design of masory structures vs design of concrete-framed structure for residential building of...

1.0 INTRODUCTION1.1 Background1.1.1 Brief history of masonry structure and reinforced concrete- framed structure design Masonry structure has been used as structure since man began building buildings. It was traditionally very widely used in civil and structural works including tunnels, bridges, retaining walls and sewage system however, the introduction of steel and concrete with their superior strength and cost characteristics led to a sharp decline in the use of masonry for their application. Over the past two decades or so, masonry has recaptured some of the market lost to steel and concrete due largely to the research and marketing work sponsored in particular by the brick development association. For instance, everybody now knows that brick is beautiful, less well appreciated. Perhaps, is the fact that masonry as excellent structural, thermal and acoustic properties. Furthermore, the permanence of masonry construction is illustrated in the many structures remaining from the days of the Greeks and romance, who were primarily masonry builders. The famous Pout de Crard, an aqueduct built across the Gard River near Nirues, France, and about 17miles from Avignon. It was built about 15 B.C and was laid without mortal, that is very hard and a fair condition well preserved cement concrete bridge along the famous Amalfi Drive in Italy, near Naples, built in about the 6th century AD, well illustrates the durability of this type of construction.Even in prehistoric times, the prototypes of our masonry structures were found in the crude dolmens and cromlechs of barbarous man. These consisted of unshaped stones set as column and partial walls and covered with a slab(s) of stones without any attempt attaching one to the other. Mortar was, of course, unknown, but piles of stone with huge natural slabs of stones spinning the intervals are to be found in the ruins at maidstone and stone henge, England, and at various other places in Europe. Gradually, those simple elements of support and cover were improved.

Perhaps, the most significant development in masonry construction was the introduction of reinforced concrete, by which masonry could be made to withstand tensile stress comparable with its compressive strength. The first authentic record of the use of reinforced concrete was at the worlds fair at Paris in 1855, when a small rowboat built by M. Lambot of mortar reinforced with wire netting was on exhibition, however, iron bars were used at least a century earlier by Architects in Italy for reinforcing the molded statuary in pertes and gardens (e.g. statuary groups in ville d` Este at Tivoli). In 1865, Francois Coignet explained the principles of reinforcing beams, slabs, arches, etc. and in 1869 took out patents on the process. In the same year, F. Joseph Monier took out patents covering many of the details of this new form of construction, and he has sometimes been called the father of reinforced concrete.

1.1.2 Typical masonry structure and reinforced concrete frame structure model

Fig 1.0 Typical masonry structure of medium height under construction

Fig.1.1: Typical reinforced concrete framed structure of medium height under construction1.2 Justification and scope of the project1.2.1 This project primarily deals with comparison in design of masonry structure and concrete-framed structure of residential building of medium height. The British standard, BS 5628, part 1-3 gives the design approach for structural use of unreinforced masonry, reinforced and prestressed masonry, and materials and components, design and workmanship of masonry structure. While the BS 8110, 1987, part 1-3 gives the design approach to structural design of reinforced concrete i.e. concrete framed -structure. However, a structural model is selected and designed to meet these codes of practice for masonry structure and concrete- framed structure of residential building of medium height. Separately and a comparison due to some certain conditions will be justified.In general, the choice of type of structure as well as the general features of the design will be determined, provided the structure has met the fundamental requirements of basis of design, by the following considerations:(i) Adequacy(ii) Stability(iii) Performance of function(iv) Economy (a) initial cost (b) relative performance (c) maintenance cost(v) Aesthetics (a) harmony (b) proportion (c) ornamentation.The scope of the project work will be on a five (5) storey building structure design with masonry structure approach and concrete frame structure, separately and compare in the course and is limited to five storey building where lateral loads are relatively small and must be designed accordingly. The structural model has regular layout and are regular in shape, and is idealized in 2- dimensional frames arranged in the orthogonal dimensions.1.3 Objectives The scopes of the project are to: Analyze the structural model of a five storey structure Design the structure as masonry structure and concrete-framed structure of a residential building of medium height and ensure that requirements are adequate and, Make a comparison of the design approaches and output. The project objectives are completed by analyzing the structural model by determining of forces and deformation of the structures due to applied loads, designing the models which involves the arrangement and proportioning of the structures and their components in such a way that the assemble structure is capable of supporting the designed loads within the allowable limit states and comparing the design output to determine the main factor that influence the choice.1.4 ContributionsThe project summarizes design practices for masonry structure and concrete framed structure of a medium height residential building. The project gives a summary of masonry structure design and concrete framed structure of medium height codes and literatures and also provides a comparison between the different approaches requirements of same structural model. Structural analysis solutions created as part of the project simplifies the design and provides clear graphical output to the design and the different in the design approaches is clarified. 1.5 Organization of project The remaining portion of the project is separated into five chapters. First a literature review (chapter 2) of masonry structure and concrete framed structure of medium height residential building and design codes, and structural models are presented. The variation found in literature discussed.A statement of the problem is presented in chapter 3. Flow charts and the program to check the analysis for the flexural, shear and probably personal analysis of concrete frame structure is presented here (chapter 3) and validate comparison of the output to existing data is given. Chapter 4 summarizes the theory conducted and analysis model for the structure, load estimation and sizing of members, mix design concrete mix/strength is discussed and modeling of the structure into masonry and concrete framed structure. Flow charts and the program to check the analysis for the flexural, shear and probably personal analysis of concretes frame structure is presented here (chapter 4) and validity comparison of the output to existing manual calculation date is given. The design of the structure i.e. masonry structure and the concrete framed structure of residential medium height structure is discussed and the structural detailing of the important section also shown. The results and discussion of the design and the comparison of it are discussed in chapter 5, also the suitability of each structure is also presented.The conclusion and recommendations are presented in chapter 6. Appendices are also attached which explains some terms as well as the analysis and design calculation sheet of relevant structures.

