8/8/2019 Shoring Scaffolding

1/10

8/8/2019 Shoring Scaffolding

2/10

Factors determining the

Pressure exerted by Concrete onFormwork:

Rate of placing of concrete in forms.

Temperature of concrete.

Weight or density of concrete Method of consolidating the Concrete.

Depth of placement.

8/8/2019 Shoring Scaffolding

3/10

Introduction

Since each structure is unique, the formwork must be designed andfabricated based on the specific requirements of each job.

The level of effort required to produce a good formwork system is as

important as the level of effort required to produce the rightcombination of steel & concrete for the structural system of theconcrete structure.

8/8/2019 Shoring Scaffolding

4/10

Design Considerations

Forms for concrete construction must support plastic concrete until ithas hardened.Stiffness is an important feature for Forms and failingto provide it may cause unfortunate results.

Forms must be designed for all the weight they are liable to besubjected.

It includes:

Dead weight of the Forms.

Plastic Concrete in the forms.

Weight of the workmen.

Weight of the Equipment.

Weight of the materials transferred to the forms.

Impact due to vibrations.

8/8/2019 Shoring Scaffolding

5/10

When concrete is placed in the form work, it is in a Plastic State andexerts hydrostatic pressure on the forms.

The Basis ofForm Design is the maximum pressure develop by the

concrete during placing.The maximum Pressure developed will depend on the rate of placing &

temperature.

The rate of placing will affect the pressure because it determines howmuch hydrostatic head will be built up in the form. The hydrostatic

head continue to increase until the concrete takes its initial set whichis normally about 90 mts.

However at low temperature, the initial set takes place muchmore slowly, so it is necessary to consider the temperature at thetime of placing.

8/8/2019 Shoring Scaffolding

6/10

Load acting on Formwork:

Possible load acing on the Formwork :

Vertical Load - Dead load of the placed concrete &Formwork.

Live load load of the workers, equipment & materials.

8/8/2019 Shoring Scaffolding

7/10

LOADS & PRESSURES

ACTING ON THE

FORMWORK

8/8/2019 Shoring Scaffolding

8/10

8/8/2019 Shoring Scaffolding

9/10

How Formwork Affects Concrete Quality

Size, shape, and alignment of slabs, beams, and otherconcrete structural elements depend on accurateconstruction of the forms.

The forms must be: Sufficiently rigid under the construction loads to maintain

the designed shape of the concrete,

Stable and strong enough to maintain large members inalignment, and

Substantially constructed to withstand handling and reuse

without losing their dimensional integrity. The formwork must remain in place until the concrete

is strong enough to carry its own weight, or thefinished structure may be damaged.

8/8/2019 Shoring Scaffolding

10/10

Causes of Failure

Vibration

Forms sometimes collapse when theirsupporting shores or jacks aredisplaced by vibration caused by:

passing trafficmovement of workers and

equipment on the formwork

the effect of vibrating concrete toconsolidate it.

Diagonal bracing can help preventfailure due to vibration.