Convert text address to cell reference address

Hi, I want to convert a concatenated text string ie. "B"&"29" to its cell cordinate addres B29 so that it can feed into If function logical value field. such as B29 is blank and I would like to check =if("B"&"29"="","yes","not blank". As the logical value can only recognize it is a text string instead. Is there any way to solve this? Thanks for kindly help.