2.0 LITERATURE REVIEW2.1 Literature review on masonry structures design Publication and papers related to the design of masonry structures (reinforced masonry) severally fall into the following categories: analysis techniques (typical chapter bending capacity) design of the structure and general detailing of the masonry structure. Reinforced masonry design as we know it today is rather recent. The principles of reinforced masonry construction are said to have been discovered by Marc Isambard Brunel, once a chief engineer for New York City, a great innovator, and one of the greatest engineers of his time. In 1813, he first proposed the use of reinforced masonry as a means of strengthening a chimney, then under construction. However, his first major application of reinforced masonry was in connection with the building of the themes tunnels in 1825. As a part of this construction project two bricks shafts were built, each 750mm thick, 15m diameter and 21m deep. These shafts were reinforced vertically with 25mm diameter. Wrought iron rods, built into the brickworks. Iron hoops, 225mm wide and 12mm thick were led in the brickwork as construction progressed. However, the genesis of the provisions for the strength design of reinforced masonry as specified in the MSJC code can be traced technical report No 4115 titled strength design of one-to-four storey concrete masonry building published by the ICBO in February 1984. This report had gone through several independent reviews before and after publication. Following the reviews, the report was received in February 1985, for two more years. Therefore, analysis and design of reinforced masonry structure is improving with the review of technical papers report on reinforced masonry structure from different professionals in the field and standardization comes up thereafter.

2.1.1 LITERATURE REVIEW ON CONCRETE STRUCTUREFrancois Marte Le Brun built a concrete home in 1832 in Moissac in which he used reinforced concrete arches of 5.4m span. He used concrete to build a school in St. Aignan in 1834 and a church in Conbariece in 1835. Joseph Louis Lambot exhibited a small rowboat made of reinforced concrete at the Paris exposition in 1854. In the same year, W.B Wkinson of England obtained a patent for a concrete floor reinforced by twisted cables. The Frenchman Francois Cignet obtained his first patent in 1855 for his system of iron bars, which were embedded in concrete floors and extended to the supports. One year later, he added nuts in the screw ends of the bars, and in 1869, he published a book describing the applications of reinforced concrete. Joseph Monier, who obtained his patent in Paris on July 16, 1867, was given credit for the invention of reinforced concrete. In 1873, he registered a patent to use reinforced concrete in tanks and bridges, and four year later, he registered another patent to use it in beams and columns.In the United States, Thaddeus Hyatt conducted several test on 50 beams that contained iron bars as tension reinforced and published the result in 1877. He found out that both concrete and steel can be assumed to behave in a homogeneous manner for all practical purpose. This assumption was important for the design of reinforced concrete members using elastic theory. He used prefabricated slabs in his experiments and considered prefabricated units to be best cost in T-section and placed side by side to form a floor slab. Hyatt is generally credited with developing the principles upon which the analysis and design of reinforced concrete are now based.A reinforced concrete house was built by W.E. Ward near Port Chester, New York, in 1875. It used reinforced concrete for walls, beams, slabs and staircase. P.B. Write wrote in the American Architect and building news in 1877 designing the applications of reinforced concrete in Wards house as a new method in building constructs.

E.L Ramsome, head of the Concrete Steel Company in San Francisco used reinforced concrete in 1879 and deformed bars for the first time in 1884. During 1889 to 1891, he built a reinforced concrete bridge in San Francisco.

2.1.1 Field behavior of masonry structure and concrete frame structureMarc Isambard Brunel (1813), a chief engineer of New York City studied the performance of masonry structure and is provided by gravity, because masonry is weak in tension, no tension can be allowed to develop at the back of the structure. This requires unreinforced masonry structures to be sufficiently massive (meaning large base width) that the resultant of all forced acting on the structure does not fall outside the middle third of the base. This requirement imposes an economic limit on the height of the masonry structures that can be built. Furthermore, slender structure proved incapable of withstanding lateral loads due to earthquakes as demonstrated by damage during seismic events. In many countries throughout the world, such as India, China, Iran, Mexico, the former USSR, and Turkey to name a few extensive damage and collapse of masonry structure during earthquakes continue to demonstrate the web for a better experience construction. Reinforced masonry provided the required answer, and thus began the present day engineered-masonry construction, which uses methods completely different from the empirical methods of the past was once evolved as merely mason`s creations came to be designed and built as engineered structures. While the concrete-framed structure of medium height.

