Leazes Arcade was originally constructed as a Jewish Synagogue in the early 1900's and was converted into a shopping arcade in 1984. It was substantially damaged by fire in 1989 such that only the external walls remained, together with some of the cast iron columns and beams. Often, cast iron crystallises in heat but in this case, the surviving cast iron was undamaged. The building was converted into student flats in 1994. It forms an interesting case study of refurbishment of a fire damaged building. The picture below shows the cast iron columns and beams. By this time, the fire damaged timber floor panels had been removed.
The additional loads imposed by two additional floors required extended foundations. Below, the steel reinforcement to one of the extended foundation bases has been placed in readiness for concreting.
An existing masonry wall, U-shaped in plan at basement level was extended through the five storeys of the new structure for maintain stability of the whole structure. The heightened part of the wall was constructed from concrete blocks, 150mm thick at ground and first floor and 100mm thick above. A reinforced concrete capping beam was cast over the existing wall so that the new concrete block wall could be more easily built above. The picture below shows the reinforcement and formwork of this capping beam prior to concreting.
A new structural steel frame was constructed to supplement the cast iron structure. The new steelwork extended from the basement to the roof. The picture below shows a typical steelwork connexion (by the way, "connexion" is correct British English, "connection" is American English. (compare with "deflexion")
The length of the steel columns was such that they had to be fabricated in shorter lengths and spliced together on site. The detail below shows how this is done. You can't just place one column section above the other because if the column ends touched, there would be unacceptable stress concentration. Instead, plates are bolted to the column sides and those plates, as well as the bolts securing them, are designed to withstand the vertical load. This means the vertical loads are diverted out of the column, into the plates, then back into the column.
Below, the precast concrete floor beams are being placed onto the steel beams. In order to save headroom, the beams are placed onto "shelf angles", which are angle sections welded onto the beam's web. The upper surface of the beams then coincides with the upper flange of the beams. Some skill is required to slot the concrete beams into the gap between the shelf angle and the upper flange of the beam.
Once the concrete floor beams have been positioned, concrete blocks are placed between them. The floor is then completed by casting a 50mm thick screed (concrete with small aggregate) over the beams and blocks. The concrete beams are inverted "T"'s and the blocks have notches in their sides which allow them to sit neatly on the concrete beams.
The picture below shows the completed floor from beneath. Note the shelf angles and the concrete blocks sitting on the inverted T section concrete beams. This type of floor has enhanced acoustic properties as compared with a timber floor. Also, it divides the building into fireproof compartments. Timber floors can be used only for three storeys or fewer. In this case, the upper three floors are timber and the lower two are concrete.
The roof void was designed for residential use and the timber common rafters and trusses were positioned on steel beams as shown below. The gable walls have been extended upwards in concrete blockwork.
The picture below shows how a timber floor is supported by steel beams and columns. The central timber floor joist could not be located directly onto the timber piece fitted into the steel beam because the column was in the way. Therefore, a short timber member has been bolted to the two neighbouring joists to carry the load from the central joist into the ends of its two neighbours, then into the steel beam.
The roof is a typical timber structure surfaced with slates. The picture below shows the timber batons onto which the slated are to be fixed. The material below the batons is called "sarking" (pronounce as in "sarcastic") and helps with waterproofing and windproofing the roof. A Dormer window is shown in the foreground and a skylight has been constructed to improve the space in the bedroom.
Once the structure was complete, each floor was divided into separate flats and rooms. The technique adopted was to fix lightweight aluminium frames as shown in the picture. The folded aluminium sheets allow cables and pipes to be threaded within the walls. Plasterboard sheets are then screwed to the aluminium sections and insulation is placed within the walls. The plasterboards are taped together, skimmed with plaster to hide the joints, then painted or wallpapered. A more traditional approach would have been to fix vertical timber pieces and nail the plasterboard sheets to those. This is called "studding". The vertical timbers are kept at uniform spacings by short horizontal lengths of timber called "noggins".