1.3 Connection Factor for Concrete 1

[sketch2099]

Some engineers utilize a load factor multiplier of 1.3 for design of pre-cast concrete connections that are sensitive to tolerances or field welding (such as corbels and dapped ends). Is this merely a design philosophy that some engineers practice or is this factor mentioned in either ACI 318 or the PCI design handbook?

 

[haynewp]

From PCI:

To ensure that the overall safety of the connection is adequate, the use of an additional load factor in the range 1.0 to 1.33 has historically been used by the industry. The need and the magnitude of this additional load factor for a particular connection must depend on the Engineer's judgment and consideration of:


1. Mode of Failure: For failures which are typically precipitated by failure of concrete due to insufficient anchorage of connection reinforcement and inserts, such as short studs it may be appropriate to use larger load factors.


2. Consequences of Failure: If failure of a connection is likely to produce catastrophic results, the connection should have a larger overall factor of safety.


3. Sensitivity of Connection to Tolerances: Production and erection tolerances as well as movements due to volume changes and applied loads produce changes in load transfer positions on the connection. Certain connections, for example corbels (see Sect. 6.8) and dapped ends (see Sect. 4.6.3), are more sensitive to load transfer positions than other connections, such as base plates. The magnitude of the additional load factor should be consistent with this sensitivity as well as the load transfer position considered in design. For example, if the most adverse combination of tolerances is used to establish the load transfer location, an additional load factor may be unnecessary.


4. Requirements of Local Codes: To prevent a connection from being the weak link in a precast concrete structure, some codes require larger load factors to be used in the analysis and design of the connections. When these factors are used, it is not necessary to use additional load factors.

 

[sketch2099]

Thanks for your help. Can you tell me what page this is on?

 

[haynewp]

6-4 of 5th ed.