2.1.2 Material for masonry structure Bricks, Blocks and Mortars for masonry structureBrick is classified as a masonry unit with dimensions (mm) not exceeding 337.5 x 225x112.5 (L.W.T). Any unit with a dimension that exceeds any one of those specified above is termed a block. Blocks and bricks are made of fired clay, calcium silicate or concrete which must conform to relevant national standards, for example BS3921 (clay units), BS187 (calcium silicate) and BS6073 part 1 (concrete units). In these standards two classes of bricks are classified, namely common and facing, BS3921 identifies a third category, engineering. There are varieties of bricks i.e. bricks may be wire cut, with or without perforations, or pressed with single or double frogs or cellular. Perforated bricks contain holes; the cross sectional area of any one hole; the cross sectional area of any one hole should not exceed 10% and the volume of perforation 25% of the total volume of the bricks. Cellular bricks will have cavities or frogs exceeding 20% of the gross volume of the brick. In bricks having frogs the total volume of depression should be less than or equal to 20%.Bricks of shapes other than rectangular prisms are referred to as Standard special and covered by BS 4729. Concrete blocks may be solid, cellular or hollow from the structural point of view, the compressive strength of the unit is the controlling factor. For reinforced and prestressed brickwork, it is highly unlikely that brick strength lower than 20N/mm will be used the design and construction.

2.1.3 Material for concrete-framed structureConcrete mixes for reinforced framed structureDilger, Ghali and Rao (1996), Dilger and Rao (1997), and Wang, Dilger, and Kuebler (2001) determined that special mix designs were required for masonry and concrete framed structure. It was found that normal concrete mixes would have segregation problem due to the spinning process and the dry or coarse mixes would not consolidate properly. Drying shrinkage, freeze thaw, chloride penetration, mix proportions and mixing time, spinning speeds and duration were all investigated. The spinning process seemed to be the cause of differential shrinkage due to the segregation of fines from the coarse aggregate. Differential shrinkage between the inner and outer layers was linked to the longitudinal cracking of concrete structure causing deterioration, reduction in strength, and reduces life expectancy. Longitudinal cracking was noted as a typical problem with concrete framed structure in service. To eliminate segregation and therefore significantly improve the strength and durability of concrete frame structure, special mix design was suggested. A mix design suggested for use in production by Wang, Dilger and Kuelber (2001) had the following components : 1255kg/m coarse aggregate, 650kg/m sand, 341kg/m cement, 34kg/m silica fume, 9.5L of plasticizer, 1.5L of air entraining agent (5.5%) and 115kg/m water.

