Using of Footing and Slab Construction - Term Paper Example

Student Name: Tutor: Title: Footing and Slab Construction Course: Institution: Footing and Slab Construction Introduction The footing and slab construction is a very critical procedure since it determines the strength of a building. A well designed footing and slab will ensure that the building is able to support all the loads it is supposed to handle. The design will however, vary depending on various factors including the soil type and the loads. The loads will include both the lie loads and the dead weights (Darwin, 2003). The material used for the construction will also determine the strength of the footing and the slab. If the construction is carried out using poor materials then the chances of collapsing is very high. During the implementation phase it is also important that a good workmanship is practiced. The correct standards of construction including the BCA standard should be adopted. This will not only ensure safety but also the quality of the work will be guaranteed. The paper will discuss the construction of footing and slab as was observed in one pf the building under construction. This will include all the procedures undertaken during the construction including the standards applied during the construction. Footing Construction Site Preparation and Excavation This process was the beginning of the implementation phase of the construction. This was done after all the machinery, materials and equipment has been mobilized to the site. Site preparation included the clearing of vegetation and removal of debris on the construction site. This included the use of simple tools and machines. This was then followed by marking the areas where excavation was to be done. The marking was done after the measurements have been completed. Since the footing was the continuous type of footing, the excavation depth was to be 1000mm while the width of the trench was 600mm. This is considering the reinforcements had to be placed on the footing. After the marking process was completed excavation works began. This was done using the excavator due to its high speed and the soil type. The ground was tough and simple tools could not be used. The soil was removed and wheeled off after the excavation. However it was not completely disposed off but was taken elsewhere on the site since it was still useful. After the excavation the trenches were leveled to ensure that the concrete will be uniformly placed. Figure 1: Site Preparation and Excavation Placing of Concrete and Reinforcements After the excavation process was completed, the next step was placing reinforcements in their correct positions. The center lines were very useful in the placing of reinforcements and were interpreted from the design. The design was however based on the loads and thus the correct size of reinforcement and their positions were determined. The BRC mesh were not used since it was a continuous footing and thus twisted bars of the Y series were used (Newby, 2001). In this particular case, there was no need for timbering since the soil was firm enough and could not collapse. The reinforcement was tied all round the trench according to the specified design details. This process was then followed by placing of the concrete. The concrete mix used was 1: 3: 6 in order to achieve the maximum strength. The concrete mixer was used to prepare the mix so as to make the process faster and save time and resources. Extra men were hired during this process for the purpose of saving time. During the placing of concrete, some of the men were also compacting and vibrate it in order to remove all the air bubbles and to make the concrete strong. This process was mainly done by the use of a poker vibrator. This was mainly because of the heavy reinforcement. The poker vibrator was very appropriate and fast at the same time. In some instances manual methods were also used to carry out the process of compaction. Figure 2: Placing of Concrete and Reinforcements Curing This is the process of hardening the concrete after it has been placed. This is for the purpose of ensuring that no cracks occur which has the potential of ruining the footing and possibly the collapse of the whole building (Beckwith, 2012). Although various methods of curing are used in the construction industry, the building was cured using water. The whole of the footing was submerged in water for almost one week to ensure that the footings acquired maximum strength. This was closely supervised as it would ensure that the building is safe. This was mainly done in the morning and evenings so as to counter the effects of evaporation. Although there was a proposal to use the curing membrane, it was not used during the construction. During this time, no further construction was being carried out around the footing. Although the footings had been submerged with water, it was still covered with used cement bags. Termite Treatment This process is important for the control of insects such as termites. They usually build their nests around the footing area which in turn causes the weakening of the structure. Continuous attack by the termites may lead to the collapse of the building. This is considering the species of termites found in Australia which are quite destructive. After the footing was completed it was necessary to guard against the termites through treatment. This was mainly done by applying the insecticides on the areas