Masonry Magazine June 1972 Page. 23
Preassembled
Block Plank
Several decades have passed since blocks were first assembled into prefabricated planks for floor and roof systems. Improvements in materials, design, assembly and erection have enhanced the benefits of this system to the point where it is a standard form of construction for moderate length spans. Planks are made from high strength hollow block containing special openings to receive prestressed cable and/or reinforcing rods and grout. Block are processed so that when they are assembled into a plank, a prescribed camber, depending on design dead and live load, exists in the finished product. On application of the design load the camber theoretically disappears resulting in a level surface. Most preassembled block plank systems are made with tongue and groove on opposite sides; when placed together in a floor assembly adjacent plank are interlocked, effecting a more even distribution of floor loads.
Installation requires the use of a crane to set the plank on its supporting structure but small adjustments can be made manually using levers to shift the plank to its final position. The system is used with or without concrete topping, but where diaphragm action is needed in both directions, a reinforced bonded topping is used.
Prestressed
Hollow Core
Hollow core, precast, prestressed slabs provide another floor system which can be erected quickly, without the need for formwork and shoring, and can be designed to slightly longer spans. They are used with or without topping but usually require grout in the space between adjacent planks. The amount and size of prestressed strands, as well as camber, are determined by assumed loading conditions for a particular structure and plank are made to order in specified lengths for the stock thickness required. As with the pre-assembled block plank, hollow cores are used to run electrical and telephone conduit, piping, heating and air conditioning air distribution, and exhaust to outside. Vertical openings for piping and ductwork can be drilled or cut into the planks. Where an opening in the floor is at least one plank in width, special hangers are used which receive the end reaction of the plank at the opening and transfer it to adjacent planks.
Precast Concrete
Solid Slabs
Multi-story buildings having a repeating floor plan and loadbearing masonry walls can be efficiently and economically built with precast, room-size solid slabs under certain conditions. Where sufficient space is available at the job site, room-size slabs are precast in stacks, starting with the roof slab and using the top surface of the lower slab as the form for the next slab; the side forms are arranged so that they can be moved upward as additional slabs are cast, somewhat similar to "slip forms". Since slabs are identical floor to floor, block outs for piping, utilities, etc. can be formed as the slabs are poured. Inserts to receive conventional lifting devices are also cast into the slab. All of these operations, as well as finishing of the slab surface are carried out at ground level where efficiency of the workmen is better. Stacks of the precast slabs are formed in locations around the perimeter of the building under construction, where cranes can then place them on completed masonry walls.
Cast-in-Place Floors
In selecting the type of floor system which will best satisfy the requirements for economy, efficiency and speed of construction of a load-bearing masonry structure the size and configuration of the building may be the determining factor. Planning should be pointed toward removing obstacles to the steady, rapid progress of the masonry.