Fatigue Behavior of Welded and Mechanical Splices in Reinforcing Steel (NCHRP Results Digest 197)
PDF courtesy of the American Concrete Pavement Association’s (ACPA’s) technical resources archives.
In reinforced concrete design, the structural engineer is faced with the task of determining where and how reinforcing bars must be spliced in a structure: The lap splice, when conditions permit and when it will satisfy all requirements, is generally the most common method for splicing reinforcing bars. However, when lap splices are impractical or uneconomic, mechanical or welded connections may he used to provide a direct connection between reinforcing bars.
There are a wide variety of proprietary mechanical connectors and welded joints that can be considered, depending on the circumstances. In new construction, for example, splices can be used to join large bars (codes do not permit lapped splices with No. 14 and No. 18 bars), where spacing is insufficient to permit lap splicing, where lap lengths are excessive, in “tension tie members,” and at construction joints where it is undesirable to have long lengths of bar protruding from the joint. In rehabilitation projects, direct connections may be used advantageously in circumstances such as bridge widening projects, where lesser amounts of sound concrete may have to be removed, or in staged construction, where working space between the stages may be limited. In some situations, in bridge rehabilitation work for example, practical considerations may dictate that splices be placed in regions of repeated stress cycles; therefore, it is important that the fatigue behavior of splices be known.
The factors affecting the fatigue of unspliced reinforcing bars are considered to be well known and provisions are included in design specifications. Conversely, information related to the fatigue behavior of mechanical connectors and welded joints is very limited, especially considering the variety of connectors and weld details available. A consequence of the limited research is that major U.S. codes and design specifications do not include comprehensive fatigue design criteria for any type of reinforcing bar splices, whether conventionally lapped bars, welded splices, or mechanical connections.