2.1.4 Published guides and specification for masonry structure and concrete framed structure design of medium height 2.1.4.1 Guide specification for masonry structure designThe guide for the design of masonry structure published by the concrete centre provides the two most common forms of multi-storey masonry construction as crosswall and cellular construction which can show as much as 10% reduction in cost. 2.1.4.2 Guide specification for concrete framed structure of medium heightThe guide for concrete framed structure published by the concrete centre adds additional information to the specification published by BS 8110. The guide gives useful enough to be referred to whenever new design is being considered, and comprehensive enough to give references to where more information could be found. The guide sits alongside our Economic Concrete Frame Elements. The guide is intended for use by structural designer.No formulae or design recommendations are given for sustainability but sustainability is becoming more and more of an issue in todays world. The guide believes that concrete can help provide a sustainable solution to the changing climate, through the use of its high thermal mass.3.0 STATEMENT OF THE PROBLEM AND MATERIALS PROPERTIES3.1 Statement of the problemIn order to provide excellent building structure at a minimal cost, good thermal and acoustic insulation, fire and weather protection, durability and wall finishes of every acceptable appearance. However, this project work is directed to the comparison of the design of masonry structure versus the design of concreteframed structure for residential building of medium height; say five (5) storey building. Ideally, the mission of the project work is to choose a structural model, allocating one for the masonry structure and the other for concrete framed structure, both having a fixed dimension of the total girth, storey height and equal headroom in both structure and then analyze the structure and carry out the design of the structural members on selected approaches based on stated codes of practice i.e. BS 5628 part 1 & 3 and BS 8110 part 1-3 respectively.The suitability of each design output is then compared based on those options stated above. In spite of the type of the designed structure that meets all the listed options, if we continue to do the design of the structure the does not provide these required options, they will not only be wasting of time and money, which jeopardizes their overall efficiency. 3.2 Material properties3.2.1 ConcreteConcrete is arguably the most important building material, playing a part in all building structures. Concrete is a mixture of cement, water, and aggregates. It may also contain one or more chemical admixtures. Within hours of mixing and placing, concrete sets and begins to develop strength and stiffness as a result of chemical reactions between the cement and water. These reactions are known as hydration .Calcium silicates in the cement react with water to produce calcium silicate hydrate and calcium hydroxide. The resultant alkalinity of the concrete helps to provide corrosion protection for the reinforcement.In order to alter and improve the properties of concretes, other cementious materials may be used to replace part of the Portland cement, e.g. fly ash, natural pozzolans, blast furnace slag, and condensed silica fume. The ratio of water to cement by weight that is required to hydrate the cement the cement completely is about 0.25, although larger quantities of water are required in practices in order to produce a workable mix. For the concrete typically used in structural concrete structure, the water-to-cement ratio is about 0.4.It is desirable to use as little water as possible, since water not used in the hydration reaction causes voids in the cement paste that reduce the strength and increase the permeability of the concrete. The use of chemical admixture to improve one or more properties of concrete is now in commonplace. In recent year, high strength concrete with low water-cement ratios has been made more workable by the inclusion of superplasticizer in the mix. These polymers greatly increase the flow of the wet concrete and allow very high strength, low permeability concrete to be used with conventional concrete construction techniques.3.2.2 Mortar Masonry mortal is a versatile material capable of satisfying a variety of diverse requirements. It is one of the main constituents of a constructed masonry structure. Mortar is required to lay masonry units. As such, it must facilitate the placement of units, contribute to the serviceability of masonry structure, provide structural performance, and exhibit the desired appearance.Mortar consists of cementitious materials to which are added water and approved additives so as to achieve workable plastic consistency. The cementitious materials may be lime, masonry cement, mortar cement, and Portland cement, and should not contain epoxy resins and derivatives, phenols, asbestos; fiber or fireclays. The mortar should be able to resist the water uptake by the absorbent bricks/blocks, e.g. by incorporating a water-retaining admixture and/or use of a mortar type that includes lime, otherwise hydration and hence full development of the mortar strength may be prevented. The mortar must also be durable. For example, if masonry remains wet for extended periods of time the mortar may be susceptible to sulphate in clay masonry units, the ground water or the soil. Masonry mortar is also susceptible to freeze/thaw attack, particularly when newly laid, which can adversely affect bond strength. It should be remembered too that the appearance of mortar is also important and that it should be in harmony with the masonry unit. In its most basic form, mortar simply consists of a mixture of sand and ordinary Portland cement (OPC). However, such a mix is generally unsuitable for use in masonry (other than perhaps in foundations and below damp-proof courses) since it will tend to be too strong in comparison with the strength of the bricks/blocks. It is generally desirable to provide the lowest grade of mortar possible, taking into account the strength and durability requirements of the finished works. 3.2.3 Bricks and BlocksBrick is defined as a masonry unit with dimensions (mm) not exceeding 337.5 x 225 x 112.5 mm (L x w x t). Any unit with a dimension that exceeds any one of those specified above is termed a block. Bricks are manufactured from a variety of materials such as clay, calcium silicate (lime and sand/flint), concrete and natural stone. Of these, clay bricks are by far the most commonly used in Nigeria.Clay bricks are manufactured by shaping suitable clays to units of standard size, normally taken to 215 x 102.5 x 65 mm. Sand facings and face textures may then be applied to the green clay. Alternatively, the clay units may be perforated or frogged in order to reduce the self-weight of the unit. Thereafter, the clay units are fired in kilns to a temperature in the range 900-1500 C in order to produce a brick suitable for structural use. The firing process significantly increases both the strength and durability of the units. In design it is normally to refer to the coordinating size of brick. This is usually taken to be 225 x 112.5 x 75 mm and is based on actual or work size of the brick, i.e. 215 x 102.5 x 65mm, plus an allowance of 10mm for the mortar joint. Clay bricks are also manufactured in metric modular format having a coordinating size of 200 x 100 x 75mm. Other cuboids and special shapes are also available (BS 4729).These must conform to relevant national standards i.e. BS 3921 (clay units), BS 187 (calcium silicate) and BS 6073: Part 1 (concrete units). In these standards two classes of bricks are identified, namely common and facing; BS 3921 identifies the third category, engineering: Common bricks are suitable for general building work. Facing bricks are used for exterior and interior walls and available in a variety of textures and colours. Engineering bricks are dense and strong with defined limits of absorption and compressive strength.Blocks are walling units but, unlike bricks, are normally made from concrete. They are available in two basic types: aircrete and aggregate concrete. The aircrete blocks are made from a mixture of sand, pulverized fuel ash, cement and aluminium powder. The latter is used to generate hydrogen bubbles in the mix; none of the powder remains after the reaction. The aggregate blocks have a composition similar to that of normal concrete, consisting chiefly of sand, coarse and fine aggregate and cement plus extenders. Aircrete blocks tend to have lower densities (typically 400-900 kg/m) than aggregate blocks (typically 1200-2400 kg/m) which accounts for the formers superior thermal properties, lower unit weight and lower strengths.Blocks are manufactured in three basic forms: solid, cellular and hollow. Solid blocks have no formed holes or cavities other than those inherent in the material. Cellular blocks have one or more formed voids or cavities which do not pass through the block. Hollow blocks are similar to cellular blocks except that the voids or cavities pass through the block. The percentage of formed voids in blocks and formed voids or frogs in bricks influences the characteristic compressive strength of masonry.For structural design, the two most important properties of blocks are their size and compressive strength. The most commonly available sizes and compressive strengths of concrete blocks in Nigeria is 450 X 230 mm, width 230mm and compressive strength 3.6N/mm and 7.3N/mm for aggregate concrete blocks as it can be used below ground. Guidance on the selection and specification of concrete blocks in masonry construction can be found in BS EN 5628; part 3 and BS EN 771-3 respectively.3.2.4 Reinforcement and TiesReinforcing bar are produced in two grades: hot rolled mild steel bars have a yield strength fy of 250 N/mm: hot rolled or cold worked high yield steel bars have a yield strength fy of 460 N/mm. Steel fabric is made from cold drawn steel wires welded to form a mesh: it has a yield strength fy of 460N/mm.The hot rolled bars have a definite yield point. A defined proof stress is recorded for the cold worked bars. The value of Youngs modulus E is 200KN/mm.The behavior in tension and compression is taken to be the same. Mild steel are produced to be smooth round bars. High yield bars are produced as deformed bars in two types defined in the code to increase bond stress.Wall ties External cavity walls are used for environmental reasons. The two skins of the wall are tied together to provide some degree of interaction. Wall ties for cavity walls are always galvanized mild steel or stainless steel and must comply to BS 1243.Three types of ties are used for cavity walls: Vertical twist type made from 20mm wide, 3.2 to 4.83mm thick metal strip Butterfly- made from 4.5mm wire Double-triangle type-made from 4.5mm wire.For load bearing masonry vertical twist type ties should be used for maximum co-action. For a low rise building or a situation where large differential movements is expected or for reason of sound insulation, more flexible ties should be selected. In certain cases where large differential movements have to be accommodated, special ties or fixings have to be used. In especially unfavorable situations non-ferous or stainless-steel ties may be required.BS 5628 (table 6) gives guidance for the selection and use of ties for normal situations.

