GPR imaging of problematic beams ceilings constructed using iron boxes method

Summary form only given. Ceiling can be made of a complete thick slab of concrete. When large apertures are needed, it can be constructed from separate concrete strips (beams) with a complete thin layer of concrete on top, creating a "T" profile. During the seventies, Israeli builders have started to build beams ceilings using thin wavy iron boxes with a "/spl lceil//spl rceil/" profile, as a technique to create the voids between the beams. The construction of such ceiling has started with the casting of very thin concrete layer with a thin non-constructing rebar net inside. This method kept the conventional construction roles of beam ceilings, including the appropriate horizontal and vertical rebar array along the beams. Later on, this method have been "improved" by the chief engineers of the Department of Public Works: the thin wavy iron boxes have been used as construction elements instead of the shear rebar and the upper rebar. This problematic method, name "Pal-Kal", has been presented as very economical since it saved time, work and material. As a result many hundreds of buildings have been built using this method. The Pal-Kal method was controversial, therefore has been "improved" again and again during the years with several nuances. In the late nineties the authorities finally prohibit the use of this method. Nowadays, after collapses of several ceilings and houses, the Israeli government has officially concluded that the buildings built with the Pal-Kal method should be inspected and repaired accordingly. In the paper we present structural GPR images of Pal-Kal ceilings and discuss their failure issues and their detectability using GPR. Images of possible delamination inside the concrete, narrow/wide and non-uniform concrete beams, distorted iron boxes and its inconsistent penetration into the lower concrete slab, possible corrosion of the iron boxes and penetration of concrete to the voids are presented and discussed.