Beer has it's strong flavor (hops and all). Personally, if I were to use fruits to add that fruity flavor, I'd add some in a few process's to gain maximum flavor, since, again, beer is strong handed over fruit..
I'd mash some in a pot with a bit of water to get as most fruit juice as possible at a low smir (low temperature).
Once you got a nice sauce reserve beside and add it 5-10 minutes before end of boil (not too early or you'll burn and lose some of the aromes). Don't worry for the fruit skin, they'll go away like your hops cake when filtering it.
You could add some more fruit while it's still hot (cooling down in ice bath) in a skin bag. Wiggle the bag a bit every 3-5 mins to get max aromes of these ones.
(The reason i'd put them twice here is to get a more accurate taste of the actual fruit in the beer. The taste in the boil will be more powerful, but overwhelmed by the beers taste and cutted of by the constent heat getting the pineapple flavor more sour, yet still distinguisheable. That second add up is to get the natural taste of the fruit back, but keep the power of the first fruits.)
I'd then take out the second fruit journey (skin bag of fruit) when putting in primary.
2nd OPTION (you can do all 3 options for a harder fruit taste)
During fermentation (BEST CHOICE IMO) make a natural fresh fruit concentrate of both strawberry and pineapple.
For this, use a masson jar, add the desired fruit up to the top and pour vodka in each (your strawberry and pineapple) leaving at inch at the top of space (don't wanna spill it and it easier to shake).
Store it in a dark relatively cool place (under kitchen counter, on top of frigde placard) and every now and then, when you think about it, give it a good shake. (More shakes, better natural concentrate)
At the end of your fermentation (~3weeks) your fruit concentrate should also be ready.
(You can find video's on youtube of how to make your own concentrate with same steps)
Add the concentrate at same time as priming sugar and you should have a nice fruity beer
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