Fig 3.1: A typical cavity wall: outer, insulation board and inner leaf with metal ties in position4.0 Theory4.1 Analytical models of the structure4.1.1 General Masonry Structure DesignThe design of bending and shear stress in masonry walls is based on the standard masonry wall approach used for all masonry members. The design for bending stress in masonry structure involves the bricks and blocks geometry.The design of the behavior of the composite unit-mortar material under various stress conditions requires a clear understanding. Masonry walls are vertical load bearing elements in which resistance to compressive stress is the predominating factor in design. However, walls are frequently required to resist horizontal shear forces or lateral pressure from wind and therefore the strength of masonry in shear and in tension will be considered.The current values for the design strength of masonry have been derived on an empirical basis from tests on piers, walls and small specimens. Whilst this has resulted in safe designs, it gives very little insight into the behavior of the material under stress so that more detailed discussion on masonry strength is required. The final strength of the structural elements formed is dependent on: The strength of the brick required (obtained from the calculation output), and The strength of the mortar required (dependent on mortar constituents and proportions)4.1.2 General Concrete-framed Structure DesignThe design of concrete-framed structure is based on approximate method approach used for concrete-framed structural members. All members of the frame are considered continuous in the two directions frame system, and the columns participate with the flat slab in resisting external loads. The effects of lateral load i.e. wind load, is also spread over the whole frame, increasing its safety. In this method, the analysis of the floor under consideration is made assuming that the far ends of the columns above and below the slab level are fixed using the moment distribution method. The thickness of the flat slab and drop panel is estimated first, and their relative stiffness based on the gross concrete sections is used. The moment and shear force are calculated and the values used to calculate for the tension, compression and shear reinforcement.To aid in the analysis of the concrete flat slab, a computer software programme (SAFE) was also used to calculate the displacement and stress values of the slab. See the attached displacement and resultant maps.4.1.3 Sizing of Members and Load Estimation4.1.3.1 Masonry structure For the masonry structure, the masonry unit of standard brick format 215mm long x 102.5mm wide x 65mm high will be used based for facing and interior wall based on manufacturers satisfied tested average strength of 20-50N/mm, texture, colour and size to meet the design requirements while the Inner leaf B and cellular wall brick of minimum average strength of 21-50N/mm that satisfied the quality control requirements.

