This article is an example of how we provide all of the technical backup that is needed to undertake the most critical tasks. In this case, the removal of load-bearing walls in a £2.5 million house with prestressed concrete floors required long-span steel beams to be hydraulically jacked in order to eliminate movement of the supported structure due to dead load deflection.
In this project there were two beams: one at second floor level and one at the first floor. Each had bolted splice connections (see right panel) to enable the steelwork to be brought into the building and assembled in-situ. The beam rests on concrete padstones at each end, to ensure the end reaction does not exceed the crushing strength of the supporting masonry. In this case, one end is on an Engineering Brick pier while the left end is on the external cavity wall.
Supporting a Concrete Floor
The precast concrete floor units span onto the beam from one side only; hence the Acrow props are arranged beneath this area. At the foot of the props, the load is spread across the beam and block floor below using railway sleepers as spreaders.
All of this was carefully planned in advance by our Engineer and a Method Statement prepared, with diagrams and schedules of equipment needed, plus a step by step sequence of operations. This is vital to ensure the safe execution of the work and to ensure that the building is not damaged in the process.
Our Engineer and Technician were present on site to direct and assist with the procedure of jacking the beams and carefully shimming the supported floors to the exact dimension specified in the structural calculations. In each case, the calculated values perfectly matched the site conditions, and no movement was observed in the supported structure when the props were released. The jacking process was completed in less than a day for both storeys.
This is just one of the examples of how Structural Engineers Cambridge Ltd can help you in your project, from concept to execution. We have the technical experience and the practical know-how that ensures that critical aspects of the works are carried out correctly, efficiently and safely.
Location: Ascot, Berkshire
Design Engineer: Tony Bellamy
Site Engineer: Charles Tallack
Site Technician: Andy Chapman
Architect and Contractor: MSpace Ltd
Bolted Splice Connections are a means of allowing long beams to be assembled in situ, while maintaining the strength of the beam. The above is a heavy-duty example used in a 203x203x60 UC section.
Note the use of High Strength Friction Grip (HSFG) bolts instead of ordinary bolts. These have load indicating washers that ensure the correct tightening force is applied. The washers have special dimples that are crushed flat as the bolt and nut are tightened.
The HSFG bolts are designed to resist slipping of the plates under design loads (unlike ordinary bolts that can bear on the sides of the holes under ultimate loads). The mating faces of the steelwork are de-scaled and degreased but not painted, to reduce the risk of joint slippage.
The plates at top and bottom are designed to carry the bending forces, while the plates each side of the web (not yet fitted in the picture) carry the shear force. The connection is specifically designed to handle the forces at that point in the beam.
These connections are usually used in Portal Frames and Loft Conversions.
If you have any questions about how these connections are designed, how to assemble them or how to obtain HSFG bolts, please contact us. We are happy to help.