Figure 5 Finite Element Analysis of slab-on-grade.
Figure 6 Slab-on-Grade Design Lookup Chart.
and, thereby, a lookup chart as shown in Figure 6. In this figure, the horizontal axis is the seismicity (SDS), and the vertical axis is the pallet weight that can be accommodated by the slab. In addition, different line types represent different slab thickness, which is overlaid above each line type. This chart clearly shows that as seismicity increases, the maximum pallet weight the slab can accommodate decreases. For the same seismicity, an increase in slab thickness supports more pallet weight. More importantly, from this chart, one can quickly estimate the pallet weight the slab can support based on the seismicity and slab thickness without the need to go through the complete design and check process. Furthermore, the study is extended to buildings with different clear heights, including 32, 36, 42, 46, and 50 feet. Instead of generating different lookup charts for buildings with different clear heights, we used the 40-feet clear building height results as the baseline case, and adjustment factors are determined by correlating the results for a building with different clear heights and baseline case results. This adjustment factor is summarized and provided in the table shown on the lookup chart. Now, utilizing the combined lookup chart and the adjustment table, one is able to very easily determine the maximum accommodated pallet weight considering a given seismicity and slab thickness for buildings with different clear heights.
Examples 1. A 40-foot clear-height warehouse is located on a site with a seismicity of SDS = 1.0g; what is the recommended slab thickness? From the lookup chart, we can easily determine that an 8-inch slab is able to support a racking system with a pallet weight of 3,000 pounds. For 7 and 9-inch slabs, the maximum pallet weights are 1,600 and 4,500 pounds, respectively. Note 22 STRUCTURE magazine
that this chart is for a 40-foot clear building, and the adjusting factor is 1.0 in that case. 2. A 32-foot clear building with seismicity of SDS =1.2g, what is the recommended slab thickness? From the chart, one can determine that 6, 7, and 8-inch slabs can support pallet weights of 400, 1,200, and 2,400 pounds, respectively. In addition, adjustment factors of 3.74, 2.14, and 1.68 should be applied. Therefore, 6, 7, and 8-inch slabs can support pallet weights of 1,496, 2,568, and 4,032 pounds, respectively. In this regard, a 7-inch slab is recommended to meet 2000lb pallet weight industry standards. 3. A 50-foot clear building with seismicity of SDS =0.9g, what is the recommended slab thickness? From the chart, the pallet weight associated with 8, 9, and 10-inch slabs is 3,500, 5,100, and 7,300 pounds, respectively. In addition, adjusting factors of 0.30, 0.39, and 0.40 should be applied. Therefore, 8, 9, and 10-inch slabs can support pallet weights of 1,050, 1,989, and 2,920 pounds, respectively. Therefore, a 10-inch slab is recommended.
Conclusions In the context of an industrial building, the design of a slab-on-grade holds the utmost importance due to its pivotal role in supporting anticipated loads imposed by rack supports. The design process, especially the selection of an optimal slab thickness, proves to be timeconsuming, primarily because it entails intricate numerical modeling. In this study, we conducted a systematic parametric analysis of slabs on grade for buildings with varying pallet weights, clear heights, and seismic conditions. We employed regression analysis to develop a convenient lookup chart, allowing for rapid estimation of the maximum pallet weight the slab can support based on its thickness and seismicity. Additionally, we created an adjustment table for buildings with different clear heights. This tool can greatly assist design teams and owners in making quick decisions, especially during the early stages of building planning, concerning the building's functionality.� Rafik Gerges, Ph. D., P. E., S. E., is a Principal with HSA & Associates and has over 25 years of experience working in consulting Structural Engineering. He is responsible for the design and construction support of major distribution centers, built-to-suit industrial facilities, office buildings, shopping malls, and a variety of other projects. Vinay Teja Meda, M. S., is a senior Structural Designer with HSA & Associates. He has 5 years of experience in Logistics and commercial building structural design. He obtained his Master’s degree from George Institute of Technology. Weian Liu, Ph. D., S. E., is an associate with HSA & Associates. Weian has 7 years of design experience in logistics, commercial, educational, and residential buildings. His key projects include multiple 4-million-sqft fulfillment centers across the nation, LAX Vertical Circulation Cores, Seattle Airport expansion, and many more. Weian obtained his PhD degree in Structural Engineering from UC San Diego.