ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
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A P R O F E S S O R ' S P E R S P E C T I V E 34 | ASPIRE Summer 2016 45-degree angle with the longitudinal bars, the splice length is equal to the summation of basic development length " l d + s ." The force triangles presented in Fig. 2 clearly demonstrate the role of additional transverse reinforcement. When the quantity of transverse reinforcement is doubled, the angle between the compression field and the longitudinal reinforcement increases (for example, θ 2 > θ 1 ). As this angle increases, the overall length of the noncontact splice decreases, as can be inferred from Fig. 1. In other words, a designer can use a shorter noncontact splice length by using an increased amount of transverse reinforcement. Conversely, a lesser quantity of transverse reinforcement can be used, if the structural geometry allows for the use of a greater splice length. Additional observations that can be made by examining the force transfer mechanism shown in Fig. 1 and 2 include: as the tension force T gets larger, that is, as the size of the bar being spliced gets larger, so does the splice length; and small portions at the ends of the bars being spliced do not contribute to the force transfer, as dictated by equilibrium. It is important to note that the qualitative discussion provided previously did not include any hard limits placed on the splice offset distance or on any other aspect of noncontact splice design. Rather, the discussion was based on first principles. N o n c o n t a c t s p li c e s a r e f r e q u e n t ly encountered in bridge substructures and designed according to the American Association of State Highway and Transportation Officials' AASHTO LRFD Bridge Design Specifications . 1 These specifications limit the splice offset (shown in Fig. 1) in flexural members to one fifth of the required splice length or 6 in. For columns with longitudinal bars that anchor into oversized shafts, this spacing restriction is waived, provided that a sufficient amount of transverse reinforcement is provided in the shafts. The splice offset limits for flexural members referenced above exis t in recognition of the limitations that exist in the available test data. The supplementary requirements that exist for the specific case of column to shaft connections stem from test data for one specific application that became available after the introduction of original provisions. Lack of a broad range of test data on noncontac t splices notwiths tanding, within this article I would like to use the load transfer mechanism in noncontact lap splices to show the transparency in using the strut-and-tie method (STM) and provide a brief historical context. Figure 1 shows the mechanics of the load transfer in a typical noncontact splice. As can be observed in this figure, the development of a compression field between the longitudinal bars that are involved in the force transfer is necessary. The inclination of this compression field (or struts) is a function of the tension force in the bars T , the quantity of transverse reinforcement provided A tr , the splice length, and the splice offset s . With that stated, let us examine some of these variables. To begin, we must recognize that the length of a noncontact splice is adversely influenced by the splice offset distance s . As the splice offset gets larger, so does the splice length. In a case where the diagonal compression field makes a NONCONTACT SPLICES by Dr. Oguzhan Bayrak, University of Texas at Austin Strut-and-tie method, history, and a few additional thoughts Figure 1. Mechanics of load transfer in noncontact splices. All Figures: Oguzhan Bayrak. Splice Offset, s Compression Field Splice Length, l d +? T T A tr Figure 2. Force triangles for noncontact splice: influence of transverse reinforcement.