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1. 0 Abstract
Engineering failures are a common thing in the field of engineering, and the failures are used as lessons to avoid such faults. The purpose of this research is to look into the Hyatt Regency Hotel Collapse and the engineering faults responsible for the collapse. The hotel section collapsed after only an year after its grand opening, showing that indeed there were some engineering failures in the constructions. The paper keenly looks at the reason behind the failure of the suspensions holding the walkways that resulted in the collapse. The paper also looks into the possible ways in which the collapse could have been avoided. There is also the focus on the impacts of the incident to the engineering practice. At the end of the paper, one should have acquired all the knowledge concerning the Hyatt Regency Hotel Collapse.
In various fields, mankind has shown his superiority and capability through coming up with different innovations. Over centuries, the innovations and achievements mankind has achieved have shown the superiority in the human race. The field of engineering has not been left behind, and in the field the innovations made have simplified human life. However, the creations of mankind have not been a hundred percent perfect. In quite a number of occurrences, there have been engineering failures that have caused the creations to be unsuccessful. The engineering failures have in most cases been fatal, and unsuspecting civilians suffer death or sustain major or minor injuries. However, despite the failures, buildings and bridges still need to be built and more engineering innovations are necessary to conquer challenges of life. The engineering failures should not be considered as setbacks; however, they should be lessons for the engineers to learn from mistakes made by others. This essay is an analysis on the Hyatt Regency Hotel Walkway collapse.
Built in 1978, the Hyatt Regency Hotel was located in Kansas City, Missouri. The construction of the Hyatt Regency Hotel, however, was completed in 1980 and the official opening done on July 1, the same year. The firm responsible for the construction of the Hyatt Regency Hotel was Gillum-Colaco International Incorporation (G.C.E. Inc.). The project actually began in 1976, but the construction started in 1978. In December 1978, Havens Steel Company was awarded the chance to construct and fabricate the atrium. In February, two months later, Havens Steel Company improved the design to be used in connections for the fourth and second floor. The walkways were not to consist of double rods, rather than a single rod. The construction of the hotel was slowed down by some construction problems that occurred during the building course.
On October 14, 1979, part of the roof collapsed, 2700 square feet. The reason for the collapse was the failure of a connection at the northern end. As a result of the collapse, the Gillum-Colaco International Incorporation looked into all the steel connections in the atrium to try and figure out the cause of the collapse. The building comprised of a forty story hotel tower, conference facilities, hotel lobby. The hotel also had an atrium with elevated walkways which were suspended from the ceiling. The walkways were 36 m (117 ft) long, 44 m (145 ft) wide, and 15 m (50 ft) high, with a weight of about 29,000 kg (64,000 lb.) approximately. The South and North wings of the hotel were connected with the second, third and fourth floors by the walkways (Pfatteichner, 2010). The walkways were made of glass, steel and concrete to ensure that they would facilitate the movement of individuals.
The second-floor walkway was suspended below the fourth-floor walkway. The walkway on the third floor was suspended independently from the atrium roof. On July 17, 1981, just a year after its opening, the second and fourth floors walkways collapsed, crashing down to the ground level. The fourth-floor walkway fell first, and it came down with the second-floor walkway. The impact on the second-floor walkway caused the second floor also to collapse. The two floors then fell on the first-floor level of the atrium and lobby causing death and injuries to the victims. The third-floor walkway was not even involved in the collapse since of its independent position. The large numbers of casualties are the individuals who were located on the second-floor walkway and first-floor level of the atrium.
2.2 Details of the collapse
At the time of the collapse of the fourth and second-floor walkways, there were approximately 2000 people in the atrium, gathered for a dance competition. The collapse resulted in the death of 114 people and more than 200 others succumbing injuries. At the scene of the collapse, 111 people passed away, while the remaining three passed away while being transported to the hospital. The rescue operations lasted for about fourteen hours and the rescue team included doctors from five hospitals, emergency personnel. EMS units and crew from thirty-four fire trucks. The number of personnel in rescue team only shows the intensity and seriousness of the accident. One of the challenges that the rescue team faced was falling debris in the hotel’s sprinkler system. As a result, the lobby was flooded, which put some of the victims at a great risk of drowning.
