Timber beams have been and still are, installed to carry weight and support floors and there are therefore numerous reasons why they might need to be strengthened.
Old beams might have sagged, become worn with age or just be required to carry more weight than had originally been intended at the time that they were installed. It is therefore quite usual to strengthen a beam rather than have to go to the upheaval and expense of replacing it.
Additional beams might well be able to be added to provide this extra strength. They could be fitted in the gaps between the existing ones or possibly be placed tight alongside the ones already in position and joined together with bolts. However, both of these methods would require the new beams to be married into the load bearing wall structure by either cutting the ends into the appropriate areas or by supporting them on special wall plates.
Another method is to cut one or more slots into the full length of the existing beam, where the depth of the cut is approximately 30 to 40 mm above the base of the beam. A length of high tensile rebar steel that conforms to BS4449 is then inserted into the slot and the two are bonded together by pouring in a structural epoxy grout.
As with all alterations that could affect the structural integrity of the building, it is advisable to make proper structural calculations and a visit to the local Building Regulation officer is thoroughly recommended.