Reinforced concrete structures are generally designed so that the separate parts act as a single unit. This makes it necessary to properly locate construction joints and provide continuity in the steel reinforcement through the joints. Just as it is impossible to cast all the concrete at the time, it is also impossible to provide, full length, continuous bars in most structures. This is because of manufacturing, fabrication, or transportation limitations. Since splices in reinforcement cannot be avoided, it is necessary for the engineer to provide for properly designed splices. In most cases, lapped splices are more economical than the other types. The length of lap varies with the concrete strength, the yield strength of the steel, and the bar size. Laps are always shown on placing drawings and will be found either in the details or in the general notes. Some typical lapped splice details are shown in the article. Field welded splices of bars in general are of two types: lap splices and butt splices. Welded laps splices with bars in contact are recommended only for #5 bars or smaller. Welded lap splices using a "back-up" plate may also be used. In either case, it is necessary to consider the bar eccentricity in the design. There are several types of welded butt splices some direct and other indirect, employing angles, plates, or sleeves. The direct splices are illustrated in the article, and require special cutting or sawing of the bar ends. An indirect butt splice with back up plate is shown in the article. An angle may be used for "back up" instead of the plate indicated. One type of commonly used mechanical butt splice is the metal filled sleeve in which the filler metal or "metallic grout" interlocks the grooves on the inside surface of the splice sleeve with the deformations on the bar. Standard shear cuts, flame cuts, saw cuts can also be used.