Joints and connections
The design and construction of joints and connections is the most important consideration in precast concrete structures. Their purpose is to transmit forces between structural members and/or to provide stability and robustness. There may be several different ways of achieving a satisfactory connection, for example bolting, welding, or grouting, but whichever is used the method should be simple and must convey unambiguous messages to the site operatives. It is important not to lose sight of the basic function of joints and connections, as Figure 9.1 certainly demonstrates. High-strength glued joints have also been attempted, at least in the laboratory as shown in Figure 9.2. The joints should not only be designed to resist applied serviceability and ultimate loads, which are relatively straight forward to predict and calculate, but they should be adequate in case of abnormal loads due to fire, impact, explosions, and subsidence, etc. Failure of the joint should not, under any circumstances, be brittle failure and lead to structural instability, ensuring ductility and the ability to maintain equilibrium under abnormal loading or loss of support. The fib Bulletin 63 ( fib 2012) addresses this problem in principle and in detail. Provisions to guard against this are provided in the form of continuous column and floor ties (see Chapter 11), which in many cases by-pass the joints. Difficult connection design in a precast concrete structure. Joints between a precast column and beam form a compression and moment-resisting connection in tests at BRE. Note that the photograph shows a historical test and might not represent current best practice (Courtesy of Building Research Establishment, Watford, UK. Copyright BRE, with permission).