The pipes in the lobby were connected to water tanks in the hotel and not to a public source of water (Evan & Manion, 2002). Therefore, it was a challenge to the rescue team since the flow of water could not be stopped. The last survivor to be rescued from the collapse, Mark Williams, spent over nine and a half hours trapped. Williams almost drowned from the flowing water, considering that all this time he was trapped, both of his legs had been pulled out of their sockets. If it was not for the order given by the Kansas City fire chief to break the hotel’s front doors, Williams could have possibly drowned. The hotel doors were trapping water in the lobby, therefore, breaking the doors allowed water to flow out of the lobby increasing the survival chances of Williams.
The rescue team was faced with quite a number of challenges and forced to engage in some quick decisions to save lives. For example, one victim had their right leg trapped and a surgeon was forced to amputate the trapped leg using a chainsaw to save the individual’s life. Those who could walk were forced to walk out of the hotel. Such activities helped the rescuers provide assistance for the individuals who were badly wounded. It also fastened the process of rescuing the victims of the Hyatt Regency Hotel (Delatte, 2008). The rescue team also faced visibility problems since they had cut power to avoid fire and the scene was filled with concrete dust. The number of individuals successfully rescued from the collapse was twenty-nine. The cooperation between the rescue team despite having many members was the reason for the successful rescuing of the victims.
2.3 Analysis of the causes of the collapse
The failure of the walkways, which led to the collapse in the Hyatt Regency Hotel, was caused by a combination of a couple of factors. However, it is significant to identify that the major cause for the collapse was an engineering failure in the design of the walkways. The proposed design of the walkways was supposed to consist of some things;
1. On each side of the walkway, wide flange beams were to be used, hanging from a box beam.
2. At the top of the box beam, a clip angle was supposed to join the flange beam using bolts.
3. On one end of the walkway was to be supported by a sliding bearing while the other welded to a fixed plate.
4. A washer and nut threaded to the supporting rod were responsible for supporting every beam box on the walkway.
As a result of the disagreements between Gillum-Colaco International Incorporation and Havens Steel Company, the design of the atrium changed to double hanger rods from single rods. The change was pushed by Havens Steel Company, since the company was not for the idea of installing the washer and nut, which would result in threading the entire rod (Petroski, 2012). A look into the actual design of the walkways before change was made shows some of the causes of the collapse. The initial design of the walkways included;
1. One end of every support rod was supposed to be connected to the cross beams on the atrium’s roof.
2. The lower end of the rod passed through the washer and nut, threaded on the box beam.
3. Four inches away from the first rod, the second rod was connected to the box beam.
4. Additional rods were also required to support the second level and the rods were suspended down.
Due to the inclusion of another rod, the load was increased on the nut attached to the fourth-floor segment. The initial load for one hanger rod before the change of the design was to be 90kN. However, because of the increase in one rod, the load of one hangar road increased to 181kN (Weingardt, 2005). Therefore, the load on the nut attached to the fourth-floor increases by double the initial load. The box beams were welded in a horizontal position, making it impossible to manage the weight of the two walkways. When the collapse occurred, the box beam split and this caused the bottom rod to pull through the box beam leading to the collapse. The change in the design of the atrium caused the capability of the walkways to be reduced. An increase in the load caused the design to have the capacity to withstand only percent of the minimum number of individuals.
The primary causes of the failures in connection that caused the collapse of the walkways include;
1. Improper design because of the failure to consider all forces involved in connection, especially when it comes to a change in volume.
2. Insufficient possibilities for movement and turning.
3. Stress concentrations as a result of improper design using rapid section changes.
4. Wrong preparation of mating surfaces and lack of proper connections.
5. Materials degrading in a connection.
6. Lack of considering the possibility of residual stresses due to manufacture or fabrication.
However, it is important to acknowledge that according to the Kansas City building code, none of the two designs was effective. By the two designs, this refers to the implemented and initial designs for the atrium. Both designs for the hanger rod did not meet the expectations of the Kansas City building code. In the two designs, the possibility of failure after making the connections was an inevitable fact. If the two building designs comprised of more redundancy, then the failure in the connections could have been prevented, avoiding the collapse. The toe-to-toe channels used in the construction of the Hyatt Regency made it possible to have weak welding. Weak welding, aided the nut to pull through the box beam assembly, leading to the collapse. If the engineers explored other channels other than the toe-to-toe, then the collapse could have been avoided.
