TMS 402-16 further increased this minimum specified compressive strength of masonry walls to 2,000 psi. For large bars placed off the centerline of the wall, these equations can produce large lap lengths.įor typical ASTM C90 masonry units and Type M or S mortar, TMS 402-13 increased the minimum specified compressive strength of masonry, per the unit strength method, to 1,900 psi. Since the bar location factor is in the denominator of the lap splice length equations of the masonry standard, decreasing the bar location factor increases the lap length. The bar location factor, K, is the smallest of the minimum cover, the clear spacing between adjacent bar splices, or nine times the bar diameter. In either edition of the masonry standard, the lap splice lengths calculated by these equations depend on the specified steel reinforcement yield strength, the specified masonry compressive strength, reinforcement size factor, the bar diameter, and a bar location factor, K. In TMS 402-16, these provisions have been harmonized between the two design methods and placed in Sections 6.1.5 and 6.1.6. TMS 402-13 has lap splice length equations for allowable stress design (ASD) in Section 8.1.6 and lap splice length equations for strength design (SD) in Section 9.3.3. The reinforced masonry design provisions found in the 2018 International Building Code (2018 IBC) reference the Building Code Requirements and Specification for Masonry Structures, TMS 402-16 (TMS 402-16). The reinforced masonry design provisions found in the 2015 International Building Code (2015 IBC) reference the Building Code Requirements and Specification for Masonry Structures, TMS 402-13/ACI 530-13/ASCE 5-13 (TMS 402-13). In some cases, this can significantly increase lap splice lengths and impact constructability. When walls are taller in areas of higher wind and seismic forces, bars may also need to be offset from the centerline of the wall to increase the internal moment arm between the tension and compression forces. Lap Splices and the CodesĪs wall heights, wind pressures, or seismic forces increase, larger reinforcing bars are required and larger bars require longer laps. However, with the new confinement steel option described in this article, the horizontal bond beam steel may be used as confinement steel and can reduce the lap splice length required in the vertical reinforcement. This may have the effect of negating the ability to use the higher grout pours. However, bond beams are mandated for areas of high seismicity and may be required for some designs in areas of low to moderate seismicity, especially if portions of the wall need to span horizontally. Horizontal reinforcing bars, placed in bond beams, may limit which grouting method is utilized due to grout flow concerns in partial-grouted walls. The reinforcement being lapped extends into the next section of wall. A new section of wall is getting started after grouting of the section below. This is because long horizontal bars can be easily placed in bond beams with minimal splicing.įigure 2. Masonry contractors have estimated that 80% of laps occur at vertical bars. However, lap splices increase the total volume of reinforcement in a wall and can impact the cost of the project. Lap splices allow the use of shorter vertical bars by transferring stresses from one reinforcing bar to another through the development of the splice. The use of lap splices improves the constructability of walls when using traditional, closed-end block ( Figure 1). The mason must lift the blocks over the bar that extends out of the previously grouted masonry, or over dowels extending out of the footing. In reinforced concrete masonry walls, long vertical bars are problematic for masons if traditional closed-end blocks are used. Reinforced masonry typically has vertical bars cast in grouted cells and may have horizontal bars cast in bond beams or joint reinforcement placed in mortar bed joints. A newer confinement-steel option is available that has the potential to significantly reduce the lap splice lengths, especially for larger diameter bars, through confinement of the structural reinforcement. Most designers who engineer reinforced masonry know that code provisions for lap splice lengths have been evolving over the past few code editions.
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