How to maintain Steel Structures of your building?

General impression is that steel structures are maintenance free; but actually it is not so. Steel is very much affected by atmospheric agencies, especially when it comes in contact of moisture. The low but continuous oxidization on the surface of structure result in their corrosion. Steel structures in marine atmosphere are more susceptible to corrosion due to presence of salt in the atmosphere.

Steel structures need regular maintenance with inspection and monitoring. If faithfully followed under competent management, structures can give totally reliable service long after their initial designed life cycle.

Preliminaries to Maintenance:

For proper maintenance, the steel structures must be periodically inspected. Maintenance of structures should be ideally a combination of analytical study and onsite inspection by a team of persons who are capable of handling both.

It is necessary to appreciate the true behaviour of the structure under actual loading conditions as occurred during the period of deterioration.

The problems encountered in this work are of varied nature and are often complex. Consequently, the inspector’s judgment is required frequently for proper evaluation of the findings.

He should be thoroughly familiar with the design and construction features so as to interpret properly what is observed and reported. He must be able to recognise any structural deficiency, assess its seriousness and initiate action necessary to keep the structure in safe condition. He should also recognise areas of the structure where a problem is incipient so that preventive maintenance can be properly programmed.

Maintenance Procedure:

Surface protection –

Before identifying the type of protective system a structure deserves, it is necessary to assess:

(i) Availability of application methods and necessary tools viz. brush, spray etc.

(ii) Durability in a specific environment,

(iii) Availability of skilled manpower.

Taking the above factors into account, a comparison has to be made of the life of various prospective systems available vis-a-vis their cost for arriving at a techno-economic solution:-

Routine deterioration like corrosion can be minimsed by

– improved design and detailing,

– Protective coating on surface and surface preparation,

– Use of special corrosion resistant steel,

– Concrete encasement of the member, and

– Catholic protection.

Protective Surface Coating:

The most commonly used systems of protective surface coating are classified as below:

(i) Metallic –

(a) Hot dip galvanizing:

Providing zinc coating to steel surface by dipping steel components into a bath of molten zinc. The system is not practicable for already erected structures. But by applying the system to members prior to erection, the life of the structure can be enhanced.

(b) Cold galvanizing:

This concept has been developed keeping in view the excellent adhesion of epoxy resins and polyurethane resins and can provide a viable substitution to hot dip galvanizing.

(c) Metalizing:

This process consists of projecting an atomized stream of molten metal at a high velocity from a special gun to a prepared surface. In normal cases, difficulty in executing the process does not encourage its extensive use.

(ii) Non-metallic:

Protective paints and coatings of different categories most commonly used are:

(a) Red lead/zinc chromate paint (pigment based),

(b) Vinyl paints.

(c) Chlorinated rubber paints, and

(d) Epoxy paints.

Rivets:

Defective or loose rivets must be removed. In the absence of pneumatic power this can be done by gauging and hammering out. Replacements if small in number can better be done by high tensile close tolerance or friction grip bolts.