The use of a back-to-back channel design that uses web stiffeners in necessary situations would have been a good replacement for the toe-to-toe channels. Bearing cross plates could also be used together with the toe-to-toe channels (Loosemore, 2000). The bearing cross plates would have made the connection much stronger, making it very hard for the nut to pull through. The channel design change from toe-to-toe channel in the fourth-floor walkway, this could have avoided the occurrence of the collapse. If the connections in the fourth-floor walkway were redundant enough, then the suspension would be strong enough to hold the increased load in the fourth-floor. At the time of the collapse, the fourth-floor was only holding thirty-one percent of the ultimate capacity of the expected connection design.
Despite Gillum-Colaco International Incorporation being awarded the tender for offering structural engineering services, the company did not carry out the services required. Instead, the company subcontracted their responsibilities to their subsidiary firm, Jack D. Gillum & Associates, Ltd. The name G.C.E. would later on be used to refer to Jack D. Gillum & Associates, Ltd. One of the project’s specifications was that the structural engineer needed to approve all shop drawings before work started. The Havens Steel Company, was a subcontractor for the Eldridge Construction Company; a general contractor in the construction of the Hyatt Regency Hotel (Weingardt, 2005). There was also an inspection team comprised of two inspecting agencies, General Testing and H&R Inspection. In the inspection team, other members were an investigating engineer, quality control official and construction manager.
The inspection team for the construction of the Hyatt Regency Hotel, despite having many members, it was incompetent. After part of the roof section collapsed while the hotel was under construction on October 14, 1979; the inspection team should have done a thorough research. In the issue of the roof collapsing, the inspection team did quite a recommendable job to come up with the reason for the collapse. However, the inspection team did not think to carry out any investigation on anything that was beyond their scope of investigation and contract. The inspection team should have offered to help the contractors inspect if there are any faults in the design or engineering work to be used. Maybe such a move might have increased the chances of a mistake being discovered and avoiding the fatal collapse. Any inspections in the design of the atrium proved that the steel connections were not prone to collapsing under any circumstances.
Another cause of the collapse was lack of proper communication between the two contractors, Gillum-Colaco International Incorporation and Havens Steel Company. The drawings for the initial design of the atrium made by G.C.E were just sketches. However, Havens Steel Company was not given this information and, therefore, considered the drawings to be final. The final design for the atrium that was changed by Havens Company was also not inspected (Vesilind & Gunn, 2011). If Gillum-Colaco International Incorporation had inspected the final design for the atrium, then the fault in the increase in the load on connections could have been discovered. Therefore, both companies are to blame for the failure to cross check their work to ensure that no mistakes were left unresolved. If the two companies had good channels of sharing information, then it would have been possible to evade the occurrence of the collapse.
2.4 Impacts on engineering practice
The collapse of the second and fourth-floor walkways of the Hyatt Regency Hotel was not taken lightly by the board of professional engineers in Kansas City. The engineers who were employees of the Gillum-Colaco International Incorporation suffered the conviction of the Missouri Board of Architects, Land Surveyors and Professional Engineers. The engineers were convicted of unprofessional conduct, irresponsibility and gross negligence in the profession of engineering. All these engineers lost their engineering licenses in the States of Taxes and Missouri as well as their membership with the ASCE being terminated. To the victims and their families who were in the collapse of the Hyatt Regency Hotel, at least 140 million dollars was awarded to them in civil lawsuits. The Gillum-Colaco International Incorporation, however, did not suffer any charges of criminal negligence. The firm was not that lucky because it lost its license to operate as an engineering firm.
The Hyatt Regency Hotel Collapse highlighted some procedural concerns and ethical concerns in the field of engineering. First, the entire incident highlighted on the lack of procedures to cater for design changes. The incident also shed light on the confusion about the person who bears the responsibility of integrity of shop details. The lesson learnt from the punishment the engineers served is that; engineers are responsible for the structural integrity of the whole building, without leaving out the shop details (Baura, 2006). Therefore, in each project, it is important for the involved parties to take responsibility and understand their roles fully. To prevent similar collapses, it would be important to follow some of these procedural changes;
1. The engineer in charge of record should ensure that all design and details are free of non-standard connections.
2. All the new designs should undergo thorough checking and inspection.
3. Any modifications made by the contractors to the details of the design should be approved by the engineer of record.
The incident put to the limelight the incompetence and irresponsibility of some project engineers. The incident also enlightens the safety of innocent unsuspecting individuals who suffer death and injuries due to the incompetence of a project engineer. The incident prompted companies in Kansas and nearby cities to take their job seriously. The project engineers were also challenged by the incident to take their jobs professionally and avoid the occurrence of an avoidable failure in the system (Harris, 2014). Before approving a design, a project engineer should consider that the safety of every person who will end up using the construction will be in his or her hands. Therefore, safety measures need to be given top priority since it among the tasks of the project engineer. The project engineer should also consider the fact that if they do a shoddy job, then they will carry all the blame.
