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The previous chapter introduced the research topic and outlined the goal of the current research, as well as the scope. This chapter focuses on past studies related to demolition constraints. The aim is to explore the findings of other researchers regarding the research topic and use it as a platform or background for the current research. In investigating the technical constraints associated with demolition works, it is imperative to consider the demolition method employed. Demolition methods are quite numerous and vary widely in their application, technology, efficiency, and costs. Pitroda and Bhavsar (2015) categorized demolition methods into conventional and non-conventional. Conventional methods involve breaking down structures by use of hand-held tools like jackhammers, chisels, and sledgehammers. On the other hand, non-conventional methods involve the use of explosives, wrecking balls, and bulldozers. . .
These can also be referred to as selective demolition methods. They are mostly used when the building possesses some degree of structural integrity. Also, these methods can be used when only partial demolition is required. For instance, the living room of a house being demolished for reconstruction while the bedrooms and kitchen remain intact. In such cases, the structure is stripped from the inside to the outside, with the construction material being sorted by type. As of now, selective demolition remains nearly the only option regarding the repurposing of buildings. The use of explosives, wrecking balls and high reach bulldozers may not be practical because of their great destructive nature. The most common form adopted involves the use of the jackhammers to crumble down concrete. Reinforcements are cut by the use of the oxyacetylene torch. The reinforcement bars are not cut until the entire block of concrete surrounding them is broken away, and their support function is no longer needed. Another variation of the conventional demolition methods is the top-down demolition. This involves the tearing down of a structure from the roof to the foundation. Mechanical machinery with a hydraulic demolishing arm is used in this case. The machinery is lifted by cranes to the top of the building. Having been set on a stable platform, the demolition starts in a top-down fashion. The selective demolition methods pose a series of technical constraints as discussed below.
Given that the demolition is carried out using hand tools, a lot of effort is required to bring down just a small section of the building (Pitroda and Bhavsar, 2015). One operative may take a couple of days to completely bring down a single column. The longer the operatives stay on site, the higher the demolition costs.
A lot of time is spent on demolishing structures using conventional methods (Zhang, 2007). This is already a violation of the regulation that states the method adopted for demolitions should take the minimum time possible. As such, conventional demolition methods are not feasible for large structures. Otherwise, if used, it will take a huge number of operatives and considerable timeframes. The project may not prove cost-effective in the long run.
While demolishing by hand, the operatives are normally in close contact with the building elements (Zhang, 2007). No hand tool is so long as to allow the operatives to keep a good distance between the hazardous elements and their bodies.
In case the building under demolition contains features such as exterior walls, cantilevered canopies, and balconies, and the area is densely built, assuring the nearby residents and structures of safety is difficult. Demolishing such structures is accompanied by the high likelihood of pieces of concrete and masonry falling down and hitting people walking or carrying out their activities in the vicinity. According to Pitroda and Bhavsar (2015), if ropes or tie wires are used for pulling down such structural members, the pulling wires should be at least 4 times stronger than the expected pulling force. Additionally, it is a requirement that the operatives be shielded from the rope or tie wires. In areas with restricted space, this may be quite difficult to achieve.
It takes a lot of effort and expertise to raise the mechanical machinery to the rooftop and place it on some stable platform in order for it to start the demolition (Foruzesh, 2016). Normally, the load applied by the machine to the floor must be carefully analyzed and sufficient support provided for the machinery. Relocation of the machinery as the demolition proceeds to the next lower floor may also be quite technical. The operation of the mechanical machines is prohibited under the following scenarios i) within 2 metres from the peripheral of the structure. ii) within 1 metre of floor openings, and iii) on any cantilevered structure. Conforming to these restrictions is at times impractical, depending on the design of the structure under demolition. Content and narrative analysis will be utilized for the analysis of qualitative data. The data obtained will give an insight to the reasons for missed medical appointments by dementia patients, the consequences and possible solutions to the issue.
This is one of the most popular demolition techniques, and it has been in use for possibly the longest time compared to other demolition methods. It is mainly used for masonry and concrete structures. The wrecking steel ball acts from outside the building. Foruzesh (2016) suggests that the method is most suitable for dilapidated buildings, silos, and other industrial facilities. The concept behind it is that concrete and masonry blocks crumble when hit by the ball. In the 1950s and 1960s, the wrecking ball was commonly used to demolish large buildings. The ball was majorly spherical with a hanging hook at the top. Lately, demolishing contractors have adopted a pear-shaped ball with its top part cut off, which makes it easy for the ball to be pulled back after penetrating through the concrete slab, wall or roof. Depending on the size of the structure being demolished, wrecking balls can weigh anywhere from 450 kg to 5,400 kg. The following are some of the technical constraints associated with the use of the wrecking ball.