Table 1: Estimation of Gravity loads on Wall A

Loading on wall A per meter runLoad/m run (KN/m)

Dead load at floorCumulative dead Cumulative live

load to floor, Gkload to floor, Qk

Calculation for floor level considered

4th floor

roof dead weight , 3.5 x 3 x 1.2 12.6

Weight of wall, 2.6 x 3.38.5821.1821.85.4

21.18KN/m

Imposed load , 1.5 x 3 x 1.25.4KN/m

3rd floor

Floor dead weight, 4.8 x 3 x 1.217.28

Wall 8.5825.8647.6621.06

25.86KN/m

90% of Imposed load,

(5.4 + (5 x 3 x1.2))x 0.921.06KN/m

2nd floor


Wall 8.5825.8673.5231.25

25.86KN/m

80% of 3 floors imposed load,

(18+21.06) x 0.831.25KN/m

1st floor


Wall 8.5825.8699.3834.48

25.86KN/m


(18+31.25) x 0.734.48KN/m

Ground floor


Wall 8.5825.86125.2431.49

25.86KN/m


(18+34.48) x 0.631.49

Table 2: Estimation of Gravity load on Wall B: Inner leaf

Loading on wall B per meter run; Inner leafLoad/m run (KN/m)

Dead load at floorCumulative dead Cumulative live

load to floor, Gkload to floor, Qk

Calculation for floor level considered

4th floor

roof dead weight , 3.5 x 3 x 0.454.725

Wall ( roof to 4th floor), 2.42 x 3.37.9912.71512.7152.025

12.715KN/m

Imposed load , 2.0252.025KN/m

3rd floor


Wall 8.5815.0627.7753.645

15.06KN/m

90% of Imposed load,

2 x 2.025 x 0.93.645KN/m

2nd floor


Wall 8.5815.0642.8354.86

15.06KN/m


3 x 2.025 x 0.84.86KN/m

1st floor


Wall 8.5815.0657.8955.67

15.06KN/m


4 x 2.025 x 0.75.67

Ground floor


Wall 8.5815.0672.9556.075

15.06KN/m


5 x 2.025 x 0.66.075KN/m

4.1.3.2 Concrete-framed structureThe section dimension of members is based on the experience and most especially already established empirical formulae. The thickness of the flat slab, drop panel dimension and thickness and column dimension are all generated on this. And these dimensions are also used in calculating the dead load values for each element. See the calculation sheets for the breakdown estimations.4.2 Modelling of the Structure into Masonry and Reinforced Concrete-framed Structure4.2.1 Masonry Structure Model

Fig 4.1

Fig 4.2

Fig 4.34.2.2 Concrete-framed Structure Model

Fig 4.4

Fig 4.5

Fig 4.6

4.3 Analysis, Design and Detailing of the Structure4.3.1 Analysis, Design and Detailing of Masonry Structure Result (from appendix A)Table 3: Design load and Characteristic brickwork strenght required for wall type "A"

FloorDesign load/mDesign characteristic strenght fk (N/mm) fk from the table 2 and clause 23.1.2 (N/mm)

design load x Ym

t

4th38.292.5120N/mm brick in 1:1:6 mortar fk =1.15 x 5.8= 6.67N/mm

3rd100.426.5920N/mm brick in 1:1:6 mortar fk =1.15 x 5.8= 6.67N/mm

2nd152.9310.0435N/mm brick in 1::3 mortar fk =1.15 x 11.4= 13.11N/mm

1st194.29812.7635N/mm brick in 1::3 mortar fk =1.15 x 11.4= 13.11N/mm

Ground floor225.814.8350N/mm brick in 1::3 mortar fk =1.15 x 15= 17.25N/mm

Table 4: Design load and Characteristic brickwork strenght required for wall type "B"

FloorDesign load/mDesign characteristic strenght fk (N/mm) fk from the table 2 and clause 23.1.2 (N/mm)

