Concrete Formwork Svstems - Part 8 pptx

8

Vertical Formwork Systems:

Crane-Independent Systems

8.1 Slipforms

8.2 Self-Raising Formwork System

As mentioned in Chapter 5, vertical formwork can be classified

into two main categories, namely, crane dependent systems and

crane-independent systems. Slipform and self-raising formwork

are classified as crane-independent systems in which formwork

panels are moved vertically by other vertical transportation mecha￾nisms.

8.1 SLIPFORMS

8.1.1 History

The history of slipforming can be traced back to the 1920s and

before. In the late 1920s, a number of concrete structures were cast

using a system of formwork that was moving during the placing of

concrete. At that time, forms were being raised by hand-screw

jacks and job-built wooden yokes. Laborers would pull ropes that

would raise the forms. Early application of slipform was limited to

storage bins and silos with a constant thickness all over the wall

height.

Since the late 1950s, slipform construction has come a long

way; locomotion is accomplished by jacks climbing on smooth

steel rods or pipes anchored at the base of the structure and the

system has been employed successfully and economically in situa￾tions which have required discontinuity of section. As a result, the

list of recent application expanded to include towers cores, bridge

piers, power plant cooling, chimney shafts, pylons, and the legs of

oil rig platforms.