The wrecking ball cannot be operated by a novice. The operator needs to be highly skilled, otherwise, the crane may end up tipping if the swing of the ball is not well calculated. This significantly endangers the life of the operator (Arpita, 2019).
For the wrecking ball to be used, it is a prerequisite that there should not be any other structure in close proximity to the one under demolition. Also, no human activity should be ongoing around the building being demolished. As such, it is not safe to use the wrecking ball in densely built areas. Foruzesh (2016) suggests that the distance of the support of the crane must be at least a half the height of the building. If the height of the building is 60m, the bottom of the crane should be at least 30 m from the building. It may not always be possible to find such a clearance around buildings.
The wrecking ball is only effective upto a certain height above the ground. This is because of the degree of swing required for the ball to attain a proper demolishing force. In case the structure includes an underground floor, the wrecking ball will not be able to be used. The steel ball will have no room to swing for the demolishing to proceed.
The wrecking ball must be used with a relatively large crane mounted on a strong driving engine. The assembling of the entire wrecking ball set up may not be possible in some areas where access is restricted. Pitroda and Bhavsar (2015) give the example of the 1924 13.2 m high 25/T 4-storey building next to the western railway Mumbai division, covering an area of almost 430m2. Having completed its design life, the building was in such a dilapidated state that only demolition was the next viable option, at least to maintain safety for trains and nearby residents. Access constraints included i four running railway lines to the east of the building, ii) an overhead equipment mast with a portal for for 5 live conductors, just about 6m from the building, iii) a masonry boundary wall about 3 m from the building, and iv) a 40 storey skyscraper about 100 m away from the building. As such, the use of a wrecking ball or high reach excavators was impractical because such heavy equipment could not access the building. The implosion method was finally settled on as the most feasible demolition method for the building.
This method has so far been the best option for skyscrapers and huge structures. The method involves the use of a three-piece wrecking arm fitted with crushers, hammers, shears. The demolition is usually carried out in a top-down fashion. Below are the major technical constraints experienced while using the high-reach arm
The actual destruction by the demolition arm is fairly fast. The problem starts when the demolished parts pile up and the equipment can no longer bring down more structural elements. A team of operatives must then embark on removing the demolished parts to pave way for the high reach arm to access parts of the building that are still standing.
Naik (2018) states that structures demolished using this method should be a maximum of 90 m tall. The arm of the high reach excavator may not work efficiently beyond this height. This limits the number of structures for which this demolition method is applicable.
This is so far the fastest demolition method used in the construction industry. It can also be referred to as explosion deconstruction. It is a highly effective demolition method as it significantly saves on time and costs. It is a popular method for bringing down multi-storey buildings, especially those that pose critical hazards were they to be demolished by other methods. Pitroda and Bhavsar (2015) argue that implosion is capable of reducing the demolition period by nearly 80%. The bulk of the time is spent on getting ready for the detonation of the explosives and cleaning up after the building goes down. After a detailed engineering analysis, explosives are strategically placed at the main structural supports of the building. Usually, holes are drilled into the selected structural members and loaded with explosives. The explosives are then detonated and the building caves in since it is no longer sufficiently supported. Foruzesh (2016) highlights the need for primary weakening of the structure before the explosives are detonated. This may involve cutting and removing portions of the shear walls and other structural members. Of late, demolition companies have resorted to wrapping entire structures in geotextile membrane and chain-link to prevent the spillage of debris (Ramaswamy (2015). There are four major categories of commercial explosives that can be used for demolition purposes - i) dynamite, ii) ammonium nitrate and fuel oil mix (ANFO), iii) slurries, and iv) two-component explosives.The major technical constraints experienced with this type of demolition method are as discussed below.
With explosives, even the most trained specialists cannot guarantee that there will be no projectiles flying away from the building under demolition. As much as several control measures are put in place, projectiles flying from the building can travel to considerable lengths and wreak havoc on neighboring properties or passers-by. During the demolition of the Calder Hall Cooling Towers in the UK, Williamson (2008) states that the ejection of high velocity small fragments was one of the top most hazards during the demolition. The cooling towers were located only 40 m from the UK's only nuclear Fuel Handling Plant and the Sellafield site has a number of other sensitive structures.
