experimental value analytical value Deflection mm Figure 10 Comparison of load v/s deflection plot for 1m arch Load v/s Deflection for 1.2m Arch 10 load kn experimental value analytical value Deflection mm Figure 11 Comparison of load v/s deflection plot for 1.2m arch editor@iaeme.com

9 Zaid Bin Nissar and M. Prakash Load kn Load v/s Deflection for 1.5m Arch Deflection mm experimental values analytical data Figure 12 Comparison of load v/s deflection plot for 1.5m arch 11. CONCLUSION Based on the experimental and analytical investigation, it can be concluded that, An average compressive strength of brick was found out to be 105 kg/cm 2 An ultimate load carrying capacity of 10kN was achieved for 1m arch, 8kN for 1.2m arch, and 6.6 kn for 1.5m arch. Max deflection experimentally and analytical were 0.46 mm and 0.41mm, for 1m arch, 0.42mm and 0.47mm,and for 1.5m arch 0.41mm and 0.53mm respectively Mode of failure of given arch was observed three hinge for all the arches. Stiffness of the arch for experimental test and analytical test was found out to be 21.7 kn/mm and 24.3 kn/mm for 1m arch span Stiffness of the arch for experimental test and analytical test was found out to be kn/mm and kn/mm for 1.2m arch span Stiffness of the arch for experimental test and analytical test was found out to be kn/mm and kn/mm for 1.5m arch span. Stiffness of the arch decreases with increase in span of the arch. It is concluded both by experimentally and analytically, that with increase in span, ultimate load carrying capacity of the arch decreases and vice versa. REFRENCES [1] V. Alecci, G. Misseri, L. Rovero, G. Stipo, M. De Stefano, L. Feo, and R. Luciano, Experimental investigation on masonry arches strengthened with PBO-FRCM composite, Composites Part B, vol. 100, pp , [2] S. B. Bati, L. Rovero, and U. Tonietti, Strengthening Masonry Arches with Composite Materials, vol. 11, no. 1, pp , [3] M. A. Bradford and B. Uy, Concentrated Load, vol. 128, no. 7, pp , [4] L. Garmendia, I. Marcos, E. Garbin, and M. Rosa, Strengthening of masonry arches with Textile-Reinforced Mortar : experimental behaviour and analytical approaches, pp , editor@iaeme.com

10 Analytical and Experimental Behavior of Unstrengthened Masonry Arches [5] F. Cakir and H. Uysal, Experimental modal analysis of brick masonry arches strengthened prepreg composites, Journal of Cultural Heritage, pp. 1 9, [6] D. V Oliveira, D. Ph, I. Basilio, D. Ph, P. B. Lourenço, and D. Ph, Experimental Behavior of FRP Strengthened Masonry Arches, vol. 14, no. June, pp , [7] S. Briccoli and B. Æ. Luisa, Towards a methodology for estimating strength and collapse mechanism in masonry arches strengthened with fibre reinforced polymer applied on external surfaces, pp , [8] A. D. Ambrisi, L. Feo, and F. Focacci, Masonry arches strengthened with composite unbonded tendons, Composite Structures, vol. 98, pp , [9] F. Cakir, Determination of dynamic parameters of double-layered brick arches, vol. 67, pp , [10] F. Cakir, H. Uysal, and V. Acar, Experimental modal analysis of masonry arches strengthened with graphene nanoplatelets reinforced prepreg composites, Measurement, vol. 90, pp , editor@iaeme.com