around the slab. Special care was however taken to avoid the insecticide from being placed on top of the footing or below the footing. The backfill was also treated later with the insecticide to ensure maximum protection. Specialized equipment was used during the handling and application process so as to ensure the safety of the workers at the site. BCA Standards During the construction of footings, the BCA guidelines were applied so as to gain approval by the authority. The authority recognizes the fact that the soil may shrink or swell due to the presence of the moisture content, tolerance of the superstructure to movement, settlement of compressible soil and the distribution of the loads around the footing. With these facts to be considered, the contractor at the site was applying most of the requirements in terms of building. The code also defines the types of materials to be used. However the contractor was not fully conforming to the standards as some of the materials were purchased locally. In terms of safety the contractor fully complied as all the measures of safety had been put in place. Design of the Footing Figure 3: Design of the Footing The design stage is very critical as it determines whether a building will withstand the forces or not. All the loads of the building will always be transmitted to the footing. This therefore makes the member very important and the design should be done with a lot of care since any slight mistake may lead to wrong dimensions and also collapse of the building. During the design of the footing, a simple method of calculation was used together with the software although the manual method was mainly applied. The following parameters were applied, Floor dead load estimate: Weight of ceiling. Weight of the wooden sheaths. Weight of the floor joist. Weight of the carpet. Roof dead load estimate: Weight of trusses. Weight of water board. Weight of dry wall ceiling. Weight pf the insulations. Wall dead load: Weight of dry wall. Weight of insulations. Weight of waferboard. To obtain the total load=∑ (Floor dead load, roof dead load, wall dead load.) To obtain the area of the footing= Total dead load/ allowable earth pressure. The method above was used to calculate the area of the footing which was then used to determine the excavations. The reinforcement was however placed by measuring the perimeter from center to center. Slab Construction The slab forms an important part of the construction of a building. This is considering the fact that the building was residential. The slab was therefore required to sustain the loads to be imposed on it and also the thermal properties it had o withstand. Figure 4: Slab Construction Site Preparation for Slab Construction Just like the case of the footing. It is also important to prepare the site for the slab construction (Brainard, 2012). However excavation is not required in most cases. However during the construction of the building it was important to remove the top vegetation which was mainly grass and vegetation. The top soil was completely removed as it may end up affecting the compaction process causing settlement which is not good for the building. After the removal, the ground had to be leveled evenly. During these process simple tools was used since the area was not large enough. It was considered that use of heavy machinery would increase the cost of operations as more fuel will be consumed. However during the leveling of the ground some equipment was used considering that this process is quite critical. Since the ground was dry no water rose to the ground level during the process and thus made the construction process much easier. Placing of Hardcore and Marrum To ensure that the slab is strong enough, it is always advisable to place hardcore at the bottom. This is done by the workmen on the site under the supervision of an experienced foreman. The hardcore had to be arranged in an orderly manner so as to try and obtain a leveled surface. Hand tools including the sledge hammers were mainly used to break the hardcore during the process. After the hardcore had been placed on the slab area, marrum was also placed. The purpose of placing the marrum on top of the hardcore was mainly for the purpose ensuring that the concreted do not penetrate into the spaces between the hardcore. This will cause a lot of wastage. Since the reinforcements were also being used, it would be difficult to arrange them in order or at one level since the hardcore may not be uniform. The marrum blinding is also important in terms of ensuring a level area is achieved and thus making it easy to arrange the reinforcement bars. Wastage of concrete is also eliminated as it will not have to flow in the spaces between the hardcore. The marrum blinding was placed for a level of 100mm wile that of hardcore was 150mm. The DPC was also spread at this point. This is an important material in the slab construction as most of the BCA codes strive at ensuring that it is placed in accordance with the requirements set. Placing Reinforcements It is important to ensure that the reinforcements are placed in their correct format. During the construction, spacer blocks were used in some areas for the purpose of achieving the desired levels. Binding wires were used to tie the reinforcement bars in their correct positions. The bar bending schedule was also used during the bending of the bars at the required positions. Thos process was quite critical and required