Does putting weight on stomach and then hardening abs, helps in building abs? was doing some excercise in which i had to keep weight on my stomach before carrying with hands.
It probably does something, but this is not how your abs are designed to work. Your abs primary job is to produce intra-abdominal pressure when you are lifting. This just means they literally press your guts against your spine to support your spine when you lift. That is your abs primary job. They also assist in any movement of the torso. It's almost impossible not use your abs to some extent when you move your body.
So is it working your abs? Eh maybe a bit. Is it the best thing to spend your time doing if your looking to increase your abdominal strength and size? Not at all.