Implosion has for long been characterized by huge volumes of dust and other air-borne particles released into the air. If it happens that the building under demolition is in a densely built area, the surrounding residents may be put at risk of respiratory and optical illnesses. This violates the regulation that states the method chosen for demolition should not cause pollution beyond permissible limits (Pitroda and Bhavsar, 2015). Additionally, implosion results in a high degree of rubble spread in the vicinity. In the case that the structure is situated near other private property, the contractors will have to deal with the burden of clearing rubble from several private properties. It is not always given that the owners of these properties will tolerate rubble in their properties. Some may end up going to court to stop the demolition if the anticipated damage is great. If the structure under demolition is next to a busy road, rubble may spread on the road and block traffic for a couple of days, depending on how fast the ground crew will be in clearing the rubble. Foruzesh (2016) suggests that a dust net or scaffolding net should be used around structures under demolition to trap dust and small pieces of demolition debris so as to safeguard the public. Considering large structures such as cooling towers being brought down by implosion, the erection of a protection net is rather impractical. First, the scaffolding will be too high so as to cover the entire height of the structure. Also, the perimeter for the protective netting may need to be very large. As such, many implosion demolitions will not make use of dust nets. Demolition debris will freely float into the air into the surroundings. Foruzesh (2016) also states that a channel or levee wall should be erected around the structure to restrict the broadcasting of the demolition debris. Depending on the surroundings of the structure under demolition, this may prove an impossible undertaking. Naik (2018) states that though asbestos may have been previously removed by experts, traces of asbestos may still be found deposited in the false ceiling inside technical ducts and other tiny rooms. This poses significant health risks to nearby residents. Williamson (2008) in a case study of the Calder Hall Cooling Towers further discusses the risk of pollution. The towers had a whopping 75 tons of asbestos piping. As much as these were removed by asbestos experts before the implosion of the towers, bits of asbestos still remained in the structure’s fabric and were possibly released into the air when the explosives went off.
Most buildings contain flammable materials in their structure and cladding. Such include any element made of plywood, wood, fiberboard, foil, and plastic. By using explosives, such materials are likely to catch fire. It may prove difficult to control the fire outbreak since the building will at the same time be collapsing. Building regulations recommend that buildings be stripped of any flammable materials before explosives are used for demolition. It may turn out to be a very tedious and sometimes impractical process to take out every piece of flammable material from the building. Additionally, Pitroda and Bhavsar (2015) state that the stripping down of flammable materials may at times pose high risk to the workers, and therefore is not carried out at all. The resultant blasting will not be clean as is required by law. According to the The OHSA Technical Manual (2020), access should be provided for heavy fire fighting equipment before the demolition job starts and throughout the entire duration of the project. As previously discussed, not every site is accessible by such heavy fire fighting equipment. More so, implosion is preferred when access to the site is limited, yet the risk of a fire outbreak still remains.
The implosion method cannot be used for timber-framed and brick structures
Implosion is known to cause considerable amounts of vibration to a given radius around the building under demolition. The effect can be compared to that of a tremor or earthquake. Depending on the amount of explosives used and the size of structure under demolition, the resulting vibration may be to a level that destroys the structural integrity of adjacent property. The walls of nearby buildings may end up cracking from floor to ceiling. Windows may shatter. The concrete frame of these buildings may also lose stability by beams and columns warping under pressure. Foruzesh (2016) also highlights the possibility of underground utility lines being destroyed. It is a requirement of the law in many countries to relocate utility lines prior to demolition, but this may not always happen due to right of way restrictions.
As earlier implied, the effects of implosion may be felt not just within the structure being demolished, but to some given radius around the structure. In case the structure is located in a high traffic area, it may be necessary to shut down quite a large number of roads within the radius to which the effects are anticipated to be felt. As much as many vehicles may be blocked from using the roads, pedestrians have been notorious for flouting the rules. This sets them in danger as no one knows how exactly the implosion will turn out. Foruzesh (2016) asserts that any obstruction of roads and sidewalks can significantly affect the movement of pedestrians and vehicle users. This usually leads to public uproar if the closure is extended beyond tolerable periods. This may force the demolition crew to work under pressure to avoid wrath from the impatient public. The demolition contractor needs to obtain authorization for traffic disruption from the police and local authorities. Even with such authorization, the public may threaten to trespass if the route under closure is critical to their daily movements.
Law requires that the immediate neighbourhood be evacuated before a given structure is demolished by the use of explosives. Depending on where the structure is located, the evacuation may not entirely be feasible. This is especially true when the neighbourhood consists of home dwellers and office workers. It may be difficult to get all people out of their homes in the name of demolition. As much as they may be aware of the danger of the implosion exercise, some simply ignore and stay in their homes. The problem of it arises when the implosion gets out of hand and these people get injured while in their homes. For workers, some businesses may not agree with closing down their premises to pave way for demolitions. These also stand the risk of injury by flying debris and projectiles.
