FORJADOS

El sistema LIFT-SLAB

Este procedimiento modifica substancialmente el proceso constructivo habitual. Con los pilares a toda altura ya colocados, se construyen sobre el suelo y unos encima de otros, todos los forjados del edificio, que posteriormente se elevan uno a uno mediante gatos situados en la parte superior de los pilares. Por último se realizan las uniones de las placas a los pilares.

Con ello se consigue realizar los forjados en óptimas condiciones, sobre un plano horizontal sin puntales ni encofrados, a cambio de una elevación delicada de cada una de las placas y la ejecución de las uniones de elementos ya terminados en donde no se establece fácilmente la continuidad.

Josep I. de Llorens i Duran
Forjados, Revista CAU

Sistemas elevables

En el caso del Lift-Slab los forjados se construyen unos sobre otros, eliminándose así todo encofrado, interponiéndose entre dos consecutivos unas láminas de separación.

Una vez que el último forjado ha alcanzado la resistencia necesaria se procede a la elevación de los mismos hasta su posición definitiva, donde unos collares dejados en la masa del hormigón son soldados a los pilares (de hierro u hormigón con pletinas a la altura de los forjados)...

Edgardo Manlho
Inventario de técnicas industrializadas
CAU nº 48 (marzo-abril 1978)

Lift-slab method of construction

"Lift slab" means a method of concrete construction in which floor, and roof slabs are cast on or at ground level and, using jacks, lifted into position.

• Lift-slab System. RIFCOM
  
  http://www.rifcomksa.com/lisftslap.htm

  " The construction technique of lift slabs was developed to provide a fast and economical method for multi-storey building construction, in which the reinforced concrete floor and roof slabs are cast around its columns at ground level using separating membranes between each slab and employing the ground floor as the initial softie form.
  After the slabs have matured, they are lifted by the hydraulic jacks, (which were previously seated on top of the pre-cast columns) to their final position and then connected permanently to columns."

• An invention that improves upon existing lift slab methods.
  David Rockwood, Associate Professor of Architecture at the University of Hawaii.
  
  http://www.mic.hawaii.edu/dev_tech/engineer/braced.html

  " Building structures are typically built by lifting relatively small components from ground level and fixing them above previously placed components. However, substantial time and cost savings are often achieved by using methods that are more systematic than is typical. Some of these methods assemble more components near ground level. The components are then lifted as relatively complete assemblies to final positions. One such method, commonly referred to as the “lift slab method”, is constructed by forming concrete slabs in a stack near ground level. Using this method, each slab is threaded through columns, and the slabs are lifted with column-mounted jacks to final spaced-apart positions. Most known lift-slab methods have limitations and drawbacks. They include high cost, complexity, unreliability and unsuitability to a variety of building forms."

• Lift-slab method of construction
  The Aspect Institute

• " VSL Climbfloor is a multi-point synchronised slab lifting system that, like the Climbform system, uses the self-climbing principle but applies it to the construction of in-situ, post-tensioned slabs. This means floor slabs can be poured on site, tensioned, then mechanically lifted into position. Climbfloor then climbs itself to a new level, another floor slab is poured on top of the first and is lifted into position and so on. "
  VSL News nº 2 (1999)

  " A 4 level car park in New Zealand uses “climbfloor” to form and lift 3 floors with a total area of 3,300m2 to final position without the use of conventional formwork systems. Each floor is cast on the previous one and jacked up into position. The climbfloor system also couples with an edgeform / climbing screen system that delivers a complete slab casting system and with prestressing provides the potential for significant savings in both materials and labour costs. In this project 36 screw jacks lift/lower/rotate the slabs within a relative accuracy of 0.1mm. The screw jacks move the slab up or down in a synchronised and controlled manner by adjusting speed settings from 1 to 3.5 mm per sec. A rotary encoder plus other monitoring devices provide the data to the microprocessors that track slab position. Lateral stability is provided by external roller guides. Once installed the jacks can self-climb to the next floor negating any additional cranage apart for removal. De-bonding agents are used to separate the new slab from the previous and foam void formers are used here to create an optimised band beam layout. Utilising 2 sets of void formers enable the next slab to be edge formed, reinforcing laid, posttensioning installed whilst the previous slab is still curing. When in the final position a variety of slab to column connections are used including bolted corbels to secure the slab. "
  VSL News nº 2 (2004)

Patología

• L'Ambiance Plaza Collapse,
  Rachel Martin
  University of Alabama.

• L'Ambiance Plaza Collapse

• Lift slab structures instability during construction
  Rusk Masih
  University of Connecticut

• HSE research report on the partial collapse of Pipers Row car park, Wolverhampton
  Quantitative study of the causes of the partial collapse on 20 March 1997

• Deficiencies Lift slab
  Zallen Engineering
  Forensic Engineering in Construction

Jackblock

• Anthony van Zutphen
  Top-to-Bottom Construction in High-Rise Buildings
  Civil Engineering—ASCE, Vol. 49, No. 3, March 1979, pp. 65-67
  Reseña en ASCE

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  Abstract: This top-to-bottom construction method, called jackblock is a cousin of lift-slab. The main components are the jack and concrete block, hence the name. The top story of a building is constructed at ground level on a large number of jacks. It is then jacked up an amount equal to its exact height and another is built underneath it. What is now a two story block is jacked up another level and the third floor and walls built underneath. These three floors are jacked up and so it goes until the building has reached its exact height. It is then anchored to the foundations. Detailed photographs and figures are included in the article. Jackblock was developed in The Netherlands where approximately 10 buildings have been built using the system since 1964.