2.5 Recommendations for future projects
During the trial the architect, detailer, technician and fabricator all testified that in the course of the construction of the hotel, they were in contact with the project engineer. Their testimonies proved that the project engineer was contacted in the issue of the structural integrity of the connection design. Every time the project engineer was contacted, he assured that he had checked the connections, and they were safe. However, the project engineer had not carried out any calculations concerning the connections and their safety. If the project manager had kept his word and done his job, he would have found out that there was a possibility of the walkways collapsing (Loosemore, 2000). The negligence of the project manager and failure to check the load capacity of an important hanger and the safety shows disregard for human life and unprofessionalism. Ethical engineers should check their work and make sure that they can assure the public of a building’s structural integrity.
Many construction projects have been faced with setbacks especially after the structures collapse. The collapse of a structure is the result of either negligence of the workers, an engineering failure or a natural cause. Cases of engineering failures are examples how the same situations can be avoided in the future. Using the Hyatt Regency Hotel Collapse for reference, there is a lot to be studied from the incident to help in the prevention of another one. Any engineer in charge of the structural integrity of the building should make sure that they do a recommendable job. When a project engineer does his or her job in a professional manner, the occurrence of a collapse or engineering failure in the structure is avoided thereby, saving human life. The design details for the project should be inspected thoroughly to ensure that under no circumstances, would there be a risk in the design details that is not dealt with.
In conclusion, it is true at this point to state that the collapse of the second and fourth walkways of the Hyatt Regency Hotel was indeed avoidable. Looking at the causes of the collapse, one factor can be identified; lack of proper communication played a significant role in the collapse. The two companies lacked good communication channels to share information that was important to the construction of the hotel (Delatte, 2008). The final design for the atrium had a fault, but no one took the time to look into any possible faults in the design. If the two companies had proper communication channels and discussed the design for the atrium, the possibility of the collapse could be reduced. The Hyatt Regency Hotel Collapse shows that, despite there being an engineering failure; there were other unrelated factors that caused the collapse of the hotel walkways.
Over time, there have been various engineering failures in the many types of creations made by man. The engineering failures go a long way to show that human is prone to making errors. Therefore, the engineering failures should be used as a lesson for new engineers to be keen with their creations. It is important for every engineer to make sure that they cross check their creation to avoid causing harm to humans. It is a violation of the code of ethics for engineers to cause harm to the public while undergoing their professional responsibilities. Instead, engineers should ensure that their professional responsibilities uphold the welfare, health and safety of the public. Any engineer that is proven to be guilty of unprofessional conduct, irresponsibility or gross negligence can end up being responsible for the tragedy he or she causes (Weingardt, 2005). Such an engineer might end up suffering suspension from the board of engineers and in some severe cases get arrested. The tragedy of the Hyatt Regency Hotel is always a classic example of engineering failures to be looked upon.
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In the current times, people are of the opinion that the built environment will end up degrading the natural environment. However, this point of view draws its hypotheses from personal opinions and not from historical facts. Some of the constructions such as the beaver dams have played a critical role in the development of the ecosystem around by creating eddies that later form wetlands (Kyvelou & Sinou, 2006). This nature of the beaver dams is indicative of the possibility of the built environment playing a role in the conservation of the environment. This is a sustainability concept that the paper will base most of its focus.
Green building is a sustainable way of construction that plays a vital role in the enhancement of the environment. The benefits that come from this approach of construction improve on the quality of life that the people lead, and environment is least hampered by the addition of buildings (Walker, 2007). Therefore, sustainable construction helps in ensuring that construction is not detriment to the diversity of the environment. Green building is all about tailoring a building and a construction site to suit the local climate, the site, culture and the community in order to reduce the use of the resources while improving the quality of life that people lead.
