2005-2020. Dismantling the Windsor Tower
On 30th August 2005, six months after the fire ravaged the building and four months earlier than expected, Calle Raimundo Fernández-Villaverde was reopened to traffic. From Calle Orense to Paseo de la Castellana, the street furniture and fixtures, road and pavement surfaces and the gardens in the surrounding area had all been renewed. The burnt-out silhouette of the formerly elegant Windsor Tower had gone forever from the Madrid townscape. Just a few days earlier, J.J. Armas Marcelo published a poignant column in the ABC newspaper “The Remains of the Windsor Tower”. He was referring to the men and women who had worked the miracle:
“They say that as work progressed and the burnt remains were dismantled through good working common sense by the operators specializing in the strange job of working without rest and in silence, experts from all over the world came to Madrid to see, study and learn from the gradual disappearance, at the rate of one floor per week, of the hulking wreck and its charred skeleton.“
On 26th February 15 years ago the siting record was signed and specialist workers started to demolish over 61,400 m³ distributed over 24 floors, from the 4th floor to the crane over the tower, and began transporting 620 tonnes of metal and over 71,000 tonnes of concrete and building rubble to recycling plants. The work was carried out in silence and without rest: work took place 24 hours a day in three shifts with an average of 60 people working on each shift.
This is the narrative of how they did it.
The Windsor Tower was in flames for approximately 20 hours between the 12th and 13th of February. The fire started on the 21st floor at around 11:05 pm. At 11:21 pm the fire-fighters were called out and 15 minutes later the fire had already devoured the entire floor. Subsequent surveys that were carried out (INTEMAC, Kono M., et al, etc.) managed to estimate the sequence of events and the speed at which the fire spread. It spread upwards first of all and in 40 minutes the 22nd floor was burning, then floors 23 and 24 (70 minutes). The 28th floor was burning 30 minutes later (as explained by Borg and Welsh). Downwards spread of the fire did not begin until 01:00 hours, at a speed of 20 minutes per floor, and at 05:40 am it had reached floor 12, and only slowed down when it had to cross the technical floor, T2, between floors 17 and 16. The fire-fighting services declared the fire extinguished at 01:00 on the 14th, and established a 48 hour safety period before access to the building was allowed so that preliminary assessments could begin.
[Collapsed zone on floors 18 to 27 – Technical Floor 1 – Technical Floor 2]
Despite the duration of the fire and the extremely high temperatures that the building underwent, the Windsor Tower did not collapse and became the 35th out of the 100 highest buildings to be voluntarily demolished. The Madrid City Hall declared the building in ruins and proceeded to undertake “Immediate Action”. Ortiz Construcciones y Proyectos was assigned the northeast zone in 1985, and consequently was responsible for providing a response service within 1 hour, 24 hours a day, 7 days a week, in the event of any emergency.
On the night of the fire, work began with support by INDAG, S.A. Grupo Ortiz’s Engineering Company who was in charge of the technical management of demolition processes and responsible for preparing a mathematical model to establish an approximate survey of the condition of the remaining structure what behavior could be expected. A few days later, INTEMAC (Technical Institute of Materials and Construction) inspected the building to take samples for testing. A total of 21 samples were tested from the undamaged floors, and from 6 of the damaged floors. Over the following days a further 22 samples from dismantled items were also analyzed.
When the fire began the Windsor Tower was undergoing a process to adapt its fire-fighting installations to current regulations. This explains several issues related to how the building performed.
The first was the existence of a crane on the tower structure. It was undamaged and could be dismantled following the company’s standard protocol.
The second is how the Windsor Tower performed when it was burning. The central rigid concrete structure housing the staircases and 10 lifts, and the fact that the building was divided into two main bodies through technical floors T1, under floor 4, and T2 under floor 17, kept the giant standing. But the enclosure of the building consisted of metal pillars that transferred the weight of the glass cladding to the bidirectional concrete slabs. The pillars comprising the lower body had been fire-proofed, with the unexplainable exception of floor 9, although this was not the case of the upper body of the building. From the pictures showing the condition of the skyscraper following the fire, the results of the lack of fire protection on the metallic structures are obvious.
The third is the circular section emergency staircase, not shown on the plans, that was included in the plans to adapt the building to current fire regulations. It was secured to the floor structures on the western façade and prevented the building from collapsing. It is easy to imagine its position when seeing the rectangular area – shaded white in the floor plan – which did not collapse.
There is something truly amazing about the dismantling of the Windsor Tower. It is something that everyone who is familiar with the extreme difficulty of working on damaged structures dreams about: nobody was injured during the process. The safety of people and objects became an obsession that conditioned how the procedure was designed. Work had to be carried out from the outside.
Demolition with explosives is the cheapest and fastest method used on structures of this size, but it was ruled out from the start since workers would have to go inside the building to place the explosives and perform selective cutting up to floor 18. The Windsor Tower had been damaged to such an extent that the smallest mistake in detonation synchronization would prevent the building from falling according to plan. The traditional system using shoring would also require work to be carried out “inside”, and was also rejected. Finally, using aerial demolishing machinery as the main system meant that huge chunks of the building would fall down. All of these systems entailed risks that were considered unacceptable.