According to Foruzesh (2016), a fence should be erected and a cloister implemented to create a demolition workshop area that is entirely separate from the public. In this cloister, no trespassing nor any unauthorised access should be tolerated. Depending on the location of the structure to be demolished, the implementation of a cloister may be rather impractical. This is especially true when the structure is located next to busy roads, office blocks or residential houses. Foruzesh (2016) additionally suggests that the radius of the exclusion zone should not be anything less than 2.5 times the height of the structure. Considering a 60 m tall structure, the radius of the exclusion zone should be 150 m upwards. Obtaining such a radius may prove impossible depending on what surrounds the structure demolition. Williamson (2008) states that during the demolition of the 88 m Calder Hall Towers, the exclusion zone was set to 200 m. It is not everywhere in the world that such an exclusion zone is possible.
According to Foruzesh (2016), one of the main public concerns is the stability of the structure following the primary weakening. It may happen that the primary weakening renders the structure unstable. This way, the structure may collapse prematurely, at a time when no one around is prepared. This may lead to casualties who may be present around the structure when it prematurely collapses.
Foruzesh (2016) suggests that all areas must be exploded until all the explosives are used up. After the building comes down, a blasting expert should review the site and ensure all explosives were detonated. Bearing in mind the amount of rubble that may be piled up by then, it may be difficult to 100% ascertain that all explosives were detonated. This also depends on the type of explosives used.
The OHSA Technical Manual (2020) asserts that all electric, gas, water, steam, sewer, and other service lines need to be cut off, capped or controlled, at or outside the structure before any demolition work kicks off. The problem comes when it is necessary to maintain the supply of such services to surrounding structures which will continue being used after the one under demolition goes down. Depending on the conditions on the ground, the relocation of the services may not be too far from the structure being demolished. Poor calculations of the appropriate location of utility lines, especially electricity lines, may prove hazardous if the implosion gets out of hand. Another technical constraint is that the preparation for the demolition exercise may not successfully proceed without the supply of electricity, gas, or water to the structure under demolition. The utility providers may find it difficult on deciding exactly when to cut off the supplies to the structure.
Ramaswamy (2015) highlights the possibility of incomplete demolition. During the demolition of the Red Roads Flats in Glasgow in 2015, two of the eight multi-storey blocks remained partially intact. The reasons for this could be i) high strength of the tower or ii) too little explosive. The preparation for the implosion by DSR Demolition had taken months. Even with such preparation and vast experience of the contractor, and with all the knowledge on explosives, the possibility of the explosives malfunctioning remains, the reason being explosives cannot be tested. The author concludes that in the end, the structure does what it wants to do. For the Red Road Flats, the cleaning up exercise was estimated to take about 2 years. The 2 demolitions that went wrong may have to undergo implosion again after the debris is cleared. Another risk is the possibility of the demolition not taking the form it was intended to. Naik (2018) gives the two major types of implosion as i) falling like a tree and ii) Falling into its own footprint. The second type is especially used in crowded areas where there is no room for the structure to fall sideways. However, as earlier discussed, implosions may always turn out the way they want to. If it was intended for the structure to fall into its own footprint and technical errors make it fall sideways, considerable damage to adjacent structures may be done. The Civil Engineering (2011) journal expounds the risk of partial demolition. The Athlone cooling towers were a twin tower earmarked for demolition. If one of the two towers failed to fully collapse, it would be unstable and would be left tilting at a dangerous angle.
For bigger structures, the explosives to be loaded onto the structure may just be too many for the process to be completed within the recommended time frame. For instance, during the demolition of the Calder hall Cooling Towers, Williamson (2008) states that more than 5,600 holes were drilled throughout the four towers for the purpose of loading the explosives. This took the contractor more than 10 days to fully load all the drilled holes. Regulations specify that there the amounts of uncharged explosives on-site at any given point in time must be kept to a minimum. For this reason, explosives were transported to the site on a day-to-day basis. This comes with the added burden of road closures to pave way for offloading the explosives. Such extended procedures may not be attainable by all contractors depending on the area of the site in question.
Pitroda and Bhavsar (2015) highlight the inadequacy of demolition standards. While construction regulations are several in any given county or country and are usually greatly detailed, the same is not true with standards concerning the demolition of buildings. The standards are somewhat separate, roughly compiled, and out of date. No highly reliable regulations exist for demolition contractors and procedures. The downside of this is possible friction with regulatory authorities. The client may not clearly aware that he is on the wrong side of the law as there may be no document to fully guide the operations.
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