However, the above metrics of looking at the concept of green construction are not conclusive. This means that one cannot look at sustainability in the construction industry from one point of view. On the contrary, the assessment of the approaches used in construction differs, and one has to come up with a multi-prolonged approach of assessing the sustainability in construction (Kyvelou & Sinou, 2006). This point makes the notion that one can assess the sustainability in construction by looking at the natural features and resource efficient features invalid. Natural and resource efficiencies may be evident or not in a building. In the event that the latter is the case, sustainability in the construction may have to take a different dimension.
Green building is not a mere assemblage of resources or a modification of the standard practices in the construction industry. Use of these misguided approaches in construction adds to the costs of construction and the savings that it makes are marginal (Kyvelou & Sinou, 2006). The real approach to green building involves the use of all approaches or steps used in construction and making them sustainable. This approach is an inclusive, and it increases the prospects of making a building that is relevant to the environment than any other. Green building often involves the integration of the interlinked issues of climate and site, the building orientation and form, materials and thermal comfort and making the most out of the aspects in concert.
Therefore, for the building to have the multiple gains of construction green building design must take place in the early steps of construction. The use of a diverse team is also necessary for the creation of synergy that comes from the different disciplines of the team. This is a departure from the conventional approaches in construction whereby most of the people are left out of the process and are brought into the decisions making procedure later (Walker, 2007). The ideas that the people may have brought in the construction will just end up being irrelevant since they cannot make a difference at advanced stages of construction. However, early collaboration can be instrumental in reducing or eliminating some of the capital and operational costs while adding to the environmental and social agenda of construction.
The integrated approach mentioned above is the main reason that makes the green buildings cost the same as the standard ones. This is possible despite that fact that some of the components used in the construction process may cost more than in the standard buildings. The green design has some elements that serve different functions in the construction that may make it possible to downsize on some of the aspects. For instance, the use of better window may lead to smaller and less costly heating systems. The use of photovoltaic panels can serve the purpose of parking shades and serve the role of power generation.
This is a real saving area for the construction industry in since the building in the United States use forty per cent of the total energy produced. They also use a lot of water. The buildings also contribute to 40 per cent of the total wastes found in the landfills. The easily available technologies can add to the efficiency in the constructions by three or four times making immense savings for the construction owners. However, the savings made are not only beneficial to the owners (Walker, 2007). The reduced energy needs from the sustainable construction approaches makes it highly possible for the government to reduce on the energy generation.
Some of the approaches that the government uses in the energy generation are not necessary green. On top of this, the needs of the building may necessities the use of other sources of energy. Most of the alternative sources of energy rely on the fossil fuels. The use of energy sufficient buildings may lead to the reduction of the pollution that comes from power generation. The other thing that the building should have is an energy efficient heating system that produces the least amount of pollution while optimizing on the heating. Most of the buildings rely on the coal powered heating plants (Dhir et al, 2005). The plants must reduce the instances of smoke coming out into the environment while increasing the chances of the building to have a stable heating that will make it habitable.
On the other hand, the construction may necessitate the use of green energies that do not pollute the environment as such. Coal in itself is not the best source of heating in that the dangers that it presents are likely to increase the dangers to the people in the event that it leaks (Khatib, 2009). Making use of an alternative source of energy such as natural gas is an option that may reduce the emissions that emanate from the buildings. However, in as much as the green construction maybe for the reduction of the energy costs to the building by generation of cheap and environmental friendly energy the answer to the heating problems may be in the insulations used. Buildings that have insulations end up using less energy than the ones with reduced insulations. The building ought to use the most efficient insulation systems that lead to low energy loss.
The sustainability in the construction industry also has its inclinations leaning towards saving energy. It is easier saving the amount of energy that one uses than using it. Burning the energy just leads to many liabilities to the company than when the company makes a conscious effort at reducing the cost (Khatib, 2009). In the case of electricity, every unit of power that the business saves has a ripple effect in that the savings reach the power generation plant. The fuels costs used in the power generation are at their minimal.
Designers and managers in the construction industry fail the sustainability test when they look at the initial costs of an establishment. For example, the use of high performance windows in the construction may lead to an increase in the initial costs. The contractors and the designers may want to reduce the costs that they incur in constructing the building (Dhir et al, 2005). However, the costs that they seem to save will come back and plague the owners of the building as well as users.
Unless the designers of the building have, foresight of the savings that the owners may save by incurring slightly higher costs makes it difficult to impart the concept of sustainability in the constructors (Walker, 2007). The designers may have to look into some of the things that are unnecessary in the construction but conventional. This reasoning comes from the realization that whatever additions can be made to the building are just as significant as the omissions that one can make in the construction.