design load x Ym

t

4th21.041.3820N/mm brick in 1:1:6 mortar fk =1.15 x 5.8= 6.67N/mm

3rd43.152.8320N/mm brick in 1:1:6 mortar fk =1.15 x 5.8= 6.67N/mm

2nd68.164.4820N/mm brick in 1:1:6 mortar fk =1.15 x 5.8= 6.67N/mm

1st95.436.2720N/mm brick in 1:1:6 mortar fk =1.15 x 5.58= 6.67N/mm

Ground floor125.058.2120N/mm brick in 1::3 mortar fk =1.15 x 7= 8.51N/mm

4.3.2 Analysis, Design and Detailing of Concrete-framed Structure (from appendix B)

5.0 Results and Discussion5.1 Comparison of the design of masonry structure and concrete-framed structure output and economic analysis of each structureThe aim of this comparison study was to provide further insight into the design outputs of masonry structure and concrete-framed sections respectively, having the same live load and structure useful purpose i.e. residential building of medium height. Based on the design outputs, these were used to calculate the quantities of each structure type and there cost using an already prepared price list of one of the foremost construction companies in Nigeria, so as to checkmate the cost applicable to each. Comparison was also made on the time of delivery of the project using the two structures construction techniques.An approximate economic analysis was also performed to determine the cost reduction associated with using of the masonry structure versus concrete-framed structure. Using an assumed labour cost per minute and measured labour times incurred into the cost, approximate savings can be determined (Table 6 and Figure 10). The material savings comes from the fact that very less formwork and iron quantities when masonry structure was used. The structure quantities and cost was prepared to show more details. Hence, too often, costs reflect the current state of the building and not the long-term of the building over its life. Economy initial cost, relative performance and maintenance cost favours masonry structure over concrete-framed structure due to fact that masonry structure shows to be flexible to the builder.

Table 5: Comparison between the various costs of the two structures elements

Concrete-framed structureMasonry structure

QuantityCost (# Naira)QuantityCost (# Naira)

Concrete volume (m)68,950/m

Columns745102300

Slab (roof & floor slab)340.823498160323.3422,294,293.00

Shear wall35.512448414.5

Edge beams14.661010807

32,059,681.50

Formwork (m)13036/ m

Columns5927717312

Slab (roof & floor slab)1334.717399149.2108414,131,024.00

Shear walls318.64153269.6

Edge beams47.43618297.48

29,888,028.28

Reinforcement (tonnes)379928/tonne7000/250 pcs

Columns8.026263049400.909

Slab (roof & floor slab)37.9050314401182.2413.902525,281,956.62

Shear wall4.266311620890.626

Edge beams0.77853295785.3458

Wall ties4837 pcs135,436.00

19,367,259.125,417,392.62

Wall (m)

Cavity wall: (utility brick 102.5mm thick facing wall)1239.56944000

Inner leaf1147.656428800

Cellular wall type C7852,355,000.00

Load bearing wall type A993.75560800

Non load bearing block24824,964,000.0021288600

Total project cost86,278,968.9068,413,266.24

It can be approximated that Seventeen million eight hundred and sixty-five thousand seven hundred and two Naira (# 17,865,702.66) can be saved per structure using masonry structure for the same purpose. Using a similar method, approximately twenty-one percent (21%) will be saved. The savings will be more significant when it is compared to the beam-slab concrete-framed structure as flat slab concrete-frame structure is more economical over other type. When many medium height building are produced, savings may be more substantial

Fig. 5.1: comparison bar chart of cost of design output5.2 Advantages, Suitability and applications of masonry structure over concrete-framed structureBoth masonry and concrete-framed structures have their advantages, suitability and application and the advantages of masonry structure over concrete-framed structure is stated below based on the criteria listed in chapter 1 i.e. cost, speed of erection, aesthetic, durability, sound insulation, thermal insulation, fire resistance and accidental damage.(i) Speed of erectionThe erection of masonry structure can quickly follow on thus achieving a faster overall construction time for the whole building. A masonry wall can easily be built in two days, and support a floor load soon after. Compare this with an in-situ reinforced concrete-framed structure column where the time taken to fix reinforcement , erect shuttering, cast concrete, cure, prop, and then strike the shutter is often more a week. In conclusion, it is worth pointing out that the speed of masonry construction is achieved without the same planning constraints that limit the application of system building.

(ii) Aesthetics harmony, proportion and ornamentationMasonry structures provide appeal of a building, it provides the human scale, is available in a vast range of colours and textures, and, due to the small module size of bricks and blocks, is extremely flexible in application in that it can be used to form a great variety of shapes and sizes of walls. it also tends to wear well and mellow with time.

(iii) Sound InsulationThe majority of noise introduction is by airborne sound, and the best defense against this traditionally is mass- the heavier the partition, the less the noise transmitted through it. It is added bonus if the mass structure is not too rigid. Brick work and blockwork provides the mass without too much rigidity. However there are many light weight wall systems also available, which perform better than the same thickness of masonry.

(iv) Thermal InsulationThe good thermal properties of cavity walls have long been recognized and, more recently, have become critical in the attempts to conserve energy. Cavity walls and diaphragm walls can easily be insulated within the void to provide further improved thermal values. Care is also required for the choice of external leaf which must resist rain penetration, insulation materials and the details employed.

(v) Fire Resistance and Accidental DamageMasonry structure always suffers less damage than concrete-framed buildings- which fact provides evidence of not only the high fire resistance of masonry structures, but also their inherent capacity to resist accidental damage.

