Controlled demolition of reinforced concrete buildings by 
       the use of explosives. The Armed Forces Hospital building 
                     C5 case study. 
                           
                           
                           
                  David José Bento Rodrigues 
                           
                           
                           
                           
                     Extended Abstract 
                           
                           
       
                           
      Supervisor: PHd Professor Doutor João Paulo Janeiro Gomes Ferreira 
      Co-supervisor: Lieutenant Colonel Engineering Raul Fernando Rodrigues Cabral 
      Gomes  
       
       
                      October 2014 
                                                          Extended Abstract 
         Abstract 
         As time advances structures in Portuguese built areas start to show high levels of degradation. When 
         rehabilitation is no longer a viable option these structures need to be demolished.  
         Given the reduced knowledge of the use of demolition methods by explosives in Portugal, this study 
         seeks to compensate existing flaws in the project and execution phases. 
         This study starts with a brief introduction, wherein the explosive demolition project methodology is 
         analysed, highlighting the calculation method used which is the base of the software used to model 
         the collapse mechanism, as well as the calculation of the explosive charges. A case study is also 
         analysed allowing understanding all the sequential work done prior to the demolition, in essence its 
         planning and execution. The main impacts of this type of demolitions are also discussed and how 
         these are both controlled and minimised. Finally, a comparative economic analysis between explosive 
         demolitions and traditional demolitions is performed. 
         All  demolition  methods  have  their  applications,  advantages  and  disadvantages.  However,  the 
         explosive demolition methods applied to high reinforced concrete buildings can be a viable solution 
         due to the advantages they present in these situations when compared to other methods. 
          
          
         Keywords: explosive method, traditional method, structure demolition, reinforced concrete building 
          
          
          
          
          
          
          
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                 Explosive demolition of reinforced concrete buildings 
                 1.    Introduction 
                 Engineering is not only about construction but also about demolition, enabling existing space to be 
                 reused. Demolition can thus be defined as a set of removal works to be applied to an existing structure 
                 leading to a new space availability. Demolition work can be partial or global and can be used on new 
                 or old structures (Brito, 1999). 
                 One  of  the  possible  methods  to  be  used  is  controlled  demolition  using  explosives,  which  was 
                 developed in Europe throughout the reconstruction of the cities that were destroyed during the second 
                 World War. Due to its advantages it later spread to the rest of the world (Jimeno et al., 1995), although 
                 it is a technique that is still little used in Portugal. 
                 This study has the objective of understanding how controlled demolition using explosives projects are 
                 executed, highlighting the calculation method used by the demolition program and the calculation of 
                 the explosive charges. All of the aspects during the preparation and execution of the program are also 
                 looked at through the analysis of a case study. A cost analysis is also made in order to be able to 
                 compare explosive demolition costs to more traditional demolition costs. 
                 2.    Explosive demolitions methods 
                 The use of explosive demolitions has grown over the years, not only in building demolition but with 
                 other types of structures like metal or reinforced concrete structures as well. Considered to be a fast, 
                 practical  and  economical  alternative  to  traditional  demolitions,  its  main  focus  is  the  use  on  large 
                 structures such as sky-scrapers, chimneys, and silos, large solid reinforced concrete structures like 
                 naval infrastructure foundations, and even the quick demolition of bridges (Lauritzen & Schneider, 
                 2000, cited by Gomes, 2010). 
                 Explosive  demolitions  consist  of  using  controlled  explosives  by  placing  small  explosive  charges 
                 (generally  less  than  50  g),  which  are  usually  placed  in  the  structural  elements  that  are  to  be 
                 demolished and confined to drillings made for this purpose (Jimeno et al., 1995; Gomes, 2010). 
                 After this placement the charges are detonated through an initiation system. The explosive charges 
                 present in the vertical elements detonate, causing a “structural vacuum” called a demolition belt, within 
                 which through gravity the structure collapses, fragmenting due to its own weight, or, when appropriate, 
                 enabling it to fall on one side, enabling easier access to the debris which can then be taken apart 
                 using traditional methods (Gomes, 2000). 
                 So as to obtain a controlled demolition, one where the structure when demolished acts as predicted, it 
                 is necessary to choose the correct collapse mechanism. Existing collapse mechanisms are implosion, 
                 telescopic, tumbling, and progressive collapse. 
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