Resources used in the construction are among the other most significant aspects of the green construction. One of the most efficient approaches used in the saving on the resources is the reduction of the consumption of the resources. In order for the reduction of the costs used in construction it highly relevant for the contractors to evaluate whether and why the new building needs to be made. In some of the cases, a mere renovation on an existing building may suffice the imperative needs of constructing a new building. The renovations save on the time, money and resources that could be otherwise put into the construction of a new building.
The company or the family that owns the building maintains the right to remain in an area with existent transport and other amenities (Walker, 2007). This also helps in reducing the sprawl into new areas and having to lay down plans of providing other social amenities. In the event that a company or a family chooses to move to a new location, the social amenities that they used in their previous area end up being underutilized. Sustainability is all about optimum use of the resources at one's disposal (Dhir et al, 2005). Renovations on the existing building optimize on the available amenities while maximizing on the capacity of the building.
The construction process must indicate the consideration for the environment. In any development site, the protection of the adjoining agricultural land, water bodies and vegetation is highly essential. Control of erosion is also significant in that it leads to enhancement of the environment. The planning of construction and demolition should be indicative of the need to reduce or eliminate the wastes. On a typical day, the debris from the construction sites account for most of the landfills. Majority of the debris that ends up in the municipal dumpsites can be reused or recycled.
The reuse of recycling is not only an environmentally friendly practice, but it could also add to the entrepreneurial ventures of the local community. In the event that the materials are reused, the sources of the raw materials used to make them will last for a longer period than when the conventional practice of dumping is in play. However, the reusing and recycling of the materials calls for a fore plan (Kyvelou & Sinou, 2006). The upfront planning is necessary in that it forecasts the possible outcomes. There must be arrangements on the storage of the debris. The contractor has to allot additional time for handling the debris such as sorting the wastes finding the potential buyers, deciding on the recyclers and arranging the logistic operations for delivery of the debris (Ma, 2011).
The other approach necessary in the construction of sustainable buildings is the third party commissioning. This process comes once the building is complete. The process involves making sure that the installed systems are running as per the plan. This process can be the ultimate way of ensuring that the costs of running the business are at their minimum. Constant maintenance and inspection of the system is also significant as a control measure since it ensures that the actual is not divergent from the plan (Khatib, 2009).
Most of the developed countries account for a lot of garbage. The Americans produce garbage in millions of tons per year. The sad aspect is that 50 per cent of the garbage can be recycled. The current levels of recycling are below the par. Materials that a company uses in the construction of the buildings should also indicate the dedication of the company to recycling. For instance, some of the construction materials can be recycled. The equipment used in the sites does not have to be new.
The items can be reused to reflect the need of optimization. Design of the buildings ought to be accommodating to recycling of the consumer goods for the time that the business is in use (Dhir et al, 2005). This practice normally entails the installation of recycling additions such as bins, extra dumpsters and chutes that are easily accessible. The maintenance plan for the building must also accommodate the option of recycling in all instances where it is applicable.
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This technical report presents the findings of concrete tests done with samples casted using PFA as a partial replacement for cement. The samples exhibited good mechanical properties desired for structural concrete, in addition to improving some of the concrete properties. The characteristic strengths of the samples containing PFA are exceptionally high and can be used in structural design.
Well cured and hardened concrete material has to be strong enough in order to be able to withstand all the structural and service loads intended to be applied to it. It must also be sufficiently durable to withstand the environmental conditions for which the structure is designed. Using high quality materials that are well mix-designed, handled and well placed and finished ensures that the concrete material produced attains high strength and becomes durable when used in structural building (Dhir, et al., 2002).
Properties of hardened concrete include: workability, creep, shrinkage, water tightness, strength and rate of strength gain, durability, and Modulus of Elasticity. These concrete properties depend on the mix design (mix proportions), the curing conditions and the environment (Shirley, et al., 2009). Concrete strength generally refer to its compressive strength, because concrete is very strong in compression and relatively weak in tension. Concrete compressive strength largely depends on the amount of cement used, the water-cement ratio, aggregates, curing conditions, age, and admixtures used (Thomas, 2007).