Therefore, with the goal of reducing any personal risks to the minimum, our experts at Grupo Ortiz designed a dismantling system by cutting off pieces of the building from the outside. The system was patented in 2009 under the name of “Building Demolition Procedure from Above the Structure”.
At this point two enormously important players came on the scene: the cranes. Two crane assemblies were employed, one on the west façade and the other on south façade. Each assembly consisted of two cranes: the first loads and lowers the pieces while the second carries the platform from where the operators control robots by remote control, making the cuts and directing the loading crane maneuvers. They were the eyes of the operation, and everything had to be perfectly synchronized. To get an idea as to the scale of these structures, we need to know that the “Liebherr 750T” crane requires 82 articulated flatbed trucks to transport it and 1 week to set it up. The equipment assembled on the western façade, located over the two basements on Calle Agustín Betancourt, required shoring of a surface area spanning 1,400 m2.
The dismantling process, which was adapted several times on the technical floors and at particularly difficult points, was very systematic and began by clearing away rubble on the floor using a remotely controlled robot. The following phases were then implemented:
- Cutting the floor structures. After surveying and identifying where the cuts should be made, a robot made the cuts through the concrete while conserving integrity of the rebar reinforcement, and making holes that could be used to secure the pieces for lifting. The operators on the platform then introduced the lifting implements that were attached to the loading crane. Once this had been done, and the crane had taken the strain of approximately 70% of the weight of the piece, the reinforcements were cut using oxy-cutting techniques. During this process the tension of the crane cables was adjusted to ensure that once the final reinforcement had been cut, the piece would gravitate. The piece would then be lifted and lowered.
- Cutting of concrete screen walls. The procedure is the same as described above, but on vertical pieces: cutting the concrete, horizontally and vertically, using a robot, making holes, securing the pieces and taking the strain of 70% of the estimated weight of the piece, and then finally cutting through the rebar reinforcements. The loading crane would then lift and lower the piece.
- Dismantling the gantries. In this case, two holes were made for securing implements, one on each end of the beam and the concrete of the pillars was demolished to the height of 1 meter, leaving the rebar reinforcement in place. Once the cables supporting the gantry were strained, the workers cut the reinforcements one by one from the platform, alternating between pillars while the tension of the cables was adjusted to regulate the strain. When all the rebar reinforcements had been cut, the gantry was balanced and lowered safely.
This description is a crude simplification of an extremely complex process that was carried out on an unstable structure and at a literally dizzying height. Dismantling of the technical floor T2 was carried out following an identical procedure but applied to enormous concrete beams measuring 3.20 meters thick. The truth should be told, but it is sometimes hard to believe.
When analyzing each step of the dismantling process, the enormous care that was taken and adaptation to the specific circumstances of the surrounding area must be taken into account. It is this level of engineering inspired by imagination that allowed lowering the lifts by fitting a cushioning bed 9 meters deep consisting of old tires. This same inspirational engineering found a solution to the problem with floor 9, bridging it across from floor 8 to 10 to avoid compression stresses on the twisted façade pillars.
The same mantra was the basis of all decisions: the safety of people “Always working from the outside” became much more than a simple phrase.
The Windsor, as the residents of Madrid knew it, characterized the city’s skyline for 26 years (1979-2005). Its 106 meters height and golden façades have been the subject matter of some spectacular photographs when lit by the sunlight from the west. In its conclusions in the report on the fire, INTEMAC pointed out that “the behavior of the concrete structure (…) when subject to intense fire was extraordinarily positive and clearly more favorable than would have been expected through strict application of building regulations”.
The damage that would have been caused had the building collapsed while in flames is unimaginable. But the Windsor Tower did not collapse, it had to be dismantled. Dismantling was carried out by a team of humans who employed the same respect, intelligence and passion for their work as those who originally built it.
Referencias utilizadas:
“Lo que queda del Windsor”. (The Remains Of The Windsor Tower)J.J. Armas Marcelo.
“Proceso de demolición del Edificio Windsor” (Windsor Tower demolition process). Information Dossier by the Government Department of Town Planning, Housing and Infrastructures. Madrid City Hall 2005
“El incendio del edificio Windsor. Investigación del comportamiento al fuego y de la capacidad resistente residual de la estructura tras el incendio” (The Windsor Tower Fire. Investigation into the fire and the residual strength of the structure after the fire). INTEMAC. 2005
“Performance of Concrete in Fire: A Review of the State of the Art, with a case study of the Windsor Tower fire”. Ian Fletcher, Audun Borg, Neil Hitchen y Stephen Welch.
“Proceso de Demolición del edificio Windsor” (Windsor Tower demolition process), Presentation by José Antonio García Miguel.
List of tallest voluntarily demolished buildings
Documentary “Proyecto Windsor. Desmontando al gigante” (“WINDSOR PROJECT. DISMANTLING THE GIANT”)