expertise to perform it. The work was supervised by qualified personnel at the site. The bars that were used were mainly the Y series. All the details were however in the drawing and had to be carefully followed to avoid errors that may end up compromising the quality of the slab. This process was carried out very carefully and all the reinforcements were placed in their correct positions. Concrete Placing This process is usually done after the reinforcement have already been put in place. This will ensure that the slab is strong. During the construction of the building, it was important to observe all the standards and procedures (Lancaster, 2005). The concrete mix that was used was the 1: 2: 4. This was to ensure that the slab was strong enough. The mixer was mainly used for the purpose of preparing the concrete. This was mainly because the amount of concrete required was large. The use of heavy reinforcements was also the reason for using this concrete mix. During the process the vibration was done in order to remove the air bubbles in the concrete. The poker vibrator was used since it was the most appropriate and it could be used with the reinforcements on. This equipment could not cause any interference on the reinforcements. Any distortion of the reinforced could lead to the interference on the strength of the slab. After the vibration w2as done, the compaction followed and it was done manually as well as using equipment for the purpose. This process was however the most tedious and time consuming of all the process during the construction. The process was then followed by the hardening process overnight. This is considering the fact that the process was completed within one day due to the large workforce and use of machines and equipment. The next step was the application of mortar. This mainly done for the purpose of leveling the slab before finishing is done. This process requires that the sand used be clear of any impurities. As such it was important for this to be observed during the construction. The sand was thoroughly sieved before it was mixed with the cement. The ratio of 1: 2 was used during the mixture. This was mainly for the purpose of ensuring that the concrete and the mortar bond together properly. The amount of water was also measured to the required standard. This ensured that mixture of the mortar was strong enough. It was then applied evenly on the surface of the slab. To check the level a horizontal level was used to ensure that the level was correct. This is mainly for the purpose of drainage and uniformity (Gajda, 2001). Curing This process is usually done for the purpose of hardening the concrete and ensuring that it dries properly without developing cracks. During the construction process it was necessary to carry out the process using curing membrane. This is mainly because the site engineer recommended it. The levels of evaporation were also very high at the time and submerging with water would have cause losses due to evaporation. This process lasted for almost one week and the slab was strong enough to withstand any pressure. BCA Standards This standard recognizes that concrete on slab is a very common means of building new homes and structures. It therefore seeks to prevent risks of collapse by ensuring that the Damp proof course and membranes are used to prevent the moisture from rising and causing the slab to be weak and hence its collapse and cracking. The code also provides for the type of material to be used and the level at which the Damp prove course should be placed. The material for the damp proof course is also specified in this code. It is also recommended that the height of the DPC should be 150mm for areas with little moisture (Building Code of Australia, 2012). This requirement was followed by the contractor although not full in some areas. The contractor in some instances did not fully comply with the requirements for testing the concrete. This is mainly because in most instances, the concrete was not tested but instead placed directly on the slab. Design of the Slab The design of the slab is also crucial when it comes to construction (Threlfall, 2008). This is considering the fact that the building under construction was new and was supposed to last for many more years to come. The fact that reinforcements were used in the construction also meant that the process had to be done well. The main disadvantage of poor design of the slab is mainly the fact that it can lead to wastage of materials. It can lead to more materials being purchased and in the long run they are not used. This cause loses to the owner of the building. The method used to design the slab was manual as well as use of soft wares. However the manual means was the most reliable as it is easily understood. The empirical formula was thus used. The following parameters were used during the design of the slab: Design depth of the slab. Ratio of effective length to design depth. The core depth. Other considerations that were made during the design included the following: The ratio of effective length to design depth should not exceed 18 and should not be less than 6. The core depth of the slab should not be less that 100mm. The effective length should not exceed 4100mm. The minimum depth of the slab is not less than 175mm. Spacing of the reinforcement shall not exceed 450mm. The reinforcement shall not be close to the outer surface. Other assumptions that were made during the