A lot of research has been ongoing to address some deficiencies of concrete, with some providing very significant efforts geared towards improving its structural performance. The existing literature shows that partial replacement of cement using mineral admixtures can significantly reduce the porosity and improve the density and durability of concrete, alongside improving the compressive strength, flexure and tensile strength. A part from enhancing concrete’s ability to exhibit greater resistance against harmful chemical attack and environmental conditions, mineral admixtures significantly contribute to sustainable environment as partial replacement of Portland cement and are normally referred to as “ less energy intensive” cementitous materials (Thomas, 2007).
Among available mineral admixtures, the most commonly used are pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS), silica fume (SF), rice husk ash (RHA) and metakaolin (MK) (Khatib, 2009). PFA has also worked well and recommended for structural use as a partial replacement of fine aggregate. This report presents the results obtained for density, compressive strength test and RC beam test for Self compacting concrete (SCC) samples tested using standard methods. The concrete cubes and cylinders were prepared by designing and batching a concrete mix using Pulverized Fly Ash (PFA) as a partial replacement of cement.
Initially, 0.035 m3 of concrete trial mix was designed using the BRE method to the specifications on page 2 and 3 of the lab manual for a test age of 28 days. VMA compounds and super plasticizer were added to the concrete sample to produce the SCC mix. From this mix, 3 concrete cubes were prepared using cubical molds with a length of 100mm, and another 3 cylindrical concrete samples were prepared using cylindrical molds 100mm diameter and 200mm long.
The masses of hardened concrete samples were measured and then the cubes tested for compressive strength using the Schmidt rebound hammer after the 28 day period of curing under a tank of water. An ultrasound of equipment was used to determine the value of elastic modulus of the concrete, and hence, its compressive strength as well. The samples were then tested for compressive strength using a destructive method under increasing load, and the maximum load at failure and the modes of failure recorded. Reinforced concrete (RC) beam was prepared by making a reinforcement cage to the bar schedule drawing in the lab and then placing it in a reinforced concrete mold measuring 1.5m by 100mm by 200mm. The beam was set as shown in the figure below.
After setting the beam, demec and deflection readings for zero load were recorded. The positions of the demec points were then measured and recorded, ensuring that the load was applied at 1/3rd beam span positions and deflections measured at mid-span. The beam was loaded in load increments of 3kN up to 30kN, recording demec and deflection readings at every load increment. After 30kN, the load increment was reduced to 1 kN and only deflection was measured. When deflection began to show large increases, the deflection gauge was removed and the beam loaded to failure and the failure load and mode of failure recorded.
Dimensions: 100mm X 100mm
Area = 10000mm2
Mass of cube in air = 2351.5g
Mass of water before placing cube = 1318.6g
Mass of water after placing cube = 33.6g
Mass of water displaced = (1318.6 – 33.6) = 1285g
Volume of water displaced = 1285cm3
Density of the cube = = 1.830g/cm3
Cube maximum load = 517.10 kN
Cube compressive strength =
Modulus of elasticity (E) =
= density of concrete (kg/m3)
= compressive strength of concrete (MPa)
E = = 18.58 GPa
Ultrasonic pulse rate =
The densities for cube 2 and 3 were calculated using the steps above and the results presented in table 1 below:
Table 1: Cubes
Cube Mass in air (g) Mass of water before placing cube(g) Mass of water after placing cube(g) Volume of water displaced(cm3) Density of cube(g/cm3) Cube maximum load(kN) Cube compressive strength (N/mm2) Ultrasonic pulse time(s) Modulus of elasticity, E(GPa)
1 2351.5 1318.6 33.6 1285 1.830 517.10 51.71 21.6 18.58
2 2366.1 1325.0 33.5 1291.6 1.832 491.84 49.18 22.0 18.15
3 2303.0 1284.9 33.6 1251.3 1.840 514.24 51.42 21.5 18.68
Mean compressive strength of the 3 cubes = 50.77 kN
Mean modulus of elasticity for the 3 cubes = 18.47
Cylindrical concrete samples
Dimensions: Diameter 100mm, Length = 200mm
Area = () = = 7853.98mm2
Cylinder Mass in air (g) Mass of water before placing cube(g) Mass of water after placing cube(g) Volume of water displaced(cm3) Density of cube(g/cm3) Cube maximum load(kN) Cube compressive strength (N/mm2) Modulus of elasticity, E(GPa)
1 3666.0 2070.7 33.6 2037.1 1.799 337 42.91 16.49
2 3680.7 2080.7 33.6 2047.1 1.797 362.52 46.16 17.08
3 3682.8 2081.6 33.6 2048.0 1.798 248 31.58 14.14
Table 2: Cylindrical concrete samplesRC Beam Testing Results
Modulus of elasticity
d = h-23mm
d = 200-23 = 177mm
h = 200mm
As = 200 x 100mm
Cube maximum load = 72.53 kN
Cube compressive strength =
Modulus of elasticity (E) = =
The mean compressive strength of the 3 cubes = 50.77 kN, so the mean static modulus is Ec is 34.
