Simpson Strong-Tie® provides grade beam anchorage solutions for the Strong-Wall high-strength wood shearwalls, which have been calculated to conform to ACI 318-14. Through funding from the Structural Engineers Association of Northern California, initial testing at Scientific Construction Laboratories Inc. confirmed the need to comply with ACI 318 requirements to prevent plastic hinging at anchor locations. Follow-up 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 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 Strong-Wall high-strength wood shearwalls (WSHW). In seismic applications, testing and analysis have shown that in order to achieve the anchor performance expected by ACI 318 anchorage design methodologies, the concrete member design strength needs to resist the amplifed anchor design demand from ACI 318-14 Section 126.96.36.199.3 and ACI 318-11 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 WSWH location when evaluating the grade beam design strength under seismic loads. The tabulated moment correlates to the lowest of the anchor tension design limits defined in the sections listed above as they relate to each WSWH 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.