design together with the symbols used included the following: PHIm = strength reduction factor for moment (0.8); f'c = 28-day concrete strength in MPa; b = width of section (1000 mm); d = depth to centroid of reinforcement in mm; M = given bending moment in kNm/m After the design has been completed by the engineer, the architect in the company comes up with the drawings including al the details and specification. The drawing is usually done through the use of ARCHICAD in order to save time and expenses. Variances After carefully studying the construction process of the footing and slab, several variances were noted. The contractors did not pay much attention on the issues of the supply of the materials. This is despite the fact that BCA recommends that the contractor must ensure that the materials are from the right supplier. Some of the materials including cement were bought locally. Some of the workers on the site were also not qualified enough. In some instances, the apprentices were allowed to supervise the works. This is a clear contravention of the roles of apprentice as spelled out in the codes. The testing of materials was also not being carried out regularly. In most cases the materials were used as they were and even the concrete was rarely tested for its strength and compression. This was mainly because the contractor was in a particular hurry to conclude the works. This is quite dangerous and it may lead to a lot of negative impacts to the workers. The building may end up collapsing after its completion and it may cause a lot of injuries and even deaths. On the other hand the safety of the workers may no be guaranteed if apprentice is to supervise the works (Danbury, 1992). The drawings may also not be interpreted correctly. These impacts are quite negative and the contractor may end up being sued or the owner encountering serious loses. Recommendations With these variances in place, some improvements ought to be recommended to avoid taking chances. The source of materials should be well known and approved by the building authority. Before the materials are used, it is also important to ensure that they are of good quality. If not, then they should not be used but instead be returned with samples to the supplier. Testing the strength of the concrete is also very important as it will ensure that the footing and the slab will last for longer without collapsing (Karade, 2003). To this effect I would recommended that samples if the concrete be collected and taken for the various strength tests. This will also be important in ensuring that necessary improvements are made on the concrete. The foremen should also be fully in control of the process as opposed to the use of apprentice. Although an apprentice should be given the opportunity to learn there should be a limitation. The contractor risks prosecution incase of an accident caused by the apprentice. The design phase should also be improved and more emphasis given to the use of soft wares as opposed to the manual means. This is mainly because a lot of time is usually wasted at this point. The contractor should also work according to the prescribed time set by the codes for the practices. This will greatly reduce the chances of substandard works that may not be approved or worse cause accidents due to collapse and failure. Conclusion In conclusion, the construction of footings and slab plays an important role in the development of the building. Without a proper footing and slab, the building may end up collapsing. There are several laws that guide these processes to ensure that accidents and failure are prevented. The BCA has several codes to ensure that these structures are build up to the expected standard. However when it comes to the implementation, some of the rules ends up being flouted by the contractors. This is very risky and it may end up with disastrous results. It is also important for the engineer designing the footing and the slab to be quite careful. This is not only for the purpose of ensuring the building does not collapse but also for the purpose of ensuring the materials do not go to waste. It is also important for the construction to be carried out as prescribed by the building codes. The time required for each stage should be put into practice. This will also prevent the buildings from collapsing which may end up causing losses and even fatalities. References Darwin, N, 2003, Dolan. Design of Concrete Structures, the MacGraw-Hill Education, p. 80-90. Threlfall, A., et al, 2008, Reynolds's Reinforced Concrete Designer's Handbook – 11th ed. ISBN 978-0-419-25830-8. Newby, F, 2001, Early Reinforced Concrete, Ashgate Variorum, ISBN 978-0-86078-760-0. Brainard, B, 2012, How to Construct a Concrete Slab, Retrieved on 2 April 2012 from, . Building Code of Australia, (2012), Moisture resistance of slab on ground construction, Retrieved on 2 April 2, 2012 from, Danbury, C, 1992, Engineering. In The New Book of Knowledge (Vol. 5, pp. 224–225), Grolier Incorporated. Gajda, J, 2001, Energy Use of Single Family Houses with Various Exterior Walls, Construction Technology Laboratories Inc. Lancaster, L, 2005, Concrete Vaulted Construction in Imperial Rome, Innovations in Context, Cambridge University Press. ISBN 978-0-511-16068-4.  Karade, S, 2003, Assessment of wood-cement compatibility: A new approach. Holzforschung, 57: 672-680. Beckwith, T, 2012, How to Time Concrete Slab Curing, Retrieved on 2 April 2012 from, Read More