Weather Conditions

Vertical forming systems are sensitive to weather conditions. Typi­cally, in vertical forming systems, the newly placed concrete is sup­ported by the wall already cast below it. The lower wall section must gain sufficient strength to support the fresh concrete above. The rate of strength gain for the lower wall is influenced by ambi­ent temperature, moisture content, and freezing and thawing cy­cles.

Подпись: Copyright © Marcel Dekker, Inc. All rights reserved.Another factor that affects the economy of the selected sys­tem is the effect of stopping forming and concreting because of extreme weather conditions. For example, in slipforming, the work is usually continuous, 24 hours around the clock, with a minimum crew requirement of 50 to 75 laborers for a medium size shear wall. If the slipforming stops because of the weather conditions, the contractor has to pay the workers a show-up time, plus the cost of inactive cranes and their operators. As a result, if severe weather conditions are expected, some vertical formwork systems, such as slip forms, should be avoided.

Construction sites are generally classified into downtown re­stricted sites and open, suburban, or unrestricted site condition. Gang and jump formwork require good crane service. As a result, it is difficult to use these formwork systems in restricted site condi­tions. On the other hand, slipform and self-raising formwork are crane-independent systems and can be used in restricted site con­ditions.