Modular ratio (m) = = =
Replacing the values of b, y, m, As and D in the equation b.y.(y/2) = m.As(d-y) and solving the resulting quadratic equation, the value of y = 176.99mm.
Maximum load = 72.53kN
The table below shows the results for the RC beam test performed
Load(kN) Stress Deflection(mm) Demec readings(
0 0 0 1 2 3 4 5
3 10.0 0.28 2.096 2.050 2.064 3.238 2.701
6 20.0 0.49 2.035 1.997 2.015 3.195 2.659
9 30.0 0.71 2.024 2.038 2.059 3.245 2.713
12 40.0 0.96 2.063 2.040 2.066 3.262 2.732
15 50.0 1.25 2.051 2.039 2.074 3.282 2.765
18 60.0 1.60 2.033 2.039 2.088 3.309 2.803
21 70.0 1.88 1.990 2.016 2.081 3.321 2.834
24 80.0 2.17 1.969 2.008 2.083 3.337 2.860
27 90.0 2.45 2.057 2.111 2.198 3.464 3.002
30 100.0 2.70 1.953 2.024 2.119 3.406 2.965
31 103.3 2.84 1.938 2.013 2.118 3.410 2.966
32 106.7 2.91
33 110.0 2.90
34 113.3 3.07
35 116.7 3.18
Elastic modulus is one of a key factor in determination of deformation of a structural element and modular ratio used in the design of members subjected to flexure. A higher value of E means that the concrete is good enough to withstand a relatively high elasticity. The typical modulus of elasticity for normal concrete is around 17GPa, while for high strength concrete, it is around 30GPa (Ramezanianpour, 2013). Concrete cubes have a relatively higher modulus of elasticity compared to concrete cylinders. High modulus of elasticity is suitable for concrete since it should be strong enough to carry all the desired loads in compression.
The strength exhibited by the samples tested is within the acceptable range of design expectation as of those where the PFA is not used. The use of PFA in structural concrete has both economic and technical benefits. It reduces permeability and produces a cohesive concrete matrix that has reduced rate of bleeding, and can self-compact (Gingos & Mohamed Sutan, 2011). The long term strength, durability and performance of the concrete are some of the great properties achieved when fly ash is used as a partial replacement for cement. Based on the proportion of PFA in the concrete mix, a significant reduction of concrete carbon footprint can be achieved.
The use of PFA as partial replacement of cement does not significantly affect the mechanical properties of concrete, including its characteristic strength. The admixture also improves some of the properties of concrete such as reduction in permeability, shrinkage, creep and resistance to chemical attack. PFA should therefore incorporated in Portland cement as a partial replacement for the cement because of its environmental benefits as well as suitability in structural concrete.
Dhir, R. K., Hewlett, P. C. & Csetenyi, L. J., 2002. Innovations and Developments in Concrete Materials and Construction: Proceedings of the International Conference Held at the University of Dundee, Scotland, UK on 9-11 September 2002. UK, Thomas Telford.
Gingos, G. & Mohamed Sutan, N., 2011. Effect of PFA on Strength and Water Absorption of Mortar. UNIMAS e-Journal of Civil Engineering, 2(1), pp. 7-10.
Khatib, J., 2009. Sustainability of Construction Materials. Amsterdam: Elsevier.
Ramezanianpour, A. A., 2013. Cement Replacement Materials: Properties, Durability, Sustainability. New York: Springer Science & Business Media.
Shirley, R., Claisse, P. & Ganjian, E., 2009. Properties of concrete using high-limepfa from a UK source. Proceedings of the ICE - Construction Materials. UK, ICE Publishing.
Siddique, R., 2007. Waste Materials and By-Products in Concrete. New York: Springer Science & Business Media.
Thomas, M., 2007. Optimizing the Use of Fly Ash in Concrete.
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