What kind of cracks?  Cracks in block walls?  Cracks in concrete floors?  Cracks in concrete walls?  Cracks in wooden beams?

And if it's a "MAJOR" structural crack, perhaps you need to be looking at total replacement and not just repair.

thanks for your reply, the cracks are actually externally on the north east corner of a building. might of exaggerated on the 'major' as i think they are treatable. do you have any info on how this problem can be repaired.

regards

What kind of cracks?  Cracks in a block wall or cracks in a concrete wall?  

cracks in a concrete wall

Are you sure you're an engineer?

So you'll need think about what's causing the cracks and try to stop whatever is causing them.  Could be foundation settlement, could be faulty concrete, could be frost heave, could be ....

Visit your local specialty supplier for crack sealants.

thanks for nothin, i could think about it all day long,i was just looking for some advice/information from someone who might specialise in the subject. dont reply if your not willing to help.

You can fill it or fix it.

Epoxy injection may fill it so that water won't get in, but filling it will not prevent further cracking or fix the cause of the crack.

If the structure was improperly designed, God onlt knows what you might need to do.

I think what Watermelon is refering too: is the vague description, lack of any technical details, no analysis and open question makes it difficult to determine solutions for your crack on the internet.  

In addion to the items Watermelon indicated settlement and movement can be caused by building on expansive clay, compressible or improperly compacted fill soils, or improper maintenance around foundations, improper materials, faulty design, equipment vibration, vehicle vibration, physical damage ..

Cheers

A couple of other thoughts aiii,
First, remember the forum in which you are seeking assistance.  Engineers like detailed, specific information.  A clear, concise account of your problem with all pertinent details will not only gain you credibility, but also help others to provide insight.
Is your building in a seismic region?  How old is it?
If a one-time event like being hit by a vehicle or an earthquake is cause of the cracks, then I agree with epoxy injection as a solution, however if it's a water problem, settlement, etc., repair of the concrete is only part of the overall fix.