implosion of structures
Post on 09-Mar-2015
Embed Size (px)
A Technical Paper On
Implosion of StructuresSubmitted To NIRMITEE 2005 By
Ankit JainEmail: - email@example.com
Sinhgad Technical Education Societys
Sinhgad College of Engineering Vadgaon Budruk, PuneImplosion of Structures1
Author: Ankit Jain, Sinhgad College of Engg. Pune, Email: - firstname.lastname@example.orgAbstractWith increase in population, society demands vertical growth of structures and removal of those structures, which hampers the growth and is not capable of accommodating the burgeoning population. Besides this, with due to consideration to the safety reason and to avoid expensive retrofitting, which is nothing but a temporary remedial measure, old structures must be replaced. This technical paper introduces us to different techniques of demolition and implosion in specific. Prime intention of this paper is to introduce civil engineers to Implosion technique of demolition.
Introduction Demolition is an activity in which construction process is reversed that is the building or part of it is disassembled and removed. Today structures are carefully dismantled and not demolished. Demolition has evolved since its inception, form wrecking ball to explosives. During its evolution it has become faster and safer and more cost effective. Need for demolition As a civil engineer why should I demolish a structure? This is the first question that comes in our minds. A civil engineering structure has an in built life of 50 to 200 years. Structure needs extensive restoration work after its design period. Structures also get damaged during natural calamities like earthquake, cyclone etc. It is very costly to repair this kind of structure. In light of this it is advisable to go for complete reconstruction of the structure. This brings in current best technologies in construction in place of the older techniques. For this to happen we need to bring down the structure, we need to demolish the structure.
Wrecking Ball Swinging balls made up of solid metals is used. Momentum of these swinging balls impart tremendous amount of energy on concrete which it cannot withstand and hence breaks into pieces, thus bringing down the structure.
Hydraulic breaker Hydraulic force is used to crush concrete between some kind of teething mechanism. This weakens the structure and causes collapse of structure. Demolition is carried out floor by floor.
Expansive material (Non Explosive technique)
This is a non explosive type of demolition. Some chemical materials expand on mixing with certain types of chemicals. These expanding chemicals provide great amount of swelling pressure. The pressure is so intense that it overcomes concretes compressive strength. This technique is a very clean non messy type of technique causing no type of pollution (noise, dust) Demolition by explosives (Implosion) Explosives are used to assist demolition of a building. The act of imploding, or precisely controlling the exploding of a building from within, may only require a few seconds to physically place the building on the ground is known as implosion. Planning However, several months of careful planning must be accomplished before an implosion can be done. In addition, depending upon size, the actual preparation of the building may take several weeks. Careful, precise planning with all parties involved in the process is mandatory in insuring a successful implosion. Demolition Method Feasibility studies should be undertaken by the construction manager to examine the cost effectiveness of imploding compared to the wrecking ball method. In some cases, the wrecking ball method will be considerably cheaper. Factors which influence these costs will be building size, asbestos abatement, type of construction, proximity to other buildings and thoroughfares, and exposure of the general public to the building during demolition, all potential sources of liability. Owners may choose implosion as a method by which to lessen exposure to the local press and media when buildings have historical or sentimental significance to the community. Implosion may also be chosen when costs are found to be comparable to or even more expensive then the wrecking ball due to the convenience associated with the implosion process.
Permissions and Regulatory Requirements The construction manager must immediately begin the process of managing a demolition once this method has been chosen by the owner. Early on, local governmental officials must be involved in the planning process. The construction manager must call meetings with officials of agencies which include, but are not limited to, the following: Building regulations, police, utilities, fire, public works, air pollution control, and the natural resources departments. The officials must be directly involved in the planning and coordinating process as each will be affected to one degree or another by the implosion. In most locales, building regulation officials will also require a demolition permit. Asbestos abatement permits will also be required if asbestos is present in the structure. The media may also become involved at this point at the discretion of the owner. In some cases the media are not notified until a day before the implosion, in order to limit spectators around the job site. Pre Blast Precautions The construction manager must also arrange for pre-seismic and post-seismic surveys around the site. Pre- and post implosion video-surveys should be made of adjacent structures, sidewalks, basements, sewer and water lines, and on exterior skins and roofs of adjacent buildings. This could eliminate any liability claims after the implosion. Also, owners of adjacent and area businesses should be notified of the date and time of the implosion, and what is being done to protect their structures. In some cases, plywood barriers are constructed and placed between the site and the businesses as a precautionary measure. Semi-trailers have also been utilized as a protective barrier, but are used primarily as a psychological boost for the adjacent owners. Preparation of Building For Implosion The building itself is prepared for implosion by basically removing the contents of the building, salvageable fixtures, and non-load bearing partitions in the basement and lower level floors. Utilities are disconnected, and the building itself is wrapped in a chain link fence. Testing of concrete is done to ascertain on site strength of it. This is done with the help of NDT (Ultrasound test, Impact hammer test). Also test blasting of selected columns is carried out to ascertain in situ concrete strength and to determine amount of explosives to be used per column. Structural columns are drilled for explosive charges which are loaded approximately twenty-four hours prior to the
scheduled blast time. The demolition contractor is generally responsible for the preparation of the building as part of the contractual agreement. Risks Management Columns are wrapped with meshes and geosynthetic materials so as to contain the flying debris. Explosives used per columns are carefully computed. A berm of earth and demolition debris is placed against the first floor in order to contain flying debris during the blast. Protective sheathing is provided on neighbouring building so as to protect them in case some debris fly and impact it. Falling debris creates mini earthquake which if not managed properly can cause damage to neighbouring buildings. For this building is allowed to fall in a sequence so as to channelize energy into ground at different time intervals. Security guards patrol the premises after the building has been loaded. Timing of Blasting Ideal weather conditions for the blast are a light breeze and a cloud ceiling minimum of 1500-2500 feet. Low cloud ceiling levels will present dispersal of dust, so normally a blast will be postponed for low ceiling levels or thunderstorms. Blast times are normally set up very early on a Saturday or Sunday morning to lesson inconveniences to the general public, especially if main thoroughfares have to be temporarily closed. Police departments help with crowd control and safety barriers prior to and during the blast. Cleaning Immediately following the implosion, construction and City Street cleaning crews will clean and water down the adjacent street, removing any dust or debris. Depending on the situation, most roads are open within one to two hours. Cost of the city street cleaning crews is charged directly to the owner via the construction manager. Waste Management Debris removal from the site is usually contacted on a per cubic yard basis by an excavating contractor. During this time, an owner may chose to recycle aluminium, copper, and steel to the area reclamation centre. All combustible and non-combustible materials must be discarded in 6
accordance with local, state, and federal laws. Every year, the disposal of construction debris and trash becomes more of an expense and problem to the contractor. Careful planning, prior to an implosion, can actually help to reduce expenses of debris removal. Test Blasting of Columns
Drilling holes for placement of explosives
Wrapping of column with geosynthetics
Blasting of column and containment of debris
Blasted columns Section. Exposed steel mesh can be seen
Types of structures that can be imploded
Cooling Towers Steel Towers
KINGDOME IMPLOSIONThis particular structure was located in Seattle, USA. This structure use to house a football stadium. It was constructed in 1976 at the cost of 67 million dollars. It was imploded on March 24 2000 at 8.50 am on Sunday. In place of this stadium a new stadium was to be constructed. Fol