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Reinforcement Specifications


Materials
Concrete and Steel
Bar spacing
Reinforcement covering
Rebar bending
To be continued >
Introduction

General

Reinforcement specifications of reinforced concrete earthquake resistant structures also satisfy the detailing requirements applying to conventional structures as during their lifespan they are rarely subjected to earthquakes.

For a structure to be earthquake resistant it must firstly abide by the regulations regarding conventional structures. However, its construction demands greater diligence because during the critical moment of the seismic event the structure will be tested to its strength limits thus proving the need for meticulous application of all the reinforced concrete rules. Beyond, therefore, the normal construction rules, other rules must be satisfied as well mainly regarding the transverse reinforcement usually consisting of dense polymorphic stirrups.

The basic specifications of antiseismic reinforcement are four:

(1) The concrete cover of the reinforcement,

(2) The minimum distance between reinforcement bars,

(3) The gradual bending of rebars

(4) The antiseismic stirrups.

The minimum required cover thickness for slab reinforcement usually ranges between 20 and 30 mm depending on the environmental conditions present throughout the building’s service life. The 20 mm would apply to a dry climate and the 30 mm to a seaside location.
The required cover is maintained only with the use of special stands called spacers. These must not be affected by corrosion and should be placed approximately every 1.00 m.
The simplest solution for providing the necessary cover thickness of the reinforcement is special plastic underlayers like the ones shown in the above figure. Usage of steel rebar spacers is forbidden as they are highly susceptible to corrosion.

When rebars corrode the resulting volume expansion leads to concrete spalling and consequently to the cracking of the plaster. Extensive deterioration affects not only the residents’ safety but also the structure’s service life.

The position of the upper (negative) slab reinforcement, either placed over the support between two slabs or over the support between a slab and a balcony (cantilever slab), can be secured only with the use of special rebar chairs.

Prefabricated element, made out of a thin steel rebar with plastic tipped legs in order to prevent corrosion of the support area between the rebar chair and the formwork.

Prefabricated element, made out of a thin steel rebar with plastic tipped legs in order to prevent corrosion of the support area between the rebar chair and the formwork.

Prefabricated, comes in packages of straight lengths. It is formed in an S shape during the placement.

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