5.3 Suitability of each structureMasonry structure of a multi-storey building on which the wind is directly applied are usually the outer cladding walls, which have their weakest axis at right angles to the wind direction. Walls best able to resist these forces are the internal cross walls and the vertical shafts forming the stair or lift. Masonry structure is more suitable when T and L and other plan configurations are used to enhance masonrys lateral load resistance. When the structure has repetitive floor plan, masonry structure has an advantage to provide repetitive load bearing wall layout. The masonry structure can still prove competitive for more flexible layout.However, architectural and planning layout design that mostly shows repetitive floors is for structures like hostel, hotel, flat and other residential buildings. So, adopting masonry structure of medium height for this type of structures will be more economical.Concrete-framed structureThe frame is the key structural element of any concrete-framed structure.Frame choice can have a surprisingly influential role in the performance of the final structure, and importlantly, also influence people using the building.However, cost alone dictates frame choice, although the most suitable choice has been selected (flat slab) which has the advantage over other concrete-framed structure types, but this cannot still be economical based on this research work. Cladding can represent up to 25% of the total construction cost if non-loadbearing was not used, which would have added more advantage of masonry structure over frame structure.However, the suitability of concrete-framed structure can be highly favoured due to its high resistance vibration.For some uses, such as laboratories or hospitals, additional measures may be needed, but these are significantly less than for other materials. In recent independent study (by the Concrete Centre, 2004) into the vibration performance of hospital floors, concrete emerge the solution least in need of significant modification to meet the stringent criteria.However, concrete-framed structure of medium height will be suitable for structures susceptible to vibration. i.e. hospital, thearter, etc.

Chapter 6: Conclusions and Recommendations for Future WorkAn investigation into the design of masonry structure and concrete-framed structure of residential building of medium height was completed. The objectives of the investigation were to analyze, design and compare the outputs of design calculations of both structures. Adequacy, stability and performance of function were assumed to have been met and satisfied in the design calculations. The mode of actions (dead live and wind loads) were also presented and analyzed. The investigation yielded the conclusion and results. Total cost reduction of an approximate value of 21% could be achieved using masonry structure instead of concrete-framed structure meant for the same function. In concrete frame structures, masonry or other materials are used to form partitions and corridor walls, etc. In so many instances, if these partition and other walls are designed in load bearing masonry they can be made to carry the loads and dispense with the need for columns and beams, while ensuring that the most economic scheme has been chosen for each material. That masonry building tends to be faster to erect, resulting in lower site overhead costs and without very large expenditure on the part of the builder. That the maintenance costs of masonry are minimal compared to concrete-framed structure since the facing wall bears a good finishing that can withstand the weather harshness and does not perennial painting. Masonry structure brick wall 102.5mm thick plastered both sides with a minimum of 12.5mm thick of plaster has an approximate sound reduction index of 46 Db which makes it more suitable in an area where noise pollution always occur. Quality control and assurance of the concrete, bricks, mortar and other materials are more important factors for masonry structure construction. Segregation caused by poor concrete, low mortal and brick strengths and wrong arrangement of wall ties could cause out-of-plane, which reduce the stability of the building. Since the load bearing construction is most appropriately used for building in which the floor area is subdivided into a relatively large number of medium size and in which the floor plan is repeated on each storey throughout the height of the building. These considerations give ample opportunity for disposing load bearing walls, which are continuous from foundation to roof level and, because of the moderate floor spans, are not called upon to carry unduly heavy concentrations of vertical load. Therefore, once the chosen model complies with all these conditions and the type of buildings which are compatible with these requirements include flats, hostels, hotels and other residential buildings. A masonry structure of medium height is recommended to be more appropriate for these types of structure (flats, hostels, hotels and other residential building of medium height) and other quality of masonry will be utilized fully while adopting it. It is recommended that an extensive comparison be undertaken to conclusively determine if design of reinforced/ prestressed masonry structure versus concrete-framed structure of residential/commercial building of medium height will be more economical because of some advantages of reinforced masonry over unreinforced masonry structures. If more investigations are performed on masonry structure, a method to entirely eliminate the concrete-framed structure than the use of masonry structure for residential building of medium height would be beneficial.

References:BS 5628: Code of practice for use of masonry; part 1: structural use of unreinforced masonry; Part 3: Materials and components, design and workmanship.BS 6399: Design loading for buildings; Part 1: Code of practice for dead and imposed loads, 1996; Part 2: Code of practice for wind loads, 1997; Part 3: Code of practice for imposed roof load.BS 8110: Structural use of concrete; Part 1: Code of practice for design and construction, 1997; Part 2: Code of practice for special circumstances, 1985; Part 3: Design charts for singly reinforced beams, doubly reinforced beams and rectangular columns, 1985.CP3: Code of basic design data for the design of buildings; Chapter V: Part 2: Wind loads.Curtin, W.G.,Shaw, G.,Beck, J.G and Bray, W.A. (1995) Structural Masonry Designers Manual, Blackwell, Oxford.DD 140-2 Recommendation for design of wall tiesInstitution of Structural Engineers and The Concrete Society, Standard method of detailing structural concrete- a manual for best practice, London,2006.Sinha, B.P, Henry, A.W and Davies, S.R (2004) Design of Masonry Structure,3rd Edition E&FN SPON, U.K

APPENDICE A

APPENDICE B

4