Simpson Strong-Tie now provides grade beam anchorage solutions for the Steel Strong-Wall, which have been calculated to conform to ACI 318-11, Appendix D. Through funding from the Structural Engineers Association of Northern California, initial testing at Scientific Construction Laboratories Inc. confirmed the need to comply with Appendix D requirements to prevent plastic hinging at anchor locations (D.3.3.2). Follow-on testing at the Simpson Strong-Tie Tyrell Gilb Research Laboratory was then used to confirm these findings and validate performance. The testing consisted of specimens with closed tie anchor reinforcement, non-closed u-stirrups and control specimens without anchor reinforcement. Flexural and shear reinforcement were designed to resist Appendix D amplified anchorage forces and compared to test beams designed for non-amplified strength level forces. The test program has proven the performance of the anchor reinforcement details developed by Simpson Strong-Tie.
Grade beam flexural and shear capacity is critical to anchor performance and must be designed to exceed the demands created by the attached structure. In wind load applications, this demand includes the factored demand from the Steel Strong-Wall (SSW) shearwall. In seismic applications, testing and analysis has shown that in order to achieve the anchor performance expected by Appendix D design methodologies, the concrete member design strength needs to resist the amplified anchor design demand from Appendix D Section D.188.8.131.52. To help designers achieve this, Simpson Strong-Tie recommends designers apply the seismic design moment listed in the table below at the SSW location when evaluating the grade beam design strength under seismic loads. The tabulated moment correlates to the lowest of the anchor tension design limits of Appendix D Section D.184.108.40.206 as they relate to each SSW model.
Closed tie anchor reinforcement is critical to maintain the integrity of the reinforced core where the anchor is located. Testing with u-stirrups that did not include complete closed ties showed premature splitting failure of the grade beam.
|Steel Strong-Wall Model||Anchor Bolt Model No.||Anchor Diameter (in.)||Anchor Reinforcement for Wind and Seismic||LRFD Applied Seismic Design Moment for Grade Beam Design (ft.-lbs.)|
|Standard-Strength SSWAB||High-Strength SSWABHS||Standard-Strength SSWAB||High-Strength SSWABHS|
|SSW12||SSWAB3/4||3/4||2- #4 Closed Ties / Wall||5- #4 Closed Ties / Wall||16000||23000|
|SSW15||SSWAB1||1||4- #4 Closed Ties / Wall||7- #4 Closed Ties / Wall||36000||44000|
|SSW18||2- #4 Closed Ties / Anchor||4- #4 Closed Ties / Anchor||48000||61000|